While both rotary dryers and fluid bed dryers effectively remove moisture from materials such as sand, fluid bed dryers provide definite benefits in terms of reduced energy consumption, a smaller footprint, reduced maintenance costs and higher efficiency.
Rotary dryers process product through a rotating cylinder. Vanes mounted inside the drum move the product forward, while lifting blades push the product from the base of the drum as it rotates, providing good contact with the heat source.
In a fluid bed, a continuous upward flow of gas suspends the product, causing it to act like a liquid, with the vibration of the fluid bed amplifying the effect of the gas. This ensures the gas and the sand are intensively mixed, giving high heat transfer and producing the optimum physical reaction, while gently handling the sand grains. Vibration of the fluid bed, while not necessary for sand, provides increased process control and reduced energy consumption.
Fluid bed dryers are significantly more efficient than rotary dryers in terms of energy consumption. Fluid bed dryers recycle heat from the flue and discharged gases, reducing the overall power requirement of the system. The option to divide the fluid bed into different compartments to make a combined dryer/cooling system also reduces energy requirements, and requires a much smaller footprint than standalone dryers and coolers.
With no moving parts inside the fluid bed, fluid bed dryers have greatly reduced maintenance and operating costs throughout their life in comparison to rotary dryers, including reduced scrubbing and baghouse costs. They also have much shorter start-up and stopping times than rotary dryers, which increases uptime and allows greater process efficiency.
Fluid bed dryers are ideal for applications ranging from sand to chemical or grains, and provide the highest efficiency, even with variations in terms of throughput, particle size and moisture levels. If sub-micron particles or extremely large, dense particles need to be processed, rotary dryers allow great flexibility in terms of processing, but the energy savings, reduced parts and maintenance costs, smaller footprint and higher processing efficiency of fluid bed drying systems make them a solid choice for sand drying.
Solutions provider Brolton Group has enjoyed significant success introducing fluid bed drying and cooling systems to two Australian-owned construction materials operations.
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Reduced energy use
As a leading provider of architectural coatings, renders, textures and paints, Queensland-based Rockcote experienced high demand for its pre-mixed render product, which required the construction of a new manufacturing facility capable of producing about 40,000 tonnes of product per year.
Rockcote places high importance on environmentally friendly practices; thus, the turnkey solution designed by Brolton Group focused on energy and resource efficiency. The production process is designed around a gravity feed system and, combined with energy efficient machinery, significantly reduces the plant’s energy requirements.
A Ventilex fluid bed drying and cooling system installed in the plant dries the sand with minimal dust generation. The sand is fed into the dryer utilising gravity-fed pneumatic operations, then exits the cooling system and is stored for batching. The fluid bed dryer provides Rockcote savings of more than 20 per cent over rotary drum dryers.
The plant has a capacity of 240 tonnes per hour (tph), with 1200 bags of pre-mixed render bagged and palletised per hour.
Brolton Group designed and constructed the plant for Rockcote, including complete civil, construction, mechanical and electrical services. The processing facility incorporated:
• Nine bulk materials in-feed system.
• Raw materials processing.
• Fluid bed drying, providing 25 per cent in savings.
• Eight weighing and dosing of additives.
• 90-second batch mixes
• Bagging and palletising of 1200 bags per hour.
• A plant capacity of 240 tph.
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Condensed clinker usage
Brolton Group also installed a fluid bed drying system at Morgan Cement International, reducing the company’s carbon footprint and natural resource utilisation.
An essential ingredient in the production of cement is clinker, which is manufactured by heating raw materials in a rotary kiln to more than 1450oC. The clinker is then ground and combined with other minerals to create cement. This process requires large amounts of energy and raw materials, and generates a significant amount of carbon dioxide (CO2).
Morgan Cement, a division of Adelaide Brighton Cement, aimed to replace a percentage of clinker from its cement with slag, reducing its site’s clinker usage. This would reduce thermal energy consumption and CO2 emissions from the site while maintaining the high performance of its cement products. Using slag allows Morgan Cement to recycle industrial by-products otherwise destined for disposal, and reduce natural resource consumption.
Slag has a high moisture content and needs to be dried for storage and use in cement production, necessitating the installation of a slag drying system. Morgan Cement acquired a new site at its Port Kembla facility for the project, and Brolton Group designed and installed a solution incorporating a Ventilex fluid bed dryer, a single front-end loader feed hopper and an extraction conveyor.
An inclined feed conveyor moves product from the extractor belt to a second incline conveyor, which then feeds product to the slag dryer inlet chute. Once processed, the dried material transfers through a lined chute to the outfeed conveyor and to the slewing conveyor, which feeds material to the stockpile via a dust suppression chute.
The Ventilex fluid bed dryer is a dryer/cooler with a 9m2 fluid bed area. The speed of the in-feed conveyor is set by the evaporative rate of the water in the product; when the water content of the slag is reduced, the speed of the in-feed conveyor increases.
At 10 per cent initial moisture, the dryer can dry 33.2 tph to a final moisture content of <0.5 per cent, and has an evaporation capacity of 3200kg. At higher initial moisture content of 15 per cent, the dried product rate is 22 tph, and at 20 per cent the rate is 16 tph. The final moisture content remains consistent at <0.5 per cent.
When at maximum capacity, the slag is dried at temperatures of 450oC to 475oC before moving to the cooler section integrated in the fluid bed, to cool the product to minus 75oC before leaving the dryer.
The exhaust is de-dusted with an automated filter installation. A portion of the exhaust air from the cooler section is recirculated, and the remainder of the exhaust air is emitted through the filter installation.
Once processing in the dryer is complete, product is conveyed into Morgan Cement’s warehouse, where it is stored ready for use in cement production.
Brolton Group provided a complete engineering service for the project, focusing on providing an optimal solution for Morgan Cement’s process flow requirements. The solution incorporated:
• Demolition and disposal of part of the existing structure.
• Complete civil, foundation and structural design and construction.
• Front-end loader (FEL) hopper.
• In-feed conveyors (comprising FEL hopper, and inline and dryer feed conveyors).
• Slewing conveyor.
• Ventilex fluid bed dryer.
• Central dust collection system and ducting.
• Siemens PLC and HMI.
Brolton Group is the distributor of Ventilex drying solutions in Australia. The company is a multi-disciplined engineering solution provider that has worked with multiple industries over a broad range of projects, from conceptual studies through to major turnkey processing facilities.
Source: Brolton Group