In the week that US President Trump decided to withdraw from the Paris climate agreement, which commits nations to significantly curb carbon emissions in order to avoid catastrophic climate change, Science magazine reports on a startup that runs on carbon dioxide without emitting it….
I remember a while back, when objections to more fossil fuel based power plants were starting to get louder, that some governments blithely asserted that it would be okay, because they could do “Carbon capture and storage,” i.e. capturing the CO2 emitted by burning the fuels and somehow storing it (usually underground). This all sounded great except that it was a completely unproven technology; it hadn’t even got out of experimental stages, never mind been adapted for industrial scale use. Commitments by both government and industry also proved to be lacking in substance. In fact, only days before that climate conference in Paris in 2015, the Conservative government in the UK cancelled a £1bn funding competition to develop the technology. (I will leave readers to speculate about the contribution of fossil fuel industry lobbying on various governments to our current situation of under-investment in renewables, considering the dire warming the globe is on track to suffer).
I have to admit, I was never really filled with enthusiasm about CCS (Wikipedia will give you a lowdown on the technologies here). It seemed to me to be that it could be money better invested in cleaner, renewable technology like solar, wind, tidal, etc., especially as the fossil fuels are still going to run out someday, so we will have to find an alternative regardless. Nevertheless, the Intergovernmental Panel on Climate Change (IPCC) regards CCS as very important to tackling climate change in a cost-effective way; without it, they estimate the costs will double (and money, as we can all see, dictates a lot of these decisions). It’s clear, too, that we can’t just switch off all those power plants that run on fossil fuels overnight; if we can find ways to retrofit them to reduce or eliminate their CO2 emissions in the meantime, so much the better.
So it’s good to see in Science magazine this week two features about promising developments with CCS. The first is is entitled “Fossil power, guilt free,” which I feel is a little bit of a stretch (it’s also behind a paywall, sorry), but it’s an innovative and potentially revolutionary system nonetheless. A conventional power plant burns fuel to generate steam which drives the turbines that generate the electricity. This power plant uses carbon dioxide itself to drive the turbines, which is a rather brilliant idea. From the abstract:
Later this year, an energy startup called NET Power plans to fire up a new natural gas–powered electricity generating station near Houston, Texas, that could usher in a new era for fossil fuel power plants. The plant is testing a first of its kind zero emissions technology that burns natural gas in pure oxygen to produces a stream of near pure carbon dioxide (CO2) that can be pumped underground, preventing it from entering the atmosphere and affecting the climate. The new plant also turns CO2 into an ally, using it to drive a turbine in a manner that makes it more efficient than conventional steam-driven turbines. The new facility is expected to produce power at roughly the same cost as conventional natural gas plants. If successful, the new approach could revolutionize the field of carbon capture and storage and help countries limit carbon emissions while still producing the electricity society demands.
The CO2 is heated until it becomes “supercritical” – a gas with the density of a fluid. This is used to drive the turbines. The waste CO2 is collected and stored underground. The figure below compares the different systems rather nicely (and rather better than I can; I’m no engineer).
The main catch is that they had to set this sytem up to work with natural gas, rather than the really dirty fuel, coal, which is what CCS was really supposed to target. Coal releases twice as much carbon pollution as natural gas, but coal power plants are also inefficient. Trying to add CCS systems to coal-based plants is actually quite difficult, due to making it even less efficient and also problems with how to deal with other poisonous contaminants such as mercury and sulphur. However, this also means that countries are increasingly switching to natural gas power stations because they’re more efficient (and cleaner) and so this system could be of real value. Crucially, it’s also competitive economically speaking, so companies won’t be put off by an enormous price tag.
What about coal though? The related feature here explores the possibility of CCS for coal, and there’s one system that’s up and running now which is reasonably cost-effective:
Petra Nova, which opened in January, is tacked onto a massive coal-fired electricity plant near Houston, Texas, and captures 1.6 million tons of carbon dioxide (CO2) per year, equivalent to taking 350,000 cars off the road. The CO2 is then piped to a depleted oil field and pumped underground, where it frees up more oil that can then be sold to help offset the costs of the carbon capture setup. Though burning that oil will send additional CO2 into the atmosphere, overall the process is carbon negative, putting more carbon underground than is released.
So CCS is becoming a viable technology that can be used, and should be used, as a matter of urgency, as long as this isn’t used as an excuse not to invest in renewable energy.
As for Trump, well, one of the reasons he supposedly he pulled out of the Paris agreement was to protect the coal industry in America (plus complaining about the money the USA would have to stump up). If that were true, then he’s missed a trick – he could have promised to keep the coal being mined and burnt in America and also promised to reduce carbon dioxide emissions by prioritising investment in CCS. It’s a lot less unreasonable than many of his promises, after all.
Service, RF. Fossil power, guilt free. Science 26 May 2017: Vol. 356, Issue 6340, pp. 796-799 DOI: 10.1126/science.356.6340.796
Service, RF. Cleaning up coal—cost-effectively. Science 26 May 2017: Vol. 356, Issue 6340, pp. 798. DOI: 10.1126/science.356.6340.798