US2750181A

US2750181A - Pebble heater

Info

Publication number: US2750181A
Application number: US264809A
Authority: US
Inventors: Donald J Quigg
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1952-01-03
Filing date: 1952-01-03
Publication date: 1956-06-12
Anticipated expiration: 1973-06-12

Description

June 12, 1956 Filed Jan. 3, 1952 FIG.

D. J. QUIGG PEBBLE HEATER 5 Sheets-Sheet l INVENTOR.

D. J. QUIGG warml ATTORNEYS June 12, 1956 J, QUIGG 2,750,181

PEBBLE HEATER Filed Jan. 3, 1952 5 Sheets-Sheet 2 A T TORNEKS' D. J. QUIGG PEBBLE HEATER June 12, 1956 5 Sheets-Sheet 3 Filed Jan. 5, 1952 FIG. 3.

INVENTOR.

D. J. QUIGG BY 4 T TORNEYS United States Patent PEBBLE HEATER Donald J. Quigg, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application January 3, 1952, Serial No. 264,809 26 Claims. (Cl. 263-19) This invention relates to pebble heaters. In one of its morespecific aspects, it relates to improved pebble heater apparatus. in another of its more specific aspects, it relates ton single shell pebble heater apparatus, In another of its morespecific aspects, it relates to pebble heater apparatus having only a single upright chamber containing a contiguous gravitatingv mass therein. In another of its more specific aspects, it relates to the conversion of hydrocarbons in pebble heater apparatus.

Apparatus of the so-called Pebble Heater type has been utilized in recent years for the purpose of heating fluids to elevated temperatures. Such apparatus is especially suited for use in temperature ranges above those at which the. best available high temperature structural alloys fail. Thus, such. equipment may be used for superheating steam or other gases and for the pyrolysis of hydrocarbons to produce variable products such as ethylene and acetylene, as well as for other reactions and purposes. Conventional pebble heater type apparatus includes two refractory lined contacting chambers disposed one above the other and connected by a refractory lined passageway or pebble throat of relatively narrow cross-section.

Refractory. solids of flowable size and form, called pebbles, are passed continuously and contiguously through the system, flowing by gravity through the uppermost chamber, the throat, and the lowermost chamber, and are then conveyed to the top of the uppermost chamber to complete the cycle.

Solid heat exchange material which is conventionally used in pebble heater apparatus is generally called pebbles. The term pebbles as used herein denotes any solid refractory material of flowable size and form, having strength, which is suitable to carry large amounts of heatfromthe pebble heating chamber to the gas heating chamber without rapid deterioration or substantial breaking. Pebbles conventionally used in pebble heater apparatus are ordinarily substantially spherical in shape and range from about /s inch to about 1 inch in diameter. In a high temperature process, pebbles having a diameter of between A to /s 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 withstanding temperature changes within the apparatus. Refractory materials, such as metal alloys, ceramics, or other satisfactory material may be utilized to form such pebbles. Silicon carbide, alumina, pericla se, beryllia, Stellite, zirconia, and mullite may be satisfactorily used to form such pebbles or may be used 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 4000 F. Pebbles which are used may be either inert or catalytic as used in any selected process.

The pebbles are heated in one of the chambers. (preferably the upper one) by direct contact therein with hot gases, usually combustion products, to temperatures genorally in the range of 1400 F. to 3200" F. The hot pebbles are thereafter contacted with the fluid to be superheated or reacted, as the case may be, in the other chamber. Generally, pebble inlet temperatures in the second chamber are about F. to 200 F. below the highest temperature of the pebbles within the first chamber. In processes for the production of ethylene from light hydro,- carbons, such as ethane, propane, or butane, the. pebble temperature inthe reaction chamber is usually in the range of 1200 F. to 1800" F. For the production of acetylene by pyrolysis of hydrocarbons, temperature in the range of 1600 F. to 3000 F. are desirable.

In the past, considerable trouble has been encountered in the operation of pebble heater apparatus for the. reason that pebbles which are heated in the pebble heating chamber are not all heated to a uniform temperature. For this reason the pebbles which are introduced into the upper end portion of the reaction chamber lack the desired uni formity of temperature which would give the best reaction of feed within that reaction chamber. The result has been that a portion of the feed stock has been overcracked and-a portion of the feed stock has been under-cracked by reason of the contact with pebbles heated to temperatures above. and below that desired for reaction of the feed. This difliculty in obtaining uniform temperatures of pebbles within the pebble heating chamber is due principally to the fact that the pebble heating chamber is one of large cross-section, and the gas flow patterns within such a chamber containing a contiguous gravitating pebble mass arev such as to permit a considerably greater contact time between gas and pebbles in one section of the chamber than is obtained in another section of the same chamber.

Another disadvantage of the conventional pebble heater type apparatus is that it is quite expensive to construct, partly because of the fact that the two chambers should be supported one above the other so as to obtain gravitating flow of pebbles throughout the entire length of the system. Such a structure requires a considerably greater supporting structure than is necessary for one of lesser strength. Another disadvantage in construction of the conventional pebble heater type apparatus is that a long elevator system is necessary, thus, posing many operational problems.

By at least one aspect of this invention, at least one of the following objects of the invention is attained.

An object of this invention is to provide improved pebble heater apparatus. Another object of the invention is to provide a single chamber pebble heater apparatus. Another object of the invention is to provide an improved method for reacting hydrocarbons in pebble heater apparatus. Another object of the invention is to provide an improved method for heating pebbles in pebble heater apparatus. Other and further objects and advantages will be apparent to those skilled in the art upon study of the accompanying discussion and the drawings.

Broadly speaking, this invention comprises a single chamber pebble heater apparatus, a single chamber forming a single Zone for reaction or treatment of gaseous materials within that chamber. The entire amount of pebble heating is obtained in the pebble recycle system utilized. for elevating the pebbles which are removed from the bottom of the reaction chamber, to the upper end portion of the chamber. A gas lift type of recycle system is utilized for returning the pebbles to the upper end portion of the reactor chamber. The lift-gas is heated to a high temperature prior to its contact with the pebbles. When certain gases are utilized as the lift-gas it is necessary to introduce larger quantities of that gas into the gas lift than when utilizing other gases in order to maintain entrainment of the pebbles throughout the entire l ngth of the gas lift.

When the heating or lift-gas is at a high temperature and when that gas has a. high heat transfer coeflicient,

the pebbles are subjected to considerable mechanical and thermal shock if the total amount of lift-gas is introduced into the bottom end of the gas lift. I have devised a method whereby the pebbles can be entrained in the lower end portion of the gas lift and maintained in entrainment through that lift without substantial mechanical or thermal shock. This result is obtained by introducing only a portion of the lift-gas into the lower end of the gas lift. That portion of the gas is sufiicient to initially entrain and fiuidize the pebbles in the lower end of the gas lift. The quantity of pebbles is sufiiciently large with respect to the quantity of heating gas that thermal shock is substantially obviated. -As pointed out above, however, the heat transfer between the hot gas and the pebbles causes a reduction in volume of the gas. For

this reason, the pebbles tend to form a denser phase as they proceed upwardly through the gas lift. In order to offset this reduction in volume of the gas and in order 'to make available a sufiiciently large number of B. t. u.s

to heat the pebbles to the high temperatures required in the system, I introduce additional heating gas portions obviates thermal shock of the pebbles.

Heating the pebbles in this manner, results in delivering each of the pebbles to the upper end of the reactor at a temperature which is substantially the same as that of any other pebble, thereby obviating the difficulty of non-uniform pebble heating encountered when using the conventional multi-chamber pebble heater system. It

should also be noted that the height of the pebble heater system of this invention is only about one-half the length of pebble heater systems wherein two chambers are disposed one above the other.

Better understanding of this invention will be obtained upon reference to the drawings. Figure 1 is a schematic 'fiow diagram of the pebble heater system and feed and effluent lines connected with such a system. Figure 2 is a schematic representation of a portion of the feed and effluent lines connected to the gas lift together with a startup system provided in connection with the gas lift. Figure 3 is a schematic representation of a portion of the feed and effluent lines connected to the gas lift together with a preferred modification of the startup system of this invention.

Referring particularly to the device shown in Figure 1 of the drawings, pebble heater apparatus 11 comprises an upright elongated shell 12, closed at its upper and lower ends by closure members 13 and 14, respectively. Pebble inlet conduit 15 extends into the upper end portion of shell 12, preferably being centrally disposed in closure member 13. It is within the scope of this invention, however, to utilize a plurality of pebble inlet conduits uniformly disposed over the top of the pebble heater apparatus. When a plurality of inlets is utilized, it is desirable to provide a pebble surge chamber in pebble inlet conduit 15 so as to obtain uniform pebble flow to all portions of the top of the pebble bed within chamber 11. Gaseous effiuent conduit 16 is provided in the upper end of shell 12, preferably in closure member 13. Pebble -outlet conduit 17 extends downwardly from the bottom extends upwardly into the central portion of gas-pebble 'separator chamber 19. Pebble inlet conduit 15 is connected at its upper end to the lower end portion of separator 19.

Gaseous inlet conduit 21, having flow control valve 22 provided intermediate its ends, is connected to thelower end portion of pebble inlet conduit 15. Gaseous material inlet header 23 is provided so as to at least partially encircle pebble inlet conduit 15 intermediate its ends and communicates with the interior of the pebble inlet conduit. Gaseous material outlet material conduit 24 is connected to the upper end portion of pebble inlet conduit 15 at a point downstream of separator chamber 19. Separator chamber 25 is connected intermediate its ends to the upper end portion of separator chamber 19 by means of conduit 26. Indirect heat exchanger 27 is connected to the upper end portion of separator 25 by means of conduit 28, that conduit being provided with flow control valve 29 intermediate its ends. Conduit 31 extends from indirect heat exchanger 27 and is connected to vent conduit 32, the latter conduit having flow control valve 33 provided intermediate its ends. Outlet conduit 31 is also connected to conduit 34 which is in turn connected to a pressurizer, such as blower 35. Conduit 34 is provided with flow control valve 36 intermediate its ends and an inlet conduit 37, provided with flow control valve 38, is connected to conduit 34 intermediate flow control valve 36 and blower 35. Conduit 24 is directly connected to conduit 28 by means of by-pass conduit 39, the latter conduit being provided with a flow control valve 41 intermediate its ends. A second by-pass conduit 42, being provided with a flow control valve 43, connects conduit 24 directly with conduit 34 at a point upstream of flow control valve 36. Feed conduit 44 extends through indirect heat exchanger 27 and through an auxiliary indirect heat exchanger 45 and is connected to the lower end of shell 12 and communicates with the chamber within that shell, preferably through bottom closure member 14.

'outlet conduit 51 extends from the portion of the combustion chamber connected to the air and fuel inlet conduits. Conduit 51 is divided into two portions, one portion 52 extending to the lower end of elevator 18. Flow control valve 53 is provided intermediate the ends of conduit 52. A second portion of combustion gas outlet 51 designated as conduit 54 extends to inlet header 23. Conduit 54 is provided intermediate its ends with a flow control valve 55. Conduit 56 extends from conduit 52 to indirect heat exchanger 45 and is provided with flow control valve 57 intermediate its ends. Gaseous effluent conduit 58 extends from indirect heat exchanger 45.

Conduit 59 extends from blower 35 to the upstream end of the section of furnace 46 which is not connected with the fuel and inlet conduits. Flow control valve 61 is provided intermediate the ends of conduit 59. Conduit 62 extends from the downstream end of the section of furnace 46 which is connected to conduit 59 and is connected at its downstream end to conduit 52 downstream of flow control valve 53. Conduit 63 extends from a juncture with conduit 52, intermediate the juncture of

conduits

52 and 62 and elevator 18, and is connected at its upper end to the upper end portion of elevator 18. Flow control valve 64 is provided in the upper end portion of conduit 63. A plurality of connecting

conduits

65, 66, 67 and 68 extend between conduit 63 and spaced points along the length of elevator 18.

Flow control valves

69, 71, 72 and 73 are provided in connecting

conduits

65, 66, 67 and 68, respectively. It is usually sufficient to utilize one connecting conduit for the addition of hot gaseous material about every ten feet along the length of the elevator. If desired, more or less of these connecting conduits and different spacings may be utilized. .A,pebble flow. controller 74 is provided intermediate the ends of pebble outlet conduit 17. This flow controller may be any one ofthe conventional controllers, such as a star valve, a gate valve, a rotatable feeder, a vibratory feeder, or the like.

Referring particularly to Figure 2 of the drawings, like numerals identify parts described in connection with Figure 1 of the drawings. In the device shown in Figure 2, a plurality of pressure drop detecting; devices such as

manometers

75, 76, 77, 78, 79 and 81 are spaced apart along the lower portion of elevator 18. Although. the manometers. have been shown schematically as liquid type, it should be, noted that the conventional dry type manometer is preferred because of the high temperatures encountered in the gas lift. Liquid type manometers are suitable when spaced from the gas pebble conduit sufficiently to maintain the liquid in a cooled condition. It is preferred that these pressure drop sensing devices be spaced apart a distance of between about one and two feet through at least the lower one-third of the elevator. The manometers are operatively connected tocontrollers 82, 83, 84, 85, 86 and 87, respectively.

Auxiliary gas conduits

88, 89, 91, 92 93 and 94 extend between conduit 63 and elevator 18. These conduits are spaced so that one of these conduits is connected to elevator 18 at a point closely approximating the lower end of each of the pressure drop sensing devices.

Valves

95, 96, 97, 98, 99 and 101 are provided for control of flow in

conduits

88, 89, 91, 92, 93 and 94, respectively, and are operatively connected to

controllers

82, 83, 84, 85, 86 and 87, respectively. In the construction shown in the modification of Figure 2, valves, 69, 71, 72, 73 and 64 are connected to a power source, not shown. Valve 102 is provided in the connecting conduit intermediate the power source and the lowermost valve 69.

Controllers

82, 83, 84, 85, 86 and 87 are also connected to a power source, not shown. Valve 103 is provided in the control line between the power source and the lowermost controller 82.

Referring particularly to Figure 3 of the drawing, the same-numerals identify parts described in connection with Figure 1 and Figure 2 of the drawings. In the device shown in Figure 3, a plurality of temperature sensing members, such as thermocouples, are provided in the shell of elevator 18 at spaced points along at least the lower one-third of the length thereof.

Thermocouples

10,7, 108, 109, 111, 112, 113 and 114 are schematically shown in Figure 3 of the drawings. Thermocouple 107 is provided above connecting conduit 67 which has valve 72 provided therein. Thermocouple 108 is provided

intermediate conduits

94 and 67, thermocouple 109 is provided

intermediate conduits

93 and 94, thermocouple 111 is provided

intermediate conduits

92 and 93, thermocouple 112 is provided

intermediate conduits

91 and 92, thermocouple 113 is provided intermediate conduits 89 and 9.1 and thermocouple 114 is provided

intermediate conduits

88 and 89.

Thermocouples

107 and 108 are operatively connected to differential controller 115, which is. in turn operatively connected to valve 101.

Thermocouples

108 and 109 are operatively connected to differential controller 116 which is in turn operatively connected to valve 99. Thermocouples 109 and 111 are operatively connected to differential controller 117, which is in turn operatively connected to valve 98. Thermocouples 111 and 112 are operatively connected to differential controller 118 which is in turn operatively connected to valve 97.

Thermocouples

112 and 113 are operatively connected. to differential controller 119 which is in turn operatively connected to valve 96.

Thermocouples

113 and 114 are operatively connected to diiferential controller 121 which is in turn operatively connected to valve 95. In the construction shown in the modification of Figure 3,

valves

69, 71, 73 and 64 are connected to a control source, not shown, as discussed in connection with Figure 2. Valve 102 is provided in the connecting conduit intermediate the control source and the lowermost valve 69. Valve 72 is also connected to a control source, not shown, by a separate conduit and valve 122 is provided in the connectingcorp duit intermediate the control source and valve 72,

Differential controllers

115, 116, 117, 118, 119 and 121 are also connected to a. power source, not shown. Valve 123' is provided in the control line between the power source and the lowermost difi'erential controller 121.

In the operation of the pebble heater of this invention, pebbles are introduced into the upper end portion of chamber 11 through pebble inletconduit 15 and form a contiguous, gravitating, gas-pervious mass within that zone. This mass of pebbles continues as a contiguous bed downwardly through the entire length of the chamher and through pebble outlet conduit 1.7 to pebble flow controller 74. The pebbles are fed by means of pebble feeder 74 into the lower end portion of gas lift elevator 18. A lift-gas is introduced into, the lower end portion of elevator 18 at a temperature of at least about 2000 F. and at a sufiicient volume and velocity to initially entrain the pebbles, in the lower portion of the elevator. Additional portions of the hot gas are introduced into the elevator at spaced points along its length through conduits 65, 66, 67, 6 8 and 63. Whenthe pebble entraining gas stream enters gas-pebble separator chamber 19, the velocity of the pebbles is so reduced as to follow those pebbles to settle from the gas stream within. separator 19.

In one aspect of the invention, fuel and air are introduced into furnace 46 through

conduits

48 and 49. The fuel and: air are burned and the resulting hot combustion products are passed by means of conduits, 51 and 52 to the lowerend of elevator 18. As pointed out above, additional portions of the hot gas stream are introduced at spaced points alongthe length of the elevator. The efiluent. gas is removed from the upper end portion of chamber- 19 through conduit 26. This effluent gas carries with it the pebble fines from the system and is passed through separator chamber 25, which is a cyclone type separator. The pebble fines are separated from the efiluent gas and are removed from the bottom portion of that chamber. The effluent gas is removed from the upper end portion of separator chamber 25 and is passed through indirect heat exchanger 27 and is removed from the system through outlet conduit 31 and vent conduit 32.

The feed tothe pebble heater system, whether it be a hydrocarbon feed or a gaseous material to be treated, is passed by conduit 44 through indirect heat exchanger 27 in indirect heat exchange with the gaseous effluent from the gas lift. A second portion of the combustion gases obtained from furnace 46, is passed by means of conduit-

s

51, 52 and 56 into. indirect heat exchanger 45 and is vented through conduit 58. The feed which is preheated in the indirect heat exchange in exchanger 27 is passed through indirect heat exchanger 45 and is additionally preheated by means of the second portion of combustion gas from: furnace 46 in the indirect heat exchange within exchanger 45. Thepreheated feed isthen introduced into the lower portion of chamber 12;.

In elevating the pebbles to the upper end portion of the elevator, it is necessary to maintain. at least a minimum pebble velocity of 5 feet per second within the elevator. In order to maintain this minimum velocity, it is necessary to introduce a sufficieut amount of gas into the gas lift to intially entrain the pebbles and to maintain the entrainment throughout the length of the elevator. When entraining gas is, introduced only into the bottom portion of the elevator, it is necessary tomove the pebbles at a velocity in the neighborhood of between about 25 and feet per second in the lower portion of the elevator in order to obtain the desired pebble velocity at the top of a 50-foot lift. The specific initial pebble velocity which is required in such an operation is dependent upon the particular lift-gas utilized. By operating in the mannor of this invention, it is possible to reduce the initial pebble velocityto within the range of 10 feet per second to 25' feet per second, depending upon the specific lift-gas utilized. The initial pebble velocity will be dependent cracked during the heating and lifting steps.

-volume of the heating gas. {heating gas, combustion products from furnace 46 may be vented through conduit 104 and valve 105, valve 106 jupon the distance between the auxiliary gas inlets in the gas lift.

Combustion products resulting from the burning of a .hydrocarbon feed and air are satisfactorily utilized as in the gas lift by burning free oxygen and hydrogen in the furnace and utilizing the resulting steam product as the lift-gas. When steam is utilized as the lift-gas, it is necessary to utilize a higher initial pebblevelocity than is used when products of hydrocarbon combustion are used as the lift-gas. This higher velocity is required because of the greater amount of shrinkage in the volume of gas due to the higher rate of heat transfer obtained with steam than with hydrocarbon combustion products.

In another aspect of this invention, a gaseous material such as methane or hydrogen is introduced into conduit 34 through flow control valve 38 and conduit 37. This gaseous feed is pressurized in blower 35 and is passed by means of conduit 59 into the portion of furnace 46 which is not connected with

inlet conduits

48 and 49. The gaseous feed is heated to a high temperature, preferably at least 2400 F. by means of the indirect heat exchange with the combustion products and by radiant heat within furnace 46. The preheated gaseous material is then passed into the lower portion of gas lift 18 by means of conduit 62 and into spaced points along the length of elevator 18 through the various supplemental inlet conduits. The advantage which is obtained by use of these gases as a lift-gas material is that the pebbles can be heated to a somewhat higher temperature than when products of hydrocarbon combustion are used. A feed of hydrogen provides a substantially higher temperature for the pebbles than does the preheated methane. When methane is used as the lift-gas, a portion of that gas is After the methane and its products are removed from the upper end of separator chamber 19 and are passed through indirect heat exchanger 27 they may be vented to the atmosphere, but are preferably utilized as a preheated feed for furnace 46. When hydrogen is used as the lift-gas, the hydrogen is removed from the upper end portion of separator chamber 19, passed through separator 25 and indirect heat exchanger 27. When utilizing this type of lift-gas, it is ordinarily not necessary to utilize the auxiliary heat exchanger 45 for preheating the feed. However, the auxiliary heat exchanger 45 may be utilized so as to obtain a desired feed temperature. The hydrogen removed from indirect heat exchanger 27 is passed by means of conduits 31 and 34 into blower 35 wherein it is pressurized and once again recycled through the indirect heat exchange in furnace 46 and into gas lift 18.

As pointed out above, one of the important features of this invention is that each of the pebbles is raised to a temperature which is substantially the same as the temperature of each of the other pebbles. In one additional heating step, a portion of the heating gas may be passed into pebble inlet conduit 15 through inlet header 23 and caused to flow upwardly through the gravitating mass of pebbles within that conduit. The gaseous effiuent is removed from that conduit through outlet conduit 24. Pebble inlet conduit 15 is considerably smaller in crosssection than any of the conventional pebble heater chambers and for this reason the heating which is obtained within conduit 15 is substantially the same for all pebbles. An increase of 200 F. to 300 F. in pebble temperature ican be obtained in this short section of a pebble inlet conduit by direct heat exchange with a relatively small If hydrogen is used as the being closed. Hydrogen can then be passed by means 10f

conduits

62, 52 and 54 into the pebble inlet conduit.

as the lift-gas, the portion of hydrogen from conduit 24 is recycled through conduit 34 to blower 35.

The modification shown in Figure 2 of the drawings is particularly important in the operation of a pebble heater in which close control of pebble How is maintained in the gas lift elevator. A pebble velocity of at least 5 feet per second is necessary to prevent the pebbles from falling out and collecting as a dense mass in the lower end portion of the pebble elevator. In order to obtain startup of the pebble heater device after pebble drop out in the elevator has occurred, it has been necessary to withdraw the mass of pebbles from the elevator so as to obtain fluidization of those pebbles a few at a time. Ordinarily, the mass of pebbles will not reach a height much greater than about one-third the length of the elevator. For that reason, this startup modification is preferably provided only in the lower one-third of the gas lift. If longer gas lifts are utilized so that greater masses of pebbles are present in the lift, more of the control elements may be used so as to extend to the top of the pebbles when they are formed as a compact bed after dropping out of the gas stream.

In the operation of this device for startup of the pebble heater apparatus, valve 102 is manipulated so as to allow a source of power to close

valves

64, 69, 71, 72 and 73. Valve 103 is then manipulated so as to permit a power source to place

controllers

82, 83, 84, 85, 86 and 87 in operation. Each control operates to initially open each of the valves to which it is connected. The controllers are also operatively connected to the pressure drop sens- -wardly through the shallow mass of pebbles in the upper portion of the bed within the elevator at such a volume and velocity as to entrain the pebbles within the elevator. As the pebbles become entrained in the gas stream, the

pressure drop across pressure drop sensing element 81 decreases so as to permit a signal to be transmitted to controller 87. Controller 87 causes valve 101 to be closed in response to the pressure drop across element 81 thus making the path of least resistance for the gas through conduit 93. This procedure is repeated until the pebbles 'are fluidized within elevator 18.

Controls on

valves

69, 71, 72, 73 and 64 may be main tained individually so that additional gas can be introduced into the portion of elevator 18 containing the fluidized pebble portion so as to augment the single stream flowing through the selected startup conduit. Once the pebbles are entrained within elevator 18, all of the auxiliary inlet conduits are opened to gas flow by manipulation of valve 102 and the startup system is then closed by the manipulation of valve 103.

In the operation of the device shown as Figure 3 of the drawings, valve 102 is manipulated so as to allow a source 'of power to close

valves

64, 69, 71 and 73. Valve 12 3 'is then manipulated so as to permit a power source to *place

differential controllers

115, 116, 117, 118, 119 and -121 in operation. 'open' one of the valves to which it is connected. As :pointed outabove, gas tends to take the path of least Each controller operates to initially resistance. Therefore,,with valve 72 remaining open, the gas tends to take the path through conduit 67 above the thermocouples except for thermocouple 107. For this reason thermocouple 107 indicates a higher temperature than thermocouple 108 and it therefore imposes a temperature differential on differential controller 115. Valve 122 is manipulated so as to cause valve 72 to be at least partially closed, thereby causing at least a portion of the hot gas to flow through conduit 94 and valve 101. As the gas flows through conduit 94 into the elevator and fluidizes the pebbles within the section above that conduit, thermocouple 108 indicates a temperature substantially the same as that indicated by thermocouple 107. As the temperature differential between the measurements indicated by thermocouple 107 and thermocouple 108 diminishes to a predetermined minimum, differential controller 11S operates to cause valve 101 to be closed. This causes the gas to pass through conduit 93 and valve 99 into the pebble mass in elevator 18, thus fluidizing the pebble mass above conduit 93. In this manner, thermocouple 109 is raised to substantially the same temperature as that indicated by thermocouple 108. As the temperature differential between these two thermocouples diminishes to a predetermined minimum, differential controller 116 operates so as to close valve 99. The remaining portion of the startup system operates in the same manner.

In another modification of this invention,

valves

95, 96, 97, 98, 99 and 101 can be selectively operated in accordance with a timing device so as to successively close the valves from the uppermost valve to the lowermost valve so as to obtain successive fluidization of small portions of the pebble mass formed within the elevator.

Many additional modifications of this invention will be apparent upon study of the disclosure and the drawings. These modifications are believed to be within the spirit and the scope of this invention.

I claim:

1. An improved pyrolysis system which comprises a closed, upright, elongated shell; a pebble inlet in the upper end of said shell; gaseous effluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means, an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber connected to the upper end of said gas-pebble conduit;

a first pebble conduit extending between said pebble inlet 1 and the lower end portion of said separator chamber; a

lift-gas feed line connected to the lower end of said gaspebble conduit; a plurality of first lift-gas inlet conduits spaced along said gas-pebble conduit; a plurality of second' lift-gas inlet conduits spaced along at least the lower one-third of said gas-pebble conduit each having a valve therein; means for operating said valves independently of each other and independently of flow in said first inlet conduits; and gaseous material efi luent means extending from the upper end portion of said separator chamber.

2. The improved pyrolysis system of claim 1 wherein a heating gas inlet conduit is connected to said first pebble conduit intermediate its ends; and a gaseous effluent conduit is connected to said first pebble conduit near its upper end.

3. An improved pyrolysis system which comprises a closed, upright, elongated shell; pebble inlet means in the upper end of said shell; gaseous eflluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gaspebble separator chamber enclosing the upper end portion of said gas-pebble conduit; a first pebble conduit extending between said pebble inlet and the lower end portion of said separator chamber; a lift-gas feed line connected to the lower end of said gas-pebble conduit; a plurality of first lift-gas inlet conduits spaced apart along the entire length of said gas-pebble conduit; a plurality of second lift-gas inlet conduits connected to said gaspebble conduit at spaced. intervals along at least the lower one-third of said gas-pebble conduit and connected to said lift-gas feed line; a valve in each of said second lift-gas inlet conduits; and, at least one controller operatively connected to each of the valves in said lift-gas inlet conduits, each of the controllers being responsive to sensing means sensitive to a variable physical condition of the gas in said gas pebble conduit at levels commensurate with the levels of their respective lift-gas inlet conduits so as to successively close said valves in the order of the uppermost to the lowermost of said valves when said variable condition progressively changes in the same order.

4. The improved pyrolysis system of claim 3 wherein a plurality of temperature sensitive elements is spaced apart along at least the lower one-third of the length of said gas-pebble conduit, said first lift-gas inlet conduits and said second lift-gas inlet conduits are connected to said gas-pebble conduit intermediate adjacent temperature sensitive elements; and a temperature differential controller is operatively connected to adjacent temperature sensitive elements and to the valve in the second liftgas inlet conduit immediately below the lowermost of each pair of adjacent temperature sensitive elements.

5. The pyrolysis system of claim 4 wherein the uppermost of said first lift-gas inlet conduits is connected to said gas-pebble conduit intermediate the two uppermost temperature sensitive elements; and including a valve in the uppermost lift-gas inlet conduit.

6. The pyrolysis system of claim 3 wherein a pressure drop sensing unit is operatively connected to said gaspebble conduit immediately above each of said second lift-gas inlet conduits; and a controller is operatively connected to each pressure drop sensing unit and operatively connected to the valve in said second lift-gas conduit immediately below the pressure drop sensing unit.

7. An improved pyrolysis system which comprises a closed, upright, elongated shell enclosing a single pebble heat-exchange chamber for heating gases by direct heat exchange; a pebble inlet in the upper end of said shell; gaseous eflluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber enclosing the upper end portion of said gas-pebble conduit; a first pebble conduit extending between said pebble inlet and the lower end portion of said separator chamber; a lift-gas feed line connected to the lower end of said gaspebble conduit; a plurality of first lift-gas inlet conduits spaced along the length of said gas-pebble conduit; a plurality of second lift-gas inlet conduits connected to said lift-gas feed line and to said gas-pebble conduit at spaced points along at least the lower one-third thereof; a valve in each of said second lift-gas inlet conduits; at least one controller operatively connected to each of said valves in said second lift-gas inlet conduits, each of the controllers being responsive to sensing means sensitive to a variable physical condition of the gas in said gas pebble conduit at levels commensurate with the levels of their respective lift-gas inlet conduits; a second separator chamber; an effluent conduit extending from the upper end portion of said separator chamber to a point intermediate the ends of said second separator chamber; a

:first indirect heat exchanger; a gaseous efiluent conduit extending between the upper end portion of said second separator chamber and said first indirect heat exchanger; efl luent outlet means extending from said first indirect heat exchanger; a feed conduit extending through said first indirect heat exchanger and connected to said gaseous material inlet means in the lower end portion of said shell; a heating gas inlet connected to said first pebble conduit intermediate said pebble inlet means and said separator chamber; a gaseous efiluent conduit extending from the upper end portion of said first pebble conduit; a furnace; combustible material inlet means connected to said furnace; and conduit means connecting said furnace and said heating gas inlet to said lift-gas inlet means.

8. The pyrolysis system of claim 7 wherein said gaseous effiuent conduit from said first pebble conduit is connected at its downstream end to said first indirect heat exchanger.

9. The pyrolysis system of claim 7 wherein a second indirect heat exchanger is operatively connected to said feed gas conduit intermediate said first indirect heat exchanger and said shell; a gaseous material conduit extends between said furnace and said second indirect heat exchanger; and effluent conduit means extends from said second indirect heat exchanger.

10. An improved pyrolysis system which comprises a closed, upright, elongated shell enclosing a single pebble heat-exchange chamber for heating gases by direct heat exchange; a pebble inlet in the upper end of said shell; gaseous material efiluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gaspebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber enclosing the upper end portion of said gas-pebble conduit; a first pebble conduit extending between said pebble inlet and the lower end portion of said separator chamber; a lift-gas feed line connected to the lower end of said gaspebble conduit; a plurality of first lift-gas inlet conduits spaced along the length of said gas-pebble conduit; a plurality of second lift-gas inlet conduits connected to said lift-gas feed line and to said gas-pebble conduit at a plurality of points spaced along at least the lower one-third of the length thereof; a valve in each of said second liftgas inlet conduits; at least one controller operatively connected to each said valve in said second lift-gas inlet conduits, each of the controllers being responsive to sensing means sensitive to a variable physical condition of the gas in said gas pebble conduit at levels commensurate with the levels of their respective lift-gas inlet conduits; a second separator chamber; a conduit extending between the upper end portion of said gas-pebble separator chamber and a point intermediate the ends of said second separator chamber; a first indirect heat exchanger; a conduit extending between the upper end portion of said second separator chamber and said first indirect heat exchanger; a gaseous effluent conduit extending from said first indirect heat exchanger; a feed gas conduit extending through said indirect heat exchanger and connected at its downstream end to said lift-gas inlet means; a furnace; combustible material inlet means connected to said furnace; gaseous efiluent conduit means extending from said furnace; a second indirect heat exchanger operatively connected to said furnace; a first lift-gas conduit connected to the upstream end of said second indirect heat exchanger; a second lift-gas conduit extending between the downstream end of said second indirect heat exchanger and said lift-gas inlet means; and a pressurizer intermediate the ends of said first lift-gas conduit.

11. The pyrolysis system of claim 10 wherein a third indirect heat exchanger is operatively connected to said feed conduit intermediate said first indirect heat exchanger and said shell; a conduit extending between the downstream end of said furnace and said third indirect heat exchanger; and a gaseous efiiuent conduit extending from said third indirect heat exchanger.

12. The pyrolysis system of claim 10 wherein a heating gas inlet is connected to said first pebble conduit intermediate said pebble inlet means and said gas-pebble separator chamber; a gaseous material efiiuent conduit extending from the upper end portion of said pebble conduit, connected to said efiluent conduit from said first indirect heat exchanger; and a heating material conduit extending from said second lift-gas conduit intermediate said second indirect heat exchanger and said lift-gas inlet means to said heating gas inlet in said first pebble conduit.

13. The pyrolysis system of claim 12 wherein said gaseous material conduit extends from the upper end portion of said first pebble conduit and is connected to said effiuent conduit from said first heat exchanger through said first heat exchanger.

14. The pyrolysis system of claim 12 wherein a gaseous material conduit extends between said effluent conduit from said first indirect heat exchanger to said first heating gas inlet conduit upstream of said pressun'zer.

15. The pyrolysis system of claim 10 wherein said furnace is a tube furnace; and said first lift-gas conduit and said second lift-gas conduit are connected to the tubes of said furnace at the upstream and downstream ends, re-

.spectively.

16. An improved method for operating a pebble heater which comprises the steps of introducing pebbles into the upper end of a single chamber; gravitating said pebbles downwardly through said chamber as a contiguous, gaspervious mass; gravitating said pebbles from the lower end of said chamber at a controlled rate into the lower end portion of a gas lift conduit; introducing a portion of a gaseous entraining fluid into the lower end portion of said gas lift conduit, below the point of ingress of pebbles thereto, at a temperature of at least 2000 F. and in sufficient volume to entrain said pebbles and to elevate said pebbles only a portion of the distance to the upper end of said gas lift conduit, whereby the temperature of said pebbles is elevated by direct heat exchange with said hot gaseous entraining fluid; introducing additional portions of said 'hot gaseous entraining fluid into said gas lift conduit at spaced points along the length thereof, whereby the temperature of said pebbles is continuously elevated to a desired temperature by direct heat exchange with said hot gases and with less thermal and mechanical shock to said pebbles than would be effected by introduction of all of said lift gas into said lower end portion of the gas-lift conduit; separating said lift-gas and said pebbles at the upper end of said gas lift conduit; gravitating said heated pebbles through a communication zone into the upper end portion of said single chamber; introducing a gaseous feed into the lower end portion of said chamber; passing said gaseous feed upwardly through said contiguous, gas-pervious pebble mass within said chamber countercurrent to the gravitating pebble flow, whereby said gaseous material is elevated to a desired temperature within said chamber, and removing gaseous effluent from the upper end portion of said chamber.

17. The method of claim 16 wherein combustible materials are burned so as to produce hot combustion products and said combustion products are introduced into the lower end and at points spaced along the length of said gas lift conduit at a temperature within the range of 2000 F. to 3200 F.

18. The method of claim 16 wherein said combustion products are introduced into the lower end and at points v spaced along the lengthof said gas lift at a temperature of at least 2400 F.

, steamproduct is introduced into the lower end and at points spaced along the length of said gas lift conduit.

20. The method of claim 19 wherein a portion of said combustion products is introduced into the gravitating mass of pebbles intermediate the ends of said communication zone and is passed upwardly through such gravitating mass of pebbles to a point near the upper end of said gas lift conduit; and the gaseous effluent is removed from the upper end portion of said communication zone adjacent the upper end of said gas lift conduit.

21. The method of claim 16 wherein said feed gas is preheated by indirect heat exchange with said gaseous effluent from said gas lift conduit.

22. The method of claim 16 wherein said lift gas is heated to a temperature within the range of between 2000 F. and 3200 F. in indirect heat exchange with combustible materials in a combustion chamber.

23. The method of fluidizing a static pebble mass within a gas lift conduit which comprises the steps of introducing hot gaseous material into the upper portion of said pebble mass within said gas lift conduit in suflicient volume to entrain said upper portion of pebbles in said gaseous material; at least partially stopping the flow of gaseous material directly into the fluidized portion of the pebble mass and introducing additional hot lift-gas successively in the lower sections of said pebble mass with concomitant reduced flow of gas directly into the fluidized portion, whereby said total pebble mass is heated and completely entrained.

24. The method of claim 23 in which said lift-gas is at a temperature in the range of 2000 to 3200 F.

25. An improved pyrolysis system which comprises a closed, upright, elongated shell; a pebble inlet in the upper end of said shell; gaseous eflluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber connected to the upper end of said gas-pebble conduit; a first pebble conduit extending between said pebble inlet and the lower end portion of said separator chamber; a furnace outside of said gas-pebble conduit and outside of said shell for producing hot lift gas; a lift-gas feed line connecting said furnace with said gas-pebble conduit below the juncture of said pebble outlet means with said gas-pebble conduit; a plurality of lift-gas inlet conduits connected with said gas-pebble conduit at vertically spaced-apart points along its length and with a hot gas source; and a gas outlet means from an upper section of said separator chamber.

26. A method of fiuidizing a static column of pebbles within an upright gas-lift conduit which comprises the steps of introducing a hot lift gas into an upper portion of said column of pebbles within said gas-lift conduit in sufficient volume and flow rate to entrain said upper portion of said column of pebbles in said hot lift gas; thereafter introducing additional hot lift gas successively in progressively lower sections of said column of pebbles so as to entrain said column of pebbles in said 'hot lift gas and elevate the same to the upper end of said conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,123,155 Woodley Dec. 29, 1914 1,202,088 Murray Oct. 24, 1916 1,232,393 Piper July 3, 1917 1,280,780 Lob Oct. 8, 1918 2,405,395 Bahlke et al. Aug. 6, 1946 2,432,503 Bergstrom et al Dec. 16, 1947 2,499,704 Utterback et al. Mar. 7, 1950 2,509,983 Morrow May 30, 1950 2,548,030 Leifer Apr. 10, 1951 2,548,522 Drew Apr. 10, 1951 2,585,984 Alexander et al Feb. 19, 1952 2,587,670 Weinrich Mar. 4, 1952 2,614,028 Schaumann Oct. 14, 1952 2,626,141 Grossman Jan. 20, 1953 2,643,216 Findlay June 23, 1953 2,684,873 Berg July 27, 1954 2,703,732 Schut-te Mar. 8, 1955

Claims

25. AN IMPROVED PYROLYSIS SYSTEM WHICH COMPRISES A CLOSED, UPRIGHT, ELONGATED SHELL; A PEBBLE INLET IN THE UPPER END OF SAID SHELL; GASEOUS EFFLUENT MEANS IN THE UPPER END OF SAID SHELL; PEBBLE OUTLET MEANS IN THE LOWER END OF SAID SHELL; GASEOUS MATERIAL INLET MEANS IN THE LOWER END PORTION OF SAID SHELL; PEBBLE FEEDER MEANS INTERMEDIATE THE ENDS OF SAID PEBBLE OUTLET MEANS; AN UPRIGHT GAS-PEBBLE CONDUIT CONNECTED AT ITS LOWER END PORTION TO THE LOWER END OF SAID PEBBLE OUTLET MEANS AND EXTENDING TO A LEVEL ABOVE THE TOP OF SAID SHELL; A GAS-PEBBLE SEPARATOR CHAMBER CONNECTED TO THE UPPER END OF SAID GAS-PEBBLE CONDUIT; A FIRST PEBBLE CONDUIT EXTENDING BETWEEN SAID PEBBLE INLET AND THE LOWER END PORTION OF SAID SEPARATOR CHAMBER; A FURNACE OUTSIDE OF SAID GAS-PEBBLE CONDUIT AND OUTSIDE OF SAID SHELL FOR PRODUCING HOT LIFT GAS; A LIFT-GAS FEED LINE CONNECTING SAID FURNACE WITH SAID GAS-PEBBLE CONDUIT BELOW THE JUNCTURE OF SAID PEBBLE OUTLET MEANS WITH SAID GAS-PEBBLE CONDUIT; A PLURALITY OF LIFT-GAS INLET CONDUITS CONNECTED WITH SAID GAS-PEBBLE CONDUIT A VERTICALLY SPACED-APART POINTS ALONG ITS LENGTH AND WITH A HOT GAS SOURCE; AND A GAS OUTLET MEANS FROM AN UPPER SECTION OF SAID SEPARATOR CHAMBER.