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Low Power Flue Gas Compressor

  1. Mar 7, 2014 #1
    I've been lurking on these forums for years now; so much of my idea-seeking brings me here, it's remarkable, even to me, that I've never created an account. Here I am now though, so let's jump in shall we?

    Background:
    I'm designing an off-grid house for myself. I have most of the details sorted and have moved on to more elaborate and speculative ideas. One of many is to use the flue gas from my fireplace to supplement a photobioreactor with CO2 and a small amount of heat.

    Before the flue gas reaches the reactor tank, most of its heat will have already been extracted and put to use, so that is of little concern here. Based on the temperature and design of the combustion chamber, we can assume that the particulate component of the gas is minimal.

    Based on the size of the photobioreactor, only a small fraction of the flue gas will need to be diverted and compressed. The flue gas will need to be compressed sufficiently to force it through an aerator under a ≈1.5 meter water column. The (greater) fraction of the gas which is not dissolved or consumed by the algae and bacteria in the reactor will be vented outside.

    Being off-grid, I will have very little energy to bring to bear. However it's done, it will have to be efficient.

    The Question:
    What are your suggestions?

    I was considering a squirrel cage blower, but I doubt it could generate the necessary pressures. A reciprocating compressor would be fairly efficient, but I'm not sure it would have the throughput I want.
     
  2. jcsd
  3. Mar 7, 2014 #2

    Baluncore

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    Science Advisor

    You are considering compressing the flue gas sufficiently to push it down against the head of water when the energy used for compression will be lost as it bubbles up to the surface.

    Consider instead, moving water from the reactor around a loop. At one place in that loop, the water contacts the flue gas and so absorbs CO2 and heat. The water then returns to the reactor where it is reinserted far from the point it was drawn. That eliminates pressure differences due to head, and permits use of a thermal syphon. Counterflow heat exchangers can be used to regulate heat flow.
     
  4. Mar 8, 2014 #3
    I like the idea of using a thermal siphon, I'll have to look into the design. Even without using a thermal siphon, flowing the water through the flue gas, instead of the other way around, really does simplify the engineering.

    I'm thinking of two rectangular plates three or four centimeters apart. Flue gas enters just above the bottom of the cell, water from just below the top. Both are diffused and intermixed. Water exits and the bottom, gas is vented out the top.

    I would use a porous packing material between the plates, but even with the relatively clean combustion of this system, I'd be afraid of creosote build up.

    Low energy consumption (possibly no added energy using a thermal siphon), and a high level of intermixing. I like it. I think I'll do some research and then make a drawing.

    Thanks for your thoughts Baluncore.
     
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