Title: Reading
Course: BFM 101 Biofuels Fundamentals > Section: BFM 101 Biofuels Fundamentals

Breadcrumb Navigation

Reading »

Reading

(2/8)

(1/8)
Bioenergy End-Products and Their Uses

Bioenergy is a form of renewable energy and comes from materials derived from recently living organisms including plants, animals and their byproducts.  Forms of bioenergy include power, heat, and liquid and gas fuels (figure 2.1).  There are many uses of these various forms of bioenergy, discussed in greater detail below.

Figure 2.1 Bioenergy products and their end-uses.  (CL Williams, 2011.)

Biopower is electricity generated from combustion of biomass, either alone or in combination with coal, natural gas or other fuel (termed co-firing).  Co-firing is generally thought to be feasible at most coal-fired plants. Most biopower plants are direct-fired systems: biomass feedstocks are burned in a boiler to produce high-pressure steam that runs turbines connected to electric generators.  The electricity produced can be distributed for industrial, residential or commercial use. The steam generated from combustion of biomass feedstocks can also be used directly power mechanical processes in industrial settings.  Technical challenges in biopower generation involve feedstock quality, boiler chemistry, ash deposition and ash disposal.  However, these challenges are being resolved as the technology advances.  Boiler efficiency in co-firing may be reduced slightly compared to the efficiency of firing 100% fossil fuel feedstocks, due to high moisture content of the biomass feedstock.  Biomass co-fired in a coal power plant can assist the utility in meeting renewable energy standards and help cut pollution from coal burning. Co-firing is generally thought to be feasible at most coal-fired plants.

Electricity generation is a relatively inefficient process; two thirds of the energy generated is wasted as heat to the environment.

Biofuels are 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 (bioethanol), gasification (syngas), pyrolysis (syngas and char), torrefaction (bio-coal), transesterification (biodiesel), Anareobic digestion (to produce pipeline quality gas). 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.

Biofuels are typically described as 1st, 2nd, 3rd, or 4th generation, reflecting process technologies and the degree to which the technology has advanced. 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.

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. Combined heat and power is many times more efficient than combustion for electricity generation alone.

Fact Sheet:
Co-generation as a path to achieve greater efficiency

Resources provided by the eXtension Farm Energy Community of Practice at http://www.extension.org/ag+energy

(2/8)