Biogas Energy


What is biogas energy?

This section is about the use of biogas in industry for the purpose of energy creation (heat and electricity) and/or non-transport fuel that can be released back into the grid for general public use.

Biogas is produced via a process called Anaerobic Digestion (AD), which results in the production of numerous gases that can then be burnt to produce energy. Anaerobic digestion is the breakdown of various plant and animal material (known as biomass) by bacteria in an oxygen-free environment. For example, the waste plant material is sealed in an airtight container, then bacteria is added, which is encouraged to multiply and grow, releasing methane and other gases as the by-product of the process. In addition, there are other by-products produced in the process which are rich in nutrients and can be used as fertiliser. The inputs in the process can be any number of biomass materials including any of the following: food waste, energy crops, crop residues, slurry and manure. In practice the process can take on waste from households, supermarkets and industry, therefore reducing the waste that goes to landfill.

The two major gases that make up biogas are methane (CH4), which accounts for about 60%-70% of the total and also carbon dioxide (CO2) which accounts for 30%-40%. Small traces of other gases can be found. Overall the way biogas is composed depends on the inputs or feedstock that goes into the AD process. In industry, biogas can be enhanced to filter out pure methane and removing other gases, which then becomes biomethane.

Biogas energy and industrial uses

Heat-only biogas energy

Biogas can simply be burned through the combustion process to produce heat only. When burned, one cubic metre of biogas produces around 2.0/2.5 kWh of thermal energy.  A proportion of the heat generated in the plant can be used first hand to power the digester and the nearby buildings. The remaining heat is discharged, and unless it is then heating and transferring hot water through a local pipe network into the home, it is wasted. This concept of heating water and transferring to homes as part of central heating is popular in some Scandinavian countries.

In the UK, to increase the concept of district heating, requires investment in new infrastructure. The generators that make this upfront investment can hopefully by the end of 2012, make good use of the Renewable Heat Incentive support.

Electricity-only biogas energy

Electricity can be generated from the combustion of biogas, which is a relatively simple process, but this requires an upgrade of the plant. Electricity is easier to transport and measure than heat and gas supply, but requires the infrastructure to feed into the grid, which is not simple and may be expensive. Generating green electricity can benefit the generators (households and communities) by making the use of  Feed-in Tariffs (FiTs) or for bigger players can maximise the Renewable Obligation Certificates (ROCs) for industrial scale production.

Combined heat and power (CHP) biogas energy

CHP or cogeneration is a process that simultaneously produces useable heat and electricity. The process of heat generation makes biogas plants more efficient than other conventional power plants, as the process to create the various gases requires heat, therefore less is wasted. In addition to then generating the heat, the plants also generate electricity, which is transported and sold like the excess heat. If generators can support the cogeneration process, then they are able to make good use of the RHIFiTs and ROCs available to them.

Biomethane liquid biogas energy

Biogas needs to be purified by extracting out the carbon dioxide and trace gases, therefore making a purer form of methane which then becomes biomethane. In the UK, the process of purification has to take place for it to be acceptable in the gas grid, where the gases are dried and upgraded to a higher methane content (upwards of 95%) so it then resembles the qualities of natural gas. This approach is already followed in the US, and other Western European countries. Refer to the National Grid for more information and supporting documentation that look at maximising the opportunities for biomethane into national supply. The DECC have announced that when the RHI scheme is finalised, it will not only include support payments for biogas combustion (see above), but biomethane injection too as a consumption fuel for homes and businesses.

Biomethane transport fuel biogas energy

Biogas energy, like the process for domestic heating fuel, can be cleaned further from other gases (carbon dioxide and trace gases), then upgraded to a pure form of biomethane and used as transport fuel. Biogas is eligible for support under the Renewable Transport Fuel Obligation.

The combustion of biomethane from vehicles are more environmentally friendly than that of burning of transport fuels such as modern petrol and diesel, thereby helping reduce greenhouse emissions. Examples of renewable transport fuels in vehicles that are formed out of biogas are compressed natural gas (CNG) or liquefied natural gas (LNG). In the UK, the number of vehicles that are CNG or LNG is a relatively low percentage compared to Germany and Sweden. As the number of of vehicles using CNG and LNG is lower in the UK, the infrastructure to support these vehicles, such as refuelling stations, is also therefore less developed than some of those countries mentioned.

Biogas energy policy development

Biogas energy hasn’t really taken off as a fuel alternative as of yet in the UK. This is partly due to the lack of infrastructure to support its development and secondly, more importantly, there is a lot uncertainty from the government around the RHI. Generators do not yet know what is actually going to form part of this scheme and the level of support that will be given to both fuel and combustion. Biogas energy generation is more expensive than conventional fossil fuels that enjoy benefits of scale and lower fuel price. The government needs to support these generators if they want the investment to happen and the price to come down in the long term.

Smaller scale producers currently benefit from the FiTs and larger scale producers from the ROCs (only for electricity generation – on the assumption the AD facility has been completed post 15th July 2009). If you are an accredited generator of renewable energy, you could be entitled to benefit from the Renewables Obligation, if you are not already doing so. To find out more information and how to benefit from renewable obligation, please visit OFGEM.




    Poplars Anaerobic Digestion Plant

Summary of Key Facts – Poplars Anaerobic Digestion Plant

The biggest anaerobic digestion (AD) plant in the UK is located in Cannock Chase, Staffordshire; it was completed in 2011 by the waste management company Biffa. The plant is located at the Poplars landfill site, which is being used to produce gas from the digestion of waste food.

The plant cost £24m to build and it is the first super anaerobic digestion plant in the UK and a strategically important step for Biffa to process waste management of food and exploit economies of scale. The plant is able to process 120,000 tonnes of commercial / industrial food and organic waste from nearby companies such as Sainsbury’s and Bakkavor.

Due to the plant being located near the landfill site, Biffa can use the existing waste management infrastructure to exploit efficiencies, such as a ready supply of suitable feedstock to allow them to produce large volumes of gas, which can be combusted to produce electricity. The total operating capacity of the plant is 6MW, which is equivalent to supplying 10,000 homes with power.

In terms of the process, waste is pumped into one of the five digester tanks, which is then heated to 70oc, allowing the AD process to work and produce the methane gas. The plant uses CHP boilers which produce both heat and electricity. About 15% of the electricity is used by the plant, but the rest is sold back to the Grid. The heat generated on the other hand is reused in the plant.

Environmental Impact Assessment of the Poplars Anaerobic Digestion Plant

This project aligns to the Government’s strategy of recycling waste to be used to produce renewable energy. One of the by-products of the digestion process is high quality soil, which can then be sold onto farms and local gardening centres in the West Midlands.

In addition, the Poplars AD plant further demonstrates its environmental credentials by helping the local community manage waste by: recycling food waste from supermarkets; digesting food and drink from manufacturers; taking waste from hotels, restaurants, caterers and homes, which is then delivered to the site from Biffa’s collection network.

Business Partners building Poplars Anaerobic Digestion Plant

Biffa had two major business partners during the building phase to complete the project by spring 2011, these were the civil engineering company GTM and anaerobic digestion technology company Ros Roca Envirotec.

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