Max:
Firstly, since this is your first time on this Forum, you are not using the correct procedure. This thread was started by terravent for another totally different topic and it belongs to him/her. You should start your own thread, specifically for the purpose you outline.
I can easily show you how to calculate the diameter of a required compressor piston for a reciprocating compressor. I can’t calculate the “legth” (sic) or length of the piston rod – and neither can anyone else. The length of the piston rod is determined by the compressor manufacturer and is independent of the gas-end calculations. It is dependent on the mechanical work, type of design, and the forces imposed on the machine.
What you have to give us is the inlet gas flowrate at the suction temperature and pressure, the stroke of the piston, the strokes per minute (or rpm), the volumetric efficiency of the cylinder, single-acting or double-acting, and the piston rod diameter if double-acting. You state that you have 19,000 Nm/hr of natural gas, but you don’t identify what you mean by “normal”. Do you mean Nm3/hr as measured at 0 oC & 1 atmosphere? There are at least three conventions in common use.
I’ll look forward to your posting.