Coal quality

Regional scarcities of coal initially drove these uses. As petroleum became more abundant and as its price fell, oil became more attractive. In firing boilers, fuel oil possessed only a slight advantage over good-quality coal in Btus per unit volume. But liquid fuels were much easier to handle and store than coal. Competitive pressures kept the prices per Btu of residual oil and coal quite close. 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDF tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°F) flame temperature (as does the cyclone boiler), has routinely blended low quality coal, and more recendy, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDF, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

Cement manufacture is a power-intensive process, which allows cement companies to buy fuel in bulk and obtain the fuel at a somewhat lower price. Also, kiln feed mechanisms are easily modified, to accept alternate fuels. Further, because temperatures in a kiln reach 2700 F, kilns can bum poorer quality coal than pulp and paper mills or even utilities, and can easily tolerate a wide variety of waste products.10 In addition, kilns can accommodate the lower priced TDF (wire-in TDF and even whole tires). These factors make the economics of supplying TDF to cement manufacturers less favorable than for pulp and paper mills.10 One cement manufacturer is paying approximately 30/ton for TDF.11... 

Utilities have the least economic incentive to use tires.8 Often, power plants that use TDF only substitute up to 5 percent of their total energy requirements with TDF. Utilities must buy better quality coal (i.e., higher heat value and lower ash) than cement plants, but have significant bulk fuel-buying power. They are not usually interested in TDF unless the price is 1 per million Btu s (MMBtu s) ( 30— 31 per ton) or less.8 The use of petroleum coke has recently been increasing in the utility industry,... 

Japan imports coking coals from the United States, Canada, Australia and many other foreign countries. Future supplies of coking coals involves some uncertainty relative to procurement of good-quality coals in sufficient quantities. Various measures have been examined to solve this problem in Japan, One such measure is the expansion of the scope of raw materials used for coke-making. 

A classic example of this occurred in the USA, when the 1970 Clean Air Act required electric generating companies to install emission abatement technology to limit sulfur emissions. Faced with significant investment costs, some companies switched from higher- to lower-quality coal. The result was an increase in sulfur emissions from dirty coal , offsetting any reductions from the end-of-pipe desulfurisation process [209]. 

Health problems caused by coal combustion are due to either the use of poor quality coal (high ash, high sulfur, or high content of toxic trace elements) or to the improper use of coal. When poor quality coal is used improperly, health problems due to coal burning can be widespread... 

In the East, most of the low sulfur coals produced customarily have been used for the production of coke for steelmaking both at home and abroad rather than for power generation. Heretofore these high quality coals have been too costly for utility use. Much of the coal used for power generation has been low-cost strip-mined coal. According to the Federal Power Commission (FPC), in the third quarter of 1972 approximately 46% of low sulfur coal delivered to utilities in the East and 92% delivered to utilities in the West were from surface mines. Correspondingly, 54% of the low sulfur coals delivered in the East and only 8% delivered... 

Classification of Coals.—Coals obtained west of Pittsburgh are generally of inferior quality. Coal may be classified according to either the proximate or the ultimate analysis. Thus Frazer s classification ... 

After the reserves of high quality coal have been exhausted, it will be necessary to use brown coals with more impurities. Extremely high-ash coals with high alkaline contents must be used in some countries even though the performance of such fuels could not be controlled with the combustion technologies available in the past. 

Oil combustion. Much higher proportions of sodium are encountered in fuel oils than in coal, and there are relatively high levels of vanadium, an element not usually found in coal. Furthermore the total non combustible fraction of oil is likely to be as low as 0.1%, whereas for poor quality coal it might be as high as 50%. 

While fifty five experimental runs have been performed only four representative runs are presented here. These are Run 24 (representative of very sour natural gas, 1.33 % H2S), Run 25 (representative of moderately sour natural gas, 2000 ppm H ), Run 40 (representative of polishing application to slightly sour natural gas, 100 ppm HaS), and Run 49 (representative of polishing application to moderate quality coal gas, 100 ppm HjS). Reproducibility of removal trends has been observed with all runs which successfully removed HjS from the process gas. 

Figure 10-31. Quasi-equilibrium gas-phase eomposition atthe gasification of low-quality coal as afunction of temperature (a) organic fraction (b) mineral fraction. In the figure, c volume fraetion of a eomponent, T, average temperature.

Krukovsky, VK., Kolobova, E.A., Lubchanska, L.I., Nikishkov, B.V (1987), Complex Plasma-Chemical Conversion of Solid Hydrocarbon Fuel in Water Vapor, in Plasma Gasification and Pyrolysis of Low-Quality Coals, p. 81, Energy Insitute, ENIN, Moscow. 

Razina, G.N., Kaftanov, S.V, Fedoseev, S.D., Kleimenov, VV (1973), Investigation of High Temperature Pyrolysis of Low-Quality Coals, Adv. of Moscow Institute of Chemical Engineering (Mendeleev University), vol. 74, p. 69, Moscow. 

Sakipov, Z.B., Imankulov, E.R., Messerle, VE. (1987a), Effectiveness of Burning Low-Quality Coals in Boilers, YVn, Gorlovka, Ukraine. 

One of the by-products of industrialization is large quantities of waste ash that remain when low-quality coals are burned for the production of electricity. It has been stated that in England and Wales during the 10-year period prior to 1961 about 25 million-tons... 

Coal preparation has been an Important segment of the coal Industry In the United States for approximately one hundred years. Its Initial use was In the production of high quality coal used In the manufacture of coke. By 1965 approximately 95% of metallurgical grade coal was processed through a coal preparation plant. The use of cleaned coal as a fuel for electric power generation and as an Industrial boiler fuel Is relatively recent. Studies conducted for the U. S. Department of Energy ( 1) and the... 

The ash in coal. The coal ash is a residue when coal sample complete combustion under prescribed condition. It is an important indicator in the study on the characteristics and utilization of coal quality. Coal ash can reduce coal oxidation heat per unit of mass, while the higher the coal ash, the lower the effective yield of carbon, then the more difficult to spontaneous combustion of coal. 

Coal straight from the ground, known as run-of-mine (ROM) coal, often contains unwanted impurities such as rock and dirt and comes in a mixture of different-sized fragments. However, coal users need coal of a consistent quality. Coal preparation—also known as coal beneficiation or... 

The temperature at which the coal oxidation reaction becomes self-sustaining and at which spontaneous combustion occurs varies generally depending on the type (nature and rank) of coal and the dissipation (or lack thereof) of the heat. For low-quality coal and where the heat retention is high, the coal starts burning at temperatures as low as 30°C-40°C (86°F-104°F). 

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