Proe 90™ Recuperator for Microturbine Applications

Abstract

Microturbines are becoming increasingly important in the distributed power generation market. These machines are typically low pressure ratio gas turbines that require a recuperator to achieve the high, 30% or more, efficiency needed to compete in this market. However, the additional efficiency gained by a recuperator can easily be offset by its high initial cost. In response to this challenge, Proe Power Systems has developed, and has a U.S. patent pending on, the Proe 90™ gas turbine recuperator. The principal feature of the Proe 90™ recuperator is that it allows a high performance (high temperature, high effectiveness, low pressure drop) gas turbine recuperator to be manufactured by simply welding, brazing, or otherwise joining standard commercial tubing without the need for special tooling or manufacturing processes. The objective in developing the Proe 90™ recuperator was to provide a recuperator for gas turbine and related applications that can attain a minimum of 90% effectiveness with reasonable size and minimal cost. It meets those objectives by: having linear, counterflow, annular flow paths that avoid any thermal “short circuits”; by having sufficient margin to accommodate potential exhaust gas fouling of the low pressure flow passages; by having all surfaces either curved or stayed by flow tubes so that they can be made from commercially available tube and sheet stock while maintaining high margins of strength and creep resistance; and by avoiding thermal gradient stresses by having all non-isothermal portions of the recuperator able to freely expand and contract. The simple manufacturing process, design modeling techniques and predicted performance of the Proe 90™ recuperator are presented. Effects of tube length, diameter, and numbers of tubes on effectiveness and pressure losses are quantified. Additional parametric data show the effectiveness losses caused by axial conduction, flow misdistribution, manufacturing tolerances, and insulation losses. The Proe 90™ recuperator is ideally suited for microturbine distributed power applications in the 20–50 kW range. With properly sized tubes, the flow regime is laminar and results in a very small pressure loss while still producing very high heat exchanger effectiveness in a low cost, compact package.