Carbon dioxide or CO2 is a greenhouse gas, released in the burning of fossil fuels – including coal. Nowadays we hear the words ‘clean coal’ a lot. Some people say there’s no such thing. We asked research engineer Howard Herzog at the MIT Energy Initiative what ‘clean coal’ means.
Howard Herzog: It means different things to different people. Historically, it first came up when people talked about taking out the criteria pollutants for coal, which are the particulates, the sulfur dioxide and the NOx.
NOx are reactive gases. You sometimes see them as haze over urban areas.
Howard Herzog: Later on, it started to mean a certain type of power plant. And now the phrase is re-emerging to mean taking carbon dioxide out of the power plants, even though a lot of us in the community refer to that as ‘carbon capture and storage’ or CCS for short.
Herzog said carbon capture and storage involves separating and compressing CO2 from the power plant exhaust and storing it underground. He talked about what’s happening now with this technology in the coal industry.
Howard Herzog: I think the next logical step we need is demonstration plants of this technology. There are a lot of these projects both here in the US and around the world being talked about. It takes a while to build these, maybe five or six years to get them up and operating. But I think in that time frame we will see some operating plants here in the U.S.
The United States currently burns over 1 billion tons of coal each year. Herzog added that – even as alternative sources of energy are being developed – the world is still heavily dependent on coal.
Howard Herzog: I ask people who think we ought to abandon coal altogether, ‘what are we gonna replace it with?’ And even if you could figure out what to replace it with in the United States, what are you going to replace it with in China, which burns about twice as much coal as we do in the U.S.?
He mentioned government subsidies for the development of carbon capture and storage technologies, including $3.5 billion in President Obama’s early 2009 stimulus package, which increased funding for demonstration projects by more than 70%. However, Herzog said, U.S. policy is still not in place to make carbon capture and storage a widespread practice in the U.S. coal industry.
Howard Herzog: There’s no policy to reduce our CO2 emissions to the atmosphere. So why are companies going to spend all this money to reduce their CO2 emissions when there’s no policy to do it and their fellow competitors wouldn’t necessarily follow suit?
He said the technologies for the ‘storage’ aspect of carbon capture and storage is already being used around the globe.
Howard Herzog: Anytime you pump fluids into the ground you have to be careful and monitor your pressures well. You don’t want to induce any seismic activity. We inject lots and lots of fluids into the ground all over. We inject CO2 into the ground for enhanced oil recovery. In Florida they inject very large amounts of wastewater into the subsurface. So those technologies are well known, and there’s nothing new about this that we haven’t done before.
Herzog believes carbon capture and storage can be beneficial in reducing greenhouse gas emissions from coal-fired power plants, but, he said, engineering challenges remain.
Howard Herzog: For any technology to make an impact, it has to be able to remove billions of tons of CO2. That’s the level we’re talking about. Right now, with CCS technology, we can remove millions of tons of CO2, but not billions. So the challenge is to scale up the technologies. I think it’s possible – more than possible, feasible – for us to get to a level of removing billions of tons if we make the correct investments.
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