US3867109A - Process for improving the bunkerability of coal - Google Patents

Abstract

This invention relates to the treatment of a coal slurry and particularly to the adiabatic flashing of the coal slurry solids removed from a centrifuge to effect a reduction in the moisture content present before the coal is sent to the pulverized coal mill or cyclone burner to improve the bunkerability of the solids.

Description

[mite States Patent [1 1 Wasp Feb. 18, 1975 [54] PROCESS FOR IMPROVING THE 3,313,251 4/1967 Jonakin 110/7 R BUNKERABILITY 0 COAL- 3,340,830 9/1967 Frey et a1..... 110/7 R 3,359,040 12/1967 Every et a1 44/51 X [75] Inventor: Edward J. Wasp, San Rafael, Calif. [73] Assignee: Bechtel International Corporation,

San Francisco, Calif. Primary Examiner-C. Dees [22] Filed: Mar. 14, 1973 [21] Appl. No.:'341,132

Related U.S. Application Data 57 ABSTRACT [63] Continuation-impart of Ser. No, 248,026, April 27,

1972, abandoned.

This mventron relates to the treatment of a coal slurry 52 U.S. c1 44/1 R and Particularly to the adiabatic flashing of the Coal 51 Int. c1019/00 Slurry Solids removed from a centrifuge effect a [58] Field of Search 044/] R 6 0/7 R duction in the moisture content present before the coal is sent to the pulverized coal mill or cyclone [56] References Cited burner to improve the bunkerability of the solids.

UNITED STATES PATENTS 2,162,200 6/1939 Kiesskalt et a1 44/51 3 Claims, 2 Drawing Figures PROCESS FOR IMPROVING THE BUNKERABILITY OF COAL This application is a continuation-in-part of my application Ser. No. 248,026 flled Apr. 27, 1972, now abandoned.

BACKGROUND OF THE INVENTION Heretofore the usual method of handling a coal slurry removed from a centrifuge has been to feed the slurry directly into a mill to pulverize the coal after which it is burned. This concept is shown in US. Pat. No. 3,340,830.

SUMMARY OF THE INVENTION Total Inherent Surface Moisture Moisture Moisture Coal before flashing but after centrifuging at 190F. 32% 20% 12% Coal after flashing 190 to 100F. 28% 20% 8% From the above table, the reduction in surface moisture is from 12% to 8%, or about one-third. Not only is 4%-less total mass sent through the boiler along with the fuel, but as an additional benefit, flashing permits easier handling of the coal. Coal with surface moisture of 8% is more handleable in a bunker than is coal with 12% surface moisture. It is preferred to maintain the surface moisture between about 5% and 8%. Thus, the coal is not dusty as long as the surface moisture is greater than 5% and, contrarywise, coal bunkerability decreases when the surface moisture becomes greater than about 8%.

The overall concept consists of the following sequential steps:

1. Heating the slurry to an elevated temperature, e.g.,

approximately 190F.

2. A mechanical dewatering operation.

3. Flashing of the heated cake from the dewatering device in a contactor which is swept by steam and a purge gas, more thanhalf of the heat required being supplied by the sensible heat in the coal.

4. Conveying the flashed cake to bunkers or other storage before utilization.

This invention is applicable to boiler fuel or a flocculated coking coal. The flocculation of coal by adding oils has been known for some time. Fairly light and expensive oils have been used. The major drawback of these oils has been that the agglomerates formed are not stable. The fine coal so flocculated becomes dusty in less than a day. The oil is apparently absorbed in the coal and because it ceases to be on the surface of the coal, it loses the ability to keep the fines agglomerated.

I prefer to use heavy oils preferably of a residual nature and which are quite viscous or even solid at room temperatures. As will appear, the mixture is heated at a high enough temperature so that the heavy oils are quite fluid to permit the flocculation to occur. I have '2 used heavy hydrocarbons having a viscosity at 190F. of less than 3 centipoises and a viscosity greater than 12 centipoises at F. The resulting inverted mixture is centrifuged hot and then the resulting mixture tumbled in contact with a sweep gas, such as air, to remove the flashing vapors. The resulting product is not only agglomerated as a stable agglomerate, but in addition,

the flashing results in a total moisture content such as 6% to 8% which is generally only achievable by thermal drying. 1

A further advantage of the present invention is that by cooling the coal after the centrifuge step, the coal is fed much more readily, enabling the width of the bunker from which the coal is fed to be materially reduced as the temperature of the coal is reduced.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowsheet showing typical steps in the practice of the invention.

FIG. 2 shows the variation of the bunker opening required against the temperature of the coal in the bunker.

DESCRIPTION OF THE PREFERRED I EMBODIMENT Referring to FIG. 1, the coal slurry is delivered from a pipeline or cleaning plant through line 6 at a temperature of about 60F. The coal can have a tar-oil mixture applied. The slurry is then passed through a heat exchanger 7 wherein it is heated by the effluent from centrifuge 8, the effluent being delivered through line 9 to the heat exchanger 7, usually at a temperature of about 190F. The effluent is thereafter sent through line 11 to a clarifier after which it may be discharged or reused.

From the heat exchanger, the coal slurry is passed through line 12 into a preheater 113 where it is heated by steam from line 14 until its temperature approximates 190F. The heated slurry is then sent through line 16 to the centrifuge 8. The cake typically delivered by the centrifuge through line 17 has a moisture content of approximately 27%-31% at 190F. The centrifuge cake is then sent through a contactor 18 where it is cooled by a purge gas delivered from line 19 to reduce the temperature of the cake to say F. The steam and purge gas are removed through line 21 while the cooled centrifuge cake is'withdrawn through line 22 and is sent to a bunker.

As will be seen from FIG. 2, there is significant decrease in the bunker width opening as the temperature of the cake approximates F. This enables the coal to be fed more readily and more after the manner of feeding coal transported by rail rather than as the usual slurried coal. 7

I claim:

1. A process for improving the bunkerability of coal which has been transported as a coal slurry, comprising the steps of heating the slurry to a temperature of about F, mechanically dewatering the slurry to produce a heated cake, adiabatically flashing the heated cake to reduce the temperature thereof to about 100F, contacting the cake with a purge gas and reducing the surface moisture of the cake to between about 5% and about 8%. I

2. A process as in claim 1 including the step of sweeping the cake with hot steam from an external source to aid the flashing operation, more than half of the dryer load being due to the sensible heat in the cake.

3. A process as in claim 1 wherein the coal slurry is mixed with a heavy hydrocarbon before being heated, the hydrocarbon having a viscosity at 190F. of less poises.

Claims (3)

1. A PROCESS FOR IMPROVING THE BUNKERABILITY OF COAL WHICH HAS BEEN TRANSPORTED AS A COAL SLURRY, COMPRISING THE STEPS OF HEATING THE SLURRY TO A TEMPERATURE OF ABOUT 190*F, MECHANICALLY DEWATERING THE SLURRY TO PRODUCE A HEATED CAKE, ADIABATICALLY FLASHING THE HEATED CAKE TO REDUCE THE TEMPERATURE THEREOF TO ABOUT 100*F, CONTACTING THE CAKE WITH A PURGE GAS AND REDUCING THE SURFACE MOISTURE OF THE CAKE TO BETWEEN ABOUT 5% AND ABOUT 8%.

2. A process as in claim 1 including the step of sweeping the cake with hot steam from an external source to aid the flashing operation, more than half of the dryer load being due to the sensible heat in the cake.

3. A process as in claim 1 wherein the coal slurry is mixed with a heavy hydrocarbon before being heated, the hydrocarbon having a viscosity at 190*F. of less than 3 centipoises and at 60*F. of greater than 12 centipoises.

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