Black & Veatch integrated a complex new asset into a major United Utilities facility at Davyhulme UK, to maximize the production of renewable energy using carbon-neutral biogas from the wastewater sludge treatment process.

As a result of the project, Davyhulme is able to generate 60 gigawatt hours of energy per year - equivalent to the needs of 25,000 homes. 

Black & Veatch was appointed main contractor for the design and construction of the sludge treatment process improvements. This required an understanding of the complex set of variables associated with steam, biogas and electrical energy production.

As part of the scheme, biogas produced by the new process is drawn off from the existing digesters. The gas passes through new and existing clean-up systems, and is stored in new gas holders prior to use in combined heat and power (CHP) engines. This renewable, carbon-neutral energy source produces electricity to use on site or export to the power grid.

The biogas is fed to five 2.4 megawatt Jenbacher CHP engines. Two of these engines were new, the others were relocated existing units. Relocation took place in a phased manner to ensure Davyhulme’s existing energy production was not affected. Using biogas to fuel the CHP engines allowed United Utilities to receive Renewable Obligation Certificates for the electricity generated.

The improvement in biogas production increases the amount of renewable electricity generated at the site, enabling the entire works to be self-sufficient. This significantly reduces plant operating costs and ultimately benefits the utility’s customers.

Enhancements to the gas processing facilities also ensure that the biogas is pure enough to be injected into the gas grid.

Hot exhaust gasses from the CHP engines are used to generate 12-bar steam in one of three steam boilers for use in the sludge process. To ensure the steam generation plant produced sufficient steam to meet various operating cycles Black & Veatch developed a dynamic steam model to optimise efficiency.