US2573747A - Pebble heater apparatus - Google Patents

Description

Nov. 6, 1951 Filed Dec. 15, 1947 L. J. WEBER 2,573,747

PEBBLE HEATER APPARATUS 2 SHEETSSHEET 1 INVENTOR.

L .J WEBER ATTORNEYS Nov. 6, 1951 Filed Dec. 15, 1947 l J. WEBER PEBBLE HEATER APPARATUS 2 Sl-lEETS-SI-IEET 2 INVENTOR.

L .J WEBER BY WW4 A TTORNEYS Patented Nov. 6, 1951 PEBBLE HEATER APPARATUS Louis J. Weber, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application December 15, 1947, Serial No. 791,736, Claims. (Cl. 263-19) 1 This invention relates to pebble heater apparatus. In one of its more specific aspects it relates to thermal conversion apparatus. In another of its more specific aspects it relates to pebble heating or regeneration chambers of pebble heater apparatus.

Thermal conversion or treating processes carried on in so-called pebble heater apparatus utilizes a flowing mass of pebbles which is heated to a high temperature by passing hot gases therethrough in a first direct heat exchange step and is then caused to contact gaseous reactant materials, furnishing heat thereto, in a second direct heat exchange. The conventional pebble heater apparatus comprises two chambers which may be disposed in substantially vertical alignment. A solid heat exchange material, such as refractory pebbles, is introduced into the upper portion of the first chamber. The solid heat exchange material flows downwardly through the chamber in direct heat exchange with a hot gaseous heat exchange material. The solid heat exchange material is heated to a high temperature in the heat exchange and is then passed to a second chamber in which the hot solid heat exchange material is caused to contact gaseous materials in a second direct heat exchange relation, furnishin heat for the treatment or conversion of the gaseous materials.

Many conventional pebble heaters are provided with a combustion chamber adjacent or in close proximity to the lower portion of the first chamber. A hot combustion gas from the combustion chamber is injected through the sides of the first chamber, better known as the pebble heating chamber. Pebbles which pass downwardly through the heating chamber contact the rising combustion gas and are heated as above described. One disadvantage of such conventional pebble .heater apparatus is that pebbles near the periphery of the pebble bed in the heating chamber are heated to a higher temperature than those in the center of the downwardly flowing bed. This is due to the fact that a greater portion of the combustion gas tends to take the path of least resistance through the pebble bed. In most pebble heater apparatus, pebbles are introduced into the pebble heater chamber through a single opening in its top. Pebbles are withdrawn from a point substantially centrally located in the area of the heating chamber. As pebbles flow through the chamber they tend to form a cone, downwardly and outwardly from the pebble inlet, and the pebbles flowing out of the chamber tend to form an inverted cone downof the chamber.

wardly and inwardly toward the pebble outlet. It will be seen that due to the cone shaped top and bottom of the bed, the area near the periphery of the bed is usually the thinnest and the point of least resistance for upwardly flowing gas. Gas tends to pass directly upwardly from the gas inlet, through the periphery of the bed and out of the effluent outlet in the top of A portion of the pebble bed below the moving cone of pebbles is relatively stagnant. Once these pebbles in the stagnant area are heated they lose very little of their heat and thus receive very little heat from the gas passing upwardly therethrough. For that reason, gas leaving the heating chamber through the efiluent outlet carries with it a considerable amount of heat which could have been imparted to cooler pebbles in the central portion of the chamber.

An object of the invention is to provide an im proved chamber for heating pebbles in pebble heater apparatus. Another object is to provide an improved method for heating pebbles in pebble heating apparatus. Another object is to provide an improved combustion chamber for a pebble heater. Another object is to provide an improved means for transporting a pebble bed within heating chambers of pebble heater apparatus. Another object is to provide means for more evenly heating a given cross-section of a flowing pebble bed in such a heating chamber. Other and further objects will be apparent to those skilled in the art on reference to the accompanying discussion, drawings, and the claims.

The term pebble as used herein denotes any solid refractory material of flowable form, size, and strength which is suitable to carry large amounts of heat from the pebble heating chamber to the gas heating chamber. Pebbles conventionally used in pebble heater apparatus are substantially spherical in shape and are from about /8 to about 1 inch in diameter. In a high temperature process, pebbles having a diameter of between about inch to about inch are preferred. The pebbles must be formed of a refractory material which will withstand temperatures at least as high as the highest temperature attained in the pebble heating chamber. The pebbles must also be capable of withstandingtemperature changes within the apparatus. Refractory materials, such as a metal or metal alloy, ceramic, or other satisfactory material, may be utilized to form such pebbles. Satisfactory pebbles may be formed of silicon carbide, alumina, periclase, beryllia, stellite, zirconia and 3 mullite in admixture with each other or with other materials. Pebbles formed of such materials, when properly fired, serve very'well in high temperatures, some withstanding temperatures up to about 3500 F. Pebbles which are inert or catalytic may be used in any selected process.

Understanding of the invention will be facilitated upon reference to the attached diagrammatic drawings in which Figure 1 is a vertical section, of a pebble-heating chamber embodying the invention. Figure 21s a plan view taken on line 2--2 of Figure 1. Figure 3 is a cross-section of the burner retainer portion of the combustion chamber. Figure 4 is a schematic view of a pebble heater apparatus showing the rela tion between the pebble heating and reactor chambers and the path of pebble recycle.

In Figure 1, pebble heating chamber Ill comprises shell I I which is closed at its ends by members l2 and I3. The walls of shell I are lined ,with insulating means, including super-retrac tory and common refractory materials l4. Common refractory materials may include block insulation, insulating fire brick, and fire clay fire brick. Super-refractory materials may include silicon carbide, mullite, alumina, or any other suitable refractory havin physical and chemical properties which give it sufiicient strength to withstand a reasonably heavy load and a high temperature without substantial breakage or deterioration. Silicon carbide may be satisfactorily used in operations utilizing temperatures up to about 3000 F. Mullite can also be satisfactorily used at temperatures up to about 3000 F. while alumina may be satisfactorily used at temperatures up to about 3300 F. The above materials may be used at those temperatures, without substantial oxidation or reaction, with most con-- ventionally'used pebbles. The bottom as well as the sides of the shell may be lined with layers of common or super-refractory materials or both. When the apparatus is operated at high temperatures the top of the heating chamber may also be insulated. The lower portion of shell II is enlarged so that combustion chamber I5 is formed between its insulated shell and wall I 6. The construction of wall I 6 is such that bricks I! used in its construction form a grill work, which grill work, in turn, forms a plurality of conduits i8, communicating between combustion chamber l5 and pebble heating chamber i9. In the preferred construction of conduits l8, the conduits in each succeedin layer from the bottom to the top of the grill work have a smaller vertical cross-sectional area than do the conduits in the next preceding lower layer. The lowest layer of conduits extend substantially into the central portion of the pebble heater area and each succeeding layer of conduits is of a shorter length so that gas emerging from the inner ends of these conduits will substantially uniformly heat pebbles within the pebble bed. The conduits may be so constructed and arranged that their outlet ends form an inverted cone. The cone surface formed by the conduits may, though not necessarily, be irregular. Extending through closure l3 in the bottom of shell II is a refractory pebble outlet 20 which, in one of its preferred constructions, comprises a plurality of refractory rings 23 in substantially vertical alignment. Rings 23 may be held in place in any conventional manner, one method being to provide the rings with inter-locking tongues and grooves. Covering the outlet ends of conduits l8 and surrounding pebble outlet 20 is sepbe built with the above (1 4 aration means, such as aggregate material 24. Aggregate material 24 is provided to prevent refractory pebbles 25 from entering conduits it. When the separation means comprises aggregate material 24, the layer of aggregate material may be of any desired thickness. The distance which pebble outlet 20 will rise in the pebble heating chamber will generally depend upon the height necessary to retain aggregate material 24 in pebble heating chamber l8. It is preferred to kee the thickness of the layer of aggregate material to a minimum. It is preferred that the cone formed by the aggregate material and the inner ends of conduits ll be from to about 60. Burners are inserted into the burner retainer portions 30 of the combustion chamber l5, which retainer portions 30 tangentially communicate with combustion chamber i5. Pebble inlet means,tsu'ch as conduit 26, is provided in closure member l2 and eilluent outlet means, such as cgiduit 21, is also provided in closure mem- Conduits ll may be formed in any conventional manner. A wall of substantially the same thickness as the insulation on the chamber wall may ribed grill work.

Refractory extensions may built within the interior of the wall, which extensions may form conduits which will extend any one of the openings in the wall or form a combined opening for two or more such openings. In the preferred construction of such conduits, the wall is so constructed that the wall itself forms the total length of the conduits. That portion of the wall may be formed of tapered bricks, which when fitted together leave a space therebetween which extends from the combustion chamber to the interior of the pebble heating chamber. The next layer of bricks is so disposed as to cover the space left between the bricks in the last preceding layer, thereby closing the top of such openin and forming a conduit between the combustion chamber and the pebble heating chamber. The tapering bricks may, though not necessarily, be of suflicient length that one brick will extend from the combustion chamber to the inner end of the conduit. It will be obvious to those skilled in the art that the length of such brick conduits may be formed of a plurality of pieces.

In Figure 4, shell ii containing pebble heating chamber 19 is provided with eiiiuent outlet 21 in its upper portion and is connected to shell 28, enclosing a gas heating chamber, by pebble outlet 20. Shell 28 is provided in its upper portion with eiiluent outlet means, such as conduits 29. Feed inlet means, such as conduit 32, is provided in the lower portion of shell 28. Pebble outlet 33 is also provided in the lower portion of shell 28, and pebble transportation means, such as elevator 34, communicates between pebble outlet 33 in shell 28 and pebble inlet conduit 26 in the top of shell II.

In the operation of the apparatus shown in Figures 1, 2, 3, and 4 0f the drawings, pebbles made from any selected refractory material, suitable for the process to be carried on within'the apparatus, are inserted into the upper portion of the heating chamber, through pebble inlet 26. The pebbles pass downwardly and cover the layer of aggregate material 24 and build up a contiguous bed of pebbles through the gas and pebble heating chambers. Gaseous combustible materials together with an oxygen-containing gas, which may be excess of that needed to supply oxygen for the combustion of the combustible materials, is

injected into the combustion chamber, disposed about the lower outer periphery of the heating chamber, through burners which communicate tangentially with the combustion chamber. Combustion gas, passing from the burner tangentially into the combustion zone, passes in a whirling motion around the combustion zone while more complete burning of the combustible material is accomplished.

Excess oxygen-containing gas may be injected through the combustion zone for the purpose of tempering or controlling the temperature of the combustion gas. The combustion gas together with any excess oxygen-containing gas passes inwardly through the conduits communicating between the combustion zone and the pebble heating zone. Greater amounts of combustion gas are conveyed to the center of the heating zone than to the periphery of such zone by the lower and longer conduits which preferably have larger vertical cross-sectional area than do the upper shorter conduits. As the gas passes from the conduits it rises through the bed of pebbles in direct heat exchange therewith, raising the pebbles to a high temperature. As the combustion gas passes from the top of the pebble bed it escapes from the chamber through efliuent outlet 21. The heated pebbles pass downwardly through pebble outlet 20 into the gas heating chamber within shell 28 as pebbles are withdrawn from the bottom of shell 28. The gas heating chamber, the pebble outlet, and at least a portion of the heating chamber are filled with the moving bed of pebbles. In some cases a surge chamber may be arranged ahead of the pebble heating chamber in the pebble flow. When such an arrangement exists, sumcient pebbles may be supplied to entirely fill the space within the heating chamber. Gaseous material is injected into the lower portion of the gas heating chamber through inlet conduit 32. The gaseous material rises through the gas heating chamber gaining heat from the downwardly flowing pebbles and passes rapidly out of the gas heating chamber through eflluent outlet conduits 29. Pebbles, which have been cooled during the gas heating step, pass out of the bottom of the gas heating chamber and are carried by elevator 34 to the upper portion of the heating chamber within shell Ii. Herein they are once again subjected to the pebble heating step described above.

The separation means used to separate the pebbles from the conduits communicating between the combustion chamber and the pebble heating chamber may be a conical refractory bailie (not shown), which baflle may be perforate to allow the flow of gas therethrough. Should such a baflle be utilized, it would be advisable to provide it with concentric retainer extensions protruding downwardly from its underneath side. Those extensions would substantially prevent gases injected through certain of the conduits from passing upwardly along the underneath side of the conical baiile to the periphery of the pebble bed. In that manner, gas flowing through certain of the conduits would pass into a certain portion of the pebble bed. When a layer of aggregate material is used as such separation means, it would also be necessary to utilize such a retainer member to prevent the combustion gas from flowing upwardly and outwardly through the aggregate materials without entering the pebble bed at a desired point.

In some instances combustion gas may be carried from the pebble heating chamber into the 6 gas heating chamber with the pebbles and combustion products may rise from the gas heating chamber, through the pebble outlet conduit, into the pebble heating chamber. Such an occurrence would cause the conditions in either chamber to be unstable. For that reason, it may be desirable to provide conduit means for injecting into the pebble conduit as a choking means, a hot gas which is inert to the reaction. The choking means would prevent other gases from passing therethrough.

When using a pebble heater chamber having an inside diameter of about 4.5 feet it is preferred to discharge about by volume of the heating gas into the central portion of the bed within a circle 1.75 feet in diameter. The temperature of the combustion zone may be controlled to any specific temperature depending upon the selected process. That, temperature may vary between about 2000" F. and about 3600 F. When the temperature is maintained at about 2400 F. the pebbles are raised to a temperature of about 2000 F. and the eiiluent which is removed from the top of the pebble heater chamber is about 900 F. The pebbles may be heated, in any selected process, to temperatures varying between about 1500 F. and about 3200 F.

The above apparatus size is intended to be merely exemplary and should not be construed as limiting the invention. As will be evident to those skilled in the art, various modifications of this invention can be made or followed in the light of the foregoing disclosure, discussion, and example, without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

1. In a pebble heater apparatus utilizing a moving bed of heated pebbles, an improved pebble heating chamber comprising a substantially vertically disposed closed outer shell enclosing a heating chamber therein; insulating means adapted so as to insulate said shell; pebble inlet means and eiiluent outlet means in the upper portion of said heating chamber; pebble outlet conduit means in the lower portion of said heating chamber; a combustion chamber disposed about the lower periphery of said chamber; combustion gas conduit means communicating between said combustion chamber and points within the lower area of said heating chamber, said conduits being disposed in layers, the lowest conduits extending into the central portion of said chamber and the conduits in each added layer being shorter than those in the next preceding lower layer, said conduits in each said added layer being smaller in vertical area than the conduits in the next preceding layer; and means to supply and burn combustible materials in said combustion zone, whereby hot combustion gas is formed, which gas passes inwardly through said gas conduit means and upwardly in said chamber, heating pebbles therein.

2. The heating chamber of claim 1, wherein said means to supply and burn combustible materials in said combustion zone comprises at least one inclined burner.

3. In a pebble heater apparatus utilizing a moving bed of heated pebbles, an improved pebble heating chamber comprising a substantially vertically disposed closed outer shell enclosing a heating chamber therein; insulating means adapted so as to insulate said shell; pebble inlet means and effluent outlet means in the upper portion of said heating chamber; pebble outlet conduit means in the lower portion of said heating chamber; a combustion chamber disposed about the lower periphery of said chamber; combustion gas conduit means communicating between said combustion chamber and points within the lower area of said heating chamber, said conduits being disposed in layers, the lowest conduits extending into the central portion oi said chamber and the conduits in each added layer being shorter than those in the next preceding lower layer; separation means within the lower portion of said chamber, which separation means is positioned so as to prevent pebbles from entering said combustion gas conduit means; and means to supply and burn combustible materials 15 4. The heating chamber 01 claim 3, wherein 20 ,44

said separation means comprises a bed of aggregate material covering the inner ends of said combustion gas conduits.

5. The heating chamberot claim 3, wherein the vertical area of said combustion gas conduit means in each added layer is smaller than the conduits in the preceding layer.

LOUIS J. WEBER.

REFERENCES CITED The following references are 01' record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,234,240 Widerwax July 24, 1917 2,184,300' Hodson et al Dec. 26, 1939 2,345,067 Osann Mar. 28, 1944 2,417,049 Bailey et a1 Mar. 11, 1947 Bergstrom Aug. 8, 1948

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