This paper discusses how bed blending systems can be applied to the utilization of fossil fuels. The subjects of quality control and available stacking and reclaiming equipment are also explored along with a case history of bed blending at Utah International Corporation's Navajo Mine.
INTRODUCTION
It will be the purpose of this paper to discuss how
bed blending systems can be applied to the utilization of fossil fuels. The paper will also deal with locations for blending systems, types of storage piles, equipment, quality control, and a case history of a bed blending application. Since the available technical material on blending is extensive, it is suggested the reader consult the bibliography at the end of this report for further information.
WHY AND WHERE TO BLEND
Four primary bed blending locations should be considered: at the mine, at the coal preparation plant, at the transshipment facility, and as part of the user's coal handling system whether it be for combustion or the conversion to synthetic fuels.
Blending at the mine is employed to increase the available mine reserves by utilizing crop coal and to reduce the need for selective mining techniques. This is accomplished
by utilizing coal or lignite that contains unacceptable properties and blending them into the desired mixture. One example of a complete coal blending system located between a strip mine and a power plant can be found at the Navajo Mine located near Arizona Public Service Company's Four Corners Power Plant in New Mexico. We will discuss this installation in detail in this report.
Transshipment facilities can economically utilize bed blending if their fuel contracts involve specific grading limitations on Btu, sulfur, and/or ash. Blending will enable them to produce a lower cost fuel by custom blending to specific specifications the coal or lignite received from various sources. When more than one mode of transportation is used to transship the coal, the offloading and reloading at the ship or rail terminal offers an excellent opportunity for blending the varying grade of coals. The blending of different coals can be accomplished without any additional major expense since a coal handling system would already be a necessity.
Equally if not more important would be the blending of raw coals from different mines or from different locations within the same mine just prior to their beneficiation. The cost of coal beneficiation has been shown to decrease markedly with increased production. Substantial benefits could be derived if the output from two or more mines was combined to provide a common feedstock to a single beneficiation plant. In considering the use of blending prior to the beneficiation process, careful attention must be paid to the washability characteristics of each coal source and to make certain that the finished blend has acceptable Btu, sulfur, and/or ash properties.
At the power plant upgrading the fuel by bed blending could result in a lower capital expenditure in boilers and auxiliary equipment since a wide latitude boiler is not required. Normally the boiler and its auxiliary equipment must be designed to accomodate the volume of the lowest Btu fuel anticipated. If the blended fuel is of a higher Btu value, the boiler can be sized smaller and thus cost less.
There is also evidence that boiler slagging could be considerably lessened by uniform Btu coal. One reason for slagging is thought to be the anomalous upward fluctuations in heat value of the incoming fuel. These fluctuations cause the fire to burn higher and hotter in the box thus inducing slagging conditions. Uniform quality fuel could eliminate this major cause of slagging.
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Frank Loeffler of Loeffler Engineering Group, is a Manufacturers' Representative and an Engineering Firm that specializes in materials handling and conveyor systems. We represent a group of companies that supply turnkey systems and related conveyor accessory products.
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