> It used a RB211 gas turbine to drive the compressor. Capturing the waste heat from the exhaust stack of that engine gave us 7MW of net generation, at a cost of $30 million, and much lower operating expenses to boot.
the main issue here is actually such a low efficiency turbine - an efficient one wouldn't have such an easy capturable exhaust heat to start with. One can understand that a gas turbine on a plane for example has weight limits so you can't tack on additional turbine stages, etc. to increase efficiency, yet for ground based it would only be about increased capital costs of such a turbine - so that means that running inefficient turbine is cheaper, i.e. the energy/fuel is still very cheap.
My understanding is that the most efficient turbines top out at about 40%. Reciprocating engines are better, but even they can't get much above 50%. There's still lots of heat there even in the most efficient engines.
You're absolutely right about the efficiency being just fine -- especially when you're a pipeline company and you just pull fuel for free out of the pipeline to run the turbine. That's a big reason why these companies haven't built these plants already.
>pull fuel for free out of the pipeline to run the turbine.
yep. The situation here and globally would be completely different if to the price of fuel, however low one can get it, the price of the emitted carbon were added. That would in particular have leap frogged our civilization efficiency.
Rankine cycle tops out at 40%, gas turbines are more like 50%, and combined cycle, which is really what's being implemented here, can reach around 60%.
When the gas is essentially free, there's not much incentive for efficiency, but they could have powered the compressor with a smaller yet more efficient combined cycle system. If you can economically extract power from a powerplant's waste heat, the original power plant was suboptimally designed.
the main issue here is actually such a low efficiency turbine - an efficient one wouldn't have such an easy capturable exhaust heat to start with. One can understand that a gas turbine on a plane for example has weight limits so you can't tack on additional turbine stages, etc. to increase efficiency, yet for ground based it would only be about increased capital costs of such a turbine - so that means that running inefficient turbine is cheaper, i.e. the energy/fuel is still very cheap.