How is biomass converted into electricity

Biomass power plant

What exactly is biomass?

Basically all organic substances of animal or vegetable origin that can be used to generate energy can be summarized under the term biomass. In contrast to fossil fuels, which cannot regenerate in the foreseeable future, biomass is a renewable energy source. Typical examples are plants and plant components, animal or vegetable waste, residual wood and biowaste.

Biomass and combined heat and power

The majority of energy from biomass is obtained in block-type thermal power stations (CHPs). This type of biomass power plant generates thermal and mechanical energy at the same time via a heat engine. The former can be used directly and the latter is used to generate electricity via a generator, i.e. converted into electrical energy. The principle behind this is also known as combined heat and power.

Due to the simultaneous production of electricity and heat, combined heat and power plants are characterized by a particularly high level of efficiency. This means that a large proportion of the energy used can be used as electricity or heat. There are both electricity-driven and heat-driven CHPs. The power plant is always powered when the operation is geared towards the demand for electrical power. In this case, the heat generated during the process is more of a by-product and is not always fully used.

What are the advantages of biomass power plants?

Biomass power plants can only achieve optimal efficiency if not only electricity but also waste heat can be used. The electrical efficiency of a CHP with a gas engine is, for example, between 30 and 40 percent, which in itself would be a rather inefficient way of generating energy. But now there is also the thermal efficiency, which is between 50 and 60 percent, and improves the efficiency of the system considerably. The heat can then be passed on to households or companies in the form of district or local heating via appropriate networks.

Biomass power plants also perform well when the environment is exposed to CO2. This can be explained by the CO2 credit run. Because as plants grow, they bind the same amount of CO2 that is released again when they are burned. And animal waste, from which energy is obtained, is ultimately made from vegetable matter. The combustion of the biomass itself does not affect the CO2 balance in the long term. In such calculations, however, the cultivation of the biomass, its transport and so on must also be required. If, for example, petrol-powered vehicles are used, the energy generation in the respective biomass power plant is not completely CO2-neutral.

Which substances are used to generate energy?

The range of possibilities is very wide here. Larger biomass power plants often work with biogas. This gas is obtained in the corresponding systems via the fermentation process, i.e. the fermentation of organic substances. The gas can then be used as fuel like natural gas. It is obtained, for example, from corn silage, cattle manure, organic waste, fodder beet or grass silage. It is important that the methane content is as high as possible, since it is only through the combustion of methane that energy can be released. The higher the methane content, the higher the calorific value. At 45 to 70 percent, biogas contains significantly less methane than natural gas at 80 percent, but it is CO2-neutral.

In the case of solid fuels, wood is primarily used in a wide variety of types and shapes. Wood pellets and wood chips are particularly popular with smaller systems, the so-called mini-CHPs, as there are comparatively few residues. In larger plants, waste wood, residual wood from wood processing and straw are used. Solid fuels generally have the advantage that - apart from drying - they do not require any complex processing in order to be able to be used energetically.

Which engines use biomass power plants?

Most biomass power plants (including thermal power plants) are operated with gas engines today. Gas turbines and ORC turbines are somewhat less common. Steam engine and Stirling engine are very rare. The gas engines are mostly normal Otto engines that are designed for operation with natural or biogas. Larger biomass power plants are increasingly using steam boilers, in which the combustion process produces superheated steam, which in turn is used to operate a steam turbine. The resulting mechanical energy is converted into electrical energy by a generator.

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