These are sedimentary, calcium carbonate rocks (CaC03). Most commonly they contain a small amount of magnesium carbonate also.Besides, usual impurities in limestones are those of iron oxides, silica, and alkalies.
The raw materials (limestone and clay) are subjected to such processes as, crushing, drying, grinding, proportioning, and blending or mixing before they are fed to the kilns for calcination or burning process.
The drying stage is typical of the Dry Process. Drying of crushed materials is essential and is achieved by heating these materials (separately) at temperatures sufficiently high to drive out uncombined water.
Each raw material is thus reduced to a required degree of fineness and is stored separately in suitable storage tanks called SILOS or bins where from it can be drawn out conveniently in requisite quantities.
The blended materials are now ready for feeding into the burning kilns. From this stage onwards, there is practically no major difference between the dry and wet processes, except in the design of the rotary kiln.
(c) Compound Formation: Lime and magnesia as formed above are combined in the next stage with silica, alumina and ferric oxide to form the basic compounds of cement, namely, the tri-calcium and di-calcium silicates, tri-calcium aluminates and tetra-calcium-alunino ferrite.
Cement is the basic ingredient of construction and the most widely used construction material. It is a very critical ingredient, because only cement has the ability of enhancing viscosity of concrete which in returns provides the better locking of sand and gravels together in a concrete mix.
Cement uses raw materials that cover calcium, silicon, iron and aluminum. Such raw materials are limestone, clay and sand. Limestone is for calcium. It is combined with much smaller proportions of sand and clay. Sand & clay fulfill the need of silicon, iron and aluminum.
Generally cement plants are fixed where the quarry of limestone is near bye. This saves the extra fuel cost and makes cement somehow economical. Raw materials are extracted from the quarry and by means of conveyor belt material is transported to the cement plant.
There are also various other raw materials used for cement manufacturing. For example shale, fly ash, mill scale and bauxite. These raw materials are directly brought from other sources because of small requirements.
Before transportation of raw materials to the cement plant, large size rocks are crushed into smaller size rocks with the help of crusher at quarry. Crusher reduces the size of large rocks to the size of gravels.
The raw materials from quarry are now routed in plant laboratory where, they are analyzed and proper proportioning of limestone and clay are making possible before the beginning of grinding. Generally, limestone is 80% and remaining 20% is the clay.
Now cement plant grind the raw mix with the help of heavy wheel type rollers and rotating table. Rotating table rotates continuously under the roller and brought the raw mix in contact with the roller. Roller crushes the material to a fine powder and finishes the job. Raw mix is stored in a pre-homogenization pile after grinding raw mix to fine powder.
After final grinding, the material is ready to face the pre-heating chamber. Pre-heater chamber consists of series of vertical cyclone from where the raw material passes before facing the kiln. Pre-heating chamber utilizes the emitting hot gases from kiln. Pre-heating of the material saves the energy and make plant environmental friendly.
Kiln is a huge rotating furnace also called as the heart of cement making process. Here, raw material is heated up to 1450 C. This temperature begins a chemical reaction so called decarbonation. In this reaction material (like limestone) releases the carbon dioxide. High temperature of kiln makes slurry of the material.
The series of chemical reactions between calcium and silicon dioxide compounds form the primary constituents of cement i.e., calcium silicate. Kiln is heating up from the exit side by the use of natural gas and coal. When material reaches the lower part of the kiln, it forms the shape of clinker.
After passing out from the kiln, clinkers are cooled by mean of forced air. Clinker released the absorb heat and cool down to lower temperature. Released heat by clinker is reused by recirculating it back to the kiln. This too saves energy.
Final process of 5th phase is the final grinding. There is a horizontal filled with steel balls. Clinker reach in this rotating drum after cooling. Here, steel balls tumble and crush the clinker into a very fine powder. This fine powder is considered as cement. During grinding gypsum is also added to the mix in small percentage that controls the setting of cement.
Material is directly conveyed to the silos (silos are the large storage tanks of cement) from the grinding mills. Further, it is packed to about 20-40 kg bags. Only a small percent of cement is packed in the bags only for those customers whom need is very small. The remaining cement is shipped in bulk quantities by mean of trucks, rails or ships.
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Cement is a material which is used to bind other materials together. Binding means it has an effect ofgluing the substances together due to cohesive and adhesive action and then hardens and sets in order to become permanent. Cement is usually not used on its own; it is mixed with other materials called aggregates to produce a combined material of desired properties.
When it is mixed with sand, gravel then concrete is produced. If it is mixed with fine aggregates then it produces mortar. Cements are prepared by materials which have a high amount of calcium or aluminium and silicon. Calcium containing materials are called calcareous materials and aluminium and silicon containing materials are called argillaceous materials. Cement is used for constructing buildings, dams, roads, bridges etc.
These are cements which require dry conditions in order to set and harden. They lose their efficiency and durability in presence of water. It sets as it dries and reacts with carbon dioxide in air. After setting it is resistant to chemical attacks.
These are cements which can set even if its surrounded by any amount of water. In such cements, the cement reacts with aggregates to form mineral hydrates which are insoluble in water. The water can protect the cement and the aggregate from chemical attacks this helping it set and harden and become very durable. An example of this type is Portland Cement.
In wet process the calcareous and argillaceous materials are grinded to required size and stored in separately silos. Before the argillaceous materials are stored it is first washed with water. Both the materials are then channeled to mill equipment where they are intimately mixed in desired proportions to form a paste. This paste is then stored in a silo for further processing.
The process of burning is carried out in rotary kiln and the rotary kiln is lined with refractory bricks. The prepared mixture stored in the silo is fed into the rotary kiln from upper side and a burning fuel is fed from the lower side of the rotary kiln in order to produce hot flame. The fuel can be oil or powdered coal or it even can be hot gases.
There is a temperature gradient inside the rotary kiln with the lowest temperature being at the upper side and the highest temperature being at the lower side. There is a countercurrent motion between the feed mixture and the burning fuel. Due to the slow rotation of the rotary kiln the temperature of the feed mixture rises gradually as it moves from the upper end to the lower end of the rotary kiln.
The temperatures are around 1000C. This part is also known as calcination zone because lime stone decomposes in this part. Calcium carbonate decomposes to form calcium oxide and carbon oxide. After the carbon dioxide escapes remaining material forms small lumps called nodules.
The temperatures in this part are between 1500-1700C. This part is also known as clinkering zone. The calcareous and argillaceous materials react to form calcium silicates and calcium aluminates. The aluminates and silicates fuse together to form small and hard stones known as clinkers.
The clinkers which are output from the rotary kiln are very hot hence they are first cooled by air in a countercurrent fashion. The clinkers are of size of about 5-10 mm. They are fed to grinders in order to grind them to reduce their sizes. The clinkers are fed into ball mill or tube mill along with powdered gypsum.
The gypsum acts as a regarding agent so that the resulting cement does not set quickly when it comes in contact with water. The mixture fed for grinding contains tricalcium aluminates which are soluble in water. Gypsum reacts with them to produce tricalcium sulfoaluminates which is insoluble in water. They retard the rate of setting of cement thus giving time for concrete placing.
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The raw cement ingredients needed for cement production are limestone (calcium), sand and clay (silicon, aluminum, iron), shale, fly ash, mill scale and bauxite. The ore rocks are quarried and crushed to smaller pieces of about 6 inches. Secondary crushers or hammer mills then reduce them to even smaller size of 3 inches. After that, the ingredients are prepared for pyroprocessing.
The crushed raw ingredients are made ready for the cement making process in the kiln by combining them with additives and grinding them to ensure a fine homogenous mixture. The composition of cement is proportioned here depending on the desired properties of the cement. Generally, limestone is 80% and remaining 20% is the clay. In the cement plant, the raw mix is dried (moisture content reduced to less than 1%); heavy wheel type rollers and rotating tables blend the raw mix and then the roller crushes it to a fine powder to be stored in silos and fed to the kiln.
A pre-heating chamber consists of a series of cyclones that utilizes the hot gases produced from the kiln in order to reduce energy consumption and make the cement making process more environment-friendly. The raw materials are passed through here and turned into oxides to be burned in the kiln.
The kiln phase is the principal stage of the cement production process. Here, clinker is produced from the raw mix through a series of chemical reactions between calcium and silicon dioxide compounds. Though the process is complex, the events of the clinker production can be written in the following sequence:
The kiln is angled by 3 degrees to the horizontal to allow the material to pass through it, over a period of 20 to 30 minutes. By the time the raw-mix reaches the lower part of the kiln, clinker forms and comes out of the kiln in marble-sized nodules.
After exiting the kiln, the clinker is rapidly cooled down from 2000C to 100C-200C by passing air over it. At this stage, different additives are combined with the clinker to be ground in order to produce the final product, cement. Gypsum, added to and ground with clinker, regulates the setting time and gives the most important property of cement, compressive strength. It also prevents agglomeration and coating of the powder at the surface of balls and mill wall. Some organic substances, such as Triethanolamine (used at 0.1 wt.%), are added as grinding aids to avoid powder agglomeration. Other additives sometimes used are ethylene glycol, oleic acid and dodecyl-benzene sulphonate.
The heat produced by the clinker is circulated back to the kiln to save energy. The last stage of making cement is the final grinding process. In the cement plant, there are rotating drums fitted with steel balls. Clinker, after being cooled, is transferred to these rotating drums and ground into such a fine powder that each pound of it contains 150 billion grains. This powder is the final product, cement.
Cement is conveyed from grinding mills to silos (large storage tanks) where it is packed in 20-40 kg bags. Most of the product is shipped in bulk quantities by trucks, trains or ships, and only a small amount is packed for customers who need small quantities.
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Cement is a kind of powdery hydraulic inorganic cementitious material, which is the most basic and widely used building material in modern society. Cement can be hardened in the air or in water, and can firmly bond sand and stone together. It is widely used in civil engineering, water conservancy, national defense, and other projects.
The most commonly seen and used cement is portland cement, or ordinary portland cement (OPC). This type of cement was invented in the early 19th century by Joseph Aspdin. It is named portland cement because its property is similar to the stone quarried on the Ise of Portland, England.
The making process of portland cement in the modern industry can be divided into the wet process, dry process, and semi-dry process. Nowadays, the dry process is the most popular cement making process which is widely adopted by cement plants all over the world for its great advantages in energy saving and environmental protection.
The raw materials needed for cement production mainly include limestone (main material, providing CaO), clay materials (providing SiO2, Al2O3 and a small amount of Fe2O3), correction raw materials (to supplement some insufficient ingredients), and auxiliary raw materials (such as mineralizer, cosolvent, grinding aid), etc. Generally, the limestone accounts for 80% of cement raw materials, which is the main cement manufacturing material.
Cement plants are usually built near the quarry of limestone so the quarried limestone can be transported to the cement plant directly by belt conveyor or other conveying systems. If the distance between the quarry and the cement plant is too long to use conveyors, the limestones will have to be transported by trucks, which means higher transportation fees and inconvenience. The short distance between the cement plant and the quarry saves transportation fees and fuel costs and makes the cement making process economical.
Apart from limestone, there are also other raw materials used in the cement making process, such as clay, fly ash, iron ore, and coal. The need for these raw materials in cement production is relatively small so it is OK to just buy them from a supplier.
Before raw materials being transported to the cement plant, they are crushed into smaller size pieces by the crusher at the quarry. Compared to large pieces, raw materials in smaller pieces are easier to be loaded and transported, and more convenient for subsequent processing.
The samples of limestones from the quarry are first sent to the laboratory of the cement plant, where they are tested and analyzed for proportioning. The proper proportioning of limestone and other raw materials is a necessary job before the beginning of grinding. The proportioning of cement raw materials is not all the same but should be determined according to the actual situation. The proportion of raw materials of different specifications of cement is also different. Generally, the proportion of components in cement raw materials is 67-75% limestone, 10-15% clay, 0.5-1.5% iron ore and 8.5-11% coal.
With the help of roller crushers or other types of crushers, the raw materials are blended and further ground into smaller pieces of raw meal in the cement plant. In a roller crusher, the rotating table rotates continuously under the roller and brought the raw mix in contact with the roller. Roller crushes the material to fine powders and finishes the job. The raw mix is stored in a pre-homogenization pile after it was ground to fine powders.
After being crushed by the roller crusher, the raw meal is ready to enter the preheater. The cyclone preheater is one of the core equipment for dry process cement production, which consists of a series of vertical cyclones locate on several stages. Inside the cyclones, raw meal meats with the exhaust gas emitting from the rotary kiln and performs suspension heat exchange with it. The suspension pre-heating process helps cement plants save energy and reduce environmental pollution.
The calcination is the core phase of the cement making dry process. The calcination of the preheated raw meal takes place in the rotary kiln of the cement plant. The rotary kiln is a huge rotating furnace in which the raw meal is heated up to 1450 C and turned to clinker.
The heat source of the rotary kiln is the flame from the burner locates on the kilns front end. Using natural gas or coal as fuels, the burner shoots high-temperature flames to calcine the raw meal. After calcination, the cement clinker will enter a cooler for cooling.
The hot clinker discharged from the rotary kiln is cooled in the grate cooler by forced air, which is extracted from the outer atmosphere by grate cooling fans. The temperature of the clinker after being cooled drops from 1350 1450C to around 120C. The cooled clinker is then transported to clinker silos or hoppers directly by conveyors for storage and later cement grinding process. The hot air in the cooler is recirculated back to the rotary kiln for reuse, which further saves energy consumption of the cement plant.
The cooled clinker is then fed to cement mills for final grinding. Many factories nowadays prefer to use ball mills for cement grinding, since this kind of mills has small product particle size distribution and is easy to operate.
The cement ball mill is a horizontal cylinder filled with steel balls or other grinding media. Inside the cylinder, the steel balls are rotated and tumbled and crush the clinker into very fine powders, which are product cement powders. During the grinding process, a small percentage of gypsum is added to the mix to control the setting time of cement.
The product cement discharged from the cement grinding mills is conveyed to the cement storage silos. Further, it is packed into bags or shipped to customers in bulk quantities by trucks, rail freight wagons, or ships. The most popular cement packing machines are roto-packers which can pack cement fast and in large quantities.
The Global CemProcess Conference is a well-established event that looks at cement process optimisation, including pyroprocessing, diagnostics, AI, process control, alternative fuels and electrical energy efficiency.
The 1st Virtual Global CemProcess Seminar took place in April 2020 - the first major virtual conference to be organised for the cement industry during the coronavirus pandemic - to great acclaim (see below). The 2ndVirtual Global CemProcess Seminar will take place on 11 May 2021.The next real-world event will take place in May 2022.
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Over 550 delegates from 82 countries have already registered for the 2021 event: Afghanistan, Albania, Algeria, Argentina, Australia, Austria, Azerbaijan, Bahrain, Bangladesh, Belgium, Bolivia, Brazil, Bulgaria, Canada, Chile, China, Colombia, Cote d'Ivoire, Croatia, Denmark, Dominican Republic, Ecuador, Egypt, Finland, France, Germany, Greece, Guyana, Hong Kong, Hungary, India, Indonesia, Iraq, Ireland, Israel, Italy, Japan, Jordan, Kenya, Korea, Republic Of (South Korea), Kuwait, Lebanon, Lithuania, Luxembourg, Macedonia, Malaysia, Mexico, Morocco, Netherlands, New Caledonia, Nigeria, Nigeria, Oman, Pakistan, Peru, Philippines, Poland, Portugal, Romania, Russian Federation, Rwanda, Saudi Arabia, Senegal, Singapore, Slovakia, South Africa, Spain, Sri Lanka, Switzerland, Taiwan, Thailand, Tunisia, Turkey, Uganda, Ukraine, United Arab Emirates, United Kingdom, United States, Uruguay, Venezuela, Viet Nam, Yemen
Including over 400 delegates from 62 countries: Algeria, Argentina, Austria, Australia, Austria, Azerbaijan, Belgium, Bolivia, Brazil, China, Colombia, Croatia, Cyprus, Democratic Republic of Congo, Ecuador, Egypt, Ethiopia, France, Germany, Greece, Guatemala, Hong Kong, Hungary, India, Indonesia, Iran, Ireland, Israel, Italy, Ivory Coast, Japan, Jordan, Lebanon, Lithuania, Macedonia, Malaysia, Mexico, Morocco, New Caledonia, Nigeria, Norway, Pakistan, Peru, Philippines, Poland, Portugal, Russia, Rwanda, Saudi Arabia, Singapore, Slovakia, South Africa, Spain, Sweden, Switzerland, Tunisia, Turkey, UAE, UK, USA and Vietnam.
14.15 Paper 9: More than a measured value: How digital measurement technology and IIOT offerings contribute to plant safety and resource efficiency in the cement industry, Kristina Rosenberger, Endress + Hauser Messtechnik GmbH + Co. KG
14.40 Paper 10: Advanced analytical approach and machine learning technics in real-time chemical analysis for cement production optimisation, using non-nuclear real-time analyzer technology based on LIBS (laser-induced breakdown spectroscopy), Marius Sugentaitis, Lyncis
19.00-20.00 Virtual CemProcess Conference Social Evening on ZOOM. Bring a drink, wear a hat ('prizes' for the best/most outlandish/spectacular hats) and be prepared for our international QUIZ. The link to Join will be sent to you by email during the day.
11.45 Paper 17: A proven mechanical and biological treatment for transforming MSW to RDF with constant and reliable quantity: a sustainable and affordable approach, Sara Dallasta, Eggersmann Recycling Technology
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Overall, the first diagram shows all the steps required for the production of cement like crushing, mixing heating, grinding, packing and the usage of the final product along with few other raw materials. Whereas, concrete production is depicted in the second diagram. Cement production involves more steps as compared to the production of concrete but the former requires less number of raw materials than the latter. Concrete is the final output which is directly used for the building process, whereas cement is a semi-finished product and needs further processing.
Firstly, limestone and clay are turned into powder by putting them in a crusher. This powder is then mixed in a mixer, after which it is put in a rotating heater. Here, this mixture is heated by applying heat externally. Then the mixture passes through a grinder, and fine cement is produced, which then is packed in a bag for further usage.
Secondly, this cement along with water, sand and gravel, as per specified proportions, is put in a concrete mixer. The concrete mixer rotates, thereby producing the final output, i.e. concrete which is directly used for building purposes.
Although the information in the sentence above is accurate, it is not presented anywhere on the diagram. You must avoid any temptation to offer any piece of information which is not mentioned in the chart.
You may observe that in case both the body paragraphs, the writer has missed the introductory statement. A simple statement, such as given below, would have been sufficient at the beginning of body paragraph 1.
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The cement production involves five stages, a straightforward process that begins with the mixing of raw materials and reaches a finale in the packaging of new cement. Making concrete is a simple process that involves mixing four ingredients in a concrete mixer.
Overall, the first diagram shows the equipment and the process of cement making. Limestone and clay are simultaneously passed through the crusher to form powder which is then mixed before passing it through a rotating heater. Once heated, this mixture is ground through a grinder. Now that the cement has been produced, it is packed into bags.
At the same time, the second diagram shows the concrete production process. For the production, the concrete mixture needs four ingredients and a concrete mixer. The concrete mix comprises half a portion of gravel (small stones), a quarter portion of sand, 10% water and 15% cement. All of these are added together in a cylindrical drum and rotate until the concrete is produced.