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Biomass
Up to the time of the industrial revolution the world’s energy supply was dominated by biomass such as wood fuels and crops grown as fuel for horses, oxen, etc. Since 1840, the start of the industrial revolution, fossil fuel usage has increased to the current level of approximately 9 billion tonnes of oil equivalents being used across the world annually. Biomass however, is still used as fuel for 14% of the world’s total energy demand.
Due to the modern reliance on fossil fuels, atmospheric concentrations of carbon dioxide (CO2) and other “greenhouse” gases have increased by 31% since the mid-nineteenth century leading to increased global warming the effects of which are now becoming all too apparent. During the last century the average temperature in England rose by 0.5°c and four of England’s warmest years since the 1770s were in the 1990s whilst eight of the hottest 10 years globally were also in the 1990s. Current climate models suggest that global temperatures may continue to rise by a further 1.4°c to 5.8°c by the end of this century. If climate change is not controlled the earth’s temperature will rise more rapidly this century than in the previous 10,000 years.
As part of the UK’s commitment to combating climate change the Government is aiming to reduce greenhouse gases by 12.5% and CO2 by 20% compared to 1990 levels by the year 2010. To do this the UK’s use of renewable energy, currently only 3% of capacity, should increase to 10% i.e. 4000MWe. Long-term aspirations are for a 60% CO2 reduction by 2050 with 40% of our energy coming from renewable sources. Biomass energy is expected to provide a significant proportion of this, not only contributing to power generation but also to the generation of heat.
Biomass fuel is derived from any organic material e.g. wood, crops and animal wastes that can be used in either raw or processed form. For example:
- Fast growing shrubs, trees and grasses like willow, poplar and Miscanthus i.e. energy crops
- Agricultural residues such as cereal straw, chicken litter and slurries
- Wood “waste” such as forest residues, tree prunings and sawdust plus untreated wood products
- Municipal solid waste
Biomass fuels from plants are carbon neutral over their life cycle as the CO2 released during energy generation is no greater than that absorbed by the plants during their growth. However, the use of machinery to produce, process and transport biomass fuels must also be taken into account. The energy ratios (the units of energy used in production compared to the units of energy generated) for a number of crops are:
- Willow SRC 1:30
- Miscanthus 1:32.5
- Poplar (single stem) 1:37
- Wheat 1:8.8
- OSR 1:3.8
- Coal 3:1 (Three primary units of energy are used to deliver one unit of electricity)
The energy content of biomass is related to its moisture content; high moisture content will slow the combustion process as the moisture must first boil off before the fuel can burn. The calorific values of various fuels are:
- SRC at 20% moisture content 15Gj/t
- SRC oven dry 18.6Gj/t
- Miscanthus at 20% moisture content 14Gj/t
- Miscanthus oven dry 16.2Gj/t
- Straw oven dry 15Gj/t
- Poultry litter 8.8Gj/t
- Municipal solid waste 9.5Gj/t
- Coal 23-31Gj/t
Biomass is not as concentrated an energy source as most fossil fuels even when it is thoroughly dry. Its density may be increased by milling and compressing the dried residues with the resultant pellets being easier to handle, store and transport but the increased processing and pellet production will inevitably reduce the energy ratio of the final fuel product.
Biomass energy in general has many unique qualities that provide a number of sustainable and environmental benefits provided it's produced, transported and converted into energy efficiently to minimise emissions. It can obviously help mitigate climate change but other advantages include:
- Strategic security in that it provides a greater reliance on domestic resources giving added control to national energy security.
- The fuels are sustainable and can be used to generate energy on demand unlike intermittant solar or wind power.
- It is a clean form of energy compared to fossil fuels: when burnt, fuel from forestry and energy crops results in little or no net emission of CO2.
- It can help to reduce acid rain as virgin, wood-based fuels such as SRC have little or no sulphur content and sulphur dioxide in emissions from fossil fuels contributes to the problem of acid rain.
- It reduces pressure on landfill sites by utilising “waste” materials as fuel.
- It helps maintain woodlands through improved management.
- Rural jobs will be created or maintained through the cultivation and processing of energy crops, the management of woodlands and also through fuel supply to and maintenance of the boilers or power plants.
- Modern biomass technology is clean, efficient, fully automated and exempt from the Climate Change Levy and there are systems available for a wide range of situations including:
o Heating single properties e.g. 15kWth needing approximately 5odt fuel per year
o Heating schools e.g. 350kWth needing approximately 100odt fuel per year
o Combined heat and power (CHP) for a housing development or industrial estate e.g. 1MWe needing up to 8,500odt fuel per year
o Dedicated or purpose built biomass power plants generating up to 40MWe
With all of these opportunities, the UK biomass industry is well positioned for expansion. Please contact CRL if you would like further information on biomass in general or energy crops in particular.
MWe = 1000kW of electrical power
kWth = 1000 watts of thermal power i.e. heat
odt = oven dry tonnes i.e. the dry weight of the fuel
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