Fueling Combined Heat and Power: EPA and WERF Initiatives and Case Studies

The United States Environmental Protection Agency (EPA) and the Water Environment Research Foundation (WERF) recognize the value and importance of implementing combined heat and power (CHP) at wastewater treatment facilities (WWTFs). To promote the benefits of CHP and encourage its implementation, the EPA commissioned the development of a CHP guidance document. The EPA-funded document provides guidance to WWTF staff and consulting engineers on the best technologies to maximize the use of digester gas to produce electrical energy and capture waste heat for beneficial use. The document considers a variety of factors to aid utilities in selecting the most appropriate CHP technology for their WWTF, including plant size, emissions requirements, heat uses, gas treatment requirements, and cost.Also in an effort to encourage more widespread implementation of CHP at WWTFs, WERF commissioned the development the Combined Heat and Power System Evaluation Tool (CHPSET). The CHP-SET is a spreadsheet-based calculator designed for evaluating CHP system performance and is intended for use by utilities already operating CHP systems. The CHP-SET calculates total system efficiencies (inclusive of appurtenant equipment electrical demands) for the production of electricity and collection of heat. The tool also provides a conversion of exhaust emissions (NOx, CH4, CO2, CO, and N2O) into units of mass per unit of net energy output.The CHP-SET was used to evaluate and document the performance of several existing CHP systems ranging in plant size from 41,600 to 1.14 million m3/d (11 to 300 mgd) of capacity. Detailed case studies based on CHP system evaluations using the CHP-SET are included in the EPA document.This paper provides an overview of the EPA and WERF projects, but focuses primarily on the case studies developed using WERF's CHP-SET and subsequently published in “Evaluation of Combined Heat and Power Technologies for Wastewater Facilities”.