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Finning Power Systems has delivered a modular combined heat and power (CHP) system powered by biogas to the Southern Water Budds Farm sewage-treatment plant.

Mark Barnes, general manager for the power and energy division at Finning Power Systems, said: ‘Adopting a modular approach has several benefits.

‘All the modules are subject to a strict factory-based quality control regime and we can use more in-house engineering resources to make sure this bespoke solution meets the client’s needs.

‘A more conventional approach with most of the work done on a site can involve a lot of disruption.

‘Finding ways of minimising this makes sense for all those involved.’ Before installing the system, the site was using biogas from the digesters as fuel to run a sludge dryer.

Finning suggested that this biogas should be used as fuel to power a Caterpillar G3520C generator set to produce 2MW of electrical power.

This makes sense for Southern Water as the site can produce its own electrical power and can also sell green electricity back to the grid as renewable obligation certificates (ROCs).

The heat recovered from this system and the dryer warms up the digesters to the optimum temperature for biogas production.

Biogas is not a perfect fuel source, because the level of contaminants varies from site to site.

For Budds Farm, the main contaminants were siloxanes and hydrogen sulphide (H2S).

Finning’s system removes such contaminants so that the generator set can use the biogas as a fuel.

The solution was delivered in four modules.

The first module was a fully packaged generator set that included synchronised switchgear and the company’s LIMA control system.

This connects to and monitors the site’s HV switchgear.

The second module was a fully packaged heat-recovery system designed to capture heat from both the jacket water and exhaust of the G3520C generator.

Module three was a gas-collection and compression station that filters and also removes some of the solids and vapour from the biogas.

The fourth module was a gas clean-up skid that removes other contaminants.

It removes siloxanes, which if left would coat the engine cylinder-head with a glass hard surface that would damage the cylinder heads and valves.

The filters use a regenerative media instead of activated carbon filters.

The charges in these last up to five years and eliminate the problem of waste-carbon disposal.

Finning Power Systems has also agreed a ten-year operation and maintenance contract with Southern Water to optimise the generator’s output and heat recovery from the available fuel.

Finning (UK) Ltd

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