A New Angle on Carbon Capture

In my last couple of posts I looked at the difficulty of meeting ambitious targets for cutting greenhouse gas emissions (GHG) without help from the lower-emitting portions of our current energy mix. Last week ExxonMobil announced that it is pursuing a new pathway for capturing carbon from power plant exhaust. That could help revive another important strategy for large-scale emissions reduction from our existing energy sources.

Carbon capture and sequestration (CCS) has fallen out of favor, lately, mainly due to the high cost and technical challenges of the early prototypes for large-scale implementation of the technology. Not only are the initial investment costs of today's CCS hardware still very high, but it is also inherently expensive to operate. That's because of the high energy consumption of the process, resulting in a "parasitic" load on the host power plant that reduces its net output by up to 20%, making the remaining output much more expensive. That creates a large deterrent in any market that doesn't provide either direct subsidies for carbon removal, or a high carbon tax or price for traded emissions offsets.

Another reason that CCS has received less attention recently is that the costs of renewable energy technologies like wind and solar power have kept falling. To some they now look cheap enough, especially with further cost improvements extrapolated, to enable us to reach our emissions goals mainly through wider deployment of solar modules and wind turbines.

Even if that were technically feasible, like most other energy industry experts I have met I am convinced that the deep emissions cuts desired for mid-century will require implementing or retro-fitting CCS onto the fleet of coal and gas-fired power plants that will likely still be in service decades from now. CCS underpins several of the emissions stabilization wedges pioneered by Princeton engineering professor Rob Socolow and his colleagues ten years ago.

What makes the approach that ExxonMobil and FuelCell Energy, Inc. have described so attractive is that, instead of being a drain on power generation, capturing CO2 via fuel cells would actually add significantly to a facility's reliable power output. It would increase revenue, rather than curtailing it.

The clever bit, and its potential advantage over current carbon-capture technology, is that CO2 capture in a carbonate fuel cell occurs as a byproduct of the power generation step. That means that it doesn't require a big, expensive, power-hungry process unit, the only function of which is to strip CO2 from flue gas and concentrate it for subsequent shipment and storage.

These fuel cells would still require natural gas for fuel, and they would produce CO2 emissions in the process of generating electricity, though at a lower rate than the coal or gas-fired plant with which they would be partnered. However, both their direct emissions and the CO2 extracted from the power plant exhaust would come out in a highly purified form suitable for geological sequestration and stay out of the atmosphere.

That brings up an important advantage of this approach over various schemes to capture CO2 directly from the atmosphere. Although the article on the Exxon/Fuel Cell Energy development in MIT Technology Review  described the CO2 concentration in power plant flue gas (5%-15%) as "low", that is still hundreds of times higher than its concentration in air.

400 parts per million of CO2 in the atmosphere may be worrying from a climate perspective, but it is still just 0.04% of air that remains mostly nitrogen and oxygen. And the lower the concentration, the harder--and normally more expensive--it is to extract. (Green plants can do this trick cheaply thanks to billions of years of evolution combined with cost-free sunlight.)

The press release makes it very clear that this new carbon-capture technology has so far only been demonstrated in the lab. Scaling it up will require additional work, and success is uncertain. Many other promising innovations, including a host of cellulosic biofuel technologies, have failed to scale. However, its potential applications are compelling enough to justify a lot of patience and persistence. I wish them luck.

IEA's Roadmap for Low-Carbon Electrification in a "Golden Age" of Gas

• The IEA's latest Energy Technology Perspectives report provides a roadmap for the long transition to sustainable energy, as well as a report card on its progress.
• It also highlights the tension between the value of natural gas in decarbonizing the current energy mix, and longer-term expectations for phasing out its use.

Last month the International Energy Agency released its latest Energy Technology Perspectives (ETP), a technology roadmap extending out to mid-century, with a major focus on the increasing electrification of global energy against a backdrop of climate change. It may also shed some light on the options for achieving the emissions cuts in the US Environmental Protection Agency's proposed CO2 regulations for power plants.

This is turning out to a big season for climate-change-related reports. The ETP arrived just a week after the US National Climate Assessment, which followed the latest volume of the IPCC's Fifth Assessment Report on climate change. The ETP caught the attention of renewables-oriented news sites for its characterization of natural gas as, "a transitional fuel, not a low-carbon solution unless coupled with carbon capture and storage (CCS)."

That might seem to contradict the general tone of IEA's earlier "Golden Age of Gas" scenario, though when that study was released in 2011 it, too, included caveats about the limitations of gas in reducing greenhouse gas emissions. From that standpoint, the new ETP is no more negative about gas than the relatively rosy (for gas) Golden Age scenario was, and in fact sees gas supporting both "increasing integration of renewables and displacing coal-fired generation."

The IEA's press release for the ETP highlighted the growth of electricity as a major energy carrier, particularly in the developing world, increasing from 17% of final global energy consumption in 2011 to 23-26% by 2050. However, it also noted, "While this offers many opportunities, it does not solve all our problems; indeed it creates many new challenges."  Among other things, that alludes to the fact that while renewables such as wind and solar power have been growing rapidly, so has coal use, with the result that, as the ETP launch presentation put it, "the carbon intensity of (energy) supply is stuck."

The emissions benefits of electricity displacing oil from transportation and other fossil fuels from industrial, commercial and residential uses will be largely negated if power generation does not also shift towards lower-emitting sources such as nuclear, hydropower, geothermal, wind and solar power. The "2DS" scenario that received far more attention in the IEA's rollout than the ETP's other two scenarios, provides the prescription and justification for that transition. However, it's important to realize that the 2DS case is not a forecast or prediction; it's what scenario experts might call a "normative scenario"--one that the authors hope to encourage, rather than expect to occur.

2DS reflects the official stance of most member countries of the IEA and links to the low-emission "450" scenario in the agency's current World Energy Outlook. Both are predicated on creating a 50% chance of limiting the average global temperature increase due to climate change to 2°C (3.6°F), compared to pre-industrial conditions. That is generally thought to require keeping the atmospheric  CO2 concentration below 450 ppm (0.045%). In their launch presentation for this report, as in other recent reports, the IEA sounded the alarm that this goal may be slipping out of our grasp. April's monthly CO2 average exceeded 400 ppm for the first time since measurements began, and it is growing at around 2 ppm per year.

The IEA makes a good case that the rapid energy transition described in their 2DS scenario is feasible and economically beneficial, despite its $44 trillion price tag, providing substantial future savings in fuel costs, or more modest ones on the discounted cash flow basis on which most investments are premised. However, they are equally candid that reaching this goal will require significantly greater commitments and actions than countries have already made--or than I would assess to be politically feasible in the current global environment.

Renewables may be on-track, but many other aspects of the low-carbon transition aren't. That's especially true for new nuclear power, post-Fukushima, and carbon capture and sequestration (CCS) on which 2DS counts for 7% and 14%, respectively, of emissions reductions through 2050.

It's worth recalling that the main scenario in the World Energy Outlook was not "450", but rather the less-restrictive "New Policies" scenario, which appears to correspond to the middle "4DS" technology scenario of the ETP. (The WEO also includes a status quo "Current Policies" scenario.)  In that context we must not let the appealing outcomes envisioned in 2DS obscure the emissions-reducing benefits of natural gas in the world we are still likelier to inhabit, based on current trends, than the one we might desire.

Only under the rapid replacement of fossil fuels by renewables and nuclear power and CO2 sequestration assumed in the 2DS/ "450" scenarios would it be true that, "After 2025...emissions from gas-fired plants are higher than the average carbon intensity of the global electricity mix; natural gas loses its status as a low-carbon fuel." Presumably in the ETP's other two scenarios, that crossover would not happen until much later, if at all.

Gas is thus still a crucial bridge to a lower-carbon world, and it will not lose that status until we have made much more progress in reducing energy-related emissions than seems likely in the near future. While I certainly wouldn't bet against the continued growth of renewable energy, the slow progress of the other elements of decarbonization leaves a vital role for gas to help fuel the beneficial electrification of energy that the IEA has highlighted, for multiple decades.

A different version of this posting was previously published on the website of Pacific Energy Development Corporation.

How Is Expanding Oil and Gas Production Consistent with Addressing Climate Change?

Last month the International Energy Agency (IEA) reported that the amount of carbon dioxide emitted for each unit of global energy use was essentially unchanged between 1990 and 2010, despite the implementation of global climate agreements and the expenditure of hundreds of billions of dollars for renewable energy projects and incentives. Just a few days earlier, the US Environmental Protection Agency released its annual inventory of US greenhouse gas (GHG) emissions, showing a 1.6% reduction from 2010 to 2011. US emissions were up 8% since 1990 but have fallen 5% since 2000 and nearly 8% from their pre-recession peak in 2007. Much of the US's recent divergence from the global trend is attributable to the displacement of coal from the power sector by shale gas.

As unwelcome as the IEA's finding was, it is unlikely to have shocked anyone who understands the scale of global energy systems and the continued reliance of many developed and developing countries on coal for power generation. The transition to lower-carbon energy systems is underway, as reflected in the details of the IEA report. However, it will take additional decades to reach targets consistent with limiting the projected global temperature increase to 2° C, which the IEA indicates would require a 60% reduction in the carbon intensity of energy by 2050 from current levels. That implies that energy companies still need to develop additional oil and gas resources in the interim, in order to support the economic activity that--among other things--will be necessary to fund the recommended investments in cleaner energy and energy efficiency.

At first glance that might seem paradoxical. After all, oil and gas account for 55% of US GHG emissions and around 40% of global emissions today. However, when gas displaces a higher-emitting fuel like coal, global emissions fall. This has been a matter of some controversy, due to uncertainty about the contribution of fugitive methane emissions from shale gas wells. Yet the estimates in the EPA inventory indicate that methane emissions from US natural gas systems actually fell by 9% between 2005 and 2011, even though US natural gas production grew by 27% over that interval, with shale gas output increasing by 950%. A new analysis from ExxonMobil indicates that on a lifecycle basis, replacing coal with shale gas in power generation reduces GHG emissions by an average of 53%, while also reducing overall freshwater consumption by half.

Assessing the role of oil in the decarbonization of global energy is more complicated. Oil exploration and development must continue, even in a static or eventually shrinking market, because reserves that have been produced must be replaced, by either new discoveries or further development of existing fields. Simply allowing today's oil fields to decline and hoping to make up their energy contribution from other sources would be very risky, particularly for the transportation sector with its extremely high reliance on oil. Moreover, four-fifths of the emissions from petroleum occur during end-use combustion. That means that most emission reductions from petroleum must come about through reduced demand, via some combination of increased fuel efficiency, fuel substitution--particularly in those markets where oil is still used in electricity generation--and/or reductions in transportation metrics such as vehicle miles traveled.

In a recent Bloomberg op-ed, Michael Levi of the Council on Foreign Relations considered the impact of increasing US oil production from the standpoint of both the "social cost of carbon" and its incremental contribution to global emissions. He concluded that even at a high estimated environmental cost, the climate impact of an extra barrel of US oil would come in under $10 per barrel, well below its economic value. He also concluded that significantly higher US oil production would add little to global emissions. Its impact would be even smaller if OPEC producers reduced output to try to preserve high oil prices. Mr. Levi addressed that scenario in an earlier op-ed.

Last month's IEA report concluded that the world is not yet on track to reduce emissions by enough to limit temperature increases to 2° C, and more must be done. Yet even if we were on that track, the IEA forecasts upon which the report was based suggest that combined oil and gas consumption in 2035 would still be about 2% higher in 2035 than in 2010, with a bit of a shift from oil to gas. On today's trajectory, both oil and gas will grow, even as renewable energy and energy efficiency expand significantly. On either basis, an all-of-the-above approach to energy encompassing oil and gas, along with renewables, carbon sequestration, nuclear power and efficiency is fully consistent with addressing climate change.

A slightly different version of this posting was previously published on the website of Pacific Energy Development Corporation. 

Engineering Carbon Out of Energy

• Because of the slow progress in displacing fossil fuels with renewables, carbon capture and sequestration should receive much more attention as a game-changing technology.
• The challenges that must be overcome for CCS to be deployed on a large scale remain significant.

Yesterday I ran across an excellent article in The Atlantic on the importance of carbon capture and sequestration (CCS).  In light of last week's warning from the International Energy Agency that efforts to reduce the carbon intensity of global energy have yielded minimal results over the last two decades, the authors' chosen title, "Learning to Live with Fossil Fuels", seems particularly apt. Although neither they nor the IEA are suggesting we abandon renewable energy, they do effectively question the conventional wisdom that climate change can only be addressed by abandoning coal, oil and natural gas within the next decade or two. 

I'm predisposed to their argument, because it aligns with my own view--the result of long and careful analysis--that the transition to a low-carbon economy is going to take a lot longer than optimists hope.  A speaker at yesterday's policy briefing on renewable energy from the Worldwatch Institute and REN21, marking the annual release of the latter group's always-useful Renewables Global Status Report, stated that long-term energy scenarios in which renewables don't significantly increase their market penetration are no longer credible, and that only scenarios including medium-to-high penetration rates by mid-century are credible today.  I had to wonder whether he had been looking at the same data as the IEA, even though he cited their "2DS" scenario in support of his view.  Sarewitz and Pielke, Jr. appear to take quite the opposite view in The Atlantic: We cannot ignore the potential of CCS, because it is not self-evident that renewables will sweep away carbon-based energy any time soon, for reasons of economics, politics, and "complex social arrangements." 

In their brief article, they do a good job of summing up the major options for capturing CO2, including some of the major challenges to be overcome, as well as how the captured CO2 might be used or disposed.  Underground storage, enhanced oil recovery, and conversion back into fuels are all technically feasible, despite significant obstacles of public acceptance, logistics, and cost. However, I believe they seriously underestimate the challenges of capturing CO2 from the air, instead of power plant smoke stacks. 

The desirability of doing so is clear; the atmosphere is everywhere, convenient to whatever use to which me might put the captured CO2, while power plants aren't always located near the oil fields, saline aquifers, or fuel markets that offer the best potential for storage or reuse. The problem is that, while 397 parts per million (ppm) of CO2 in the air is high enough to cause great concerns about global warming, it is still quite low in engineering terms.  Expressing it as a percentage it's 0.04%, or about 1/1000th the typical concentration of CO2 in flue gas.

Before writing this post I literally dusted off one of my old chemical engineering texts to look up the equations of mass transfer.  I was reminded that the flux, or flow, of molecules from one fluid into another--from air into the capture medium, for example--is proportional to the difference in their concentration in the two fluids.  What that means in practical terms is that extracting the same quantity of CO2 from the air as from flue gas will entail larger and more complex hardware, more energy, and probably a much higher cost per ton, barring a breakthrough that emulates green plants, which use chlorophyll, sunlight, water and nutrients to do this cheaply on a vast scale every second of the day during the growing season.

In any case, have a look at the article and give some thought to how CCS might, as the authors suggest, "transform the political debate" around mitigating climate change.