Souping Up Alaska's Coal
Alaska has about half of the total coal reserves in the United States. Better yet, almost all Alaska coals have an extremely low sulfur content, a great selling point in a time when the world is powerfully concerned about air pollution. Yet somehow the world isn't rushing to buy Alaska's coal.
So far, neither are Alaskans. The cost of extracting coal here, like the cost of doing many other things, is high, and potential coal mining sites are usually far from existing roads or other transportation. We have inexpensive competing fuels, oil and natural gas. Even if we didn't, there are not very many of us--which means not enough local customers to make developing small-scale new mines economically worthwhile.
These reasons might be overcome, but one difficult problem would remain: the majority of the coals that can be strip mined, the most affordable method, are wet. They are low-ranked in the hierarchy of coals because they have a low heating value per unit weight. A low-rank coal that appears perfectly dry to casual examination can actually contain as much as 30 percent water by weight. That also raises transportation costs--in effect a skipper is hauling three tons of water in every ten tons of coal.
Drying the coal is one answer. Most commercial drying processes use hot gases to evaporate the coal's moisture. The drying temperatures are too low to change the coal structure permanently, so as soon as it is exposed to water (or even humid air), the coal takes up moisture again.
If the coal is subjected to higher drying temperatures, above 450 degrees Fahrenheit, its structure is permanently altered so that it won 't reabsorb water. It is a more expensive process, used most efficiently on coal that has been pulverized. Handling dried pulverized coal can be tricky, due to problems with dust generation and the potential for spontaneous combustion or explosion.
To get around those problems, processes have been developed that keep coal in lumps or produce pellets or briquettes from dried pulverized coal. They work, but add more cost.
So far, the most promising technology to improve Alaska's wet coals involves---ironically---making them wetter still. This process, called hydrothermal processing or hot-water drying, yields a liquid coal-water fuel that can be burned almost like oil.
The process is like cooking coal in a pressure cooker. The coal is heated to high temperatures in water: the water is kept in the system by high pressures. The heat and pressure affect the coal in minutes, just as if it had spent millions of years more in the earth. It undergoes more "coalification" and gains in fuel value. The resulting liquid coal has about the same heating value per pound as the original coal, but is far more easily handled.
The technical feasibility of this process already has been demonstrated in a 2.5-ton-per-day process development unit at the University of North Dakota Energy and Mineral Research Center. In Alaska, the Mineral Industry Research Laboratory at the University of Alaska Fairbanks is actively working on developing HWD technology for Alaskan coals. They are also training the young scientists who can participate in establishing any local liquid coal industry. The present studies aim mostly at process improvements that bring down costs to make coal-water fuels competitive in the international market,
If this technology works as hoped, the new fuel is a candidate for present oil-fired burners, for diesel and turbine engines, and for advanced applications like entrained gasifiers and fluid-bed combustors. Neatly enough, coal-water fuels can be transported by pipeline, so perhaps when the trans-Alaska pipeline no longer pumps oil to waiting tankers, it can be used to carry liquid coal.
