Yeah, it's unclear whether those 5 and 7MW figures quoted are electricity production or just heat energy.
Not to imply that "just heat energy" is useless -- https://en.wikipedia.org/wiki/District_heating is the term for using waste industrial heat to heat up homes in the surrounding areas. More common in Europe and Canada than the US I believe.
Cogeneration is when the concept is used specifically by electricity plants. It's used mostly in places that have need to generate their own electricity and heating like college and hospital campuses -- by harvesting the waste heat for another localized purpose, it becomes cheaper than relying solely on the grid.
A gas turbine has about 25-30MW thermal in the exhaust gasses, typical is gas at 480C and 90kg/s. At those temperatures we can convert that to electricity at about 20% efficiency. We lose about a megawatt in parasitic load such as pumps.
Thanks for clarifying and giving the conversion numbers!
Something like district heating has much higher infrastructure and coordination costs, but compared to an electricity conversion of only 20%, it's interesting to think about how other applications could have potentially higher efficiencies from that same waste stream.
Anyone know if there are examples of industrial parks that have been designed with waste stream "stacking" in mind? Instead of converting exhaust to electricity at 20% efficiency, could that power production waste heat be sent to something like a kiln or a chemical producer that needs heat as input?
All geothermal projects in Canada will require a direct heat off-take to be viable. In fact the revenue from direct heat use will generally be more than electricity sales. The 5MW plant in Alberta I referenced was built around a proposed industrial park, with the idea being to create a district heat system that upgraded the heat in some facilities and donated it at other facilities.
The best use of heat is as heat, without converting it. The problem is that heat doesn't travel very well, 5-8 km is really the practical limit before insulation costs swamp revenues. And a lot of industrial heat is too far away from a viable user of that heat. If the facility can use the heat internally their process engineers have already incorporated that (through pinch analysis etc).
We have one project now where we're replacing a heat exchanger that is supplying process heat from the exhaust with a power plant, but then using the waste heat from the power plant (still 80% of it left!) to replace the process heat. Overall efficiency will be around 60%.
Not to imply that "just heat energy" is useless -- https://en.wikipedia.org/wiki/District_heating is the term for using waste industrial heat to heat up homes in the surrounding areas. More common in Europe and Canada than the US I believe.
Cogeneration is when the concept is used specifically by electricity plants. It's used mostly in places that have need to generate their own electricity and heating like college and hospital campuses -- by harvesting the waste heat for another localized purpose, it becomes cheaper than relying solely on the grid.