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Biogas Production. Organic material is collected from farms and factories and mixed with waste water to form an organically rich sludge (pictured right). Organic material used for energy production is referred as biomass and can include crops specifically grown for energy production as well as organic waste. Biomass derived energy is becoming increasingly important and in the USA biomass derived electricity is predicted to become second only to hydroelectricity in the league table of electricity from renewable resources.

Biogas Production from Farm Waste

Biogas Production. Excess water is removed from the sludge in order to concentrate the biomass. The concentrated sludge is then heated and piped into enzymic hydrolysis tanks (pictured below) where biochemical breakdown of the biomass content of the sludge begins. The hydrolysed sludge is then passed through blast coolers (pictured right) because the post-hydrolysis temperature would be too high for the bacteria in the next phase. In cold weather the blast coolers might not be used because if the outside temperature is low enough the sludge will cool naturally.

Biogas Production - Sludge Hydrolysis

Biogas Production. The biogas (comprised mainly of methane) produced by the bacteria is extracted from the gas dome at the top of the digesters (the extraction pipe is pictured below on the outside of the digester tank)  and either sent directly to on-site electricity generators or stored in Gas Holders for future use ( a gas holder is pictured right).

Biogas Production - Extraction of the Bio-Gas from a Sludge Digester


Biogas Preoduction. Heat Exchanger.

Biogas Production. The heated biogas is used as fuel for the massive V8 engines of the Combined Heat and Power units (CHPs), examples of which are pictured below. The V8 engines in turn drive the generators that produce the electricity.

It's worthy of note that recent research by the European Environment Agency (EEA) has concluded the use of biomass to replace coal in electricity and heat production gives far greater reductions in Green House Gas (GHG) emissions at a far lower cost than producing and using biomass to replace diesel fuel in transport.

Biogas Production - Sludge Aeration

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Biogas Production - Post Hydrolysis Sludge Cooling

Biogas Production. In the next phase the hydrolysed sludge from the hydrolysis tanks is fed into the belly of large digester tanks (as pictured below) where bacteria digest the biomass content of the sludge producing biogas as a by-product.The process is known as anaerobic digestion because air or more specifically oxygen is not required.

The anaerobic bacteria employed to digest the biomass are principally Escherichia coli, (better known as E.coli) of a type (strain) found in the human gut. The precise strain however and the operating temperatures of the digesters are closely guarded commercial secrets! The temperature inside the digesters is monitored from a Control Room (pictured bottom left) and regulated by heat exchange pipes that run inside the digesters.

Biogas Production - Sludge Entry to Digester


Biogas Production - Biogas storage in a Gas Holder.

Biogas Production. Raw biogas cannot be sent to the gas grid because it contains many impurities so biogas is mainly used to generate electricity on the site where the biogas is produced. The resultant electricity can of course be exported to the electricity grid and makes a significant contribution to government targets.for renewable energy.
The biogas is firstly heated by passing it through heat exchangers (pictured left) where heat is provided by waste heat from the units that produce electricity. Because those units produce heat as well as electricity they are known as Combined Heat and Power units (CHPs).

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Biogas Production - biogas is used to power CHPs to produce electricity.

Biogas Production. Every stage of biogas and electricity production is monitored and controlled 24/7 from a Control Room (pictured below). Electricity produced by the CHPs is sent to a sub-station where the voltage is increased. From the sub-station the electricity is sent via underground cables to a high voltage pylon at the end of a branch of the electricity grid (pictured right).

In a fraction of a second that electricity finds its way via the grid to sub-stations all over the country where the voltage is decreased before the electricity is finally distributed to homes such as yours. In that way biogas may have helped to boil the water that made your coffee (or tea) this morning!

Biogas Production - every stage is monitored 24/7 from the Control Room
Biogas Production, Combined Heat and Power Units
Biogas Production. Electricity Exported to the National Grid

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