US2013803A - Cracking hydrocarbon oils - Google Patents

Description

Sept. .10, 1935. I E Wl [SOM 2,013,803

CRACKING HYDROCARBON OILS Filed April 14, 1931 BY /A/ 49%,@1 vga/WQ W. ATTORNEYS Patented Sept. 10, 1935 UNETED STATES zonen PATENT FFCE CRACKING HYDROCARBON OILS corporation of Maine Application April 14, 1931, Serial No. 529,979

9 Claims.

This invention relates to improvements in the cracking of higher boiling hydrocarbon oils, such as kerosene and gas oil character stocks, for the production of lower boiling hydrocarbon oils, such as gasoline and in particular motor fuel gasoline.

The invention relates particularly to improvements in cracking operations carried out at high cracking temperatures, upwards of lO F. At such tem eratures the higher boiling stock supplied to the operation is maintained in the vapor phase, substantially completely, throughout the cracln'ng operation proper. Small amounts oi tarry matter or carbonaceous matter formed during the cracking operation or very small amounts of very heavy constituents of the stock may be carried in the oil-vapor mixture as a fog or mist, but the predominating proportion of the eil is in the vapor phase. For this reason, such operations have commonly been designated vapor phase cracking operations.

The products of cracking operations in which higher boiling oils are subjected to such high cracking temperatures include, if the conditions are otherwise appropriate, constituents of special value as components of motor fuels. Such operations are thus of special value and application in the production of motor fuel gasoline having a relatively high critical compression or having anti-knock properties when burned in the usual type oi gasoline internal combustion engine.

Not all of the results ci cracking operations in which higher boiling oils are subjected to such higher cracking temperatures are advantageous. Normally such operations tend to involve formation of unstable unsaturated constituents boiling within the range of the desired lower boiling oil products, gasoline, for example. The presence of such unstable unsaturated constituents in the lower boiling oil products in turn renders these products unstable and the elimination of such constituents from these products involves at best further rening operations increasing the cost of production.

If the higher boiling oil, after being heated to a high initial cracking temperature, is maintained in totality at this high cracking temperature, or at a temperature increasing somewhat from the initial high cracking temperature, for a prolonged period of time, the tendency toward formation of such unstable unsaturated constituents is suppressed and is superseded by a tendency toward the formation of aromatic constituents, which are not unstable and which do not introduce unstability into the desired oil products, and which, as constituents of the desired oil products, are usually even more valuable, with respect to the properties of these oil products as motor fuels, than are such unstable unsaturated constituents. 5

In operations in which the necessary heat is suppliedA by heat exchange between the oil and hotter products of combustion, the maintenance of the oil stream flowing through the cracking operation at the requisite high cracking tempera- 1o tures for a suiciently prolonged period of time has involved the maintenance of relatively small temperature differentials between the heating gases and the oil stream throughout that part of the heating operation in which the oil stream is l5 being maintained at a high cracking temperature, as distinguished from that part of the heating operation in which the oil stream is being initially brought to that high cracking temperature, with consequent reduction in the capacity of the heat transferring surfaces used in this inst-mentioned part of the operation.

The present invention provides for the maintenance of the oil stream in such 'cracking operations at a high cracking temperature for a period of time which may be prolonged to any desired extent without involving the disadvantages incident to the maintenance of low temperature differentials between heating gases and the oil stream. vides ior the progressive stabilization of the products oi cracking operations in which `higher boiling 'oil is heated to high cracking temperatures enabling the production of lower boiling oil products having the desirable characteristics of the products of such operations, so far as they are desirable in motor fuels for example, while containing but a minimum of unstable unsaturated constituents.

According yto thepresent invention a stream of 40 higher boiling oil is heated to an initial high cra-cking temperature and 'is then ymaintained at a temperature not less than that initial temperature for a-prolonged period of Atime by passing the stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with hotter products of combustion and to `digestion without extraneous heating. The expres-sion in totality as used lin the preceding sentence and elsewhere in fthe -speciiication and 50 claims of this application is intended to mean Ya composite mixture lof all of the fluid oil products initially supplied to the rst cycle or subsequently produced therefrom irrespective of whether they are in the vapor orliquid state. Inother Words,

In another aspect the invention pro- 30` it is intended to mean that the separation and separate discharge of either light oil vapors or heavy liquid oil at any point in or intermediate successive cycles is precluded. The temperature to which the stream of oil is initially heated is advantageously a temperature upwards of 1000 F., or better upwards of 1100a F. During heat Xchange with hotter products of combustion in each cycle, the temperature of the oil stream is increased somewhat, and during subsequent digestion without extraneous heating in each cycle the temperature of the oil stream decreases somewhat, due to absorption of heat in the cracking reactions and to heat losses, but the period of digestion in each cycle is limited, with respect to the rate of temperature decrease during digestion and with respect to the extent of temperature increase during heating, so that the temperature of the oil stream as it passes from each digestion to the subsequent heating of the next cycle is not lower than that to which the stream of oil is initially heated. The variation in temperature of the oil stream during each cycle may be made very small without limiting the total period of time at which the oil stream is maintained at a high cracking temperature by increasing the number of cycles. This temperature variation is advantageously limited not to exceed F., or better not to exceed 25 F. The heating gases passing in heat exchange with the oil stream in each cycle may advantageously be at a temperature F., 300 F., or more, higher than the maximum temperature of the oil stream.

'I'he invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally, in Fig. 1, in sectional elevation, one form of apparatus adapted for the practice of the invention, but it is intended and will be understood that this further description and illustration are for the purpose of Vexempliiication and that the invention is not limited thereto. The invention may be practiced in other and different forms of apparatus; reference will be made in the following description to some other forms of apparatus adapted for the practice of the invention. Figs. 2 and 3 of the accompanying drawing are graphs illustrating relations between time and temperature which may be maintained in the practice of the invention.

In the apparatus illustrated in Fig. 1, a heating coil 4 for initially bringing the stream of oil to a high cracking temperature and a plurality of heating coils 5, 6 and 'l, for heating, or reheating, the stream of oil in each of the series of heating-digesting cycles through which the stream of oil is passed after being brought to an initial high cracking temperature, as well as a nal heating coil 8 are arranged in a common heating furnace 9. These heating coils may, however, be arranged in separate heating furnaces. The initial heating operation, bringing the oil to a high cracking temperature, is advantageously eiected in as short a time as possible and consequently the heating coil 4, or its equivalent arranged in a separate furnace for example, is advantageously arranged for a maximum heat input, that is by radiation rather than by convection. The heating coils 5, 6 and I may be heated by radiation rather than by convection, but in general these heating coils, or their equivalent, are more advantageously heated by convection.

In the apparatus illustrated in Fig. 1, the heating coil 4 is arranged in the roof of the furnace over the rebox l0 which is divided from a heating flue H by a bridge wall l2 and the heating coils 5, 6, 7 and 8 are arranged in the heating flue I l. The heating coils 5, 6, 'l and 8 are advantageously arranged in the heating flue Il so that the oil ilow through them is generally countercurrent to the flow of heating gases over them, as illustrated. The preponderating proportion of the heat absorbed by the heating coil 4 is transmitted to it from the fire-box as radiant heat. The heating gases from the hre-box pass over the bridge wall I2 and through the heating iiue Il to the stack flue i3. A part of the escaping heating gases is advantageously recirculated through the heating flue H, being reintroduced through iiue l. Air for combustion of the fuel burned to supply the heat required in the operation is advantageously preheated by heat exchange with the remaining part of the escaping heating gases and supplied to the lire-box through port l5, fuel, fuel oil for example, being supplied through the nozzle I6. It will be understood that duplicates of the ilues i3 and M, the port I5 and the nozzle i6 are arranged at the opposite end of the furnace illustrated.

The recirculation of heating gases through the heating flue and such recirculation of heating gases in conjunction with the supply of preheated air for combustion in apparatus such as that illustrated is described in Letters Patent Numbers 1,574,546 and 1,57%,547 granted February 23, 1926 and Number 1,623,773 granted April 5, 1927 to Sinclair Refining Company on applications of John E. Bell.

In the apparatus illustrated in Fig. l, the digesters il', i8 and ES consist of a plurality of drums relatively long with respect to their diameter arranged in a thermally insulated chamber 20. The deposition or" carbon and tarry matter tending to be greatest in the regions in which the temperature is decreasing, these digesters are arranged to afford a maximum of convenience with respect to necessary cleaning. The apparatus illustrated comprises but a single digester for carrying out the digestion in each of the series of heating-di- 4 gesting cycles; two or more digesters may be connected in series for carrying out the digestion in each heating-digesting cycle. In place of the enlarged drums illustrated a thermally insulated coil affording an equivalent time factor may be used, but the enlarged drums are in general more advantageous since they are more easily cleaned and since the pressure drop through an equivalent coil is greater.

In practicing the invention in the apparatus illustrated, for example, a stream of oil is .forced by means of pump 2! in totality through the heating coil through the heating coil 5 and the digester i9, through the heating coil 5 and the digester IS, through the heating coil 'l and the digester Il, through the heating coil 8 and then through connection 22. As the oil enters the heating coil i (point A) it may have, for example,

a temperature oi 400-500" F., as it enters the heating coil 5 (point B) it may have, for example, a temperature of 1000-1l00 F., as it enters the digester IS (point G) it may have, for example, a temperature of 1050-1150 F., as it enters the heating coil 6 (point D) it may have, for example, a temperature of 1000-1l00 F., as it enters the digester I8 (point E) it may have, for example, a temperature of 1050-1150 F., as it enters the heating coil (point F) it may have, for example, a temperature of 1000-l100 F., as it enters the digester I1 (point C) it may have, for example, a temperature of 10501150 F., as it enters the heating coil 8 (point I-I) it may have, for example, a temperature of 1000-l100 F., and as discharged from the heating coil 8 (point I) it may have, for example, a temperature of 1050-1 150 F.

The temperature in the fire-box vIii may approximate, for example, 2200-2509" F., and the temperature at which the heating gases escape through stack flue i3, after being tempered by the recirculation of part of these heating gases through the stack iiue lf3, may approximate, for example, 1306-1500" F. By recirculating through the heating flue il a relatively large proportion of the heating gases escaping through stack flue 1 3, the temperature of the mixture of heating gases as it enters the upper end of this heating flue may be brought fairly close to that at which it escapes therefrom enabling the maintenance, in conjunction with generally countercurrent circulation of the oil stream with respect to the heating gases in the heating flue, of fairly uniform temperature differentials between the heating gases and the oil throughout the heating flue.

The furnace may be operated so that the increase in temperature of the oil stream as it passes through the heating coils 5, 6 and 'l approximately equals the decrease in temperature of the oil stream as it passes through the digesters il, i8 and i9, respectively, or so that the increase in temperature of the oil stream as it passes through each heating coil is somewhat greater than the decrease in temperature of the oil stream as it passes through the successive digesters. In the latter case the mean temperature of the oil stream gradually and progressively increases as it passes through the series of cycles after being heated to the initial high cracking temperature at which it is supplied to the rst of the cycles.

After discharge through the connection 22 the stream of hot oil products may be subjected to any desire-d operation for the separation and recovery of its components, for example, into tar, into higher boiling fractions, and into lower boiling fractions, including or corresponding to the desired lower boiling oil products. The oil may be supplied to the cracking operation under pressure just sufficient to force it through the successive heating coils and digesters into the separation and recovery apparatus or it may be supplied under a higher pressure and this margin of pressure released as the hot oil products are discharged from the final heating coil 8, by means of valve 23 for example. The discharge pressure from the final heating coil 8 may approximate, for example, atmospheric pressure or higher pressures up to 30G-500 pounds per square inch or even higher. To. check the cracking reactions as the hot oil products leave the iinal heating coil 8, a stream of relatively cool oil may be supplied through connection 2li in amounts suiiicient to reduce the temperature of the composite stream of oil discharged through connection 22 to a point such that further cracking of the oil products discharged frorn the heating coil 8 is inhibited or prevented.

Figs. 2 and 3 are graphs illustrating relations between time and temperature which may be maintained in the practice of the invention. Referring to Fig. 2, this graph illustrates the heating of a stream of oil to a high initial cracking temperature, at the point so designated on the drawing, 1l00 F. for example, followed by the subjection of this stream of oil in a series of cycles to alternate heating to a somewhat higher temperature, 1l25 F. for example, and digestion during which its temperature decreases to a temperature approximating the initial high cracking temperature, 1100 F. for example. Referring to Fig. 3, this graph illustrates the heating of a stream of oil to a high initial .cracking temperature, at f the point so designated on the drawing, ll F. for example, followed by the subjection of this stream of oil in a series of cycles to alternate heating to a somewhat higher temperature, 1125- 11.40 F. for example, and digestion during which 10 its temperature .decreases by a margin somewhat less than that to which it is reheated in the next heating, 25 F. for example.

The separation and recovery operations described in an application led June 13, 1927, l Serial Number 198,621, by Harry L. Pelzer, may be used with advantage in conjunction with the heating operation of this invention. The coking operation described in an application filed February 18, 1929, Serial Number 340,996, by Harry L. Pelzer, may also be used with advantage in conjunction with the heating operation of this invention.

I claim:

1. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating zone and heating said stream of oil to an initial high cracking temperature suflicient to effect substantial Vaporization of said oil .at the pressure to which it is subjected and maintaining it at a temperature not less than said initial high cracking temperature for a. prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in an enlarged digestion Zone without extraneous heating or substantial extraneous cooling.

2. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating zone and heating said stream of oil to an initial temperature upwards of 1000 F. and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said -stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the cil in said cycles and to digestion in an enlarged digestion zone without extraneous heating or V substantial extraneous cooling.

3. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a, stream of liquid oil to an elongated heating Zone and heating said stream of oil to an initial temperature upwards of 1100 F. and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in 'an enlarged digestion zone without extraneous heating or substantial extraneous cooling.

4. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating zone and heating said Stream of oil to an initial high cracking temperature sucient to eiect substantial vaporization of said oil at the pressure to which it is subjected and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in an enlarged digestion zone without extraneous heating or substantial extraneous cooling, the temperature variation in each cycle not exceeding F.

5. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating zone and heating said stream of oil to an initial high cracking temperature sufficient to eiect substantial vaporization of said oil at the pressure to which it is subjected and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in an enlarged digestion zone without extraneous heating or substantial extraneous cooling, the temperature variation in each cycle not exceeding 25 F.

6. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating Zone and heating said stream of oil to an initial high cracking temperature suil'icient to effect substantial vaporization of said oil at the pressure to which it is subjected and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion at a temperature exceeding the maximum oil temperature by at least F. and to digestion in an enlarged digestion zone Without extraneous heating or substantial eX- traneous cooling.

'7. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hydrocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heating zone and heating said stream of oil to an initial high cracking temperature suilicient to eiect substantial vaporization of said oil at the pressure to which it is subjected and maintaining it at a temperature not less than said initial high cracking temperature for a prolonged period of time by passing said stream in totality through a series of cycles in each of which it is subjected 5 successively to heat exchange with products of combustion at a temperature exceeding the maximum oil temperature by at least 300 F. and to digestion in an enlarged digestion zone without ex- Y traneous heating or substantial extraneous cool- '10 ing.

8. In the cracking of higher boiling hydrocarbon oils for the production of lower boiling hyj drocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated 15 hea-ting Zone and heating said stream of oil to an initial high cracking temperature suicient to elect substantial vaporization of said oil at the prevailing pressure, subsequently passing said stream in totality through a series of cycles in 20 each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in an enlarged digestion zone without extraneous heating or substantial extraneous cooling, and con- 25 trolling the duration of the successive heating and digestion operations so that the temperature of the oil in each successive heating operation increases not more than 100 F. and so that the temperature of the oil in each successive digestion 30 operation decreases but by an amount not more than the increase in temperature in the immediately preceding heating operation.

9. In the cracking of higher boiling hydroca-r- Y. bon oils for the production of lower boiling hy- 35 drocarbon oils, the improvement which comprises supplying a stream of liquid oil to an elongated heated zone and heating said stream of oil to an initial high cracking temperature suicient to elect substantial vaporization of said oil at the 40 prevailing pressure, subsequently passing said stream in totality through a series of cycles in each of which it is subjected successively to heat exchange with products of combustion hotter than the oil in said cycles and to digestion in an 45 enlarged digestion zone without extraneous heating or substantial extraneous cooling, and controlling the duration of the successive heating and digestion operations so that the temperature of the oil in each successive heating operation in- 50 creases not more than 25 F. and so that the temperature of the oil in each successive digestion operation decreases but by an amount not more than the increase in temperature in the immediately preceding heating operation. 55

EDWARD W. ISOM(

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