25 September 2009

David Keith on Air Capture

In today's Science, David Keith makes a compelling plea for more attention to air capture of carbon dioxide. Here are a few excerpts:
Air capture is an industrial process that captures CO2 from ambient air, producing a pure CO2 stream for use or disposal . . . Near-term development of air capture only makes sense if it can be realized at a sufficiently low cost. . . Air capture is neither a silver bullet nor a hopeless dream: It is simply another chemical engineering technology. Disputes about cost can only be resolved by developing a few air capture technologies to the point where they can be independently evaluated. Costs cannot be understood until specific processes are developed to a far greater technical depth than has been achieved to date. As with other energy technologies, it is not possible to determine the cost through small-scale university research alone. Instead, costs will only become evident with pilot-scale process development and when costing can be performed by contract engineering firms with relevant expertise.
Remarkably, Keith asserts that:
There are no government funding programs that specifically target the development of air capture, and I estimate that the total annual expenditure for these efforts is currently less than $3 million per year, of which more than half is private.
He argues why there should be such a program of investment:
A more substantial investment of government R&D funding is warranted for at least three reasons. First, early estimates suggest that air capture will be competitive with technologies that are getting large R&D investments. For example, the cost of cutting CO2 emissions by displacing carbon-intensive electricity production with roof-mounted solar photovoltaic panels can easily exceed $500 per ton of CO2. Yet even skeptics (10) suggest that a straightforward combination of existing process technologies could probably achieve air capture at lower cost. And the fact that several groups have raised private money for commercialization suggests that there are investors who believe that it is possible to develop technologies to capture CO2 from air at costs closer to $100 than $500 per ton of CO2.

Second, air capture offers one route to make carbon-neutral hydrocarbon fuels (CNHCs) for vehicles by using captured CO2 to make synthetic fuels. Deep reductions in emissions from the transportation sector will require a change in vehicle fuel. Each of the three leading alternative fuel options—electricity, biofuels, and hydrogen—faces technical and economic hurdles that preclude major near-term reductions in transportation emissions. CNHCs represent a fourth, fundamentally different alternative: a method for converting primary energy from carbon-free sources such as solar or nuclear power into high–energy-density vehicle fuels compatible with the current vehicle fleet. It is unclear whether CNHCs will be competitive with the three leading alternatives, but they are promising enough to warrant R&D support on a par with efforts aimed at advancing the alternatives (20). Finally, air capture allows negative global CO2 emissions. Although this is a distant prospect, it is important because it represents one of the few ways to remediate human impact on the carbon cycle, an impact that is otherwise all but irreversible.
I have emailed David to ask if his cost numbers should be in terms C not CO2. Even so, as written the costs are squarely in the middle of the range that I discussed in my recent paper on air capture:

Pielke, Jr., R. A., 2009. An Idealized Assessment of the Economics of Air Capture of Carbon Dioxide in Mitigation Policy, Environmental Science & Policy, Vol. 12, Issue 3, pp. 216-225.

In that paper I concluded:
Air capture may or may not contribute to efforts to stabilize greenhouse gas concentrations. But so long as scientists and policy makers frame climate policy as in terms of stabilizing concentrations of atmospheric carbon dioxide, then given current indications of its potential effectiveness and cost, air capture deserves to be among the options receiving attention in the international climate policy debate.


Roger Pielke, Jr. said...

David graciously replied to my request and his reply indicates that these cost estimates are not apples to apples with Keith et al. 2006 (which reported much lower costs) because they represent other assumptions such as discounting (ug). I have asked David for a short paragraph of explanation, as readers could very easily misinterpret the cost numbers as representing the simple technical cost.

Joel Upchurch said...

I still think we should be looking at algae fertilization to sequester CO2. I think the risk of doing more experiments is over stated. There are dead areas in the ocean where we can do experiments with with minimal damage to other marine life and there is no indication to date that the algae blooms will sustain themselves without further fertilization. We still need to figure out what kind of algae is optimal for CO2 sequestration and the best way to grow it.

David said...


The cost of any energy product depends on the cost of money. For technologies like wind power, nuclear power, or for that matter air capture capital costs tend to dominate operating cost.

Any statement about $/ton-CO2 requires one to first estimate the cost of capital and then convert it into an amortized $/t-CO2 figure cost using some capital charge factor. One then adds the operating costs including fuel and O&M.

When we calculate the current cost of our air capture technology (which I do not comment on publicly) we use a 15% overall capital charge factor. We also use assumptions about construction contingency (~30%) and similar factors. Given the controversy around air capture, my goal is to choose conservative assumptions so that when we come out with cost numbers they will be obtainable in the real world.

These costs are necessarily different from (and larger than)the cost that might be appropriate in a long-run model of climate policy where one might use cost of capital associated with social discount rates; and, one might make assumptions about technological improvements.

These comments would apply to almost any high capital cost energy technology. That is why when comparing technologies it's often better to focus on $/kW of average power rather than $/kWhr or $/GJ.

David Keith

Roger Pielke, Jr. said...


Thanks. No doubt most readers of your Science article will be interested in apples-to-apples costs appropriate in a long-run model of climate policy.

I used $100 to $500/tonne C in my 2009 paper (based on a literature review). Do you have any reason to believe that the costs might be lower than covered by this range (again from the standpoint of long-term climate policy)?


Post a Comment

Note: Only a member of this blog may post a comment.