Conveyors: fluid current – With adjunctive substance added – Solid
Patent
1991-11-04
1992-12-08
Focarino, Margaret A.
Conveyors: fluid current
With adjunctive substance added
Solid
406197, B65G 5330
Patent
active
051692678
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of transporting coal and more particularly to an improved method of the transportation of lump coal by suspending it in a slurry and then pumping the resulting mixture through a pipeline.
BACKGROUND ART
The transportation of solids over long distance by slurry pipeline has been applied to a wide range of materials, including coal, iron ore, limestone, phosphate and numerous other minerals. With regards to coal transportation, it has been a tendency in many countries to build power generating stations in the environs of the mine itself and to transmit the resulting output of energy by high voltage transmission lines. As will be appreciated, use of a slurry pipeline would permit the power station to be sited wherever desired. Studies have indicated that, as an alternative to rail transit of coal or to mine mouth generating plants, slurry pipelining is the least expensive option.
However, the conventional slurry pipeline technology has some disadvantages in that preparation of a fine coal/water slurry at the mine site, as well as coal separation at the terminal, impacts the unit transportation cost, setting the lower limit of competitiveness with alternative transportation modes for low annual tonnage and short distance.
The use of lump coal in a coal/water slurry proved to be feasible but was found to require high pumping power and resulted in excessive wear of the pipeline. U.S. Pat. Nos. 2791471, 3073652 and 4685840 provide good examples of prior art coal/water slurry transport.
To eliminate, or at least minimize, rapid settling and so reduce wear and required pumping power it was realized that a slurry vehicle of a density similar to that of the lump coal was highly desirable. Several kinds of slurry composition have been proposed. U.S. Pat. Nos. 3,637,263 and 3,719,397 disclose coal slurry transport using a magnetite/water vehicle; In particular U.S. Pat. No. 3,637,263 teaches the use of two compositions of slurry, coal fines and water on the one hand and coarse coal, magnetite and water on the other hand. U.S. Pat. No. 4,721,420 discloses the transportation of coarse coal particles in a dense liquid carbon dioxide vehicle.
DISCLOSURE OF INVENTION
In contrast to the slurry pumping/flushing/slurry pumping method disclosed in U.S. Pat. No. 3,719,397, through a single pipeline, the present invention uses a slurry pipeline and a return pipeline for the vehicle. Once the advantages of a vehicle return pipeline are contemplated, optimization of the vehicle is to be considered. With the stabilized fine coal vehicle slurries previously considered, the density of the vehicle was less than that of the coal. Under laminar flow conditions there is no turbulence to support the particles but, while there may be some minor lift forces due to the laminar velocity profile, basically the coal is carried along as a so-called "sliding bed". With the reduced relatively density and perhaps some reduction in solid friction coefficient due to lubrication, the pressure gradient is less than with conventional coarse coal but it is still a "sliding bed" situation. This is reflected in the pipe wear rate which, although considerably reduced by the low velocity, has been shown to e still very high compared with conventional fine coal slurry where the particles are supported by turbulence.
It is thus apparent that density differential between the coarse particles being transported and the vehicle slurry is most important. The maximum advantage will occur when the vehicle density equals the average density of the coarse coal. One way of achieving this is to use slurry of finely-divided, high specific gravity solids such as magnetite (Fe.sub.3 O.sub.4). However, if the vehicle slurry is composed of water and magnetite alone, concentrations of 33 to 38% by weight are required. At such relatively low concentrations the magnetite suspension tends to be unstable and unable to give the required support to the lump coal. In the present invention this is countered by the addition of co
REFERENCES:
patent: 2359325 (1944-10-01), McConnell
patent: 3637263 (1972-01-01), Wasp
patent: 3719397 (1973-03-01), Wasp
patent: 3881775 (1975-05-01), McPherson et al.
patent: 4685840 (1987-08-01), Wolff
patent: 4721420 (1988-01-01), Santhanam et al.
Focarino Margaret A.
Kannofsky James M.
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