Typical Wood Pellet Cooling System
- After the wood pelletizing process, the wood pellets enter the inlet hopper of the MBHE at temperatures typically around 70 C to 100 C. The bed of product, ranging from 1 to 200 metric tons per hour, then flows at a controlled speed through the heat exchanger bank(s)—usually 0.3 meters per minute—while cooling water at 20 C to 30 C flows countercurrently within the plates’ internal channels. The number of heat exchanger banks required depends on the duty of the process conditions and necessary surface area to meet the cooling temperature target.
- The flow of wood pellets is controlled by a sliding ladder feeder equipped with a pneumatic actuator positioner that ensures uniform mass flow and even product temperatures at the outlet. A level probe or transmitter in the inlet hopper maintains the proper level as it controls the instrumentation on the feeder.
- The MBHE is static, with the only moving part being the feeder at the outlet. It is isolated from the rest of the installation to avoid any transmission of vibrations.
- If the MBHE is installed in a hot, humid location, a small amount (less than 1,500 standard cubic feet per minute) of dehumidified purge air may be injected between the heat exchanger banks to prevent condensation from forming inside the column.
- MBHEs can easily be retrofitted into existing processing facilities, as they have a small installation footprint (less than seven feet by seven feet) and can be used in conjunction with current equipment. As the heat exchanger banks are modular, additional banks can be added in the future when a plant considers increasing capacity.
How MBHEs Help Decarbonize
- Reduce primary energy consumption: Water is a more effective cooling medium than air, absorbing up to 24 times as much heat, resulting in lower power requirements to circulate the much lower volume of cooling medium. While air coolers typically consume around 4 to 5 kilowatt hours per metric ton (kWh/mt) of wood pellets, an MBHE consumes, on average, just 0.4 kWh/mt of wood pellets.
- Eliminates emissions: Because air is not being used as the heat transfer media, emissions are reduced to near zero. An MBHE will emit approximately 0.42 kilograms per 1 kWh, which is approximately eight times less than traditional cooling technologies.
- Waste heat recovery: With advances in heat pump technology, it is now feasible to recover the heat extracted from wood pellet cooling rather than discharging it to the environment. The heat pump system extracts the thermal energy from the cooling water to a refrigerant via a plate-and-frame heat exchanger. Then, a small pump will move the refrigerant through a refrigerant cycle, resulting in an amplification of the heat. Typically, the heat amplification is three to four times the power input of the pump.
- This heat is then extracted from the refrigerant—for example, to air using a finned-tube, air-to-liquid heat exchanger. This heated air can be sent to the dryer burner to displace a material amount of fossil fuel energy needed to produce the hot drying air. Alternatively, the recovered heat can be transferred to water, and the heated water can be used in other processes such as steam production.
Conclusion
- The path to greener wood pellet production requires a comprehensive approach that involves making sure each stage aligns with broader sustainability goals. The cooling stage has always been an essential part of ensuring a quality finished product. Yet the technology employed at this stage must now do more.
- Plate-based MBHEs provide wood pellet producers with an energy-efficient, near-zero emissions solution. By combining plate heat exchange design with uniform mass flow to indirectly cool wood pellets, the technology avoids having to rely on energy-intensive ancillary equipment to get the job done while virtually eliminating emissions and opening the door to additional waste heat recovery options.
Keypoints :
- Traditional wood pellet cooling methods are energy-intensive, requiring large amounts of air to cool the wood pellets. MBHEs, on the other hand, use water as a cooling medium, which is far more efficient. This results in lower energy consumption and reduced emissions.
- Additionally, MBHEs have a smaller footprint, making them easy to retrofit into existing facilities. Moreover, the heat extracted from the cooling process can be recovered and reused, further enhancing energy efficiency.
Note: The information in this article is for reference only and may change depending on the manufacturer and source of raw materials. For the most accurate information, you should consult experts, wood pellet suppliers or contact Overc.vn to answer your questions and problems related to wood pellets and wood chips.
Source:
- Biomass Magazine
- Overc Team synthesise, analyse and write articles.
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OVERC was established in Vietnam, which has 17 FTA (Free Trade Agreement).
Vietnam is one of the countries with the most FTAs in the world.
Our main activities are manufacturing and distributing Wood Pellets and Wood Waste. Our wood pellet products, which are made from Acacia veneer residual 100% or wood waste (logs, sawdust, wood chips, wood shavings,…), have been exported to many countries around the world such as Japan, Korea, EU, etc.
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