Co-Production of Ethanol and Electricity from Waste
9 June 2005
A gasification/biocatalytic process developed for BRI Energy by a team led by Dr. James L. Gaddy enables the co-production of electricity and ethanol (and/or hydrogen) from any carbon-based material, such as municipal solid waste; biosolids & animal wastes; biomass waste; used tires & plastics; and hydrocarbons (coal, natural gas, refinery tars &waste oils).
The BRI process utilizes a culture of acetogenic bacteria (Clostridium ljungdahlii, picture upper right) that ingests synthesis gas (gasified wastes) and emits ethanol at a yield of some 75 gallons or more per dry ton of biomass. From used tires or hydrocarbons it can yield approximately 150 gallons or more per ton.
The process involves three main steps:
Gasification. Thermal gasification at temperatures of up to 2,200°F in a reducing, oxygen-starved atmosphere “cracks”organic materials and reforms them into simple CO, CO2 and H2 gases.
Before being introduced to the bacteria in a fermentation tank in the next stage, the synthesis gases must be cooled to approximately 97°F—a process that generates an enormous amount of waste heat that can be used to create high temperature steam to drive electric turbines.
Fermentation. The acetogenic Clostridium ljungdahlii convert the carbon monoxide into ethanol.
Distillation. Ethanol is separated from hydrogen and water.
The BRI process will gasify any carbon-based material whose moisture content is less than 30% (by weight). Any mixture of plastics, tires, manure, paper or yard wastes, construction debris, furniture, hazardous wastes, crop residues, timber slash, etc., can be converted into synthesis gas, and then to ethanol. Only the inorganic fraction is not converted. The remainder, which is nonhazardous, is discharged from the gasifier to be landfilled or recycled in products like cement blocks or paving.
BRI’s plants will also operate on natural gas, petroleum and coal—and these hydrocarbons can be blended with biomass to increase by up to 100% the overall gallon-per-ton output of the plant.
The utilities used in operating a BRI plant, with the exception of water, are supplied internally from the plant’s waste heat.
The entire process, from the time the waste material is fed into the gasifier to the creation of ethanol, takes less than seven minutes, according to the company.
Plant design is governed by the maximum size of today’s gasifiers. BRI’s plants will be modular and their capacities can be expanded. The company envisions a single module combining two gasifiers, each with a capacity of approximately 125 tons of waste per day, and two fermenters.
Each module will process some 85,000 tons of biomass annually to produce 7.0 million gallons of ethanol, also generating 5 MW of power. The amount of ethanol and electricity to be produced by any module can be varied according to energy demand.
Theoretically, a mid-sized BRI Renewable Energy Plant could process 1,000,000 tons of municipal solid waste, waste tires and/or biosolids per year, producing 80 million gallons of ethanol and generating 50 MW of power, 35 MW of which is excess to the operation of the plant. Such a plant would require ten modules and approximately 30 acres.
The DOE, which has awarded BRI some $2.4 million in grants to develop and demonstrate the technology, notes:
The problems with the application of gasification have been economic, not technical. In the past, the product from gasification has been electricity or heat source, and the low value of these products in today’s market is insufficient to justify the capital and operating costs. However, if gasification is coupled with the production of a higher value liquid fuel, the combination could be a viable alternative energy technology.
The process of combined gasification/fermentation has been under development by BRI for several years. The feasibility of the technology has been demonstrated, and plans are under way to pilot the technology as a first step toward commercialization. The conversion of a waste stream, the disposal of which is costly, into a valuable fuel adds both environmental and economic incentives.
BRI has patented its process, the bacterial culture, and the critical methods of maintaining the environment in which the bacteria operate. (Microbes can have issues: nutrients, vitamins, minerals, toxins, contaminants, perturbations like pH. The reliability of such a process as BRI’s is absolutely dependent on the ability to maintain the vitality of the culture.)
Dr. Gaddy has a pilot plant in Fayetteville, Arkansas, which has been producing ethanol using his BRI process virtually 24/7 for the past four years.
The technology is now at the point of commercialization and BRI is in discussions for plants across the United States and in several foreign territories. The company expects the first commercial plants to commence construction within six months or so.
BRI Energy Backgrounder (from a presentation to the Millinocket Area Growth and Investment Council)
Klasson, K.T.; Elmore, B.B.; Vega, J.L.; Ackerson, M.D.; Clausen, E.C.; Gaddy, J.L., “Biological Production of Liquid and Gaseous Fuels from Synthesis Gas.” Applied Biochemistry and Bioengineering, Vol. 24/25, 1990, pp. 857-873.
Tanner, R.S.; Miller, L.M.; Yang, D., “Clostridium ljungdahlii sp. nov., an acetogenic species in clostridial rRNA homology group I.” International Journal of Systematic Bacteriology, Vol 43, 1993, pp. 221-231
TrackBack URL for this entry:
Listed below are links to weblogs that reference Co-Production of Ethanol and Electricity from Waste: