Fuel and related compositions – Coal treating process or product thereof
Reexamination Certificate
1998-12-22
2001-05-15
Medley, Margaret (Department: 1714)
Fuel and related compositions
Coal treating process or product thereof
C044S501000, C044S591000, C044S592000
Reexamination Certificate
active
06231627
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and composition for reducing the oxidative deterioration of bulk materials. In particular, the invention relates to the reduction of oxidative deterioration of solid fuel materials, such as coal.
BACKGROUND OF THE INVENTION
When bulk materials contact the ambient environment, they are subject to oxidative deterioration because of contact with oxygen and air. Such oxidative deterioration can have many negative effects. For example, when a solid fuel material, such as coal, is being transported from a mine to a utility or is in storage at a utility, it is subject to oxidation. One negative aspect of such oxidative deterioration is a loss in the thermal value of the coal. Depending upon the type of coal and its water content, among other factors, between 1% and 5% of the thermal value of coal can be lost from the time it is mined until the time at which it is consumed. These losses are sizeable in the domestic United States utility industry, which consumes about 800 million tons of coal per year. Such losses are particularly significant for low rank coals such as lignite and sub-bituminous coals, especially for such materials which have been upgraded by thermal treatment to reduce moisture. Moreover, low level oxidation of coal generates heat. As a result, there is a significant risk of certain coal materials self-igniting, resulting in a risk to property and life.
Most efforts to reduce oxidative deterioration have focused on reducing the risk of self-heating and thereby self-ignition of coals. The problem has been addressed by a variety of approaches. One such approach is by compacting coal as it is transported or stored. By compacting coal, the surface area of the coal that is in contact with the ambient environment can be reduced. Such a reduction of surface area contact reduces the amount of coal available for oxidation by the ambient environment. Another approach has been to flatten and trim coal piles to decrease the ability of the coal pile to hold heat and therefore generate enough heat through self-heating to self-ignite. In addition, contacting coal materials with various fluids, such as hydrocarbon based materials, has been used.
While the more chronic problem of loss of economic value of bulk materials, such as the loss of heating values in coal, has been recognized and studied, adequate widespread use of strategies for significantly reducing economic losses from this problem have not been achieved. Therefore, a need exists for reducing the oxidative deterioration of bulk materials.
SUMMARY OF THE INVENTION
The present invention includes a method to reduce oxidative deterioration of bulk materials, particularly including oxidizable and highly reactive bulk materials. In preferred embodiments, the bulk materials in question include solid fuel materials, bulk food products, sulfide ores and carbon-containing materials such as activated carbon and carbon black. In further preferred embodiments, the solid fuel material can be coal, upgraded coal products, oil shale, solid biomass materials, refuse derived (including municipal and reclaimed refuse) fuels, coke, char, petroleum coke, gilsonite, distillation byproducts, wood byproduct waste, shredded tires, peat and waste pond coal fines.
The method includes preparing a first amount of the bulk material in a first size, and preparing a second amount of the bulk material in a second size. These two size fractions are then combined. The proportions in which the first and second sizes are combined is controlled so that the resulting porosity of the combination of the bulk material is about 40% or less. By reducing the porosity from what might otherwise be present after the preparation of the bulk material, the surface area of the bulk material in contact with the ambient environment is reduced. This then reduces the amount of bulk material available to the ambient environment for oxidation. In addition to the reduced surface area, the reduced porosity provided by this method inhibits the rate at which gas may flow through the bulk material. This reduced gas flow also limits the oxidative deterioration of the bulk material by reducing the amount of oxygen available to the bulk material for oxidation. A further benefit of the disclosed method is that the reduction in porosity also results in an increase in the density of the bulk material, thereby reducing the volume of the bulk material that must be handled and stored for a given tonnage of the bulk material.
The steps of preparing amounts of the bulk material in two different sizes may be accomplished through a variety of methods. Such methods may include crushing or grinding or pelletizing the bulk material. In a preferred embodiment of the present invention, the bulk material is crushed to a particle size of 2 inches or less. A first fraction of the crushed material, ranging in particle size from about ½ inch to about 2 inches particle size, is recovered. Separately, a second fraction of less than 4 mesh particle size is recovered, as is a third fraction of about ½ inch to about 4 mesh particle size. The first and second fractions are reserved while the third size fraction is further crushed to about less than 4 mesh particle size. The first, second and third size fractions are then combined, resulting in a bulk material having a porosity of 40% or less.
In a further embodiment of the present invention, a bulk material having a porosity of 40% or less is prepared as described in the above-mentioned embodiments. This bulk material is then aggregated into a storage pile until the bulk material is ready for use. This method of storing a bulk material results in lower rates of oxidative deterioration than might otherwise be achieved.
In addition, the present invention includes a bulk material that may be produced as described in the disclosed method. Such material will have a porosity of 40% or less, gained by the bi-modal particle size distribution achieved by the described method. In further embodiments, the method may include contacting the prepared bulk material with an inert gas or heat transfer medium. When the bulk material is aggregated into a storage pile, contacting the bulk material with an inert gas or heat transfer medium may include the step of adjusting the density of the gas or heat transfer medium, so that the gas or heat transfer medium remains in contact with the bulk material in the storage pile for the maximum amount of time.
DETAILED DESCRIPTION
The present invention concerns a method to reduce oxidative deterioration of bulk materials, and bulk materials prepared according to the disclosed method. The term “bulk materials” refers to any solid materials which are produced, shipped and/or stored in quantities that are generally measured on a tonnage basis, and preferably includes oxidizable and highly reactive materials. Bulk materials can include solid fuel materials, bulk food products, sulfide ores and carbon containing materials, such as activated carbon and carbon black.
Solid fuel material, as used herein, generally refers to any solid material that is combusted for some useful purpose. More particularly, solid fuel materials can include coal, upgraded coal products, and other solid fuels. The term “coal” includes anthracite, bituminous coal, sub-bituminous coal and lignite. The present invention is particularly suited for bituminous coal, sub-bituminous coal and lignite. The term “upgraded coal products” includes thermally upgraded coal products, coal products produced by beneficiation based upon specific gravity separation, mechanically cleaned coal products, and coal products such as stoker, breeze, slack and fines. The present invention is particularly suited for thermally upgraded coal because of significantly increased risk of oxidative deterioration and/or self-ignition. Thermally upgraded products are likely to have a higher rate of oxidation because of formation of reactive components which increase the rate of oxidation. In addition, such materials typically have
Berggren Mark H.
Kenney Charlie W.
Reeves Robert A.
Hazen Research Inc.
Medley Margaret
Sheridan & Ross P.C.
Toomer Cephia D.
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