US2185566A - Process for the manufacture of ethylene - Google Patents

Description

Jan. 2,` 1940. F. PORTER ET AL 2,185,566

PROCESS FOR THE MANUFACTURE OF E'H'YLENE 1 Filed July 14, 1957 /l/az'er d [My/em 60.5 n

B/ah/ef 7 ATT t ORNEY Patented Jan. 2, 1940 PATENT oFFlcle.

2,185,566 PROCESS FOB. THE MANUFACTURE 0F ETHYLENE Frank Porter, Syracuse, N. Y.,

Duncan, Petersburg, Va.,

and John Moyle assignors to The Solvay Process Company, New York, N. Y., a corporation of New York Application July 14, 1937, Serial No. 153,496

1o claims.

This invention relates to themanufacture of ethylene. It is particularly directed to the op'- eration of paired regenerative cracking units in the cracking of mineral hydrocarbons in vapor or gaseous phase.

The manufacture of ethylene by cracking hydrocarbons, such as ethane, propane, butane, and higher hydrocarbons or mixtures thereof, such as gas oil, kerosene, crude petroleum or topped petroleum, requires for Vellicient operation the maintenance of relatively high temperatures in the cracking zone.l Temperatures in the range 780 to 1050 C. have been found most satisfactory. Attempts to attain such cracking temperatures by heating the hydrocarbons or mixtures containing them through heat transfer walls of steel or other metals result in rapid destruction of the apparatus with consequent heavy replacement costs. Iron surfaces furthermore have a deleterious effect upon the desired reaction. As a consequence it becomes desirable to use refractory materials, but such materials do not possess the combination of tensile strength and heat conductivity essential for indirect heat transfer operations.

The use of regenerative types of equipment y possessesthe advantage that highly refractory materials'may be employed and a relativelylong equipment' life may be obtained. lThis typeof equipment is subject to the disadvantage, however, that it is more diiicult to control within narrow ranges of temperature and consequently optimum conversion efficiencies usually are not obtainable.

It is an'object of the present invention to improve the'control of the operating cycle of regenerative equipment for the manufacture of ethylene whereby high yields of ethylene may be obtained. f I

It is a further object of the invention to so utilize the heat storage capacity of the refractory material that a maximum of heat may be usefully employed for the cracking operation.

In 'accordance with the present invention a pair` of refractory heat storage chambers of any suitable type is employed. These heat storage units are arranged for alternate operation in a cycle involving a blast period wherein one of the unitsv is heated by combustion gases and a cracking period wherein a mixture of the hydrocarbon to be cracked and steam is passed through the unit thus heated to effect cracking and formation of ethylene from the hydrocarbon.

While the customary procedure in cracking by regenerative equipment involves a blast period followed by a cracking period in the same the present -process involves blasting one unit while the other unit is still at a temperature sufficiently high for cracking and then passing, steam through the first unit prior to admixing it with hydrocarbon to be cracked and passing the mixture through the second unit. After this, cracking period is terminated, the flow is reversed, the first (or steam-treated) unit now being employed for the cracking and the second unit for the preheating of steam.

By employing the rst unit to preheat the steam to be mixed with hydrocarbon, the portion of refractory material nearest the inlet for steam is cooled to approximately the inlet temperature for the steam and on reversal of the cycle this refractory material absorbs heat from thev cracked hydrocarbon steam mixture. By this procedure the sensible heat of lthe steamhydrocarbon mixture is returned to the refractory material so that the cracked hydrocarbon steam mixture leaves the apparatus at substantially lower than usual temperatures with a consequent saving in fuel cost. At the samev time, since the newly blasted refractory is in a highly unstable thermal condition, the use of this refractory for preheating steam serves to stabilize the refractory and render it more suitable for the cracking operation subsequently to be conducted therein. Thus, if a bed of refractory material is heated by means of combustion gases, the temperature of the refractory nearest the combustion attains a very high temperature Whereas refractory more remote from the comunit,

bustion is at a sharply lower temperature. Simiu larly in a short blast period the refractory surfaces are heated to a high temperature but the heat does not penetrate uniformly into each piece of refractory; With the passage of time the high temperature of the surface is reduced by conduction to the interior of each piece of refractory, so that while not materially less heat is present, it is now present at a lower temperainto the rsecond unit in a direction concurrent v purge with steam following this idle period assists in maintaining the low temperature at the outlet for the subsequent cracking.

In order that the present invention may be more fully understood, there follows a description of one embodiment of the invention which -is illustrated in the accompanying drawing,

wherein Fig. 1 shows diagrammatically a pair of twin cracking units with the necessary gas and oil lines and recovery apparatus, adapted for the production of ethylene from crude petroleum or other mineral hydrocarbons, and

Figs. 2 to 9 respectively show the operation of the twin regenerative units'in successive periods of the operating cycle.

With particular reference to Fig. 1, numeral I temperatures, for instance clay-bonded silicon carbide. Numeral 4 is a second unit identical with unit I. The units and packing are shown approximately to scale.

A single conduit 5 connects opposite sides of units I and 4 near the top. A crude oil line 6, having a valve 1, leads to conduit 5 from a preheater 8 fed by feed pump 9. The preheater is shown with a by-pass IIJ for temperature control. An air blower II supplies air by way of conduit I2, provided with valve I3, to conduit 5. Tar for use as fuel or for other purposes can be stored in tank I4 having a valved draw-off I5 and connected by line I6 with pump I1 and preheater I8. A line I9 having a valve 20 leads from the preheater to conduit 5. Conduits 2| and 22 provided with valves 23 and 24 join a draw-off conduit 25 connected with a stack 26 (having a valve 26a) and a cooling tower 21. Conduits 2I and 22 are also joined to steam inlets 28 and 29 respectively.

Tower 21l is composed of three sections packed with any suitable material. The lowermost section 30 has at its top tar inlet spray 3| and at its bottom a basin 32. A pump 33 is arranged to circulate tar from basin 32 through a cooler 34 to the spray inlet 3|. A draw-off line 35 leads to storage tank I4. The middle section 3B of the tower is employed for the purpose of removing entrained mist or spray. It is provided with packing but is wet only with the mist which is collected. 'I'he top section 31 has at the top a spray inlet 38 for water and a gas outlet 39. At its bottom, it is provided with a draw-oil! 40 leading to decanter 4I which in turn has an oil outlet 42 leading to storage tank I4. 'I'his draw-oi! may be provided with a bleed 43 for separate withdrawal of the oil so that it may be treated apart from the tar recovered in section 30 if desired. The tar decanter alsoJs equipped with water outlet 44 and drain 45.

The above apparatus may be operated for the production of ethylene in the following manner- Tar or any suitable fuel is pumped from storage tank I4 by means of pump I1 through preheater I8 and pipe I9 into conduit 5 in which it is atomized into air simultaneously forced by blower II through conduit I2 into conduit 5. The mixture is ignited by anyconvenient means (not shown). For initial heating to bring the apparatus to operating temperature both units may be blasted at the same time or the umts may be blasted individually and successively.

The operation of a representative cycle is as follows:

The flow during the blast period for unit I is shown in Fig. 2. With valves 1, 24, 28, and 29 closed and valves I3, 20, 23, and 26a open, preheated tar is burned with air in the combustion space above packing 3 in unit I. The combustion gases pass down through unit I and through conduits 2I and 25 to stack 26 and out the stack. This blast is continued until the refractory near the top of the packing in unit I has attained a temperature around 1500 C. The packing may be around 600 C. at the bottom.

.When the above temperature conditions have been attained, a short purge shown in Fig. 3 is conducted. Valves I3 and 20 are closed and the valve on line 29 is opened for a brief period to pass steam up through unit 4, down through unit I, and out through the stack. This brief purge removes any air that may be in the units and thereby avoids the possibility of explosions in the subsequent cracking step. This purge also may cool the packing at the bottom of unit 4 somewhat so that the temperatures in unit 4 at the end of the purge are around 100 C. at the bottom and 1050 C. at the top. In unit I the purge serves to reduce the temperature slightly at the top and to increase the temperature at the bottom so that after the purge the packing in this unit may be around 1400 C. at thev top and 700 C. at the bottom.

'I'he subsequent cracking step is illustrated in Fig. 4. Valves 23 and 26a are now closed. Steam ow is shut o in line 29 and turned on in line 28. Valves 1 and 24 are opened. Feed pump 9 is thus caused to force oil through preheater 8 and through inlet line 6 into conduit 5. This oil may be at a temperature of around 200 C. and a pressure of 200 to 300 pounds per square inch. Pump 9 may be operated either intermittently or continuously. In the former case it will be started' at the same time that valve 1 is opened. In the latter case it will be provided with sufdcient excess storage 'capacity so that it will not be overloaded during the period Valve 1 is closed. Steam enters by way of line 2l, passes up through the packing of unit I and is'thereby heated to a temperature around 1000 C. to 1200 C. 'Ihe flows of oil and steam are preferablyl controlled to provide a weight ratio of 1.7 part of steam for each part of oil. The oil is atomized into the steam as it passes through conduit 5 and the resultant mixture then passes down through the packing of unit 4, out through conduit 22 to conduit 25 andthence into tower 21. The gas mixture in its passage through unit 4 passes rst through the upper hot zone where cracking takes place. This cracking zone may be defined as that zone in which a temperature above about 780 C. prevails. 'I'he mixture passes then through a lower aisance 3 cooling zone where the heat' of the mixture isy given up to the cooler-refractory. The tem- `perature of the gases leaving unit 4 during this periodmay be around 150 C. to 300 C. at the start of the period and around '250 to 400 C. at the end of the period. n

The partially cooled, cracked gases pass through section 30 of tower 21 countercurrent to a ilow of washing tar which further cools the gases and washes tarry constituents therefrom. This washing is preferably controlled (by regulation of the il/ow of water through heat exchanger 34) so as to maintain a temperature between 100 and 150 C. in the stream of gases entering section 31. Any entrained matter caught in section 38 will, of course, be returned to section 30 where it is blended with the tar used for washing. In section 31 thevgases are further cooled by contact with water to recover lremaining oil constituents and the major part percent ethylene may be obtained. 'Ihe flow` through the cracking unit may be substantially constant toprovide a time in the cracking zone around .03 to .07 second or the flow may be 'graduated providing a cracking time on the' order of 0.006 second when the zone is hottest up to around 0.3 second when it has cooled off to 850 C. This cracking period is terminated when the temperature. at the top of the packing in unit 4 has been cooled to such an extent that efcient cracking cannot be obtained without undesirably reducing the speed of the gases; for instance, when the maximum temperature has dropped to around 780 to 850 C. The temperature at the bottom of the packing may be as high as 300 to 400 C. by this time.`

At this point valve 1 is closed and the ow of steam is permitted to continue for a short period to purge the system of oil vapors. The flow is shown in Fig. 5. Since the direction of steam flow is not altered in this step, the general temperature conditions will not be materially affected.

After the brief purge is completed, the apparatus'is ready f or the blast or heating of unit 4, flow for which is shown in Fig. 6. Steam ow f through linev 28 is cut oil' and valves I3, 20, 24, and 26a are opened so that the blast passes down through unit 4 and out through the stack. During this period, unit I is permitted to lie idle or soak unit during the previous cracking step has removed a considerable proportion of the stored heat. 'I'he unit may now have a temperature at the top of the packing around 1100 C. and at the bottom around y100 C. During the idle period the top temperature may drop slightly and the bottom temperature rise.

When unit 4 has attained the desired operating temperature, say around 1500 C. at the top, valves I3 and 20 are closed, and steam is admitted through line 28 to purge the system as shown in Fig. 7.

After this brief purge the stack valve 26a is closed, the flow of steam through line 28 is out off and through line 29 turned on. Valve 1 is opened to injectthe hydrocarbon to be cracked The passage of steam through this into the steam passing through conduit 5 and n 1 is closed, and the passage of steam is con-.-

1. The method of operating a pair of refrac-V tory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises heating refractory material in unit A by passing a hot gas in contact therewith while unit B is maintained idle and at least a portion of the refractory material in unit B is maintained at a temperature above 780 C., subse` quently and before substantial heat is abstracted from unit A passing steam through unit A to heat said steam, forming a mixture of said steam with the hydrocarbon to, be cracked and passing the mixture through unit B while refractory material in unit B is ata temperature between 780 C. and 1050 C., subsequently heating refractory material in unit B by passing a hot gas in contact therewith while unit A is maintained idle and at least a portion of the refractory material in unit A is maintained at a temperature above '780 C., subsequently and before substantial heat is abstracted from unit B passing steam through unit B to heat said steam, forming a mixture of said steam with additional hydrocarbon to be cracked, and passing said mixture through unit A, while refractory material in unit A is at a temperature between '780 C. and 1050 C.

2. The method of operating a pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises heating refractory material in unit A by Aunit B is at a temperature between 780 C. and

1050 C., subsequently heating the refractory material in unit B by passing a hot gas in contact therewith while unit A is maintained idle and at least a portion of the refractory material in unit A is maintained at a temperature above '780 C., before substantial heat is abstracted yfrom unit B passing steam through unit B in a direction countercurrent to the previous flow of steam and hydrocarbon therethrough to cool refractory in unit B and to heat said steam, forming a mixture of said steam with additional hydrocarbon to be cracked and passing said mixture through unit A while refractory material in unit A is at a temperature between 780 C. and 1050 C. in a direction countercurrent tothe aforementioned passage of steam through unit A. l

3. 'I'he method of operating a pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises heating refractory material in unit A to a temperature above 1050 C. by passing a hot gas in contact therewith while at least a portion of the refractory material in unit B is maintained at a temperature between 780 C. and 1050 C., subsequently passing steam through unit A to heat said steam, forming a mixture of said steam with the hydrocarbon to ,be cracked and passing the mixture through u nit B, subsequently heating refractory material in unit B to a temperature above 1050 C. by passing a hot gas in contact therewith while at least a portion of the refractory material in unit A is maintained at a temperature between 780 C. and 1050 C., subsequently passing steam through unit B to heat said steam, forming a mixture of said steam with additional hydrocarbon to be cracked, and passing said mixture through unit A.

4. The method of operating a pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises blowing unit A with fresh hot combustion gas to heat refractory material therein while at least a portion of the refractory material in unit B is maintained at a temperature above 780 C., subsequently passing steam through unit A to heat said steam, forming a mixture of said steam with the hydrocarbon to be cracked and passing the mixture through unit B while refractory material in unit B is at a temperature between 780 C. and 1050 C., subsequently blowing unit B' with fresh hot combustion gas to heat the refractory material therein while at least a portion of the refractory material in unit A is maintained at a temperature above '180 C., subsequently passing steam through unit B to heat said steam, forming a mixture of said steam with additional hydrocarbon to be cracked, and passing said mixture through unit A while refractory material in unit A is at a temperature between 780 C. and 1050 C.

5. The method of operating a. pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises blowing unit A with fresh hot combustion gas to heat refractory material therein while at least a portion of the refractory material in unit B is maintained at a temperature above 780 C., subsequently passing steam through unit A in a direction countercurrent to the direction of flow of said combustion gas through said unit to heat said steam, forming a mixture of the resulting heated steam with the hydrocarbon to be cracked and passing the mixture through unit B while refractory material in unit B is at a temperature between 780 C. and 1050 C., subsequently blowing unit B with fresh hot combustion gas to heat refractory material therein while at least a portion of refractory material in unit A is maintained at a temperature above 780 C., subsequently passing steam through unit B in a direction lcountercurrent to the flow of combustion gas therethrough to heat said steam, forming a mixture of the resulting heated steam with additional hydrocarbon to be cracked, and passing said mixture through unit Awhile refractory material in unit A is at a temperature between 780 C. and 1050 C.

6. 'Ihe method of operating a pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene,'which comprises blowing unit A with fresh hot combustion gas to heat the refractory material therein to a temperature above 1050 C. while at least a portion of 'the refractory material in unit B is maintained at a temperature above 780 C., subsequently passing steam through unit A in a direction countercurrent to the flow of combustion gas therethrough to heat said steam, forming a mixture of the resulting heated steam with the hydrocarbon to be cracked and passing the mixture through unit B, subsequently blowing unit B with fresh hot combustion gas to heat refractory material therein to a temperature above 1050 C. while at least a portion 'of the refractory material in unit A is yet at a temperature above 780 C., subsequently passing steam through unit B in a direction countercurrent to the flow of combustion gas therethrough to heat said steam, forming a mixture of the resulting heated steam with additional hydrocarbon to be cracked, and passing said mixture through unit A in a direction countercurrent to the aforesaid ow of steam therethrough.

7. The method of operating a pair of refractory regenerative units, A and B, for cracking hydrocarbons to produce ethylene, which comprises blowing unit A with fresh hot combustion gas to heat the refractory material therein to about 1500 C. while a portion of the refractory material in unit B is maintained at a temperature above 780 C. and another portion thereof is maintained at a temperature below about 400 C., then passing steam serially through units B and A to expel combustion products, subsequently passing initially cool steam through unit A in a direction countercurrent to the flow of combustion gas therethrough to heat said steam and cool a portion of refractory material therein to a temperature below about 400 C., forming a mixture of the resulting heated steam with the hydrocarbon to be cracked and passing the mixture through unit B first in contact with refractory material thereinl at a temperature between 780 C. and 1050 C. and then in contact with refractory material therein at a temperature below 400 C., subsequently blowing unit B with fresh hot combustion gas to heat refractory material therein to about l500 C. while a portion of the refractory material in unit A is yet at a temperature above I'780 C. and another portion thereof is maintained at a temperature below about 400 C., then passing steam serially through units A and B to expel combustion products, subsequently passing initially cool steam through unit B in a direction countercurrent to the ow of combustion gas therethrough to heat said steam and cool a portion of refractory material therein to a temperature below about 400 C., forming a mixture of the resulting heated 4steam with additionalA hydrocarbon to be cracked, and passing said mixture l through unit A first in contact with refractory material therein at a temperature between 780 C. and 1050 C. and then in contact with refractory material therein at a temperature below 400 C. and in a direction countercurrent to the aforesaid flow of steam therethrough.

'- sage serially 'through the two units, which comprises blowing unit A with fresh hot combustion gas with a direction of gas flow away from the connected unit Aaforesaid so as to heatthe refractory material ,in unit A while atleast a mipart of. therefractory material in unit B is at l a temperature above 780 C., subsequently passing steam through-unit A in a direction countercurrent to thel direction of low of said combustion gas through lunit A to heat said steam and lto cool thel refractory material in unit A,

forming a mixture of the resultant heated steam with hydrocarbon to be cracked and passing the mixture through unit B while refractory mau terial in` unitB is at'a temperature between '780 C. and 1050 C.'in a direction of flow away from its connected'ed aforesaid, subsequently blow- Ving unit B with fresh hot combustion gas with a direction of.,.gas iiow awayjfrom its connected endA aforesaidso as to heat the refractory materialin unit Bwhileat least a part of the refractory material vin unit "A is at a temperature, above 780.C.; subsequently passing steam through unitB- in'a direction countercurrent to vthe direction of flow of said' combustion gas l aothroughV unit-B to hear said steam and to4 cool the refractory ,material in unit B, forming a mixture of the resultantiheated steam with hydrocarbonv to be-cracked and passing the mixture through unit vA while refractory material in unit 'ss A is au:- a. temperance between '180 c. and 1050 C. in a directionof flow away from its connected I Y end aforesaid.

i 9. In the operation of a pair of refractory regenerative units A and B in a four-period cycle with intermediate steam purges for the vproduction of ethylene, the methodwhich cornprises. in period 1 blong unit A with'hot combustion gas to heat the refractory material therein to a temperature above *780* C. while causing-unit B to remain idle at a temperature above 780 C., in period 2 passing the Isteam through the refractory material of lunit A to.

heat the steam, mixing vthe resultant heated steam with hydrocarbon to be cracked and passing the mixture through unit B while refractory therein is at a temperature between 780 C. and 1050 C., in period 3 blowing unit B with hot combustion gas to heat the refractory material therein to a temperature vabove .'180 C. while causing unit A to remain idle at a temperature about 780 C., and in period 4 passing steam through unit B to heat the steam. lmixing the resultant steam with hydrocarbon to be cracked and passing the mixture through unit A while refractory thereinis at a temperature between '180 C. and.1050 C. Y

l0. The method of the preceding claim wherein the flow through unit A in periods 1 and` 2 is countercurrent, the iiow through `unit B in periods 2 and 3 is concurrent, the flow through unit B in vperiods 3 and 4 is countercurrent, and` the flow through unit A in periods 4 and 1 is "Patent o, ,18'5, Soo.

csnmrcms oF CORRECTION.

' January 2, 19m.

n FRANK'PQRTER ET A L. ed .th'at error appears 'in the printed specification It is herebycertifi Page 5, sec- 'of -the above numbered patent requiring'correcton es follows: ond eo1umn,-l1ne 21, claim 9, for the word 'fbout" read above; and

the case 1n the' Patent office. signes and sealed this 15th any; of Februarbs. D.4 19m.

Henry 'Van rsdale,

(Seal)V -the seid Letters Pstentshould be read with this correction therein that the saguenay conformatothe record of l' Acting Commissioner' of Patents.

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