With the Environmental Protection Agency’s Clean Power Plan causing such a stir, coal-fired utilities are likely weighing their options and looking for alternatives that could help them reduce their carbon footprint. One fairly straightforward strategy that takes advantage of ample, affordable, and available fuel that also qualifies as a renewable energy resource in the eyes of the EPA is biomass.
To date, the utility industry has been hesitant to consider converting from fossil fuel to biofuel because there is so much variation in biomass, which makes delivering consistent fuel to any boiler challenging. Biomass can also be much harsher on equipment than coal, which makes plant managers and owners apprehensive.
Luckily, with the right experience and knowledge, both of these potential issues can be surmounted. What follows is a basic overview of the two most common strategies for transitioning to a biomass-fed boiler system — co-firing and complete conversion.
Co-firing is the simplest way to integrate direct-fired biomass into your utility plant. Essentially, it entails buying processed wood pellets to burn alongside coal. The fuel is mixed before it enters the boiler conveyor system and the two forms of fuel are co-fired with each other.
Biomass wood pellets have been processed to a state where they have similar heating values to coal and pass through the boiler coal handling, pulverizing, and burner equipment without a hitch. Frequently, direct co-firing will enable a facility to utilize its current fuel-feed system, making it an affordable option to start.
Because co-firing can be started without new equipment, it’s often a good option for facilities that are constrained in terms of budget, space, or both. It should be noted, though, that a high-volume plant serving up a lot of power will probably negate the capital cost benefits of co-firing since biomass pellets can quickly get expensive.
Transitioning to a completely direct-fired biomass setup requires new fuel-feed equipment and is therefore more capital intensive than co-firing, but it positions a plant to take advantage of inexpensive fuel sources such as wood chips, sugar cane husks, and construction debris. Also, existing coal equipment can often be retained during a complete biomass conversion project and a complete conversion may make a plant eligible for government subsidies or other programs with financial benefits.
Three Areas to Pay Attention to
There are three main factors to take into account when designing a biomass fuel handling system. In the first place, a biomass fuel handling system will typically require more space than a coal setup because biomass, whatever its form, does not stack as tightly as coal.
Biomass also doesn’t flow as easily as coal, which means that it requires distinct conveyor and metering equipment — machinery capable of pushing and pulling it through the system, preventing any stacking, and grinding it up into usable sizes.
Lastly, the materials handling and boiler equipment will endure much greater volume throughputs, erosion, and corrosion from biomass since dirt and sand embedded in the fuels will inevitably get into the system. Strategies for resisting this wear and removing these abrasive particulates need to be incorporated into the system.
Whatever the particular needs of your biomass system, there are three key pieces of equipment that will need to be incorporated: reclaimers, fuel processing equipment, and biomass-specific metering bins.
Biomass materials such as bark, wood chips and sawdust are often stored in large piles fed by transfer conveyors, which proceed from the sites where biomass fuel is delivered. Heavy-duty reclaimers work to pull the fuel from these massive piles onto the boiler feed conveyor system, guaranteeing a consistent fuel feed. Some of the most common types of biomass reclaimers include underpile drag chain reclaimers, circular screw reclaimers , and traveling screw reclaimers.
Fuel Processing Equipment
Unlike coal, which tends to be more uniform and easier to manage, biomass fuels clump in ways that often stymie existing coal conveyance equipment such as metering reclaimers, screw feed bins, chute work, and boiler feed spouts. To prevent this, biomass fuels need to be properly screened and sized to specifications before they proceed to the boiler.
The irregular size and flow characteristics of biomass material require metering bins with rugged screws at the bottom. These mechanisms pull the biofuel through the system at the desired rate and prevent bridging of woody biomass. Without them, any system runs the risk of interruptions in the fuel delivery and improper fuel distribution to the boiler.
From Intro to Action
If you’re ready to learn more about biomass conversion, the next step would be to talk to a firm that is experienced with these sorts of projects. We at ProcessBarron have been constructing and maintaining biomass fuel handling systems for over 20 years for the pulp and paper industry. We’ve also been involved in dozens of biomass conversion projects for the power industry, providing our clients with total systems solutions and cost-savings strategies.
To review one of our biomass transition projects in detail, please download our case study, “Anatomy of a Coal to Biomass Conversion,” which tells how we helped convert ReEnergy Holding’s 60-megawatt Fort Drum Black River facility to biomass.