The Design of an Open Rankine-Cycle Industrial Heat Pump

Abstract

An open Rankine-cycle heat pump is ideally suited for producing low-pressure industrial process steam. Because steam serves as both the heat pump motive fluid and process fluid, the system achieves a unique simplicity and versatility. No intermediate refrigerant fluid exists for which to construct a process interface or impose a temperature limit. Interface components such as the heat pump condenser are not required. Moreover, the use of water vapor eliminates toxicity and flammability risks inherent with most closed-cycle heat pump fluids. The control strategy is simple. Low-pressure (subatmospheric) water vapor, generated by flashing steam at a temperature below that of the waste stream, is compressed to the process pressure and temperature by an electric-motor-driven, multistage compressor train. This strategy permits the heat pump to accommodate upsets such as sudden changes in the waste stream flow and/or temperature, as well as fluctuation within the process stream.