Method and apparatus for the transfer of entrained solids
United States Patent Mitchell [75] Inventor: Willard N. Mitchell, Baytown, Tex.  
 [73] Assignee: Exxon Research and Engineering Company, Linden, NJ.  
 [22] Filed: Aug. 7, 1973 [21] Appl. No.: 386,231  
 [52] U.S. Cl 302/24, 48/77, 48/197 R, 302/64, 302/66 [51] Int. Cl B65g 53/04 [58] Field of Search 48/210, 202, 197 R, 62 R, 48/63, 64, 73, 77, 78, 86 R, 203, 206; 302/17, 24, 53, 55, 64, 66; 34/10, 57; 137/268, 604; 208/164; 23/288 S; 201/12, 13, 31; 202/262 [56] References Cited UNITED STATES PATENTS 758,118 4/1904 Sticker 302/24 2,694,623 11/1954 Welty et al 48/197 R 2,713,590 7/1955 48/206 2,716,055 8/1955 2,879,145 3/1959 2,881,133 4/1959 2,902,433 9/1959 3,295,895 1/1967 METHOD AND APPARATUS FOR THE TRANSFER OF ENTRAlNED SOLIDS OTHER PUBLICATIONS Gasification by the Moving-Burden Technique J.  
 W. R. Rayner in Journal of the lnstitute of Frel Mar. 52.  
 Primary E.raminerS. Leon Bashore Assistant E.raminerPeter F. Kratz Attorney, Agent, or Firm-J. E. Reed [57] ABSTRACT Solid particles are transferred from a standpipe or similar vessel in which a stream of particles moves downwardly in dense phase flow to a transfer line burner or other vessel in which the particles are carried upwardly in dilute phase flow by withdrawing the downwardly moving dense flow stream of particles from the first vessel, reducing the cross-sectional area of the a quantity sufficient to produce a rapid transition from dense phase flow to dilute phase flow.  
 20 Claims, 4 Drawing Figures PATENTEUAPR 1 ms SHLU 2 I]? 2 E A Alli A FIG. 2.  
 METHOD AND APPARATUS FOR THE TRANSFER OF ENTRAINED SOLIDS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the transport of solid particles in gases and is particularly concerned with the transfer of particles from standpipes and similar equip ment to transfer line burners and the like during coal gasification and related operations.  
 2. Description of the Prior Art Many of the processes proposed for the gasification of coal and similar carbonaceous materials rely upon fluidized solid techniques for transporting solid particles from one vessel to another. Typical of such processes are those in which finely divided coal is reacted with synthesis gas in a hydrogasification zone, the char produced is contacted with steam in a steam gasification zone to produce the synthesis gas, and a portion of the char is circulated through a transfer line burner to supply the heat required. The char particles which are thus circulated are withdrawn from a fluidized bed in the steam gasification zone, passed downwardly through a standpipe containing a J-bend, and then fed upwardly into the lower end of the transfer line burner. The unburned solids recovered at the top of the burner are discharged into another standpipe and conveyed through a similar J-bend back to the fluidized bed reaction vessel. The standpipes and J-bends used are designed to avoid abrupt changes in the flow path and thus promote smooth flow of the solids streams.  
  Although systems of the type described above have been used satisfactorily, experience has shown that proper control of the circulating char particles is often a problem. It has been found that pressure surges often develop in the steam gasifier and that these are transmitted to the standpipe from which the char particles are fed through the .I-bend into .the burner. This affects the feed rate, results in rarefied areas in the burner where very little char is present, and sometimes results in stagnant areas near the burner wall immediately above the feed inlet. Because of this uneven distribution of the char particles and combustion air, localized overheating of the char to temperatures in excess of the ash fusion temperature often takes place. The softened ash tends to stick to the burner walls and may eventually plug the burner if the ash deposits are not removed. Efforts in the past to eliminate the pressure surges which are largely responsible for these and related difficulties have been only partially successful.  
 SUMMARY OF THE INVENTION This invention provides an improved method for the transfer of char particles or other finely divided solids from a standpipe or similar vessel in which a stream of solids moves downwardly in dense phase flow to a transfer line burner or other vessel in which the solids are carried upwardly in dilute phase flow which at least in part alleviates the difficulties outlined above. In accordance with the invention, it has now been found that the problems caused by pressure surges and related phenomena can be at least partially eliminated by passing the downwardly moving dense phase stream of solids leaving the standpipe or similar vessel through a tapered nozzle-in which the cross-sectional area of the stream is reduced by a factor of from about L2 to about 10, abruptly changing the direction of flow from a substantially horizontal to a substantially vertical upward direction, injecting sufficient gas to maintain dense phase flow at the point where the particles began to move upwardly, and thereafter introducing sufficient additional gas to promote a rapid transition from dense phase to dilute phase flow. Laboratory work and pilot plant tests have shown that this method minimizes the effect of pressure surges and permits smooth flow of the solids without the erratic behavior encountered with systems employed in the past.  
  The apparatus employed in practicing the method of the invention will normally comprise a conduit containing a tapered flow restriction and an abrupt 90 bend downstream of the restriction. The cross-sectional area of the inlet side of the flow restriction will generally be BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is a flow sheet depicting schematically a coal gasification process carried out in accordance with the invention;  
 FIG. 2 is an enlarged, sectional view of a gasifier inlet device useful in the process of FIG. 1;  
  FIG. 3 is a cross-sectional view of the apparatus of FIG. 2 taken about the line 3-3; and  
  FIG. 4 is an enlarged, longitudinal cross-section through a burner inlet device suitable for use in accordance with the invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The process depicted in FIG. 1 of the drawing is an endothermic process for the production of a product gas stream of relatively high methane content by the treatment of bituminous coal, subbituminous coal, lignite, solid petroleum residua or similar carbonaceous solids with steam at high temperatures. The solid feed material employed in the process, preferably a bituminous or lower rank coal, is introduced into the system through line 10 from a suitable solid feed preparation plant or storage facility which is not shown in the drawing. To permit the handling of this feed material in a fluidized system, the coal or other carbonaceous solid is introduced in a finely-divided state, preferably less than about 8 mesh on the Tyler Screen Scale. The process is operated atelevated pressure and hence the coal or other feed material employed is fed into vessel 11, from which it is discharged through star wheel feeder or similar device 12 into line 13 at the system operating pressure or at a slightly higher pressure. Steam may be introduced through line 14 to facilitate flow of the solids from vessel 11. In lieu of or in addition to the use of a feed hopper as shown, parallel lock hoppers, pressurized hoppers, or aerated standpipes operating in series may be used to raise the input solids stream to the required injection pressure. The use of such systems for handling coal and other finely-divided solids at elevated pressures has been described in the patent literature and will be familiar to those skilled in the art.  
  The solid particles admitted into the system through line 13 are entrained in a feed gas stream introduced through line 14 and are fed through shrouded nozzle 15 into gasifier 16. High pressure steam or product gas may be used the feed gas stream. The use of product gas is normally preferred. This gas is introduced into the system at a pressure between about 50 and about 1000 pounds per square inch gauge, depending in part upon the pressure at which the gasifier 16 is operated and the solid feed material employed. Steam is introduced through line 17 into the shrouded nozzle in order to keep the feed injection nozzle temperature below about 600 F. Where coal is employed as the feed material, this aids in avoiding fouling of the nozzle with agglomerating coal solids. If a severely agglomerating coal is employed as the feed material, an injection nozzle specially designed to promote intimate and extremely rapid mixing of the injected coal with the hot solids in the gasifier will normally be employed. Nozzles suitable for this purpose have been described in the prior art.  
  The gasifier vessel 16 employed in the system of FIG. 1 contains a fluidized bed of char particles which are introduced into the lower part of the vessel through inlet section 18, which will be described in greater detail hereafter. Steam for reacting with the char and maintaining the solids in the fluidized state is introduced into the lower portion of the gasifler below distribution grid or similar device 19 through line 20. Steam for controlling movement of the solids through inlet section 18 is introduced through lines 21, 22, 23 and 24. The total steam rate will normally range between about 0.5 and about 2.0 pounds of steam per pound of coal feed. The upflowing steam and char form a fluidized bed which extends upwardly above grid 19 to a level above the point at which coal solids are introduced into the gasifier. The lower portion of the gasifier above the grid, indicated by reference numeral 25, thus serves a steam gasification zone. Here the steam introduced near the lower end of the vessel reacts with carbon in the hot char to form synthesis gas in accordance with the reaction: H O +C H +CO. The hydrogen concentration in the gaseous phase of the fluidized bed is essentially zero at the point of steam injection near the bottom of the gasifier. As the steam moves upwardly through the fluidized char particles, it reacts with the carbon and hence the hydrogen concentration in the gaseous phase increases. The temperature in the steam gasification zone will normally range between about l450 and about l800 F. The superficial gas velocities in the fluidized bed will generally range between about 0.2 and about 3.0 feet per second. I  
  The inlet 18 near the lower end of the gasifier 16 is shown in greater detail in FIGS. 2 and 3 of the drawing. As can be seen from FIG. 2, this apparatus includes an inclined entrance section 30 which extends downwardly at an angle of about 60 from the horizontal, a substantially horizontal intermediate section 31, and a substantially vertical exit section 32. Vertical line 21 for the introduction of steam or other control fluid extends downwardly into the top of the entrance section a short distance upstream of the intermediate section. Horizontal line 22 for the introduction of steam or other control fluid passes through the wall of the entrance section on or near the center line of the intermediate section and extends horizontally into the entrance section to a point near the juncture between the two.  
 The diameters of these lines should be sufficient to permit the injection of steam or other gas in the desired quantities at a pressure in excess of that within the gas ifier. The intermediate section of the device contains a conical flow restriction 33 having an upstream crosssectional area of from about 1.2 to about 10 times the cross-sectional area of the downstream outlet. The walls of this flow restriction will normally taper inwardly from the inlet to the outlet at an angle of from about 15 to about 45 to the horizontal. The particular dimensions chosen will depend primarily upon the velocity and volume of the incoming dense phase char particles and the extent to which the particles are to be accelerated in the first stage of the device. Vertical or discharge section 32 extends at substantially right angles to the horizontal section of the device, thus producing an abrupt change in the direction of flow from substantially horizontal to substantially vertical. Vertical steam or other control fluid inlet line 23 extends upwardly into the bottom of the device at or near the center line of the vertical section. Horizontal steam or other control fluid inlet line 24 extends into the wall of the vertical section on or near the center line of the horizontal section and thus substantially opposes horizontal steam inlet line 22. Line 24 is not always essential and in some cases may be omitted. The diameters of inlet lines 23 and 24 will generally, but not necessarily, be similar to those of lines 21 and 22. The exit section extends upwardly within gasifier 16 to a central opening in grid 19 to permit the discharge of the entrained solids into the open space in the gasifier above the grid.  
  The upper part of the fluidized bed and gasifier 16 serves as a hydrogasification zone, indicated by reference numeral 35, where the feed coal is devolatilized and a part of the volatile matter thus produced reacts with hydrogen generated in steam gasification zone 25 to produce methane as one of the principal products. The point at which the coal feed stream is introduced into the gasifier and hence the locations of the steam gasification and hydrogasification zones will depend primarily upon the properties of the particular coal or similar material which is employed as the feedstock. it.  
 is generally preferred to maximize the methane yield from the gasifier and minimize the tar yield. Generally speaking, the amount of methane produced increases as the feed injection point is moved near the top of the reaction vessel. The tar, which has a tendency to foul. downstream processing equipment, generally increases as the feed injection point is moved upwardly in the.  
 gasifier and decreases as the feed point is moved near the bottom of the vessel, other operating conditions being the same. The solid feed material should generally be introduced into the vessel at a point where the hydrogen concentration in the gas phase is in excess of about 15% by volume, preferably between about 25 and about 50% by volume. The upper surface of the fluidized bed, indicated by reference numeral 36, will normally be located at a level sufficiently above the feed injection point to provide at least about 4 seconds of residence time for the gas phase in contact with the fluidized solids in hydrogasification zone 35. It is preferred in general that the residence time for the gas in contact with the solid phase above the point at which the coal or similar feed material is injected be between about 7 and about 20 seconds. It will be understood, of  
 course, that the optimum hydrogen concentration at the feed injection point and gas residence time above the point of feed injection will vary with different types and compositions of coal or other feed material and with variations in the gasifier temperature, pressure, steam rate and other processing conditions. Higher rank coals nomially require somewhat more severe reaction conditions to obtain practical reaction rates than do coals of lower rank. Similarly, higher reaction temperatures and steam rates normally tend to increase the hydrogen concentration in the gas phase and thus reduce the solids residence times required for gasification of a given feed material.  
  The heat required to sustain the overall endothermic reaction taking place in the gasifier 16 and maintain the operating temperature in the range between about l450 and about l800 F. is provided by withdrawing a portion of the char solids from the fluidized bed through line 40 and passing this material through burner inlet device 41 into the lower end of transfer line burner 42. The burner inlet device is similar to that employed on the gasifier and is shown in greater detail in FIG. 4 of the drawing. This device includes an entrance section 43 which slopes downwardly at an angle of about 60 from the horizontal and thus forms a continuation of line 40, a substantially horizontal intermediate section 44, and a substantially vertical exit section 45 which is connected to the lower end of the burner. Vertical steam or gas inlet line 46 extends downwardly into the top of the entrance section a short distance upstream of the intermediate section. Horizontal steam or gas line 47 passes through the wall of the entrance section on or near the center line of the intermediate section and extends horizontally into the entrance section.  
 to a point near that at which the flow stream changes direction as it passes from the entrance section to the intermediate section. As was the case with the gasifier inlet device described .earlier, the diameters of the steam lines extending into the entrance section should be sufficient to permit the injection of steam or other gas in the required quantities at a pressure in excess of that within the burner. The intermediate section of the device contains a conical flow restriction 48 having an upstream cross-sectional area of from about 1.2 to about l0 times the cross-sectional area of the downstream outlet. The walls of this flow restriction will normally taper inwardly from the inlet to the outlet at an angle from about to about 45 to the horizontal. Again, the particular dimensions chosen will depend primarily upon the velocity and volume of the incoming dense phase char particles and the extent to which the particles are to be accelerated in the first stage of the device. Vertical section 45 extends upwardly at substantially right angles to the horizontal section of the device so that the solids stream undergoes an abrupt change in direction from substantially horizontal to substantially vertical. Steam or gas inlet line 49 extends upwardly into the bottom of the device on or near the center line of the vertical section and the burner above it. Horizontal steam or gas injection line 50, which may be omitted if desired, extends into the wall of the vertical section on or near the center line of the horizontal section so that it substantially opposes horizontal steam inlet line 47. A  
  The solids leaving injection device 41 move upwardly in dense phase flow into the lower portion of the transfer line burner. An oxygen-containing gas, preferably air or a mixture of air and flue gas, is introduced through line 52 and multiple injection nozzles 53 in a quantity sufficient to promote a rapid transition from dense phase flow to dilute phase flow. The amount of gas used in the composition employed will depend in part upon the chemical and physical characteristics of the char particles, the amount and composition of the entraining gas moving upwardly from the injection device, theparticle acceleration required to achieve dilute phase flow, the distribution of the injection nozzles above the burner, the dimensions of the system, the combustion efficiency, the heat losses which occur, and other factors. The use of a plurality of nozzles spaced at regular intervals about the burner periphery as shown promotes more uniform contact between the injected gas and the upflowing solids and thus improves combustion efficiency and aids in avoiding localized overheating.  
  Additional oxygen-containing gas is injected into the burner through line 55 and associated nozzles 56 at a second point above the first injection point. Here the particles are further accelerated. If the gas injected at the lowermost nozzles contains significant quantities of oxygen, nozzles 56 will preferably be located sufficiently above the lowermost nozzles to permit the consumption of essentially all of the oxygen previously introduced before additional oxygen is admitted. Studies indicate that the oxygen introduced into contact with the hot char particles near the lower end of the burner is consumed very rapidly, generally in from about 0.00] to about 0.2 second. The required spacing of the second set of nozzles above the lowermost nozzles can therefore be calculated. Additional oxygen-containing gas may be introduced into the burner near the upper end thereof through line 58 and nozzles 59 if desired. The total amount of oxygen introduced into the burner should normally be sufficient to permit the combustion of enough carbon to effect a temperature rise in the unburned particles of from about 50 to about 300 F., preferably about 200 F. The total amount of oxygen required and the volume of oxygen-containing gas which will thus be needed for a particular set of operating conditions can be calculated. In general, it is normally preferred to inject air at the rate of from about 0.02 to about 0.2 pound per pound of char being circulated through the burner. If an oxygen-containing gas having a lower oxygen content than air is used, as will often be the case, the gas injection rate will have to be increased accordingly. The total residence time of the char solids within the burner will normally range between about 0.3 and about 5.0 seconds. Residence times of this order are generally necessary because of the burner length required to handle the solids from a commercial-size fluid bed reactor andbecause of limitations on gas velocity which are imposed by the necessity for avoiding excessive particle attrition.  
  The movement of solids from line 40 into the transfer line burner 42 is controlled by means of burner inlet device 41. The dense phase solids stream moving downwardly through line 40 into the inlet device will typically have a velocity in the range of from 0.05 to about 0.3 foot per second. These values may vary considerably, of course, depending upon the density of the char particles being circulated, the dimensions of the particles, and the amount of gas present in the stream. The stages acceleration of the solidsstream is started by steam or gas introduced into the inlet device through lines 46 and 47. This injected steam or gas results in smooth flow of the particles into nozzle 48 and tends to counteract the reduction in velocity which would otherwise take place due to the change in direction of flow as the particles move from the inlet section of the device into the intermediate section. By varying the amount of steam or gas injected through lines 46 and 47, the flow into the injection device can be shut off completely or increased from the initial level to about 0.2 foot per second or higher, again depending upon the characteristics of the particles and other factors. Because of the reduction in cross-sectional area between the inlet and outlet of the tapered nozzle, the particle stream is accelerated to a velocity of from about 0.2 foot per second or somewhat higher to a final velocity between about 0.5 foot per second and about 1.5 feet per second or more, depending in part upon the ratio between the inlet cross-sectional area and the outlet cross-sectional area. As indicated earlier, this ratio may range between about l.2:l and about :1 Ratios of from about 3:1 to about 7:1 are normally preferred. The passage of the solids stream through the nozzle, in addition to accelerating the solids, tends to isolate the downstream fluid system from pressure surges occurring within the gasifier and thus results in more uniform conditions within the transfer line burner.  
  The direction of the stream of solids emerging from the outlet of nozzle 48 changes abruptly as the stream moves from the intermediate section to the discharge or exit section of the device. Steam or gas, preferably a flue gas or similar mixutre of low oxygen content, is injected through line 49 in sufficient quantity to aerate the upflowing char. It is important that the volume of gas introduced at this point be sufficiently low to maintain the stream in dense phase flow. Excessive gas will result in fluidization of the char particles and the formation of large gas bubbles which tend to cause uneven flow of the solids into the lower end of the burner. Line 50 is normally closed offby means ofa valve not shown in the drawing but may be used for the introduction of gas to start flow after flow has been terminated by regulation of the gas introduced through lines 46 and 47. The inlet device 41 thus serves both as a means for regulating the flow of solids into the burner and as a means for shutting off flow completely. This obviates the necessity for using slide valves and similar devices which have not proved entirely satisfactory in the past.  
  As indicted earlier, the dense phase upflowing stream of solids entering the lower end of the transfer line burner is accelerated sufficiently to promote a rapid transition from dense phase flow to dilute phase flow by gas introduced through line 52 and nozzles 53. The superficial gas velocity is increased to a value of from about 10 feet per second to about feet per second or higher. This gas stream will normally contain sufficient oxygen to start burning of the char particles but hold the temperature rise to a minimum. This reduces the change of a few particles contacting a large quantity of air and thus becoming overheated. The use of four or more inlet nozzles spaced around the periphery of the burner aids in obtaining smooth acceleration of the particles and further limits the likelihood of overheating. The use of six or more inlet nozzles is generally preferred. By the time the char reaches the second burner stage adjacent nozzles 56, the particles are moving at transport velocity. The oxygen containing gas introduced at this point promotes further acceleration of the char until a superficial gas velocity within the range I of from about to about feet per second with little disruption of the flow stream is obtained. The crosssection area of the burner above nozzles 56 will preferably be somewhat larger than that below the nozzles in order to permit the introduction of additional quantities of air or other oxygencontaining gas while maintaining the desired velocity. In most cases, it is preferred that the cross-sectional area above the nozzles be about twice that of the burner below the injection nozzles. Multiple nozzles are again employed to obtain effective distribution of the air or gas in the solids stream. In a typical installation, eight or more individual air inlet nozzles spaced about the burner may be employed.  
  Nozzles 59 near the upper end of the burner serve as the third stage injection point. Here sufficient air to complete heating of the char to the desired final temperature of from about l500 to about l950 F. is introduced through four or more peripherally spaced nozzles. These nozzles are preferably located a sufficient distance below the upper end of the burner to permit complete reaction of the air with the char before the char particles are discharged. As pointed out earlier, the reaction is generally completed within from about 0.001 to about 0.2 second and hence the nozzles will generally be placed about 30 to 36 inches or more below the top of the burner. The superficial gas velocity above the third injection stage will normally be about 40 feet per second or higher. Although only three injection stages are employed in the system shown in the drawing, it will be understood that the invention is not restricted to three stages and that additional stages may be provided to further distribute the air or other oxygen-containing gas in the upflowing stream of char particles if desired. Additional oxygen may be introduced close to the upper end of the burner to convert carbon monoxide to carbon dioxide. This results in the generation of additional heat which is in part transferred to the suspended char particles, improves the overall combustion efficiency of the burner, and permits the carbon monoxide content of the flue gas stream to be controlled at the desired level. A carbon monoxide analyzer and an air inlet line which is controlled in response to changes in the carbon monoxide content may be employed for this purpose if desired.  
  The gases and hot suspended solids leaving the upper. end of the transfer line burner are introduced into a separation zone 60 which will normally contain one ormore centrifugal separators designed to separate the larger solid particles from the combustion gases and discharge them through dipleg 61 for return to the reactor 16. Supplemental steam or other gas may be injected into the dipleg as necessary through line 62 to control the solids flow rate and facilitate movement of the solid particles around bends in the line. The combustion gases taken overhead from separation zone 60 are conducted through line 63 to a second separation zone 64 where fines not taken out in the first zone are removed. These fines are conveyed downwardly through diplet 65 to fines feeder vessel 66 from which they may be discharged through line 67 into line 40 for return to the transfer line burner. The fines can also be returned at other points in the system. The overhead flue gas stream from separation zone 64 is discharged through line 68. This gas may be passed through addi- 9 tional centrifugal separators, and scrubbed or further processed before being discharged into the atmosphere ifnecessary to. comply with applicable pollution control regulations.  
  The char particles from the transfer line burner are fed from line 61 into the lower end of gasifier 16 by means of gasifier inlet device 18. The downflowing char moves from line 61 into the entrance section 30 of the inlet device in dense phase flow. Steam introduced through vertical line 21 and horizontal line 22 entrains the char through nozzle 33 where the particles are accelerated. The flow rate is controlled by varying the amount of steam introduced through lines 21 and 22 and can be shut off entirely if desired. The accelerated stream and additional steam introduced through line 23 move upwardly through the exit section 32 of the inlet device in dense phase flow. Additional steam may be introduced through line 24 to start the particles moving again after a shutdown. The upflowing stream moves upwardly into the gasifier and is discharged above grid 19. Steam introduced through line passes upwardly through the openings in the grid and accelerates the particles sufficiently to effect a transition from dense phase to dilute phase flow and form a fluidized bed. It will thus be apparent that the gasifier inlet device functions in a manner similar to the burner inlet device 41 and that both of these devices thus permit the transfer of solid particles from a standpipe or similar device into a vertical burner or the like without the difficulties which have characterized the use of .l-bends and similar devices employed in the past.  
  The gaseous products formed in gasifier 16 by the reaction of steam and char in the steam gasification zone 25 and by devolatilization of the feed coal and reaction of the volatile products with hydrogen in hydrogasification zone are carried upwardly from the fluidized bed and pass through a solids separation zone where entrained solids are removed from the gas stream and returned to the fluidized bed. The product gas is taken overhead from separation zone 70 through line 71 to separation zone 72 where fines are taken out by means of a centrifugal separator or the like. These fines pass downwardly through line 73 to the fines feeder 66 for return to the transfer line burner. The gases from zone 72 pass through line 74 to a second fines separation zone 75. Here smaller fines not taken out in zone 72 are removed and discharged downwardly through line 76 to the tines feeder. The overhead product gas stream is discharged through line 77 to conventional downstream processing units for the recovery of heat and further processing of the product gas.  
  The advantages of the method and apparatus of the invention are illustrated by the results obtained in a coal gasification pilot plant using a transfer line burner for the heating of char particles. These particles were originally transferred from the fluidized bed reaction vessel tothe burner through a conventional J-bend similar to those used in fluidized catalytic cracking units. The quantity of air introduced into the burner was controlled so that the average temperature rise of the char would be no greater than about 200 F., assuming continuous smooth flow of the char. With an entering char temperature of between l500 and i700 F., the final char average temperature was between l700 and l900 F., below the ash fusion temperature..Continuous operation of the pilot plant showed that deposits were nevertheless being formed on the burner walls, apparently because of improper distribution of the combustion air so that some of the char particles received a disproportionately large amount of the available oxygen. Studies of the flow pattern through the burner showed that flow was erratic and that there were rarified areas within the burner where little char and large quantities of air were present. A part of this erratic flow was due to pressure surges occurring within the gasifier. These pressure surges were being transmitted down the standpipe leading from the gasifier, through the .I-bend, and upwardly into the burner. This produced variations in the amount of coal char fed to the burner and in the air-char ratios. Stagnant areas were found to exist near the wall of the burner immediately above the feed inlet point. Continued operation of the system ultimately resulted in plugging of the burner with ash deposits adhering to the burner walls.  
  Following the above, the transfer line burner was fitted with a feed inlet device of the type depicted in the drawing. This device included an inlet section which sloped downwardly at an angle of 60 from the horizontal and was provided with horizontal and vertical gas inlet lines as shown. The intermediate section of the device contained a conical flow restriction or nozzle having an inlet diameter of 2.32 inches and an outlet diameter of 0.97 inch. The nozzle walls tapered at an included angle of 30. The cross-sectional area at: the nozzle inlet was 5.7 times the area at the outlet. Downstream of the nozzle the flow path underwent an abrupt change from substantially horizontal to substantially vertical. Gas inlets were provided on the horizontal and vertical center lines of the intermediate and exit sections of the device as depicted in the drawing. All of the gas inlet lines were fitted with metering devices for regulating the amount of steam introduced through each of the lines. The burner itself was fitted with nozzles for the injection of air at three vertically-spaced points. The first point was located just above the cone at the lower end of the burner above the injection device. Six inlet nozzles were located at evenly spaced points about the burner periphery. The second air injection point was located about 5 feet above the first point and eight peripherally spaced injection nozzles were used. The cross-sectional area of the burner above the second injection point was twice that of the lower portion of the burner. The third stage air injection point near the top of the burner included four peripherally spaced nozzles.  
  During operation of the modified system, the downflowing char from the gasifier was fed into the transfer line burner injection device at a velocity of about 0.2 foot per second. The char was accelerated to about 1 foot per second in the nozzle in the intermediate section of the injection device. Steam was injected in the quantities required to provide this acceleration and compensate for the loss in velocity when the stream of solids change direction from substantially horizontal to substantially vertical just downstream of the nozzle. The upflowing solids in the exit section of the injection device were maintained in dense phase flow to avoid the information of gas bubbles apt to produce uneven flow within the burner. At the first air injection stage at the lower end of the burner, sufficient air was injected to promote a transition from dense phase to dilute phase flow and increase the superficial gas velocity to 20 feet per second. Burning started at this point but the temperature rise was kept low to minimize the danger oflocalized overheating. At the second air injection point sufficient additional air was introduced to accelerate the char particles and obtain a superficial gas velocity of about 35 feet per second. The air injected at the third point further accelerated the char and raised the superficial gas velocity to about 40 feet per second. It was found that this permitted very smooth feeding of the char and that the solids moved upwardly through the transfer line burner in a uniform fashion with no appreciable surges or other erratic behavior. Measurement of the amount of deposits formed during continuous operation of the system over an extended period showed that the staged acceleration results in about a lS-fold decrease in the rate of deposit buildup. The amount of deposits with the conventional system and the system of the invention were as follows:  
 .l Bend System Staged Acceleration System The advantages of the staged acceleration system of the invention are clearly apparent.  
 I claim:  
  1. A method for the transfer of solid particles from a first vessel in which a stream of said particles moves downwardly in dense phase flow to a second vessel in which said particles are carried upwardly in dilute phase flow which comprises:  
 a. withdrawing the downwardly moving dense phase stream of particles from said first vessel;  
  reducing the cross-sectional area of said stream of particles by a factor of from about L2 to about while introducing sufficient gaseous fluid into said stream to maintain the particles in dense phase flow;  
 c. abruptly changing the direction of flow of the stream of particles of reduced cross-sectional area from a substantially horizontal to a substantially vertical direction by directing said stream upwardly into said second vessel while injecting sufficient additional gaseous fluid upwardly into said stream of reduced cross-sectional area to maintain the particles in dense phase flow; and  
 d. thereafter introducing upwardly into said second vessel sufficient gaseous fluid to effect a rapid transition from dense phase flow to dilute phase flow.  
  2. A method defined by claim 1 wherein said crosssectional area of said stream of particles is reduced by passing the particles through a tapered nozzle.  
  3. A method defined by claim 1 wherein said crosssectional area of said stream of particles is reduced by a factor of from about 3 to about 7.  
  4. A method as defined by claim 1 wherein said particles comprise carbonaceous solids.  
  5. A method as defined by claim 1 wherein said gaseous fluid injected to effect said transition comprises an oxygen-containing gas.  
  6. A method as defined by claim 1 wherein said additional gaseous fluid comprises steam. I  
  7. A method defined by claim 1 where the rate at which said particles are transferred from said first vessel to said second vessel is varied by varying the amount of said gaseous fluid introduced into said stream of particles to maintain the particles in dense phase flow.  
  8. A method as defined by claim 1 wherein said second vessel is a gasifier and said gaseous fluid injected to effect said transitioncomprises steam.  
  9. A method as defined by claim 1 wherein said second vessel is a transfer line burner and said gaseous fluid injected to effect said transition comprises air.  
  10. A method as defined by claim 1 wherein additional gaseous fluid is injected into said second vessel at at least one level higher than the level at which said transition from dense phase to dilute phase flow takes place.  
  11. A method as defined by claim 1 wherein said dense phase stream of solid particles is withdrawn from said first vessel with a velocity in the range of from about 0.05 to about 0.3 foot per second.  
  12. A method defined by claim 1 wherein the cross-sectional area of said stream of particles is reduced.  
  13. A method as defined by claim 1 wherein said gaseous fluid injected to effect said transition is introduced upwardly into said second vessel in an amount sufficient to produce a superficial gas velocity of from about 10 to about 25 feet per second and sufficient additional gaseous fluid is later introduced at a higher level in said vessel to produce a superficial gas velocity between about 30 and about feet per second.  
  14. Apparatus for the transfer of a stream of solids from a first vessel to a second vessel which comprises an inlet device for said second vessel including means defining an entrance section containing a downwardly sloping passageway communicating with said first vessel, said entrance section including means defining at least one inlet for the introduction of a control fluid into said passageway; means defining an intermediate section containing a substantially horizontal passageway having an upstream cross-sectional area of from about L2 to about 10 times the downstream crosssectional area; and means defining a discharge section containing a substantially vertical passageway extending upwardly from said substantially horizontal passageway and communicating with said second vessel, said discharge section including means defining at least one inlet for the introduction of a control fluid into said substantially vertical passageway.  
  15. Apparatus as defined by claim 14 wherein said passageway in said entrance section slopes downwardly at an angle of about 60 from the horizontal.  
  16. Apparatus as defined by claim 14 wherein said passageway in said intermediate section tapers inwardly at an angle of from about 15 to about to the horizontal.  
 17. Apparatus as defined by claim 14 wherein said substantially horizontal passageway has an upstream cross-sectional area from about 3 to about 7 times thedownstream cross-sectional area.  
  18. Apparatus as defined by claim 14 including a first control fluid inlet in the upper wall of said sloping passageway and a second control fluid inlet extending into said sloping passageway and substantially aligned with the longitudinal axis of said substantially horizontal passageway.  
  19. Apparatus as defined by claim 14 wherein said inlet for the introduction of fluid into said substantially vertical passageway is substantially aligned with the longitudinal axis of said substantially vertical passage-