While the U.S. Congress has evidently shelved any legislation dealing with limiting carbon dioxide emissions, the rest of the world is investing billions of dollars in Carbon Capture and Storage (CCS) technologies (IHS Chemical Week May 7/14 2012, Pp. 27-29). It’s only the U.S. that acts as if carbon dioxide emissions are no problem. Interestingly, even ExxonMobil Corporation, up to recently a renowned doubter in the area of global warming and the effect of greenhouse gases, has strongly come out in favor of a carbon tax. I personally favor a carbon tax over “Cap and Trade”, because it is simpler and keeps it out of the realm of speculation and bankers. In any case, a snowball in hell would have a better chance than any legislation offering a new tax or Cap-and-Trade legislation, both of which would raise electricity rates. So, any advances in CCS in this country are being made in the private sector: not in large power plants but at industrial boilers where CO2 is needed for tertiary oil recovery,
The best chance for CCS in power plants would be EPA rulemaking for new coal-based power plants to install “clean coal” technologies, but that’s a non-starter currently, because even the proposed stricter rules on nitrogen and sulfur oxide emissions are meeting with stiff resistance from the coal industry. But let’s peek into the future, for the U.S. probably a distant one, but also for China, which is becoming a lot “greener” in its attitude and approach to coal-based electricity generation, given the horrible pollution in Beijing and other parts of the country and the fact that China does not have a glut of natural gas (like we do) to use instead of coal.
But it is not only pollution that is driving China to move towards “clean coal” technologies and alternative energy generation. Scientists there have concluded that global warming is already showing serious effects, for example in sea water levels rising quite remarkably in Shanghai and Tianjin and in rapid melting of snow and glaciers in different parts of China. President Hu said that China would set targets to cut carbon emissions per unit of GDP by a double margin by 2020. A 1000 megawatt “clean coal” plant using gasified coal is being built in Inner Mongolia and a 250-megawatt plant using similar technology is being constructed in Tianjin.
There are basically three ways to reduce or eliminate carbon dioxide from a power plant using coal. All of them raise the capital cost and production cost of electricity generation, though monetising the captured CO2 would in part offset that. But it will be difficult to find markets, particularly near power plants, for the huge amounts of CO2 generated. The three alternatives are (a) scrubbing the flue gases emanating from the boiler with a solvent such as amine and then separating and storing the CO2, (b) Gasifying the (powdered) coal with oxygen in a high temperature gasifier, where the fuel produced is fed to a combined cycle (gas turbine and steam turbine) installation to generate electricity and the CO2 is collected and stored and (c) Using oxygen instead of air in a relatively conventional boiler so that the product of combustion is essentially only CO2 (no nitrogen, since no air). This requires recycling much of the CO2-rich flue gas to control the combustion temperature, with the net CO2 withdrawn and stored.
Process (a) treats massive amounts of flue gas (because of the nitrogen from air-based combusion), requires huge scrubbers and a whole chemical plant, and will probably not be used for large power plants. Process (b) relies on maintenance-prone coal gasifiers and has an expensive flowsheet. Process (c), which is also suitable for retrofits, may be the best approach.(see flowsheet below). A 30-megawatt plant using that technology, designed by Linde, is in operation in Vettenfall, Germany.
If carbon dioxide indeed causes global warming and we need to limit future emissions, we only have two choices: Switch as much power generation as possible to non-carbon-emitting sources: nuclear, solar, wind, geothermal, hydroelectric, tides, etc or install carbon capture facilities in existing and/or new plants.