US1826782A - Art of cracking hydrocarbons - Google Patents

Description

Oct. 13, 1931. E. c. HERTHEL ET A1.

ART OF CRACKING HYDROCARBONS Filed June l1, 1927 BY m ATTORNEYS Patented Oct. 13, 1931 UNITED STATES :PATENT or-r-lcliz EUGENE C. HERTHEL, OF CHICAGO, ILLINOIS, AND HARRYYL. PELZER, OF HIGHLAND, INDIANA, ASSIGNORS TO SINCLAIR VREIIEINIINTG- COMPANY, vOIE NEW YORK, N. Y., A

CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS ,i

Application filed June 11,

This invention relates to improvements in the cracking of heavier and higher boiling hydrocarbon oils, such as gas oil, for the production therefrom of lighter and lower boil ing hydrocarbon oils, such as gasoline and gasoline-containing pressure distlllates.A

This invention relates particularly to 1mprovements in operations in which the heavier and higher boiling hydrocarbon oils are cracked by distillation under pressure. One important purpose of the invention 1s improvement of the continuity of such pressure distillation operations. Another 1s reduction of the stresses to which the apparatus in which such operations are carried out 1s' commonly subjected. Other improvements provided by the invention will appear as the description proceeds. i

'Heat is required to maintain the high temperatures used in such lpressure distillation operations and also to carry out the cracking operation. This heat is commonly supplled by heat transfer through heating tubes from heating gases including hot products of combustion from a fire-box in which fuel is burned; this invention relates particularly to operations carried out in such apparatus. j

In order to attain maximum capacity in any `particular apparatus, high rates of heat transfer through such heating tubes are usually maintained in operation, ordinarily by maintaining high temperature differentials between the heating gases passing over lthe heating tubes and the oil flowing through the heating tubes.

The products of the cracking reaction include, in addition to the desired lighter and lower boiling oils, asphaltic and pitch-like constituents which tend to deposit in such heating tubes, impeding heat transfer from the. heating tubes to the oil flowing through them.- If such deposits do form, the heating tubes are deprived of the protective effect of the oil flowing through them in absorbing heat and overheating, which may be and fre- 1927, serial No. 198,247.

tates the periodic shut-down of pressure stills t 1n which such cracking operations are carj ried out, thusy interfering with continuity of operation.

Where high rates of heat transfer are maintained, the formation of such deposits According to the present invention, the

burden of heat transfer through the heating tubes of the apparatus in whlch the operation is carried out is reduced, these heating tubes are subjected to relatively mild heating conditions, and the concentration in the charge of oil undergoing pressure distillation of constituents tendin to cause objectionable deposits in the eating tubes is controlled. The concentration of such objectionable constitutents in the pressure still charge is controlled in a dual manner; by circulating the charge of oil through a bed of absorbentor desulphurizing or filtering material, and by supplying raw oil to the' charge vand discharging pitch-laden oil or tar from the charge during operation and restricting the proportion of the total raw oil supplied to the operation that is taken off as a distillate. The burden of heat transfer through theheating tubes is reduced byreturning-to the'operation a large part of the heat escaping from the pressure still in which the operation is carried out by heat exchange between raw oil supplied to the operation and both vapors escaping from the pressure still andpitch-laden oil or tar discharged from the pressure still. Mild heating conditions, those to which the heating tubes are subjected, are advantageously maintained by recirculating over the heating tubes in ad- Overheating becomes Vmixture with fresh hot products of combustion from the dre-box in which fuel is burned .out inthe specific apparatus illustrated but that this specific apparatus is shown for the purpose ot' illustration and as one form of apparatus which is particularly advantageous. e t Y The pressure still illustrated comprises a bulk supply drum l. a battery of heating tubes 2, and circulating )connections 3, 4 and 5 including a circulating pump 6 for circulating oil from the bulk supply drum upwardly through the heating tubes and back to the bulk supply drum. A bed of finely divided absorbent or iltering or desulphurizing material 7 is arranged in the bulk supply drum on a suitable support 8 adapted to retain the finely divided material but to permit free passage of oil extending entirely across the path of'circulation oftthe still charge. This support may consist, for example, of one or more screens of appropriate dneuess arranged between perforated plates or gratings. Connection 9 is provided for discharging pitch-laden oil `or rar during operation. Connectiony 10 is provided yfor supplying cool oil to the bearings of the circulating pump 6. Connection 11 is provided for pumping out the still at the end of a run and for initally charging it at the-*beginning of a run.' The heating tubes 2 are arranged in the heating due of a furnace 12 provided with a {ire-box 13 from which hot products of combustion. pass through the heating due to a stack due 14. A return due 15 is rovided for recirculating through the heating due a part of the heating gases escaping to the stack due 14.

' This return due is provided with suitable Y Cn forcing means, suchas a steam jet blower as illustrated, or a fan or other blower.

A redux tower 16 is arranged above the bulk supply drum 1. Vapors escaping from the bulk supply drum enter the lower end of this redux tower through vapor line 17 and i vapors remaining uncondensed escape from `the upper end through vapor line 18 to a condenser 19 arranged to discharge into a receiver 20. The distillate product is discharged from receiver 20 through connection 21 and uncondensed vapors 4and4 gases through connection 22. The'pressure in the system 1s maintained and regulated by means raw oil into the upper end of the redux tower 1 6. Reflux condensate and admixed unvaporized raw oil from the lower end of he redux tower into the upper end of circa lating connection 3 through connection 25. Badies, or other suitable means, are arranged in the redux tower 16 to promote intimate contact and heat exchange between oil and condensate dowing downwardly therein and vapor-s rising therethrough.

It will be understood that the bulk supply drum, the circulating connections 3, 4 and 5 and also the redux tower/16 are thoroughly lagged or thermally insulated to prevent or reduce heat loss. y

The heat exchanger 26 comprises a pair of headers 27 and 28 connected by tubes 29 extending through a shell 30. Connection 31 is provided for passing pitch-laden oil or tar y discharged from the pressure still, through connection 9, through the tubes of this heat exchanger and out throughconnection 32. By-pass connection 33 is provided in the tar line around the heat exchanges. Raw oil is circulated through the shell of this heat eX- 'changer; in through connection 34 and out through connection 35,

Raw oil is supplied to the pressure still by means of either or both of pumps 36 and 37. Either or both of these pumps may be used to supply all of the raw oil introduced into the still, that introduced through the redux tower as well as that introduced directly, by means of connection 38; or the raw oil introduced thrbugh the redux tower may be supplied by means of pump 37 independently of that introduced directly by means of pump 36. A portion of the raw oil may be forced into the pressure still through the bearings of the circulating pump 6 by means of connection 10, cool raw oil being employed.

for 'this purpose, to cool and lubricate the pump bearings. Raw oil preheated by passage through the heat exchanger 26 is discharged through oonnections 39 and 40 into circulating connection 4 or through connections 41 and 24 into the upper end of the redux tower 16. By-pass connection 42 is provided between connections 34 and 35.

Appropriate valves are provided in the several connections for control and regulation of the dow `of oil therethrough as'illustrated. The discharge of pitch-laden oil or tar from the pressure still may he controlled and regulated by ,means of valve 43 or by means of valve 44, more advantageously by means of valve 43. When the discharge of pitch-laden oil or tar is controlled and regulated by means of valve 43, some vaporization may take place in the heat exchanger 26 and in the connections between the pressure still` and the heat exchanger, but there seems tolbe less tendency ico nos

toward stoppage of the discharge connections. i

In apparatus of the type illustrated, in which the normal operating charge of the pressure still is about 10,000 gallons, the bed of finely divided material may, for example, consist of from 4 to 7 tons of fullers earth of -30 mesh. Other absorbent or.desulphuriz in'g or filtering materials, such as calcined bauxite or pulverized coke, are useful in carrying out the invention, but fullers earth, or similarabsorbent earths or clays, is particularly advantageous. F ullers earth seems to combine in itself valuable fabsorbentyfiltering and desulphurizing,properties which coact to benefit the pressure still operation. Fullers earth also seems to have a selective action with reference to more objectionable constituents among which certain sulphur compounds seem to be important.

In carrying out the invention in a pressure still of the type illustrated, in which the normal operating charge'of the pressure still is about 10,000 gallons, the still is initially charged, for example with about 8,000 gallons of gas oil, and broughtl to operating conditions of temperature and pressure in. the usual Way. For the production of gasoline or a gasoline-containing pressure distillate from a gas oil character charging stock, the still may be operated under a pressure in the neighborhood of 125 pounds per square inch, for example, or higher or lower pressures may be used. Pressures up to 300 pounds per square inch, or higher pressures, for example, may be used, particularly where the charging stock is of lighter character or contains a substantial proportion of kerosene character components. After the still reaches operating conditions of temperature and pressure, the introduction of raw oil into the upper end of the reflux tower is begun while vapors including vapors of the desired distillate product escape into the refiux tower from the still and the introduction of raw oil is regulated to condense and reflux to the still those com? ponents ofthe vapors heavier and higher boiling than desired as components of the distillate product. Operating under a pressure of '125 pounds per square inch for the production of gasoline, for example, the introduc'tion of raw oil into the upper end of the reflux tower may be controlled and regulated vtomaintain the temperature of the vapors escaping from the upper end of the tower in .the neighborhood of 450 F. or at some other predetermined value. Before the concentration of asphaltic or pitch-like constituents in the circulating charge of oil in the still reaches an objectionable value, that is vshortly after the introduction of'raw oil into the upper end of the reflux tower is begun, the discharge of pitch-laden oil or tar is started i' and the rate at which raw oil is supplied to thev operation is increased to maintain the still charge. Part of the raw oil supplied to the operation, or in some cases all of it, is

then passed in heat exchanging relation with f the discharged pitch-laden oil or tar in the heat exchanger and thereby preheated before introduction'intothe pressure still system. At this point in the operation, the rate at which distillate is taken off, the rate at which pitch-laden oil or tar is discharged and the rate at which raw oil is suppliedto the operation may somewhat exceed 1,000 gallons per hour, 1,500 gallons per hour and 2,500 gallons per hour, respectively. 4The supply of raw oil and discharge of pitch-laden oil o r tar may be regulated so that the proport1on of the total oil supplied to the operation,

In this operation, a substantial part of the n heat in the vapors escaping from the pressure still and in the pitch-laden oil or tar discharged from the pressure still is absorbed by the raw oil supplied to the operation and 1s thus returned to the operation. The heat so returned to the operation reduces the burden of heat transfer on the heating tubes. At the same time, the bed of absorbent or desulphurizing or filtering material through which the still charge is circulated acts to reduce the concentration of asphaltic and pitch-like constituents in the oil flowing through the heating tubes while the concentration of asphaltic and pitch-like constituents in the circulating charge of oil. is further limited by the supply of raw oil and `discharge of pitch-laden oil or tar and reinar the operation, the heat lin the"discharged oil or tar is largely returned to the cracking 'operation proper. The corresponding reduction in the amount of heat that must be transferredthrough the heating tubes makes possible the maintenance of milder `conditions iu the heating furnace Without reduction of the capacity of the pressure still.

'llhe maintenance of milder furnace condif tions and the supply of raw oil and discharge of ptch-laden oil or tar and restriction of the amount taken off as distillate assist in' improving continuity of operation and the maintenance of milder furnace conditions is made possible, although a relatively. large amount-.of pitch-laden oil or tar may be discharged during operation', by returning to the operation a large part of the heat escaping from the pressure still in the vapors taken off and in the oil or 'tar discharge-d. These milder furnace conditions are advantageously maintained by recirculating a relatively large proportion of the heating gasesl again over the heating tubes with fresh hot products of combustion, say as high a proportion as 70% to 90% or more, for example. The improved continuity of operation makes possible an increase'in productionaper still per day without increasingthe stresses iniposed on the apparatus.

In one mode of operation, cool raw oil is introduced into the upper end of the reiux tower and all of the oil preheated by heat exchange with discharged oil or tar is introduced directly into the circulating charge of oil in the still. All or part of the raw oil introduced into the upper en d of the reflux tower, however, may be' preheated by passage through the heat exchanger. As the quant1t-y of raw oil passed through the heat l exchanger increases, the'temperature of the preheated oil decreases, and as the temperature of the raw oilv introduced into the upper end of the reflux tower increases, an in-` creasing amount may be introduced without increasing the reiuxing effected in the tower. In some cases, accordingly, lall of the raw -oil introduced into the upper end of the. re-

ux tower may be preheated. Excepting that supplied to the bearings of the circulating pump, all of the raw oil supplied to the operation may he preheated and introduced into the upper end of the reflux tower, or if the refluxing action is too great part of the preheated raw oil may be supplied directly to the circulating still charge. To increase the reiluxing action` part of the preheated raw oil may be supplied directly to the circulating still. charge and a part ot the raw oil supplied to the reiuxing operation cool without heat exchange with discharged oil or tar.

vlit is particularly advantageous to introduce the raw oil into direct contact with the vapors in the reuxing operationwhere it is preheated or partly preheated; the heat exchange between the vapors in thev reiuxing operation and the raw oil supplied thereto may however -be indirect.

We claim:

1. An improved method of cracking hydrocarbon oils. which comprisesv circulating a charge of oil in a pressure still from a bulk supply drum' through heating tubes and back to the bulk supply drum and heating it to a cracking temperature inthe heating tubes, maintaining a bed of finely dividedsolid material extending entirely across the path of the circulating charge of oil in the bulk supply drumftaking 0E vapors fromethe bulk supply drum under pressure and subjecting them to a reiluxing operation, introducing raw roil lnto the vapors 1n the refluxing operation and Y returning reflux therefrom together with ad-V mixed unvaporizedraw oil to the circulating charge of oil, discharging pitch-laden oil' from the circulating c harge of oil and pre-J I.

heating raw oil by heat exchange therewith, and supplying raw oil so'preheated directly to the circulating charge of oil.

` 2. An improved method of cracking hydrocarbon oils, which comprises circulating a charge of oil in a pressure still from a bulk supply drum through heating tubes and back vto the bulk supply drum and heating it to a cracking' temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking oi vapors from the bulk supply drum under pressure and subjecting i them to a refluxing operation, discharging pitch-laden oil from the circulating charge of oil and preheating raw oil by heat exchange therewith, and supplying raw oil so preheated in part directly to the circulating charge of oil and in part to the refluxing operation, and returning reflux from the reuxing operation together with raw oil supplied thereto to the circulating charge of oil.

3. An improved method of cracking hydrocarbon" oils, which comprises circulating a charge of oil in a pressure still from a bulk supply drum through heating tubes and back to the bulk supply rdrum and heating it to a cracking temperature rin the heating tubes, maintaining a bed of'finely divided solid material `extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking off vapors from the bulk supply drum`under pressure and subjecting them to a ,reiiuxing operation, discharging pitch-laden oil from the circulating charge of oil and preheating raw oil by heat exchange therewith, supplying raw oil so preheated 1ny part directly to the circulating charge of oil and in part to the refluxing operation, supplying additional cool raw oil to the refluxing operation, and returning reiiux from the reduxing operation together with raw oil supplied thereto tothe circulating Lcharge of oil.

4. An improved method of cracking hydro- Icarbon oils,I which comprises circulating a them to a'reduxing operation, 'discharging' pitch-laden oil from the circulating charge of L supply drum through heating tubes and back to the bulk supply drum and heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking oftl vapors from the bulk supply drum under pressure and subjecting them to a refluxing operation, supplying raw oil to the refluxingGoperation and returning reflux therefrom together with raw oil supplied thereto to the circulating charge of oil, discharging pitch-laden oilifrom the circulating charge of oil, supplying raw oil directly to the circulating charge of oil and preheating all of the raw oil so supplied directly to the circulating charge of oil by heat exchange with pitch-laden oil discharged therefrom.

v6. An improvedmethod of cracking hydrocarbon oils, which comprises circulating a charge of oil in a pressure Vstill from a bulk supply drum through heating tubes and back to the bulk supply drum and heat- -ing it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking off vapors from the bulk supply drum under pressure, discharging pitch-laden oil from the circulating charge of oil in sufficient quantity to maintain said charge of oil substantially constant, supplying to the circulat-ing charge ofoil raw oil preheated by heat exchange with vapors taken off from the bulk supply drum and with dischargedt pitch-laden oil, and restricting the amount .taken off as distillate not to exceed about 45% of the total raw oil supplied to the pressure still including the initial charge.

7. An improved method of cracking hydrocarbon oils, which comprises circulating a charge of oil in a pressure still from a bulk supply drum through heating tubes and back to the bulk supply drum and heating it toa cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path ofthe circulatin charge of oil in the bulk supply drum, ta 'ng off vapors-from the bulk supply drum under pressure, discharging pitch-laden oil` from the circulating charge of oil in suiiicient quantity to maintain said charge of oil substantially constant, supplying to the circulating charge of oil raw oil preheated by heat exchange With vapors taken 0H fromthe bulk supply drum and With discharged pitch-laden oil, and restricting the amount taken of't1 as distillate not to exceedgabout 40% of the total raw oil supplied to the including the initial charge.

pressure still 8. An improved method of cracking hydrocarbon oils, Which comprisescirculating a charge of Aoil in a pressure still from a bulk (supply drum through heating tubes and back to the bulk supply drumand heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking off vapors from the bulk supply drum under pressure and subjecting them to a refluxing operation, supplying raw oil to the refluxing operation and returning reflux therefrom together with raw oil supplied thereto to the circulating charge of oil, discharging pitch-laden oil from the circulating charge of oil in sutiicient quantity to maintain said charge of oil substantially constant, andk preheating raw oil by heat exchange therewith, supplying raw oil so preheated to the circulating charge of oil, and restricting the amount taken off as distillate not to exceed about 45% of the total raw oil supplied to the'pressure still including the initial charge.

9. An improved method of cracking hydrocarbon oils, which comprises circulating a charge of oil Iin a pressure still from a bulk supply drum through heating tubes and' back to the bulk supply drum and heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking ofi' vapors from the bulk supply drum under pressure and subjecting. them to a refluxing operation, supplying raw oil to the refiuxing operation and returning reiux therefrom together with raw oil supplied thereto to the circulating charge of oil, discharging pitch-laden oil from the circulating charge of oil in sulficient quantity to maintain said charge of oil substantially constant and preheating raw oil by heat exchange therewith, supplying vraw oil so preheated to the circulating chargeitto a cracking temperature'in'the heating tubes, maintaining a bed of finely divided solid material extending entirely across the Ill() path of the circulating charge of oil in the bulk supply drum, taking off vapors from the bulk supply drum under pressure, discharging pitch-laden oil from the cir'culating charge of oil in suicient quantity to maintain said charge of oil substantially constant, supplying to the circulating charge of oil raw'. oil preheated by heat exchange with vapors taken oil' from thebulk supply drum and with discharged pitch-laden oil, and restricting the amount taken oil as distillate not to exceed about 50% of the total raw oil supplied to the pressure still including the initial charge. i f

11. An improved method. of cracking hyl drocarbon oils, Which comprises circulating a charge of oil in a pressure still from a bulk supply drum throughheating tubes and back to the bulk supply drum and heating it to a cracking temperature in theheating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking off vapors from the bulk supply drum under pressure, dis

charging vpitch-laden oil from the c1rculating charge of oil, and supplying directly to the circulating charge of oil raw oil preheated by heat exchange with discharged pitch-laden oil. k

12. An improved method of cracking hydrocarbon oils, which comprises circulating a charge of oil in a pressure still from a bulk supply Vdrum through heating tubes and rback to the bulk supply drum and heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking olf vapors from the bulk su ply drum under pressure7 disconstant, supplying to the circulating charge of oil raw oil preheated by heat exchange with 'discharged pitch-laden oil, and restricting the amount taken off as distillate not to exceed about of the total raw oil supplied to the pressure still including the initial charge. f

EUGENE C. HERTHEL. HARRY L. PELZER.

charging pitch-laden oil from the circulating charge of oil in suilcient quantity to maintain said charge of oil substantially consta'nt, supplying to the circulating charge of oil ravv oil preheated by heat exchange With discharged pitch-laden oil, and restrict-V ing the amount taken ol as distillate not to exceed about of the total raw oil supplied to the pressure still including the initial charge.

13. An improved method of cracking hydrocarbon oils, which comprises circulating a charge of oil in a pressure still from a bulk supply drum through heating tubes and back to the bulk supply drum and heating it to a crackin temperature in the heating tubes, maintaining a bed of finely divided solid material extending entirely across the path of the circulating charge of oil in the bulk supply drum, taking 01T vapors from the bulk supply drum under pressure, discharging pitch-laden oil from the circulating charge of oil in sucient quantity to maintain said charge of oil substantially

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