We did a successful demonstration project back in 1982 -- sticking a turbine in a natural gas pipe to recover some of the energy used to compress it by the pipeline company.
Flow was 20 million cubic feet per day
Transmission line pressure was 500 psig
End user pressure was 90 psig
There was a simple pressure-reducing valve taking the 500-to-90 drip.
Put a turbine in parallel with the PRV, got about 950 kW out of it, 24/7. Simple induction generator. Cost back then was just a hair under $400,000. We used a plain steam turbine with special seals, controlled it to 90 psi backpressure.
We had to heat the gas back up to send it on to the plant, due to ground-freezing issues.
Net sale (electric revenue minus cost of gas burned to re-heat the gas stream) was over $150,000 per year.
It was a really fun project! It worked dandy for about 10 years, then fell victime to maintenance neglect.
Good on ya,
Goober Dave
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