US2520096A - Fluid heater and reactor unit - Google Patents

Description

Aug. 22, 1950 1. HARTER FLUID HEATER AND REACTOR UNIT Filed April 27, 1946 INVENTOR Isaac Harrier BY 7 ATTORNEY Patented Aug 22, 1950 UNITED STATES PATENT OFFICE FLUID HEATER AND REACTOR UNIT Application April 27, 1946, Serial No. 665,417

Claims.

This invention relates in general to apparatus for the thermal decomposition of pyrolysis of organic compounds, and more particularly, to apparatus for the thermal cracking of vaporphase hydrocarbons under relatively low pressures and high temperatures.

The thermal cracking of vapor-phase petroleum hydrocarbons at W pressures and high temperatures has been heretofore proposed, but such processes did not survive in commercial practice because of poor heat conduction, eXces sive coke formation, and extreme sensitiveness to operating conditions attributable in large part to the apparatus in which such processes were attempted.

The general object of this invention is the provision of an improved apparatus for the thermal cracking of vapor-phase hydrocarbons at relatively low pressures and high temperatures which are characterized by a high rate of heat transfer to the hydrocarbon vapor being treated, low amount of coke formation, and the maintenance of stable operating conditions throughout the operating period. A further and more specific object is the provision of an apparatus of the character described in which a stream of hydrocarbon feed stock is continuously introduced into a low pressure reaction chamber and heated to a cracking temperature therein by intimate contact with a circulating fluent mass of inert refractory heat transfer material to produce a cracked gas mixture having a predetermined composition, while any coke or carbon residue from the cracking operation is continuously removed from the reaction chamher and subsequently utilized for supplying a portion of the heat requirements of the refractory heat transfer material under eiiicient heating conditions.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated and. described.

Of the drawings:

Fig. 1 is a somewhat diagrammatic elevation, partly in section, of apparatus embodying the invention for the thermal cracking of vaporphase hydrocarbons.

2-2 of Fig. 1; and

Fig. 3 is a horizontal section taken on the line 3-..3 of Fig. 1.

While the invention in its broader aspects is adapted for the treatment of a wide range of hydrocarbon materials, the apparatus illustrated is particularly designed and especially adapted for the thermal treatment of petroleum hydrocarbons, such as natural gas or gasoline, arti fi-. cial illuminating gas, gasoline vapor, oil vapor, gas oil vapor, parafiin series hydrocarbons, olefin series hydrocarbons,and cyclic hydrocarbons of the naphthene and benzene series, capable of being heat-treated to produce a cracked gas mixture.

Processes and apparatus for the pyrolysis of petroleum hydrocarbons to produce acetylene and other gaseous compounds have been heretofore proposed, for example, in the Hasche Pate. ents 2,236,534, 2,236,535 and 2,219,679. One of the major disadvantages of such prior processes and apparatus is the difficulty of continuously heating the feed stock to the optimum cracking temperature and of maintaining such heating temperatures in the reaction chamber for long peliOdS of time without interrupting the operation for the elimination of carbon deposits.

In accordance with the present invention the apparatus in which the hydrocarbonaceous feed stock is treated consists of a vertically elongated fluid heater having a substantially cylindrical fluid tight casing ll lined with an annular wall of high temperature refractory material [2. The upper end of the heater is formed by a conical plate i3 also lined with high temperature refractories and having a central heating gas outlet M controlled by a damper 55. An inlet for solid heat transfer material is arranged in one side of the plate I3, while an access opening ii is located at the opposite side. The in.-.

terior of the fluid heater is divided into an upper or heating chamber is in which solid heat transfer material is heated to a predetermined temperature and a lower or reaction chamber 2| in which the hydrocarbonaceous feed stock is sub,

jected to the desired thermal decomposition by heat absorption from the heat transfer material therein. The refractory lining !2 is shaped to provide an inverted conical formation for both the upper chamber ill and lower chamber 2|, and an unobstructed connecting throat passage 22 of circular cross-section and substantially smaller diameter than the average diameter of either chamber Zil or 2|. The throat 22 has a slight flare downwardly to facilitate the flow of solid heat transfer material therethrough. The lower end of the lower chamber 2i is formed by an inverted frusto-conical screen 25 open at its lower end and concentrically arranged with respect to a central opening 26 in the inverted conical bottom 21 of the casing The annular space between the screen 25, casing I and bottom 2'! forms an inlet chamber 28 for the hydrocarbonaceous feed stock which is supplied thereto through a pipe 29 above the upper end of the screen 25 and the lower end of a depending annular refractory baflle 30.

In operation the chambers and 2| and throat 22 are normally filled to approximately the levels indicated by a fluent mass or column of incombustible refractory heat transfer material 3|, which is chemically inert relative to the hydrocarbonaceous feed stock. The heat transfer ma-- terial is supplied to the upper chamber '20 through the conduit l6 and discharged from the lower chamber 2| through the opening 26. A continuous downward flow of the refractory material 3| through the chamber 2! throat 22 and chamber 2| is maintained by regulable transfer means consisting of a discharge pipe 32 connecting the bottom opening to the housing 33 of a fluid sealing variable speed rotary pocket feeder 34. The feeder outlet end is connected through an expansion joint 36 and inclined conduit 31 to a box 38 opening to the lower part of an elevator casing 40. Openings in the box 38 permit the amount of heat transfer material in the system p to be increased or decreased as desired. The elevator casing is of welded gas-tight construction and encloses an elevator 4|, shown as of a slow speed continuous bucket type, having overlapping buckets which are partly filled with heat transfer material at the normal rate of material circulation. The elevator is driven by an electric motor 42 through a speed reducer and a chain and sprocket connection to the elevator head shaft. The elevator buckets empty into a discharge pipe 44 having a lower side outlet 45. The outlet 45 is connected to an inclined pipe 48, an expansion joint 49, and opens to the inlet pipe It. With this arrangement a continuous circulation of refractory heat transfer material can be maintained externally of the fluid heater between the discharge opening 26 and inlet pipe H5, so that the mass or column of heat transfer material within the chambers '20 and 2|, and throat 22, will descend at a predetermined rate, dependent upon the speed of the feeder 34 and elevator 4|.

A relatively wide range of refractory materials can be used as the heat transfer material 3|, the material chosen depending upon the particular operating conditions to be maintained in the unit. The material selected should have a high strength, hardness, resistance to thermal shock, and resistance to fusing together at high temperatures. Such materials may be ceramic refractories or corrosion resistant alloys and alloy steels, in small pieces of regular or irregular shape, such as sized grog, pebbles, or crystals of mullite, silicon carbide, alumina, or other refractories. As disclosed in a copending application of E. G. Bafley and R. M. Hardgrove, Serial No. 502,580, now Patent No. 2,447,305, substantially spherical pellets of uniform shape and size in the range of to 1" in diameter and formed of a mixture of calcined Georgia kaolin, raw Georgia kaolin, and a binder, fired to 2850-3000 F., have been successfully used. The pellet size is generally a compromise between a diameter small enough to minimize thermal shocks, impact forces, and to provide a large heat transfer surface, and a diameter large enough for economical manufacture, and to withstand the desired gas velocities without lifting. Pellets of inch and 1% inch diameter have been found suitable.

When the apparatus of the present invention is used in the manufacture of acetylene for example, a hydrocarbon feed stock such as natural gasoline, which is a mixture of paraflin hydrocarbons containing five or more hydrocarbons, mixed with steam is continuously introduced at a low temperature and a pressure slightly above atmospheric into the annular inlet chamber 28 through the conduit 29, the vapor mixture entering the lower chamber 2| throughout the height and circumference of the screen 25. The chamher 2| is proportioned in height, flow area, and

volume and a pellet size selected to permit a very rapid passage of the hydrocarbonaceous vapor upwardly through the interstices in the descending mass of highly heated refractory pellets 3'2. The intimate contact between the ascending vapor and descending mass of heat transfer material causes the vapor to be heated to a cracking temperature before reaching the upper end of the mass in the chamber 2| and cracking of the vapor occurs in the upper part of the mass. A rapid quenching of the gaseous end products to a temperature at which acetylene is stable is essential and this is effected by the arrangement of a circular series of gas outlets in the upper end of the chamber 2| above the level of the lower end of the throat '22 and the location of a heat exchanger having a high rate of heat absorption in each outlet 50. In the apparatus illustrated, each heat exchanger consists of an inclined cylindrical drum 5| having a downwardly dished tube sheet 52 at its upper and lower ends connected by tubes 53 through which the outgoing gases flow. A heat absorbing fluid, preferably water, is supplied to the lower end of each drum 5| through a pipe 54 connected to an annular supply pipe 55.

The steam generated in each drum is withdrawn through a pipe 55 connected to an annular steam main 5'! leading to a point of use, such as the diluent steam supplied to the vapor inlet pipe 29. The upper end of each drum is closed by a plate 58 to which a gas outlet pipe 59 is connected for delivering the cooled cracked gas mixture to an annular duct 60. The cooled gas mixture is then scrubbed to eliminate tar and oil particles in suspension, and then treated in a well known manner to separate into acetylene, ethylene, and fuel gas fractions.

The refractory pellets are heated to the desired temperature while in the upper chamber 20 by utilizing a portion of the fuel gases generated in the lower chamber 2!. For this purpose a circular series of symmetrically arranged downwardly inclined ports 62 are formed in the side wall of the chamber 20 intermediate the height thereof and the superjacent portion of the wall arranged to form an annular downwardly inclined baffle 63 overlapping the inner ends of the ports 62, and thus preventing the entrance thereto of the refractory pellets. An annular wind box 64 having one or more air inlet connections 65 thereto, opens to the outer end of the ports 62. Fuel gas is supplied to the ports 62 through valve controlled pipes 66 projecting downwardly from an annular supply duct 61 through the wind box 64 into the outer portion of the ports 62. With this arrangement a combustible mixture of fuel and air, initially ignited in any suitable manner, is supplied to the ports 62 and the pellet mass in the chamber 20 is heated by the resulting series of symmetrically arranged flames impinging on the pellets intermediate the height of the chamber 20. The heating gases thus generated distribute substantially uniformly throughout the pellet mass and flow upwardly through the inter stices therein in intimate contact with the descending pellets. The heating gases flow out of the chamber through the gas outlet M, with the gas outflow regulated by the damper l5 to control the pressure in the chamber 20. The relative pressures in the chambers 20 and 2'! can be advantageously regulated to provide zero or a downward or upward gas flow through the throat 22 by regulating the operation of damper l5 by control mechanism responsive to the pressure differential across the throat 22, as disclosed and claimed in said copending application of E. G. Bailey and R. M. Hardgrove, Serial No. 502,580. To facilitate this result, the. throat 22 is preferably made with the smallest diameter which will permit the pellets to flow therethrough without danger of bridging over therein, and pressure taps I0 and H are arranged in the lower part of the chamber 20 and upper part of the chamber 2! respectively, to measure the pressure differential across the throat. Separation of the gases in the upper and lower chambers can be further insured by the introduction of an inert sealing gas, such as steam, into the throat through a valve controlled pipe 13.

In addition to the control provisions described, the supplies of steam and hydrocarbonaceous vapor to the lower chamber and of fuel gas and air to the upper chamber are manually or' automatically regulated in any suitable manner. These controls in conjunction with therpressure differential and pellet circulation controls described facilitate the maintenance'of optimum operating conditions in the unit.

Representative operating conditions for the pyrolysis of natural gasoline involve the introduction of a. mixture of natural gasoline and steam diluent, in the proportions of approximately gasoline and 70% steam, at a temperature of 250 F. and a pressure of 3 p. s. i.. into the lower part of the'pellet mass in the chamber 2|. The chamber 2| is proportioned to provide a pressure drop of 1 p. s. i.. and av time of travel. of 0.1 second of the vapor mixture through the lower chamber. The pellets enter the upper chamber 20 at a. temperature of 550 F. and are heated therein to a temperature of 2700 F. Under these conditions the hydrocarbonaceous feed stock will be rapidly heated to a maximum temperature of about 2380 F. in the lower chamber, which is approximately the optimum crackin temperature for the pyrolysis of natural gasoline. The pellet temperature in the upper. part of the lower chamber is sufficiently high 'to maintain the hydrocarbonaceous vapor at the desired cracking temperature for the short time necessary (less than 0.1 sec.) to produce a cracked gas mixture having a high yield of acetylene. The intimate contact of hydrocarbons with a high temperature mass of refractory material has been found to facilitate the cracking operation, and consequently the formation of acetylene. The cracked gas mixture is cooled in about 0.03 second to a temperature of 750 F., at which acetylene will be stable. The heating gases enter the upper chamber at a temperature of about 2900 F. and leave through the outlet I4 at 750 F. Any carbon deposition on the pellets while in the cracking zone of the lower chamber will pass with the pellets to the elevator and be burned off on their return to the upper chamber 20 thereby providing part of the heat requirements in that chamber. A constant circulation of pellets through the unit is maintained at a rate of approximately 12 cycles per hour.

When the apparatus of this invention. is used and the described operating conditions are adhered to a gaseous end product of uniform composition can be continuously maintained. A high yield of acetylene is produced together with an amount of fuel gases more than sumcient to supply the heat requirements of the unit. The. inverted conical formation of the chambers 20 and 2| is particularly advantageous, insuring a. substantially uniform distribution of the fluids introduced at the narrowed cross-section thereof and minimizing the pellet lifting effect of the ascending gas streams by the progressively increasing flow areas available. The rapid quenching of the cracked gaseous mixture by the heat exchangers as the gases leave the reaction chamber facilitates the control of the time of heat treatment and this makes it possible to a large extent to prevent deleterious overcracking of the resultant gas mixture. The substantial heat recovery by the heat exchange units in cooling the outgoing cracked gas mixture also provides a practicable overall thermal efiiciency.

In view of the foregoing examples of particular applications of the apparatus of this invention to a specific process, it will be obvious to those skilled in the art that the apparatus is adapted for the continuous thermal decomposition of a wide range of fluid hydrocarbons under uniform operating conditions, the contact time, reaction temperature and degree of quench being controlled in each case to secure the optimum end product.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention known to me. those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by the claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

l. A fluid heater comprising an upper chamber having a solid material inlet and a heating gas outlet at its upper end and a solid material outlet at its lower end, a lower chamber having a solid material outlet and a gaseous fluid inlet at its lower end and a plurality of circumferentially equally spaced gaseous fluid outlets at its upper end, a throat passage of substantially reduced cross-section merging with said upper chamber material outlet and projecting into the upper end portion of said lower chamber, a feeder arranged to regulate a gravitational movement of a cont nuous mass of gas-pervious refractory heat transfer material downwardly through said upper chamber, throat and lower chamber, a conveyor arranged to receive heat transfer material from said feeder for delivery to the solid material inletv at the upper end of said upper chamber, means for heating said heat transfer material while in said upper chamber. and an indirect contact heat exchanger opening directly into each of said lower chamber fluid outlets to quench the hot gaseous fluid leaving said lower chamber by heat exchange with a vaporizable medium.

2. A fluid heater comprising walls defining an upper heating chamber having a solid material inlet and a heating gas outlet inits upper end,

an inverted frusto-conical lower end portion of said walls defining a downwardly tapered portion of said chamber ending in a vertically elongated throat passage, plurality of circumferen tially spaced fuel burners arranged for the introduction of heating gas into said upper chamber at a position intermediate its height for upward flow therethrough to said heating gas outlet, walls defining a lower chamber of downwardlytapering circular cross-section having a solid material outlet and a gaseous fluid inlet in its lower end portion, the upper Wall portion of said lower chamber encircling the lower end portion of the inverted frusto-conical wall of said. upper chamher in radially spaced relationship, a feeder arranged to regulate the gravitational movement of a continuous mass of gas-pervious solid heat transfer material downwardly through said upper chamber, throat and lower chamber, and a plurality of circumferentially equally spaced tubular heat exchange units positioned alongside the tapered wall of said upper chamber with the lower end of each unit opening directly into the annular space between the exterior surface of the wall defining said throat passage and the interior surface of the upper end portion of said lower chamber wall to receive the gaseous fiuid passed upwardly through the lower chamber from said gaseous fluid inlet. 7 3. A fluid heater comprising walls defining an upper chamber of downwardly tapering circular cross-section substantially throughout its height and having a solid material inlet and a heating gas outlet at its upper end and a solid material outlet at its lower end, walls defining a lower chamber of downwardly tapering circular crosssection substantially throughout its height and having a solid material outlet and a gaseous fluid inlet at its lower end, a throat passage of substantially reduced cross-section merging with said upper chamber material outlet and projecting into said lower chamber to define an annular gaseous fluid outlet between the exterior wall of the throat and the upper portion of said lower chamber wall, a feeder arranged to regulate a gravitational movement of a continuous mass of gaspervious refractory heat transfer material downwardly through said upper chamber, throat and lower chamber, a, conveyor arranged to receive heat transfer material from said feeder for delivery to the solid material inlet at the upper end of said upper chamber, a plurality of circumferentially spaced fuel burners arranged for introducing heating gases into said upper chamher at a position intermediate its height for upward flow therethrough in direct contact heat transfer relation with the mass of gas-pervious heat transfer material therein, and a plurality of circumferentially spaced tubular heat exchangers opening into said lower chamber gaseous fluid outlet and arranged to quench the hot gaseous fluid leaving said lower chamber. 4. A fluid heater comprising walls defining an upper heating chamber having a solid material inlet and a heating gas outlet in its upper end, an inverted frusto-conical lower end portion of said wall defining a downwardly tapered lower end portion of said chamber ending in a vertically elongated throat passage of substantially for upward'fiow therethrough to said heating gas outlet, walls defining a lower chamber of downwardly tapering circular cross-section having a solid material outlet and a gaseous fluid inlet in its lower end portion, the upper wall portion of said lower chamber encircling the lower end portion of the inverted frusto-conical wall of said upper chamber in radially spaced relationship,- a feeder arranged to regulate the gravitational movement of a continuous mass of gas-pervious solid heat transfer material downwardly through said upper chamber, throat and lower chamber,- and a plurality of circumferentially equally spaced tubular heat exchange units positioned alongside the tapered wall of said upper chamber: with the lower end of each unit opening directly into the'annular space between the exterior surface of the wall defining said throat passage and the interior surface of the upper end portion of said lower chamber wall to receive the gaseous fluid passed upwardly through the lower chamberfrom said gaseous fluid inlet, each of said heat exchange units having a cross-sectional dimension substantially equal to the radial dimension between said throat and lower chamber walls.

'5. In a heat exchange device of the general type-having an upper chamber enclosing an inert fluent gas-pervious mass of solid heat transfer material, a'lower chamberenclosing a mass of such material, a passage forming a throat between said upper and lower chambers and en-' closing a mass of such material connecting said material masses, means external of said chambers and throat to return the material from an exit in the lower chamber to an inlet to the upper chamber, means for heating the material in the upper chamber by direct contact countercurrent relationship with a heating gas, means for heating a fluid to be' heated by'direct contact counter-' current relationship with the heated material within said lower chamber, the lower end portion of said throat cooperating with the upper end portion of said lower chamber to define an annu lar heated fluid outlet chamber, the improvement comprising a plurality of tubular vapor generat-' ing heat exchange units circumferentiall'y equally spaced about said upper chamber and throat passage with the heated 'fluid entrance end of each unit opening directly into said annular heated fluid outlet chamber at positions substantially equally spaced from the upper'sur face of the refractory heat transfer material within said lower chamber.

' ISAAC HARTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATJ s

Claims (1)

1. A FLUID HEATER COMPRISING AN UPPER CHAMBER HAVING A SOLID MATERIAL INLET AND A HEATING GAS OUTLET AT ITS UPPER END AND A SOLID MATERIAL OUTLET AT ITS LOWER END, A LOWER CHAMBER HAVING A SOLID MATERIAL OUTLET AND A GASEOUS FLUID INLET AT ITS LOWER END AND PLURALITY OF CIRCUMFERENTIALLY EQUALLY SPACED GASEOUS FLUID OUTLETS AT ITS UPPER END, A THROAT PASSAGE OF SUBSTANTIALLY REDUCED CROSS-SECTION MERGING WITH SAID UPPER CHAMBER MATERIAL OUTLET AND PROJECTING INTO THE UPPER END PORTION OF SAID LOWER CHAMBER, A FEEDER ARRANGED TO REGULATE AGRAVITATIONAL MOVEMENT OF A CONTINUOUS MASS OF GAS-PERVIOUS REFRACTORY HEAT TRANSFER MATERIAL DOWNWARDLY THROUGH SAID UPPER CHAMBER, THROAT AND LOWER CHAMBER, A CONVEYOR ARRANGED TO RECEIVE HEAT TRANSFER MATERIAL FROM SAID FEEDER FOR DELIVERY TO THE SOLID MATERIAL INLET AT THE UPPER END OF SAID UPPER CHAMBER, MEANS FOR HEATING SAID HEAT TRANSFER MATERIAL WHILE IN SAID UPPER CHAMBER, AND AN INDIRECT CONTACT HEAT EXCHANGER OPENING DIRECTLY INTO EACH OF SAID LOWER CHAMBER FLUID OUTLETS TO QUENCH THE HOT GASEOUS FLUID LEAVING SAID LOWER CHAMBER BY HEAT EXCHANGE WITH A VAPORIAZABLE MEDIUM.

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