Modelling and Simulation of the Freezing Systems and Heat Pumps Using Unisim ® Design C
Abstract—The paper describes the modeling and simulation of the heat pumps domain processes. The main objective of the study is the use of the heat pump in propene–propane distillation processes. The modeling and simulation instrument is the Unisim® Design simulator. The paper is structured in three parts: An overview of the compressing gases, the modeling and simulation of the freezing systems, and the modeling and simulation of the heat pumps. For each of these systems, there are presented the Unisim® Design simulation diagrams, the input–output system structure and the numerical results. Future studies will consider modeling and simulation of the propene–propane distillation process with heat pump.
COMPRESSION RESORPTION CYCLES IN DISTILLATION COLUMNS
Distillation columns are generally operated very inefficiently from an energetic point of view. At the bottom, a boiler is required to vaporize the mixture while at the top heat is rejected to the environment. Vapor recompression heat pumps have been very successful in the realization of extremely large energy savings. For larger temperature lifts between top and bottom, the temperature glide in the absorber and desorber of compression-resorption heat pumps reduce the thermodynamic temperature lift and make these heat pumps a competitive solution. In this paper the performance of a diabatic column with the resorber of an ammonia-water compression-resorption heat pump integrated in the stripping section of the column and the desorber in the rectification section will be compared with the performance of an adiabatic column. The conventional boiler / condenser option and a vapor recompression option will both be investigated. The impact of ammonia-water concentration on performance and operating conditions will also be discussed.
Active compressor surge control using a one-sided controlled bleed/recycle valve
Surge is an aerodynamic flow instability which limits stable compressor operation for low mass flows. The stable operating region can be expanded using the so-called active control. In this study, plenum pressure measurements and a one-sided controlled bleed/recycle valve are used for active surge control in a laboratory-scale gas turbine installation. This control valve is nominally closed and only opens to stabilize the system in the nominal operating point. The influence of the control valve capacity and bandwidth on system performance is also examined. Using a bounded linear feedback controller, surge limit cycles are stabilized in the desired set-point, and stable operation can be sustained in this operating point with zero control valve mass flow. Surge point mass flow can be reduced significantly using this control strategy.