Currently, I'm trying to determine a PSV relief load using HYSYS. My source is a H2 header with an operating pressure of 700 psig. There are two control valves in series. The first regulates the pressure that feeds the second valve, and the second valve regulates the flow to a stripping column. I'm trying to simulate actual operating conditions so I know that my model is accurate. Next, I need to simulate each of the valves wide open to determine my relief loads for the PSV. I've entered the source information (pressure, temperature, composition) to my feed stream. I've entered the valve characteristics (Cv, Km). I was hoping that I could enter a destination pressure, and HYSYS would calculate the flow through the valves.
This is not the case. HYSYS doesn't calculate the pressure drop through the valves, so the outlet of the first valve remains unconverged. I then tried removing the destination pressure with the hopes of manually entering a flow until the outlet pressure of the second valve matches operating or relief conditions. HYSYS seems to need a pressure drop across the valve which I do not have.
Does anyone have a suggestion on how to determine a flow through two valves without a pressure drop? I'm using steady-state mode, so I'm not sure if dynamic mode would help. Any suggestions are greatly appreciated.