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I'm working on a project where I need to size a CHP unit for district heating. I saw that this is usually done based on the heating requirements set, however, since we have a limited supply of biogas that we would like to use, we wanted to select it based on that. How should we go about doing this?

Andre Costa Guerreiro
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  • Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. – Community Nov 19 '22 at 16:02
  • So how do you decide who will get to be cold? Each go without heat for a day? – Solar Mike Nov 19 '22 at 16:31

2 Answers2

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  1. Start with your gas availability, look up its energy density and work out your available energy from that.
  2. If your gas is produced at a constant rate decide if you are going to have storage capability so you store off-peak and have an increased peak demand capability. If so, then decide on the peak value.
  3. From E = Pt (energy, power and time) you can work out the peak power output from your gas.
  4. Size the burner / boiler from the figure obtained in the previous step.
Transistor
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  • Find out the actual heating demand (peak demand + year round actual demand)
  • Find out the biogas availability (amount & variation)
  • Find out the temperture levels the district heating is suppoed to work at and keep these in mind when specifying the CHP
  • decide on a CHP size based on average gas flow
  • decide if you need / want gas storage. More than a few hours are typically not (economically) possible.
  • Is your CHP larger than the actual heat demand parts of the year? Consider finding an additional "customer"
  • Install a heating source matched to the actual peak demand that is not biogas fueled (natural gas, pellets, whatever) as a backup for when the CHP is in maintenance or the biogas source is down. Consider a dual fuel option: Boiler with burner for natural gas and biogas is a classic, so you can still use the (cheap) biogas if the CHP is down.

Note that CHP modulate poorly, compared to burners, and don't like stop and go operation. Typically our CHP will be controlled by biogas availibilty. The burner should "react" to heat demand in the system.

In a district heating system, you will probably separate the produces from the system with a heat exchanger. Get a good idea what flow and return temperatures you want from your CHP before talking to suppliers.

mart
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