Solid Biomass Fuels
Woody Biomass | Agricultural Crops & Residues | Municipal Solid Waste | Waste Tires | Construction Debris | Links
Robert A. Harris et al. produced a definitive report, Potential for Biomass Energy Development in South Carolina, completed in 2004 for the South Carolina Forestry Commission. The study describes the amounts, locations, and types of forest biomass and agricultural crop residues available. Forest biomass includes: logging residues, pre-commercial thinning, commercial thinning, southern scrub oak, mill residues, urban wood waste, forestry biomass, and agricultural wastes and byproducts. Harris describes available biomass-to-energy technologies, costs for transportation, potential job creation, and economic benefits. Harris identified 22 million tons of forest biomass available yearly for energy use, equivalent to powering ten 40 megawatt biomass power plants, potentially displacing 4.8 million tons of coal (1/3 of all coal used for power production in South Carolina.
Most dedicated biomass fueled power generators use direct-combustion boilers coupled with steam turbines. These generators typically possess a biomass combustion chamber with equipment to evenly distribute biomass fuel over a grate which separates the ash from the burning biomass. The generated heat creates steam in an adjoining high-pressure water tube boiler which feeds process steam through a multistage steam turbine.
Another biomass generator is a simple cycle gas turbine. This generator uses a primary chamber devoid of air to gasify the biomass, which then passes into a secondary combustion chamber where the gas is used to produce heat. These plants tend to be inefficient, small, and expensive compared to traditional power generation from coal and natural gas. However, a more efficient and less expensive form of biomass power is known as a combined-cycle biomass gasification system. Biomass is converted to a gas, in an atmosphere of steam or air, and produces a medium to low-energy content gas. This biogas powers the combined-cycle power generation plant similar to the simple cycle. These plants unfortunately have not yet reached America, but with further study could be a reliable form of biomass power generation. The University of South Carolina (USC) plans to build a simple cycle gas turbine on their Columbia campus to go online as soon as summer 2007. The plant will produce approximately one megawatt of electricity, equaling about 85 percent of campus energy needs. The USC plant will utilize 10-20 million tons of biomass over the course of its operating life and save almost $2 million annually.
Using woody biomass for co-firing in coal-fired power plants has also been described as a source of power in the Harris report, but in need of further study. Co-firing involves mixing woody biomass with coal to reduce the amount of coal used in the process. Co-firing has been tested with a variety of boiler technologies. Though it decreases efficiency by a marginal amount, it increases air quality significantly. The main problems identified with co-firing are the logistics of storage, handling, and preparing the biomass fuel, as well as safely and efficiently adding the fuel to the combustion chamber.
Already many operations have realized the benefits of wood fuel and the South Carolina Energy Office website, www.energy.sc.gov, lists two regularly-updated inventories of current wood waste power: 1) an inventory of known users of wood waste for energy and 2) an inventory of producers of wood waste. According to these inventories, 62 commercial and industrial operations in South Carolina use 4 million tons of woody biomass annually for energy purposes. The SC Energy Office also identified 115 producers of waste wood products making about 5.5 million tons of woody biomass available for energy purposes
Alternately, agricultural wastes and energy crops have been identified as a source of fuel for electrical generation. More studies need to be done to better understand the economic benefits of agricultural wastes and energy crops in South Carolina. The report, Potential for Biomass Energy Development in South Carolina, by Robert Harris et al., showed no economic incentives currently exist to derive biomass from crop residues because federal law requires at least 30 percent of the soil surface be covered by plant residues to control erosion and maintain soil productivity. Additionally, due to the seasonality and low energy density of crop residues, it may not be as reliable and economical when compared to forest biomass. Switchgrass has sometimes been mentioned as a possible new crop to be grown solely for energy use, but there has been no serious analysis of the potential for switchgrass or other crops grown for conversion to useful energy through combustion or gasification.
Municipal solid waste is used to generate electricity at the Montenay Charleston Resource Recovery facility in North Charleston which burns 220,000 tons of solid waste per year, approximately 75% of the waste produced in Charleston County. The majority of the generated steam is used to produce 92,600 MWh/year, of which 70,000 MWh is sold to Progress Energy. Around 285,000 lbs of steam per year is sold to the US Navy, the rest is used to generate electricity. The Montenay Charleston contract with Charleston County expires in 2009, with discussions underway to extend the contract. Originally, the federal government purchased the steam from this facility for use at the local Naval Shipyard. A facility in Hampton, South Carolina was constructed in the 1980s to provide steam to a local manufacturing plant, but this facility converted to a medical waste incinerator and is now closed. The Wellman Energy Plant in Johnsonville at one time burned municipal solid waste, but now generates power from in-waste produced by the plant.
In 2005 South Carolina sent nearly 3.5 million tons of solid waste to permitted landfills according to SC Department of Health and Environmental Control report, SC Solid Waste Management Report FY 2005. Though burning this amount of waste would produce approximately 2 million MWh of electricity, the economic and environmental considerations of combusting municipal solid waste for energy purposes make this form of energy less desirable. According to the Environment Protection Agency, burning 3.5 million tons of municipal solid waste would produce approximately 3 million tons of carbon dioxide in addition to other noxious chemicals and gases. Landfill-gas-to-energy projects and energy savings from recycling appear to be preferable energy derivatives from municipal solid waste. However, if recovered properly, a portion of municipal solid waste could generate power in a more environmentally feasible way.
Waste tires are another form of biomass energy and due to their abundance could generate a reliable supply of power. In 2005, 261 tons of waste tires were sent to landfills in South Carolina according to the SC Department of Health and Environmental Control report, SC Solid Waste Management Report FY 2005. Junkyards and waste tire facilities collected the remainder. According to estimates from the SC Department of Health and Environmental Control, approximately 60,000 tons of waste tires are generated each year and of that 45,000 tons are burned for fuel. Two known factories in South Carolina use tire derived fuel to generate onsite power. International Paper Company in Richland County uses 20,000 tons of tire-derived fuel each year to produce steam. The Blue Circle Cement Waste Tire Processing Facility in Harleyville also incinerates tires as a secondary fuel for the cement-making process. Burning tires releases similar air pollutants as fossil fuel-based power generators and therefore is not an environmentally preferred alternative. Despite the existence of waste tire incineration in South Carolina, no known studies have evaluated the environmental and economic feasibility of burning waste tires on a large scale.
In 2005 approximately 1.7 million tons of construction and demolition debris were sent to South Carolina landfills according to the SC Department of Health and Environmental Control report, SC Solid Waste Management Report FY 2005. Unfortunately, no known studies have evaluated the economic and environmental feasibility of burning construction and demolition debris in South Carolina and no known facilities in South Carolina use this waste for fuel.
For more information about solid biomass fuel please visit the following websites:
