rotary dryer for biocoal

rotary dryers

rotary dryers

Weve built a reputation on building the best rotary dryers in the industry. All of our dryers are custom designed to suit the unique processing needs of your material. Whether you require low or high inlet temperatures, short or long residence times, counter current or co-current flow, FEECOs design team can design a rotary drum dryer for your application.

Rotary dryers are a highly efficient industrial drying option for bulk solids. They are often chosen for their robust processing capabilities and their ability to produce uniform results despite variance in feedstock.

The drum is positioned at a slight horizontal slope to allow gravity to assist in moving material through the drum. As the drum rotates, lifting flights pick up the material and drop it through the air stream in order to maximize heat transfer efficiency. When working with agglomerates, the tumbling action imparted by the dryer offers the added benefit of further rounding and polishing the granules.

All FEECO equipment and process systems can be outfitted with the latest in automation controls from Rockwell Automation. The unique combination of proprietary Rockwell Automation controls and software, combined with our extensive experience in process design and enhancements with hundreds of materials provides an unparalleled experience for customers seeking innovative process solutions and equipment.

Rotary dryers are known as the workhorse of industrial dryers. They are able to process a wide variety of materials, and can lend a hand in nearly any industry requiring industrial drying solutions. Some of the most common industries and materials in which rotary dryers are employed include:

Unlike direct dryers, indirect dryers do not rely on direct contact between the material and process gas to dry the material. Instead, the rotating drum is enclosed in a furnace, which is externally heated. Contact with the heated drum shell is what dries the material.

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Our rotary dryers are built to the highest quality standards, with longevity in mind. The best part about buying a FEECO rotary dryer, is that you get the security of knowing your equipment is backed by over 60 years of experience, material and process knowledge, and a proven track record.

biocoal: the key to turning the coal industry around?

biocoal: the key to turning the coal industry around?

A recent white paper by William Strauss, PhD of FutureMetrics LLC, looked at a strategy that could breathe life back into the dying US coal industry, and the answer comes from an unlikely place: implementing policy to support the co-firing of wood biomass pellets (biocoal) at pulverized coal plants.

Please note: While Strauss refers to wood pellets in his white paper, the technically correct term for the material is biocoal. True wood pellets have a lower heating value than biocoal and would actually derate power facilities if co-fired alongside traditional coal. To be technically correct, this article will refer to the material as biocoal.

Biocoal, also commonly called black pellets, is a synthetic form of coal produced from biomass that looks, handles, and performs like traditional coal products. Strauss claims that policy aimed at co-firing could be the answer to the woes of the coal industry.

While many are quick to blame the state of the coal industry on increasing environmental regulation, many claim that a less obvious culprit has actually been at work: low energy costs resulting from the recent glut of natural gas and oil.

These low energy costs have come at great expense to the coal industry; as power facilities switch over to low cost natural gas, demand for coal has decreased, resulting in a painful demise of plant closures, aging coal infrastructure, and major unemployment.

According to the Energy Information Administration (EIA), between 2014 and 2015, coal-generated power plummeted by a staggering 226,000 gigawatt-hours, while natural gas-generated power went up by 208,000 gigawatt-hours.

In his paper, Strauss claims that legislation in place to co-fire coal with biocoal would actually create more jobs than coal-generated power alone, and would also far exceed the number of jobs associated with natural gas; according to Strauss, a 400-MW facility that co-fires 10% biocoal has an impact of about 1,757 jobs, while coal alone only results in about 1,686. Jobs created by the extraction and pipelining of natural gas fall well below at around 576.

Strauss claims that policy supporting co-firing would create guaranteed demand for coal, helping to revitalize the downtrodden industry. But its not just the coal industry that would benefit from such legislation; this strategy would also reinvigorate the forest products industry with a new product stream.

The US forest products industry has shown some recovery after its decline, but its nowhere near its former glory, leaving many looking for a solution. As Strauss claims in his white paper, co-firing could hold the key to the revitalization.

The co-firing policy would not only result in more jobs, but it would also inject substantial investments into the manufacturing of biocoal plants, along with the related engineering, construction, and hauling needed to support the industry.

Transforming biomass into biocoal serves to maximize and concentrate the heating value of the product, while also improving combustion. Biocoal is also much easier and less costly to handle and transport than raw biomass, and allows facilities to run at the same capacity without derating.

To process biomass into biocoal, residuals of the forest products industry are first dried in a rotary dryer. This reduces the moisture content and improves combustion. The dried biomass is then processed in an oxygen-free environment of an indirect-fired rotary kiln to remove the volatile components.

As a leader in thermal processing, FEECO provides biomass dryers and complete dryer islands for reducing moisture content in biomass fuel sources. In addition, we engineer custom rotary kilns for processing biomass into biocoal, biochar, and activated carbon. For more information, contact us today!

choosing a rotary dryer: single pass vs. triple pass

choosing a rotary dryer: single pass vs. triple pass

Rotary dryers are the industrial dryer of choice for everything from minerals and ores to fertilizers and specialty chemicals. One decision buyers are often faced with in selecting a rotary dryer for a given application, particularly when looking to dry high-moisture materials such as compost or biosolids, is whether to go with a single-pass or triple-pass rotary dryer.

While both designs offer distinct benefits, those looking for a drying solution that will minimize downtime and remain reliable in the long term should opt for the single-pass rotary dryer. Heres why.

Single pass rotary dryers consist of a single, heavy-duty drum through which material and products of combustion are passed while the drum, set on a slight slope to allow gravity to assist in moving material through, rotates.

Triple pass rotary dryers consist of three lighter-duty drums of differing diameters nested inside each other. The drum is not set on a slope, but rather relies on pneumatic conveying to carry material through the unit.

Material is fed into the innermost drum, and is pushed out the end of that drum where it falls into the middle drum. Similarly, the material works its way through this drum, out the end, and into the remaining, outermost drum shell, where it moves through and is discharged at the end.

The main advantage provided by the triple pass design is that it allows the drum length to be reduced for a smaller footprint. This is because the triple pass dryer achieves a longer retention time through the multiple pass system as opposed to additional length. While this is one area where single pass dryers concede to triple pass dryers, the benefits typically stop there.

Triple pass dryers are a much lighter-duty solution compared to single pass dryers, relying on less robust drum shells and tire arrangements. This offers an initial savings in capital cost, but significantly reduces the service life of the dryer. This lighter-duty design also means that triple pass dryers are much more prone to experiencing issues in high-demand settings.

In contrast, because single pass dryers rely on a single shell, that shell is designed to be much more robust and durable. Single pass rotary dryers have a well-deserved reputation of lasting for decades when properly maintained, though this does also depend on selecting a reputable rotary dryer manufacturer.

In addition to fewer mechanical and structural issues, single pass rotary dryers are also less prone to clogging than triple pass dryers; because material is initially fed into the smallest inner drum with the triple pass design, there is less space for the material to fall as it moves through the drum, even with the help of lifting flights. This often results in material clumping up and subsequently clogging the dryer.

The larger diameter of the single pass dryer, combined with the lifting flights, gives material adequate space to fall through the air stream, a motion that can also help to break up any potential clumps. As a result, single pass dryers are less susceptible to clogging issues.

Because triple pass dryers pneumatically convey material through the drum, they require a high air velocity. This leads to the need for a larger induced draft (ID) fan and exhaust handling system, ultimately increasing energy requirements.

As a result of the higher volume of air used by triple pass dryers, they also require a larger exhaust gas treatment/air pollution control system. Single pass dryers still require an off-gas treatment system, but it can be much smaller due to the reduced air volume utilized.

Single and triple pass rotary dryers are commonly compared in selecting a dryer for high-moisture applications. While the triple pass dryer costs less and offers a smaller footprint, the reduced service life and reliability are substantially reduced and in most cases, not worth the sacrifice. Single pass rotary dryers are robust, offering a significantly longer service life and more reliability. Other benefits of the single pass design include less potential for clogging, lower energy costs, and reduced off-gas treatment requirements.

FEECO rotary dryers provide every industry from mining and minerals to fertilizer and agriculture with the most reliable drying solution. Our single pass dryers are custom built for optimal processing efficiency and long-term reliability. Plus, they are backed by our extensive parts and service program. For more information on FEECO rotary dryers, contact us today!

biocoal from biomass

biocoal from biomass

Biocoal, a product produced by thermally upgrading biomass, has been gaining traction throughout the world as countries look to more renewable energy sources in an effort to reduce dependence on coal and mitigate greenhouse gases.

Biomass is a broad term that covers plant products and by-products. From forest product residuals to sugarcane bagasse, the term biomass is used to describe anything with a cellulosic structure. And while biomass itself is used as a fuel source, upgrading biomass to biocoal offers many benefits.

Biocoal is produced by processing dry biomass in an inert environment (no oxygen) at high temperatures, a process referred to as pyrolysis. Depending on the temperatures and the characteristics of the end product, the process may also be referred to as torrefaction. This process is commonly carried out using an indirect-fired rotary kiln.

The conversion of biomass to biocoal varies depending on the characteristics of the source material. In general, however, biomass is processed at temperatures between 500 to 800F at a specific retention time to produce the biocoal product.

The torrefaction process increases the energy value of the biomass, making it comparable to conventional coal heating values. Some thermal degradation occurs during torrefaction, reducing the mass of the material and resulting in more concentrated energy per unit weight.

Although biomass has already been dried to an acceptable amount for use as a fuel source, the conversion to biocoal further reduces the moisture content of the material. While this helps to improve the energy value of the material, it also causes the material to be hydrophobic, meaning it will not absorb moisture from the air. As such, it requires no special storage requirements an enticing characteristic for power plants. The reduced moisture can also decrease transportation costs where applicable.

Unlike fossil coal, biocoal does not contain sulfur, nitrogen oxides, or mercury. Additionally, the ash content is much lower than traditional coal. These factors combine to yield a much cleaner burn, reducing greenhouse gas emissions.

The use of biocoal not only aids in protecting the environment through reduced greenhouse gases, but it also opens up the opportunity for companies to purchase carbon offsets, further improving the economics of implementing biocoal as an alternative to fossil fuels.

Biocoal is an especially viable option because it performs like conventional coal products. Unlike other biomass products such as wood chips or pellets, power plants need to make very few, if any, changes to their facility to utilize biocoal as a fuel source. This is because biocoal can be ground, allowing it to be easily integrated into existing systems because it performs like the traditional pulverized coal. The biocoal can then be blended and co-fired with traditional coal.

In addition to use at coal-fired power plants, biocoal is also catching the interest of cement producers, where a significant amount of energy in the form of coal and petroleum coke are currently used as a fuel source.

Biocoal as a renewable energy source is a developing market and will play an important role in reducing greenhouse gases and our reliance on coal. In the face of climate change and increasing legislation, biocoal is an attractive option to reducing toxic emissions and meeting carbon footprint goals.

rotary dryers for improvement of centrifuged materials

rotary dryers for improvement of centrifuged materials

Centrifuges are a critical and growing asset in modern industrial processing, allowing processors to separate solids from liquids in the pursuit of a wide range of production goals. But production is not always complete after the centrifuge; depending on the end use of the material and its unique characteristics, drying is often necessary following the centrifuge. In this way, drying is frequently essential in preparing centrifuged materials for subsequent processing or disposal.

While centrifuges remove a large portion of the materials moisture, some moisture still remains in the material exiting the centrifuge. This moisture content may be suitable for some applications, or when the material will be landfilled, but may present challenges if the material requires subsequent processing, or if the remaining moisture content inflates transportation costs or tipping fees.

As anyone transporting bulk solids knows, the more moisture a material contains, the less efficient shipping becomes, as one is essentially paying to transport water. Thus, if moisture is removed, shipping the same amount of material costs less.

Although significantly reduced in moisture content, the material exiting the centrifuge may still contain enough moisture to clog downstream production equipment. In this case, a post-centrifuge dryer further reduces the moisture content to help ensure a smooth flow of material throughout the production line.

In addition to promoting a smoother flow of material, drying is also a means of preparing material for subsequent processing techniques, which is applicable in a wide range of settings. If the material will be granulated, for example, drying is used to bring the material into the required moisture range for optimal agglomerate formation.

Material may also be dried in order to prepare it for processing in a rotary kiln. In this case, drying improves flowability of the material a necessity in rotary kiln processing. Drying also makes the kiln more efficient, as the kiln will not have to be used to reduce moisture content. Some materials may also require a drying step prior to the kiln in order to achieve the desired chemical reaction or phase change.

One of the key applications for rotary dryers in drying centrifuge cake is the processing of sludges. Centrifuges are widely applied in sludge processing to recover valuable materials, or to process sludges for more efficient landfilling by decreasing transportation costs and reducing material volume. Drying further contributes to these efforts for materials such as:

For these materials, drying is used to produce a saleable product by removing the remaining moisture content, or preparing the material for a granulation process. In the case of ammonium sulfate, for example, crystals exiting the centrifuge typically contain around 1.0 2.5% moisture. The rotary dryer further reduces the moisture content to below 1.0% for a marketable product.

Dryer design for any application is largely dependent on the material characteristics and processing goals. While this means that the dryer should be configured around the material and process objectives, it is also one reason why rotary dryers are chosen for such applications.

In addition to providing a stable, high-capacity drying solution, rotary dryers are extremely flexible, allowing them to be tailored to precise process specifications via design and fabrication customizations. Rotary dryers employed for drying materials from a centrifuge may be designed to accommodate a wide range of configurations, most importantly, mode of heating (direct or indirect) and air flow direction (co-current or counter-current).

Since materials exiting the centrifuge are often in the form of a cake, knockers are a common addition to rotary dryers. A combustion chamber may be used in cases where product quality is important and therefore, direct flame contact is undesirable.

Dryer testing programs such as those conducted in the FEECO Innovation Center are vital to establishing key process parameters and gathering data for the design of a commercial-scale dryer. For drying, testing generally centers around:

Whether used in the crystallization process or for treating wastewater sludge, rotary drum dryers play an essential role in treating centrifuged materials, allowing processors to achieve more efficient disposal and transportation, as well as produce a saleable product.

FEECO is the leading provider of custom rotary dryers for a wide range of applications, centrifuged materials included. Our custom dryers have a well-earned reputation for longevity and reliability, and are backed by testing in our Innovation Center. We also offer a parts and service program for evaluating and improving dryer performance, conducting routine maintenance and repairs, and so much more. For more information on our rotary dryers, contact us today!

rotary drum dryer systemworking principle and design -palet

rotary drum dryer systemworking principle and design -palet

The Materials to be dried enter into the dry zone of special combination plates are thrown by drying plate for vertical movement because of angle difference and rotational motion of the drying plate. After making heat exchange with the materials, the high-temperature furnace gas discharged into the cylinder evaporates water and drys the material, it can prevent the material from sticking on the inside of the cylinder. It is a part of the pellet mill plant.

Qingdao PALET Machinery can design and supply the Rotary Dryer Machine,dryer equipment for the customers especially according to the information of material. This raw material is wood chips, sawdust, etc.

1. The capacity is different. The output capability of the rotary drum dryer ranges from around 1000 to 5000kg /h at most while the sawdust flash dryer can produce around 100-2000kg/h. The air flow dryeris suitable for drying the wood powdersawdustect.

2. The price is different. The air flash dryer is cheaper than that of the rotary drum dryer price. How to select the dryer? When purchasing the dryer, it is better to consider the all-around situation of your dryer and pellet production and find a suitable dryer.

Qingdao palet machinery co,.ltd is a professional manufacturer of biomass wood pellet mill, wood pellet plant, rotary dryer, activated carbon rotary klin,activated carbon machine, hammer mill, crusher, etc.

coal rotary dryer-zhengzhou dingli new energy technology co.,ltd

coal rotary dryer-zhengzhou dingli new energy technology co.,ltd

Coal drum dryer is mainly composed of hot blast stove, belt feeding machine, drum dryer, belt discharging machine, induced draft fan, cyclone dust collector, bag filter (or wet dust collector) and operation control system. Equipment used downstream drying process, its working principle is as follows: wet material after entering drying drum divided into the following workaround: one is the feeding area, the coal into the area exchanged with high temperature and hot air quickly evaporate moisture, the material in large Angle of guide plate copy, to be imported under a workspace;2 The copy plate area, the coal in this area is copying by copy board forming curtain material, the material with good contact with hot air, the moisture in coal rapid evaporation become water vapor, water vapor was siphoned off by induced draft fan, so as to achieve the aim of coal drying;The moisture of coal in this area is less than 15% (or less) under the state of loose, after heat exchange the materials achieve the required moisture state, and discharging out;Three is a discharging area, do not set copy plate roller in the region, the material in this area scroll taxiing to the discharge port, then complete the whole drying process.

1. Solve coal feeding uniformity and roading inside the dryer, overcome the problem such as intermittent feeding, before plugging material, transient capacity big, etc, which is the premise to improve the evaporation intensity.(1) With unique design of the buffer bin and feeder mechanism, overcome uneven feeding of intermittent feeding problems; (2) Set up large dip Angle on the roller feeding end unpowered spiral propeller, not only evenly sent the wet slurry into drum drying section, but also make large pieces of wet coal cutting and scattered;

2. Improve the internal structure design of the dryer, maximize the increasing the heating area between material and hot air, which is the basis of increase evaporation strength.(1) Constantly optimize roller structure layout and the feed plate design, the final setting is now a unique internal feed roller plate structure and different effect of mixing drum of whole section distribution. The dryer with all "material curtain "even no dead Angle, no gap, the maximum increase the heating area of the coal and hot air, and the heat exchange area, make the coal moisture to evaporate rapidly and was taken away by hot air. (2) With the original rotary drum dryer dry layer patent technology. According to the different particle's material inside the drum's heating speed and speed different, set up more groups of layer drying device, dropping grate, control of small particle materials drying and pulverization, too large particle materials have different internal and external heat drying uneven phenomenon, ensure dry uniformity.

3. Reasonable selecting hot blast stove furnace, optimizing its internal structure design and laying quality, reduce the air leakage rate, reduce the oxygen content in the hot air less than 5%, 700-1200 arbitrary random control process requirement of temperature points, provide the dryer with homogeneous stable heat source,which is the reliable safeguard of coal dryer running with high strength.

4. Measurement and control system adopts PLC frequency conversion control technology, temperature, pressure, oxygen concentration, speed equipment, process parameters on-line interlocking spreading, realize automatic detection and control of the whole system have centralized, on-site switching function, guarantee system to maximize capacity, optimal quality, the most energy-saving mode, the safety explosion protection and stable operation.

5. Optimizing the allocation of gravity settling +cyclone dust collector + wet cyclone/bag dust collector level 3 by dust bag filter dust removal equipment, dust concentration < 30 mg/Nm3, guarantee dust emission standard.

6. The unique modular design, the manufacture, transportation, installation, assembling and commissioning platform, service concept in a more optimized design manufacturing, installation services return customers more convenient transportation, guarantee the customer's maximum benefit.

7. Solve the traditional dryer downstream caused in the process of the direction of dehumidifying system temperature reduced water vapor return material, improve the efficiency of drying, achieve the goal of deep dehydration.

9. Half carbon coke cooling machine used with raw coal dryer series, recycled half carbon carbocoal heat used for coal drying and dewatering, both to achieve LAN charcoal semi coke dry quenching cooling, and to get low moisture LAN charcoal carbon coal, and make full use of heat energy for the depth of the coal removal moisture, temperature preheating, reduce subsequent pressure of coal chemical industry equipment, comprehensive utilization of heat energy, energy conservation, environmental protection, the perfect process is more reasonable.

biomass drying - vulcan drying systems

biomass drying - vulcan drying systems

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Biomass, the by-product of pulp and paper, agriculture, and municipal sludge, is perhaps the oldest source of renewable energy on Earth. Biomass' use in energy production is currently growing worldwide at an exponential rate. Studies show the by-product could provide up to14% of U.S. electricity consumptionin coming decades due to its clean, sustainable, and economical nature. The demand is present and with multiple challenges associated with drying biomass which need to be mitigated, it's smart to trust the experts at Vulcan Drying Systems.

When used on a variety of cellulose materials, such as hemp, bagasse (sugar cane waste), brewers grains,grass, andsawdust, Vulcan Drying Systems Biomass Drying Systems increase the materials' energy value while also producing a high-quality source of energy.

Processing begins in the dryer. Vulcan Drying Systems'Direct Fired Rotary Dryersare proven performers, producing a high-volume, low moisture product that is consistent and easy to ship and store. After passing through the dryer, dried biomass is discharged to a conveyor for further sorting. The vapor from the process is pulled through the air pollution control system to remove fine particulates from the vapor stream.

Even though biomass is possibly the oldest source of renewable energy on Earth, when taken through Vulcan Drying Systems'drying process, it has more added value than conventional biomass. Vulcan Drying Systems will help you capture a new revenue stream in a biomass drying system while efficiently mitigating the processing challenges that come with air pollution, emissions, and vapor.

Thermal drying is a proven technology that has been used in a variety of industries and applications. Another example is in the agricultural industry where crops, grains, and animal feed can be dried to facilitate easier storage and more efficient transportation. These benefits can be seen in a large range of products, showing that almost any material can be appropriately dried in order to save time and money.

Concerned about the feasibility of processing your biomass material? Schedule a test in our pilot testing facility where you will be provided with exceptional customer service, extensive experience, product ingenuity, and engineered solutions to help you find the perfect process for your material. Our testing center contains two units, one direct-fired and one indirect-fired, providing options to generate your desired results.

Ready to start working on the specifics for your very own Vulcan Drying Systems Biomass Drying System? Our Technical Sales Engineers are available to discuss your project with you and determine the best course of action moving forward. Our team has decades of combined experience working with systems designed to help with biomass drying.

rotary-drum dryer technology may aid large-scale biocoal production | 2018-04-20 | process heating

rotary-drum dryer technology may aid large-scale biocoal production | 2018-04-20 | process heating

Supplementing the use of coal with biomass a woody or energy crop has become desirable in the production of electricity for a number of reasons. Coal power plants that have tried to fire dried biomass have learned of the necessity of costly modifications to do so effectively. Yet at the same time, many coal-fired power plants have realized that the benefits of co-firing dried biomass are great enough to warrant the necessary modifications. Some coal-fired power plants, however, have not been able to make the necessary changes or have not found them to be cost effective.

This article will look at the factors affecting thermal processing biomass to augment coal power plants during the production of electricity. Specific thermal processing technologies can help optimize such processes.

One way to increase the practicality of co-firing biomass in a coal plant is by using torrefied biomass rather than dried biomass. While this is not a new idea, the specifics are not always well understood.

Drying biomass merely removes the water present in the biomass. This is a necessary step but not enough to fully prepare the biomass for use as co-firing biomass at coal-fired power plants. The inherent properties of dried biomass are such that plants using it must shut down more frequently than is typical for cleaning and repairs.

Torrefaction is the process whereby biomass woody or otherwise is heated in a low oxygen environment to a point where chemical changes start to occur. During the thermal processing, a portion of the dry solids are converted to gas (torrefaction gas, syngas, producer gas, etc.).

If dried biomass is used for co-firing in coal power plants, the lignins in the biomass materials the organic polymers act as glue. Lignins are especially problematic for pulverizers, which are equipment used to grind the coal and co-firing material into a fine dust. The pulverizers increase the surface area of the coal before it enters the firebox. Pulverizing lignins require more power, and the lignins can leave behind a gummy substance that must be cleaned.

When heated to the right temperature and time conditions with torrefaction, the biomass becomes the solid end-product that resembles coal visibly and physically. The process of torrefaction actually breaks the lignin bonds inherent in biomass that make biomass undesirable for co-firing with coal. This helps avoid problems such as gummed-up grinders and the interior of the boilers. (If not avoided, such conditions decrease plant efficiency and require more-frequent shutdowns for cleaning and repairs.) The end product is much more coal-like in physical characteristics, and the coal plant does not require modifications to the co-fire torrefied biomass.

Densifying torrefied wood or biomass into a pellet form often is referred to as biocoal because it is so similar to coal and originates from biomass. Torrefied biomass also is hydrophobic. (Neither green nor dried biomass can be stored outside for any length of time because both absorb water and start composting.) Torrefied material can be stored outside in wet conditions indefinitely with little worry of decomposing or absorbing water. Also, because torrefaction removes moisture and converts part of the dry solids to gas, the final energy per unit weight of the final product is higher, decreasing the shipping cost per unit energy.

The nature of green biomass is the main hindrance to torrefying it on an industrial scale. (Green biomass is the term used to describe newly harvested biomass before processing.) Any internet research into the properties of biomass from trees, energy crops and other sources especially moisture content yields extremely varied numbers in all metrics.

Feedstock inconsistency can be a problem, but some equipment can be used to improve feedstock consistency. Industrial rotary-drum dryers have been used to handle the property variations of dissimilar crops for decades. Industrial rotary-drum dryers can be designed to process green biomass to a material of uniform moisture content. Tapping experience with other rotary-dried products allows rotary dryer manufacturers to better anticipate the challenges and power requirements that green biomass trees in particular present for grinding and sizing equipment.

Since 2009, Konza Renewable Fuels LLC, a manufacturer of torrefaction systems for biocoal, has performed many successful test runs on its torrefaction test facility. In a sample test, the test unit, which is composed of two rotary drums, converted green biomass with a gross heating value (GHV) of 8,660 BTU/lb at 0 percent mcwb (moisture content wet basis) to torrefied biomass with energy content of approximately 9,500 BTU/lb at 0 percent mcwb.1 Konza Renewable Fuels test unit is capable of producing torrefied wood in a continuous process.

With a uniform moisture content, downstream processing of the material appropriately is much easier. This is true whether the biomass is ultimately used for strand board, pellets, shavings or other end products. A rotary-drum dryer used in series with a torrefaction reactor can address problems of inconsistent infeed. The dryer creates a uniformly dried product from varyingly sized and moisture-content biomass before it is torrefied in the torrefaction reactor.

In the process, the uniform and dry material exits the first rotary-drum and enters a second rotary-drum thermal-processing system. The torrefaction reactor heats the infeed material to temperatures between 482 and 536F (250 and 280C) in a low oxygen environment. Internal flighting in the rotary-drum dryer and torrefaction reactor lift and separate the infeed product. This helps ensure that the product contacts the gases long enough to be heated all the way through. In the dryer stage, this dries the entire particle to a uniform moisture content throughout, regardless of size. Likewise, in the torrefaction reactor, this action heats the entire particle to the required temperature throughout, regardless of size.

Allowing the particle to rest during the drying process between bursts of falling through the gas stream and being pneumatically conveyed toward the exit solves both of these problems. This is accomplished with three dryer design characteristics:

The resting periods allow heat to penetrate into the core of the particle to drive moisture from the center outward. Overheating the particle or heating it too intensely can overdry the shell and potentially damage it while the interior heats.

Any number of crops or byproducts can be torrefied and pelletized into biocoal. Farmers also can raise biomass crops such as switchgrass, miscanthus, bamboo and eucalyptus specifically for torrefaction.

Some types of biomass will grow where no food crops will grow. This means previously unusable land can become productive. Recent advances in aquaponics technology also can be applied toward growing energy crops using fish waste as fertilizer and less water than conventional crops.

In conclusion, being able to co-fire biomass in the form of biocoal without modifications to a coal-fired power plant is nearly realized due to recent advances in torrefaction technology. While the technology needed to make biocoal has existed for several decades, the challenge has been producing it on a large scale at a reasonable ROI. Industrial rotary-drum dryer technology may be just the key to unlocking large-scale biocoal production.

This schematic shows the process flow for a two-drum rotary torrefaction system. The hot gases flowing from the dryer combustion chamber to the dryer drum are the combination of combustion gas, torrefaction gas and reheated dryer recycle gas. Green biomass enters the dryer drum from the system infeed hopper.

The product tumbles through the dryer drum conveyed by the hot dryer gases. The dryer outlet hopper separates most of the product from the dryer outlet gas. The dryer outlet gas flows through the cyclone bank, where the remaining particles separate from the gas stream. The dryer outfeed screw transfers the product separated by the outlet hopper and the cyclone bank to the torrefier drum.

The dryer outlet gas exiting the top of the cyclones is reheated in the heat exchanger bank. It then splits between the heat recovery system, dryer inlet and torrefier drum inlet. The heat recovery system heats the reheated dryer vent gas entering it to a temperature high enough to destroy the volatile organic compounds (VOCs) in the torrefaction gas. The hot, clean gases from the heat recovery system provide heat to the heat exchanger bank and then exit the system through the stack.

Dry biomass and reheated dryer outlet gas enter the torrefier drum. The product tumbles while being heated to a temperature that drives off about 30 percent of the dry solids and 10 percent of the energy. It becomes a coal-like substance that is roughly 9,500 BTU/lb. The torrefier outlet hopper drops the product into the torrefier outfeed screw.

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