Sabtu, 21 April 2012
Three Motivations For Biomass Thermal Conversion
A. Renewability Benefit
Fossil fuel like coal, oil and gas are good and convenient source of energy, and they meet the energy demands of society very effectively. However, there is one major problem: Fossil fuel resources are finite and not renewable.Biomass on the other hand, grows and is renewable. A crop cut this year will grow again next year; a tree cut today may grow up within a decade. Unlike fossil fuel, then, biomass is not likely to be depleted with consumption. For this reason, its use, especially for energy production, is rising fast.
We may argue against cutting trees for energy because they serve as a CO2 sink. This is true, but a tree stops absorbing CO2 after it dies. On the other hand, if left alone in the forest it can release CO2 in a forest fire or release more harmful CH4 when it decomposes in water. The use of a tree as fuel after its life provides carbon-neutral energy as well as avoids greenhouse gas release from deadwood. The best option is new planting following cutting, as is done by some pulp industries. Fast-growing plants like switch grass and Miscanthus are being considered as fuel for new energy projects. These plants have very short growing periods that can be counted in months.
B. Enviromental Benefit
With growing evidence of global warming, the need to reduce human-made greenhouse gas emissions is being recognized. Emission of other air pollutants, such as NO2, SO2, and Hg, is no longer acceptable, as it was in the past. In elementary schools and in corporate boardrooms, the environment is a major issue, and it has been major driver for biomass thermal conversion such as pyrolysis for energy production. Biomass has a special appeal in this regard, as it makes no net contribution to carbondioxide emission to the atmosphere.
Regulations for making biomass economically viable are in the place in many countries. For example, if biomass replace fossil fuel in a plant, that plant earns credit for CO2 reduction equivalent to what the fossil fuel was emitting. This credits can be sold on the market for additional revenue in countries where such trades are in practice.
Carbon Dioxide Emissions
When burned, biomass release the CO2 it absorbed from the atmosphere in the recent past, not millions of years ago, as with fossil fuel. The net addition of CO2 to the atmosphere through biomass combustion is thus considered to be zero.
Most virgin or fresh biomass contains little to no sulfur. Biomass-derived feedstock such as municipal solid waste (MSW) or sewage sludge does contain sulfur, which requires limestone for capture of it. Interestingly, such derived feedstock also contains small amounts of calcium, which intrinsically aids sulfur capture.
A combustion system firing fossil fuel can oxidize the nitrogen in fuel and in air into NO, the acid rain precursor, or into N2O, a greenhouse gas. Both are difficult to remove. In a pyrolysis system, nitrogen appears as either N2 or NH3, which is removed relatively easily in the syngas-cleaning stage.
Nitrous oxide emission results from the oxidation of fuel nitrogen alone. Measurement in a biomass combustion system showed a very low level of N2O emission (Van Loo and Koppejan, 2008, p.295)
Dust and Other Hazardous Gases
Highly toxic pollutants like dioxin and furan, which can be released in a combustion system, are not likely to form in an oxygen-absenced pyrolyzer. Particulate in the syngas is also reduced significantly by multiple gas clean up systems.
C. Sociopolitical Benefit
The sociopolitical benefits of biomass are substantial. For one, biomass is locally grown resource. For one, biomass is a locally grown resource. For a biomass-based power plant to be economically viable, the biomass needs to come from within a certain distance from it. This means that every biomass plant can prompt the development of associated industries for biomass growing, collecting, and transporting.
Some believe that a biomass fuel plant could create up to 20 times more employment than that created by a coal-or oil-based plant (Van Loo and Koppejan, 2008, p.1). The biomass industry thus has a positive impact on the local economy.
Another very important aspect of biomass-based energy, fuel, or chemicals is that they reduce reliance on imported fossil fuels. The volatile global political landscape has shown that supply and price can change dramatically within a short time, with a sharp rise in the price of feedstock. Locally grown biomass is relatively free from such uncertainties.