US3438867A - Disentrainment of coal particles in pneumatically charged coke ovens - Google Patents

Description

Aprll 15, 1969 H, S AWL 3,438,867

DISENTRAIIMZENI OE COAL PARTICLES IN PNEUMATICALLY CHARGED COKE OVENS Filed June 2, 1966 CHARGING STAGE OUTLET TO BY-PRODUCT RECOVERY 2 h] N a W W D C) M W IO 2 2 S g3 U Q r 9: 6 INVENTOR f 3 HARVEYS.AUV!L BY 'U ATTORNEY United States Patent 3,438,867 DISENTRAINMENT OF COAL PARTICLES IN PNEUMATICALLY CHARGED COKE OVENS Harvey S. Anvil, Ashland, Ky., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed June 2, 1966, Ser. No. 554,735 Int. Cl. (11% 49/02, 37/00, 35/00 US. Cl. 201-40 8 Claims This invention relates to the disentrainment of coal particles in a coke oven and more particularly to the disentrainment of coal particles in a coke oven which is pneumatically charged with fluidized coal.

In conventional methods of charging Wet coal to a coke oven, under favorable conditions the carry-over of coal dust into the by-product system is about 10 pounds per charge. This amount increases to 50 pounds per charge under less favorable conditions.

In pilot plant trials wherein dry pre-heate-d coal was pneumatically charged to a commercial coke oven, relative amounts of coal carried out of the oven were judged by comparisons of the color and opacity of the exit gases from ovens charged with pre-heated coal with those from ovens charged conventionally. These comparisons indicated that under favorable conditions, the coal carried out of the oven during pro-heated charging was about 1 /2 to 2 /2 times that carried out of the oven during conventional charging. This carry-over of coal takes place during the charging operation which usually lasts about 10 minutes in the case of pneumatic charging.

The present invention applies to a system in which dry pre-heated coal is charged to coke ovens through a pipeline entering the oven chamber near one end. The coal enters the oven in a dense phase state in a carrier stream of gas. The amount of coal dust rising to the top of the charged chamber and into the free space above the coal may vary widely, between as little as 100 pounds up to as much as 2500 pounds or more depending on several factors including amount and rate of introduction of the coal. As the carrier gas and any gases generated by the coal leave the oven chamber they will carry entrained coal dust out of the oven chamber. Most of this coal dust must be removed to prevent contamination of the byproduct system.

Coal dust in the exit gases is undesirable since it contaminates and makes the tar by-product difficult to process. It also clogs the spray outlets for re-circulated liquor in the by-product system. When it exceeds about 50 pounds per charge, the tar by-product cannot be processed satisfactorily with the processing equipment ordinarily used.

It was proposed to remove such coal dust using a cyclone disentrainment apparatus to remove the dust from the gases sent to the by-product system. However, this method was found to be impractical and expensive because the cyclone tended to gum-up and because of the requirement of a considerable amount of additional equipment.

It is one object of this invention to provide for the effective disentrainment of coal particles from gases evolved when a coke oven is pneumatically charged with fluidized coal.

It is another object of this invention to prevent the contamination and fouling of the by-product system of coke ovens by coal particles or dust liberated when charging with fluidized coal.

A further object of this invention is to provide an effective means for the disentrainment of coal particles from gases evolved when a coke oven is charged with preheated fluidized coal without the use of expensive additional equipment.

Other objects and advantages of the present invention will be evident from the following description of the invention and the accompanying drawings.

The present invention involves a method for the disentrainment of coal particles entrained in the gases evolved when a coke oven chamber is charged by introducing dry fluidized coal and carrier gas into one of a battery of heated coke ovens. In accordance with the present invention, the carrier gas and any carbonizing gases together with entrained coal dust are withdrawn from an outlet in the charged coke oven chamber at a point remote from the point of introduction of the coal and carrier gas. The withdrawn gas stream is then introduced into at least one of the other coke oven chambers in the battery which is in the coking stage whereby the coal dust in the gas stream comes into contact with the bed of coal and is removed from the gas stream in substantial amounts. Then the gas stream with a permissible amount of entrained coal dust is passed into the by-product systern.

The invention will be more clearly evident and described in detail with reference to the accompanying drawings, in which:

FIGURE 1 is the plan view of a plurality of adjacent coke oven chambers in a coke oven battery illustrating the use of jumper pipes to connect the central zone of one oven chamber with an end zone of the oven adjacent to it.

FIGURE 2 is a vertical section taken along line 22 of FIGURE 1.

Referring to the drawings, three adjacent oven chambers of a by-product coke oven battery adapted for pneumatic or fluidized charging of dry pre-heated coal are shown in FIGURE 1 for purposes of illustrating the invention. Methods and apparatus for the drying, pre-heating and pneumatic transfer of coal are known as illustrated in L. D. Schmidt US. Patent 3,047,473 of July 31, 1962. As shown in FIGURE 1, the fluidized coal is charged into an empty heated oven chamber 12 from a pneumatic transfer line or pipe 13. The oven chamber 12 is a typical coke oven chamber having a capacity of about 10 to 22 tons of coal and is charged with the fluidized coal at a rate usually between about 0.8 to 3.0 tons per minute, more usually between 1 to 2.5 tons per minute. The amount of carrier gas employed to deliver the coal along line 13 may vary widely in rate between about 5 to 100 pounds per minute, usually between 30 to pounds per minute depending largely on the rate of coal introduction. The pneumatic transfer line 13 is preferably equipped with a bleed line 14 just prior to the point of introduction into the chamber 12 whereby the carrier gas may be removed and the amount of such gas actually entering chamber 12 substantially reduced. The carrier gas is preferably steam although coal gas and other gases substantially free of elemental oxygen may be suitably employed. The time for pneumatic charging of oven chamber 12 may vary and is usually between about 5 to 15 minutes.

The pneumatically transferred coal entering chamber 12 contains large amounts of fine coal dust varying widely between about /2 to up to as much as 4 tons or even more per charge, usually between about 1 to 2 /2 tons per charge. A. substantial and usually the major portion of such dust becomes trapped or is retained below the level of the coal in the charged chamber 12 and thus does not represent a threat to the by-product recovery system.

The coal dust escaping into the free space at the top of oven chamber 12 along with the introduced carrier gas and other oven gases forms a gas stream containing the coal dust which flows toward the end of the chamber 12 opposite the end of coal introduction. In accordance with the present invention, the gas stream containing the carrier gas and coal dust that are evolved as the coal settles in oven chamber 12 are taken out through opening 15 by means of line or jumper pipe 16 to the adjacent oven chamber 17 containing previously charged coal which is desirably already in the coking stage, i.e. the coal is at a temperature above about 600 F. FIGURE 1 also shown a corresponding arrangement for transfer from an adjacent chamber (not shown) to chamber 12 involving an opening 18 in chamber 12 and a jumper pipe 19. None of the gases in chamber 12 will travel through opening 18 or line 19 since valve 21 in line 19 will be closed. The gases pass through opening 15, line 16 and opening 23 into oven 17 since valve 24 is open. The existing gases from oven 12 will pass into oven 17 by the draft created between the ovens due to pressure differences. The size of the jumper pipe needed may vary according to the type of charging of oven 12. It was found that when charging under turbulent conditions a 9 inch square jumper pipe was sufficient to convey the gases from one oven to another. As shown particularly in FIGURE 2, pipe 16 is equipped with clean-out doors 37 and 38 to permit removal of any dust deposits that form within the pipe 16.

The gases entering the oven chamber 17 flow over the bed of coal in oven 17 and substantial amounts of the entrained particles of coal dust are removed as the gas advances toward the by-product recovery outlet 25. Removal of the coal dust from the gas stream in chamber 17 is effected both by adherence of the dust to the leveled coal in the chamber and also by adherence to the walls of chamber 17 above the coal. The uneven surface of the coal at the top of the coal column in chamber 17 slows the progress of the gases and creates eddy currents promoting deposition of the fine dust on the coal and chamber walls. The residence time of the gases in chamber 17 will vary.

Deposition or removal of the coal dust in oven chamber 17 is enhanced by heating and maintaining the coal dust in the plastic range of temperatures for coal, i.e. 650950 E, where the coal dust is tacky and even more readily deposits on the chamber walls and previously accumulated dust. Such heating and deposition of the dust are desirably effected by having the coal in chamber 17 at least at a temperature at which the coal is undergoing coking, i.e. at least at a temperature of 600 F. Preferably, the coal is well into the coking stage and at a temperature above 1300 F., or at least about A the way through the coking cycle. In practice, the temperature of the coal in chamber 17 will depend upon the overall cycle of charging and coking employed in the particular coke oven battery. Accordingly in one preferred cycle, the chamber 17 will be at least about /2 to /4 the way through the coking cycle and the coal at a temperature above about 1700 F. Introduction of the gas containing coal dust into chamber 17 at such an advanced coking stage generally produces excellent results and also provides maximum available space above the coal for deposition due to the shrinkage of the coal column in this later coking stage. The gases advancing through the chamber 17 may be passed out of opening 25 into the by-product system. In situations where high coal dust contents must be handled, or where further high purity is desired, the gas stream passed through chamber 17 may be subjected to further processing by passing through one or more additional chambers. For this purpose, the chamber 17 is equipped with an opening 26 leading to line 27 to direct the gas stream processed in chamber 17 through line 27, with valve 28 open, to opening 29 and oven chamber 22. The gas stream from chamber 22 may then be sent to the byproduct recovery system through outlet 31 or through line 32 and opening 33 to another oven chamber (not shown).

The preferred connection between adjacent oven chambers as illustrated in FIGURE 1 is the central zone of oven chamber 22 with that zone of oven chamber 17 which is remote from the end at which it is charged. Thus, openings 18, 23, and 29 are in the central zones of ovens 12,

17, and 22 respectively while openings 15, 26, and 33 are openings at those ends of the ovens remote to the points at which they are charged and preferably just before the by- product outlets 34, 25, and 31. For example, in adapting heretofore conventional oven batteries, connections between adjacent ovens may be made through the roof openings used to charge the oven by larry car. However, the invention is not limited to the particular positioning and arrangements of connections illustrated. Generally, it is preferred that the gases evolved pass over a bed of coal in the adjacent oven chamber equivalent to at least about half of the length of the oven chamber. More usually, the gas stream with the entrained coal dust will pass over 50 to percent of the coal bed in the adjacent oven chamber.

The distance between the top of the beds of coal 39 and 41 and the top of ovens 12 and 17 will typically vary from to 2 /2 feet and usually will be about 1 to 2 feet. Through the free space in chamber 12 will pass the gases evolved from chamber 12 during charging on their way to the by-product outlet 25 in chamber 17. As these gases swirl in chamber 17 they will deposit coal particles on the sides of the oven chamber and on the bed of coal. Furthermore, since the coal dust particles will be heated to within the plastic range of temperatures of coal the coal particles will be sticky and deposit easily in chamber 17. This deposit will eventually cover a substantial portion of the bed of coal and fill a substantial portion of the free space above the bed of coal. Such a deposit carbonizes in chamber 17 and forms a frangible, porous deposit which is very brittle and easily crumbled under pressure. Thus it is readily removed along with the coke by means of the ram or pusher that discharges the coke from oven chamber 17 at the end of the coking cycle.

In practicing the present invention it is usually more preferred to effect the desired removal of coal dust from the gas stream during passage through a single oven chamber. Removal in only a single oven chamber has the advantage of permitting greater flexibility in selection of the charging and coking cycle for the overall coke oven battery and avoids the possibility that any one oven chamber will have to be employed to effect removal of dust originating from more than one chamber during a single cycle of the coke oven battery. Generally, a single oven chamber will remove substantial amounts of coal dust. However, the capacity of a single oven chamber to remove coal dust is not unlimited and in the typical oven chamber may vary between about 300-600 pounds of coal dust depending upon several factors including temperature of the oven chamber or stage of coking in the chamber, length of travel to the coal dust-containing gas stream in the chamber, and available space above the column of coal in the chamber. It can be appreciated therefore that removal of the coal dust in a single chamber in practical operation requires consideration of the amount of coal dust actually in the gas stream entering that chamber, and, in turn, the amount of dust liberated and entrained in the gases in the free space above the charged oven. Such an amount of coal dust, as discussed above, can vary widely and it is generally desirable to introduce fluidized coal potentially capable of liberating an amount of coal dust which will eventually enter the adjacent or removal oven chamber in an amount not exceeding the removal capacity of the chamber plus tolerable contamination in the gases finally exiting to the byproduct outlet, e.g. not more than about 50 pounds of dust. In situations where the amount of coal dust in the entering coal is in the higher ranges it has been found that the dust eventually liberated for carry-over may be controlled within the limits of the removal capacity of a single adjacent oven chamber without reducing the efficiency of the charging operation.

According to one preferred procedure it has been found that the dust liberated from the charged coal may be substantially reduced by bleeding or removing carrier gas from the fluidized coal just prior to entry or charging into chamber 12 from line 13. For this purpose the bleed line 14 is employed to vent between about 20% to 95% of the carrier gas in the fluidized stream, preferably between about 40% to 90% of the carrier gas. The structure and operation of such a venting apparatus is explained in the copending U.S. application of L. D. Schmidt, Ser. No. 382,609, filed July 19, 1964. In the charging of a typical coke oven chamber the amount of carrier gas will be reduced to preferably between about 5 to 30 pounds per minute entering the chamber, or to between about 5 to 15 pounds per ton of coal charged. Bleeding of the carrier gas reduces the amount and velocity of gas within the charged oven chamber and accordingly reduces the amount of dust entering the free space above the charged coal by promoting settlement of the coal dust within the established coal column in the chamber. According to another preferred procedure it has been found that the liberation of coal dust in the charged oven chamber 17 may be substantially reduced by preheating of the charged coal to a higher range of temperatures of at least about 350 F. up to about 650 F., preferably between 400 F. to 600 F. While such preheating tends to increase the amount of gas and gas velocities in the charged chamber by releasing by-product vapors from the coal, it has been found that overall a substantial reduction of liberated coal dust is effected. All the factors involved in such reduction are not known for certain although it is believed that the higher temperatures enable the coal dust to be more readily heated within the hot oven to the condition where the dust more easily adheres to the coal within the charged chamber. In a situation where the entering coal stream contains very substantial amounts of coal dust it is generally desirable to pre-heat the coal in the stream and/ or reduce the amount of entering carrier gas to control the coal dust eventually entering the removal chamber. P-re-heating and/ or bleeding of the carrier gas are especially effective in reducing carried-over coal dust to below 300-600 pounds so that removal to 50 pounds or less of dust in the gas entering the by-product system may be accomplished within a single adjacent oven chamber. Furthermore, it may also be employed to produce exceptionally good results by reducing the coal carry-over to 20 pounds or less within a single oven chamber.

It will be understood that the disentrainment method will take a variety of forms when applied to existing commercial ovens, because of the variety of conditions existing in various plants. Thus, the illustrations of the method that constitutes the invention given above are not intended to limit the invention in any way but are merely descriptive of the method. All modifications which fall within the spirit of the present invention are claimed as part of the present invention.

I claim:

1. A method for the disentrainment of coal particles entrained in the gases evolved when a coke oven chamber is charged by introducing a stream of coal and carrier gas into one of a battery of heated coke ovens which comprises:

(a) withdrawing a gas stream of carrier gas containing entrained coal dust from an outlet in the charged oven chamber at a point remote from the point of introduction of said coal and carrier gas;

(b) introducing and passing said withdrawn gas stream into at least one of the other oven chambers in the battery while said other chamber is in the coking stage whereby the said entrained coal dust comes into contact with the bed of coal and chamber walls; and

(c) withdrawing the said gas stream from said charged oven chamber with substantially reduced amounts of entrained coal dust.

2. The method of claim 1 in which said other oven chamber is in a coking stage sufficient to heat coal dust in the gas stream to a temperature within the plastic range of temperatures for coal.

3. The method of claim 1 in which the gas stream containing the entrained coal dust is passed over between about 50 to percent of the length of said other oven chamber.

4. The method of claim 1 in which the coal in the stream entering the oven chamber being charged is pre-heated to a temperature between about 350 F. to 650 F.

5. The method of claim 1 in which between 20% to of the carrier gas is removed from the stream of coal prior to entry into the oven chamber being charged.

6. The method of claim 5 in which the carrier gas is steam and a sufficient amount is vented off just before the coal stream enters the oven such that 5 to 30 pounds of steam per minute enter the Oven being charged.

7. The method of claim 5 in which the carrier gas is steam and in which 5 to 15 pounds of steam per ton of coal charged enter the oven being charged.

8. The method of claim 5 in which the coal in the stream entering the oven being charged is pre-heated to a temperature between about 350 F. to 650 F.

References Cited UNITED STATES PATENTS 7/1962 Schmidt 201-31 3/1968 Schmidt 201-40 U.S. Cl. X.R. 202262

Claims (1)

1. A METHOD FOR THE DISENTRAINMENT OF COAL PARTICLES ENTRAINED IN THE GASES EVOLVED WHEN A COKE OVEN CHAMBER IS CHARGED BY INTRODUCING A STREAM OF COAL AND CARRIER GAS INTO ONE OF A BATTERY OF HEATED COKE OVENS WHICH COMPRISES: (A) WITHDRAWING A GAS STREAM OF CARRIER GAS CONTAINING ENTRAINED COAL DUST FROM AN OUTLET IN THE CHARGED OVEN CHAMBER AT A POINT REMOTE FROM THE POINT OF INTRODUCTION OF SAID COAL AND CARRIER GAS; (B) INTRODUCING AND PASSING SAID WITHDRAWN GAS STREAM INTO AT LEAST ONE OF THE OTHER OVEN CHAMBERS IN THE BATTERY WHILE SAID OTHER CHAMBER IS IN THE COKING STAGE WHEREBY THE SAID ENTRAINED COAL DUST COMES INTO CONTACT WITH THE BED OF COAL AND CHAMBER WALLS; AND (C) WITHDRAWING THE SAID GAS STREAM FROM SAID CHARGED OVEN CHAMBER WITH SUBSTANTIALLY REDUCED AMOUNTS OF ENTRAINED COAL DUST.

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