Coal goal

In the mid-1970s, the United States power generation industry transitioned to purchasing fuel as "energy" rather than fuel as coal "by the ton." By 1980 nearly all coal fired plants in the Eastern part of the US were burning with an average of less than 12 percent ash and moisture content less than 8 percent.

The power companies were facing increased demands on meeting new air quality regulations outlined in the 1970 Clean Air Act. This legislation was passed to reduce the Acid Rain problem facing the US. In order to meet these clean air requirements, coal fired power plants installed expensive SO2 scrubbers, which generally work well with coals with less than two percent sulfur. Since most Eastern coals have more than this, washing coal became a necessity.

In addition to reducing the sulfur to below 2 percent, washing coal also removes a large percentage of ash. This is a simple process known as gravity separation: ash sinks and coal floats. By 1990, the "Acid Rain" problem was solved; in part by burning washed coal as well as the addition of SO4 scrubbers.

Thus since the passage of the first Clean Air Act of 1970, US power producers have been buying coal by its energy content, subject to constraints on ash, sulfur and moisture. In order to determine the most cost effective method of meeting these constraints, the utility industry sponsored the development of a fullscale coal washing facility at Homer City, Pennsylvania. This plant was fully computer controlled and had the ability to easily change the "coal washing" flow sheet.

Under EPRI's direction, when a new mine was opened, about 40 coal cars would be shipped to Homer City for determination of the best flow sheet. This would typically find the combination of separation equipment that would cause the least loss of coal energy while meeting the sulfur constraints. Once the flow sheet was determined, a modular coal preparation plant would be built at the mine mouth. Throughout the late 1970s, hundreds of these modular coal washing plants were erected in West Virginia. These plants typically cost less than $5 million in 1980 and were erected in less than 30 days. Each modular plant was controlled with a digital computer and several innovative control system patents were awarded for this work.

Until the mid-1990s, the power generation industry was regulated. This meant that any increase in fuel cost or decrease in efficiency was passed directly to the consumer of power. Thus the industry was not as interested in efficiency improvements, but simply being able to operate the plant within the environmental guidelines, which limited particulates and sulfur emissions. However, since deregulation, the industry began focusing on producing power more efficiently, since any improvement in efficiency goes directly to corporate profit.

In addition to lowering the heating value of the fuel, ash has a detrimental effect on combustion and subsequent generation of power. The basic measure of efficiency in the US is "heat rate" normally measured in BTU/kWh (MJ/kWh) of power produced. Heat rate is the same as the inverse of efficiency, thus a decrease in heat rate is an increase in efficiency.

In China, the standard measure of efficiency is grams of coal per kilowatt hour (g/kWh) of power produced. But this measure is not efficiency (the ratio of the energy out divided by the energy in). Since the heat content of the purchased coal varies greatly from hour to hour and from day to day: thus (g/kWh) must be compensated for the true heating value of the coal, which must be accurately measured. This measurement is difficult to make and is expensive and time consuming if done according to standards.

There is a wealth of literature available from the US EPRI showing actual fullscale tests of the benefits from washing coal. A recent full scale test of a 550 MW plant sponsored by the US Department of Energy demonstrated a 1 percent increase in the output of the plant when burning washed coal. The benefits of burning washed coal include: reducing transportation costs, increasing availability of the plant, increasing its actual capacity to produce power, lowering the power consumption of process equipment, and decreasing the amount of CO2, NOx, and mercury emitted from the plant. Clearly, burning washed coal results in large returns for the small increases in the price of deep cleaned coal.

Additionally, since the mid-1990s, the world has become more aware of the importance of the carbon dioxide and nitrous oxide emissions (a greenhouse gas that is 298 more damaging than carbon dioxide). There is now sufficient support in the US Congress that it is likely they will pass a carbon "Cap and Trade" system in the next session. This will further stimulate interest in combustion efficiency as well as more accurate measurements of the actual mass of carbon emissions from the power plants; since under a Cap and Trade system, the carbon has monetary value.

What impact would this have on China's energy policy if power generators started purchasing energy rather than tons? A study (China Energy Technology Assessment) published in 2003 by Dr. B. Eliason and Dr Yam Yee Lee (China) recommended burning clean coal. This study was the result of over five years of research by over 100 leading researchers worldwide including China. The study included an intensive study of how this would work in Shandong province.

One of the major benefits from washing coal at the mine mouth is the reduction in coal transportation costs. For example at one large plant in Inner Mongolia, the ash content of the received coal was 46 percent. Thus every ton of "coal" shipped contains 460 kilograms of ash.

Additionally, ash is typically much harder than coal and hence the pulverizers use more energy. Equipment component wear is also increased due to the harder material and higher velocities necessary to deliver the equivalent energy. One plant in US reported a 17 percent reduction in pulverizer power by shifting to cleaned coal.

During the 2008 winter snow storms, the China rail transportation system was unable to deliver coal. Transporting washed coal would have effectively nearly doubled the transportation capacity of the railroads to deliver energy to the coal fired plants.

A second benefit is ash disposal. If the coal is washed at the mine, then 46 percent of the material can be used to recondition the mine. Open pit mines in the US are required to return the mine site to near natural conditions. This is done by returning the reject material from the washing process to the mining area. But burning high percent ash coal is causing new Chinese plants to have lower availability, higher occurrences of tube breaks, higher erosion rates in precipitators, and lower capacity than planned.

Coal cleaning technology is available from multiple suppliers including suppliers with local manufacturing facilities. The water consumption in these plants is low since most is treated and re-used. A plant of this size can handle large tonnage of run of mine coal and can be installed in multiples to handle very large mines. Thus expensive custom designed plants are not required.

It seems reasonable even with the recent downturn in coal prices and reduction in demand for power that now is the time for China to begin implementing a policy to clean coal at the mine mouth. This short term slowdown is not expected to change the fact that China's appetite for power is continually increasing.

Burning clean coal will automatically increase the transportation capacity by nearly 50 percent and will significantly improve performance of the power plants in terms of efficiency. Additionally, coal preparation plant installations could qualify for UN Carbon Emission Reduction credits since they may meet the requirement of "additionality." United Nations "CER" are currently valued at $20 Euro per tonne. Assuming a 1 percent reduction in coal consumption due to clean coal combustion, it is likely that 100,000 or more tons per year of carbon credits can be earned by burning clean coal at a 1200 MW plant. If the modular plant costs $5 million, it will pay for itself even if the coal is washed at the power plant.

With the temporary slowdown in the China economy, now is the time to re-assess the value of washing coal in China. Perhaps it is time to dust off the China Energy Technology Assessment reports and take a fresh look at the benefits of burning washed coal.

The author is chief technologist, OSIsoft, Inc, USA. The views expressed in the article are his own.

(China Daily 11/17/2008 page5)