Very interesting! Nice work Jeff tracking this down. I’ve worked on several similar projects, actually one in Sioux City, but that was dealing w/ Human Poo.
Yes, it can require up to 40% of the methane created to sustain the anaerobic digestion process, in other words heat up the influent solids and keep the digester contents at ~ 95 deg F using boilers burning the very biogas the process is creating. The demands to sustain the process are much lower in the summer season, typically 15-25% of peak winter loads. Typically, you need to scrub the biogas to remove H2S, although it’s not always necessary depending on boiler design, gas quality, etc.
The next step, if you are going to be injecting into the natural gas pipeline is to scrub the CO2 out of it, (biogas is ~ 65% methane, and 35% CO2). This is the more complicated process and although being widely used in Europe, it is still very new in the US. To get every last bit of CO2 and H2O removed, which is required by some utilities to inject gas into their NG grid, you have to compress the gas and push it through molecular sieves. I know this step is very energy intensive, but I do not have a number for it. If designed right, the pressure is boosted enough (>300 psig) to overcome the losses to push through these sieves (microscopic membranes) and then it enters the NG pipeline at the appropriate pressure.
What is really cutting-edge is refining this gas to form CNG, which can be used in the modified tractor-trailers that are collecting the manure in the first place. They are doing this at a few solid-waste plants in Europe.
Cool... thanks for the details, doinkman...
This sounds like a great thing. Given that we are approaching peak oil production, we need all the alternate sources of energy we can get.
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