Shiroli M.I.D.C, Kolhapur Precast Infrastructures Plot No. C-10, \'Deepak Tiles\'. Plot No. C-10, \'Deepak Tiles\'. Plot No. C-10, 'Deepak Tiles'.,, Shiroli M.I.D.C, Kolhapur - 416122, Dist. Kolhapur, Maharashtra
Laxmi Engineers commenced in to its operations in the year 1991 as a small scale industry under the name & style of M/s LAXMI ENGINEERS in MarudharIndustrial Area, Jodhpur, the biggest industrial town of Rajasthan, situated in western part of India, 600 kms in south of New Delhi and 1000 kms in north of Mumbai. It is well connected with road, rail and air to all metro cities.
Laxmi Engineers was established by a senior veteran technocrat Late Sh. M L Sharma ji, who have had vast experience for more than 50 years in the field. Now, the affairs of the company handle by Mr. Vijay Sharma, a commerce graduate, together with technical, commercial & marketing of the Company.
We are designer, manufacturer, supplier and exporter of Cement Plant projects upto 300 TPD capacities based on VSK technology, Clinker Grinding Plants upto 500 TPD capacities, White Cement Grinding Plants, Cement Blending Plant, Jumbo Bag Unloading and Bag Packing Plants, Ball Mills, Jaw Crushers, Roller Crushers, Hammer Mills, Screw Conveyors, Belt Conveyors, Bucket Elevators, Pneumatic Air Lift, Feeders, Rotary Dryer, Bag Packing Machineries and Mineral Grinding Plants.
The company prides itself on developing products, which exceed market expectations. Laxmi Engineers has been the recipient of many national and international export awards, acknowledging the superior standard and world acceptance of both the organisation and its products. The company has adequate experience in manufacturing of Plants and Equipments for more than 30 years and had commissioned more than 80 cement projects in India, besides overseas countries Bangladesh, Nepal, Kuwait, Nigeria, Sri Lanka, Mexico, Ethiopia and Bhutan.
If youre thinking about set up a cement factory (or cement plant), you must weigh the pros and cons of it many times. There is no doubt that youve considered all your musts, such as locations, cement plant design, cement plant layout, etc. But the most important thing is absolutely cement factory cost how much does it cost to build a cement factory? Maybe you also want to know the potential investment you dont see coming.
According to the data we know, the total cost of a cement plant is estimated to be US$ 75 to US$ 100 per ton. One thing to be clear, this is just an estimation, in the real cement plant building, the cement factory cost is affected by various factors, including the significant difference in cost of land, availability of limestone mines, etc.
The cement factory cost is based on changing factors like size, location, labor, raw materials, and current real estate trends, which make it impossible to nail down a perfectly accurate, one-size-fits-all answer. So lets list the cost item needed in building a cement factory, everyone can get your own plant according to these items.
As we all know, the cement production line is made up of various types of cement equipment, the cement factory cost depends on the cement factory machine you choose. For some buyer who has abundant funds, might choose high-quality equipment, which increases the cost of the cement production line. At the same time, high-quality cement plant also brings considerable economic benefits and market returns.
At present, the new-type cement plant has advantages of high profit, quick effect, high efficiency, energy saving, environmental protection, easy operation, and low cost. The hot-sale cement plant is composed of following cement factory machines:
If you are ready to buy a cement plant, it is suggested to choose a cement plant manufacturer with a large scale and strong strength, which will provide full cement equipment and service, also ensure the quality and performance. In general, for the customer who wants to buy the whole cement production line, the cement plant manufacturer will give more preferential policies. On the contrary, the strength of small-scale manufacturers is limited, cement equipment types are not complete enough, need to buy from different manufacturers, not only trouble but also increase the cost of investment.
Investors have different requirements for the daily output of the cement factory, so we can find a large capacity cement plant and mini cement plant in the real case, and the investment capital will also be different. Generally, the higher the output value, the higher the investment, because the model requirements for cement equipment will be higher, and the price of equipment will naturally rise, but the value of the benefits to customers will be greater.
Enterprise competition is a side factor that affects the cement plant price. The more intense the competition, the cheaper and more affordable cement equipment prices. On the contrary, if there are fewer cement plant manufacturers and the competitiveness is weak, there is no obvious threat between the companies. Cement plant prices will generally maintain a normal state or relatively increase, which is a manifestation of natural laws.
Except for above elements, there are some other factors involved in the cement factory cost, such as labors, raw materials cost, cement plant design and so on, labors cost is always related to the location and your scale of cement factory; as for the cost of the raw materials, the place where is near mineral resource will be recommended, which will reduce your transportation cost. For most large cement plant manufacturers, they can provide custom solutions to cement plants, also supply the EPC project for equipment or cement plant.
1. Can anybody tell me Cement Production flow?2. How can we configure the cost centers for cement plant to arrive fixed and variable cost for preparation of cost sheets for analysis purposes??3. Can anybody provide me a document on configuration of cement costing so that it will be helpful for me because i am developing the software for cement costing.RegardsSriram MRamco Cements LtdHyderabad
Hi:Are you from accounting/finance department?On what I understand the cement plant can be divided into the following cost center:1. Crusher - This will depend on the number of your crusher facilities. In our case we have 4 crusher facilities located in different areas around the plant, so we have 4 cost centers. The crusher cost center will include the primary crusher, secondary (if any until third stage crushing), until bridge reclaimer2. RawMill - This will include the areas from the rawmaterial bins, rawmill proper, rawmill recirculation, until the Blending Silo (where you store the rawmeal).3. Kiln - This is from the conveying mechanism after the blending Silo, Preheater, Kiln Proper, Clinker coolers and clinker conveying system. NOTE: you can create sub-cost center if you like.4. Cement mill - From the conveying system of Clinker silo, to cement mill proper until Cement Silos.5. Packing - This include all the flow clain and bucket elevator from Cement Silo until the rotopacker.Fixed cost are normally includes the Maintenance stock, external labor, rentals, fees, wages, other fixed costVariable cost includes refractory bricks, castables, electricity, fuels, rawmaterials, liners, grinding ball/rollers..Best regards,
1. Crusher - This will depend on the number of your crusher facilities. In our case we have 4 crusher facilities located in different areas around the plant, so we have 4 cost centers. The crusher cost center will include the primary crusher, secondary (if any until third stage crushing), until bridge reclaimer
Dear, First of all you must have to develop the norms shee, norm sheet means consumption of all the comodities per ton of cement.For emapleITEMUnitLimestoneton / ton Clinker1.078Shaleton / ton Clinker0.385Iron Oreton / ton Clinker0.077Total Raw Materialton / ton Clinker1.540Furnace Oilton / ton Clinker0.00125Coalton / ton Clinker0.14195TDFton / ton Clinker0.00400Furnace Oil Equivalentton / ton Clinker0.0805Diesel at KilnLtr. / ton Clinker0.150Diesel at QuarryLtr. / ton Raw Material0.850Gypsumton / ton Cement0.050Performance improver (L.S)ton / ton Cement0.000Power (Gross)Kwh / ton Cement105.00Paper BagsNo. / ton Cement20.200Refrectory ConsumptionMagnesite Bricks (M.Ton)Alumina Bricks (M.Ton)Alumina Castable (M.Ton)Fire Bricks (Gm/ton of Clinker)Grinding Media (M.Ton)Grinding Media (Gm/ton of Cement)You have to work on these lines.I can only give you a tip, salary and wadges and other expances can be calculated from your Finance. Once agian i have to clear you that it is just an example, you have to develop your own data.Regards
ITEMUnitLimestoneton / ton Clinker1.078Shaleton / ton Clinker0.385Iron Oreton / ton Clinker0.077Total Raw Materialton / ton Clinker1.540Furnace Oilton / ton Clinker0.00125Coalton / ton Clinker0.14195TDFton / ton Clinker0.00400Furnace Oil Equivalentton / ton Clinker0.0805Diesel at KilnLtr. / ton Clinker0.150Diesel at QuarryLtr. / ton Raw Material0.850Gypsumton / ton Cement0.050Performance improver (L.S)ton / ton Cement0.000Power (Gross)Kwh / ton Cement105.00Paper BagsNo. / ton Cement20.200
You have to work on these lines.I can only give you a tip, salary and wadges and other expances can be calculated from your Finance. Once agian i have to clear you that it is just an example, you have to develop your own data.
Cement plant is necessary for cement production, mainly consist of a series of cement equipment apply for preparation of cement raw materials, clinker production, and finished cement production, such as cement mill, cement crusher, rotary kiln, cement roller press, cement dryer, clinker cooler, cement silo, and related cement plant equipment. AGICO CEMENT is a cement plant manufacturer who owns ability to manufacture cement equipment and provide EPC turnkey project for cement plant.
AGICO Cement is a cement plant manufacturer with production capacity of 30,000 tons of equipments and structure parts and 20,000 tons of casting parts.own production equipment of 8m Vertical Lathe, 10m gear rolling machine, 8m Gantry milling machine, 200mm floor-type boring and milling machine,1203200mm bending machine, 150t crane and 40t electric furnace.
When it comes to achieving the best energy consumption, what are the key factors a cement producer needs to address? In this article, extracted from the newly published Cement Plant Environmental Handbook (Second Edition), Lawrie Evans presents a masterclass in understanding and optimising cement plant energy consumption. By Lawrie Evans, EmCem Ltd, UK.
As control of sources, generation, distribution and consumption of energy is central to many current world issues, controlling the industrys energy footprint is a matter of intense interest to governments. This is recognised in such initiatives as ISO 50001, the World Business Council for Sustainable Developments Cement Sustainability Initiative, Energy Star in the USA, PAT in India and CO2 taxes/trading in Europe and in other countries.
For the cement industry, there are three main drivers to energy consumption: electrical power fuel customer demand for high-strength products that require a significant proportion of high-energy clinker as a component.
For the producer, these factors have a significant influence on cost competitiveness, usually accounting for over 50 per cent of total production costs, so that accurately and continuously monitoring energy usage must be a way of life for any producers technical team. The introduction of CO2 taxes in Europe and elsewhere adds a further twist to the story. For major groups, especially, decisions made in balancing maintenance, investments, operations and purchasing requirements all have to take into account the impact on their energy footprint.
Globally a cement major such as Italcementi consumes annually some 6000GWh of power and 35,500,000Gcal of heat for a total of 5Mtpe. This is the same total energy as consumed by approximately 1.6m Italians or 0.6m Americans per year. For fuel-related energy costs, the worldwide industry has largely moved to efficient preheater/precalciner processes and has found many options to switch to cheaper fuels, with the global drive to alternative fuels still proceeding. For electrical energy, options to reduce unitary costs are much more limited in scope. Most countries still have power generation/distribution systems that are effective monopolies and the cement producers cost control capability is usually limited to selecting the appropriate contract and taking opportunities offered in lower-cost off-peak power tariffs, where they exist.
Figure 1 illustrates the wide variation in the cost of power across 14 countries. The average country cost of electrical power at an industrial level varies enormously. When the added complexity of on and off peak power costs, interruption clauses, supply charges versus energy charges, etc, are added, the evaluation of the benefits of energy saving investment can become very complex. Typical cement plant power costs can range from EUR39 to EUR170/MWh.
The most important first step in controlling energy consumption is to be aware of the relative importance of the process areas where most energy is consumed. Figure 2 shows a typical breakdown of electrical energy consumption at a cement plant. The most obvious area for attention is that of grinding, both raw and cement. In either case, grinding is, by design, a very inefficient process.
The ball mill has been the industrys workhorse for over a century and despite its estimated meagre four per cent efficiency, little has changed over the years other than increases in the wear resistance of mill internals and the scale of the equipment. The addition of closed circuiting and progressively higher efficiency separators has improved cement product quality and produced higher outputs for a given mill size, but the case for adding or upgrading separators on energy saving alone has proved to be poor, unless the products are >4000Blaine. Starting from the 1970s, a new generation of mills appeared. Vertical mills (see Figure 3) were common for solid fuel grinding, generally with spring-loaded rollers. The principle of the new generation of vertical mill was to direct higher pressure from the grinding element to the material bed using hydraulic systems. From this approach the roller press, CKP (pre-grind vertical rollers) and Horomill all developed.
The gas-swept vertical mill quickly became the raw mill of choice. Grinding energy was approximately 50 per cent of the ball mill and the drying capabilities allowed direct processing of materials of up to 20 per cent moisture content. The main energy issue was the high power consumption of mill fans, with pressure drops of 100mbar not uncommon with high nozzle ring velocities (>70m/s) and internal mill circulating loads of >1000 per cent. Manufacturers have countered this generally satisfactorily with pressure drops reduced by lower nozzle ring velocities and the addition of external spillage elevator recirculation systems plus higher-efficiency separators.
Better seal designs for mill roller assemblies and pull rods have reduced the inevitable inleaking air issue and its impact on power consumption. However, it remains a design where issues of wear and reliability are more challenging than for ball mills, and these issues have not diminished with increased scale. For raw grinding with relatively dry raw materials, the combination of the roller press and V separator is a viable alternative with far lower mill fan power.
For cement grinding, the technology development away from ball mills has taken a different route. The development of roller presses in the 1980s took advantage of the benefits of higher-pressure grinding and many presses were retrofitted to ball mills as pregrinders. The main benefit was seen at lower Blaines as the first generation of presses suffered from stability problems when attempts were made to grind more finely by recirculating separator rejects. These problems are now largely resolved and the combination of a V and third-generation dynamic classifier separators together with a roller press can produce finished cement with high energy efficiency.
The Horomill and CKP systems have also enjoyed some market success and have provided good energy efficiency levels compared to ball mills. The vertical mill option has been slower to enter the cement grinding market. Grinding bed stability problems offered a challenge which the major manufacturers battled with, until finally a significant number of mills began to be installed in the late 1990s, and this has multiplied in the past decade. However, in pure energy efficiency terms, the benefit of grinding power reduction is countered by the very high power required by mill fans. In addition, the absence of the heat generated in a ball mill and the high volume of air required by the vertical mill have required the provision of waste heat from cooler exhausts and/or auxiliary furnaces to dry raw materials and achieve a limited dehydration of gypsum.
A typical comparison of three competing technologies is given in Table 1, demonstrating that an efficient ball mill/third-generation separator, CKP/ball mill/third-generation separator and vertical mill on a typical 4000Blaine limestone cement show little overall difference in energy consumption. Considering the higher capital cost, and more demanding maintenance and operating regime, there is no clear energy case to favour some of the modern variants.
Even for solid fuel grinding, there has been a minor trend back to ball mills. This is most evident for petcoke grinding, where the demand for very low residues, and the very hard and sometimes abrasive nature of high-sulphur cokes has resulted in ball mill selection.
Many of the grinding design issues, which are still under debate, are usually very clear in other areas of process selection: high-efficiency process fans and low-pressure drop preheaters adequately-sized bag filters for the main exhaust to avoid high pressure drops and poor bag life avoidance of pneumatic transport systems low-energy raw meal homogenisation silos.
The main continued discussions are those of two- or three-fan systems for the raw mill/kiln or single filter for kiln and cooler, precipitator or bag filter for the cooler exhaust and two or three tyre kiln. For a bag filter on a separate cooler the main equipment energy efficiency issue is the air-to-air heat exchanger, but this is often substituted with a water spray in the cooler or more recently, by using a ceramic filter capable of operating at above 400C.
Finally, in design terms, the most difficult decision is to avoid overdesign by applying too many safety factors. Post-commissioning audits often uncover a high contribution to poor energy efficiency from under-run equipment operating where it cannot perform efficiently.
In normal operations maintenance also plays a major part in ensuring energy efficiency. The impact of poor plant reliability upon overall electrical energy consumption is often under-estimated. In the kiln area, 100 short/medium stops (30 minutes to eight hours) per year can cost up to 5kWh/t clinker. The avoidance of inleaking air, correct alignment of motors, stopping compressed air leaks, etc are all part of the value of good maintenance.
In the key area of grinding there are important factors to control. For ball mills, ball charge level, lining and diaphragm condition must be monitored and maintained in near-optimum condition. Mill stops, defined as mill motor off, and measured by mean time between failures (mtbf), are frequently poorly recorded and the resolution of underlying issues is frequently not addressed.
Instability, where ball mill feed is stopped and the mill ground out, is also infrequently recorded or acted upon. When it comes to mill control, operators rarely concentrate on pushing mill production when the kiln is regarded as the key. Expert systems on mills should be universal and well tuned.
Grinding aids can give benefits of 5-15 per cent in production but need to be continuously evaluated for cost effectiveness. Unfortunately, their cost has risen more rapidly than the cost of energy in recent years and the economic balance has to be re-evaluated. The benefit of aids on cement flowability has to be considered, along with the added scope for reduction of cement clinker content with some modern additives. Correct timing on the maintenance of a first chamber cement mill lining and the successful implementation of an expert system on a cement mill both offer benefits in terms of power consumption (see case studies panel). Accurate process measurements are also key to energy saving opportunities. Air compressors are another area for attention. Often, these are multiple units operating on a cycle of on- and off-load. Replacement of one (of three) with a variable-speed type (see Table 2) can provide rapid payback. Even lighting and buildings offer excellent opportunities for power savings. Table 3 shows the 40-80 per cent energy savings that can be achieved by simply replacing old lighting systems. Buildings such as the new Italcementi Group Research and Innovation Centre (i.lab) in Bergamo, Italy, demonstrate that good building design creates significant savings.
A major change has occurred in the last 20 years in the area of in-house generation of electrical energy by cement manufacturers, most significantly using waste heat recovery (WHR) from the pyroprocessing line. Figure 4 shows the areas suited to heat recovery for power generation, and WHR technology is already applied to preheater and cooler exhausts.
The modern technology originated in Japan in the 1980s, where high power prices and large-scale operations combined to produce useful economic returns, with most applications using steam boilers at the preheater exhaust. Little further development happened outside Japan until the turn of the century, when a combination of lower capital cost, Chinese equipment, and the idea to improve recovery by splitting cooler exhausts into higher and lower temperature streams combined to offer the paybacks necessary for the technology to expand, first inside China and then beyond.
The results of WHR have been impressive, eg, with the 19MW net achieved from a combined installation on two five-stage precalciner kilns (5500tpd and 7500tpd) in Thailand being typical. Options for the technology are evolving with other thermodynamic cycles being applied: steam Rankine cycle with various enhancements the most widely applied technology organic Rankine cycle a variety of organic fluids applied and favoured at lower gas temperatures Kalina (ammonia/water) cycle supercritical CO2 cycle.
There are also further developments which can increase the power recovered, including recycling the lower temperature cooler exhaust, meal bypassing preheater stages to boost exit temperatures and the use of alternative fuels and excess air, also to boost preheater exit temperature and energy recovery. Other options for power generation can use the land owned by the cement plant for raw material reserves. These include wind farms photovoltaics, concentrated solar panels or growing and burning biomass either to boost power in a WHR system or for use in an internal, stand-alone power generation plant.
The evaluated cement plants with carbon capture based on reactive gas-liquid and gas-solid systems were modeled and simulated using ChemCAD software package. The developed models for CO2 capture were validated by comparison to the experimental / industrial data. A cement plant without carbon capture was considered as a benchmark case but it was not modelled, the main techno-economic and environmental indicators for the benchmark case were based on key references in the field (IEA-GHG, 2008).
The mass and energy balances for the cement plant concepts with carbon capture were used furthermore to evaluate the key plant performances. The designs were optimized by performing a heat integration analysis (using pinch technique) for maximization of the overall energy efficiency (Smith, 2005). As an illustrative example, Figure1 presents the hot and cold composite curves for the calcium looping cycle (Case 3).
In both investigated cases, an additional coal-based combined heat and power (CHP) unit is required to cover the ancillary energy consumption of the cement plant with carbon capture. As main energy consumptions of the carbon capture designs one can mention: thermal regeneration of the chemical solvent (Case 2) and calcium-based sorbent (Case 3) as well as CO2 conditioning (drying and compressing). The main technical and environmental indicators of the two investigated carbon capture technologies to be used in conjunction with a cement plant are presented in Table2.
As can be noticed from Table2, both cases have a small surplus of electricity (after ancillary plant consumptions were covered) to be sent to the grid. The carbon capture rate is 90% for both designs but the quantity of captured CO2 per ton of cement is significant better for Case 3 (calcium looping). Another important aspect which reflects better performances of calcium looping design in comparison to gas-liquid absorption is the fuel ancillary consumption which is about 52% lower (154MWth vs. 234MWth).
The next evaluation targeted the economic performances of the cement plant with carbon capture. For estimation of the capital expenditure (CAPEX) as well as the specific investment costs (reported as Euro per ton of cement), the cost correlation method was used (Smith, 2005). The key mass and energy flows processed through each main plant systems (e.g. cement plant, carbon capture unit, CO2 conditioning, air separation unit, power plant etc.) were considered as scaling parameters e.g. captured CO2 flow and heat provided to the looping reactors (as well as their volumes) were consideredas scaling parameters for gas-liquid absorption and calcium looping cases (Romano et al., 2013). The complete methodology of capital cost estimation using the cost correlation method is presented by Cormos (2016b). Table3 presents the specific capital investment for the main plant components as well as the total value.
As presented in Table3, the specific capital investment costs for cement plants with carbon capture are higher than for the cement plant without carbon capture (benchmark case) by about 112% for Case 2 and about 75% for Case 3. The calcium looping technology shows significantly lower investment costs than the gas-liquid absorption design due to higher energy efficiency and lower energy penalty for carbon capture.
The operating expenditure (OPEX) was estimated using a commonly used methodology (Peters and Timmerhaus, 1991). The OPEX costs can be broken in two main components: fixed and variable costs depending on their variations with plant output. Figure2 presents the fixed and variable OPEX costs for the investigated cement plants. The carbon capture designs have higher OPEX costs compared to benchmark case with about 90% for gas-liquid absorption case and about 60% for calcium looping case.
The cement production cost significantly increases when CO2 capture is applied (95% for gas-liquid absorption and 63% for calcium looping) as well as CO2 avoided cost. However, calcium looping method shows far better values than gas-liquid absorption.
The audited cement plant contains nearly 94 Mots whose power is greater than 18 kW and that are not equipped with VFD. These Mots belong to the IE1 energy class (according to the classification of IEC 60034-30). Table 11 presents the main operating characteristics of these Mots.
From Table 11, it can be observed that several Mots operate at low charge levels (e.g., Mot 12, 33, 41, and 52). Therefore, installation of VFD for these electric Mots could be considered as a potential solution to reduce energy consumption.
The Ramla cement plant (see Fig. 1 for an aerial photo of the plant) has been in operation for 46 years. The original process at the Ramla cement plant to produce cement from limestone, which is the base material of cement, was a so-called wet line process. The original wet line had a capacity of 1,800 TPD (Tons Per Day). The first new production line producing cement through a so-called dry line process was commissioned in 1994. This line has a capacity of 5,000 TPD and is very successful. Building on its success, Nesher decided to build a second dry line. On the 10th of August 1997, Benjamin Netanyahu, Israel's former Prime Minister, laid the cornerstone at the Ramla plant for the second 5,000 TPD dry line. The new dry line, which is currently in the running-in stage, will join its 5,000 TPD sister dry line and the older 1,800 TPD wet line. The wet line will be phased out soon and thus the anticipated new total plant capacity will be 10,000 TPD. To save costs, Nesher decided to use the existing limestone handling and transport facilities to handle the increase in transport loads. This was made possible by relatively minor modifications to the existing infrastructure. in particular to the belt conveyor system. The raw materials needed to supply all three plants are now transported from a quarry 3.5 km away from the plant via the existing (upgraded) conveyor belt system.
Cement plants have been conserving water in their plants from the beginning as most cement plants have had to make their own arrangements to obtain water required for the plant and for drinking and household purposes.3.1.1.Cement plants procure water from the nearest perennial sources of water like rivers and streams by digging wells in their beds and pumping it and storing it in the plant/quarries/housing colony.3.1.2.Plenty of water is required even in dry process cement plants to cool bearings, compressors, after-coolers, gearboxes and for conditioning towers preceding ESPs. All water used for cooling is invariably collected and taken to a cooling pond and recirculated in the system. Only 10-15% water is added to allow for loss by evaporation.3.1.3.Process water is not required in a dry process cement plant. However if an ESP is used to clean preheater exhaust gases, a cooling tower is necessarily installed to bring down the temperature to about 140C. Gases are cooled by spraying water on the gases in the cooling tower. Water evaporates and is consequently lost. This is a significant quantity.3.1.4.This loss of water can be avoided if the ESP is replaced by a bag filter. However penalty there is a penalty for the higher pressure drop in the bag filter and the necessity of cooling gases to ~120140C by admitting ambient air to suit the materials of bags. If glass bags which can stand a temperature of ~275C are used this dilution can be avoided. Generally speaking the ESP can be avoided at the design stage itself if the plant is located in an area of scanty rains and water scarcity.Performance of the ESP is uncertain during startup and closing down periods. Presently the trend is to avoid an ESP for this reason also.
Plenty of water is required even in dry process cement plants to cool bearings, compressors, after-coolers, gearboxes and for conditioning towers preceding ESPs. All water used for cooling is invariably collected and taken to a cooling pond and recirculated in the system. Only 10-15% water is added to allow for loss by evaporation.
Process water is not required in a dry process cement plant. However if an ESP is used to clean preheater exhaust gases, a cooling tower is necessarily installed to bring down the temperature to about 140C. Gases are cooled by spraying water on the gases in the cooling tower. Water evaporates and is consequently lost. This is a significant quantity.
This loss of water can be avoided if the ESP is replaced by a bag filter. However penalty there is a penalty for the higher pressure drop in the bag filter and the necessity of cooling gases to ~120140C by admitting ambient air to suit the materials of bags. If glass bags which can stand a temperature of ~275C are used this dilution can be avoided. Generally speaking the ESP can be avoided at the design stage itself if the plant is located in an area of scanty rains and water scarcity.
The steam is condensed in condensers and returned to the circuit. Water used to condense steam is itself cooled in cooling towers operating in a closed circuit; that water is used again by recirculation. Therefore, only makeup water is required. The same is true of waste heat recovery boilers. Even where DG sets are used to generate power, diesel engines are cooled by water which in turn is cooled in cooling towers and returned to the circuit.
This water is generally wasted after use, though sewage water can be used after treatment for nondrinking purposes like gardening. As a matter of fact authorities who sanction a cement plant project stipulate that a sewage treatment plant has to be installed in the plant. There should be zero effluent discharge from the plant.
Often, as mines get developed, underground resources of water become available and actually supplement the main source of water. Pits in excavated/exhausted mines can be used to serve as reservoirs of water. These are available year round for mining machinery and crushing plant when located in mines.
Often, currently, used mines are consciously developed and landscaped to serve as recreation or picnic spots. Reservoirs in mines thus serve a dual purpose, as a source of water and as lakes. When treated the water can also be used in swimming pools.
Presently there is great emphasis on greening of the plant and its surroundings, including the housing colony. Green belts are created around the plant and colony to serve as dust and sound barriers. It is mandatory to create such belts between the plant and the highway/township.
In the context of cement plants, rainwater harvesting (RWH) has many dimensions.1.Rainwater is collected and stored in natural/artificial ponds or lakes to counter the salination of groundwater in coastal areas.For this purpose check dams are constructed across streams and rivulets.2.A system called garland canals is constructed to collect the groundwater and lead it to reservoirs in quarries or reservoirs created by check dams.This water can be used in the cement plant for manufacturing, in captive power plants, and for domestic use in colony.As a matter of fact many cement companies are supplying water for drinking purposes and for agricultural purposes to neighboring communities on an increasing scale. Some have installed desalination plants also.The authorities sometimes stipulate that the cement company should not draw water from an adjoining river/stream.3.RWH is used to recharge bore wells within the plant's own area and colony.Water is collected from rooftops and led through pipes to collection pits near the bore wells to recharge them. Water is then available year round, even in summer months.
As a matter of fact many cement companies are supplying water for drinking purposes and for agricultural purposes to neighboring communities on an increasing scale. Some have installed desalination plants also.
Extracts from a typical letter of consent for a cement plant project at a green field site or for an expansion show the emphasis the authorities are putting on water conservation. Cement plants of the future will have to be green. See Annexure 1.
Waste oil is a unique hazardous waste with a long history of utilization. Typical sources of waste oil include automotive oils, machinery cutting and cooling oils, and other sources of lubricants. The opportunities to use this material as an opportunity fuel are worldwide. U.S. waste oil production and consumption exceeds 4.2 109 l/yr (1.1 109 gal/yr), of which 67% is burned as fuel and another 4% is rerefined . A significant quantity is generated in Canada annually as well. Blundell  reports that 200 106 250 106 l/yr (53 66 106 gal/yr) of waste oil is generated in the Ontario province alone; of this 15% is burned in cement kilns, 7% is burned in small furnaces, and 27% is refined again.
In the United Kingdom, 447,000 tonnes of waste oil are generated annually, of which 380,000 tonnes are usedlargely as fuel . Significant attention has been given to this waste disposal problem/energy resource opportunity in such other locations as Bulgaria , New Zealand , Spain , and throughout the European Union. States from California  to Vermont  are paying particular attention to waste oil, its use as a blending fuel, and its proper disposal.
The general fuel characteristics of waste oils are shown in Table 5.21. Note the differences between mineral oil and synthetic automotive oil. Note also the broad range in properties, particularly as associated with mineral oil.
Typical trace metal concentrations have also been measured in waste oils, as shown in Table 5.22. Note that there are significant differences between typical concentrations in the United States and in New Zealand.
There are three basic uses of waste oil as a blending fuel: in small space heaters and boilers, in larger boilers, and in cement kilns. Of these, cement kilns are the most prominent due to their continued search for low-cost alternatives to coal, oil, and traditional energy sources. In New Zealand, for example, two cement kilns dominate the use of all waste oil in that country. Typical emissions from the combustion of waste oil in various applications are shown in Table 5.23. Note that SO2 is not shown in this table because of its dependency on the sulfur content of the incoming fuel.
Given the typical emissions associated with firing waste oils, it is useful to consider case studies of firing waste oils in cement kilns . Therefore, an example of cofiring waste oils in cement kilns in Germany is presented.
A study utilizing data from cement plants in Germany was done to estimate the emissions of various metals as a function of waste material . There are 76 cement kilns in operation, of which 40 are permitted to use alternate fuels such as tires, waste oil, waste wood, and so forth. A typical cement kiln consisting of a raw mill section, a preheater-rotary kiln section, and a cement mill section was used to describe cement production in Germany. Using partitioning factors based on information from operating kilns, a mass balance model was developed for this typical kiln. Using this information, elemental distributions were calculated for cadmium, lead, and zinc when using waste oils at the maximum allowable rate of 30%. The results are shown in Table 5.24. The results show that nearly all the trace metals exit with the clinker, and destruction and removal efficiency (DRE) numbers for the three metals are estimated to be 99.96% for lead, 99.95% for zinc, and 99.94% for cadmium.
A green cement plant is one that is designed to conserve natural resources of all kinds and that contributes to the release of the greenhouse gases (GHG) to the atmosphere to the least possible extent consistent with the quality of cement produced.
Release of CO2, a greenhouse gas, is inherent in the process of the manufacture of cement, as CO2 is released from limestone, the basic raw material of cement during the process of calcining. One kilogram of calcium carbonate releases 0.44kg of CO2. Therefore, in making 1kg of clinker, approximately 0.51kg CO2 gets released into the atmosphere.
A vital component of total carbon dioxide released to the atmosphere is the CO2 released in the process of combustion of fuel fired in the kiln and calciner in the clinkerization process. The quantum released is directly related to the quantum of fuel fired and the quantum of carbon in it.
Again, by the same logic, the obvious way to reduce emissions is to reduce the heat requirement, or what is called specific fuel consumption, and/or to use fuels with less carbon or those that are carbon neutral.
Alternate fuels have been successfully used in many countries in kilns and calciners. In Europe the cement industry is progressing toward zero fuel costs. Great possibilities exist for using wastes of industry and agriculture that have heat value as secondary fuels in kilns and calciners.
Production of cement also requires a supply of electrical energy, expressed as kwh/ton of cement. Electrical energy is presently produced mostly by burning fossil fuels like coal and oil. Thus reduction of electrical energy by making cement indirectly means a reduction in electrical energy produced and thereby in GHG released to the atmosphere. If 1 kwh is used in a cement plant, the generating station has to produce much more to allow for transmission losses and for its own inputs. In some countries transmission losses are small, say 10%, but in some countries (India for one) they are more than 30%.
Cement plants can further contribute significantly to reducing GHG emissions by converting waste heat in the exhaust gases from the kiln and cooler into electricity using waste heat recovery systems (WHRS). There is plenty of scope in existing dry process cement plants to produce power from waste heat.
Due to recent developments in technology it is now possible to generate power even from waste gases in modern cement plants with low heat contents by using the organic Rankine cycle and the Kalina process. It is estimated that between 20 to 30% of the energy required by a cement plant can be generated by installing WHRS. Energy so generated can be used in the plant or fed to the grid.
All fossil fuels emit CO2. Biomass fuels are carbon neutral. Sources of energy like wind, solar and hydraulic are not only totally free of carbon but on top are renewable, and also inexhaustible. Increasing attention is being paid to making them viable sources of energy.
Thus, making or designing a green cement plant in effect means:1.providing facilities for making blended cements in an adequate measure2.designing components like calciners to reduce obnoxious gases like NOx, SO2, etc.3.provide providing for processing and firing alternative fuels which will reduce the quantum of CO2 released4.designing burners and firing systems for available alternative fuels5.if required, providing for bypass of kiln gases which can contain excessive alkalis and chlorides as a result of firing certain alternative or waste fuels6.providing for waste heat recovery systems to generate power or for other applications7.consideration of making composite cements, which are a form of blended cements1.8.1.To this list will soon be added:1.using/making substitute cements2.using renewable energy
There are developments which aim at reducing the GHG emissions by physically collecting CO2 emitted and storing it and making it available to other industries that have use for it, and even for making cements of new types.
Apart from the two major aspects described regarding sustainability and GHG emissions there is more to making a cement plant green:1.keeping the environment green by planting trees and taking up schemes for afforestation2.adopting more scientific mining methods that cause minimum damage to the environment by minimizing mining footprints3.reclaiming used mines for landscaping, creating water reservoirs, etc.4.creating green belts in and around plant and colony5.installing water conservation schemes like rainwater harvesting, water treatment for recycling6.designing and constructing green buildings in the cement plant wherever possible to make maximum use of natural light, ventilation, etc.
The cement industry is consciously making efforts in various areas (listed in section 1.8) and is very much interested in making existing plants green and in designing new plants as green plants.1.11.1.Blended cementsPresently almost all cement plants the world over are making blended cements. In India itself ~ 74% of cement made is blended cement. Slag adding up to 60% has been used up. Fly ash is available but further increase in the quantum of Portland Pozzolana Cement (PPC) is limited unless the ceiling to which fly ash can be added is raised. This change can only be sanctioned by national entities that govern standards of cement, like the Bureau of Indian Standards in India.1.11.2.Alternate fuelsThe main problem is the selection of a fuel that is steadily available in required quantities over a long period of time and which would have reasonably uniform physical and chemical properties, such as calorific value.1.11.3.Waste heat recoveryIntroducing waste heat recovery systems requires heavy capital investment and therefore requires careful planning and engineering.In the subsequent sections and chapters all these aspects have been covered in detail so as to present a comprehensive picture of what it takes to make a green cement plant.
Presently almost all cement plants the world over are making blended cements. In India itself ~ 74% of cement made is blended cement. Slag adding up to 60% has been used up. Fly ash is available but further increase in the quantum of Portland Pozzolana Cement (PPC) is limited unless the ceiling to which fly ash can be added is raised. This change can only be sanctioned by national entities that govern standards of cement, like the Bureau of Indian Standards in India.
The main problem is the selection of a fuel that is steadily available in required quantities over a long period of time and which would have reasonably uniform physical and chemical properties, such as calorific value.
All over the world, sizes of cement plants have increased both as single production units and also in terms of total capacity in one place. Basic processes and, hence. stages of manufacture in green cement plants are the same as those in conventional cement plants. When making blended cements, both the requirements of limestone for a given capacity of the plant and also the area for mining lease reduce drastically.
With the size of the plant capacities of individual machinery, units like crushers, mills, and kilns also increase correspondingly. Therefore, increases in the size of a plant should be accompanied by growth and developments in cement making machinery so as to maintain, and even improve, efficiency and productivity of cement plants.
It is economical to have a single production unit for a given capacity. This would have been difficult without developments like low pressure drop cyclones for preheaters, vertical roller mills with multi drives, high efficiency separators, roller presses, and a number of ways these can be integrated in circuits. Various developments in designs of clinker coolers with+70% efficiencies, developments in designs of low nox calciners, and two support kilns are just some of the developments that have made large green cement plants a reality. Features like co-processing alternate fuels and waste heat recovery systems are also integral parts of large green plants.
With the size of the plant, the quantities of bulk materials to be handled and stored increase correspondingly. A balance has to be struck between economy and continuity of operation in planning layouts of large cement plants. Multiple units are installed to maintain continuity of operation in the event of breakdowns.
New, large plants make at least two types, sometimes more, of cements. Hence, sections of cement grinding, storage, and dispatches have to be planned carefully to cater for the market in the best possible manner. Dispatches can be by road, rail, (even by sea in case of exports), and in bagged or bulk cement. The plant has to plan its facilities carefully, taking these factors into account. Split location has become common.
Operating efficiencies of large plants are highsp. fuel consumption is around 650 - 700kcal/kg clinker; sp. power consumption is between 65-80kwh/ton; and man hours required per ton of cement are as low as 0.15.
Because of their size, it is possible for large plants to invest in renewable energy, such as solar or wind power. Automation and process control are of an advanced nature. New concepts using key performance indicators (KPI ) and dashboard control are coming in vogue. Large plants have to integrate and manage three or more power systems like grid power, captive thermal power, waste heat recovery power, and also solar or wind power. This, itself, is a challenging job.
CO2 emissions from cement production are incurred through the consumption of fossil fuels, the use of electricity, and the chemical decomposition of limestone during clinkerization, which can take place at around 1400C. The decarbonation of limestone to give the calcium required to form silicates and aluminates in clinker releases roughly 0.53t CO2 per ton of clinker . In 2005, cement production (total cementitious sales including ordinary Portland cement (OPC) and OPC blends) had an average emission intensity of 0.89 with a range of 0.650.92t CO2 per ton of cement binder . Therefore, the decarbonation of limestone contributes about 60% of the carbon emissions of Portland cement, with the remaining 40% attributed to energy consumption, most of which is related to clinker kiln operations; the WWF-Lafarge Conservation Partnership  estimated that the production of clinker is responsible for over 90% of total cement production emissions.
In view of the fact that the requirement for decarbonation of limestone presents a lower limit on CO2 emissions in clinker production, and that there exist technical issues associated with the addition of supplementary cementitious materials (SCMs, including fly ash and ground granulated blast furnace slag), which restrict the viability of direct Portland cement supplementation by SCM above certain limits, the possibility to reduce CO2 emissions using Portland chemistry is limited. The WWF-Lafarge Conservation Partnership  expects that the emissions intensity of cement, including SCM, could be reduced to 0.70t CO2 per ton of cement by 2030, which still amounts to around 2 billion tons of CO2 per annum worldwide, even if cement production does not increase from its current level.
Fig. 10.6 shows the CO2 emissions of various binder designs as a function of Portland cement content. There have been a limited number of life-cycle analyses (LCA) of geopolymer technology. One reasonably extensive research program carried out in Germany  has provided information regarding the selection of precursors and mix designs for a range of geopolymer-based materials. However, geographic specificity plays a significant role in a full LCA, so there is the need for further studies considering different locations in addition to a wider range of mix designs spanning the broader spectrum of geopolymers. The main carbon-intensive and also the most expensive ingredient in geopolymer cement is the alkali activator, which should be minimized in mix design. McLellan et al.  provided further detail, while Habert et al.  concluded that geopolymer cement does not offer any reduction in carbon emissions; such a conclusion needs to be drawn with caution.
Sodium carbonate is the usual Na source for the production of sodium silicate. The different processes for conversion of Na2CO3 (or NaOH) and SiO2 to sodium silicate, via either furnace or hydrothermal routes, differ by a factor of 23 in CO2 emissions, and up to a factor of 800 in other emissions categories . It is therefore essential to state which of these processes is used as the basis of any LCA. Moreover, the best available data for emissions due to sodium silicate production were published in the mid-1990s , so improvements in emissions since that time have not been considered. Sodium carbonate itself can be produced via two main routes, which vary greatly in terms of CO2 emissions. The Solvay process, which converts CaCO3 and NaCl to Na2CO3 and CaCl2, has emissions between 2 and 4t CO2 per ton of Na2CO3, depending on the energy source used. Conversely, the mining and thermal treatment of trona for conversion to Na2CO3 has emissions of around 0.14t CO2 per ton of Na2CO3 produced plus a similar level of emissions attributed to the electricity used. This indicates an overall factor of 510 difference in emissions between the two sources of Na2CO3 .
A commercial LCA was conducted by the NetBalance Foundation, Australia, on Zeobonds E-Crete geopolymer cement, as reported in the Factor Five report published by the Club of Rome . This LCA compared the geopolymer binder to the standard Portland blended cement available in Australia in 2007 on the basis of both binder-to-binder comparison and concrete-to-concrete comparison. The binder-to-binder comparison showed an 80% reduction in CO2 emissions, whereas the comparison on a concrete-to-concrete basis showed slightly greater than 60% savings, as the energy cost of aggregate production and transport was identical for the two materials. However, this study was again specific to a single location and a specific product, and it will be necessary to conduct further analyses of new products as they reach development and marketing stages internationally. Fig. 10.6 shows a comparison of the CO2 emissions of four different E-Crete products against the Business as Usual, Best Practice 2011, and a Stretch/Aspirational target for OPC blends. It is noted that in some parts of the world (particularly Europe), some of the blends shown here in the Stretch/Aspirational category are in relatively common use for specific applications, particularly CEM III-type Portland cement/slag blends, but this is neither achievable on a routine scale worldwide at present, nor across the full range of applications in which Portland cement is used in large volumes.
In this study, Aspen Plus software is used to model a cement kiln on the basis of energy and mass balance principle with the stoichiometry known of the chemical reactions. Different unit operation blocks were used to carry out specific tasks of the process, such as fuel decomposition, combustion, chemical reactions, cooling, and separation. In the current model all combustion was carried out on an energy balance basis. Combustion of the conventional fuel as well as the alternative ones took place in two Aspen Plus operation blocks. The two blocks were RYIELD and RGIBBS, where decomposition and combustion occur, respectively. Stoichiometric air was fed directly into the RGIBBS reactor block. Decomposition heat from the RYIELD reactor was transferred directly to the RGIBBS reactor block. The combustion residue and generated heat were then carried to the next series of operating blocks where clinkerization reactions occur in the presence of heat. The clinkerization process of the kiln was carried out by using three reactor blocks with the mass balance principle. A typical mass balance system of the kiln is given in Figure 9.6 which shows the required input and predicted output from the kiln to produce 1kg of clinker. The reaction stoichiometry of the clinkerization process is known as the process is well established. The mass balance principle along with the reaction stoichiometry allow the use of the Aspen Plus RSTOIC reactor block to model the kiln. A series of reactor blocks were used for the different phases of clinkerization that occur at increasing temperatures inside the kiln. Kiln gas is separated from the product flow and hot product is cooled down using a heat exchanger operation block. Air with ambient temperature is used to cool the hot clinker and finally the tertiary air and clinker are separated by a separator block.
Large numbers of methods are available in the Aspen Physical Property System and two property methods, namely the IDEAL and SOLIDS property methods, were chosen for the current kiln model. The properties of solid and fluid phases cannot be calculated with the same type of model. Therefore the components were distributed over the sub-streams of types MIXED, CISOLID, and NC and their properties were calculated with appropriate models. When the solids are decomposed into individual components, they normally occur in the CISOLID sub-stream. A CISOLID component can be in simultaneous phase and chemical equilibrium in the RGIBBS model. Fluid components always occur in the MIXED sub-stream and they were treated with the IDEAL model which accommodates Raoults law and Henrys law. Permanent gases may be dissolved in the liquid and can be modeled by using Henrys law. NC sub-stream represents the nonconventional component stream and all the alternative fuels are categorized in this class. HCOALGEN and DCOALIGT models were used for enthalpy and density calculation which is suitable for coal and other solid alternative fuels.
The manufacturing processes of cement may vary with respect to equipment design, method of operation, and fuel consumption. The cement manufacturing process includes the quarry, raw meal preparation, preheating of raw meal, kiln, clinker cooling, grinding, storage, and dispatch. In this process the calcium carbonate is heated to 900C to decompose into calcium oxide (CaO, lime), and CO2 is generated in the calcination process. After that in the cement kiln, the clinkerization occurs at high temperatures of 1400 to 1500C. In this process, calcium oxide reacts with silica, alumina, and ferrous oxide to form the silicates, aluminates, and ferrites, respectively. These are the main components of the clinker. This clinker is then ground in the ball mill together with gypsum and other additives to reduce cement. The main energy-intensive phase of the cement production process is the precalciner, kiln, and during the production of clinker. A large amount of thermal energy is required to create enough heat for the cement kiln and precalciner.
Based on the type of cement kiln process, alternative fuels can be utilized in the kiln together with the primary fuel (usually coal). Alternative fuels are injected with primary fuel by using a multichannel burner, which is capable of introducing solid and liquid fuel at the same time in the burning zone. Alternative fuel is selected on the basis of price, availability, energy content, moisture, and volatile content. The range of alternative fuel is extremely wide. These alternative fuels can be tires, plastic, paper, agricultural waste, organic material, pasty wastes, solvents, grease, oily wastes, landfill gas, pyrolysis gas, etc.
Cement is an inorganic, nonmetallic substance with hydraulic binding properties. Mixed with water, it forms a paste that hardens due to formation of hydrates. After hardening, the cement retains its strength. There are numerous cement types due to the use of different sources of calcium and different additives to regulate properties. The exact composition of cement determines its properties.
In 1999, global cement production was estimated to be 1600million tons. Because of the importance of cement as a construction material and the geographic abundance of the main raw materials, cement is produced in virtually all countries. The widespread production is also due to the relatively low price and high density of cement, and this in turn limits ground transportation due to high transport costs.
The most common raw materials used for cement production are limestone, chalk, and clay. The collected raw materials are selected, crushed, and ground so that the resulting mixture has the desired fineness and chemical composition for delivery to the pyro-processing systems. The grinding process differs depending on the pyro-processing process used. The feed to the kiln is called raw meal.
Clinker is produced by pyro-processing the raw meal. The raw meal is burned at high temperatures, first by calcination of the materials and then by clinkerization to produce clinker. Various kiln types have been used historically or are used around the world. Besides the rotary kiln, the vertical shaft kiln is used mainly in developing countries. In industrialized countries, the ground raw materials are processed predominantly in rotary kilns. In processing without precalcination, the decomposition (calcination) of CaCO3 to CaO and CO2 takes place in the kiln. The clinker is cooled. The cooling air serves as combustion air. The largest part of the energy contained in the clinker is returned to the kiln in this way.
Grinding of cement clinker together with additives to control the properties of the cement is done in ball mills, roller mills, or roller presses. Coarse material is separated in a classifier to be returned for additional grinding. Power consumption for grinding depends strongly on the fineness required for the final product and the use of additives.
Cement production is a highly energy-intensive process. Cement making consists of three major process steps: raw material preparation, clinker making in the kiln, and cement making. Raw material preparation and cement making are the main electricity-consuming processes, whereas the clinker kiln uses nearly all of the fuel in a typical cement plant. Clinker production is the most energy-intensive production step, responsible for approximately 70 to 80% of the total energy consumed. Raw material preparation and finish grinding are electricity-intensive production steps. Energy consumption by the cement industry is estimated at 6 to 7 EJ or 2% of global primary energy consumption.
The theoretical energy consumption to produce cement can be calculated based on the enthalpy of formation of 1kg of Portland cement clinker (which is 1.76 MJ). In practice, energy consumption is higher. The kiln is the major energy user in the cement-making process. Energy use in the kiln depends basically on the moisture content of the raw meal. Most electricity is consumed in the grinding of the raw materials and finished cement. Power consumption for a rotary kiln is comparatively low.
An accurate estimation of the baseline SEC value is an important step in the PAT methodology. Each Designated Consumer is dynamic in nature and its performance depends on the technology incorporated and business demand. The baseline SEC could be computed considering the average performance of last 3 years as it captures variations in manufacturing practices and operating conditions.
A simple calculation of the baseline SEC gives a broad indication of the energy intensity of a plant. However, it is necessary that a robust calculation of the baseline SEC be designed to reduce the impact of variations in plant operating conditions. Such normalization factors may be considered based on a few significant plant operating parameters.
The clinker output from the pyroprocessing unit is either sent to the grinding unit or exported to other cement plants or exclusive grinding units. Such clinker exports can cause variations in the baseline SEC.
Cement plants typically produce a variety of products in a given year and the product mix could vary from year to year based on market supply and demand conditions. Product changes can cause variations in the energy intensity of a cement plant.
Conversion factors: Industries operate in a dynamic market environment and have to manufacture multiple products to suit the prevailing business conditions. For instance, in cement industry, the major products are OPC, PPC, and PSC. The conversion factors could be used to convert these to an equivalent major product, which varies from plant to plant. The conversion factors required are the following:Clinker to OPCClinker to PPCClinker to PSC
Performance factors:a.SECelectrical:Electricity energy is required for different subprocesses such as clinker grinding, mining, and the clinkerization process. Therefore, electricity consumption could be estimated in two stages: from mining to clinkerization and for clinker grinding. Total electrical SEC of a plant includes packaging and plant utilities, but excludes power supply to the colony.b.SECthermal:Thermal energy is required for pyroprocessing and calcining. The thermal energy consumption is based on the total quantity of fuel used and the GCVs of the fuels used in burning the raw meal (RM). The thermal SEC is the energy (kcal) required to produce 1kg of clinker.
Electricity energy is required for different subprocesses such as clinker grinding, mining, and the clinkerization process. Therefore, electricity consumption could be estimated in two stages: from mining to clinkerization and for clinker grinding. Total electrical SEC of a plant includes packaging and plant utilities, but excludes power supply to the colony.
Thermal energy is required for pyroprocessing and calcining. The thermal energy consumption is based on the total quantity of fuel used and the GCVs of the fuels used in burning the raw meal (RM). The thermal SEC is the energy (kcal) required to produce 1kg of clinker.
The simple calculation of gate-to-gate SEC does not account for variations in plant-specific factors such as export and import of clinker, conversion of the product mix to equivalent major product, and the CPPs net heat rate and share of power exported to the grid.
In this section, the application of the baseline methodology for sample cement plants is illustrated. The results are based on a study of nine sample plants. The study highlights the diversity among the sample plants. The diversity exists in a number of performance factors, operating conditions, and parameters such as capacity, product mix, CPP efficiency, conversion factors, energy input mix, and import or export of clinker. The simple baseline SEC and the normalized baseline SEC for the sample plants are also compared.
Industrial case studies: A comparative parametric study of nine sample plants is shown in this section. These plants differ from each other across several parameters. A brief description of the sample plants is provided below:
Plant P1: Plant P1 employs a dry process with an annual cement production of 3.383Mt. The total energy consumption is 2.479106Mkcal. About 98% of the final product is PPC, while the rest 2% accounts for OPC. It imported 0.15Mt clinker and also exported 0.0104Mt clinker in the same year.
Plant P2: About 1.04Mt of cement is produced in plant P2 by the dry process. The product profile constitutes 75% PPC, 20% OPC, and 5% PSC. The unit also supplies clinker to other cement plants. The total electricity consumed within the plant is estimated to be 80.13MkWh, while the total energy, electrical and thermal together, is calculated to be 992.44billion kcal.
Plant P3: This unit with dry processing technology has produced 2.96Mt of cement. The total energy consumption is 4.9206M kcal. The cement variants produced are OPC (30%), PPC (11%), and PSC (24%). One of the key aspects of this unit is the amount of exported clinker (1.107Mt).
Plant P4: This plant also follows dry processing technology and has produced 0.99Mt of combined cement variety with an estimated total energy consumption of 1.01106M kcal. A total of 86% PPC and 13% OPC is produced. This plant imports clinker (0.059Mt).
Plant P5: With 77.30% capacity utilization, this unit has produced 4.2Mt of OPC and PPC varieties. About 20% of the total clinker produced is exported. A total of 1.10Mt of clinker is exported and 0.02Mt is imported. The total energy consumption of this unit is estimated to be 6.0406Mkcal. About 82.309M kWh of electricity is exported (highest among nine plants).
Plant P7: Combined cement production is 1.36Mt with 86.33% capacity utilization. The main production is PPC cement (94%). A significant amount of electricity is supplied to the grid. The total energy consumption is 0.989106M kcal.
In this section, the plants are compared on the basis of specific parameters. The comparison showcases the diversity that exists between the cement plants. The results of this comparison can be utilized to better understand the challenges that the cement industry faces in improving its energy efficiency and in the development of a more robust baseline SEC.
Production and capacity utilization: Figure 3.3.28 shows the comparative performance of nine industrial units with respect to installed capacity and actual cement produced. The capacity utilization of the sample plants ranges from 37% to 116%.
Electricity consumption: Figure 3.3.29 shows the electricity generated and consumed in the sample plants. It is observed that some plants are purchasing electricity from the grid while others generate more than their consumption and export the surplus power to the grid.
Solid fuel consumption: Coal is the common solid fuel used in the nine plants; however, three units import coal with higher GCV. The GCV of Indian coal ranges between 3412 and 5379kcal/kg. The GCV of imported coal ranges between 5540 and 6884kcal/kg. P5 consumes lignite along with Indian and imported coal. Figure 3.3.30 shows the total coal consumption in the nine plants and Figure 3.3.31 shows the GCV values of the coal consumed.
Liquid fuel consumption: In this section the nine cement units are analyzed with respect to the quantity of liquid fuels used. Figure 3.3.32 shows the GCV of liquid fuels. The energy consumption from liquid fuels is shown in Figure 3.3.33. Plants P1P5 use a variety of liquid fuels.
Total energy used for process heating: Figure 3.3.34 shows the energy used for process heating across plants. Plant P5 utilizes more energy for process heating (5106M kcal), while plant P2 accounts for the least (0.59106M kcal).
Performance indicators: Figure 3.3.36 shows the comparison of performance indicators across the nine plants. The thermal SEC ranges from 702 to 1045kcal/kg clinker. The electrical SEC up to clinkerization ranges from 55.5 to 82.1kWh/ton clinker. The electrical SEC for cement grinding ranges from 27.6 to 45.7kWh/ton cement.
Total energy consumption: The total energy consumed is calculated by adding the total thermal energy and the total electricity consumed in the plant. The electricity purchased from and exported to the grid is multiplied by the standard energy conversion rate (1kWh=860kcal).
Equivalent major grade cement: Equivalent major grade cement can be estimated using the cement conversion factors. The amount of OPC, PPC, and PSC can be converted to an equivalent major grade cement (among the different grades) using the different conversion factors. The total clinker exported and imported can also be converted to equivalent major grade cement. The total equivalent major grade cement is calculated by adding the above two equivalent grade cements. Figure 3.3.39 shows the equivalent major grade cement across the different plants along with the actual combined cement production.
Cement manufacturing comprises various subprocessesRM grinding, preheating, precalcining, clinkerization, and grinding. Energy is consumed in each of the subprocesses. A major portion of the energy consumed is thermal energy (8090%) and the rest is electrical. The clinkerization subprocess consumes the largest share of thermal energy, whereas cement grinding mills consume the highest electrical energy .
High preheater exit gas volume and temperature, high pressure drop across the preheater, high moisture content in the fine coal, incomplete combustion of coal, low heat recuperation efficiency of grate cooler, high cooler air exhaust temperature, high clinker temperature, low efficiency of major process and cooler fans, and underloading of motors resulting in low operating efficiency are some of the major factors that result in higher energy consumption within the major subprocesses.
Several energy audit studies have estimated 510% energy savings in thermal and electrical energy consumption by adopting different energy conservation measures. It is estimated that the saving of 5kcal/kg of thermal energy and 1kWh/ton cement of electrical energy will result in total savings of about Rs 6million per annum in a typical 1Mt plant.
There are several energy efficiency measures that have either already been adopted or could be adopted by the industry. However, the actual set of measures that is suited for a particular Designated Consumer would be based on the specific operating conditions.
Energy efficiency technologies:In preheaters and precalciners, low pressure drop and high efficiency cyclones could be used instead of conventional cyclones. In addition, pressure drop could be reduced by installing an additional cyclone parallel to the existing top stage cyclone.In a typical kiln, the charge composition and quantity could be modified. Additional measures include arresting the false air entry and optimization of several operating parameters.High efficiency ESPs and pollution control devices.Existing ball mills could be replaced by vertical roller mills (VRM). The SEC of a ball mill is about 2026kWh/ton of RM while a VRM consumes 1418kWh/ton-RM, resulting in a 30% SEC reduction.Installation of variable frequency drives in major electrical motors and fans.CPP: In 2007, around 2250MW capacity of CPP was installed by the cement industry. Reduction of net station heat rate and auxiliary power consumption, and installation of high efficiency boilers and condensers are some of the ways to increase the efficiency of CPPs.
In preheaters and precalciners, low pressure drop and high efficiency cyclones could be used instead of conventional cyclones. In addition, pressure drop could be reduced by installing an additional cyclone parallel to the existing top stage cyclone.
CPP: In 2007, around 2250MW capacity of CPP was installed by the cement industry. Reduction of net station heat rate and auxiliary power consumption, and installation of high efficiency boilers and condensers are some of the ways to increase the efficiency of CPPs.
Alternative fuel resources (AFR): Presently, a very small percentage of alternate fuels are being used in cement plants in India, whereas, a high percentage of thermal substitution has been achieved in some plants abroad. There is a large scope of increasing the percentage of AFR such as industrial wastes, rice husks, tires, etc.
Clinker is the main constituent of portland cement. Clinker consists of calcium oxide and other mineral oxides (iron, aluminum, and silicon) and has cementious activity when reacted with water. Clinker is produced by pyroprocessing in large kilns. These kiln systems evaporate the free water in the meal, calcine the carbonate constituents (calcination), and form cement minerals (clinkerization). In the chemical transformation, calcium carbonate is transformed into calcium oxide, leading to a reduction in the original weight of raw materials used. Furthermore, cement kiln dust may be emitted to control the chemical composition of the clinker. Clinker production is the most energy-intensive stage in cement production, accounting for more than 90% of total industry energy use and virtually all the fuel use.
The main kiln type used throughout the world is the large-capacity rotary kiln. In these kilns, a tube with a diameter up to 8m is installed at a 34 angle and rotates one to three times per minute. The ground raw material, fed into the top of the kiln, moves down the tube toward the flame. In the sintering (or clinkering) zone, the combustion gas reaches a temperature of 18002000C. Although many different fuels can be used in the kiln, coal is the primary fuel in most countries.
In a wet rotary kiln, the raw meal typically contains approximately 36% moisture. These kilns were developed as an upgrade of the original long dry kiln to improve the chemical uniformity in the raw meal. The water is first evaporated in the kiln in the low-temperature zone. The evaporation step requires a long kiln. The length-to-diameter ratio may be up to 38, with lengths up to 230m. The capacity of large units may be up to 3600 tonnes of clinker per day. Fuel use in a wet kiln can vary between 5.3 and 7.1GJ/tonne clinker. The variation is due to the energy requirement for the evaporation and, hence, the moisture content of the raw meal. Originally, the wet process was preferred because it was easier to grind and control the size distribution of the particles in a slurry form. The need for the wet process was reduced by the development of improved grinding processes.
In a dry kiln, feed material with much lower moisture content (0.5%) is used, thereby reducing the need for evaporation and reducing kiln length. The dry process was first developed in the United States and consisted of a long dry kiln without preheating or with one-stage suspension preheating. Later, multistage suspension preheaters (i.e., a cyclone) or shaft preheaters were developed. Additionally, precalciner technology has recently been developed in which a second combustion chamber has been added to a conventional preheater that allows for further reduction of kiln energy requirements. The typical fuel consumption of a dry kiln with four- or five-stage preheating varies between 3.2 and 3.5GJ/tonne clinker. A six-stage preheater kiln can theoretically use as low as 2.93.0GJ/tonne clinker. The most efficient preheater, precalciner kilns, use approximately 2.9GJ/tonne clinker. Kiln-dust bypass systems may be required in kilns in order to remove alkalis, sulfates, or chlorides. Such systems lead to additional energy losses since sensible heat is removed with the dust. Figure 3 depicts the typical specific energy consumption for different kiln types in use throughout the world.
Figure 3. Energy consumption and losses for the major kiln types: wet process, Lepol or semiwet, long dry, dry process with four-stage suspension preheating (SP), and dry process with four-stage suspension preheating and precalcining (PC/SP).
Once the clinker is formed, it is cooled rapidly to ensure the maximum yield of alite (tricalcium silicate), an important component for the hardening properties of cement. The main cooling technologies are either the grate cooler or the tube or planetary cooler. In the grate cooler, the clinker is transported over a reciprocating grate passing through a flow of air. In the tube or planetary cooler, the clinker is cooled in a countercurrent air stream. The cooling air is used as combustion air for the kiln.
In developing countries, shaft kilns are still in use. These are used in countries with a lack of infrastructure to transport raw materials or cement or for the production of specialty cements. Today, most vertical shaft kilns are in China and India. In these countries, the lack of infrastructure, lack of capital, and power shortages favor the use of small-scale local cement plants. In China, this is also the consequence of the industrial development pattern, in which local township and village enterprises have been engines of rural industrialization, leading to a substantial share of shaft kilns for the total cement production. Regional industrialization policies in India also favor the use of shaft kilns, in addition to the large rotary kilns in major cement-producing areas. In India, shaft kilns represent a growing portion of total cement production, approximately 10% of the 1996 production capacity. In China, the share is even higher, with an estimated 87% of output in 1995. Typical capacities of shaft kilns vary between 30 and 180 tonnes of clinker per day.
The principle of all shaft kilns is similar, although design characteristics may vary. The shaft kiln is most often cone shaped. The pelletized material travels from top to bottom, through the same zones as those of rotary kilns. The kiln height is determined by the time needed for the raw material to travel through the zones and by operational procedures, pellet composition, and the amount of air blown. Shaft kilns can achieve reasonably high efficiency through interaction with the feed and low energy losses through exhaust gases and radiation. Fuel consumption in China varies between 3.7 and 6.6GJ/tonne clinker for mechanized kilns, with the average estimated at 4.8GJ/tonne clinker. In India, presumably, shaft kilns use between 4.2 and 4.6GJ/tonne clinker. The largest energy losses in shaft kilns are due to incomplete combustion. Electricity use in shaft kilns is very low.
Given the environmental challenges inherent in Portland cement manufacture (high thermal and electrical energy demand, need to quarry large quantities of limestone and clay and the emission of greenhouse gases, especially CO2), the study and development of cements based on the reuse of waste of varying origin is a priority line of research and technological innovation in the pursuit of industry sustainability. A broad range of types of waste can be used in blends with Portland cements, representing an environmentally friendly and clinker-saving way of production.
Of the 27 types of cement listed in the European Standard EN 197-1:2011 (Sanjun and Argiz, 2011), 26 contain some manner of mineral addition which can include industrial residues such as siliceous or calcareous fly ash, blast-furnace slag, or silica fume. All of the aforementioned additions are industrial by-products and dependent on the content of natural radionuclides some of them are listed as naturally occurring radioactive materials (NORMs). The trend of industrial by-product recycling is expected to continue. The draft of the common cements standard prEN 197-1:2016 includes five new cement subtypes with higher amounts of by-products; in particular, siliceous fly ash and blast-furnace slag. In addition to the earlier, new potential cement constituents are being explored, such as ground coal bottom ash, paper sludge ash, silicon-manganese slag, copper slag, and so on (Argiz et al., 2013; Vegas et al., 2006; Sabador et al., 2007; Frias et al., 2006; Garca Medina et al., 2006; Siddique, 2003).
Industrial waste and by-products are used not in blends with Portland cement, but may also be added during clinkerization itself, partially or totally replacing the virgin raw materials in the raw meal (limestone in particular) or contributing as secondary fuel. Very different types of waste or by-products can be used as partial raw meal replacements, including crystallized blast-furnace slag (Puertas et al., 1988), waste from the manufacture of clay-based products (Puertas et al., 2010), aluminum recycling (Paval) (Blanco-Varela et al., 2000), etc. Efforts are also being made to use alternative fuels in OPC production: in countries such as the Netherlands, Austria, Germany, and Norway, these fuels account for over 60% of the total. The sources vary widely in nature, including shredded tires, solvents, water treatment plant sludge and used oil, among others (Pontikes and Snellings, 2014).
Another avenue for manufacturing eco-efficient cements is the development of new materials wholly different from ordinary Portland cement. Due to their mechanical and durability properties, versatility alkali-activated cements (also known as geopolymers) are among the most prominent of these new materials (Palomo et al., 2014). These cements are defined as the binders resulting from the chemical interaction between alkaline solutions and natural (clay; possibly thermally treated) or the result of human activity (industrial waste or by-products) aluminosilicates with a high- or low-Ca content, possibly having also Fe. Alkaline activation calls for two basic components: (1) a solid precursor that is prone to dissolution (most often amorphous or vitreous) and (2) an alkaline activator. The aluminosilicates may be natural products such as metakaolin or industrial by-products such as blast-furnace slag or aluminosiliceous fly ash. The alkaline solutions able to interact with aluminosilicates to generate such new binders include alkaline metal or alkaline-earth hydroxides (ROH, X(OH)2), weak acid salts (R2CO3, R2S, RF), strong acid salts (Na2SO4, CaSO42H2O), and R2O(n)SiO2-type siliceous salts known as waterglass (where R is an alkaline ion such as N, K, or Li). From the standpoint of end product strength and other properties, the most effective of these activators are NaOH, Na2CO3, and sodium silicate hydrate (waterglass). Industrial by-products are presently also being studied for use as possible alkaline activators. Patents have been awarded for the use of industrial waste or by-products such as ash from rice husks, silica fume, and urban and industrial vitreous waste as potential alkaline activators to replace the family of substances known as water glass (Puertas and Torres-Carrasco, 2014). Here also, the main components of these cements may be NORMs.
The foregoing is indicative of the high potential for reuse and valorization of industrial waste and by-products in the manufacturing of cement and other construction materials. To be apt for such purposes, the waste must exhibit certain chemical, physical, and microstructural characteristics that favor their reactivity and behavior. Next to the binder described so far, the aggregates to be used for mortar and concrete production can also be residues and NORM in particular. Considering that they could be used in a proportion close to 80% in concrete volume, they might have a substantial contribution in the concentration of radionuclides in the final building materials.
The main ceramics which are produced using raw materials that can contain enhanced concentrations of natural radionuclides are refractories as well as tiles in which zirconia (the main source of natural radionuclides) is mixed with other constituents. In refractories, the applications cover the production of either prefabricated units (bricks) or the use as a mortar for in situ applications, for example, in kilns. Not every zirconia can be considered as NORM and in some cases only smaller amounts of zirconia are used, hence, not every refractory has enhanced levels of natural radionuclides. This is controlled by the composition of the refractory, which depends on the required properties in terms of temperature, chemical corrosive circumstances, and whether abrasion is an issue. Refractories with enhanced levels of natural radionuclides can be found in the glass industry (kilns) and sometimes in the ceramic brick or tiles kilns. Zirconium is also a common opacifier of ceramic glazes. In general, the glazes show activity concentrations below 1kBq/kg for the main natural radionuclides, and only their production deserves control.
Other areas where significant amounts of by-products, such as fly ash, mining tailings, etc., are incorporated are clay-based formulations, ceramic bricks for example. Despite the often notable amount of by-products employed, the concentration of natural radionuclides in such ceramic materials is, in general, similar to that of common ceramic bricks.
Considering the present state of the art of cement making, there is very little scope for reducing fuel consumption further (from 700kcals to 650kcal/kg), unless clinkerization takes place at lower temperatures.
Developed countries have made good progress in this direction. Major producers like India have a long way to go. The potential for generating power by installing WHR is shrinking because of improvements in fuel efficiency even when state of the art technologies like the Ormat Rankine cycle or Kalina cycles are adopted.
Even if total CO2 emissions are reduced from the present level of ~700kg/ton of OPC to 560kg (see ref. 1 in preface), a reduction of 20%, the emission level will still be higher than the target set, e.g., 525kg/ton of clinker set by IPCC to be achieved by 2020.
It is therefore necessary to also seek other avenues to achieve this objective. One possibility that is being seriously followed is to capture CO2 from the exhaust gases and store it safely in liquid form.1.2.1Carbon capture and storage (CCS) schemes are being considered for thermal power plants. They envisage separating CO2 from the flue gases (kiln exhaust gases from cement kilns), collecting it, compressing it, transporting it in liquid form through pipelines and storing it in deep underground reservoirs.1.2.2Technologies for compressing and transporting are available. Technologies for capture are under various stages of development. Some have been developed on a small scale but none yet on the scale required for todays cement plants.
Carbon capture and storage (CCS) schemes are being considered for thermal power plants. They envisage separating CO2 from the flue gases (kiln exhaust gases from cement kilns), collecting it, compressing it, transporting it in liquid form through pipelines and storing it in deep underground reservoirs.
Technologies for compressing and transporting are available. Technologies for capture are under various stages of development. Some have been developed on a small scale but none yet on the scale required for todays cement plants.
It is envisaged that fossil fuel is replaced by hydrogen as fuel. However this technology has not yet been tried out in a cement plant. Because hydrogen is explosive it cannot be used by itself. It has to be diluted with nitrogen or steam.
Two main schemes under development are:1.amine scrubbing2.carbonate looping.1.6.1Amine scrubbingIn this, CO2 is first absorbed by monoethalomine. It is then separated from the amine solution, dried, compressed and transported to a storage site.It is easily possible to install the amine capturing equipment in the gas circuit of the cement plant without major modifications. Equipment needed to be installed is shown in flow chart of Fig. 3.1.2.Figure 3.1.2. Carbon capture and storage (CCS) flow chart for amine scrubbing process.(Source: PCA R&D Serial No. 3022).CO2 is compressed in a compression plant in which gas is dried and compressed to a pressure of 110bar and transported in a pipeline. The main disadvantage of amine scrubbing is that it is often degraded by oxygen and impurities like SOx and NOx. It is expensive to install.1.6.2Carbonate looping:The basic principle is:CaO+CO2=CaCO3CaCO3=CaO+CO2This scheme is in early stages of development. It envisages lime carbonation and calcination. It is based on separation of CO2 from the combustion gases by using lime as an effective sorbent to form CaCO3.CO2 is then separated from the carbonate at high temperatures by using CaO as a regenerable sorbent.Reverse calcination produces a gas rich in CO2 and regenerates CaO for subsequent cycles.Carbonation reaction in the first stage takes place in a fluidized bed combustor at temperatures of ~650-850C.Carbonate particles are separated from flue gas and are sent to the calciner where at ~950C CO2 is separated and taken to storage.A small amount of fresh sorbent calcium carbonate needs to be added to the system to maintain the overall sorbent activity. In this process of capturing CO2, it is necessary to deal with mass flows 60 times larger than those required to produce clinker.Using lime purge materials from the calcium looping process as a raw material substitute in cement production allows considerable savings of fuel and CO2 emissions. See a flow chart of the scheme in Fig. 3.1.3.Figure 3.1.3. Carbon capture and storage (CCS) carbonation-calcination loop process.(Source: Modeling and analysis CO2 capture in industrial sectors GHG Science & Technology).Ironically, more CO2 emissions occur in systems with CCS because of lower operating efficiency. Further developments are awaited.
It is easily possible to install the amine capturing equipment in the gas circuit of the cement plant without major modifications. Equipment needed to be installed is shown in flow chart of Fig. 3.1.2.
CO2 is compressed in a compression plant in which gas is dried and compressed to a pressure of 110bar and transported in a pipeline. The main disadvantage of amine scrubbing is that it is often degraded by oxygen and impurities like SOx and NOx. It is expensive to install.
This scheme is in early stages of development. It envisages lime carbonation and calcination. It is based on separation of CO2 from the combustion gases by using lime as an effective sorbent to form CaCO3.
A small amount of fresh sorbent calcium carbonate needs to be added to the system to maintain the overall sorbent activity. In this process of capturing CO2, it is necessary to deal with mass flows 60 times larger than those required to produce clinker.
Using lime purge materials from the calcium looping process as a raw material substitute in cement production allows considerable savings of fuel and CO2 emissions. See a flow chart of the scheme in Fig. 3.1.3.
There are quite a few projects under various stages of implementation all over the world in the power sector. However it is too early to say whether CCS will be a viable proposal for even large cement plants.
In this process CO2 in the flue gases of thermal power plants is led to seawater, where it reacts with the salts in seawater to produce a cement-like product. This has been described in Section 9 on cement substitutes.
The clinkerization process has been used since many decades and involves solid state reaction between oxides of starting materials. Due to the solid state reaction, high energy is required to allow the diffusion of atoms and molecules of crystals. Raw materials used to produce CSA (yeelimite or 4CaO3Al2O3 SO3 or C4A3) can be any matter that can supply CaO, Al2O3, and SO3. Pure reagents such as calcite (CaCO3), alumina (Al2O3), and calcium sulfate compounds (CaSO4, CaSO41/2H2O, CaSO42H2O) are a good choice to produce pure CSA or yeelimite phases. The required stoichiometry is 4:3:1 for CaO:Al2O3:SO3 to obtain 4CaO3Al2O3SO3. The yeelimite phase and the belite phases are unavoidably formed when starting materials contain SiO2. This cement is therefore called CSAB. There were several reports of using various inorganic wastes to produce CSA cement. El-Alfi and Gado (2016) used marble sludge waste from a marble processing factory to prepare CSAB cement via clinkerization. This waste mainly contained only calcite (CaCO3), as identified by X-ray diffraction. To synthesize CSAB, hemihydrates calcium sulfate and kaolin were the sources of sulfate and Al2O3, respectively, to form yeelimite. This research showed a preference to form yeelimite when the kaolin (Al2O3 source) content was increased. The recommended conditions were 25:20:55 of kaolin:hemihydrate:marble waste and only 1200C of firing temperature. The calculated cement phase using the modified Bogue equations consisted of 22.30% of yeelimite, 43.6% of C2S, 1.58% of C4AF, 18.62% of calcium sulfate and 3.76% of CaO. The strength development after cement hydration was about 36MPa (28 days curing) without additional calcium sulfate compound. Costa et al. (2016) studied the production of CSAB cement using aluminum anodizing sludge as Al2O3 source. Aluminum waste contained mainly Al2O3 and SO3 approximately 73.6wt% and 20.5wt%, respectively. The raw mix contained 18.5:7.3:72.9 of aluminum anodizing sludge:calcium sulfate:lime stone. The raw mix was fired at 1250C for 30minutes. The resulting CSAB composed of 28.8wt% of orthorhombic yeelimite, 6.7wt% of cubic yeelimite, 39.1wt% of belite, 7.4wt% of brownmillerite (C4AF), 4wt% of anhydrite, 8.2wt% of alite and 5.9wt% of periclase. The measured belite (C2S) and alite (C3S) formations were questionable because starting materials had no SiO2 content. The compressive strength of hydrated paste at 28 days curing was 41.7MPa. Viani and Gualtieri (2013) used thermal transformed cementasbestos to prepare calcium sulfoalumiante cement. The cementasbestos mineral, which was a CaO and SiO2 source, composed of 33.1wt% of SiO2, 49.2wt% of CaO, 5wt% of Al2O3, 7.67wt% of MgO, and 2.12wt% of Fe2O3. -C2S, amorphous, C4AF, mayenite and periclase of this waste were approximately 62wt%, 13wt%, 5.5wt%, 7.3wt%, and 5.0wt%, respectively. This waste was used to prepare CSA using 29:25:15:31 of cementasbestos: gibbsite: gypsum: calcite. The given cement consisted of 41.6wt% of yeelimite, 26.3wt% of -C2S, 1.4wt% of C4AF, 9.2wt% of CaO, 8.3wt% of CaSO4, and 11wt% of amorphous phase. There was no report on strength development in this work. Iacobescu et al. (2013) synthesized calcium ferroaluminate belite cements using electric arc furnace steel slag (EAFS) as one of the raw materials. EAFS composed of 32.50wt% of CaO, 26.30wt% of FeO, 18.10wt% of SiO2, 13.30wt% of Al2O3, 3.94wt% of MnO, 2.53wt% of MgO, and 1.38wt% of Cr2O3. Mineralogical compositions of EAFS were 41wt% of C2S, 14.7wt% of gehlenite, 12.0wt% of wustite, 10.0wt% of magnetite, 9.4wt% of C4AF, 7.2wt% of C12A7, 3.7wt% of merwinite, and 2.0wt% of spinel. The used raw mix was 62:20:8:10 of lime stone:bauxite:gypsum:EAFS. The obtained cement contained 44.6wt% of C2S, 33.0% of C4AF, 19.7wt% of yeelimite, and 3.9wt% of calcium sulfate calculated by Rietveld X-ray diffraction. The calculated and measured mineralogical compositions were relatively similar. After hydration, the cement with addition of 20wt% FGDgypsum (flue-gas desulfurizationgypsum) could gain strength up to 44MPa at 28 days curing. Katsioti et al. (2006) examined the use of jarositealunite precipitates from a stage of a new hydromettalurgical process in order to produce SAC clinker. The jarositealunite precipitate consisted of 16.55wt% of Al2O3, 39.66wt% of Fe2O3, 1.20wt% of SiO2, and 44.98wt% of SO3. The precipitate can be Al2O3, Fe2O3, and SO3 sources. The mineralogical compositions were jarosite, goethite, akaganeite, epsomite, and alunite. The raw mix contained 52.4:30.9:5.4:11.3 of lime stone:bauxite:gypsum:jarositealunite. The firing temperature was set at 1300C. As calculated by the modified Bogue equations, the obtained cement clinker consisted of 44.90wt% of C2S, 16.37wt% of C4AF, 28.35wt% of C4A3, and 10.18wt% of CaSO4. There was no report of the additional calcium sulfate compound. The strength development of the cement after hydration was approximately 34MPa at 28 days curing. The strength developed from those several SACs was promising when compared to commercial CSA cement (Trauchessec et al., 2015). The shortage of Al2O3-bearing materials to produce CSA cement is now a serious concern worldwide. Looking for alternative inorganic wastes such Al2O3-containing materials is inevitable. The previous research lists, as mentioned above, are good examples for substituting the primary Al2O3 source. Bauxite residue from Bayers process (Al2O3 manufacturing process) was currently considered to produce calcium sulfoalumiante cement, due to its great availability all over the world (approximately 2.7 billion tons) (Pontikes and Angelopoulos, 2013). The average chemical compositions of the bauxite residue was 46.1wt% of Fe2O3, 18.4wt% of Al2O3, 10.8wt% of SiO2, 9.9wt% of TiO2, 9.7wt% of CaO, 5.1wt% of Na2O. Its mineralogical compositions can be in various forms; hematite (-Fe2O3), goethitie (-FeOOH), magnetitie (Fe3O4), boehmite (-AlOOH), gibbsite (-Al(OH)3), diaspore (-AlOOH), sodalite, crancrinite, quartz, rutile, anatase, calcite, etc. The bauxite residue has been used to produce belite-sulfoaluminoferrite cement (BCSAF) at an industrial scale by Lafarge to obtain -C2S, C4A3 and C2AxF(1x) solid solution which showed similar performance compared to OPC.
There was a study in the synthesis of aliteyeelimite cement (Ma et al., 2013). Alite phase was preferred rather than belite in a combination with yeelimite in terms of its steel corrosion resistance and very high early strength requirement. However, the process to produce aliteyeelimite cement is more complicated because the formation temperature of alite and yeelimite is different. As previously mentioned, a suitable temperature for yeelimite formation is below 1300C while the alite formation requires heating up to 1300C. This study proposed different firing profiles compared to previous studies. Two-cycle firing was carried out in order to sustain both phases. A first cycle was at 1450C for 30minutes, followed by air-quenching. The second cycle was at 1250C for 1hour followed by air-quenching. The subsequent cement clinker consisted of yeelimite, alite, C4AF, C3A, and anhydrite. For one cycle of firing, the cement clinker had lower contents of yeelimite and alite but larger amounts of C3A. For two-step firing, the first and second cycles were to form alite (C3S) and yeelimite (C4A3), respectively. With two-cycle firing, C3A and anhydrite were transformed to C4A3 and C4AF during the second step.
The idea to produce belite sulfoaluminate (BSA)ternesite cement was proposed, in order to study its hydration and strength development (Shen et al., 2015). Ternesite is calcium sulfosilicate (C5S2) which can be formed when excess calcium sulfate exists together with belite (C2S) phase at approximately 11501250C. Above 1250C, ternesite decomposes. There were many reports indicating a slow hydration of ternesite but providing better hydration at later age. Due to different formation temperatures of C4A3 and C5S2, heat treatments of two cycles were used to maintain ternesite in the clinker. The first and second cycles were carried out at 1270C and 10001200C, respectively. With the use of one cycle, there was no ternesite formation in the clinker. BSAternesite cement synthesized with the second cycle heat treatment at 1150C for 15minutes, contained 34.5wt% of C4A3, 20.3wt% of C2S, 8.2wt% of C4AF, 5.1wt% of C, and 31.9wt% of C5S2. For BSA cement, 33.8wt% of C2S (33.8wt%) was formed instead of ternesite together with 38.9wt% C4A3. With regard to strength development, BSA cement had better early age compressive strength but BSA with ternesite gained the better strength at later ages while gaining similar heat evolution. The difference between hydration product development of BSA and BSAternesite clinkers was the development in stratlingite phase from BSAternesite clinker, whereas no stratlingite was formed from BSA clinker. It was believed that stratlingite was causing the later age strength development (Martin et al., 2017).
After clinkerisation, the exiting hot clinker is cooled in the clinker cooler, while the released heat is used to heat the combustion air. The exhaust air from the cooler can also be used to generate power and dry materials. Main clinker cooler technologies include grate, planetary and rotary coolers. Grate coolers are often preferable compared to other cooler technologies, because they possess a larger capacity (12,000tonnes/day) than conventional coolers (4000tonnes/day). Grate coolers are recover heat more efficiently.
Planetary and rotary coolers can be replaced by grate coolers to improve the efficiency of a cooling system. Grate coolers can provide pre-heated tertiary air to pre-calciners. Modern coolers can improve the heat efficiency by 7075%. Current 2nd generation grate coolers, which have an efficiency of 5065%, can be optimised by exchanging the grate plates for more efficient plates. The aeration system can also be modified depending on the cooler type. The installation of grate coolers could save up to 8% of the fuel used by the kiln. However, despite improving the efficiency of energy use, grate coolers require more power (between 3 and 6kWh/tonne clinker) compared to planetary and rotary coolers (ECRA, 2009).
Retrofitting of grate cooler in cement manufacturing is a common practice due to their influence on the performance and economy of cement plant. Currently, only half of the installed capacity of clinker cooling corresponds to best available technology (Moya etal., 2011).