US2039835A - Method of coking hydrocarbons - Google Patents

Description

May 5, 1936- R. s. PETERSEN Er AL 2,039,835

METHOD OF COKING HYDROCRBONS Filed Dec. 18, 1933 Hw EN WN NN km2@ 123k Patented May. 5, 1936 UNITED STATES PATENT OFI-'lola'. l

METHOD 0F COKING HYDBOCABBONS Application December 18, 1933, Serial No. 702,846

2 Claims.

This invention relates to a new and improved method of coking hydrocarbons. During past years the method of coking heavy residues in externally heated steel coking stills has been extensively used. On account of the very heavy maintenance and labor cost this method has been gradually replaced by coking either in the reaction chamber of cracking units or in coking chambers internally heated by hot oils or vapors to the point where coking takes place. In both these methods the coke produced is usually greatly reduced in value due both to its being broken up in removal and also its high percentage of volatile matter.

In United States Patent No. 1,805,711', a successful method of coking such hydrocarbons is described. This method has been found to produce a much more satisfactory grade of coke than prior methods and also does away with the diiiiculties of removal which heretofore have existed. We have found that with certain charging stocks a tendency to coke up the heater was in evidence and also that the overhead oils produced were not of as low viscosity and cold test as might be desired.

It is an object of the present invention to provide a new and improved method of coking hydrocarbons.

It is a further object .to provide a method in which the charging stock for the coking step is treated to remove volatiles and lighter fractions before being introduced into the coking unit.

It is an additional object to provide a method in which'the charging stock is heated as well as stripped of its lighter constituents so that the through put of the coking unit is increased.

It is also an object to provide a coking method adapted for the production of valuable by-products.

0ther and further objects will appear as the description proceeds.

This invention relates more specifically to an improvement on that step in the coking process which comprises heating the charging stock before its introduction into the coking ovens. This is accomplished by taking the usual heavy residues from previous operations usually at a temperature of between 700 F. and 800 F., under usual discharge pressure and flashing into a tower, preferably under vacuum conditions. The release of pressure results in flashing off gas oil and lighter distillates which may be contained therein. These ascend through the trays of the column in the tower. A drawoif deck located at a suitable point vertically of the tower, enables (c1. 19a-4s) a stream of gas oil to be removed from the tower. Thisstream is pumped through a heater where its temperature is raised usually in excess of 850 F. In turn it is again discharged into the tower at a point separated from the drawoii deck by bubble trays, over which reflux is passed. The hot vapors discharged into the tower further increase the temperature of the bottoms, thus flashing oil additional light fractions and increasing the gravity of the bottoms to, in some cases, as low as 1 to 3 A. P. I. gravity. This material is then fed into the ovens at a temperature preferably above '750 F. where it readily cokes. The overhead products from the oven may be discharged into the same tower below the bubble decks if this is desired. With proper fractionation the products of the operation are coke, gas, gas-oil, and distillate, all of good quality and readily saleable. The distillate may be fractionated to have a desired end point or returned to the main cracking unit for rerunning.

In actual operation this method has resulted in keeping the heater as well as the tower free from carbon deposits for long periods, both of which are highly desirable. A further advantage is the greater production of overhead products in the tower rather than in the oven. 'Ihis decreases the load on the oven, thus increasing the through put, and also results in a better quality of product. The passage through the heater also reduces the viscosity and pour point of the gas oil which is removed for sale, thus greatly increasing its value.

We have shown in the single figure of the accompanying drawing, somewhat diagrammatically, an elevation of one layout of apparatus adapted for carrying out our\improved methods of treatment.

In the drawing the line II serves to introduce the charging stock, this line being controlled by a valve I2 and terminating at I3 below the trays in the fractionating or flash tower Il. Line Ila, controlled by valve I3b, may also be used if desired toheat the feed by introducing it with the heated material from the pipe still. The line I5 leads from the upper end of the tower Il through condensers vI6 to a gas separator I1. The gas line I8 leads from the top of the separator. The distillate line I9 leads from the bottom of the separator through pump 20 to the junction of lines 2I and 22 controlled by valves 23 and 24 respectively. The line 2| leads to any desired distillate using or holding apparatus. 'Ihe line 22 leads to the upper portion of the tower Il andservea to 1 return the distillate for use in reiiuxing in the tower.

'I'he tower I4 is provided with drawo'i! decks indicated at 23 and 23. The line 21 leads iromthe deck 23, this line being controlled by valve 23 and leading to any desired holder for distillate drawn oil' at this point. The line 23 leads from the deck 23 through pump 33 to a junction with line 3| controlled by valve 32. The line 3I passes through cooler 33 and leads to any desired holding apparatus for the gas oil drawn of! at this point. The line 23 leads on to a Junction with line 34, line 34 being controlled by valve 33. 'Ihis line 34 has a branch 33 leading into the top of the iiash tower 31. The line 34 further continues through valve 33 to a junction with line 33. Line .33 is provided with branches 43 and 4I leading into the top of the overhead oiitakepassages 42 and 43 which lead from the coke ovens 44 and 43.

Beyond the junction with line 34, the line 23 is controlled by valve 43 and leads vto the pipe still 41. The line 43 leads from the pipe still into the lower end of the iractionating or iiash'tower I4. 'I'he bottom of the iractionating or ilash tower I4 is provided witha drawoii 43 which passes through pump 33 to a Junction with line 3l which is controlled by valve 32. The line 3| connects' the feed line II with the line 43. The line 49 leads through valve 33 and valve 34 to a discharge into the lower portion oi the ash tower 31. The line 43 is provided with a by-pass line 35 which connects to the line 43 on opposite sides of valve 53. 'I'he line 33 is provided at its opposite ends with valves 33 and 31. The line 33 is located in an enlargement 33 in the ontake iiues from the heating passages 33 and 33 located below the floors oi' the coke ovens 44 and 43.

'Ifhe line 49 is further provided with branch lines 3| and 32 controlled by valves 33 and 04 respectively, these branch lines leading into the top of the coke ovens 44 and 43. The oil'take passages 42 and 43 from the coke ovens Join in thev main 65 which discharges into an intermediate portion of the ilash tower 31. The line 33 is provided for carrying oit the overhead from the flash tower 31, this line extending from the top ot that tower to a point below the drawoii deck 23 in the iractionating or ilash tower I4. The line 33 is controlled by valve 61. '111e lower portion of the flash tower 31 is provided with an cfftake 33 passing through pump and leading through valve 10 to the line 1I controlled by valve 12. The line 1I leadsintotheend ofthemain 33 and mayserve to introduce liquid for ilushing the line. 'Ihe line 13 controlled by valve 14 passes through cooler- 13 and leads to the line 33. 'I'he lower end oi' the iiash tower 31 is also provided with Vthe ontake line 16 which passes through pump 11 and leads through valve 18 into the lower portion of the iractionatlng or ash tower I4.

In one method of carrying out our improved treatment of liquid hydrocarbons, the liquid hydrocarbons will be led through feed line II, past valve I2 and into the lower end of the fractionating or ash tower I4. Ii desired some or all o! the hydrocarbons may pass through line I3a, past valve I3h to a Junction with lineA 43 to further heat the feed. The valve 32 will be closed. 'Ihis ieed liquid or charging stock may be at a temperature oi approximately 780 F. and under approximately 50 pounds pressure. It will be discharged into the lower end oi the tower I4 and the lighter portions will iiash oi! and pass upwardly through the tower. The overhead passing out oi' the top -of the tower goesv through condenser-s I3 still 41 from which they are returned to the bottom o! the tower I4. These lighter products may be heated in the pipe still to a temperature of vfrom 850 to 1100 degrees F. without danger of serious deposit oi' carbon in the still. These heated products will carry into the hash tower I4 suiiicient heat so as to maintain the heat loss by the vaporization of the charging stock in the bottom of that tower, and will be further flashed in the tower upon discharge therein. The distillate in the ilash tower 31, which will come in hot from the coking ovens, may also be added to the material in the bottom oi tower I4, being added through line 13. Further, the overhead from the iiash tower 31 may be introduced at an intermediate point into the tower I4 through line 33.

The heavy bottoms from the bottom of tower I4 are forced through line 49 by pump 53 and discharged through lines 3'I and 32 into the top oi' the coke ovens 44 'and 43. Ii' desired, these bottoms may be further heated by closing valve 33 and opening valves 33 and 31 in which case the bottoms will pass through the line 55 and be heated by the hot products of combustion leaving the flues oi the ovens. A portion oi the gas oil drawn oil' through line 29, Vinstead of being heated in the pipe stili and returned to the tower I4, will be passed through the line 34 and line 36 and used as a reiluxing agent in the ilash tower 31. A portion of this gas oil may be also used to wash down the oii'takes 42 and 43 of the coke ovens. 'I'he distillate from the bottom oi the tower 31 may partly be used for washing down the oil'takes 42 and 43, being led to that point through lines 33 and 4I and 42. This material may be also passed through line 1I to wash down the main 33. 4Gas oil from the tower I4 may be also used to wash down the main 33 ii desired, or these two materials may be mixed for that purpose.

It will be understood that the volume of feed inthetower I4willbesuchastogivetimein the tower for the proper vaporization of the lighter constituents ot the feed material. The apparatus shown is by way of illustration only and it will be understood that the method may be carried out in other and diiierent forms oi apparatus. As an example oi' such modifications the functions oi' the towers 31 and I4 may be carried on in a single unit, in which case the overhead from the coke ovens would be introduced into the lower portion oi' the combined unit.

In one case oi' actual operation l2 A. P. I. charging stock was introduced into a unit through line II at a temperature of 750 F. into the base of iractionating tower I4; A considerable amount oi' gas oil contained in the hot tar was distilled by the reduction in pressure to approximately 2" oi' mercury vacuum. The temperature maintained at the base of the tower was on the order oi.' 730 F. The gas oil distilled was fractionated in the tower and withdrawn from drawoi! deck 23 through line 23 at a temperature of 600 l". In pipe still 41 this was mildly cracked by heating to a temperature of 930 F., being then reintroduced into tower I4 through line 48, thereby supplying heat for the distillation and fractionation of the gas oil derived from the tar charging stock. 'The stripped tar remained liquid at the base of tower I4, and was then transferred by pump 50 and line 49 directly into the coke ovens in which, by the addition of heat through the refractory floor, it was reduced to a hard, dry coke. Gas and vapors formed in the ovens, after leaving the coke layer, were reduced in temperature to approximately 600 F. in order to prevent further cracking. I'his cooling was effected by introducing cool oil. 'I'he vapors and any entrained carbon particles were then washed by hot reflux in the equivalent of flash tower 31, this washing zone having been incorporated in the base of tower I4 for simplicity of construction. When operating as described above and charging a tar derived from a cracking operation the following yields were obtained: 400 end point distillate-3.3%; 22 A. P. I..gas oil of low cold test-55.9%; coke 14.6%; gas 26.2%.

It will be further understood that the method itself is capable of modification and change to meet varying conditions and requirements and we contemplate such variations as come within the spirit and scope of the appended claims.

We claim:

1. A method of coking hydrocarbons in fluent form which comprises passing said hydrocarbon charge to a flashing zone maintained at subatmospheric pressures, passing vapors formed directly to a fractionating zone in which said vapors are fractionally condensed by refluxing to form a condensate containing materials of high viscosity and high pour point, drawing off fractionated condensate from the fractionating zone, heating said condensate to a temperature in excess of 850 F. whereby the viscosity and pour point are reduced, returning said condensate to the flashing zone which flashing zone precedes the fractionating zone from which said high viscosity and high pour point condensate` is withdrawn, withdrawing additional condensate of low pour point and low viscosity as a product of the operation at a point above the drawoff of the high viscosity, high pour point condensate, utilizing the heat of the condensate returned to the flashing zone to drive oi! simultaneously additional lighter fractions from said charge, thus reducing the charge to a pitchy material of approximately 1 to 3 A. P. I. gravity, discharging the pitchy material while hot into an externally heated coking chamber under approximately atmospheric pressure, distilling of! volatiles in said chamber, separating said overhead volatile products into liquid and relatively clean vaporous fractions in an intermediate zone, fractionating said vaporous fractions in said first mentioned fractionating zone, passing liquid portions from the intermediate zone to the ash zone, and coking the pitchy material to a hard, dense coke.

2. A method of coking hydrocarbons in fluent form which comprises passing said hydrocarbon charge to a flashing zone maintained at subatmospheric pressures, passing vapors formed directly to a fractionating zone in which said vapors are fractionally condensed by refluxing to form a condensate containing materials of high viscosity and high pour point, drawing oft' fractionated condensate from the fractionating zone, heating said condensate to a temperature in excess of 850 F. whereby the viscosity and pour point are reduced, returning said condensate to the flashing zone which flashing zone precedes the fractionating zone from which said high viscosity and high pour point condensate is withdrawn, withdrawing additional condensate of low pour point and low viscosity as a product of the operation at a point above the drawoff o1' the high viscosity, high pour point condensate, utilizing the heat of the condensate returned to the flashing zone to drive of! simultaneously additional lighter fractions from said charge, thus reducing the charge to a pitchy material of approximately 1 to 3 A. P. I. gravity, further heating the pitchy material and discharging the pitchy material while hot into an externally heated coking chamber under approximately atmospheric pressure, distilling off volatiles in said chamber separating said overhead volatile products into liquid and relatively clean vaporous fractions in an intermediate zone, fractionating said vaporous fractions in said first mentioned fractionating zone, passing liquid portions from the intermediate zone to the flash zone, and coking the pitchy material to a hard, dense coke.

ROY S. PETERSEN. CHARLES W. ANDREWS.

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