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Our existing natural gas pipelines can handle storing up to 10% added hydrogen gas. If we were to start ramping up biogas production from waste streams we coul

Our existing natural gas pipelines can handle storing up to 10% added hydrogen gas. If we were to start ramping up biogas production from waste streams we could produce some, if not all of the methane that goes along hydrogen in natural gas. This would utilize existing infrastructure, and help with energy production at night (think heating) when solar is unavailable. Hydrogen is only difficult to store if it is pressurized, at low pressures there are low losses due to adiabatic expansion. Embrittlement is only a concern when you're holding back high pressures, and isn't a big concern for pipelines which can conceivably hold a large amount of reserve fuel. I think the purified oxygen is an overlooked resource, as it can be used at, or near, the electrolizer as a method of producing pure syngas from waste organic matter using gasification. Normally woodgas or producer gas isn't desirable because it is made from atmospheric air as the oxidizer which contains a large amount of inert nitrogen which takes up space and produces nitric oxides at high temperatures. By using pure oxygen one can produce higher temperatures in the gasification reactor, and a purer syngas. This could be stored, and then used along with the hydrogen to produce heat and electricity in existing natural gas turbines when it is needed.

pfdietz 4y ago
The use I would think of for the oxygen would be burning fuels in Allam cycle turbines. These use supercritical CO2 and burn fuels with oxygen in the CO2 (oxygen is needed so nitrogen doesn't build up in the CO2). The products of combustion are water and CO2. Water condenses and can be reused (an Allam cycle turbine burning natural gas would be a net producer of liquid water); CO2 from burning natural gas would be tapped off in pure form at zero marginal cost (unlike other CO2 capture methods.) Allam cycle turbines burning hydrogen would not make CO2, of course, but they'd avoid the need for NOx reduction stage after the turbine. One could also imagine a system where CO2 is captured and stored, then used to make methane from hydrogen, that is also then stored. You'd need three kinds of storage reservoirs (methane, CO2, and oxygen) but perhaps this could be easier than storing hydrogen.
- nanomonkey 4y ago
  I'm curious if this could be utilized with less pure fuels such as organic wastes rich with oils and waxes. Supercritical CO2 is often used to remove oils and waxes from organic matter and clothing. The high temperatures and pressures might even be sufficient for pyrolysis of the organic matter, allowing for further removal of combustable materials. Of course organic materials are highly variable and full of other volatiles that may harm the turbines (i.e. sulfur, fatty acids, etc.). Sadly the purity of the exhaust gases would likely be effected as Nitrogen from proteins, along with other elements are going to end up in the exhaust stream. These could all be distilled out, or scrubbed, but with higher energy costs. Still there are lots of exciting developments that can be made to cogeneration power production using organic waste streams.
  - pfdietz 4y ago
    There are plans to use this cycle with coal, but it would be gasified first and the syngas cleaned up.
    - nanomonkey 4y ago
      Agricultural waste seems like a better use case, but that's just my sensibilities. A fluidized bed of 700C supercritical CO2 would be able to thermally crack woody biomass quite effectively. The remaining biochar could be used for carbon sequestration (reverse mining) by adding it to soil as an amendment to improve it's nutrient holding capabilities, ion exchange and friability.

pfdietz 4y ago

The use I would think of for the oxygen would be burning fuels in Allam cycle turbines. These use supercritical CO2 and burn fuels with oxygen in the CO2 (oxygen is needed so nitrogen doesn't build up in the CO2). The products of combustion are water and CO2. Water condenses and can be reused (an Allam cycle turbine burning natural gas would be a net producer of liquid water); CO2 from burning natural gas would be tapped off in pure form at zero marginal cost (unlike other CO2 capture methods.) Allam cycle turbines burning hydrogen would not make CO2, of course, but they'd avoid the need for NOx reduction stage after the turbine. One could also imagine a system where CO2 is captured and stored, then used to make methane from hydrogen, that is also then stored. You'd need three kinds of storage reservoirs (methane, CO2, and oxygen) but perhaps this could be easier than storing hydrogen.

nanomonkey 4y ago
I'm curious if this could be utilized with less pure fuels such as organic wastes rich with oils and waxes. Supercritical CO2 is often used to remove oils and waxes from organic matter and clothing. The high temperatures and pressures might even be sufficient for pyrolysis of the organic matter, allowing for further removal of combustable materials. Of course organic materials are highly variable and full of other volatiles that may harm the turbines (i.e. sulfur, fatty acids, etc.). Sadly the purity of the exhaust gases would likely be effected as Nitrogen from proteins, along with other elements are going to end up in the exhaust stream. These could all be distilled out, or scrubbed, but with higher energy costs. Still there are lots of exciting developments that can be made to cogeneration power production using organic waste streams.
- pfdietz 4y ago
  There are plans to use this cycle with coal, but it would be gasified first and the syngas cleaned up.
  - nanomonkey 4y ago
    Agricultural waste seems like a better use case, but that's just my sensibilities. A fluidized bed of 700C supercritical CO2 would be able to thermally crack woody biomass quite effectively. The remaining biochar could be used for carbon sequestration (reverse mining) by adding it to soil as an amendment to improve it's nutrient holding capabilities, ion exchange and friability.