BIOMASS ENERGY Biomass consists of all living plant matter as well as organic wastes derived from plants, humans, marine life, and animals. In addition trees, grasses, animal dung, as well as sewage, garbage wood construction residues and other components of municipal waste are all examples of biomass Biomass energy is the first form of energy exploited by man. Biomass is the natural energy for conversion of solar energy to high-energy content products that can be stored transported, and used conveniently.

CHARACTERISTICS OF BIOMASS Biomass energy is a renewable Connected to farming -economics Multiuse – food, shelter, energy, materials Environmental concerns include land and water use, fertilizer and other nutrient requirements Naturally diffuse and distributed – harvesting and transport and distribution are important

SOURCE OF BIOMASS ENERGY The main source of biomass energy is from the sun. Plants grow by the process of photosynthesis in which sunlight transforms two abundant raw materials, water and carbon dioxide, to carbohydrates and other complex organic compounds of great natural and commercial value. The reaction is shown below: –Average solar incidence is about 4000 W/m2/day –Biomass capture efficiency is ~ 1% –Thin film photovoltaic efficiency is ~ 10% The process is intermediate in the formation of glucose/sucrose, cellulose polymers, fuel for plant respiration, or variety of other compounds depicted in the figure below:

RENEWABILITY INDICES AND BIOMASS RESOURCES Semi quantitative measure of the rate of regeneration was proposed by Paul Weisz (1978) Since biomass is considered as a renewable there is the need to estimate how rapidly it is regenerated in quantities that are useful to humans. His idea compared the time for regeneration of commercially meaningful quantity of the resource quantity of the resource under scrutiny, T r to a time at which the resource will be beneficial to mankind T u

RENEWABILITY INDICES AND BIOMASS RESOURCES CONT.

Table 10.1 Selected Dimensionless Time Constant Related to the Renewability of Biomass RENEWABILITY INDICES AND BIOMASS RESOURCES CONT.

BIOMASS RELEVANCE TO ENERGY PRODUCTION BIOMASS UTILIZATION Figure 10.2 Explain the biological and thermal routes of biomass energy conversion

ADVANTAGES AND DISADVANTAGES Advantages –It is renewable and domestic available –Its disperse nature leverages its potential impact by enabling it to function as a distributed energy source. –Biomass derived products can substitutes those of plastics and metalic products which require abundance of energy. –Its use as a source of energy offers another major benefit to sustainability namely a pathway to manage municipal and agricultural waste. –It has the potential to combat the atmospheric buildup of the greenhouse gas CO 2 –It act as a feedstock and has lower sulfur content

ADVANTAGES AND DISADVANTAGES Disadvantages –It has low energy content compared to coal and petroleum derived fuels –Intensive cultivation may stress water resource and deplete soil nutrients –The wide dispersion of biomass combined with the low intensity of production per unit land areas are serious disadvantages when there is a need to supply huge amounts of energy to a small area. –It has high cost of transportation

US BIOMASS RESOURCES

Estimated Potential Production Rates of Biomass for Energy in 2050 Table 10.2

Estimated Residual Biomass for the US Table 10.3

Selected Properties of Biomass Relevant to its Use as a Fuel Table 10.4

Trace Element Emissions from Wood- Fired Boiler Table 10.5

THERMAL CONVESION OF BIOMASS Biomass to Electricity –Co-firing with coal to reduce sulfur emissions and smooth a transition to reduced fossil dependency –Repowering (ie is backlifting an existing generating station to switch to biomass fuel, or add a biomass-fired generator to an existing fossil fueled unit) –Direct combustion in a Rankine cycle to raise steam to operate a turbine generator –Various configurations of combined cycles in which the biomass is first gasified and the gas then combusted to generate steam or, in a gas turbine, to provide motive power with the option for extracting additional electricity from the waste heat –Thermal of hydrothermal conversion of the biomass to other fuels that, after substantial cleaning, are combusted to generate steam or motive power, or fed to a fuel cell for direct conversion to electricity

BIOMASS TO FUELS Bioethanol in the United States Bioethanol from Corn Corn grain is the feedstock – with a current capacity of ~144 M dry tons – equivalent to 10 – 14 B gallons of ethanol – ~10% of U.S. fuel consumption Current ethanol production is ~2 B gallons Liquid fuel additive/replacement – environmentally friendly oxygenate – fuel flexible cars can use blends up to 85% ethanol Subsidized heavily to make it competitive with gasoline

PRESENT TECHNOLOGY FOR PRODUCTION OF BIOETHANOL FROM GRAIN CORN FEEDSTOCK

TRANSIONING TO BIOREFINERIES

BIOMASS TO ELECTRICITY EXAMPLE OF US INSTALLED CAPACITY

CHALLENGES TO BIOMASS BASED ELECTRICITY PRODUCTION Low heat to power efficiency of combustion steam turbines – 18-24% (14,000-19,000 Btu/kWh) Alkali and other trace metal deposits and emissions Particulate Deposits and Emissions NOx Emissions Cost of Electricity – $0.065 – 0.08/kWh Lower Energy Density – Oxygen = wt % dry basis Use of Land, Water, Nutrients Displacement of Higher Value Crops

BIOCONVERSION Bioconversion or biochemical processing refers to the direct or adaptive use of the chemistry of living things to transform one substance to another eg. Fermentation BIOGAS ~ 50%vol CH 4, 50%vol CO 2 –From Anaerobic Digestion of wet Biomass – Animal, Human Wastes – Sewage Sludge – Crop Residues By-Products: Nitrogen-rich Sludge (Fertilizer) and Fewer Pathogens Extensive Use in India and China (Millions of Digesters); Industrialized Countries (Stockyards, Municipal Sewage, ~5000 Digesters) Major Goals – Environmental Neutralization of Waste – Fertilizer From Waste

BIOGAS FROM ANAEROBIC DIGESTION Gas Production Rate –0.2 Nm3/m3/day Floating or Fixed Cover Digesters (Villages: China, India) –4-8 Nm3/m3/day industrial Scale Technology (Dilute Industrial, Municipal Wastes) Estimated Costs of Biogas $/million Btu – Household 11.6 – Village 5.8 – Industrial

OVERALL PROCESS CHEMISTRY FOR PRODUCTION OF BISGAS BY ANAEROBIC DIGESTION OF WET BIOMASS COMPLEX ORGANIC MATTER SHORT CHAIN ACIDS ALCOHOLS, H 2 etc. CH 4 CO 2 MINERAL AND NITROGEN-RICH EFFLUENT SLURY Bacteria that promote fermentation and acetic acid fermentation Bacteria that promote methane formation 35-55ºC Process Variables: pH, feed-rate & C/N ratio, solids residence time (SRT), hydraulic residence time (HRT), stirring Simple technologies SRT and HRT of order weeks

FIXED DOME SMALL SCALE ANAEROBIC DIGESTER FIGURE 10.7

FLOATING COVER SMALL SCALE ANAEROBIC DIGESTER FIGURE 10.8

POTENTIAL ADVERSE ENVIRONMENTAL IMPACTS OF BIOMASS PRODUCTION AND UTILIZATION FOR ENERGY

OPPORTUNITIES FOR BIOMASS Reducing Greenhouse Gas CO 2 Restoring Forest Resources Renewable Carbon Source for Energy Future Dominated by Non-Carbon Based Electricity, e.g. Nuclear, Geothermal, and Solar. Biomass Becomes Significant Raw Material for: – Liquid Hydrocarbon Fuels–Chemicals – Other High Value Products