A pinch of Chemical Engineering

A live, engineering topic in this environmentally conscious time is how to reduce the carbon footprint of the various methods of producing electrical power; coal, oil, nuclear, wind, tidal and so on.

Coal fired power stations are regarded as very polluting because an unavoidable by product of the combustion of coal is carbon dioxide. Carbon dioxide is a greenhouse gas widely regarded as bad for the environment.

There are, though, apparently still large reserves of coal globally available close to some regions with a high demand for power. For other areas further away it is economically transportable. The extraction cost is quite reasonable compared to some other sources of energy. If the emissions problem could be solved there would be some potential economic benefit if coal could be used. Thus it is that some projects are looking at ways to reduce or eliminate the problem of carbon dioxide emissions.

Diagram from http://www.co2storage.org.uk/

The whole carbon cycle including CCS

This is where the idea of Carbon Capture and Sequestration [commonly known as CCS] comes from. See the diagram above. This project, or series of alternative projects, will have many problems in addition to the engineering ones. However the engineering is what will feature in a simple way in this post. The project, as does the engineering, has two flavours although they overlap a bit: petroleum engineering and chemical engineering.

What is this CCS; what does it need to do? Whole textbooks and complete journals of technical research papers can and will be devoted to the projects. In this post we can only touch upon the first, major challenges in the simplest possible way. The Lad is using his engineering judgement and that without close experience of the problems. He apologises to the engineers struggling in the field if he does not do justice to their work. Please add your comments and enlighten us.

The carbon capture phase is one of chemical engineering whilst the sequestration draws upon much oil-drilling technology, which is petroleum engineering.

The gas fumes normally pour from the Power Station chimney as a fast-flowing mixture of carbon dioxide, CO2, and many other gases and particulates. From this we must remove the CO2. We could scrub the fumes in some fluid. Try an analogy here. You pour sugar [equivalent to the CO2] into a cup of tea [the scrubbing] and the sugar dissolves. Imagine that the sugar also bonds with the tea molecules. This is equivalent to passing the gas fumes and grabbing all the CO2 and holding it back whilst the remainder continues on. That’s easy enough with tea and sugar and not quite so easy with CO2. But that’s only the start of what the engineer has to arrange.

Now she has to get the sugar out of the tea again. That’s stripping the CO2 out again. That’s carbon capture and quite a clever trick but chemical engineers perform clever tricks all the time. Then there’s the sequestration. All you have got to do is to take the CO2 somewhere and bury it. How does this grab you? Say, drive it out to the middle of the North Sea – and The Lad means DRIVE it using a lot of power – and 10000ft down.

Think of doing all this at a rate of about 2000 tons an hour. Do it reliably and without hesitation for every hour. 24/7. This is for 1000tons of coal per hour, taking from the atmosphere and binding to a similar amount of oxygen. This is for one power station alone. There are, of course, other power stations.

Engineers have faced bigger problems. Not many, The Lad admits, but some. Think of Nuclear Power Stations, big bridges, rockets to the Moon and back, and tunnels. Your modern group of engineers on being presented with this project will smile slowly. “OK.” they’ll say, “Let us at it” They are facing their old enemy: the forces of nature in several of their myriad forms. They have to overcome forces to pull the CO2 out of the flue gas. Then overcome those forces again to pull the CO2 back out again after the stripping process. Then they have to force again the CO2underground into the tiny pores in some rock.

Stripping is taking a lot of power to achieve. Problem one is to need to use less power than the Power Station is generating. The Lad supposes that that’s obvious enough. Well, obvious or not it does not make it easy to achieve. If it takes a lot of power to do, maybe they will try to find a catalyst to reduce the required power. In many chemical processes where compounds interact beneficially it may, naturally, proceed quite slowly. However, some chemical compounds speed up the process solely by their presence and, by the end of the process, are still present and unchanged. You could regard such catalysts as being a form of lubrication of the process. There is a catalyst in your car doing a similar job to clean up your exhaust [but not CO2]. And that is platinum or something similarly expensive.

The Lad is willing to bet about another of the problems. Problem two is, he is willing to bet, the process will need high pressure to work. The engineer tries to design such chemical plant out of steel because it is less expensive than most other materials. So add to that, Problem three. CO2 frequently morphs into carbonic acid which is nasty and corrosive to most steels. Unless you take great care in designing your plant pressure vessels and piping, this is like taking a pin to a balloon.

Most of the mentions in the media so far have told me only that sequestration consists of putting the carbon into porous rock underground. There is nothing on the carbon capture phase of the process. The media do not have engineers, you see. They do not understand much of the problem. Correction, they do not understand any of the problem.

One Bing ref is

This is from ‘World Resources Institute, a US based ‘thinktank’. They claim that they are independent. The WRI first  video mainly [most of the 5 min video – but not all] speaks of the injection process, not of the capture and sequestration processes and any difficulties thereof.

Of course another is

Also project funded partly by EU and many other Big Oil and other companies, called CO2Remove. Link to this is [could not link to this – try again later!!!!]

is a 5 yr study project funded by the European Commission under the Sixth Framework Programme


This study project is coming to an end with a Feb 2012conference in France.

Engineering is one of the three drivers in the advancement of the human race. This blog aims to give to career seekers and also to the general public a taste of how this might be so. They are not well served by the current media. It is an engineer posting: not a ‘scientist’. It describes real professional engineering as it is in the real world usually in the present and occasionally as it was in the recent past.





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