Finham Sewage Treatment Works Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications | 0.2 July 2020 Severn Trent Water EPR/YP3995CD/V006 Thermal Hy drolysis Process Pla nt a nd Biogas Up gra de Plan t Va ria tion Ap plica tions Sever n Tr ent Wa ter Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications Finham Sewage Treatment Works Project No: Project Number Document Title: Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications Document No.: Revision: 0.2 Document Status: <DocSuitability> Date: July 2020 Client Name: Severn Trent Water Client No: EPR/YP3995CD/V006 Project Manager: Mark McAree Author: James Killick File Name: Document2 Jacobs U.K. Limited Jacobs House Shrewsbury Business Park Shrewsbury Shropshire SY2 6LG United Kingdom T +44 (0)1743 284 800 F +44 (0)1743 245 558 www.jacobs.com © Copyright 2019 Jacobs U.K. Limited. 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Document history and status Revision Date Description Author Checked Reviewed Approved i Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications Contents Non-Technical Summary................................................................................................................................................... iii 1.1 Description of New Site Activities ..................................................................................................................................... 1 2. Application Forms – separately sent ................................................................................................................. 6 3. Form C2 Responses ............................................................................................................................................... 7 4. Form C3 Responses ............................................................................................................................................ 17 Appendix A. Current CMS Certificate Appendix B. Air Dispersion Model Appendix C. BAT Assessment ii Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications Non-Technical Summary This is a substantial variation to the existing Severn Trent Water Limited environmental permit for the Finham Sewage Treatment Works, near Coventry, as a result of an upgrade to the works. The Finham Sewage Treatment Works currently treats sewage sludge by anaerobic digestion to produce a stabilised sludge product and biogas. The sludge product is taken off site for land spreading in agriculture or to alternative outlets. The biogas is currently used in the CHP engines on site to generate electricity and heat for the site to use. The purpose of the variation is three-fold; Firstly, for the installation a Thermal Hydrolysis Process Plant, which is a new directly associated activity (DAA), and includes the addition of: ▪ A sludge cake import facility; ▪ Pressure sludge screens for indigenous primary sludge; ▪ A thermal hydrolysis process (THP) plant to pre-treat the sludge prior to digestion; ▪ Sludge dewatering buffer tanks, dewatering centrifuges and THP feed silos for the THP plant; ▪ An ultraviolet (UV) treatment plant for final effluent for use with the THP plant; ▪ A polymer plant serving the dewatering centrifuges and a potable water booster pump station serving the polymer plant and other THP users; ▪ An odour control plant to abate the odour from the cake bin at the sludge import facility, the sludge dewatering buffer tanks and the THP feed silos; ▪ Relocation of two 2.5 MWth Jenbacher engines to combust natural gas (with biogas option) to produce electricity and heat for the use within the site/processes; ▪ Two 4.1 MWth composite boilers in a boiler house to supply steam to the THP plant; ▪ A multi-flue stack; ▪ Lightening protection masts. Due to the new boilers and CHP relocation, an air model has been prepared for this DAA. The second aspect is to add a new DAA to the permit, comprising a biogas upgrade plant. This plant is designed to take biogas produced within the anaerobic digestion processes at the site and make it suitable for injection into the National Gas Grid. The system includes a new biogas holder. As part of the safety system for the new upgrade plant and associated biogas holder, a new emergency flare will be installed as part of the process. There is the addition of two new emission points to air associated with this proposal. Although there are new air emission points for the biogas upgrade plant, there is no increase in gaseous emissions to air requiring air modelling. An H1 model for the minor releases associated with the biogas upgrade plant has been provided. The third variation is the addition of a specified generator, as defined in Schedule 25A of the Environmental Permitting Regulations. This consist of a single, 1.1 MWth diesel powered generator used for STOR located at the site. The operation of this generator is independent of the sewage related activities at the site. Emissions to air from new and existing CHP engines, boilers and diesel generator at the site have been subject to computer modelling using ADMS (version 5.2.2). The results of the detailed dispersion modelling indicate that the existing CHP engines, boilers and diesel generator with the additional CHP engine and boilers are unlikely to result in any unacceptable impacts on air quality at sensitive human receptors or at protected conservation areas included in the assessment. The operation of the new THP and biogas upgrade plant are considered new directly associated activities of the permitted activities at the site. Existing directly associated activity relating to the provision of power and heat at the site is amended with the decommissioning of the two existing Jenbacher CHP engines (leading to the removal of emission points A1 and A2), their associated stacks and the existing biogas flare (removal of emission iii Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications point A6). These CHP engines are to be refurbished, relocated, converted to run on biogas or natural gas and be integrated into the THP scheme; the existing biogas flare will become redundant. As a result of these changes, four new emission points are to be added; one emission point associated with the THP plant – A7a, A7b, A7c and A7d; one new emission point for the diesel generator – A8; and two new air emission points on the biogas upgrade plant – A9 and A10. The operation of the generator will be the addition of a new specified generator to the existing permit. There are no proposed changes to the listed activities of the site. The introduction of the THP plant will lead to an increase in the quantity of biogas produced, the production of an enhanced sludge product, that has the advantage of being able to be land spread all year round, and achievement of a lower odour emission. The relocation and re-use of the CHP engines and the decommissioning of the flare will deliver an improvement in energy efficiency, a reduction in the emissions of combustion products to atmosphere and an associated reduction in the ground level concentrations of pollutants in the vicinity of the installation. iv Thermal Hydrolysis Process Plant and Biogas Upgrade Plant Variation Applications 1. Technical Description This is a substantial variation to the existing Severn Trent Water Limited environmental permit for the Finham Sewage Treatment Works. The purpose of the variation is to add two new directly associated activities to the permit, comprising a thermal hydrolysis plant, associated combustion/thermal plant and biogas upgrade plant. In addition, there is the addition of a new specified generator at the site, used in the capacity market. This is a new unit under the regulations due to a change in STOR contract. The thermal hydrolysis process plant (THP) is used for the pre-treatment of indigenous and imported sewage sludge prior to digestion within the site’s existing anaerobic digesters. Under the current permit numbering scheme this will be DAA AR14. Associated with the thermal needs of the THP will be two relocated CHP and two new boilers, operating four individual flues via one stack emission point. Two existing CHP engines on site will be decommissioned, refurbished and relocated from their current location, to meet the thermal demands for the THP and to provide electricity on the site. The CHP engines will combust natural gas with a biogas option. The biogas upgrade plant is used to upgrade the biogas produced within the onsite anaerobic digesters and make this biogas suitable for injection into the National Gas Grid. Under the current permit numbering scheme this will be DAA AR15 1.1 Description of New Site Activities Thermal Hydrolysis Process Plant The Thermal Hydrolysis Process Plant utilises the application of heat and pressure to pre-treat sewage sludge prior to anaerobic digestion. Through pre-treating the incoming sludge, the biogas yield will be increased and dewatering