Biomass to bioenergy
Biomass refers to renewable energy coming from biological material such as trees, plants, manure, and sometimes waste. Using various transformation processes such as combustion, gasification, pyrolysis the biomass is either transformed into biofuels, bioheat or bioelectricity and used for energetic purposes.
In the Renewable energy directive (2009/28/EC) biomass is defined as follows: "Biomass means the biodegradable fraction of products, wastes and residues from biological origin from agriculture (including vegetable and animal substances), forestry and related industries including fisheries and aquaculture, as well as the biodegradable fraction of industrial and municipal waste".
Biomass is the fourth largest energy source in the world after coal, oil and natural gas – and is the largest and most important renewable energy option at present and can be used to produce different forms of energy, thus providing all the energy services required by the society.
Wood is the oldest form of biomass known to mankind. For centuries wood was used for heating, cooking and industrial purposes. In the developing world wood is still used for the same reasons. In the 18th and 19th centuries, wood was gradually replaced by cheap fossil fuels (coal, oil and gas) which were easy to handle and had higher energy density. Nowadays there is a growing interest in bioenergy which can be used in an efficient way using modern technologies for the production of heat, electricity and transportation fuels. Biomass, used in a sustainable manner, is a regenerative source of energy.
Biomass originates from forest, agricultural and waste streams.
- Forest and wood-based industries produce wood which is the largest ressource of solid biomass. Biomass procurement logistics from forest to bioenergy plants are subject to major improvements. The sector covers a wide range of different biofuels with different characteristics – wood logs, bark, wood chips, sawdust and more recently pellets. Pellets, due to their high energy density and standardised characteristics, offer great opportunities for developing the bioenergy market worldwide.
- Agriculture can provide dedicated energy crops as well as by-products in the form of animal manure and straw. Available land can be used for growing conventional crops such as rape, wheat, maize etc. for energy purposes or for cultivating new types of crops such as poplar, willow, miscanthus and others.
- Biodegradable waste is the biomass that can cover several forms of waste such as organic fraction of municipal solid waste, wood waste, refuse-derived fuels, sewage sludge, etc.
Each biomass resource has different characteristics in terms of calorific value, moisture and ash content, etc. that requires appropriate conversion technologies for bioenergy production. These conversion routes use chemical, thermal and/or biological processes. Finally biomass/bioenergy can be classified according to its end use as follows:
Biomass for heat production
Heat production: Combustion of solid biomass of wood for heat production is the main bioenergy route in the world, with a constant drive for improved efficiency and reduced pollutant emissions. Several systems can be considered, depending on the size. Small-scale heating systems for households typically use firewood or pellets. Medium-scale users typically burn wood chips in grate boilers while large-scale boilers are able to burn a larger variety of fuels, including wood waste and refuse-derived fuel. Heat can also be produced on a medium or large scale through cogeneration which provides heat for industrial processes in the form of steam and can supply district heat networks.
Biomass for electricity production
Electricity: Combustion followed by a water vapor cycle is the main technology for the time being but new technologies are emerging such as ORC-plants. Co-combustion of biomass and coal is also under implementation by electric utilities. Biogas from anaerobic digestion is mainly used on site for cogeneration applications. The solid and liquid residues from the process are often used as fertilisers on farm land.
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Croatian Center of Renewable Energy Sources (CCRES)