Forms of bioenergy

Biopower? is electricity generated from combustion of biomass?, either alone or in combination with coal, natural gas or other fuel (termed co-firing). Most biopower plants are direct-fired systems. That is, biomass feedstocks are burned in a boiler to produce high-pressure steam which runs turbines connected to electric generators. The electricity produced can be distributed for industrial, residential or commercial use (figure 1). The steam generated from combustion of biomass feedstocks can also be used directly power mechanical processes in industrial settings (figure 1). There are several technical challenges in biopower generation involving feedstock quality, boiler chemistry, and the deposition and disposal of ash. Co-firing is generally thought to be feasible at most coal-fired plants.

Figure 1 Bioenergy? products and their end-uses. (CL Williams, 2011.)

Biofuel? is liquid, gas and solid fuels produced from two types of biomass materials – plant sugars and starches (e.g., grains), and lignocellulosic materials (e.g., leaves, stems and stalks). Liquid and gas biofuels are produced through fermentation, gasification?, pyrolysis?, torrefaction, and transesterification conversion technologies. The primary use of liquid and gas biofuels is transportation. When raw biomass is suitable as-is, such as wood chips, or when densified, as in the case of sawdust pressed into pellets or briquettes, it can be burned directly in furnaces for heat, for example.

Alcohols produced through fermentation of sugars derived from wheat, corn, sugar cane, etc. are known as first generation biofuels. Non-food crops (such as perennial grasses?) are used in production of second generation biofuels?. Cellulosic plant materials, for example, are used to produce cellulosic ethanol?, a second generation biofuel. Third generation biofuels are derived from algae. Fourth generation biofuels include syngas, char and bio-coal derived in bio-chemical and thermo-chemical processes like pyrolysis, gasification and torrefaction.

Figure 2. Combined heat and power system. (U.S. EPA.)

Heating and cooling can be derived from steam and waste heat generated in biopower generation and biofuel conversion processes. Combined heat and power (CHP), also known as co-generation, is the simultaneous production of electricity and heat from a single fuel source, including biomass (figure 2). In a gas turbine CHP plant, hot exhaust gases from the combustion process are captured in a heat recovery unit and used to heat steam which is then used in heating and cooling of various indoor environments. In steam boiler CHP plants steam is produced that runs electric generates and for heating/cooling (figure 2). Cooling from CHP plants is achieved when thermal energy is passed through absorption chillers or desiccant dehumidifiers. Heating and cooling from CHP facilities can be used in institutional, commercial, municipal, and residential settings (figure 1). Overall energy system efficiency is relatively high in CHP facilities because they make use of waste heat that would otherwise be lost to the environment.

Anerobic Digestion and Biogas

UW Extension have created seven modules focused on the use of anaerobic digestion technologies. Details of the process are introduced, as well as factors that influence start-up, operation and control of anaerobic digesters at different scales.

Contact Us:

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Carol Williams clwilliams4@wisc.edu
(608) 890-3858 (office)
(515) 520-7494 (mobile)
Department of Agronomy
1575 Linden Dr.
University of Wisconsin, Madison, WI 53706

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Researchers from University of Wisconsin and the Wisconsin Department of Natural Resources visit a grassland bird study site in southwestern Wisconsin. Photo by AERG.