Is anyone developing direct carbon capture for home HVAC system based on natural gas?

Question

I live in Minnesota and I am concerned about my carbon footprint. I know that heating and cooling are large contributors to emissions globally.

This video from the excellent Youtube channel Technology Connections concisely describes why directly burning fossil fuels in homes for heating is preferable for now in cold climates, until carbon neutral energy generation can produce and store much more energy for the grid. It is less efficient to generate electrical power via natural gas or coal, transmit it to homes and use it to run an electric furnace than it is to burn the fuel directly.

https://www.youtube.com/watch?v=56DSH8tKUvo

Update: New video from Technology connections makes the case that heat pumps with current tech actually change this math, because they move around energy from the environment, they can be more than 100% efficient. So in short, this is more evidence to back up the respondents to this question. Moving to heat pumps ASAP will reduce carbon output, even with the current grid that has lots of fossil fuels in the mix. And things only get better as energy generation decarbonizes.

https://www.youtube.com/watch?v=MFEHFsO-XSI

I also know that carbon capture technology exists, targeted at a few areas that I'm aware of personally. There are direct carbon capture technologies for the transportation sector, like this company backed by YC for capturing carbon directly from trucks.

https://remoracarbon.com/

I also know of even more discussion happening around capturing carbon from the air. This has the nice impact of being able to correct our historical emissions if used widely enough. These projects however are energy intensive in themselves, as they are looking for a proportionally sparse amount of carbon in regular air that is mixed with lots of nitrogen an oxygen. I do understand that planting trees may be more efficient than any of these mechanical/chemical processes in the short term, but that isn't really the point of this discussion.

https://climeworks.com/

I tried looking around to see if there is anything being developed that can apply this same principle of direct carbon capture on transportation vehicles, and attach it to a furnace. So far I haven't found much, mostly just articles about technology about potentially turning AC units into carbon capture devices, but these seem again to be pulling carbon out of the air, not capture furnace emissions directly. It seems like an easy path to reduce current emissions, I have a carbon dense stream of gas I intentionally vent out of my house so I don't build up CO2 in my living space, but could I instead put that into a carbon capture device?

I did find one article discussing this directly, but it was published pretty recently and says the work is pretty theoretical at this point. https://www.sciencedirect.com/science/article/pii/S0360132321010209

Is there something obvious I'm missing that explains why this isn't being discussed more? Does an HVAC system produce too much exhaust to process right away? Could we install a holding tank for the exhaust that would be fed into a carbon capture system?

I do understand that any carbon capture system doesn't magically destroy the carbon, this system would produce some liquid or solid that contains carbon and oxygen. Like the climeworks site says of its capture technology's biproducts "Once the CO₂ is captured, it can be permanently and safely turned into stone through rapid mineralization which is a natural occurrence where the CO₂ reacts with basalt rock." So maybe it is simply a problem of being too much of a hassle to get people to properly handle these byproducts if a residential system like this was developed?

Answer 1

This is not practical.

There are two main ways in which carbon dioxide can be captured from gas burning equipment.

One is that there's a plant that liquifies air and creates a pure stream of oxygen. Then the pure stream of oxygen is mixed with carbon dioxide in 20% / 80% ratio to create an atmosphere that's 20% oxygen and contains absolutely no nitrogen at all. Then the combustion produces a mixture of carbon dioxide and water. You remove the water, for example by cooling the stream and discarding liquids, and then redirect part of the CO₂ to input to create the 20% oxygen / 80% carbon dioxide atmosphere. The rest of CO₂ becomes your waste stream, that you have to transport away in pipelines.

Unfortunately, liquifying air and creating pure oxygen takes lots of energy, and the air liquefaction equipment is very expensive and takes lots of space. Also cooling the waste stream to be able to discard water wouldn't be simple either, probably the equipment to do that takes lots of space and cost lots of money. Furthermore, you need a secondary set of pipelines only to transport CO₂ away.

A second possibility is that you have a plant that converts 20% carbon dioxide / 80% nitrogen stream from ordinary in-air combustion to a stream of carbon dioxide only and a stream of nitrogen only. This takes somewhat less energy than air liquefaction, but it still is highly expensive and takes lots of space. You won't install these kinds of equipment at home. You still would have the problem of needing a secondary set of pipelines.

It isn't realistic to transport a mixture of 20% carbon dioxide / 80% nitrogen in pipelines away from your home because that would mean you need pipelines five times as big.

There is a far easier and cheaper solution. It's ground source heat pumps. They can operate realistically at COP=4. When combined with a central power plant burning natural gas at 50% efficiency, you get 200% total efficiency, twice that of in-air combustion that releases its waste to atmosphere and far more than twice that of oxyfuel combustion or removal of carbon dioxide from the waste stream. Furthermore, the centralized power plant that burns natural gas is in a far better position to use these expensive and space-consuming techniques to remove carbon dioxide from its waste. The pipelines carrying waste CO₂ away from the centralized power plant are cheaper to build than a CO₂ pipeline network reaching every home. Also, the 200% total efficiency is assuming that 100% of electricity at all times is produced from natural gas. In reality, 70% will be wind power, maybe 15% will be solar power, maybe 7.5% will be hydropower and maybe 7.5% will be natural gas peaker plants. So in reality in the electricity production structure of tomorrow, the total efficiency from natural gas to heat won't be 200%, it will be 2666.66...%.

Also, the natural gas peaker plants will surely be modified to run on hydrogen produced from electrolysis in the future. This means 0% of electricity comes from natural gas. Thus, the efficiency that was 200% initially and then 2666.66...% will eventually be infinite!

Even today, ground source heat pumps are far more viable option for this case. Tomorrow, they will be even more viable. The day after tomorrow, the ground source heat pump uses 0% natural gas for its electricity production.

Answer 2

There are some very interesting new approaches to this problem which have the potential to dramatically change the calculus for point-of-emissions CO₂ capture and storage.

First, a technique using liquid gallium and silver-gallium nanorods in an ultrasonic bath acts to electrochemically reduce solute CO₂ into O₂ gas and solid C particulates. The input energy of 230kWh per tonne of CO₂ makes this an interesting possible route for the scenario you propose. source: https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.202105789

Secondly, another technique pyrolyzes bulk plastic waste particles into a carbonaceous substrate having pores sized to enable it to absorb a significant % of it own weight in CO₂, at low temps, and re-release CO₂ gas above 75°C.

The low temperature absorption performance may make it somewhat viable to use in capture-and-sequester home systems. but systems which recirculate the material for repeated extraction/concentrated/release may be able to use this as a cost effective stage to isolate diffuse CO₂ from flue gas streams and further process that concentrated CO₂ into more stable/more economically useful compounds. source: https://pubs.acs.org/doi/pdf/10.1021/acsnano.2c00955 Plastic Waste Product Captures Carbon Dioxide in Nanometer Pores

Turns out the 'secret sauce' is pyrolyzing the plastic in the presence of potassium acetate. That, and really high temperatures -600°C/1112°F.

So, to the extent of my awareness, there are no commercially available 'bolt-on' solutions to household carbon capture from your HVAC.

If one wanted to use HVAC specific CO₂ streams to enrich a greenhouse atmosphere, so long as the appropriate precautions against CO poisoning and CO₂ safe human respiration levels are in place and operating properly, is not an impossibility given a large enough greenhouse.

Net CO₂ reduction, by such means as supporting long term, persistent natural carbon sequestration through rewilding or other actions to reverse habitat loss may be the best, most immediate response to the continued use of CO₂ emitting home heat sources.

As has already been state; an answer to this for new installations may be ground thermal heat pumps, to avoid burning petroleum for heat in the first place. I think though, for existing installations, were maybe a few years away from the 'CO₂ non-emitting' add-on for gas powered home HVAC.