US2747680A

US2747680A - Water quench and tar remover for cracked gases

Info

Publication number: US2747680A
Application number: US275840A
Authority: US
Inventors: Myron O Kilpatrick
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1952-03-10
Filing date: 1952-03-10
Publication date: 1956-05-29
Anticipated expiration: 1973-05-29

Description

y 29, 1956 o. KILPATRICK 2,747,680

WATER QUENCH AND TAR REMOVER FOR CRACKED GASES Filed March 10, 1952 QUENCHED 8. PURIFIED GAS INVENTOR.

MYRON O. KILPATRICK A ORA/E75 United States Patent WATER QUENCH AND TAR REMOVER FOR CRACKED GASES Myron 0. Kilpatrick, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application March 10, 1952, Serial No. 275,840 13 Claims. (c1. res-2 This invention relates to gas purification. In one aspect, it relates to the removal of tar from cracked gas. In another aspect, it relates to a method and apparatus for absorption and scrubbing. In another aspect, it re lates to phase separation or skimming.

Hydrocarbon cracking is known to be accompanied by tar formation. The presence of tar in a cracking effiuent causes operating difliculties by depositing in pipes, valves, blowers, etc. It is, therefore, desirable to remove the tar as soon as possible after the cracking step.

It is known to quench a cracked gas with water to cool the gas and elfect a partial removal of tar. Complete removal of tar is not thus obtained. It is also known to use an oil for quenching and tar removal. However,

most oils do not have the desirable heat-removing capacity that water has.

This invention provides the desirable quenching and tar removal properties of both water and oil. It does so in a simple, unitary system of apparatus, and effects an improved separation of oil, water, and tar from each other so that the oil and the water are readily available for recycling to the quenching apparatus.

According to this invention, gas effluent from a cracking system is contacted first with Water and then with oil in the same quenching zone to remove an and quench the gas. The function of the Water is primarily to cool the gas and scrub tar therefrom. The function of the oil is primarily to cool the gas further and remove any remaining tar therefrom by absorption or solution and scrubbing.

In a specific embodiment ofthe invention, the oil, the water, and the tar are removed from the quenching zone to a stratification zone, where the mixture stratifies into three phases, namely, an oil phase, a water phase, and a tar phase. The tar phase is withdrawn from the system. The oil and the water phases are separately recycled to the quenching zone.

In a further embodiment of the invention there is provided a quenching and tar removal apparatus comprising a quenching zone, gas inlet means in a lower part of said quenching zone, water introduction means in an intermediate part of said quenching zone, oil introduction means in an upper part of said quenching zone, gas withdrawal means at the top of said quenching zone, liquid withdrawal means at the bottom of said zone, stratification means communicating with said liquid withdrawal means, means for separately recycling oil and water from said stratification means to said quenching zone, and means for removing tar from said stratification means.

In another embodiment of the invention there is provided a stratification apparatus comprising a generally horizontal tank, oil skimming means in said tank, tar collecting means in said tank, oil withdrawal means attached to said skimming means, tar withdrawal means attached to said tank, and water withdrawal means attached to said tank.

The attached drawing illustrates one embodiment of the invention.

"ice

The gas quenched according to this invention will ordinarily be a gas withdrawn from a thermal cracking system such asa pebble heater. It will ordinarily have been preliminarily quenched to a temperature in the range 500 to 1000 F. before entering the system illustrated in the drawing.

The gas enters tower 2 through inlet 3 and passes upwardly through tower 2. Water introduced through inlet 22 and cooler 18 passes to spray means 5 in tower 2. The water counter-currently contacts gas in the tower, cools it and removes tar therefrom by scrubbing action. The gas which has been contacted with water passes up- Wardly through trays 4 and is counter-currentlycontacted with oil introduced through inlet 21, cooler 19 and onto the top tray in tower 2. The oil further cools the gas and removes the last traces of tar therefrom by scrubbing and absorption or solution. Cooled and scrubbed gas substantially free of tar is withdrawn through outlet 5 at a temperature in the range 50 to 200 F., preferably about F. The gas can be passed through condensing means 8 to remove therefrom by condensation any oil vapor remaining in the gas or it can be bypassed through conduit 7 and withdrawn through outlet 9. Any condensed material is returned to tower 2 through conduit 2t and inlet 21.

A mixture of water, oil and tar is withdrawn from the bottom of tower 2 and passed to settler 11. in settler 11 the mixture stratifies into an upper oil layer, intermediate water layer and lower tar layer. Oil collects in skimming member 12, which is attached to the top of settler 11 and which includes skimming member 12a and oil removal member 12b. The oil collected is removed through member 1212, conduit lS, and. conduit 17 and is recycled through inlet 21 to the top of tower 2. If desired, part of the oil may be withdrawn through outlet 23, and passed to means not shown for purification i. e., removal of dissolved tar. Water is recycled through conduit 16, inlet ,22 and cooler 18 to spray means 5. Baffie 13 in settler 11 serves to separate tar from water by retaining the tar and not allowing it to enter recycle conduit 16. Tar is withdrawn from the system through outlet 14 in the bottom of settler 11. If desired, settler 11 can be provided with a conical or pyramidal bottom to facilitate collection and removal of tar. Certain tars contain constituents which are insoluble, in part, in aromatic solvents and have a higher specific gravity than Water (See Perry, Chemical Engineers Handboo second edition, 1941, N. Y., McGraw-Hill Book Co., Inc., page 2375).

The oil used in the process of this invention is preferably an oil which is predominantly aromatic. Examples of suitable oils are benzene, toluene, anthracene oil; predominantly aromatic kerosenes having, for example, a boiling point in the range of 200 to 500 F; and a predominantly aromati-c gas oil, such as a gas oil recycled in a cracking system and having a boiling range of 400 to 700 F. Those skilled in the art will recognize that most of the foregoing solvents have a specific gravity less than that of Water. When a solvent having such a specific gravity is used, the embodiment shown in the drawing will be utilized exactly as shown. However, those skilled in the art will also recognize that certain anthracene oils have a specific gravity greater than 1. (See: Thorpes Dictionary of Applied Chemistry, fourth edition, volume 3, page 211, Longmans-Green & Co., N. Y., 1939). From the foregoing, those skilled in the art will recognize that when such an oil is used the relative positions of the oil and water layers in the stratification zone will be reversed with respect to that shown in the drawing.

Variation and modification are possible within the scope of the disclosure and claims to this invention, the essence of which is that a gas from a cracking system can be.

cooled and tar removed therefrom by contacting first with water and then with oil and that the oil, the water and the tar obtained can be separated from each other by stratification, the invention being conducted in a unitary system of apparatus comprising a quenching tower and a stratification means.

I claim:

1. A process for quenching a cracked gas and removing tar therefrom which comprises passing said gas upwardly through a quenching zone, contacting said gas with water in a lower part of said zone, contacting said gas with a predominantly aromatic oil in an upper part of said zone, recovering a quenched and purified gas from an upper part of said zone, removing a liquid mixture from a lower part of said zone, causing said mixture to stratify into an oil layer, a water layer, and a tar layer, recycling said water layer and at least part of said oil layer to said quenching zone, and withdrawing said tar layer from the system.

2. The process of claim 1 in which said oil is benzene.

3. The process of claim 1 in which said oil is toluene.

4. The process of claim 1 in which oil is an anthracene oil.

5. The process of claim 1 in which said oil is an aromatic kerosene.

6. The process of claim 1 in which said oil is an aromatic gas oil.

7. The process of claim 1 in which said gas is initially at a temperature in the range 500 to 1000 F. and is quenched to a temperature in the range 50 to 200 F.

8. Apparatus for quenching a gas and removing tar therefrom, said apparatus comprising in combination: a gas-liquid contactor; gas inlet means in a lower part of said contactor; gas outlet means in an upper part of said contactor; water introduction means in an intermediate part of said contactor; oil introduction means in an upper part of said contactor; liquid withdrawal means in a lower part of said contactor; stratification means communicating with said liquid withdrawal means; means for separately recycling oil, and water from said stratification means to said contacting means; and means for withdrawing tar from said stratification means.

9. The apparatus of claim 8 in which said water introduction means is a spray means and in which the upper part of said contactor contains gas-liquid contacting trays.

10. Apparatus for separating water, oil, and tar by stratification, which comprises, in combination: a generally horizontal tank; liquid inlet means at one end of said tank; liquid collecting means attached to the top of said tank and including two side wall members, a bottom member and a liquid withdrawal member in open communication with the interior of said collecting means through said bottom member, one of said side wall members being attached to the top of said tank and to said bottom member, and the other of said side wall members being attached to said bottom member and extending upwardly to a level below the top of said tank, the latter side wall member being positioned intermediate the firstmentioned side wall member and said liquid inlet means; a vertical baffle attached to the bottom of said tank; tar withdrawal means connected to the bottom of said tank; liquid withdrawal means connected to the bottom of said tank; said bafiie being positioned between said liquid withdrawal means and said tar withdrawal means and adapted to prevent tar from entering said liquid withdrawal means.

11. A process for quenching a cracked gas and removing tar therefrom which comprises passing said gas upwardly through a quenching zone, contacting said gas with water in a lower part of said zone, contacting said gas with an oil in an upper part of said zone, causing oil to flow downwardly through the entirety of said zone and water to flow downwardly through the entirety of said lower part of said zone recovering a quenched and purified gas from an upper part of said zone, removing a liquid mixture from a lower part of said zone, causing said mixture to stratify into an oil layer, a water layer and a tar layer, and recovering each of said layers separately.

12. Apparatus for quenching a gas and removing tar therefrom, said apparatus comprising in combination: a gas-liquid contactor; gas inlet means in a lower part of said contactor; gas outlet means in an upper part of said contactor; water introduction means in an intermediate part of said contactor; oil introduction means in an upper part of said contactor; liquid withdrawal means in a lower part of said contactor; and stratification means communieating with said liquid withdrawal means and comprising a closed container adapted to contain liquid, said container being in open communication with said liquid withdrawal means at one end of said container, liquid collection means attached to the top of said container and including two side wall members, a bottom member, and a liquid withdrawal member in open communication with. the interior of said collecting means, one of said side wall members being attached to the top of said container and to said bottom member and the other of said side wall members being attached to said bottom member and extending upwardly to a level below the top of said container, the latter side wall member being positioned intermediate the first-mentioned side wall member and said liquid withdrawal means, a vertical baffle attached to the bottom of said container and extending across said container to the walls thereof, tar withdrawal means at the bottom of said container, liquid withdrawal means connected to the bottom of said container, said vertical battle being positioned between said liquid withdrawal means and said tar withdrawal means and adapted to prevent tar from entering said liquid withdrawal means.

13. A process for removing tar from a gas, which process comprises introducing said gas into one end of a scrubbing zone, introducing water at an intermediate part of said scrubbing zone and causing water thus introduced to flow countercurrently to said gas, introducing oil adjacent the opposite end of said zone and causing thus introduced oil to flow countercurrently to said gas substantially throughout the length of said zone, withdrawing oil, water and tar at the end of said zone adjacent the point of gas introduction, and withdrawing scrubbed gas from said zone at the end adjacent the point of oil introduction.

References Cited in the file of this patent UNITED STATES PATENTS 748,981 Oliver Jan. 5, 1904 911,314 Maranville Feb. 2, 1909 963,401 Solvay July 5, 1910 1,116,903 McClintock Nov. 10, 1914 1,457,877 Doty June 5, 1923 1,487,768 Torrey Mar. 25, 1924 1,830,178 Sperr Nov. 3, 1931 1,905,423 Rhodes et a1. Apr. 25, 1933 1,960,679 Parkhurst May 29, 1934 2,457,959 Walker Jan. 4, 1949 2,675,095 Bogart Apr. 13, 1954 2,676,670 Gagnaire Apr. 27, 1954 2,715,948 Lewis et al. Aug. 23, 1955 FOREIGN PATENTS 591,094 France Apr. 1, 1925

Claims

11. A PROCESS FOR QUENCHING A CRACKED GAS AND REMOVING TAR THEREFROM WHICH COMPRISES PASSING SAID GAS UPWARDLY THROUGH A QUENCHING ZONE, CONTACTING SAID GAS WITH WATER IN A LOWER PART OF SAID ZONE, CONTACTNG SAID GAS WITH AN OIL IN AN UPPER PART OF SAID ZONE, CONTACTING OIL TO FLOW DOWNWARDLY THROUGH THE ENTIRETY OF SAID ZONE AND WATER TO FLOW DOWNWARDLY THROUGH THE ENTIRETY OF SAID LOWER PART OF SAID ZONE RECOVERING A QUENCHED AND PURIFIED GAS FROM AN UPPER PART OF SAID ZONE, REMOVING A LIQUID MIXTURE FROM A LOWER PART OF SAID ZONE, CAUSING SAID MIXTURE TO STRATIFY INTO AN OIL LAYER, A WATER LAYER AND A TAR LAYER, AND RECOVERING EACH OF SAID LAYERS SEPARATELY.