*2.2. Step 2: Build and Simulate Di*ff*erent Heat Pumps*

The HPs are simulated according to the data of the heat source and heat sink of Step 1. It takes the temperatures and the required heating or cooling duty of the process. In this work, JCHP, VCHP, and TCHP have been simulated by Petro-SIM [27], as shown in Figure 2. The use of Petro-SIM is similar to Aspen Hysys, as both are fork projects of the Hyprotech Hysys versions in the past. The main advantage of using Petro-SIM is that KBC has added dedicated modelling components for energy-related process units, such as boilers, turbines, compressors and HPs.

Fluid packages are based on the Peng-Robinson model [30] in combination with the Lee–Kesler Equation of State as a standard package in Petro-SIM.

Referring to the cases in Figure 2 the similarities between the three different HP cycles are as follows.


A critical difference is that the working fluid of a JCHP always maintains the working fluid in a gaseous state. After being cooled by the Sink, the working fluid, generates work through the Expander in the JCHP, as shown in Figure 2a, instead of using a let-down valve as in the other two cycles. In a VCHP, the working fluid has a phase change in both heat exchangers. In the Hot-side-HX, it is condensed from a gas to a liquid phase. In the Cold-side-HX, it is heated from the liquid phase to the gas phase, as shown in Figure 2b. In a TCHP, an intermediate heat exchanger is often added, and the working fluid follows a transcritical cycle, as shown in Figure 2c.

To make the simulated HP reflecting the performance of the real HP very closely, it is necessary to specify reasonable values of the device parameters in the simulation case, matching as close as possible the HP cycle and its measured indicators—mainly temperatures, pressures of the working fluid, the minimum approach temperature (ΔTmin) of the heat exchangers and the isentropic efficiency of the compressor and expander. ECOP [23] has developed a special rotation HP with embedded compressor/expander that achieves high entropy efficiency for a JCHP. In this study, the JCHP model adopts the performance characteristics of that specific compressor/expander [23]. A common turbocompressor unit is used as the compressor of VCHP and TCHP, which is the most used type for industrial-scale HPs [31]. A formula for the relationship between the isentropic efficiency and compression ratio of compressors was proposed by Wang et al. [32]. It is assumed that the recoverable waste heat duty of process streams is known to recover waste heat of process in this study. This can be achieved by a "Adjust" unit (ADJ; Figure 2) to regulate the flow of the working fluid or source to fix the heat duty of the Cold-side-HX when the process stream as the source for a HP. When the process stream as the sink of a HP, this can be achieved by adjusting the flow of the working fluid or sink to fix the heat duty of the Hot-side-HX.

**Figure 2.** Simulation flowsheet of the heat pump as output from Petro-SIM: (**a**) JCHP, (**b**) VCHP and (**c**) TCHP.
