While biomass has existed since the earth was formed, the past few decades have witnessed an increased interest in using biomass stock in unique ways. These innovative ideas have created a distinction between “modern” and “traditional” biomass. Modern uses repurpose waste products with a biological origin into new products or bioenergy.
Whether modern or traditional, during its conversion, biomass often requires dust mitigation efforts to prevent accidents and promote worker safety. Methods of supplying this include proper maintenance and industrial housekeeping practices, in addition to biomass dust collector systems, depending on the application. Understanding the hazards and how a dust collector works can help biomass processing operations realize cleaner air quality and improved safety.
Biomass is a broad term that describes renewable organic materials derived from the waste associated with living organisms, such as animals or livestock, plants and microorganisms. Sources range from food waste to crop residue, sewage sludge, wood or even algae.
Some of the many uses for converted biomass include bioenergy, biochemicals, animal feed, soil amendments, carbon sequestration, food additives and consumer products from adhesives to cosmetics. However, biomass requires a drying process as part of its conversion into useful purposes. The dust resulting from drying and subsequent processes poses various workplace hazards, from biological pathogens to possible combustion or even explosion.
Biomass Dust Hazards – Fire and Explosion Risk
One of the primary uses of biomass is for fuel, and wood products supply one of the primary biomass feedstocks for this purpose. Any facility producing energy, even biofuels, must consider fire and explosion mitigation.
The use of biomass for fuel is increasing, increasing the risk of potential incidents. According to the International Energy Agency (IEA), biomass accounts for approximately 10% of the world’s primary energy supply. In the United States in 2021, it accounted for 5% of our total energy supply.
Types of biomasses that can create the most hazardous dust can vary depending on multiple factors, including particle size, shape and chemical composition. Generally, biomass materials that are very dry and finely ground tend to produce the most dangerous, combustible dust.
Examples of biomass that are more prone to producing hazardous dust include sawdust, wood chips, rice husks and straw. These materials are common to woodworking, paper manufacturing and agricultural industries. For example, sawdust has a high explosive potential due to its fine particle size and lower moisture content compared to other types of biomasses.
The Triangle of Combustion
The triangle of combustion requires fuel, oxygen and heat. These three elements exist in abundance in a wood pellet plant. Processes for converting biomass into energy or an industrial ingredient often generate dust which can quickly accumulate on machinery, rafters, cable trays, conduit and piping, supplying the fuel for combustion.
Dryers, hammer mills, pelletizers, and even the conveyors and machinery moving material from one location to another can contribute to combustibility. For example, moving or manipulating a combustible product creates friction and heat. Add in oxygen and dust for fuel and combustion is a real threat. An additional factor, confinement, such as wood dust in an enclosed bin, turns that fire into a potential explosive.
Due to the above hazards, there is a need for increased focus on how this dust is stored, transported and collected in the system. This includes ways to prevent the dust from being produced, preventing it from escaping the system into the plant and using properly designed dust collection systems.
When there is potential for dust escaping into the plant, it is essential to establish specific guidelines on safe levels regarding fire and explosion risk. Sections in the plant with possible fire or explosion risks due to explosive atmospheres and/or mixtures are called hazardous (or classified) locations or areas. A Class/Division system is commonly used in the United States and Canada. In other parts of the world, a Zone system is typically used.
NFPA Regulations and Dust Hazard Analysis
The National Fire Protection Association (NFPA) tracks fire and combustion incidents in industrial or manufacturing properties. It noted that U.S. fire departments respond to an average of more than 37,000 fires each year (2011-2015) at industrial or manufacturing plants.
Considering this, NFPA devotes more than one standard to regulating dust control to help prevent fires and explosions. The following list relates to biomass dust control:
Standards 61, 652, 654 and 655 describe dust control measures.
NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Wood Working Facilities covers wood biomass and pellet plant protection.
NFPA 61 was written for Agricultural and Food Processing Facilities or agricultural-based biomass. This standard specifically calls out enclosed vessels, such as bins, hoppers, enclosed bucket elevators, etc., as primary areas of concern.
The NFPA 68 Standard on Explosion Protection by Deflagration Venting helps detail the type of venting and engineering that can be applied to a dust collection system, with the design and protective measures based on the explosive nature of the dust.
It is worth noting that there are significant changes on the horizon for NFPA 652, which will incorporate all commodity-specific standards within the single directive in the future, including biomass materials from a wide range of feedstocks.
In wood pellet and biomass industries, facilities using wood-based products must conduct a dust hazard analysis (DHA), which examines the potential for hazardous atmospheres and ignition sources. As of January 1, 2022, facilities that process agricultural-based products also need to complete a DHA, and these DHAs, regardless of industry, must be revalidated every five years.
Other recommendations include spark detection systems, typically associated with conveyors and dust collection systems. The appropriate extinguishing system should accompany these recommendations.
And based on NFPA 68, dust collection systems should include explosion venting and explosion isolation on the inlet and outlet (if required). This equipment can help control or prevent deflagration from moving through equipment and sparking a secondary explosive event.
Health Concerns an Issue with Some Biomasses
The challenges presented by biomass dust, however, involve not only combustibility but also biohazards. Chicken manure is one example. Its dust contains organic matter such as bacteria, fungi and other microorganisms, including pathogens such as salmonella and e. coli. These can pose a health risk to employees.
Chicken manure is a type of biomass that can be used as a renewable energy source, primarily through anaerobic digestion. This process produces biogas or creates feedstock for combustion to generate heat and/or electricity. The type of dust it generates depends on the manure’s age, moisture content, and method of handling and processing.
As a result, proper sanitation processes and equipment for minimizing and capturing the dust generated is critical. Sometimes, a wet scrubber may be required for odor control and/or to neutralize the constituents present.
Prolonged or repeated exposure to fine biomass dust can negatively impact employees' health. In addition to risks associated with potential pathogens such as those listed for chicken manure, other types of biomass dust can create health issues if not properly contained. For example, the dust associated with wood products contains toxins which may cause allergic respiratory symptoms, mucosal and non-allergic respiratory systems, and even lung cancer.
Working with an Expert Dust Collection Firm
Sly LLC offers at least twenty years of experience working within the biomass industry. Add this to its 100+ year history in dust collection overall, and companies can rest assured that any dust collection system designed and engineered by Sly LLC staff will supply effective dust control for any particulate matter.
Sly offers a full range of dust collection equipment customized to fit each industrial scenario. Whether a baghouse, wet scrubber, or loading spout is required, the team at Sly can optimize dust capture for improved air quality, safety, and maintenance. We can explain the ins and outs of a biomass dust collector and which type of system will best apply.
A Unique Biomass Product in South Florida
As one example, Sly developed a system for a bioenergy facility in South Florida, which was converting biomass feedstock into electrical power and renewable fuel. The facility needed a dust collection system to capture particulates resulting from drying palm fronds, a fibrous plant material. When dried, the resulting dust has a low bulk density and a high combustibility potential.
Sly installed a dust collection system and baghouse with special modifications designed to manage the lightweight, potentially combustible particulates resulting from drying the biomass feedstock. Engineered design modifications included a higher rear inlet on the baghouse to collect the particulates from the dryer and explosion-proof venting for safety.
The baghouse incorporated one other customized feature, a reinforced structure designed and built to withstand high winds of up to 140 MPH. This area of South Florida is subject to severe weather outbreaks due to hurricanes. Further details are included in this case study.
Sly LLC is happy to consult on the results of the dust hazard analysis conducted in compliance with NFPA regulations and design and engineer a collection system to protect life and property. Download our white paper to learn more about Sly LLC and its experience with biomass dust collection equipment and systems. Or give us a call and discuss your specifications with our engineers.
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