US2908625A - Olefin production process - Google Patents

Description

Oct. 13, 1959 v. MEKLER ETAL OLEFIN PRODUCTION PROCESS Filed Jan. 17, 1955 AUnited l States Patent() OLEFIN PRODUCTION PROCESS `Valentine Mekler, Hastings ln Hudson, and August H.

Schutte, `lackson Heights, N.Y., and Karl J. Korp, Altadena, Calif., assignors to The Lummus Company, New York, N.Y., a corporation of Delaware Application January 17, 1955, Serial No. `482,031

t 6 Claims. (Cl. 208-454) This invention relates to improvements in apparatus for the production of gaseous olefins vfrom heavy residual hydrocarbons such as asphalt, tars and heavy reduced crudes.

In Schuttes Patent No. 2,526,696, the advantages were disclosed of carrying out the'conversion of heavy oils to oletns by a two-stage cracking process wherein the oil was iirst subjected to a liquid phase, relatively low temperature cracking to produce a maximum amount of low carbon residue, vaporous products and simultaneously convert the heavy carbon forming constituents of the oil into coke, followed by a short-time high temperature cracking of the gaseous and vaporous products from the Such a method represented a sigm'cant improvement over previous processes for the high temperature cracking of .residual oils wherein these oils were charged directly to the high temperature olen producing pyrolytic zone. The direct application of the heavy oil inevitably resulted in carbon formation Yon the heating surfaces, tar

V,tirst reaction to produce maximum yields of valuable formation and the production of undesirable quantities of finely divided carbon and oil soot, resulting in low oleiin yields and in operational difficulties. In many cases, these operations have also been hampered by the necessity of providing for burning oif of the carbon deposit after a very short on-stream period, the heat evolved usually being in excess of the process heat requirements.

In the co-pending application of Schutte, Serial Number 440,321, filed June 30, 1954, now Patent No. 2,789,-

084 an improved version of the two-stage cracking of heavy oils to oleins is disclosed, one feature of whichl is to obtain a greater degress of independence between the operating conditions in the coking zone and in the vapor phase cracking zone. .In this application, as in `,the previous patent 2,526,696, the vapor phase cracking was carried out by passing the vapors from the coking, i,

zone through a relatively shallow bed of highly preheated solid particles and providing the endothermic cracking heat by circulating these particles through va reheating zone.

In the present invention, following a preliminary cokev removal, the coking zone vapors are cracked in regen erative furnaces which are used in pairs to give cony tinuous ilow, each furnace utilizing stationary refractory masses for heat storage and operating with cyclic reheating.` VThis method has several advantages. It obviates .the necessity for circulating highly preheated heat very economical ultimate cost.`

y 2,908,625 Patented oef. 131959 ICC A further advantage of this sequence of operations is the avoidance of many of the problems of gas cleanupproducts these heavier materials must be removed Vprior' to the recovery step in order to prevent fouling of equipment, gumminig up of heat surfaces and like problems. In the initial cleanup of the gases, even at low pressures, the temperatures prevailing in the bottom section ofthe absorption and rectification equipment are high enough to produce fouling and polymerization and most designs merely localize the operational diculties in this preliminary cleanup step. The combination of processing steps disclosed :in the present invention makes it possible to eliminate these diiculties while simplifying the recovery system and improving its economy and heat recovery.

The principal object of the present invention is to integrate a coking system, a regenerative furnace system and a recovery and purification `system whereby low cost residual oil is converted into useable coke and a maximum yield of gaseous oleiins under readily controlled conditions and at a minimum cost of end products.

A still further object of our invention is to integrate a coking system with regenerative furnaces and fractionation apparatus whereby optimum temperatures and pressures may be employed in all parts of the system with maximum heat recovery, whereby the products from each section of the system may be most effectively utilized for 'the production of maximum yields of ethylene and/or acetylene. p

Further objects and advantages of our invention will appear from the following description of a preferred form of embodiment thereof taken in connection with the attached drawing which is a flow diagram illustrative of one form of apparatus for carrying out the invention.

The integrated unit more particularly shown may be more effectively understood if it is considered to include several sections as follows: l

VThe first major section is the coker or decoking section, wherein the residual carbon and the heavy ends are removed Vfrom charging stock.` As will be understood hereinafter, the selected removal of certain constituents of the heavy residue of such charging stock is particularly helpful for subsequent processing of lighter hydrocarbons thusproduced. l

The second major section includes regenerative crack- ,ing furnaces of which several examples are known, but

in which the Wulff type is preferred. It is in this section that the gas, gasoline, and gas oil overhead from the coker plus steam are economically converted to .high yields of olens.

A third section may be considered to be the gas cleanup section and this includes the removal of aromatics in one step and the treatment for the removal of acidic gaseous constituents particularly H28 and CO2.

If desired, a fourth section maybe used in which acetylene is converted to ethylene by suitable catalytic methods, particularly where high yields of ethylene are required with a minimum of acetylene contamination.

VThe nal stage of the apparatus includes fractionation equipment which also may be of well known type in whichV the specific olens are recovered as desired. i

The foregoing stages of the apparatus are hereinafter described in greater detail: Y

Coker section Thelowest cost oleiin product is economically made from the lowest cost raw material and whereasit has been common practice to produce olenes from normally out, it can also be cracked to a significantly high yield ofeolens.

As heretofore determined, such material is unsuited for any direct conversion to olens. We have found, however, that when `the residue is decarbonized, by the removal of solid coke of commercial grades, the over- 'head vapors plus superheated steam make 'an unusually satisfactory charge to a regenerative furnace first because of the improved hydrogen-carbon ratio of the vapors and second because of the improved volatility of lthe product as a result of the decarbonization of the charge.

The coker section lthus includes as a primary step, any of the well known coke production units Whether of the continuous gravity type shown by the Schutte Patent 2,561,334 or of the fluid type or of the more generally used delayed coker type. For purposes of explanation, the latter type is 'illustrated but it will be understood that this is only one of the types that may be used.

With a reduced crude, vacuum bottoms or coal tar which may have a range of 020 API and from 0.7% sulfur, it is iirst desirable to heat the oil to about 200- 400 F. so that it can be effectively handled. This oil is then passed in line 10, through a coil 11a in the tubular heater 11 wherein it is further heated and is then passed through line 12 to a flash tower 13. As will be hereinafter described, the light ends are ashed from this mate- `rial and the fuel oil residue is removed through line 14 and then pumped through a second coil 11b in the heater 11, orrit can be taken off as product through line 14C as desired.

In coil 11b, the fuel oil is heated to around900-950" F.

' and under such a pressure that when it passes through transfer line 15 into a coke drum 17, the solid coke will form in the well known manner.

Usually two or more coke drums 17 and 17a are used in parallel with switch valve 18 directing the material first into one drum and then into the other while the first is being cleaned out. Coke is removed through lines 19 or 19a and the overhead is removed at 20 or 20a.

The coker overhead which is removed at about 800 to 900 F., is introduced through line 21 into the lower part of flash tower 13 and thereby aids in driving off the light ends from the fuel oil removed at the bottom. As will be noted, this fuel oil, if there is any excess Vover coking requirements, may be used as heater fuel through line 14b.

The overhead in line 22 from the flash tower 13 then becomes the charge to the regenerative furnace 23. In

' general when processing a reduced crude with l0-20% Conradson carbon, the overhead contains in the order of 5060% of a gas oil fraction having a boiling range of S50-850 F.; a gasoline fraction of around 10-15 of a boiling range of C to 350 F. and approximately 5 to 15% of normally gaseous material. The coke already removed accounts for about 20-30%-all being based on original charge.

Regenerative furnace system i' center, is lled with refractory tiles of special design.

The ends of the furnace are provided with plenum boxes and battles for the proper distribution of feed to the furnace.

Exhaust steam is superheated and mixed with the 'A coker vapors before entering each pair of furnaces.

These furnaces are operated in pairs on a regenerative cycle, heat being removed from the refractory tiles by the pyrolysis of the gas feed and restored by the combustion of fuel gas with preheated air. A complete cycle for each furnace consists of a pyrolysis step and a heating step in the forward direction followed by a pyrolysis step and a heating step in the reverse direction. Each step usually occurs for approximately one minute. The time of these steps may, however, be varied according to needs. A description of the complete cycle follows. Y

(a) The steam-gas mixture is introduced at the front end of a furnace, pyrolysis occurs and the cracked gas is withdrawn from the back of the furnace.

(b) Air is introduced at the front of the furnace and preheated by the refractory tile before the air reaches the combustion zone. Fuel gas is admitted to the combustion zone and hot combustion gas passes through the refractory tiles and out the back of the furnace.

(c) The pyrolysis step is repeated with the steam-gas mixture owing in the opposite direction Vto lthat described in step (a), i.e. back to front.

(d) The heating part of the cycle is repeated and the air and combustion gases flow through the heater in the opposite direction to that described in step (b), i.e. back to front.

So that there will be a continuous acceptance of the vapors in line 22 and a like continuous discharge of cracked oletinic hydrocarbons from the furnace system 23, a pair of furnaces are employed with appropriate switch valves operating as disclosed in the afore-mentioned article.

Although the regenerative furnaces are generally operated at about one-half atmosphere absolute pressure, in both the heating and cracking cycles, when acetylene is the preferred product, we prefer to operate at one to two atmospheres absolute pressure when ethylene is the preferred product. The charge ,(hydrocarbon plus steam) rate is increased, in such operation, so that the time of residence of the feed is the same as it would be if the furnace were at one-half atmosphere absolute pressure.

The following table better illustrates furnace operating conditions where the major oleinic product desired is either ethylene or acetylene.

Preferred operating conditions in regenerative furnace Ithas been observed that the acetylene yield approaches the theoretical maximum as the steam-hydrocarbon ratio is increased but economic considerations limit the amount of steam to practical limits. Yields Vof acetylene under optimum conditions may vary from 25 to 40% by weight of hydrocarbon charge to the furnaces.

Where ethylene is the preferred major product an increase in feed rate also increases the production capacity of a given furnace. For instance, if the pressure is one atmosphere, the production capacity would be about double that at one-half atmosphere. However, if the pressure on the furnace is too high polymerization and loss of the olens to higher molecular weight products can occur in the cooler parts of the checker work. Hence, the preferred choice of pressure is about one to two atmospheres.

Gas for combustion purposes within the pair of furnaces is provided from off-gas sources throughout the system and enters in line 24.

'After rapid heating in the regenerative furnace to the 'reaction temperature of 15001800 F. or higher depending on the products desired, the crackedhydrocarbons are automatically quenched to about 900 F. by the refractory mass in the heat side of the furnace as described 4in the afore-mentioned article.

' To obtain further heat economies we have shown a waste heat superheater 25 in which the furnace exhaust Igases in line, 26fgive up heat to steam entering in exchange relation through line 27. The cooled exhaust gases then pass tostack 28' while the superheated steam in line 29 is mixed with the vapors in line 122 for cracking and dilution purposes. Steam is used to prevent coking on the refractory tiles as well as a diluent to reduce polymerization of unsaturates, etc. A dry feed would cause a marked decrease in yield. Usually one pound of steam is used per pound of charge but this'ratio may be 'varied as required.

The cracked effluent from furnace 23 which includes either'a major portion of ethylene or acetylene depending upon furnace operating conditions and which has been partially quenched to halt further reaction is passed through line 30 to a quench and tar separator 31. Preferably water is used as the 'quench material being introduced through line 32. Tar, steam and other contaminants are removedthrough line 33.

Summary of yields from regenerative furnaces Gas cleanup section The quenched gas leaves the separator through line 34 and is temporarily retained in the sour gas holder 35, after which it is passed through line 36 to a compressor '37b From the compressor the gas goes to an absorber 38 by passage through line 39 and cooler 40. In the 'absorb'erQCss andraromatics are removed as bottoms through line 41 with the net overhead of oleiinic gases passing through line 42 to a second compressor 43. Abvso'rption oil entering the absorber near the top through "line 44 may beobtained from an absorption oil stripper 45 which is located in the recycle line 46 of ilashtower .13. Steam enters thestripper A45 through line 47 with the Aabsorption oil flow in line 4'4 to the absorber 38 ,passing through circulation pump 4S, reboiler 49 and exchanger 50.

A portion of the absorber bottoms in line 41 may be forwarded to ash tower as a reflux with the remainder being diverted through line 51 to a rerun tower 52. Overheads from the tower 52 pass through line 53 to condenser 54 and accumulator 55. Distillate from the accumulator may be passed in part to the rerun tower as reflux in line 56 and in part to line 57 as product C5s and aromatics while gases from the accumulator 55 may pass in line 58 to join the absorber overhead gases in line 42. Bottoms from the rerun tower may pass in line 59 through cooler 60 to unite with bottoms in line 41 from absorber 38.

The absorber overhead gases in line 42 which have been compressed at 43 are passed through line 61 to an acidic acid removal section indicated generally at 62.

Within this section acid gases including H28 and CO2 may be removed in any well known manner.

Acetylene conversion and fractionation sections VFrom the aromatic removal stage and the acid Vgas removal stage the olelnic gases, including a major portion of ethylene and some acetylene, may pass through line 63 to an acetylene conversion system indicated generally at 64. Such a system is provided where the major product desired at the finalv output is ethylene. To accomplish the conversion the acetylenes in the gases in line 63 may be hydrogenated to olefns in any well known manner. vImpurities of the acetylenes conversion may be removed at 65.

The gaseous olefns pass .from the acetylene conversion system through line 66 and are compressed at 67 prior to entering fractionation system 68. The compressed gases including a major percentage of ethylene in` our preferred embodiment are fractionated in a known manner which may include two or more stages of fractionation (notshown). In such a fractionation system aromatics would be generally removed as tower bottoms with tower overheads including thane, ethylene, propane, Vpropylene and C4 hydrocarbons removed to recovery apparatus for separation into product gas streams 69, 70, 71 and 72 which may include off gas or recycle, ethylene, propylene and a C4 cut.

When recovering a 41% ethylene yield and a 65% total olen yield from the total regenerative furnace product, the principal furnace and tower operating conditions are those shown in the following tabulation.

Summary of furnace and tower operating conditions 1 Charge to flash tower.

2 Charge to coker. Y

If itV is desired to produce a high yield of acetylene,

the reaction temperature of the furnaces may be increased to the optimum temperature range of 1800 to 2200". C.

and about 1/2 yatmosphere absolute pressure with high -steam dilution under which circumstancesthe yield of acetylene will be in the order of 29% for a total yield Tof olens of in the order of 58%.

While we have shown and described a preferred form 'of embodiment of our invention, We are aware that lvariations may be made thereto and we therefore desire a broad interpretation of our invention within thescope 'of the disclosure herein and the following claims.

We claim: l. The process for thermally treating -a heavy hydro- 'carbon charge to simultaneously produce coke and predominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule: which comprises preheating said hydrocarbon charge to a temperature :below its cracking temperature and in the order of Iabout 700 to 800 F.; introducing said preheated charge into a flash zone wherein light ends are flashed from said preheated charge; withdrawing as a bottom stream from said flash zone normally liquid hydrocarbons having a boiling range of heavy fuel oil; heating said bottoms to about 900 to 950 F. and introducing said heated bottoms, a portion of which is in the vapor phase, into a coking zone; maintaining the temperature and pressure in said coking zone so as to mildly crack the liquid port-ion of said heated bottoms whereby the unvaporized portion of -said bottoms is ultimately converted to dry coke and additional vapors; withdrawing overhead vapors from said coking zone and introducing said vapors to said ash zone at a point below the point of introduction of said preheated charge whereby, during contact with said preheated charge, said light ends are ashed from said charge and the heaviest liquid constituents of said vapors having a boiling range of fuel oil are condensed; withdrawing noncondensed vapors including gas, gasoline and gas oil and said light ends from the upper part of said flash zone; mixing said noncondensed vapors and light ends with superheated steam and passing the mixture through a cracking zone in direct heat exchange contact with a hot thermally yregenerated refractory mass contained therein; maintaining said mixture in said cracking zone for a period of from a fraction o-f la second to several seconds; maintaining the temperature of the refractory material in said cracking zone in the range from 1500 to 2200 F. thereby producing an effluent containing a high percentage of unsaturated hydrocarbons having less than four carbon atoms to the molecule; quenching said euent; separating as product said unsaturated hydrocarbons from said quenched etlluent; and withdrawing dry coke from said coking zone as product.

2. The process lfor thermally treating a heavy hydrocarbon charge to simultaneously produce coke and predominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule as claimed in claim 1 wherein said ash Zone is maintained under a pressure of about to 30 p.s.i.g. and said coking `zone is maintained under -a pressure of about to 35 p.s.1.g.

3. The process for thermally treating a heavy hydrocarbon charge to simultaneously produce coke and predominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule as claimed in claim l wherein the mixture passing through the regenerative cracking zone is heated to from about 1500 to 1800 F. and the predominant unsaturated hydrocarbon contained in the cracking zone efuent is ethylene.

4. The process for thermally treating a heavy hydrocarbon charge to simultaneously produce coke and predominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule as claimed in claim 1 wherein the mixture passing through the regenerative cracking zone is heated to from about 1800 to 2200 F. and the predominant unsaturated hydrocarbon contained in the cracking zone eiuent is acetylene.

5. The process -for thermally treating a heavy hydrocarbon charge to simultaneously produce coke `and predominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule: which comprises preheating said hydrocarbon charge to a temperature below its cracking temperature and in the order of about 700 to 800 F.; introducing said preheated charge into a Hash zone wherein ilight ends are ashed from said preheated charge; withdrawing as a bottom stream `from said flash zone normally liquid hydrocarbons having a Iboiling range of heavy fuel oil; heating said bottoms to about 900` to 950 F. and introducing said heated bottoms, a portion of which is in the vapor phase, into a coking zone; maintaining the temperature and pressure in said coking zone so as to mildly crack the liquid portion of said vheated bottoms whereby the unvaporized portion of said bottoms is ultimately converted to dry coke and additional vapors; withdrawing overhead vapors from said coking zone and introducing said vapors to said flash zone at a point below the point Vof introduction of said preheated charge whereby, during contact with said preheated charge, said light ends are ashed from said charge and the heaviest liquid constituents of said vapors having a boiling range of fuel oil are condensed; withdrawing noncondensed vapors including gas, gasoline and gas oil and said light ends from the upper part of said flash zone; mixing said noncondensed vapors and lightends with superheated steam and passing the mixture through a cracking Zone in direct heat exchange contact with a hot thermally regenerated refractory mass contained therein; maintaining said mixture in said cracking Zone Vfor a period oftrom a fraction of a second to several seconds; maintaining the temperature of the refractory material in said cracking Zone in the range from 1500 to 2200 F. thereby producing an eiuent containing a high percentage of unsaturated hydrocarbons having less than four carbon atoms to the molecule; quenching said effluent; passing said quenched eflluent through a `contact with a light absorption oil whereby aromatics and C5Jr hydrocarbons in said efuent are absorbed by said `absorption oil; separating said efuent, free of aromatics and C5,L hydrocarbons, into normally related gaseous hydrocarbon constituents; fractionating said normally related constituents into separate gaseous unsaturated hydrocarbon products; and withdrawing dry coke from said coking zone as product.

6. The process for thermally treating Ia heavy hydrocarbon charge to simultaneously produce coke andpredominant yields of gaseous unsaturated hydrocarbons having less than four carbon atoms to the molecule `as claimed in claim 5 wherein the light absorption oil passing through the contact with saidv quenched elluent comprises a side stream from said flash zone and a portion of said absorption oil, after said contact, including absorbed aromatics and C5+ hydrocarbons is passed to the top of said flash zone as reux.

References Cited in the le of this patent UNITED STATES PATENTS 1,490,862 Smith Apr. 15, 1924 1,907,029 Andrews et al. May 2, 1933 2,245,819 Porter A--- June 17, 1941 2,310,317 Roberts Feb. 9, 1943 2,552,277 Hasche May 8, 1951 2,580,002 Carrier Dec. 25, 195.1 2,656,307 Findlay Oct. 20, 1953 2,731,508 Iahnig et al Ian 17, 1956 OTHER REFERENCESl Sachanen: Chemical Constituents of Petroleum (1945), Reinhold Publishing Co., New York. l

Bixler et al.: Industrial and Engineering Chemistry (1953), vol. 45, pages 2596-2606,

Claims (1)

1. THE PROCESS FOR THERMALLY TREATING A HEAVY HYDROCARBON CHARGE TO SIMULTANEOUSLY PRODUCE COKE AND PREDOMINANT YIELDS OF GASEOUS UNSATURATED HYDROCARBONS HAVING LESS THAN FOUR CARBON ATOMS TO THE MOLECULE: WHICH COMPRISES PREHEATING SAID HYDROCARBON CHARGE TO A TEMPERATURE BELOW ITS CRACKING TEMPERATURE AND IN THE ORDER OF ABOUT 700 TO 800*F., INTRODUCING SAID PREHEATED CHARGE INTO A FLASH ZONE WHEREIN LIGHT ENDS ARE FLSHED FROM SAID PREHEATED CHARGE; WITHDRAWING AS A BOTTOM STREAM FROM SAID FLASH ZONE NORMALLY LIQUID HYDROCARBONS HAVING A BOILING RANGE OF HEAVY FUEL OIL; HEATING SAID BOTOMS TO ABOUT 900 TO 950*F. AND INTRODUCING SAID HEATED BOTTOMS, A PORTION OF WHICH IS IN THE VAPOR PHASE, INTO A COKING ZONE; MAINTAINING THE TEMPERATURE AND PRESSURE IN SAID COKING ZONE SO AS TO MILDLY CRACK THE LIQUID PORTION OF SAID HEATED BOTTOMS WHEREBY THE UNVAPORIZED PORTION OF SAID BOTTOMS IS ULTIMATELY CONVERTED TO DRY COKE AND ADDITIONAL VAPORS; WITHDRAWING OVERHEAD VAPORS FROM SAID COKING ZONE AND INTRODUCING SAID VAPORS TO SAID FLASH ZONE AT A POINT BELOW THE POINT OF INTRODUCTION OF SAID PREHEATED CHARGE WHEREBY, DURING CONTACT WITH SAID PREHEATED CHARGE, SAID LIGHT ENDS ARE FLASHED FROM SAID CHARGE AND THE HEAVIEST LIQUID CONSTITUENTS OF SAID VAPORS HAVING A BOILING RANGE OF FUEL OIL ARE CONDENSED; WITHDRAWING NONCONDENSED VAPORS INCLUDING GAS, GASELINE AND GAS OIL AND SAID LIGHT ENDS FROM THE UPPER PART OF SAID FLASH ZONE; MIXING SAID NONCONDENSED VAPORS AND LIGHT ENDS WITH SUPERHEATED STEAM AND PASSING THE MIXTURE THROUGH A CRACKING ZONE IN DIRECT HEAT EXCHANGE CONTACT WITH A HOT THERMALLY REGENERATED REFRACTORY MASS CONTAINED THEREIN, MAINTAINING SAID MIXTURE IN SAID CRACKING ZONE FOR A PERIOD OF FROM A FRACTION OF A SECOND TO SEVERAL SECONDS; MAINTAINING THE TEMPERATURE OF THE REFRACTORY MATERIAL IN SAID CRACKING ZONE IN THE RANGE FROM 1500 TO 2200*F. THEREBY PRODUCING AN EFFLUENT CONTAINING A HIGH PERCENTAGE OF UNSATURATED HYDROCARBONS HAVING LESS THAN FOUR CARBONS ATOMS TO THE MOLECULE; QUENCHING SAID EFFLUENT; SEPARATING AS PRODUCT SAID UNSATURATED HYDROCARBONS FROM SAID QUENCHED EFFLUENT; AND WITHDRAWING DRY COKE FROM SAID COKING ZONE AS PRODUCT.

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