Davyhulme WwTW is United Utilities’ largest sewage and sludge treatment facility. Currently, circa 2000Nm3/h of biogas produced by the digesters is used in Combined Heat and Power engines to generate renewable electricity and provide heat for the sludge digesters.
To reduce the reliance on fossil fuels such as diesel and natural gas, to find other innovative uses for biogas and to decrease carbon emissions, a project is currently being developed to treat about 230Nm3/h of this biogas. After consideration of various technologies, pressure swing adsorption is the preferred technology to upgrade the methane content from circa 65% methane to greater than 96% methane in the fuel (biomethane) along with ancillary processes to remove other minor impurities such as siloxanes. The biomethane produced will meet the relevant quality standards suitable for two uses. Firstly, the biomethane will be used to replace diesel in some of United Utilities sludge tankers which will operate in dual-fuel mode. Secondly, working with National Grid Gas, some of the biomethane may be injected into the natural gas network for domestic use.
The project development has considered the relevant biomethane quantity and quality requirements, the biogas quality and the treatment of the off-gas. All these factors are crucial to the design and operation of a biogas to fuel plant.
The project is part funded by the Anaerobic Digestion Demonstration Programme as an industry wide demonstration plant. This programme is managed by Defra and forms part of Department of Energy and Climate Change’s National Environmental Transformation Fund. It is being delivered by The Waste and Resources Action Programme (WRAP).
Keywords: Biogas, biomethane, pressure swing absorption.
Davyhulme WwTW is United Utilities’ largest sewage and sludge treatment facility with a population equivalent of 1.6M, serving the city of Manchester. Currently, about 39000tdspa of sludge is digested at the works. This produces about 2000Nm3/h of biogas which is used in Combined Heat and Power (CHP) engines to generate renewable electricity and provide heat for the sludge digesters.
In 2013, a major project will be commissioned at Davyhulme WwTW with the treatment of additional sludges and the installation of a thermal hydrolysis plant; this will increase the biogas production to about 4200Nm3/h. This project, Sludge Balanced Asset Programme (SBAP) is discussed further by Jolly (2010).
The SBAP project is being built for United Utilities by Black & Veatch, who have also been assisting with the design of the biogas to fuel plant.