Development of an Exhaust Enthalpy Control Unit to Augment Combined Heat and Power Applications

One of the primary challenges facing DG/CHP systems involves effective design and operational match with potential end applications. A key weakness in the deployment of many DG/CHP systems is the inability of the installed system to properly match up with the actual load that it is being asked to serve. In general, it is difficult to optimally match the demand of both electricity and thermal requirements with a single system as a result of variations in loads with season, site operational changes, and other factors. It seems apparent that improved flexibility in how a DG/CHP system’s electricity/thermal production ratio is established will provide more flexibility in how a given system can meet a given demand profile. While examples of temperature increase via supplemental burners are available for small scale systems, a system to control both exhaust temperature (increase and decrease) and overall flow rate is not available. This paper describes the results of a multi-year program sponsored by the California Energy Commission to develop and demonstrate an exhaust energy tailoring system that will provide flexibility in both temperature adjustments and overall exhaust flow to meet the requirements of various heat recovery systems while providing low emission when coupled with a commercial distributed generation “prime mover”. The program integrated a multi-stage Rich/Quick-mix/Lean combustion system operating on the vitiated exhaust stream from a Capstone Model “iCHP65” to provide flexible wide range control of the exhaust energy and quality. Additionally, the integrated system reduced both the criteria pollutant concentration levels and emission rates over the Capstone unit alone. This paper describes the development of the unique vitiated air combustor system as well as full scale test results.