6 ms·

What does the energy balance for this process look like? I don't know anything about it, but I would guess that it takes some energy to pull the CO2 out of the

What does the energy balance for this process look like? I don't know anything about it, but I would guess that it takes some energy to pull the CO2 out of the air and turn it into fuel. That's gotta come from somewhere? How does it become carbon neutral?

breakyerself 5y ago
Since they're already removing co2 from the atmosphere as part of the process they could divert some of that to get sequestered underground. The process could be carbon neutral or carbon negative even.
callesgg 5y ago
If you are on a aircraft carrier you have nuclear reactors for power.
- systemvoltage 5y ago
  My inner voice: "Scale those damn bastards! Build a whole bunch of these, stack 'em on land and boy you've got yourself something really special. Nuclear driven CO2 suckers." Tell me why this is a bad idea?
  - nradov 5y ago
    That's not a bad idea necessarily, it's just not economical for regular civilian use. Fossil fuels are still far cheaper than synthetics regardless of the power source.
    - Aachen 5y ago
      I'm not sure the Paris agreement optimises for "far cheaper" but for a maximum temperature increase instead. The consumer can't be expected to individually take one for the team (as it is presumably cheaper in the long run to not deal with a globally failing ecosystem) so through legislation and incentives we'd transition to clean energy, not necessarily by making something cheaper. Of course, where possible the solution is to just use batteries, but try telling frequent fliers that they'll need to take a train in the future. We're going to need some synthetic fuels where energy density is paramount.
  - colechristensen 5y ago
    If you wanted to retool a big chunk of the world economy you could indeed solve the co2 problem by mass producing nuclear reactors attached to synthetic hydrocarbon plants that dumped the products in deep mines. You would have to spend trillions of dollars though.
    - systemvoltage 5y ago
      If we assume the price for a carrier nuclear reactor + generator would stay the same. Wouldn't the costs come down simply from basic economies of scale? The costs are high because we've build a few dozen of these ever.
      - colechristensen 5y ago
        building reactors has a lot of up front expense, operating them is expensive, and you would have to make a whole lot of them to make a meaningful dent
philipkglass 5y ago
I'd guess that 30-40% of the original electrical energy gets stored as chemical energy. If the electricity originally comes from nuclear power or renewables, the life cycle carbon footprint is far lower than for fossil fuel. It's still not exactly carbon neutral because even nuclear power has a non-zero CO2 footprint, but it's tiny compared to the status quo. Since many military aircraft are going to need chemical fuels indefinitely, it makes sense that the Air Force is interested in electricity-to-fuels. There was an analogous surge in researching coal-to-liquids in the 1970s after the oil price shocks. Liquid fuels are going to have at least military demand for a very long time, and planners are interested in mitigating supply threats before they become supply emergencies.
- mulmen 5y ago
  So this is less efficient than something like pumped hydro for energy storage, yeah? But what about the density? Or maybe a better question is how does energy/m^3 storage compare between pumped hydro and fuel synthesis? Could we do some kind of closed-loop combustion process where we capture the exhaust gas then re-synthesize the fuel? Or are the conversion losses just too great?
  - SilasX 5y ago
    I don't think the point is to compete with power grid energy storage, but for cases where the energy must be in the form of aircraft fuel, so it doesn't quite matter if it's less efficient on all metrics that pumped hydro -- unless you plan on running a cord from a dam to the planes.
dredmorbius 5y ago
Energy is lost in the process. Flexibility and utility are gained, in the form of a high-enegy-density (by both volume and mass) energy store with excellent storage capabilities, a widely-developed extant handling and utilisation infrastructure and knowledge, and, considering the capabilities, extremely positive safety and interactions properties: hydrocarbon fuels are non-explosive, non-toxic with incidental exposure, and do not erode metallic or polymer components of fuel and power systems. Net energy loss is at least 40% of input (hydrolysis to produce hydrogen), as well as the energy cost of carbon capture (this varies by methods). For seawater-based carbon sourcing, net synthesis costs of about 50% are what I've seen (see my earlier long comment on sources and references). For seawater extraction: "CO2 extraction from seawater using bipolar membrane electrodialysis", Matthew D. Eisaman et al is a 2011 paper discussing CO2 extraction via a "BPMED" (bipolar membrane electrodialysis) process. It delivers CO2 at 1.52 kWh/kg, vs. a value of 0.54 kWh/kg cited by Terry, though it's not clear on first reading if Terry performed actual experiments or used theoretical values. http://talknicer.com/co2extraction.pdf http://talknicer.com/co2extraction.pdf My recollection is that atmospheric extraction costs are 1.5--3x higher, though I'm uncertain of that precise figure. Recovered energy through Carnot and Rankin-cycle engines is on the order of 20--40%. The round-trip energy recovery from input electricity to delivered motive power is about 10--20%. Those are inherent to the processes and cannot be improved on. Note that electric generation itself converts only about 30--40% of input thermal energy (from a nuclear reactor in the US Navy's scenario). Again, this is an unavoidable energy loss given the physics of thermal-to-mechanical energy conversion Military aircraft and marine vessels can make at best limited use of direct electrical power given limitations of batteries, extension cords, and transmission lines, particularly with regard to energy and power demands. Any fuel, even
- bobthepanda 5y ago
  And as far as flexibility goes, there are military bases in hostile territory with fuel demands far exceeding what the normal supply chain demands even if it were reliable.
  - dredmorbius 5y ago
    Land-based synthesis strikes me as more problematic. There's a lot of gain in offsetting fuel use entirely (solar and wind generation, both of which see fairly extensive use). For a large established base there might be some benefit. But there's also the last-mile problem. Aircraft are effectively addressing the last-mile fuel delivery problem directly (by carrying it with them). They tend not to loiter long over the engagement area. Long-mission drones might be an exception to this. If sufficiently lightweighted and dedicated largely to surveillance, these could benefit by solar + battery electric power. Personnel risks would be low, and aircraft flight dynamics improve as scale is decreased (square-cube law of lift (square) vs. mass (cube) relation. This is the inverse of aerostats, which are more efficient at providing lift with size.
barney54 5y ago
The energy balance is significant negative. The point is to take cheap renewables and renewable hydrogen to make the fuel so I can be carbon neutral. But basic thermodynamics says it will always be energy negative.
- bobthepanda 5y ago
  Well, the point is not really to make it carbon neutral, but rather to reduce the amount of liquid fuel that needs to get supplied to a base, since tanker trucks and ships are fairly soft targets.
  - yCombLinks 5y ago
    The environmental standpoint has a separate goal with synth fuels than the government, which is the goal OP was focusing on.

breakyerself 5y ago

Since they're already removing co2 from the atmosphere as part of the process they could divert some of that to get sequestered underground. The process could be carbon neutral or carbon negative even.

callesgg 5y ago

If you are on a aircraft carrier you have nuclear reactors for power.

systemvoltage 5y ago
My inner voice: "Scale those damn bastards! Build a whole bunch of these, stack 'em on land and boy you've got yourself something really special. Nuclear driven CO2 suckers." Tell me why this is a bad idea?
- nradov 5y ago
  That's not a bad idea necessarily, it's just not economical for regular civilian use. Fossil fuels are still far cheaper than synthetics regardless of the power source.
  - Aachen 5y ago
    I'm not sure the Paris agreement optimises for "far cheaper" but for a maximum temperature increase instead. The consumer can't be expected to individually take one for the team (as it is presumably cheaper in the long run to not deal with a globally failing ecosystem) so through legislation and incentives we'd transition to clean energy, not necessarily by making something cheaper. Of course, where possible the solution is to just use batteries, but try telling frequent fliers that they'll need to take a train in the future. We're going to need some synthetic fuels where energy density is paramount.
- colechristensen 5y ago
  If you wanted to retool a big chunk of the world economy you could indeed solve the co2 problem by mass producing nuclear reactors attached to synthetic hydrocarbon plants that dumped the products in deep mines. You would have to spend trillions of dollars though.
  - systemvoltage 5y ago
    If we assume the price for a carrier nuclear reactor + generator would stay the same. Wouldn't the costs come down simply from basic economies of scale? The costs are high because we've build a few dozen of these ever.
    - colechristensen 5y ago
      building reactors has a lot of up front expense, operating them is expensive, and you would have to make a whole lot of them to make a meaningful dent

philipkglass 5y ago

I'd guess that 30-40% of the original electrical energy gets stored as chemical energy. If the electricity originally comes from nuclear power or renewables, the life cycle carbon footprint is far lower than for fossil fuel. It's still not exactly carbon neutral because even nuclear power has a non-zero CO2 footprint, but it's tiny compared to the status quo. Since many military aircraft are going to need chemical fuels indefinitely, it makes sense that the Air Force is interested in electricity-to-fuels. There was an analogous surge in researching coal-to-liquids in the 1970s after the oil price shocks. Liquid fuels are going to have at least military demand for a very long time, and planners are interested in mitigating supply threats before they become supply emergencies.

mulmen 5y ago
So this is less efficient than something like pumped hydro for energy storage, yeah? But what about the density? Or maybe a better question is how does energy/m^3 storage compare between pumped hydro and fuel synthesis? Could we do some kind of closed-loop combustion process where we capture the exhaust gas then re-synthesize the fuel? Or are the conversion losses just too great?
- SilasX 5y ago
  I don't think the point is to compete with power grid energy storage, but for cases where the energy must be in the form of aircraft fuel, so it doesn't quite matter if it's less efficient on all metrics that pumped hydro -- unless you plan on running a cord from a dam to the planes.

dredmorbius 5y ago

Energy is lost in the process. Flexibility and utility are gained, in the form of a high-enegy-density (by both volume and mass) energy store with excellent storage capabilities, a widely-developed extant handling and utilisation infrastructure and knowledge, and, considering the capabilities, extremely positive safety and interactions properties: hydrocarbon fuels are non-explosive, non-toxic with incidental exposure, and do not erode metallic or polymer components of fuel and power systems. Net energy loss is at least 40% of input (hydrolysis to produce hydrogen), as well as the energy cost of carbon capture (this varies by methods). For seawater-based carbon sourcing, net synthesis costs of about 50% are what I've seen (see my earlier long comment on sources and references). For seawater extraction: "CO2 extraction from seawater using bipolar membrane electrodialysis", Matthew D. Eisaman et al is a 2011 paper discussing CO2 extraction via a "BPMED" (bipolar membrane electrodialysis) process. It delivers CO2 at 1.52 kWh/kg, vs. a value of 0.54 kWh/kg cited by Terry, though it's not clear on first reading if Terry performed actual experiments or used theoretical values. http://talknicer.com/co2extraction.pdf http://talknicer.com/co2extraction.pdf My recollection is that atmospheric extraction costs are 1.5--3x higher, though I'm uncertain of that precise figure. Recovered energy through Carnot and Rankin-cycle engines is on the order of 20--40%. The round-trip energy recovery from input electricity to delivered motive power is about 10--20%. Those are inherent to the processes and cannot be improved on. Note that electric generation itself converts only about 30--40% of input thermal energy (from a nuclear reactor in the US Navy's scenario). Again, this is an unavoidable energy loss given the physics of thermal-to-mechanical energy conversion Military aircraft and marine vessels can make at best limited use of direct electrical power given limitations of batteries, extension cords, and transmission lines, particularly with regard to energy and power demands. Any fuel, even

bobthepanda 5y ago
And as far as flexibility goes, there are military bases in hostile territory with fuel demands far exceeding what the normal supply chain demands even if it were reliable.
- dredmorbius 5y ago
  Land-based synthesis strikes me as more problematic. There's a lot of gain in offsetting fuel use entirely (solar and wind generation, both of which see fairly extensive use). For a large established base there might be some benefit. But there's also the last-mile problem. Aircraft are effectively addressing the last-mile fuel delivery problem directly (by carrying it with them). They tend not to loiter long over the engagement area. Long-mission drones might be an exception to this. If sufficiently lightweighted and dedicated largely to surveillance, these could benefit by solar + battery electric power. Personnel risks would be low, and aircraft flight dynamics improve as scale is decreased (square-cube law of lift (square) vs. mass (cube) relation. This is the inverse of aerostats, which are more efficient at providing lift with size.

barney54 5y ago

The energy balance is significant negative. The point is to take cheap renewables and renewable hydrogen to make the fuel so I can be carbon neutral. But basic thermodynamics says it will always be energy negative.

bobthepanda 5y ago
Well, the point is not really to make it carbon neutral, but rather to reduce the amount of liquid fuel that needs to get supplied to a base, since tanker trucks and ships are fairly soft targets.
- yCombLinks 5y ago
  The environmental standpoint has a separate goal with synth fuels than the government, which is the goal OP was focusing on.