US2972393A - Process for treating coke oven gas - Google Patents

Description

Feb. 21, 1961 s. B. BUSH PROCESS FOR TREATING COKE OVEN GAS Filed March 25, 1959 INVENTOR STANLEY BBUSH MQW@ ATTORNEY' PROCESS FOR TREATIN G COKE OVEN GAS Stanley B. Bush, Ramsey, NJ., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed Mar. 25, 1959, Ser. No. 801,745 6 claims. (cl. 18s-12o) This invention relates to a process for treating coke oven gas and, more particularly, for cooling coke oven gas containing naphthalene.

In the recovery of by-products from coke oven gas, the gas is passed through a primary cooler where it exits saturated with naphthalene at about 98 to 103 F. The gas exiting the primary cooler is passed though an extractor for the separation of tars and then through a sulfuric acid saturator for the removal of ammonia. The gas leaving the saturator is carried to a final cooler in order to reduce the gas temperature suiiiciently for efiicient removal of light oil constituents (i.e. benzol and its homologues) from the coke oven gas. In the final cooler, the coke oven gas is cooled by direct contact with cooling water to a temperature of about 75 to 90 F., at which temperature naphthalene precipitates in the form of crystals. The naphthalene slurry leaving the final cooler is collected in pans. Most of the naphthalene rises to the surface of the water where it is skimmed off and recovered. The residual water is generally recooled and recirculated to the final cooler. For the sake of efiiciency, coke oven gas has been subjected to final cooling in multicompartment, spray-type towers. However, in such operation, sublimed naphthalene accumulates on the surface of the cooling water as blocking and insulating deposit and clogs up spray devices and other parts of the equipment.

The principal object of the present invention is to provide an etcient and economical process for final cooling vof coke oven gas containing naphthalene. Other objects and advantages of the invention will be apparent from the following description and accompanying drawing.

In accordance with the present invention, a process for cooling coke oven gas containing naphthalene to temperature at which naphthalene crystallizes out is carried out by passing a stream of the coke oven gas upwardly through a series of superposed vertically elongated contact zones, spraying cooling water downwardly, countercurrent to the stream of colte oven gas, through said series of contact zones, accumulating cooling water passing downwardly in the form of a pool at the bottom of each contact zone and out of direct contact with said coke oven gas, decanting water containing surface naphthalene crystals from the pool in each contact zone ex- -cept the lowermost and iiowing the decanted material, out of direct contact with the coke oven gas, to the pool in the subjacent contact zone, withdrawing liquor remaining after the decantation from upper pools and -spraying said liquor into lower contact zones, removing 'water containing naphthalene crystals as a slurry from the lowermost zone and recovering cooled coke oven gas from the uppermost zone.

In preferred practice of the invention, the cooling water is introduced in the form of a substantially conical .spray from the top portion of each contact zone, except -the uppermost, and the coke oven gas is passed through 'y United States Patent O rifice substantially the shape and form of the conical spray. In addition, it is preferred to accumulate the cooling water sprayed into each zone, except the lowermost, in a substantially annular receiving space positioned in the lower peripheral portions of said zone.

One type of apparatus which may be used in practice of the invention involves a countercurrent contact tower comprising a plurality of successive contact chambers. Each chamber contains a spray device at its top and an open-ended frusto-conical baffle extending upwardly from the walls of the chamber to the central portion thereof for directing gas flow inwardly toward the spray. A substantially annular receiving space for collecting liquid spray is provided between the chamber walls and the lower end of each baffle. In connection with each receiving space, a pump is provided for discharging liquid withdrawn from the receiving space to the spray device of the subjacent chamber. Further, each receiving space is provided with an overow pipe disposed so as to discharge collected liquid containing surface naphthalene into the receiving space of the subjacent chamber.

I have found that in operation of the process of this invention, economical and efficient cooling of the coke oven gas is accomplished and surface naphthalene which would otherwise plug up various parts of the apparatus, as well as represent loss of naphthalene, is readily removed from the system. Further, the process permits use of cooling equipment designed for maximum heat transfer efficiency, Moreover, it has been found that the vprocess of the invention enables such efficient contact of coke oven gas and cooling water that ammonia present in the coke oven gas may be absorbed in the water during the cooling, thus obviating necessity for prior removal of ammonia in a sulfuric acid saturator. In carrying out such operation, it is necessary to use cooling water which is substantially free of ammonia.

Theattached drawing represents a vertical sectionalV View of apparatus used in attaining the objects and advantages of the present invention.

In the drawing, a countrecurrent contact towerY is shown which comprises a vertical cylindrical shell or casing l having a gas inlet line 2 and a cooling water outlet line 3 in the bottom of the casing and a gas outlet line 4 and a cooling water inlet line 5 in the top part of the casing. The contact tower is provided with a series of interconnected, vertically contiguous contact chambers disposed between the sets of inlets and outlets. Within the tower is disposed a series of open-ended frusto-conical , baffles 9, 9a, 9b, 9c and 9d. These baffles which extend upwardly from the walls of the tower to the central portion thereof serve to define the respective contact chambers of the tower. v

Coke oven gas which has been cooled in a primary cooler, e.g. to rabout 98 to 103 F., and has then been denuded of tar and, if desired, of ammonia is introduced at a temperature of about to 130 F. through line 2. This gas which contains naphthalene in non-saturating amount passes upwardlythrough each contact chamber and finally passes out of the vtower through line 4. Cooling water, which may be fresh or salt water, is introduced at a temperature of about 70 to 85 F. via line 5 to spray means 6 comprising a plurality of pressure spray nozzles disposed at the top of uppermost chamber 7. The cooling water sprayed downwardly from spray means 6 is collected as a pool in a substantiallyanuular receiving space 8 positioned between the walls of the tower and baffle 9. Spray means 6 possesses the added function of reducing entrainment of liquid in the coke oven gas before it exits the tower.

An overflow pipe 12 extends downwardly from the pool in receiving space 8 into the subjacent chamber and' permits overflow ofk water containing surface naphthalene into the receiving space 3a below. Pipe 12 desii-ably is sealed by extending it below the surface of the liquid in receiving space 8a. Although the overflow pipe, as shown, is within casing it may be positioned loutside the casing, if so desired. In order to provide for removal of all of the surface naphthalene, it is preferred that about 7 to 15%, e.g. about 10%, of the total cooling water be allowed to overow to the next receiving space. With progressive overllowing of the cooling water containing surface naphthalene through overilow pipes 12a, 12b, 12e and 12d, all of the surface naphtbalene is recovered as a slurry in the bottom of the tower.

The lower portion of cooling .water in receiving space 8 flows through pipe .i4 and is pumped by means of pump through line 16 to spray means 1l for spraying into subjacent chamber 13. Spray means 11, like the spray means in each lower section of the tower, comprises a pressure spray nozzle. While only one spray nozzle is preferred, as shown in the drawing, a plurality of nozzles may also be employed.

As the gas passes upwardly through battle 9 which contines it laterally to the general space occupied by the spray, it meets the descending spray of cooling water from spray means l1. Similarly, as the gas passes upwardly through each of batlies 9d, 9c, 9b and 9a, it contacts spray from spray means iid, lic, 1lb and 11a, respectively. The gas rst enters the confines of each bae at relatively low velocity and accelerates as it is directed toward the center of the tower. Finally, when it exits the top of the baie, it decelerates. At points of acceleration the transfer coefficient between liquid and gas is high, whereas at points of deceleration detrainment of liquid from the gas occurs. Preferably, the cooling water is introduced into each chamber, except the uppermost, in the form of a substantially conical spray, and the coke oven gas is passed through substantially the shape and form of the conical spray. Such operation insures cooling efficiency by providing maximum liquid-gas contact.

The lower portion of the cooling water collected in receiving space 8a flows through line 14a and is pumped by means of pump 15a through line toa to spray means 11a for spraying into subjacent chamber 17. The lower portion of the cooling water collected in receiving space 8b is removed through line 141; and pumped by means of pump 15b through line 16h to spray means 11b for spraying into subjacent chamber i8. Similarly, the lower portion of the cooling water collected in receiving space 8c ows through pipe 14e and is pumped by means of pump lSc through line 16C to spray means llc for spraying into subjacent chamber 19. Finally, the lower portion of the cooling water collected in receiving space 8d is removed through line 14d and pumped by means of pump 15d through line 16d to spray means 11d for spraying into subjacent chamber 21.

The slurry of naphthalene collected in the bottom of chamber 21 is removed from the tower through line 3. Chamber 21 is provided with an inclined base 22 to facilitate removal of the slurry. Naphthalene may then be recovered from the slurry by any conventional procedure, such as by decantation or by scrubbing with a suitable solvent, e.g. creosote oil.

The cooled coke oven gas exiting the tower through line 4, usually at a temperature of about 75 to 90 F., is saturated with naphthalene and may be further treated to recover its naphthalene and light oil constituents.

While six contact chambers are shown in the drawing, any number of chambers may be employed, depending, ofcourse, upon process requirements.

The gas-liquid contact provided by operation of the illustrated tower makes it possible to obtain a highly efficient molecular interchange between gas and liquid, and, atl the same time, makes it possible to remove surface naphthalene from the system so that plugging of 4 the apparatus at various points does not occur. Moreover, as indicated before, the ammonia content of the gas may be efficiently removed during the present operation.

ln typical operation, coke oven gas which has been subjected to primary cooling and has been denuded of tar contains about grains of naphthalene per hundred cubic feet of gas. The gas is introduced at a temperature of about to 130 C. and at velocity of about 4,000 feet per minute into the tower through inlet 2. The actual velocity of the gas as it passes upwardly through the tower is about 300 feet per minute. Cooling water at a temperature of about 70 to 85 F. is sprayed at the rate of about 5 gallons per 100 cubic feet ot colte oven gas (SLP.) into the uppermost chamber of the tower, countercurrent to the upwardly rising gas. rlhis water cools the gas to a iinal temperature of about 75 to 90F., thereby causing precipitation of naphthalene crystals.

The cooling water sprayed into each chamber, except the iowermost, collects as a pool in the receiving space between the chamber walls and the lower end of the baille or the subjacent chamber. Cooling water containing naphthalene crystals on its surface overflows from the pool at the rate of about 100 gallons per minute to the receiving space of the subjacent chamber. Liquor is withdrawn from the lower portion of the pool, pumped to the spray device of the subjacent chamber and sprayed thereinto. With progressive overiiowing of the water containing surface naphthalene crystals, the naphthalene crystals are nally removed as `a slurry from the bottom of the tower through line 3. Naphthalene may then be recovered from the slurry by scrubbing with creosote oil.

The finally cooled gas exits the tower through line 4 at a temperature of about 75 to 90 F. and contains about l5 to 60 grains of naphthalene per hundred cubic feet of gas. This gas may then be subjected to further conventional processing in order to recover naphthalene and light oil therefrom.

Although certain preferred embodiments of the invention have been disclosed for purposes of illustration, it is evident that various changes and modification-s may be made therein without departing from. lthe spirit and scope of the invention.

l claim:

1. A process for cooling coke oven gas containing naphthalene to temperature at which naphthalene crystallizes out which comprises passing a stream of the coke oven gas upwardly through a series of superposed vertically elongated contact zones, spraying cooling water down.- wardly, countercurrent to the stream of colte oven gas, through said series of contact zones, accumulating cooling water passing downwardly in the form of a pool at the bottom of each contact zone and out of direct contact with said coke oven gas, decanting water containing surface naphthalene crystals from the pool in each contact zone except the lowermost and flowing the decanted material, out of direct contact with the colte oven gas, to the pool in the subjacent contact zone, withdrawing liquor remaining after the decantation from the upper pools and spraying said liquor into lower contact zones, removing water containing naphthalene crystals as a slurry from the lowermost zone and recovering cooled colte oven gas from the uppermost zone.

2. A process as claimed in claim 1 wherein the cooling water is introduced in they form of a substantially conical spray into the top portion of each contact zone, except the uppermost, and the coke oven gas is passed through substantially the shape and form of trie conical spray.

3. A. process as claimed in claim 2 wherein the cooling water sprayed into eachcontact zone, except the lowermost, is accumulated in a substantially annu-lar receiving space positioned in the lower peripheral portions of said zone.

4. A process as claimed in claim 3 wherein the coke oven gas is cooled from a temperature of about 120 to 130 F. to a temperature of about 75 to 90 F.

5. A process for cooling colte oven gas containing naphthalene from a temperature of about 120 to 130 F. to a temperature of about 75 to 90 F. which cornprises passing a stream of the coke oven gas upwardly through a series of superposed vertically elongated contact zones, spraying cooling water downwardly, countercurrent to the stream of coke oven gas, through said series of contact zones, accumulating cooling water passing downwardly in the form of pool at the bottom of each contact zone and out of direct contact with said coke oven gas, permitting about 7 to 15% of total cooling water containing surface naphthalene crystals to overflow, out of direct contact with the coke oven gas, from the pool in each contact zone except the lowermost to the pool in the subjacent contact zone, withdrawing liquor remaining after the decantation from the upper pools and pumping said liquor to spray means for spraying into lower contact zones, removing water containing naphthalene crystals as a slurry from the lowermost zone and recovering cooled coke oven gas from the uppermost zone.v y

6. A process as claimed in claim 5 wherein the coke oven gas contains ammonia, as well as naphthalene, and the water employed for cooling the gas is substantially free of ammonia.

References Cited in the tile of this patent FOREIGN PATENTS 1,868,886 Collins July 26, 1932 2,484,918 Wentworth Oct. 18, 1949 2,810,450 Hartmann z Oct. 22, 1957

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