Biomass - Using Anaerobic Digestion

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Background Information

Global Energy Use

Many countries rely on abundant and readily available energy, primarily fossil fuels. Fossil fuels consist of crude oil, natural gas and coal and are unmatched as a source of energy. Unfortunately they are all non-renewable.

Long term forecasts show that world energy demand will dramatically rise because of population growth (6 billion to 9 billion people over the next 50 years) and increased standards of living.

graph: Fig.1 Growth in Global Energy Use 1900-1997

Growth in global energy use 1900–1997

(Royal Commission on Environmental Pollution)

This heavy reliance on fossil fuels may have serious consequences for many nations if supply begins to dwindle, as expected. One example is that rising oil prices are usually followed by U.S. recessions(Eureka Alert!)and unemployment rates have risen following significant increases in the real price of oil.

This increased energy demand, coupled with the lack of sustainability and environmental concerns of current energy sources creates serious concerns for the energy industry, and the world as a whole.

Current UK Energy Use

In the UK, the pattern is similar. Since 1990, the energy consumption has increased from 265.1 TWh to 374.7 TWh in 2002.

graph: Fig.2 UK Rate of Energy Use 1900-1997

UK Rate of Energy Use 1965–2020

(Royal Commission on Environmental Pollution's 22nd Report)

Fuel Type Electricity Produced (TWh)
1980 1990 2000 2001 2002
Coal 190.0 208.0 114.7 125.4 118.6
Oil 33.9 21.1 5.9 4.8 4.2
Gas 1.6 1.6 145.0 138.8 148.7
Nuclear 32.3 58.7 78.3 83.0 81.1
Hydro 7.3 7.9 4.2 3.2 3.9
Other Fuels 7.3 7.9 9.3 9.2 9.8
Net Imports - 11.9 14.2 10.4 8.4
Total 265.1 309.4 371.6 374.8 374.7

Electricity Production 1980 – 2002 (DTI White Paper)

Currently the UK relies heavily on gas, coal and nuclear to produce 94% of its energy requirements. Fossil fuels are a finite resource and already the UK has to import some to meet demand. Even now, it is a fact that Norway will be a major source of gas imports over the next decade. (DTI Energy White Paper) It is estimated that by 2020, the UK will be importing energy for 75% of its primary energy needs.

One way to cope with these above issues is to implement renewable energy sources. These sources must be able to deliver substantial energy supply with minimal environmental impact. One such alternative is biomass.

What is Biomass?

Biomass is any organic matter on the Earth’s surface, which has inherent chemical energy content. Bioenergy utilises biomass (usually dead organisms and waste products) to generate energy in the form of heat, electricity or motion.

It can be thought of as a store of energy that is continuously being replenished. This energy is stored in plants and it goes through a series of processes that involve chemical and biological stages.

Why is Biomass renewable?

The capture of solar energy as fixed carbon via photosynthesis is the key initial step in utilising biomass:
CO2 + H20 + light + chlorophyll => CH2O + O2

This extremely important photochemical process as the plants can actually capture and store this solar energy. This stored energy can be then be used as a fuel source.

Burning the biomass returns the CO2 that was absorbed as the plants grew to the atmosphere and releases the energy. Biomass is commonly stated as having no net release of CO2 if the cycle of growth and harvest is sustained (called carbon neutral). This is not strictly true as it takes some energy (and therefore a discharge of CO2) to grow, harvest and/or transport the biomass for use as a fuel source. However the use of biomass fuels can result in the displacement of emissions of carbon dioxide ordinarily released using fossil fuels. This displacement will depend entirely on the efficiency with which the biomass energy can be produced and used.

The absorption and release rate of carbon is an important part of the Carbon Cycle, which is explained below:

Carbon Cycle

All living organisms (plants and animals) contain the carbon atom. Under normal conditions, carbon compounds can be solid, liquid, or gas. Carbon atoms continually move through living organisms, the oceans, the atmosphere, and the crust of the planet.

Plants absorb CO2 from the atmosphere during photosynthesis (called primary production) and release CO2 back into the atmosphere during respiration. Another major exchange of CO2 occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis. This movement is known as the carbon cycle. The paths taken by carbon atoms through this cycle are extremely complex, and may take millions of years to come full circle.

picture of carbon cycle

(Taken from Global Climate Change Website)

Existing Global Biomass Use

Biomass fuel is available throughout the world. Wood residue, the dominant fuel, is readily available where there is an active forestry industry. Biomass currently provides 14% of the world’s energy requirements.
IEA Bioenergy

In 1994, generation of biomass electricity in the EU was 11.9TWh. This is projected to increase to 27TWh in 2010 if appropriate measures are put in place. Total worldwide energy generation from biomass is currently 127TWh/year and is set to rise to 291TWh/year.

However difficulties can arise in collecting reliable and detailed biomass energy data because biomass is usually non-marketed and is used in a traditional manner. Developing nations such as Nepal use most biomass as primary fuel sources (as high as 90%), mainly for cooking and basic heating. The United Nations Environment Programme (UNEP) believes that when managed effectively, “biomass is a sustainable energy source.” (Biomass Energy: Data, Analysis and Trends (IEA Conference Proceedings 23-34th March 1998),

Currently it is mainly Sweden and Finland that use substantial amounts of forestry residues within the EU but there are opportunities for other EU countries to follow this lead. Agricultural residues are difficult to burn efficiently, but the technology is being developed, mainly in Denmark.