Luiz:
I’ve done the conversion of conventional reciprocating natural compressor to air service while I worked many years ago in Latin America. I’ve also done one 3-stage air reciprocating compressor to natural gas service. I didn’t find that the conversions I did were difficult. Tedious, troublesome, and detailed – but not difficult.
You fail to state what type of compressor you are talking about and all the critical characteristics – like stages, pressures, make, type of drive, lube/non-lube, etc., etc. Why is it that so-called professional engineers that write in queries about compressors to this Forum somehow forget (or don’t know) the differences between a positive displacement machine (recip) and a dynamic machine (centrifugal)? There is a world of difference in their operation and control – some of it involves inherent hazards and important control techniques. Yet, it seems everyone just thinks that a “compressor” just compresses gas and they are all the same. Wrong.
Unless you have a deep and experienced understanding of compressors (both dynamic and positive displacement) you would be wise not to attempt the conversion. Pmover and Zapster are essentially telling you the same advice. This is not a project for a “fast learner”. You either know your S_ _ t or you don’t. And I can only judge what I read in this thread: You haven’t defined the type of machine and you obviously haven’t done it (or seen it done) before. Consequently I wouldn’t attempt it if I were you. What is meant by “low pressure mode”? 350 psig is deemed as “low pressure gas” by me when referring to compressors. Is that what you mean? Also, what do you mean by “5% ppm of sulfur”? Are you referring to H2S? Or is it SO2 or SO3? Sulfur is normally a solid element and is not present in natural gas as such. Without specifics, you can’t generate specific answers.
Specific answers to your queries are:
1) Yes, it is possible to use an air compressor (370 cfm) to compress natural gas with minor modifications.
2) “Replacement, like sealing, o'rings, explosion proof motors, etc.” – including piston rings, piston rod seals, cylinder valves, intercoolers, cylinder liners – are not “minor”. I did my conversions in Latin America for 2 main reasons:
(a) Long delivery on new equipment;
(b) Available used local compressors with minimum hard currency cost.
Unless you have similar imposing conditions and the experienced technical help locally to carry out the conversion, I wouldn’t try it if I were you.
But if you decide to go ahead, good luck and good engineering.