Application of a two-stage centrifugal steam compression system as part of a cascade high temperature heat pump
In this study the integration and operation of a two-stage centrifugal steam compression system as part of a cascade high temperature heat pump is described. The system will be implemented in a pulp and paper mill in order to use waste heat and provide steam at 6.1 bar(a), for drying purposes. At first, the integration concept of the demonstration case is described. The system to be developed should be capable of providing steam between 6.1 and 11.1 bar(a), which is needed for a broad range of paper products. Subsequently, that leads secondly and with respect to a future commercialization of the two-stage compression system to the requirement of a modular system in terms of performance as well as of the general setup (construction, drive, assembly etc.). Therefore, the piping and instrumentation diagram of the two-stage system is presented. This is followed by the findings and lessons learned while carrying out the design and operation of an existing steam centrifugal compressor. Based on that, the preliminary design as well as the optimization of the flow path is described, including the boundary conditions (material choice, design constrains, inlet conditions etc.). Lastly, steady-state and quasi-static simulations have been conducted for performance evaluation of the two-stage system. The discharge pressure required for a wide range of paper types can be achieved. Additionally, the quasi-static time series has been performed to check if the stages match while starting up the system. At first a base case was carried out to ensure a stable operation, which is followed by an optimization. It is shown, based on the optimization, a surge margin of 15% and a prevention of choke, can be achieved in any operating point.