Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1987-12-10
1989-08-01
Hruskoci, Peter
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
209 4, 209 5, 210752, 210787, B01D 2126
Patent
active
048531332
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the de-watering of small coal.
Small coal is coal in the size range 38 to 0.5 mm. Many coal mines produce a considerable quantity of coal in this size range which is washed in water to remove mineral matter. It is then necessary to recover the small coal from the water. This is done, for example, by using centrifuges. However, the product from the centrifuging step still contains significant quantities of water. It would be desirable to find a method of decreasing the water content of the de-watered product still further. However, the cost of obtaining any additional water removal must be considerably less than the cost of installing and operating the water removal system.
Various specific mixtures of surfactants and kerosine have been proposed as coal de-watering agents. We have found however that either the improvement obtained by the use of these proprietary materials is not sufficient to justify the expense of using them of they lead to subsequent processing problems.
According to the present invention the process for reducing the water content of wet small coal comprises the successive steps of:
(1) adding to the small coal, a quantity of a water soluble anionic surfactant in the range 25 to 200 ppm based on weight of water in the wet small coal,
(2) subjecting the coal to a centrifugation step, and
(3) subsequently adding a foam-suppressing amount of a cationic organic compound to the aqueous effluent from the centrifugation step.
The process of the present invention may be applied to coal in the size range 38 mm to 0.5 mm, for example coal in the size range 13 to 0.5 mm.
At the concentration of anionic surfactant used in the process of the invention an economically useful reduction of moisture content can be obtained without requiring the use of an excessive amount of cationic organic compound to suppress the foam.
The water content of coal before it is subjected to the process of the present invention may for example be in the range 9 to 17% by weight.
The anionic surfactant may be for example a dialkylsulphosuccinate, an alkyl sulphate, an alkyl aryl sulphonate, or an alkyl ether sulphonate.
An example of a dialkyl sulphosuccinate which may be used is one in which the alkyl groups contain from 5 to 12 carbon atoms in the alkyl group. A particular example which may be used is dioctylsulphosuccinate.
The alkyl aryl sulphonate may be a sulphonate in which the aryl group is a benzene group or a napthalene group, and is preferably a dialkyl sulphosuccinate. The alkyl group may contain from 3 to 12 carbon atoms in the alkyl group.
The alkyl sulphate may contain for example from 8 to 15 carbon atoms in the alkyl group. It is preferred to use alkyl sulphates containing 12 carbon atoms in the alkyl group (lauryl sulphate).
The alkyl ether sulphates preferably have from 8 to 15 carbon atoms in the alkyl group, and from one to 10 alkoxy groups, preferably ethoxy groups.
It is particularly preferred to use the alkyl sulphosuccinates and the alkyl ether sulphates. The alkyl ether sulphates have the advantages of being available at lower cost.
The cation associated with the anionic surfactant may for example be sodium or potassium, but sodium is usually preferred on the ground of costs.
Surfactants are commercially available at various concentrations in solvents. When reference is made to a quantity of surfactant in this specification this should be understood as referring to the amount of active ingredient in the commercial preparation, unless the contrary clearly appears from the context.
The quantity of anionic surfactant added to the small coal is in the range 25 to 200 ppm (based on weight water in the wet coal fed to the process). It is preferred to use quantities in the range 50 to 100 ppm. In commercial scale and preparation plants it is particularly preferred to use quantities in the range 70 to 24 ppm based on the weight of water in the wet small coal fed to the dewatering process or 8 to 24 ppm based on the weight of coal.
The addition of anionic surfactant is prefera
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Flynn Steven A.
Rutter Paul R.
Hruskoci Peter
The British Petroleum Company p.l.c.
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