Fertilizer for the garden. Dish detergent by the kitchen sink. Electricity to power lights over your workspace. These are a few examples in the vast and growing “bioeconomy,” which some studies say tops US $4 trillion. Moving from a fossil fuel-based to a biobased economy is expected to contribute to climate and environmental protection as well as reduce our dependency on fossil fuels and make our resources more affordable, accessible and sustainable.
Biomass materials appear in obvious and subtle ways in everyday products, services, and industries. Their uses are as diverse as the sources for biomass, with types and varieties ranging from wood chips and sawdust to agricultural or municipal waste and even algae.
Biomass sometimes requires conversion to realize its useful purpose. It is the conversion process that creates dust and other compounds. Biomass dust collection is designed to capture and remove airborne particles generated during processing, handling or storage. The challenge is determining the right equipment and modifications to maintain efficiency and safety standards. This is not very easy due to the wide variety of source materials for biomass.
Types of dust collection equipment used in biomass
Dust collection equipment might include a baghouse, wet scrubber, cyclone or loading spout, depending on the type of dust that requires collecting, other constituents present, and the type of processing. For example, in a wood-fired application designed to generate electricity, a cyclone might remove the embers before entering a baghouse (embers entering a baghouse can set the bags on fire).
A biogas processing facility might use a baghouse and a wet scrubber for odor control or acid gas removal. In this case, the material selected for the wet scrubber must meet the gas challenges. If it contains many acids, for example, that eliminates carbon steel, the choices are stainless steel or fiberglass. Some installations require two baghouses, one for the dryer and one for the boiler. Depending on the particulate loading, particulate characteristics and required removal efficiency, a venturi and scrubber combo may be the solution.
When loading the resulting dry product into tank cars, open trucks, ships, or other forms of transportation, a loading spout can help mitigate the dust clouds produced during the loading process for removal or shipping. The loading spout is attached to the bottom of a silo or conveying system. Spouts are designed for open trucks or piles, tanker loading or combined loading spouts. Each situation is unique.
A baghouse is one of the most common types of biomass dust capture equipment. The baghouse filters out and collects the dust particles from the airstream using various filtration media. As the dust-laden air passes through the filter media, the dust particles are trapped and accumulate on the filter surface, while clean air is discharged into the atmosphere, commonly through the exhaust fan. The type of filter used depends on the nature and size of the dust particles, the particulate loading, temperature, and the volume of air to be filtered.
A baghouse can be a key part of the process. For example, a baghouse can be used as a filter receiver which is a high vacuum device used in pneumatic material transfer as a collection device to separate the material from the pneumatic air. These special baghouses can handle higher pressures.
For nuisance dust collection, depending on the particulates value and amount, a baghouse will either capture the nuisance dust for disposal or recycle the product back into the production stream. Dust collection systems can also capture particles at transfer points such as conveyors. Overall, baghouse systems are versatile and efficient.
Special considerations for dust capture during biomass processing
Special considerations that can impact the equipment selection, modifications, or the filter media can include:
Combustion characteristics: Many types of biomass are highly combustible and can pose an explosion hazard if ignited. Design engineers familiar with combustible materials can incorporate explosion mitigation features into the dust collection system to help prevent or contain any incidents. This can include explosion panels, spark detection apparatus, explosion isolation valves, grounding and more. Of course, proper maintenance and industrial housekeeping practices are a must.
Dust's Abrasive nature: Some biomass ash types can be highly abrasive. This abrasiveness can cause significant wear and tear on the dust collection equipment. Proper material selection can help create a more durable system able to withstand the dust’s abrasive nature.
Moisture content: Biomass materials can vary in their moisture content. Moisture can build up in ductwork and filters in a baghouse, leading to clogging and reduced performance efficiencies. Animal manure is one example of biomass that can have a high moisture level if not properly dried. The moisture percentage is one critical factor when designing a dust collection system, especially if the moisture will not be in vapor form.
Amount of ash: When combusting biomass material, certain types of biomass can produce more ash than others. Wood and palm fronds fall into this category. The projected or known ash level contributes to the dust collector's load factor.
Bulk density: Bulk density is one factor that contributes to dust collector sizing. The lighter the material, the less likely it is to fall into the hopper. Design engineers must select the correct interstitial velocity, so the ash falls into the hopper properly, or change how dust enters the collector.
Condensed gases: Some biomass processes might produce an acid in the gas stream. In vapor form, the gas passes through the bags. However, if it condenses and forms a liquid, the materials can cause corrosion or damage to the bags. The temperature must be maintained over the dewpoint to keep the acid in gas form to control this. In addition, condensable gases impact the material selected for the bags and cages. For high-acid environments, material selection will tend toward stainless steel, fiberglass, or Hastelloy, especially if a wet scrubber is used since the gas will cool below the dewpoint and form liquid acid.
Temperature and odor control: Venturi wet scrubber combinations are typically used in high-temperature processing to cool down the gas stream (via quench). A venturi scrubber quenches the gas to bring it down to saturation temperature. It also captures particulates or corrosive gases. For example, it can take ammonia out of a gas stream, a function the baghouse cannot perform.
An additional function wet scrubbers perform is odor control. Caustic chemicals or sodium hypochlorite can be added to the scrubber to significantly, if not wholly, eliminate the odor, depending on the source. Chicken manure is an example of biomass being converted to a saleable product yet has a strong odor.
No company in the industry has a more extensive history of designing and building dust mitigation equipment and systems than Sly LLC. With its broad range of variables, choose to work with a company that understands the biomass industry’s unique challenges and requirements regarding effective dust management.
Read more about our experience with biomass companies in our white paper or select case studies detailing Sly’s approach and solutions. Trust Sly LLC to fabricate a biomass dust collection system that improves air quality, maintains plant safety, and delivers cost-effective, durable performance.
Author: Al Moretti, Dry Segment Sales Manager
Al has been with Sly for over 2 years and in the dust collection industry for over 25 years.