US1919672A - Process for cooling and safeguarding oil cracking apparatus - Google Patents

Description

July'z, ||l THOMAS ET AL PROCESS FOR vCOOLING AND SAFEGUARDING `OIL'CRACKING APPARATUS LOA wwe n? H4 @wxv 7W Patented July 25, 1933 e mias-7s- ArNr vrei/cs HENRY rnoiues, or itin-LEY raux, CLAREN A. THOENGATE, on onEsfrEu, rENNsYL CE n. Tarieven, or NEMA, 'AND FREDERICK venin, inssIeNons To sUN OIL COMPANY,

on riemen-Eurem, rENNsYLvANrA, A Conronsfri'on OE NEW JnEsEY rnoonss :son COOLING AND sarnsrrnunine ort CnnCxiNe ArPnRA'rUs Application i'led'Marcli 20, 1930. Serial No. 437,352;

@ur invention relates to the art of cracking hydrocarbon oils by subgecting oil flowing through tubes to a cracking temperature for a sufi'icient length of time' to eifect a part orI tual cleaning operation it is necessary .to coolv the furnace containing the heating coils' and remove the oil and Oil vapors from the coils. This is frequently accomplished by forcing through the tubes, after the furnace fires have been turned out, relatively cold oil, Which graduallv absorbs the heat contained-in the furnace brickwork andy tubes, after Which steam under pressure may be turned into the coils to remove the oill vapors.- Such procedure'requires a considerable amount of timel and itis desirable, from a commercial standpoint, to reduce this non-operating time'to the practicable minimum.

One of the main objectsof the inventionV is to more quickly cool the heating coils when it is f desired to shut down the apparatus. Another object of the invention is to reduce the expense of the cooling operation.

During the cracking operation. any serious oil leak or break may result'in a serious lire. Still another object of the invention is to provide safeguards against serious results in the eventof leakage o r breakage.

Our 'invention involves a. means and proc-` ess vof cooling` which eliminate the cost of pumping oil through the coils for `cooling effect and eliminate, also, the introduction of boileifprodiiced steam vinto the coils for the purpose of removing oil and. oil vapors. The equipment for cooling kthe heating coils is, to a substantial extent, the same equipment that is available for use, in case of leakage or breakage, to prevent serious consequences.

The invention is adaptable to various crackiiio` plants and processes and may be embodied in many different forms. To illustrate the invention, We have shovvn.,l in4 the v products.

accompanying drawing, a` diagram ofl a typi cal cracking plant provided with equipment adapted to effect the objects hereinbefore specied. y

The heating coil 2 is'placed in a furnace 1. The heating coil may consist of a plurality of tubes or sets of tubes connected in series or in parallel. Element 3 is a heat exchanger utilized to cool the cracked oil to the desired temperature for-v further processing and which returns the excess heat so removed to Y the charging stock entering heating coil 2 through pipe line 13. Tank 1 contains the Oil to be processed. Pump 5 reino-ves the oil from tank 4 through pipe line 6 and forces it through heat exchangers 7 and 8. These` heat exchangers 7 and S transfer heat from some of the products from fractionating tower` 9 to the charging oil. `From these heat'exchangers the oil flows through pipe line 10, in which is interposed a pump 11 which provides the high pressure required` to force the .oil through heat exchanger 3, heating coil 2, line 13 and throttle valve.12. After being` heatedr and .cracked in heatingcoil 2 the oil passes out through pipe line 13,' throttle valve 12, heatk exchanger 3. and thence into fractionating tower 9 Where the cracked oil is separatedA into the desired Gasoline vapor or distillate, together with the so-c'alled fixed or incondensible gases, passes from the top of fractionating tower 9 through line 14 into condenser 15 and thence into gas separator 16.,Y The incon densible gases are disposed of through line 17 and gasoline or'distillate through line 18 into receiver 19. 'A portion of the gasoline is pumped fromgas separator 1G by means of line 2() and pump 21 into the Lipper part, of fractionating tower 9 in order tobe revaporized and: thus absorb the required amount of vheat to effect refluxing in fractionating tower 9. v

An intermediate product, which normally Will be gas oil, passes from the central sec-' tion of tower 9 through line 22 and heat exchanger 7 and thence to receiver23 through line 24j Y y A heavier product, Which Will ordinarily be used as fuel oil, passes from the bottom of tower 9 through line 25, heat exchanger 8, and cooler 26 to receiver 27.`

The above description discloses the flow of oil in the normal cracking process, during which the carbonaceous deposit accumulates in heating coil 2, pipe line 13, and perhaps heat exchanger 3. rlhis deposit tends to decrease the heat transfer between the furnace gases or other heating medium and the oil. lt increases the amount of pressure required to force the oil through heating coil 2 and by its insulating action tends to cause over heating of the metal tubes comprising the heating coils. Consequently it becomes necessaryv to shut down the equipment and clean it.

Because of the inflammable nature of the material being processed, it is common practice to provide, for use in emergencies, a means for quickly disposing of the oil in the system. ln the apparatus being described, two such provisions are made. The first provision consists of pipe line 28, and a hand or power operated valve 29, which may be opened to quickly discharge the oil from heating coil 2 into a suitable receiver or stack 3l, which is located at a safe distance from the cracking apparatus; also an automatic relief valve 30 which opens in the case of an excess pressure in the system and which also discharges to the same receiver or stack. Tater is sprayed into the top of the stack by means of line 32 for the purpose of cooling the oil vapor as it rises through the stack. A sewer 33 is furnished to dispose of the condensed oil and water. The second provision consists of a so-called circulating system consisting of a water-cooled coil 34 through which the oil leaving heat exchanger 3 may be discharged, by means of line 35 and valve 3G, into tank 4 or tank 23. This circulating coil 34 may be used to cool the oil passing from heating coil 2 and heat eXchanger 3 at any time it is not desired to put it into tower 9.

A water supply line 37 is connected to the suction. of charging pump 11 and is so arranged that by manipulation of valves 38 and 39 the charging oil may be shut off and water introduced into the pump.

rlhe following procedure is observed in shutting down the processing equipment:

The fuel to the burners in the furnace is shut off. Valve 38 is opened which admits water to the suction of charging pump 11. Check valves 40 and 4l prevent water from backing into oil line l() or oil from entering water line 37 depending upori Whether the oil pressure or 'water pressure isthe higher. Valve 39 on oil line 10 is shut olf. Pump 5 is then stopped. The amount of water passing through pump 1l is regulated as desired either by cl'ianging the speed of the pump or by throttling the discharge of the pump by means of valve 42. The water rate is regulated as necessary so as to maintain an established pressure at the discharge side of pump ll. This pressure generated by pump ll and the pressure of the steam into which the water is converted when it reaches the hot sections of the apparatus drive the oil and oil vapors out of heating coil 2 through line 13. The amount of time required to do this is of course largely dependent upon the pressure maintained on the system and the volume of oil to be displaced. The plant opera-tors learn by experience the approximate time required and before water or steam reaches the outlet of heat-ing coil 2 a small bleeder valve 43 in line 13 is opened. As soon as steam or water appears at bleedcr valve 43 emergency valve 29 is opened and valve 44 on line 13 at the inlet to tower 9 is closed, thus permitting the water vapor to discharge into the bottom of stack 31 through line 23. Pumping of water into heating` coil 2 is continued until the temperature has dropped enough to permit the tube cleaning crew to begin work.

It will be realized that, due to the specific heat and latent heat of evaporation of water being much higher than that of oil, the apparatus is cooled down to the desired temperature within a small fraction of the time that would be required by circulating cold oil through the tubes. Furthermore, the removal of oil and oil vapors from the hea-ting coil has been accomplished during this cooling period. f

One of the features of the invention not yet'described consists of means for quickly dissipating the pressure existing in heating coil 2 after water has been forced into it for the desired amount of time. T he heating coil in such an apparatus may consist of several thousand feet of tubing connected in series. A considerable amount of time would be required to relieve the water vapor pressure from one or both ends of the coil, especially since the water laying in the tubes continues to evaporate after the pumping isv discontinued. Furthermore, it is not considered safe to remove plugs from the return bends connecting the tubes until the pressure in the tubes is practically atmospheric, as otherwise workmen engaged in the work might be scalded.

Connections into the return bends with valves 45 have been provided which are opened as soon as pumping of the water into heating coil 2 is discontinued. The water vapor under pr-essure is thus permitted to escape at a plurality of openings. If disagreeable to discharge the vapor into the ati mosphere, pipe connections 46 to available sewers may be provided. @rdinarily these are disconnected during cracking operation of the apparatus and blank flanges are bolted to the outlet of the valves 45. This is done to preclude the possibility ofV oil leaking through the Valves and into the sewer and escaping observation by the plant operators.

Having now full described our invention, what we claim and desire to protect by Letters Patent is v l. The process of cooling the heatingcoil of an oil cracking apparatus in which hydrocarbon oil under pressure flows continuously through a pipe coil which is subjected to heat sulici-ent to raise the oil to a cracking temperature, and in which cracked hydrocarthe How of water through the pipe coil and by-passing the same until the pipe coil has cooled suliciently to p-ermit manualoperation thereon, and then venting the pipe coil intermediate its ends to quickly dissipate the pressure therein.

y 2. The process of cooling the heating'coil of an `oil cracking apparatus in which hydrocarbon oil under pressure Hows continuously through a pipe coil which is subjected to heat suiificient to raise the oil to a cracking temperature, and in which cracked hydrocarbon `rflows towards a fractionating equipment,

which comprises discontinuing the supply of heat to the coil, flowing water under pressure through heat interchanging apparatus, wherein the water is heated by fluid from the coil, and thence through the coil, thereby Y elifecting conversion of water into steam and v driving oil ahead of the steam and water'out of and beyond the coil and beyond the heat exchanging apparatus, and at about the time that steam beginsto outflow from the pipe Y coil by-passing the steam, owing the bypassed steam together with oil vapor mixed therewith toward a locus of cooling, iiowing water to said locus to eect the cooling of the oil vapor by intimate contact therewith, and

continuing the iiow kof water through the pipe coil and by-passing the same until the f pipe coil has cooled suliiciently to permit manual operation thereon.

l HENRY THOMAS.

CLARENCE H. THAYER. FREDERICK A. THORNGATE.

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