Saturday, 27 March 2010

Vehicle Carbon Capture

We all hope battery technology will improve enough to make electric cars attractive, but if it does not I for one would pay a very hefty price, perhaps £5/litre of fuel ($3200/tonne of CO2 produced at today’s exchange rate) before I abandoned my car. Fortunately it is possible to capture carbon dioxide from the atmosphere or from vehicles for much less than that.

The options I favour revolve around quicklime (CaO). The average factory gate quicklime cost in the USA is published and was $101/ton in 2009. The material is made by decomposing limestone (CaCO3) in a kiln. When quicklime recombines with carbon dioxide it may form either the carbonate (CaCO3) or, if in solution, the bicarbonate (Ca(HCO3)2). Based on the carbonate, the cost of quicklime per ton of carbon dioxide absorbed would be $129. There are of course other essential costs including the cost of capturing and sequestering the carbon dioxide produced as the quicklime is made.

One way to use quicklime is simply to dump it in the ocean.

Another is to use quicklime to turn sodium or potassium carbonate into the hydroxide by precipitating the insoluble calcium carbonate as in the Kraft paper process. Solutions of sodium or potassium hydroxide can be used to capture carbon dioxide from the air by reforming the carbonate.

Alternatively the hydroxide could be used in a vehicle either in solution or perhaps, as weight is crucial, as the solid or a slurry. At the limit of solubility the range would be 100 miles for 150 kg of potassium carbonate solution in a vehicle doing 30 miles per imperial gallon. This compares favourably with current battery technology and recharging with potassium hydroxide solution at the gas station would be much quicker than recharging a battery. Moreover the vehicle could still be driven for hundreds of miles with the hydroxide exhausted, if necessary.

If quicklime could be used directly as solid particles, 150 kg would give a range of 228 miles but reaction rate might be too low, although the high temperatures available in the exhaust should help. Also carbonate might blanket the quicklime giving poor conversion and to make matters worse the particles might stick together with all the water vapour in the exhaust gases, making discharge very difficult. Quicklime is of course the key component of cement.

Solid lithium hydroxide is used to remove carbon dioxide at ambient temperature in spacecraft, where weight is crucial. In a vehicle 150 kg of lithium carbonate would correspond to a range of 308 miles. But unfortunately regeneration is currently difficult and expensive because of the low solubility of lithium carbonate when using the Kraft process and the relatively low melting point of lithium carbonate combined with the very high decomposition temperatures when emulating quicklime manufacture.

I have not yet worked out whether the higher concentration of carbon dioxide in exhaust gas is enough to tip the cost advantage against capture from the atmosphere. The logistics of the latter certainly look much easier and of course there are economies of scale and a free choice of location to suit sequestration and perhaps provide low cost energy/fuel.

Thursday, 28 January 2010

Readiness of Carbon Capture

Recent reports from the World Future Energy Summit say that “speakers pointed to the maturation of CCS and many successful pilot facilities around the world. And they set the expectation that the industry is now ready to see production facilities built in large numbers.”

Carbon capture is not new technology. We have been capturing carbon dioxide on an industrial scale from the partial oxidation of coal, oil and gas for many decades in the chemical industry. We have been reinjecting carbon dioxide down the well to enhance oil recovery for many years. The IPCC say the same in their report on carbon capture.

To be sure the capture and storage technology have not yet been put together and used on a large power generation plant. Process selection, cost estimates and performance will no doubt improve as we gain design, construction and operational experience, but that does not mean there is any likelihood of the technology not working. What is currently lacking is not the know-how but the economic incentive to apply it, except to demonstrate the technology.

I remember when we wanted to get lead out of gasoline, everyone said they were not ready, it would be very difficult and expensive. Then along came a tax incentive of a few pence per litre and it all happened painlessly. I suspect carbon capture will be the same. When the fuel producers are obliged to place contracts for carbon capture and sequestration for a proportion of the carbon in their fuel, as I propose, I think there will be power companies from around the world competing to take their money. I hope we will be left wondering what all the fuss around cutting emissions was about.

Thursday, 14 January 2010

More on Global Warming

As anticipated the world agreed to limit global warming at Copenhagen but could not agree who should do it and who should get how much money from whom. Perhaps the politicians will be more open to new approaches now that their single-minded pursuit of cap and trade with offsets has got them nowhere.

Among people polled there is strong support for the alternative scheme detailed in my previous blog in November. In a recent Times Online live debate 85% voted that "Fossil fuel companies should be obliged to sequester an increasing fraction of the carbon content of the products they sell to avoid dangerous climate change"

This motion was proposed by Myles Allen, head of the Climate Dynamics Group at the University of Oxford. Darren Johnson who is Chair of the London Assembly and a Green Party councillor also voted in favour because energy conservation and renewables will be much more attractive if we have to pay for sequestration when using fuel. He saw the proposal as a transitional measure in the move to a renewables/efficiency led programme but I see it as a long-term way of growing our affluent industrial society without stressing the planet.

Ed Miliband, Secretary of State for Energy and Climate Change, has failed to even acknowledge my emails on the proposed scheme but Norman Baker my local Liberal Democrat MP has offered to chase him for a response and I will shortly ask him to do so.

The International Energy Agency (an intergovernmental organisation) say that stabilising the climate in 2050 would cost at least 70% more without carbon capture.

Myles Allen pointed me to a paper which shows how very slowly atmospheric carbon dioxide concentration would decline even if emissions stopped. The ocean currently absorbs 2.2 billion tonnes/year of carbon (as noted in my November blog) but as described in the paper, uptake would fall to about a quarter of that value (ie only 6% of current emissions) if atmospheric carbon dioxide concentration stopped rising today.

The arctic ocean downwelling flow corresponding to the ongoing carbon uptake of 0.54 billion tonnes/year predicted in the paper gives an ocean turnover time of 2500 years. The 0.54 billion tonnes/year also implies that only about 1.4 billion tonnes/year of carbon in dead organisms sinks far enough to contribute to the measured increase in dissolved inorganic carbon in the cold downwelled polar water that fills the ocean below about 500 metres depth. Most of the often quoted 10 billion tonnes/year of sinking solid organic matter must decompose in the shallower water and leave the dissolved carbon there.

The observed 2 ppm per year increase in atmospheric carbon dioxide concentration would explain the other three quarters of the current 2.2 billion tonnes/ year of oceanic carbon uptake if the top 350 metres of the ocean were well mixed.

The ongoing ocean carbon uptake would be higher if the atmospheric carbon dioxide concentration were higher, because more carbon would dissolve in the icy water downwelling to the deep ocean. But even if the atmospheric concentration were allowed to level out above 500 ppm (compared to today’s 388 ppm) the ocean would only continue to absorb at the rate of 10% of today’s emissions.

A reduction to that level will be difficult but not impossible to achieve without sacrificing worldwide growth or our living standards. Recovery efficiency for carbon capture will need to approach 100% but no doubt this will be possible with the right financial incentive. Overseas holidays and year-round exotic perishable produce have become a key part of our standard of living, but planes need fuel and cannot easily capture carbon. Aviation already accounts for 2% of carbon emissions and this will probably rise as incomes rise substantially in China and India. Biofuel use on such a scale may not be politically acceptable as pressure grows to feed an expanding population without increasing the area under cultivation. There will also be a residual fuel requirement for transport, heating etc. in remote locations without the possibility of a mains electricity supply.

But for sure every year that we delay cutting back on our emissions we are squandering at least ten years of our children’s meagre ration. They will not thank us for going round the same old loop over and over again ignoring the obvious option of obliging fuel producers to pay for the capture of the carbon dioxide their fuels produce.