Monday, October 19, 2009

The other meaning of "Clean Coal", and related mineral preparation

There is a lot of talk about Clean Coal these days. The Federal Government are issuing, though DoE, a significant number of requests for proposal (RFP’s) seeking those ideas to improve the combustion and reduce the carbon dioxide emissions when coal is burned. Largely these are related to the combustion process itself and the consequent separation of the carbon dioxide, which is where there is a relatively large body of expertise within the Universities, and where progress is likely to be incremental, given that most of the technologies in place are relatively mature and well-known.

Of lesser importance, it would appear, are the pre-cursor parts of the coal cycle that prepare coal for combustion, or those post-combustion parts where the gas, after concentration, is to be sequestered. Part of this lack of interest, I suspect, comes from the lack of experience within the Government and the funding agencies in these areas. Thus there is no-one to speak for them when the funding pie is divided and money is allocated to the different processes seen to be contributing to solving the problems.

Yet in the end these are the parts of the process that will prove to have as great a contribution to the solution of the problems as any. Coal is inherently a dirty fuel – by which I mean that is it virtually impossible to go into a coal mine or operation where coal is being processed without the dust leaving a residue on your skin, requiring that you either wash or take a shower to become clean again. That dust is part of the coal structure – we used to call it fusain – and it is defined as
the only constituent in coal which blackens objects with which it comes in contact.
In that classification the other constituents are clarain, durain and vitrain.

But most coal isn’t found as just a mix of these four parts. Coal was formed as vegetation (including trees) collapsed into the mud, and other plants grew on top of it. Mud got into the layers between the plant remains, and occasionally local water floods would carry sand and other material in and over the plants. As the swamps sank, and the vegetation grew thicker the band of material thus had thin layers of other material interspersed with the coal itself. As the layer was buried beneath later sediments (deposition was largely during the Carboniferous era, some 300 million years ago, or roughly a little longer ago than the time it takes the Solar system to go once around the galaxy). it was compressed and while the vegetation turned, in the end, to coal the included beds became shale, and sandstone or limestone layers within it.

When coal was mined a century ago the miners filled tubs of coal that held roughly a ton, with each tub marked with the miner’s “token”. When the tub came to the surface it was judged by management and if it was felt that it contained too much rock, then the tub was not counted as part of the miner’s production for the day. Thus there was a reliance on the miner himself to make sure that the coal being “loaded out” was just coal and did not contain rock, or dirt as it became colloquially known.

As mining became more automated, the pick of an individual miner was replaced with the multitude of picks that are mounted on the rotating drums of most mining machines. These drums are alternately raised and lowered to mine out the full section of the coal, and they indiscriminately mine, break up and load onto shuttle cars, or conveyors, the resulting mixture of small coal with some waste rock. Now there is little control of the coal quality at the face (apart from making sure that little of the rock above and below the coal is also mined). The coal, as a result, comes to the surface with the contained dirt still in it, and in many parts of the world that is what is then sold to the customer.

However the rock contents don’t burn well, and the residue can fuse to form clinkers that clog furnaces and reduce firing efficiency. So as the market grows for the mine from local consumption to a larger market, pressure comes to bear to “clean” the coal by “washing” it. In a simple form this involves running the coal through a bath that contains fluid of a carefully selected density. Coal floats in that medium, while the rock settles to the bottom. And thus the two are separated and the washed coal can then be sold to the customer as something that will burn in a cleaner way.

So why write about this tonight, rather than holding it over for a technical talk on a Sunday? Well the problem comes down to this – in the past the job of cleaning up the minerals that came out of the ground – whether separating the coal from the waste, or getting the valuable mineral components out of the different ores and waste rock in which they are found was allocated, at most universities to the Mineral Preparation division, which often ended up as a sub-group of Metallurgy.

Skip forward a decade or two and now Metallurgy departments have been merged, often with Ceramics, into Mineral Engineering or Science, and it is these departments where some of the more exciting research is done on nano-materials and the components that go into the electronic circuits on which we all rely. These folk also work on materials such as those sought to improve the operational lifetime of existing and planned power plants. Hiring new faculty into these departments will usually bring on board faculty that work at these cutting edges of those areas, and the world makes considerable progress from their efforts. But in the process, since in many departments total faculty numbers remain fixed, this has come at the cost of not replacing those who are experts in the fields of Extractive Metallurgy. Nor has the field of Coal Preparation seen strong support, as other issues have claimed greater visibility and funding.

So now here we are – we need cleaner coal to be supplied to the power stations, so that it can reduce the burden of dealing with the combustion products. As the ores from which valuable minerals come become leaner (the richer veins having been mined) it becomes more important, as part of the economic operation of the mine, to get the most mineral for the least cost from the ore. (Mines have closed when they could not do this well).

Who will provide that knowledge? Who is funding the research to advance it? Sadly the answers in both cases are likely to be almost no-one. It is a critical part of the continuation of our industrial society, but, being neglected, it has lost its voice and champions.

Sadly it takes more than the stroke of the pen by the Administration to create or recreate that collection of experts and as the current generation now retire, we will all, in time, mourn in one way or another, their passing.

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