Can coal be clean?
Black and Veatch experts talk about clean coal technologies
There are plans to build two clean coal power plants in the UAE, the first coal-fired generation in the region. Black and Veatch project managers Bob Slettehaugh and Tom Guenther talk about the technology available.
What is clean coal? Is it a clearly defined term?
Tom: I don’t believe that clean coal is a defined term. I suppose there could be certain groups that may have their own definition of it but I’ve been following carbon capture for about eight years now and, for the most part, clean coal involves cleaning up the traditional pollutants from coal fired flue gas –SOx, NOx, particulates and Mercury - and also removing carbon (CO2) to some significant extent.
What are some of the main technologies available?
Bob: In terms of coal-fired generation in general, Black & Veatch has got a great deal of experience in pulverised coal and some of the more traditional clean up systems. We’ve also looked at a number of advanced technologies including gasification but also super critical pulverised coal and ultra-super critical pulverised coal using much higher temperatures and pressures than were used in the 70s and 80s to increase the efficiency.
The more efficient we get the less the emissions are for the same power output. Lately, as the NOx and SOx and particulate matter control technology has matured, the focus and research has been on carbon capture (CCS) or reduction systems.
Tom: There’s three different categories of carbon capture. You have pre-combustion capture, postcombustion capture and oxy fuel combustion. In pre-combustion capture you’re basically taking the carbon out of the fuel before it’s combusted and what that requires is gasification of coal so you transform the coal into a gas with carbon monoxide and hydrogen gas.
Pre-combustion capture has not been demonstrated to a great extent yet. There is a plant in the US that’s under construction – the Kemper County IGCC plant in Mississippi which is being developed by Mississippi Power, part of Southern Company. That plant is 582 MW and is planned to be in operation by the end of this year though there have been schedule delays and it probably will be delayed into early next year.
Post-combustion capture is more developed. You take the flue gas from a traditional coal-fired plant and remove the pollutants and then you use a solvent system to absorb the CO2 out of the gas.
There is a plant in Alabama – Plant Barry, also owned by Southern Company – a 25 MW demonstration plant using Mitsubishi technology to remove 500 tons per day of CO2, compress it and send it to a field for sequestration.
There’s another plant called Boundary Dam in Saskatchewan, Canada. It’s under construction and probably will be in operation within the next few months or so, and that will be the equivalent to adding carbon capture to a 150 MW power plant. It will produce 110 MW after the energy penalty. That project is going along fairly well and so far the signs are good.
Oxy fuel combustion is kind of a hybrid of the two previous technologies. It’s where air is used to combust coal. The flue gas you end up with is primarily CO2 and water and it’s pretty easy to separate the water out of the flue gas and you end up with a pretty high concentration CO2 flue gas.
That technology has only been demonstrated to about 10 MW. And then there is another project under way in the US called FutureGen 2.0, a 200 MW oxy fuel plant in Illinois but it’s currently only in the front end engineering and design phase so they’re still trying to decide exactly what it’s going to look like and cost and whether they want to proceed with the project.
Bob: Probably the most successful carbon capture project commercially uses pre-combustion at Basin Electric’s Great Plains Synfuels plant in North Dakota. They don’t produce power but they gasify coal to produce pipeline quality natural gas and the captured CO2 is piped to Canada for enhanced oil recovery.
It’s actually a revenue stream for them so it’s probably one of the largest demonstrations of carbon capture in the world. The gasification component has been operating since the 1980s and the CCS part of it has been operating since 2000. When you talk about clean coal there’s probably less than 10 commercial size IGCC plants in operation in the world.
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What percentage of the carbon emissions needs to be captured for a coal power plant to be considered clean?
Tom: Generally, when we say full carbon capture it’s about 90%. After that there’s diminishing returns so no one tries to capture 100%. The Basin Electric pre combustion capture project is around 50%, Kemper County is about 65%.
Bob: Full carbon capture is 85-90% but there’s also a band that’s closer to 65-70% where you get the carbon emissions down to the equivalent of a natural gas combined cycle and then in some cases you might look for lighter carbon capture of around 30%.
Tom: I think generally when you talk about full scale commercial plants, that’s going to be 60% capture and above. When you remove 60% of the CO2 from coal then you’ve basically made it equivalent to a natural gas CCGT plant on a lb CO2 per MW basis.
Is it not the case that using this technology makes projects commercially difficult or even unviable?
Tom: It is very expensive both from a capital cost standpoint and operationally. For instance, if you were going to do a coal project with carbon capture today you would probably select post combustion capture and that would add about 75% to the capital cost of the power plant.
So if your plant costs $1bn you can add another $750m just for the carbon capture component. And it doesn’t end there. There are operational costs for water and chemicals, which is not so bad, but then there is the energy penalty on the power plant for adding the CCS.
All of the carbon capture processes are very large energy users and so typically if you go for full CCS you’re going to lose 25-30% of your power output from the plant, depending on the technology that you use.
Bob: There’s a lot of government funding for research around the world to advance the technology, bring down costs and reduce energy penalties. If there’s a significant push and development of the technology, then the market would be there to serve thousands of plants around the world.
In some parts of the world where there’s no natural gas and coal cheaply is available, but reducing greenhouse gas and CO2 emissions are important, then you can afford to put more capital into some projects.
In North America, where natural gas is very cheap at the moment, why would any project developer choose coal with CCS technology attached?
Tom: The only reason to use CCS is to address climate change and so the projects that are going forward with it are doing so with government funding or subsidies to try to demonstrate the technology in the hope that it can be improved and the cost reduced in the future. There’s only a few projects that are using it.
Bob: Before the oil shale boom, natural gas prices in the US were heading up and we were seeing a number of gasification projects that were looking to produce pipeline quality natural gas similar to the Basin Electric plant in North Dakota.
The price of coal was very stable and so you’d have a stable price of gas over the long term. But following the shale gas revolution the price of gas in the States fell quite a bit and since then there’s been very little activity in coal. So I think the projects that did go forward had quite a bit of government funding and they were demonstration plants to try to advance the technology.
What about other regions where gas is not abundant and coal is cheap? Might coal fired power with CCS be an option?
Tom: In other regions, even though coal might be considerably cheaper than natural gas or oil feedstock, once you add carbon capture I don’t think it would be cheaper than those fuels. If you just want to burn the coal without carbon capture then sure. But countries like India, China, South Africa and Indonesia are continuing to build coal plants without carbon capture.
Ras Al Khaimah, in the UAE, is developing a project that will capture the carbon and sell it for enhanced oil recovery. Do you know of similar projects that have successfully used this business model?
Bob: The Basin Electric plant in North Dakota does that where they’ve got an enhanced oil recovery market just across the border with Canada and they sell over 2 million tonnes per year. It depends on how big the market is and how much they can support in terms of new plants before the market gets saturated and you’re paying to get the CO2 off your hands. I do think there are opportunities in various parts of the world where it makes sense depending on the geology and the distance required to transport the CO2.
Black & Veatch has been serving communities in the Middle East since 1922. The company has executed projects – consulting and construction roles; plus engineer, procure, construct (EPC) – in all of the GCC states.