US2045114A - Vapor phase cracking apparatus - Google Patents

Description

Patented June 23, 1936 UNITED STATES PATENT OFFICE Ernest W. Zublin, Fort Worth, Tex., assignor to Texas Pacific Coal & Oil 00., Fort Worth, Tex.,

a corporation of Texas Application July 14, 1933, Serial No. 680,345

4 Claims.

This invention relates to an apparatus for heating and cracking mineral oils and more particularly to an arrangement of flues and other apparatus elements for controlling the temperature and quantity of heating gases employed in heating vapor phase cracking units such as expander chambers.

Cracking of hydrocarbons may be accomplished by heating oil in the liquid phase, in the vapor phase or in the combined phases to a temperature Well within the cracking temperature range. For any given equipment for continuous conversion, the time of reaction is governed by the rate of flow of fluid through the unit and the size of the reaction vessel. At any particular rate of flow of oil the temperature of the cracking stock is determined by the temperature of the flue gases or other heating medium employed. It has now been found that the fixed gas and the gasoline yields depend largely on the temperature and the time factors in the unit as does the octane number of the gasoline produced. Heretofore it has been diflicult and commercially impossible to accurately control these factors to obtain best results. The apparatus of the present invention has a great flexibility, permitting more accurate control and hence is a considerable improvement over prior practice. The aim of modern processes is to operate under such conditions as to obtain the maximum gasoline output of the highest octane number with minimum production of fixed gas. The degree of success attained depends on a single time-temperature combination. The relation of time to temperature is found to be so critical that any substantial deviation from the optimum combination results either in a reduction in the quantity of the gasoline produced or in the octane number, or an increase in the gas production. Essentially, the principal object of the present invention is to provide an apparatus capable of attaining the optimum temperature in the shortest possible time, and of then maintaining the oil at that temperature for the exact time required for best results.

One feature which distinguishes the present apparatus from that heretofore used is the provision of a means for accurately controlling the temperature and volume of the flue gases employed for heating the expander equipment. In prior vapor phase apparatus wherein substantially all of the cracking was effected in the expanders, the oil vapors were raised comparatively slowly from incipient cracking temperature to the desired temperature. Where a series of expanders were employed the heating gases were passed serially therethrough, making it necessary that the heating gases be initially heated to quite a high temperature in order to retain suflicient heat to properly heat the subsequent expanders. This fact made it necessary to have one or more 5 special alloy expanders to withstand the temperatures of the initial gases which, in order to properly crack the oils, would have to be unusually high. The present apparatus besides providing for more accurate control of tempera- 10 tures in the expander equipment, makes it unnecessary to employ expensive alloy steel in the construction of the expanders, ordinary steel being satisfactory.

Another important object of this invention is 15 to provide means for recycling and re-circulating some of the heating gases after they have passed through an expander back to the inlet flue containing the hot gases to dilute and cool the gases,

with the result that the initial temperature of 2Qv the gases contacting the bottom of the expander are reduced, thus making it unnecessary to use expensive alloy equipment in such apparatus.

Another object of the invention is to provide a means for heating vapor phase expanders 25 adapted for cracking hydrocarbons which in cludes means for varying the temperatures maintained in the various portions of the apparatus such that the cracking may be carried on at that temperature best suited for each particular type 30 and grade of hydrocarbon treated, thus providing an apparatus of greater flexibility than heretofore obtainable.

Another object of the invention is to provide a siphon pump in the hot gas inlet conduit lead- 35 ing to an expander the suction side of which siphon pump is connected by a suitable conduit to the outlet flue to withdraw a portion of the cool gases and to reintroduce them into the hot gases thereby reducing their temperature, the 40 amount and relative temperature of said gases being suitably controlled.

Another object of the invention is to provide a plurality of dampers controlling the fiow of gases from the furnace through the expander or ex- 45 panders and through the various additional heat exchange equipment, such that precise control of the amount of heat transferred to the expander or expanders can be had without Waste.

Further objects and advantages of the inven- 50 tion will appear from the following description thereof taken in connection with the attached drawing in which Figure 1 is a diagrammatic representation of a preferred embodiment of the vapor phase cracking apparatus, and

Figure 2 is a vertical sectional view taken transversely through an expander unit manufactured in accordance with the principles of the present invention.

With reference to the drawing in detail, there is diagrammatically illustrated a pair of connected expanders l0 and I2 having vapor inlets II and I4 connected near their bottoms and outlets l3 and I5 for the processed vapors connected near their tops. The position of the inlets and outlets may be in reversed relation if so desired. Although two expanders are shown it is obvious that the novel features of the invention are equally applicable to any number of expanders.

The expanders l0 and I2 are preferably of the type described and claimed in the copending application of I. Morris Levine, Serial No. 664,294, filed April 4, 1933, although it is contemplated that other types of conversion apparatus may be employed if desired. The expanders l0 and I2 are substantially identical and it is thought that a description of one will suffice for the other. Each expander involves in its general organization an inner expander tank 5|] surrounded by a casing 52 which is provided with a removable dome 54 having an outlet 56 in the top thereof, said dome 54 being attached to the casing 52 in any suitable manner. The lower end of the casing 52 is provided with an inlet 58 into which the heating gases from the furnace 20 are admitted. Extending vertically through the expander tank 50 are a plurality of heating tubes l6 through which the heating gases are adapted to pass. An inlet conduit extends through the casing 52 and wall of the expander tank 50 to a point adjacent the bottom of the chamber provided within the tank. An outlet conduit |5 leads from the interior of the expander tank 50 adjacent the top thereof through the casing 52 for conducting the cracked hydrocarbon vapors from the apparatus.

The flue gases for heating the expanders are produced in a suitable furnace 20 situated most desirably directly below or adjacent to the expanders. A gas jet 2| using air from the supply line 22 is employed to furnish the heating gases, but any other hot flue gas source may be substituted therefor.

Connecting the expanders I0 and l2 and the furnace 2|! there is a hot gas intake conduit 24 adapted to conduct the heating gases to the expanders. This hot gas intake conduit 24, at a point near the furnace is provided with a siphon pump 25 of the Venturi type and has a by-pass 26 provided with a damper control 21. Beyond the siphon pump 25 the hot gas intake 24 is branched forming the intake line 240. leading to the expander l0 and intake line 24b to the expander |2. At the point where this line branches there is a two-way damper control 29 adapted to operate in such manner as to vary the amount of hot gases entering either of the expanders. Instead of this one damper, two independent dampers (not shown) may be provided in the branch lines.

The hot gases after heating the expanders pass through the outlet lines 30a and 30b to the. discharge conduit 30 leading ultimately to the stack. Suitable heat exchangers 32 and 34 are connected in the conduit 30, the former preferably heating the charging stock and the latter preheating the air for the furnace. The air heated by the heat exchanger 34 may be introduced through the conduit 22 into the burner 2| under pressure produced by any desired means, such as by the blower 45. If desired, or found necessary, a steam jet or blower (not shown) may be placed in the stack for assisting passage and final discharge of the heating gases.

The discharge conduit 30 has a plurality of offtake lines 35, 36 and 31, respectively provided with damper controls 38, 39 and 40. All of these lines lead to a recirculation conduit 4| connected into the hot gas intake conduit 24 at the siphon pump 25 therein.

In operation the oil charging stock is preferably initially passed through the heat exchanger 32 and is then conducted through a suitable additional heater or vaporizer 46 wherein it is completely vaporized. The vapors produced pass through the inlet into the first expander |0 out through lines l3, through line l4 into expander 2 and finally out through line l5 to be quenched and fractionated as desired.

Due to the heating gas from the furnace 20, the temperatures in the expanders are such that the desired chemical changes of cracking take place.

The control of the heating in the expanders is effected by operation of the illustrated dampers. The hot gases from the furnace 2|] pass through the hot gas intake conduit 24 into the respective expanders, the amount of heat for each expander being dependent upon the position of the two-way damper 29. Inasmuch as each expander receives some of the fresh flue gases, it is unnecessary that the heating gases be as hot as when the expanders are connected for series heating, as heretofore practiced. Thus each expander may be made of ordinary metal, thereby avoiding the use of expensive alloys formerly found necessary.

The heating gases after passing through the expanders and heating the vapors therein then pass out in the gas conduit 30 through the respective heat exchangers and finally up the stack. The exchangers each reduce the temperature of the heating gases by a number of degrees with the result that the offtakes 35, 36 and 31 withdraw gases of different temperatures to be recycled into the initial heating gases. The amount of gases recirculated depends upon the suction caused by the siphon pump as well as the positions of the off-take dampers 38, 39 and 40. The temperatures of said gases depends upon which of said dampers are opened and which closed. Obviously a wide range of temperatures can be had by operation of said dampers singly or in combination.

The hot gases passing through the siphon pump 25 cause a reduction of pressure in the recirculation conduit 4| and draw cooler gases from the gas discharge conduit 30 into intimate mixture With the hot furnace gases, the suction force in the siphon pump being controlled by the damper 21. The resulting lower temperature gases makes it possible to equalize the temperatures of the gases circulating through the expanders to that desired without having excessively hot gases contact with the expander chambers making it possible to build the expanders of ordinary materials and reducing the number of failures due to burnouts.

By the recirculation of cool gases and the definite control of the temperature of the gases, the temperature of said gases need not be higher than that degree actually required for proper heat exchange in the expanders. Furthermore, with more accurately controlled temperatures and better use of the sensible heat of the exhaust gases, a considerable economy is effected in the amount of fuel consumed.

Another feature of importance is that the ex- 75 cess heat of the heating gases is conserved in the heat exchangers 32 and 34, the said gases being thereby efliciently reduced in temperature and made suitable for diluting and partially cooling the hotter gases formed in the furnace. Without this recirculation the temperature of the heating gases is dependent upon the combustion temperature which usually cannot be reduced without sacrificing efiicient combustion.

The provision of heat exchangers is of importance to the commercial success of the equipment because the lower temperature differentials between the flue gases and vapors lowers the heat exchanging efliciency per unit surface.

Another important feature is that the apparatus is flexible and can be successfully controlled for converting many difierent types and qualities of hydrocarbons. A slight variation in position of the dampers results in materially higher or lower temperatures in either or both expanders with the result that the hydrocarbon vapors may be heated very rapidly or very slowly as desired, making it possible to obtain optimum operating conditions of time and temperature for the greatest yield of the best quality gasoline.

The siphon pump 25 is highly efiicient in recycling the relatively cooler gases for it may be constructed of a material such as carborundum which is unaffected by the high temperature of the heating gases. The use of special heat resisting materials can be avoided if the siphon pump is positioned very close to the tip of the burner 2| thereby causing the larger part of the combustion and heating to occur at a point in the flue beyond the siphon pump, leaving the same relatively cool. In this position, the driving force operating the siphon pump is obtained by the pressure on the gas line as well as that on the air line. A blower might by used instead of the siphon pump though with less satisfactory results. If so desired the heater 46 may be supplemented by an additional heater to superheat the vapors to a temperature below, equal to, or above that at which cracking commences.

While I have shown a preferred embodiment of my invention, I am aware that modifications may be made thereto and I therefore desire a broad interpretation of my invention within the spirit of the description herein and of the claims appended hereinafter.

I claim:

1. In combination with two or more expander chambers for converting hydrocarbon vapors having inlet and outlet conduits for the passage of hydrocarbon vapors in series therethrough and a plurality of heating tubes within each chamber for the intimate indirect heating of the vapors by the conduction of heating gases therethrough,

a heating gas control system including a source of heating gases, conduits for conducting said heating gases from said source to said chambers for passage through said heating tubes, damper means adapted to proportion the hot gases lead to the chambers through said conduits, means to 5 conduct cooled spent gases issuing from the expanders to a stack, and means to recirculate part of said cooled gases from said stack back to said intake conduits to reduce the initial temperature of the gases conducted to the chambers.

2. A plurality of expander chambers for cracking hydrocarbon oils in vapor phase having vapor inlet and outlet conduits, connected for passage of vapors in series and each chamber having a plurality of heating gas tubes extending therethrough, means to heat gases for the intimate indirect heating of the vapors including a hot gas source, means to dilute the hot gases with cooler gases, means to introduce the diluted gases into the heating tubes of each chamber, and a regulated means to proportion the amount of mixed gases between the expander chambers.

3. Apparatus for cracking hydrocarbon vapors which comprises an expander chamber having vapor inlet and outlet means and a plurality of heating tubes extending through said chamber for conducting heating gases into intimate indirect heating of the vapors within the chamber, a conduit for conducting hot flue gases to the heating tubes, and a conduit for conducting the gases away from the heating tubes, a gas recirculating conduit connecting the first conduit and the second conduit, a siphon pump in the first conduit in communication with the recirculating conduit adapted to withdraw some of the gases from the second conduit through the recirculating conduit to the first conduit to cool the gases therein, damper means in the recirculating conduit adapted to vary the amount of cooling gases recirculated, a second chamber connected in series 40 with the first chamber with respect to vapors and in parallel relation with respect to heating gases, and means to proportion the amount of heating gases conducted to each chamber.

4. A plurality of expander chambers connected in series relation for cracking hydrocarbon oils in vapor phase having vapor inlet and outlet conduits, each of said chambers having a plurality of internal heating gas tubes extending therethrough and around which said vapors are adapted to pass, means for indirectly heating the vapors in said chambers including a source of heating gases, means for diluting the hot heating gases with cooler gases, means to introduce the diluted gases into the heating tubes of the chambers to indirectly heat the vapors in the same, and means to proportion the flow of diluted gases to the heating tubes of said chambers.

ERNEST W. ZUBLIN.

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