Why is the Process simulation needed? (for EPC Project)

 Why is Process Simulation Needed? (for EPC Project)

When I joined an EPC Company…

When I joined an EPC company as a process engineer, process engineers were busy doing process simulations. I saw a senior process engineer doing a process simulation by using HYSYS or Pro II for the EPC project of oil & gas / petrochemical / refineries.

But Heat and Mass Balance(HMB) already existed!!

The thing that I couldn't understand was that there had already been HMB given by  a FEED company after being awarded the EPC project. All kinds of the process documents such as PFD, P&ID, HMB, etc., had already existed. The funny thing to me was that the senior engineers were inputting the process conditions (temperature, pressure, pressure drop, flow rate, compositions of feed streams, etc.) by referring to HMB given by FEED, they literally just copied the input data and pasted it into the HYSYS. Then they had almost the same results as the HMB. They had created their own HMB extracted from the HYSYS simulation. 

So, I couldn't understand why the senior process engineers were recreating HMBs even though there already was an HMB.

Then I became aware of the reason.

The EPC company receives ITB documents that are created during the FEED stage, however the native simulation file is not given to the EPC. First of all, that is why the EPC has to verify the design done by the FEED company and try to find design errors or mistakes, which could be a risk to us if we don't find those errors after being awarded the project. In order to verify FEED's HMB or other process documents, the EPC company needs to redo the simulation and compare their results to the FEED company's HMB. 

Another reason that the EPC company carries out the simulation is to extract other process information that can not be found in the FEED documents. For instance, PSV relieving conditions are needed for process engineers to carry out the relieving load calculation. In order to get that information, you need to make a simulation based on normal operating scenarios, then you can change the pressure and temperature to make relieving conditions. Thus, the EPC company needs some native simulation files for certain calculations.