Biomass Electricity Generation
Biomass is a term that describes organic material including plants and algae, among many others. Because there are a great variety of approaches to generating electricity from biomass, it can be a complex topic. Some of the most common techniques are described below.
Burning biomass (commonly with coal, but also alone) to produce heat that boils water into steam (for use in turbines) is fairly common and utilizes well-known technologies. The fuels that can be used for this process are numerous and all affect the overall economics and environmental impact of the project.
Biomass can also be gasified, which is a chemical process similar to combustion, with the end result of carbon monoxide, carbon dioxide, and hydrogen gases being produced along with the release of heat (to generate steam). The gases formed can then be combusted to generate steam to power a turbine.
Biomass can also be digested in a special chamber by microorganisms which results in the production of methane gas and CO2 (Figure 1). Methane can be combusted to produce steam to turn a turbine. Biomass electricity facilities are tied to the fuel they will use (often sourced from close by to save on costs of transportation), but can be built to any desired size. 300 MW for a combustion or gasification facility is common, while anaerobic digesters are often less than 50MW.
Figure 1. Laforge Holsteins Anearobic bio-digestor in St. Andre, NB. The facility uses waste food materials from McCains as well as manure and other biomass materials.
- Upfront Costs – The wide range of technologies and fuels mean that prices vary, with between $1,000,000 and $6,000,000 per MW being common.
- Fuel costs – Varies widely, biomass fuels can often be waste materials from other industries like wood chips, sugar cane stalks, waste food materials, and even manure. With this said, fuels cost between $1 - $6 per GJ of raw energy.
- Flexibility on the grid – Most current biomass facilities use combustion and steam systems to generate power and are comparable to coal plants in how quickly they can have their output increased or decreased (which is to say, slowly in both cases). They can be turned on and off at will, however, and have some ability to meet fluctuations in demand.
- Environmental impact – There are CO2 emissions associated with biomass, but because the material removed carbon from the air in its growth phase, the process is theoretically carbon neutral (what was taken from the air during growth is released when burned). In actuality, transportation of fuels, processing and inefficiencies can all lead to overall emissions of around 30 g CO2 per kWh.