As we have been discussing CHP and Biomass Power Stations recently, I though that it might be interesting to explore this subject in more detail. I live in East Anglia in England, a largely agricultural area that is leading the way in Biomass electricity production, so this is a matter of local interest for me. Lets start with the definitions:

Biomass is plant (and animal) material that can be used in a combustion chamber to create heat, produce steam and drive turbines. For example, wood chippings, straw, animal dung and other plant material. This is called renewable as the plant material can be grown again absorbing the CO2 released by the combustion process. In some cases trees are planted and grown specifically to produce fuel for the plant thereby (it is argued) removing CO2 ahead of the combustion release.

Biomass can be greener than fossil fuel but there are many socioeconomic issues such as upward pressure on food prices caused by diverting agriculture towards growing fuel crops that make this a less attractive and more problematic option. 

Combined Heat and Power (CHP) is a technique used to improve the abysmal inefficiencies of steam driven power plants (roughly 70% of the input energy is dumped as heat). CHP simultaneously delivers electricity and hot water delivering much better efficiencies (provided the hot water can be used). CHP can offer efficiencies against input energy of 60%, double that of conventional power plants. The hot water from the plant can be used to drive domestic heating, absorption chillers for data centers or agriculture.

Important Note: CHP only works out green if a valuable use can be found for the hot water.

Lets get back to biomass. In the case of straw and other waste material, the alternative is composting, where much of the CO2 is locked up in the bodies of the organisms that decompose the waste, although some is released into the atmosphere in the process.

The world’s biggest straw-fired power station, at the Elean Plant in Sutton near the cathedral city of Ely, East Anglia, started work in autumn 2000. This plant is the world’s first power station burning poultry litter and other agricultural wastes has recently been joined by another plant near Thetford, also in East Anglia.

On a visit to the Sutton station, the United Kingdom’s then Minister of Agriculture Nick Brown said

“This is a very impressive project. The government is committed to promoting cleaner and more sustainable ways to meet our energy needs. Help for the energy crops sector is a key part of the England Rural Development Programme and 30 million pounds sterling will be spent on this over the next seven years.”

One expert estimate is that by 2050 the world will be burning greater quantities of renewable rather than fossil fuels. To make this possible the pioneering power stations have had first to crack the technological and environmental problems involved in burning fuels such as straw left in fields after cereals have been harvested and the mixture of wood shavings, straw and poultry manure from broiler poultry farms, in other words, biomass.

For example, straw is naturally rich in the hard reinforcing substance, silica. The removal of silica from the furnace where straw is burned caused problems in earlier straw-fired power stations. But in a new design used in the Elean plant at Sutton, the silica is made use of, by allowing it to accumulate on the walls of the tubes where the steam that drives the turbine is superheated.

But if power stations burning alternative fuels are to be really widely built, then they will have also to demonstrate that they can provide power as cheaply as or more cheaply than stations powered by fossil fuel. This they have yet to manage; biomass-powered stations in the UK, as in other countries, require subsidy from the government.

Rupert Fraser, deputy chairman of Fibrowatt, the UK company that built the world’s first poultry-litter powered stations at Eye and Thetford, points out that many experts believe that the money being spent in this way by the UK and other governments should be regarded not as subsidy but as “investment for the future”.

Mr Fraser said:

“Only if the cost of power from renewable fuels is competitive with that of power from fossil fuels will renewable fuels become widely used, especially in the developing world. And experience shows that the only way to bring costs down to that point will be to build enough power stations to solve all the problems of any new technology, and to gain the substantial cost reductions associated with large-scale manufacture.”

Steps towards this end are well under way. Fibrowatt has projects under development in the United States and the Netherlands and plans to develop further projects in the US, Spain, Italy, France, Belgium and Japan.

Energy Power Resources, the UK-based company responsible for the Elean power station, intends to develop more such plants, at Corby in the English Midlands, and elsewhere. 

These power stations will be designed to burn a mixture of biomass fuels, including woodchips and purpose-grown energy crops such as Miscanthus, as well as poultry litter, straw and other agricultural waste.

In this way they will contribute largely to the industrial experience and infrastructure needed if renewable fuels are to play the part in power provision that economists and environmentalists agree in hoping they will, in the not-too-distant future.