Sunday, January 23, 2011

A Brief Look at Coal

The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago. All living plants store solar energy through a process known as photosynthesis. When plants die, this energy is usually released as the plants decay. Under conditions favourable to coal formation, the decaying process is interrupted, preventing the release of the stored solar energy. The energy is locked into the coal.
Coal formation began during the Carboniferous Period - known as the first coal age - which spanned 360 million to 290 million years ago. The build-up of silt and other sediments, together with movements in the earth's crust - known as tectonic movements - buried swamps and peat bogs, often to great depths. With burial, the plant material was subjected to high temperatures and pressures. This caused physical and chemical changes in the vegetation, transforming it into peat and then into coal.
Images from World Coal Org
Proven coal reserves are sufficient to meet world demand at current levels for about 120 years. But proven coal reserves are only a fraction of the total coal resource. Proven reserves are apt to expand significantly should the need ever arise.
ResourceThe amount of coal that may be present in a deposit or coalfield. This does not take into account the feasibility of mining the coal economically. Not all resources are recoverable using current technology.
ReservesReserves can be defined in terms of proved (or measured) reserves and probable (or indicated) reserves. Probable results have been estimated with a lower degree of confidence than proved reserves.
Proved ReservesReserves that are not only considered to be recoverable but can also be recovered economically. This means they take into account what current mining technology can achieve and the economics of recovery. Proved reserves will therefore change according to the price of coal; if the price of coal is low proved reserves will decrease.
The chart above displays global reserves of coal, gas, and oil by region. As with coal, gas and oil reserves are ranked as proved or not proved. Proved reserves are apt to increase as economic conditions and technological sophistication changes. A good example of that is the huge expansion of shale energy resulting from improvements in horizontal drilling and fraccing technologies.

US coal deposits as currently understood are pictured above. The US has the largest coal resource of any single nation. In addition, the US has the largest overall hydrocarbon resource, when kerogens are included. Canada and Russia belong in the same category of top ranked overall hydrocarbon resource nations. Persian Gulf nations are in the "enviable" position of having more easily accessible, economically valuable, and readily usable hydrocarbon resources.
Coal varies in quality, depending upon its life history during formation. An important thing to remember is that even the cheapest and dirtiest coal can be utilised cleanly with gasification technologies. Cheap dirty coal can be cleanly utilised via IGCC with CHP, or via coal to liquids technologies with also utilise gasification.

Another means of utilising dirty and/or hard to get to coal, is via in situ gasification. That approach is being explored in Alaska, Canada, and China -- and has been tested in Europe and New Zealand.

It is believed that the coal resource is the largest hydrocarbon resource of all. But that is unlikely to be true, given the little-known mechanisms of hydrocarbon production and transformation inside the Earth's mantle -- which feeds hydrocarbon of unknown quantity (mostly wet gas) back into the crust. Much of that mantle-originated gas is likely to end up as methane clathrates beneath sea sediments -- the bulk of which has almost certainly been recycled many times via plate tectonics.

The planet's carbon cycle is far more vast and deep than most analysts understand, involving organic and non-organic carbons. Photosynthetic microbes and plants are key to the global cycling of carbon -- as are unimaginably powerful geologic processes. The Earth is floating in hydrocarbons.

If humans are smart, they will move beyond their dependency on hydrocarbons as fuels within the next several decades. At that point, the total cumulative human consumption of the global hydrocarbon resource will have been a tiny drop in a very big bucket.

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