What they said.
P&ID's are piping and instrument diagrams. This reflects the process flow including all majore equipment such as vessels, pumps, compressors, piping and instruments. Obtain a typical symbology legend sheet and some P&ID's for the flow diagrams to be meaninful.
Process simulations can be static or dynamic. The PROCESS SIMULATOR requires the flow paths and equipment data for the process equipment. Then they do magic for chemical engineers. Search for Aspen Technology, SimSci, etc.
BTW, the other responders know lots more about process simulation than me.