AboutW.A. (Bill) Stevens Expertise I'm a professional mechanical engineer.
I can explain the economic tradeoffs of making electricity from natural gas, coal, nuclear, solar, and biomass energy sources. I have a pretty good understanding of the science on global warming and can explain how these energy conversion technologies affect that process. I can tell you why we have to build more nuclear plants, keep using coal, and cut way back on using natural gas to make elctricity. I can de-mystify the concepts of efficiency and energy conservation. But, I'm not an electrician so I don't do wiring! :-)
Experience
Past/Present clients EPA, DOE, USAID, World Bank, Bechtel, U.S. Generating, numerous electric utility and independent power companies, industry.
Question Bill,
I just ran across a question you answered and I was impressed also I'm confused on a few things about Btu, kWh and how much electricity can a process produce when I know the Btu output. I have a technology that will produce 12,462,000,000 Btu a day and I would like to know how much kWh can I get each day? Also with the same amount Btu how much Biomethane can be produced in one day in CF3? Thank you, Richard
Answer Richard -
That's an awful lot of waste heat you've got available!
If your waste heat Btus are at a high enough temperature, like above 1000F, you can theoretically get an energy conversion efficiency that's almost as good as the average coal-fired electric power plant, say 33%. Meaning that 33% of those heat Btus are converted to electrical energy kWhs. Let's first see how many kWhs per day can be obtained at that high efficiency.
First: 1 kWh is identical to 3412 Btu, if the Btus are converted at 100% efficiency. So if all your Btus were converted at 100% efficiency, you'd have 12,462 million Btu per day divided by 3412 Btu per kWh = 3.65 million kWh per day. But no conversion process operates at anything like 100% efficiency. At a more realistic and very good efficiency like 33%, you'd get only 1/3 as many kWhs ... or about 1.2 million kWh per day. That's probably the best that you could get if your waste heat stream is at 1000F or more.
Second: If your waste heat stream is at a much lower temperature, like say 300F, the best conversion efficiency you can get will be much lower than in the above high temperature example. At such a low temperature, the conversion efficiency might be as low as 10-15%. At 10% efficiency you would only get 365,000 kWh/day of electrical energy. Nothing to sneeze at ... it could supply the electrical requirements of maybe 30,000 average homes!
Third: If the waste heat is at a really low temperature, like 100F, you'll have trouble getting any net electrical energy from it at all.
Fourth: The waste heat may be free of cost, free fuel so to speak. But the energy conversion process will be very expensive even at the high temperatures, and becoming unbelievably expensive if you're starting with low temperature heat.
I don't know much about methane processes, so won't try to help you with that question. Sorry.
