Water removal technology increases biogas CHP performance

Louise Smyth

New water removal technology increases biogas CHP performance

The UK’s anaerobic digestion (AD) industry has continued to grow in the face of challenging market conditions, with almost 600 AD plants now in operation. Although biomethane facilities are increasing in popularity, the vast majority of the UK’s AD sites are electricity combined heat and power (CHP) plants.

With subsidies for renewable electricity generation dwindling, it is more crucial than ever that each part of the AD process is optimised if a plant is to be commercially successful.
An often-overlooked area is ensuring that any water present in the raw biogas is removed; if water enters a CHP engine it can decrease its efficiency, resulting in reduced biogas yields and engine damage. The new biogas dehumidification system (BDS) from HRS Heat Exchangers removes water from biogas, protecting CHP engines from corrosion and cavitation. It also comes with a heat recovery section as standard, increasing
an AD plant’s overall energy efficiency.

Increased profits

The importance of optimising an AD plant cannot be underestimated. Although many of today’s operators invest time and money in performance-enhancing additives and systems, removing water present in the raw biogas can be a lower priority. But with CHP engines being one of the most expensive pieces of equipment to replace on an AD plant, this is a false economy. Additionally, an inefficient CHP engine will result in lower electrical output and higher capex, and therefore reduced profits – a 1MW digester operating at even 80% capacity could be losing as much as £16,000 each month.
“The BDS reduces biogas temperatures from around 40°C to approximately 5-7°C, condensing more than 90% of the water volume,” explains Matt Hale from HRS. “It works via a chiller system that supplies a coolant that is transferred to heat exchangers. Biogas flows on the product side of the exchanger, while the coolant flows on the service side. As the biogas cools, the water condenses from the gas, leaving a clean and dry biogas ideal for use in CHP engines.”

Energy efficiency

Heat recovery comes as standard. The resulting cold biogas is used to pre-cool any incoming biogas, reducing the load on the final cooling heat exchanger and recovering as much as 20% of the energy needed for the process. Any extra investment required is soon recouped in energy cost savings.

Suitable for AD plants of all sizes, the BDS comes skid-mounted for easy access and freedom of movement, and features an automatic control panel for full process control. It can also be adapted for ATEX-compliant applications.

Future-proofing AD plants

“Following a series of enquiries for a system to dehumidify biogas, we are delighted to launch the BDS,” says Hale. “With a CHP engine being one of the most expensive pieces of equipment on an AD plant, protecting it makes good business sense. By removing water from biogas before it enters a CHP engine, the BDS helps to extend an engine’s lifespan, protecting it against corrosion and cavitation. We are expecting a high demand from existing AD operators looking to optimise their process even further and prolong the lifespan of their CHP engine.”

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