Having understood the importance of a process flow diagram(PFD) from: What is a Process Flow Diagram (PFD)?: The Basics, here is a comprehensive list of the common symbols of process equipment used in preparing PFDs and P&IDs. I have dealt with some of these symbols listed here before in Common P&ID Symbols Used in Developing Instrumentation Diagrams but here again is a comprehensive list of basic and specialized symbols that you will find useful.
After reading this post, to gain more proficiency in understanding P&IDs, Process equipment symbols and Piping System in Process Plants, please consult the following books for further reading:
Piping and Miscellaneous Symbols:
Positive Displacement Pumps Symbols:
Storage Vessels Symbols:
Centrifugal Compressors Symbols:
Positive Displacement Compressors Symbols: