US2584621A - Pebble heater - Google Patents

Description

Feb. 5, 1952 M.'A. RYAN PEBBLE HEATER Filed oct. 2o, 1947 0 9 000000 DQDD D QQ Q @009D 09OD\\\\\\\\ \\\\\\\\O s 0D. D0 1/ BY mwm Patented Feb. 5, 1952 f PEBBLE HEATER` Martin A. Ryan, Bartlesville, Okla., assigner to- Phillips Petroleum Company,y a. corporation of4 Delaware Application October 20, 1947, Serial No. 780,925'

(Cl. 23e-27.7)

5 Claims.

This. invention involves vimprovements in theconstruction of pebble heaters.

One object of this invention is to provide a pebble heater in which the topY of thek reaction chamber lies in a plane parallel4 to the angle of repose of the pebble content thereof.

Another object of the invention is to provide an adjustable means for varying the free space between the topof the-reaction chamberV and thev pebble bed therein.

A more specic` object of the invention is to provide an adjustable discharge 'spout for the restricted entrance of the reaction chamber hav-` ing ak discharge lip lying in the plane of the angle of repose of the pebble bed therein.

A still more specific object of the invention is to provide a removable dischargek spout of this type.

Another object of the invention is to provide an improved and simple form ofY heat exchanger quencher by means 'ci which the effluent gases from the reaction may be cooled immediately after removal from the pebble bed.

A more specific object of the invention is to provide means associated with the eilluent gas outlets from the reaction chamber by means of which these gases may be quicklycooled' below predetermined temperature.

A still more specific object of the invention is to provide means for use with a pebble heater operatingY as a high. temperature cracking unit for hydrocarbon fluids to produce an olefinrich cracked gas for quenching the gas. below its: critical temperature to prevent excessive polymerization of the oleiin content thereof.

Another object of this invention is to provide the above improvements in combination.

Other and more detailed objects of the invention will be apparent from the following disclosure oi the embodimentsV thereof illustrated in the attached drawings.

This invention resides substantially inthe combination, construction, arrangement and relative location ci parts, all as will be described in detail'below. l

In the accompanying drawings,

Figure 1 is a vertical,A central, cross sectional view through the upper portion of a pebble heater showing the features of this invention applied thereto, with some parts in elevation; and

rFigure 2- illustrates amodication of a` Ydetail ofv the `structiu'e of*r Figure l. I

While pebble vheater'urnits" are' employed.y in various processes they""are frequently'used'in the high temperature cracking of hydrocarbon iluids to produce a highly olenic cracked gas. As is well known in the art, such units comprise two or more chambers arranged in vertical relation and connected by a constricted section or conduit. The upper chamber is employedV for thepurpose of preheating the pebbles before they pass through the constriction into the lower chamber which is the reaction chamner.

In the high temperature crackingYV of hydrocarbon iluids to produce olein-rich cracked gas,A it is essential that the residence time 0f the reactants in the reaction Zone be controlled andlimited, usually to a relatively short period of the order of 0.65 second or less. In addition, as is well known, in order to secure a maximum yield of olefins this process is carried out at a maximum temperature and a minimum pressure. The temperature of the eiiluent gas is of the order of 1500 F. As is well understood, the free space above the pebble bed of the reactor must be minimized and the cracked gas or reaction products be withdrawn from the high temperature reaction zone and cooled or quenched below the reaction temperature as quickly as possible. This objective is attained in part in this invention by providing means for reducing the amount of free space above the pebble bed and by subjecting the reaction products to cooling almost immediately after leaving thepebble bed.

Pebble heater operation, with which this invention is concerned, may be utilized in a Va.- riety of chemical processes and treatments in which extremely fast heating of the reactants and very rapid quenching of the reaction products are required. In carrying out this operation, the residence time of the reactants in the conversion zone is very short, in some cases it may be of the order of 1/ioo of a second. It is also imperative that the reaction products be withdrawn immediately from the high tempera-,- ture zoneand quenched to a temperature below the reaction level. In the cracking of ethane to produce ethylene the temperature in the conversion o1' reaction zone may well be in the order of 1800" to 1900 F. with a residence time of .01k to .03 second. In order to produce the maximum yield of ethylene by eliminating side reactions, such as polymerization, it is essential that the eiiiuent cracked gas be rapidly quenched to a temperature below about l000 F.

mits achievement of very short residence time by means of a specially designed reaction chamber in which the top wall or head lies at an angle such that it isA parallel to the top of the pebble bed which is allowed to assume its natural angle of repose. As a still further improvement, means are provided to control the free space between the top of the pebble bed and the wall of the vessel thus making it possible to vary the residence time of the reactants in the conversion zone.

In some instances the reaction products have been rapidly quenched by direct injection of some fluid such as water or steam into the efuent line from the reaction zone. However, there are many cases where a direct quenching procedure cannot be tolerated. In high temperature hydrocarbon conversions, such as cracking and dehydrogenation, for example, the production of ethylene or acetylene which are to be separated from the reaction products by low temperature fractionation, the use of adirect quench is not desirable because of the extensive dehydration which would be required prior to the separation steps. In other chemical processes or syntheses, such as the production of HCN from ammonia and carbon monoxide, production of CS2 by reacting hydrocarbon vapors with sulfur containing gases and other syntheses involving HF as a reactant, a direct quench cannot be tolerated because the reaction product may combine or react with the quenching material. The newv quenching means disclosed in this invention makes it possible to conduct these processes in a pebble heater type apparatus, without undesirable side reactions, dilution of product with resulting separation difficulties and other disadvantages. In Figure l a metallic reaction vessel 2 is provided with a refractory lining l which extends upwardly into a restricted conduit extension of a housing 20 to form a lining therefor having a restricted passage 5 therethrough. An insulating lining 2l is provided with a shoulder 2|', as shown, upon which a shoulder throat member 23, likewise of highly refractory material, may rest with the aid of refractory shims 24 by means of which the length of the projecting lower end thereof may be varied. rlhe lower end of the throat member is of conical form as illustrated at 23 and the inclination thereof is substantially that of the angle of repose of the pebble bed A. It will be seen that by varying the thickness of the shims 24 the space betweenY the top surface 6 of the pebble bed and the sloping refractory wall 1 can be varied to meet particular conditions. The top of reaction vessel 2 is inclined, and the insulating lining l is similarly inclined so that its inner face 1 will be substantially parallel to the face 9 of the pebble bed. n

The top wall 1 obviously will be of conical form in the case of a cylindrical construction, and in accordance with this invention it lies at an angle such that it will be parallel to the top E of the pebble bed 4 which is allowed to as- 4 duit 5 through which the pebbles pass from the preheatlng chamber above (not shown).

It will be understood that the longer the throat member 23, that is the more it projects below the discharge end of the conduit 5, the greater will be the free space between the top wall of the reaction vessel and the top 6 of the pebble bed, and Vice versa. Thus the free space thus formed can be adjusted and minimized to the most suitable size for particular operating conditions.

Overlying the sloping wall 1 forming the top of the reaction vessel is a flat metallic housing 21 which may be in the form of a collar extending continuously around the top of the vessel, or a pair of separate semi-circular housings as illustrated. As shown, it is provided with one or more cooling inlet conduits 21A and outlet conduits 21B by means of which a cooling gas or liquid can be forced therethrough at the desired rate. Extending al1 the way through this relatively flat housing is a metallic conduit 2S which opens into the reaction vessel and is welded or otherwise connected to the adjacent Wall thereof. The tube 29 is provided with a series of radial vanes 28 on the interior and a plurality of circumferential vanes 3D on the exterior. The upper ends of the tubes 29 are provided with flanges or other connecting means and are connected to any suitable offtake pipe or manifold (not shown). It will be noted that the inner ends of the tubes 29 opencthrough a tortuous path 25 into the free space above the pebble bed through refractory block 25 and discharge into the pipe or manifold (not shown) to Which they are connected. It will be understood therefore, that the eluent gases pass into the free space between the upper surface 6 of the pebblev bed d and the wall 1 of the reaction vessel, and from there directly into and through the tubes 25 and 29 substantially immediately after they issue from the pebble bed. In passing through the conduits 29 they are in heat exchange relation with the cooling fluid surrounding these tubes, so that they lose heat rapidly by conduction through the metal wall of the tubes 29. The internal vanes 28 and the external vanes 30 aid in effecting a rapid heat transfer from the hot eiliuent unsaturated, or perhaps olefin-rich gases to the cooling fluid passing through the housings 21. Thus the gases issue from 29 into the manifolds (not shown) at temperatures below the critical temperature for the reaction involved minimizing, in the case of the olefinrich gases, excessive polymerization thereof in the case of acetylene, the formation of carbon black, and in the case of other products, other well known undesirable side reactions. As the cooling need only be to 600 F. to l000 F., depending on what side reaction is to be prevented, it is preferred to use a coolant in 21 around vanes 30 that is selected as suitable for use at such temperatures. While, of course, water and other liquids that vaporizre, or gases or vapors can be employed, it is preferred to use molten salts, or molten metals that preferably do not vaporize at the temperatures involved, although ones that do vaporize can be used. Other coolants such as diphenyl or other high temperature resistant substances may be used. Y

As illustrated the heat exchanger housings 21 in this case are in the form of two separate members of the required circumferential length with respect to theftop of the reaction vessel, and each having oneA or more tubes 2.9 extending e2 therethrough. To facilitate construction the tubes 29 are Welded to plates 29 which in turn are Welded into similarly shaped openings in the inclined Wall in the top of the reaction vessel as shown. At the lower end the tubes 29 pass through openings in the lower walls of the housing 2l and are welded thereto. At the upper end they are Welded to plates 29 through which they pass and which in turn are welded into similarly shaped openings in the top wall of the housings 21. As previously mentioned tubes 29 are provided with a series of internal radial vanes 28 and external circumferential vanes 39 to increase the heat absorbing reaction thereof.

In the construction illustrated the insulating lining 2| for the reaction vessel is shaped in the region of the inlet ends of the tubes 29 to receive removable highly refractory insert members 25 which have the non-linear passages 25' therethrough establishing communication between the free space above the pebble bed and the interior of the tubes 29. In the form illustrated in Figure 2 the passages 25 are merely offset suiciently so that the area of the top of the pebble bed opposite the entry end thereof is not directly exposed to too large a dark space. As those skilled in the art Will understand under these conditions the exposure of the hot pebble bed to a cool dark space will cause the hot pebbles exposed thereto to radiate heat at an excessive rate, causing an undue cooling of the portion of the pebble bed exposed to the dark space. In some cases cooling may be carried to a point below the proper reaction temperature, possibly causing undesired reactions and undue deterioration of the pebbles in that region. The members 25 are made removable in the event that it may become desirable to replace or change them for any reason. The housings 21 are provided With inlets 21A and outlets 27B for the cooling fluid. One of the most e'lcient ways cf making passage 25 tortuous enough to hide metal surfaces 28 from pebbles 6, and yet be short, is to make it helical.

When desired, the inserts 25 may be provided With several passages arranged, for example, in a manner similar to that illustrated in Figure 2, or in the form of helixes to minimize the dark space effect previously explained. Thus, a plurality of passages 25A are illustrated in Figure 3 5 as being offset or of helical form to accomplish this objective. In some cases the longitudinal vanes 28 may be given a helical or distorted form. Thus, for example in the arrangement of Figure 1 if they are thus formed the cool dark space effect will be minimized.

The construction of Figure 2 is practical in.

is reduced to a minimum and is subject to control for that purpose.

From the above description it will be apparent to those skilled in the art that the subject matter of this invention is capable of some variation Without departure from the novel subject matter thereof. I do not prefer therefore to be limited only as required by the claims granted me.

What is claimed is: y

1. In a vessel for effecting heat exchange between 11p-flowing gases and down-flowing pebbles, the combination comprising a vessel having a top Wall, a restricted pebble supply conduit prcjecting into said vessel through said top wall, an eflluent gas takeoff conduit mounted on said top Wall, a circulatory liquid housing surrounding said conduit, internal radial vanes on said conduit, and external circui .ferential vanes on said conduit and Within said -housing.

2. In the combination of claim l, a throat member formed With a flange around its external circumference, the flange forming a collar for supporting said throat member in position in the reactor, the level of said throat member being adjustable by the inclusion of shims between the collar and the reactor top.

3. In the combination in accordance With claim 1, the throat member being formed with a discharge opening tapered to denne essentially the angle of repose for the bed of pebbles.

4. In a pebble reactor, the combination comprising a reaction vessel, said vessel having a conical top wall, a restricted heated pebble sup- .c ply conduit at the apex of said vessel and pro- 5. In the combination of claim 4, an inlet member for said conduit comprising a refractory member having a tortuous path therethrough, said refractory member minimizing the cool dark space effect.

MARTIN A. RYAN.

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

UNITED STATES PATENTS Number Name Date 1,102,714 Bornmann July 7, 1914 1,892,742 Walter Jan. 3, 1933 2,348,156 Sheppard May 2, 1944 2,434,567 Jahnig Jan. 13, 1948 2,447,306 Bailey Aug. 17, 1948 OTHER REFERENCES Norton: Article in Chemical and Metallurgical Engineering, July 1946, vol. 53, pp. 116-119 (pp. 117 pertinent).

Claims (1)

1. IN A VESSEL FOR EFFECTING HEAT EXCHANGE BETWEEN UP-FLOWING GASES AND DOWN-FLOWING PEBBLES, THE COMBINATION COMPRISING A VESSEL HAVING A TOP WALL, A RESTRICTED PEBBLE SUPPLY CONDUCT PROJECTING INTO SAID VESSEL THROUGH SAID TOP WELL, AN EFFLUENT GAS TAKEOFF CONDUIT MOUNTED ON SAID TOP WALL, A CIRCULATORY LIQUID HOUSING SURROUNDING SAID CONDUIT, INTERNAL RADIAL VANES ON SAID CONDUIT, AND EXTERNAL CIRCUMFERENTIAL VANES ON SAID CONDUIT AND WITHIN SAID HOUSING.

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