How can I cheaply compress biogas up to 200psi in a steel Liquid Propane tank? I need something cheap, probably DIY.
Try fridge compressor, it can compress up to 250psi. But dry the gas before compressing because wet gas can gum the compressor. You can also increase stored gas by scrubbing out CO2 (can be quite expensive).
But I don't think compressing it is worth the effort. Remember the energy you waste while compressing or purifying. It is just better to use it directly in a diesel engine or for cooking/heating.
@Farmking, that makes sense.
You can't really tell until you know the cost of building a CO2 scrubber and the fridge compressor cost. We don't have these details yet.
I finally found out that biogas is best used with standby engines without compression.