Biomass – An Emerging Fuel for Power Generation.
The European market for biomass-fired power and heating is more developed than that of the United States, mainly due to stringent European regulatory requirements and broad public support for renewable initiatives. Denmark, for example, enacted legislation as early as 1993 requiring increased use of biomass in energy supply. At present, the 27 nations of the European Union (EU) have agreed to raise the share of renewables in the energy mix to 21 percent for electricity and 20 percent for heat by 2020. In 2005, two-thirds of all EU renewable energy came from biomass, which is expected to retain a significant share of EU renewables going forward.
As a result of these regulatory requirements, growing public awareness and the Kyoto protocol, the market for biomass in Europe is strong and growing. According to the European Biomass Association, the EU will increase its biomass consumption from 13 million tons annually today to 100 million tons by 2020.
it is impossible to know how close it will come to the realities of 2020. Nonetheless, the analysis makes three issues clear. First, if these forecasted levels are going to be approached much less achieved, a variety of wood and agricultural biomass sources will be required to meet anticipated demand. Second, a supply of purpose-grown biomass sources will be needed as residuals alone will not be sufficient. And third, competition for biomass resources could become fierce. Add in local or geographic implications and the supply equation for any individual utility could become very interesting.
Type of Biomass
Biomass fuel can come in many flavors. The right choice for a particular power plant will depend on biomass availability and cost and fit with boiler and environmental requirements. Wood-based and agriculturally-based biomass are potential fuel sources. However, major regional differences exist in the local availability of potential biomass resources.
Biomass can be purpose-grown as fuel or it can be the byproduct of, or residual from, another process. The advantage of purpose-grown biomass is the stability of supply of biomass fiber and increased efficiency in harvesting the biomass. The main disadvantage of purpose-grown biomass is that it can compete with other uses for the land or the product. For example, using some types of roundwood as a fuel source would take that supply “out of circulation” for the lumber and pulp/paper industries. Using residual biomass is typically less expensive and competes less directly with the primary use for that biomass. This is especially important for agricultural products. However residual biomass, such as corn stover and tree branches, is not always harvested with the primary material, making collection difficult.
Biomass fuel can also be “raw” or pelletized. The process of pelletizing the fuel typically increases the Btu content by removing moisture from the biomass. It also standardizes the fuel’s size and shape. However, pelletizing the biomass is typically energy intensive and requires the capital cost of the pellet plant as well as drying and pelletizing equipment.
New technologies could potentially shift the economics of biomass sourcing. One example is torrefaction, a process by which biomass is heated in a low-oxygen environment at 250 C to 320 C before pelletizing. The economics of this process have yet to be proven in large-scale operations, but supporters point to attractive qualities of the torrefaction process: higher energy content (around 11,000 Btu/lb.), lower moisture content and increased stability in storage (indoor storage may not be required).
Many types of biomass, such as traditional wood pellets, will require inside storage. A 100 MW plant could burn an estimated 400,000 tons of biomass pellets annually. If three months’ supply was required, or 100,000 tons, a storage warehouse 180 feet wide by 1,200 feet long could be required. Alternatively, 10 10,000-ton silos could be used. If a generating station had units burning both biomass and coal, storage space and infrastructure for each fuel would be required. Other handling equipment, such as conveyors and stacker/reclaimers, may have to be modified or replaced altogether with equipment better suited to the type of biomass fuel selected.
Storage and handling infrastructure also must take into account biomass’s high combustibility. This is true for both pelletized and raw biomass. Wood pellets are not as durable as coal and produce more combustible dust. Dust control systems, temperature sensors and fire suppression systems may be required to support safe operations. In storage and handling design, the distances that pellets are dropped either into storage or through the conveying process should be managed to limit pellet damage and dust creation.
Source: Renewable energy World website