US3891402A - Transfer line burner system - Google Patents

Abstract

Carbonaceous solids are heated by introducing a stream of such solids into a transfer line burner, injecting sufficient oxygencontaining gas into the burner at two or more separate points to burn a portion of the carbon and generate heat, controlling distribution of the oxygen-containing gas to maintain temperatures below the ash fusion temperature and convert carbon monoxide to carbon dioxide, and withdrawing heated solids from the burner.

Description

United States Patent Nahas et al.

1 1 TRANSFER LINE BURNER SYSTEM [75] Inventors: Nicholas C. Nahas; Edward L. Wilson, both of Baytown, Tex.

[73] Assignee: Exxon Research and Engineering Company, Linden, NJ

[22] Filed: June 25, 1973 [21] Appl. No.: 373,554

[52] US. Cl. 48/197 R; 201/31 [51] Int. Cl.. Cl0j 3/12 [58] Field of Search 48/202, 206, 204, 210,

48/147 R, DIG. 4; 201/38, 9, 31; 252/373,

[56] References Cited UNITED STATES PATENTS 2.374660 5/1945 Belchetz et a1, 252/417 2,588,075 3/1952 Barr et a1 1 v 1 1 48/206 2,654,665 10/1953 Phinney 1 1 1 48/206 2 667,410 1/1950 Pierce 1 1 1 48/196 2,694,623 11/1954 We1ty.1r. at al. 48/197 2,729,552 1/1956 Nelson et a1 48/197 2.741.549 4/1956 Russell 0. 48/206 COAL FE ED 1.0

FEED GAS STEAM STEAM Primary ExaminerS. Leon Bashore Assistant E.mminer-Peter F. Kratz Attorney, Agent, or Firm-James E. Reed [57] ABSTRACT Carbonaceous solids are heated by introducing a stream of such solids into a transfer line burner, injecting sufficient oxygemcontaining gas into the burner at two or more separate points to burn a portion of the carbon and generate heat, controlling distribution of the oxygen-containing gas to maintain temperatures below the ash fusion temperature and convert carbon monoxide to carbon dioxide, and withdrawing heated solids from the burner.

5 Claims, 1 Drawing Figure PRODUCT GAS "FLUE GAS CARBON MONOXIDE CUNTROLLE R 1 1 s y n 33 i TEMP.

CONTROLLER 32- [ff 30 2s 1 OXYGEN CONTAINING GAS STEA

PATENTED JUN 2 4 I575 -D PRODUCT GAS D FLUE GAS COAL FEED FEED GAS 4DILUENT GAS H H G NwL U. L I m? W RN M A AOM MZ 6 M M T 2 W C C C 9 I o llllllllll J 3 7 2 1| 4 3 Q 0 3 3 3 3 n m d. g 8 7 6 3 3 3 3 2 4 9 2 J A. 5 m a n. a w. 2 m

STE AM TRANSFER LINE BURNER SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the heating of fluidized beds containing coal particles or other carbonaceous solids and is particularly directed to coal gasification and related processes in which heat is generated by burning a portion of the carbonaceous solids in a transfer-line burner.

2. Background of the Invention The production of carbon monoxide and hydrogen from steam and coal char or other carbonaceous solids is a highly endothermic reaction. One of the more attractive methods for providing the heat required to carry out this reaction involves the use of a fluidized bed reaction zone and a transfer-line burner. Typically, such a burner consists of a large vertical line into which a steam of char particles or other carbonaceous solids is continuously introduced from the reaction zone. The carbonaceous solids are entrained by gas and carried upwardly through the burner to an overhead separation zone where gases and entrained solids are separated. The unburned solids are then returned to the reaction zone. Sufficient heat to maintain the fluidized bed at the desired reaction temperature is generated by introducing air near the lower end of the burner. The amount of air employed is regulated so that only part of the solids are burned to form carbon dioxide. Ash and fines are carried overhead from the separation zone and can be removed by scrubbing or other conventional treatment before the flue gas is discharged.

Although the use of a transfer-line burner as described above has important advantages over other heat generating systems, experience has shown that the combustion taking place in the burner is difficult to control. The oxygen present in the input gas stream reacts with the hot char or other solids at rates such that localized overheating may take place near the injection nozzles. If the transient, localized temperature rise ex ceeds the ash fusion temperature, plugging problems and other difficulties may be encountered. In addition, studies have shown that the combustion efficiency in such burners is often poor and that effective pollution control may pose additional problems.

SUMMARY OF THE INVENTION The present invention provides a method for controlling the operation of transfer-line burners used in coal gasification and similar operations which at least in part alleviates the difficulties outlined above. In accordance with the invention, it has now been found that the operation of such burners can be effectively controlled by injecting an oxygen-containing gas into the burner at two or more separate points and regulating distribution of this gas to minimize ash fusion and the formation of carbon monoxide. The oxygen-containing gas is preferably introduced at a first point near the lower end of the burner and at one or more additional points downstream from the first point. The amount of oxygen introduced at the first point will preferably be sufficient to generate a substantial portion of the heat required to raise the solids in the burner to the desired temperature. The oxygen thus provided is quickly consumed in burning carbon to form carbon dioxide. As the gaseous products and unburned solids move upwardly within the burner, the carbon dioxide is partially reduced to carbon monoxide in accordance with the reaction: CO +C 2C0. The amount of oxygen introduced downstream from the first point will preferably be sufficient to burn substantially all of the carbon monoxide to carbon dioxide and provide additional energy for heating the unburned solids.

It is preferred to regulate the total quantity r." air or other oxygen-containing gas admitted to the transfer line burner by means of thermocouples located in the reactor and a temperature controller to which the thermocouples are connected. The temperature controller actuates an electrically or hydraulically operated valve in the air or gas line and thus controls the amount of air or gas introduced so that the reactor temperature remains at the desired level. It is also preferred to regulate the amount of air or other oxygen-containing gas introduced downstream from the first point by means of an electrically or hydraulically operated valve controlled by a carbon monoxide analyzer and controller connected to the flue gas outlet from the burner. Any increase in the concentration of carbon monoxide in the flue gas stream will thus be sensed by the analyzer and additional air or oxygen-containing gas will be admitted through the valve to reduce the carbon monoxide concentration to the desired level.

The method of the invention permits substantially better control of the combustion in transfer-line burners than has generally been obtained in the past. The introduction of a portion of the total air or other oxygen-containing gas near the lower end of the burner and the introduction of additional air or gas at one or more points downstream from the initial air or gas inlet reduces the likelihood of localized overheating and the attendant problems due to ash fusion, results in more efficient combustion and the transfer of greater quantities of heat to the suspended solids, and makes possible substantial reductions in the amount of carbon monoxide in the flue gases, thus reducing pollution problems and simplifying any later treatment of the flue gases which may be necessary to comply with applicable pollution control regulations. These and other advantages make the method of the invention attractive for use in a variety of different applications.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE in the drawing is a schematic flow sheet of a process for producing a methane-rich gas from coal in which the improved transfer-line burner system of the invention is used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process depicted in the drawing is one for the production of product gases of relatively high methane content from bituminous coal, subbituminous coal, lignite, solid petroleum residua or similar carbonaceous solids. 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 feed preparation plant or storage facility not shown in the drawing. To permit handling of the feed material in a fluidized system, the coal or other carbonaceous solid material is introduced in a finely-divided state, preferably less than about 8 mesh on the Tyler Screen Scale.

The system depicted in the drawing is operated at elevated pressures and hence the coal or other feed material introduced through line 10 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. In lieu of or in addition to this type of an arrangement, parallel lock hoppers, pressurized hoppers, or aerated stand pipes operating in series may be employed to raise the input coal stream to the system operating pressure. The use of such devices for handling coal and other finelydivided solids at elevated pressures has been described in the patent literature and will therefore 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 l4 and fed into gasifier 15. High pressure steam or product gas may be used as the feed gas. 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 gasifier 15 is operated and the solid feed material employed. The feed stream is introduced into the gasifier through a shrouded nozzle provided with steam admitted through line 16 to keep the feed injection nozzle at a temperature below about 600 F. and thus avoid fouling of the nozzle with agglomerating coal solids. If an agglomerating coal is employed as the coal feed material, an injection nozzle 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 15 employed in the system shown in the drawing contains a fluidized bed of char particles which are introduced into the lower part of the vessel through line 17. Steam for reacting with the char and maintaining the particles in the fluidized state is introduced into line 17 through line 18. Additional steam may be introduced through line 19. The total steam rate will normally range between about 0.5 to about 2.0 pounds of steam per pound of coal feed. The upflowing steam and char form a fluidized bed which extends upwardly above distribution grid or similar device to a level above the point at which the coal solids are introduced into the gasifier. The lower portion of the gasifier vessel above grid 20, indicated by reference numeral 21, serves as a steam gasification zone. Here the steam introduced through lines 18 and 19 reacts with carbon in the hot char to form synthesis gas in accordance with the reaction: H O+C H -l-CO. At the point of steam injection near the bottom of the gasifier, the hydrogen concentration in the gaseous phase of the fluidized bed is essentially zero. As the steam moves upwardly through the fluidized char particles. it reacts with the carbon, and the hydrogen concentration in the gaseous phase increases. The temperature in steam gasification zone 21 will normally range between about l450 and about 1800 F. The gas velocities in the fluidized bed will generally range between about 0.2 and about 3.0 feet per second.

The upper part of the fluidized bed in reactor vessel 15 serves as a hydrogasiflcation zone, indicated by reference numeral 22, where the feed coal is devolatilized and a part of the volatile matter thus produced reacts with hydrogen generated in zone 21 to produce methane as one of the principle products. The point at which the coal feed stream is introduced into the gasifier and hence the location of the steam gasification and hydrogasification zones depends primarily on the properites of the particular coal which is employed as the feedstock. ltis 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 coal feed injection point if moved nearer the top of the reactor. The tar, which has a tendency to foul downstream processing equipment. generally increases as the coal injection point is moved upwardly in the gasifier and decreases as the coal input point is moved nearer the bottom of the reactor, other operating conditions being the same. The coal feed should generally be injected into gasifier 15 at a point where the hydrogen concentration in the gas phase is in excess of about l5 percent by volume, preferably between about 25 percent and about 50 percent by volume. The upper surface of the fluidized bed 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 hydrogasiflcation zone 22. It is preferred in general that the residence time for the gas in contact with the solid phase above the point of coal feed injection be between about 7 and about 20 seconds. It will be understood, of course, that the optimum hydrogen concentration at the coal injection point and gas residence time above the point of coal injection will vary with different types and compositions of feed coal and with variations in the gasifier temperature, pressure, steam rate and other processing conditions. Higher rank coals normally require somewhat more severe reaction conditions to obtain practical reaction rates than do coals of lower rank. Similarly, higher reactor 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 coal feed.

As indicated earlier, the temperature in gasifier 15 is normally maintained within the range between about I450 and about i800 F. The heat required to sustain the overall endothermic reaction taking place in the gasifier and maintain this operating temperature is provided by withdrawing a portion of the char solids from the fluidized bed through line 23 and passing this material into the lower end of transfer line burner 24. Steam may be injected into line 23 in the vicinity of bends in the line in order to promote smooth flow of the solids and avoid any danger of clogging. Similarly, a diluent gas, flue gas for example, may be injected through line 25 to further aid in suspending the solids and entrain them in dilute phase flow as they move upwardly through the transfer-line burner. An oxygen-containing gas, preferably air, is introduced into the burner through line 26 in a quantity sufficient to promote combustion of a portion of the char and thus provide the heat necessary. The amount of air or gas introduced should be sufficient to raise the temperature of the upflowing solids stream from an initial level of from about l4SO to about l800 F. to a final level between about 1500 and about l950 F. The particles recycled from the burner to the fluidized bed will generally be at a temperature of from about 50 to 300+ F. higher than the bed temperature, preferably about 200 F. or higher. The amount of carbon which must be burned to carbon dioxide to generate the necessary heat and the quantity of oxygen that will be required for this purpose will depend upon the quantity and type of solids being handled, the amount of diluent gas present, the combustion efficiency, the heat losses which occur, and other factors. In general, it is normally preferred to inject air at the rate of from about 0.02 to about 0.20 pound per pound of char being circulated. If an oxygen-containing gas having a lower oxygen content than air is used, the gas injection rate will have to be increased correspondingly.

The flow rate of gas introduced through line 26 is adjusted by means of valve 27. This valve is actuated by a control system that in net effect measures the temperature in the gasifier by a device 29 such as a thermocouple or pyrometer and by means of controllers in the system positions valve 27 to hold the desired temperature. Although only one thermocouple or the like has been shown, a plurality of such devices spaced about the inner wall of the reactor will normally be used to monitor the temperature of the fluidized bed. In response to the input from these thermocouples, the controller increases or decreased the amount of oxygencontaining gas which passes through valve 26. This in turn increases or decreases the amount of heat generated within the burner and thus permits maintaining of the fluidized bed at the required temperature level. In lieu of thermocouples or pyrometers, other temperature sensing equipment designed to monitor the bed temperature may be used. Such equipment may be obtained from commercial sources.

Combustion theory indicated that the oxygen introduced into contact with the hot char particles near the lower end of the transfer-line burner is consumed very rapidly, generally in from about 0.001 to about 0.0] second. Because of the burner length required to handle the solids from a commercial-size fluid bed reactor and the limitations on gas velocity imposed by the necessity for avoiding excessive particle attrition, the total residence time of the char solids in the burner will normally range between about 0.3 and about 5.0 seconds. The combustion gases in a conventional burner therefore remain in contact with hot char particles for a relatively long period of time following the generation of heat and the formation of carbon dioxide in the combustion process. As the particles and hot gases move upwardly in the burner, a portion of this carbon dioxide is reduced to carbon monoxide until an equilibrium is established. This formation of carbon monoxide consumes heat and reduces the overall efficiency of the combustion process taking place in the transfer-line burner. The carbon monoxide, if not removed, also contributes to pollution problems and makes cleanup of the flue gases from the burner more difficult. in addition, a large quantity of oxygen injected near the lower end of the burner can produce localized overheating, which can result in temperatures in excess of the ash fusion temperature and lead to plugging problems and other difficulties.

To alleviate the problems referred to above, the oxygen-containing gas introduced to the transfer-line burner through line 26 and valve 27 is injected into the burner at two or more separate points along the burner. A portion of this gas enters the burner near the lower end through line 30 and multiple injection nozzles 31 spaced about the burner periphery to promote effective contact between the gas and the solids moving upwardly through the burner. The remaining oxygencontaining gas passes upwardly through line 32 and is introduced into the burner through one or more downstream injection lines 33, 34 and 35 and the associated peripherally-spaced nozzles 36, 37 and 38. It is generally preferred that the injection lines be spaced sufficiently far apart to permit consumption of substantially all of the oxygen as the upflowing particles move between the nozzles associated with one line and those associated with the next line. A spacing of at least 30 inches in normally advantageous.

The oxygen-containing gas introduced near the upper end of the burner, through line 35, is passed through an electrically or hydraulically-operated control valve 39 which is connected to a carbon monoxide analyzer and control unit 40 of conventional design. Such units are available from commercial sources. The flue gases from the burner are sampled continuously through line 41 to operate the control unit. If the carbon monoxide content of the flue gases from the burner increases beyond a predetermined level, the control unit opens valve 39 wider to increase the amount of air or oxygen-containing gas introduced through line 35 and reduces the quantity admitted upstream of line 35. The additional oxygen thus admitted near the upper end of the burner reacts with carbon monoxide in the gas stream to convert it into carbon dioxide, thus reducing the carbon monoxide content of the gases leaving the burner. This generates additional heat which is in part transferred to the suspended solids in the gas stream, improves the overall combustion efficiency of the burner, and maintains the carbon monoxide in the flue gases at the desired level.

The gases and hot suspended solids leaving the upper end of the transfer-line burner are introduced into a separation zone 42 which will normally contain one or more centrifugal separators in which the larger solid particles are separated from the combustion gases and conducted through dipleg 43 back to the reactor 15. The solids are transferred from the dipleg into line 17, from which they are returned to the fluidized bed by means of steam introduced through line 18. Supplemental steam may be injected into the dipleg as necessary to control the solids flow rate and facilitate movement of the solid particles around bends in the line. Most of the ash formed in the burner is carried overhead with the flue gases and discharged from separation zone 42 through gas line 44. Some char fines will normally also be present in the flue gases. The ash and fines can be removed from the gas stream by passing the gases through additional centrifugal separators, scrubbing the gases, and the like.

The products formed in gasifier 15 by reaction of the steam and char in steam gasification zone 21 and devolatilization of the feed coal and reaction of the volatile products with hydrogen in hydrogasification zone 22 are carried overhead from the fluidized bed and pass through a gas solids separating zone 45 where entrained solids are removed from the gas stream and returned to the gasifier-burner system. The product gas is taken overhead from the separation zone through line 46. This gas may be further treated for the removal of fines and other undesirable constituents in the conventional manner and then employed as a fuel gas.

The nature and objects of the invention can be more fully understood by considering the results of pilot plant tests of a transfer-line burner and an example of a coal gasification process in which a transfer-line burner constructed in accordance with the invention is employed.

EXAMPLE 1 Pilot plant tests were carried out with a transfer-line burner used for the combustion of coal char particles to heat a fluidized bed. The burner was operated at a temperature of approximately l800 F. and 50 pounds per square inch gauge pressure. Air was injected into the lower end of the burner and samples of the flue gases produced were taken at three different sampling points in the burner. The first such point was located 12 feet above the air injection point, the second point was feet above the air injection nozzles, and the third point was near the upper end of the burner, 46 feet above the air injection point. The gas residence time between the air injection nozzle and each sampling point was calculated and the flue gas samples at each point were analyzed to determine the amounts of carbon dioxide and carbon monoxide present in each sample. The results obtained are shown in the following It can be seen from the data in Table I that the gases produced in the transfer-line burner contained significant amounts of both carbon dioxide and carbon monoxide. lnitial combustion of the char following the introduction of oxygen-containing gas at the air injection nozzle evidently took place very rapidly so that all of the injected oxygen was consumed within a very short distance of the nozzle. As the gases moved upwardly through the burner, the concentration of carbon dioxide decreased and the carbon monoxide concentration increased, indicating that carbon dioxide was being reduced to carbon monoxide in the presence of the hot char. The gas residence times indicated in the table show that this reduction of carbon dioxide takes place rapidly until equilibrium between the carbon dioxide and the carbon monoxide is approached or established.

The equilibrium concentrations of carbon dioxide and carbon monoxide in the presence of carbon is a function of temperature. The relative proportions of the two gases that will be present for a carbon dioxide partial pressure of one atmosphere in the presence of hot carbon at various temperatures is shown in Table II below.

It can be seen from the values in Table ll that the equilibrium partial pressure of carbon monoxide is much greater than that of carbon dioxide at temperatures of l400 F. and higher and that, at temperatures representative of those at which most transfer-like burners normally operate. the amount of carbon monoxide present will therefore be greater than the amount of carbon dioxide if equilibrium is reached. The data set forth in Table I tend to confirm this.

Following the tests described above, the transfer-line burner employed earlier was modified to permit the injection of supplementary air at the 12 foot level. Samples of the gases generated in the burner were then taken at the 25 foot level while operating the burner at about l800 F. and 50 pounds per square inch gauge. The amount of air introduced at the air injection nozzle near the lower end of the burner was the same as in the earlier case. The amount of supplementary air injected at the 12 foot level was varied and the gas samples recovered at the 25 foot level were analyzed to determine the amounts of carbon monoxide and carbon dioxide present. The results obtained are set forth in Table III.

TABLE II] Effect of Supplementary Air at Second Injection Point Supplementary 0 Carbon Oxide Rates.

The data in Table lll demonstrate that the injection of small amounts of oxygen-containing gas into the transfer-line burner at a second point downstream from the point at which gas was initially injected to permit combustion of the char produced a significant reduction in the amount of carbon monoxide present in the gas stream and a corresponding increase in the amount of carbon dioxide present. This conversion of carbon monoxide to carbon dioxide increases the amount of heat available for raising the temperature of the carbonaceous solids present in the gas stream, improves the combustion efficiency of the burner, and alleviates pollution control problems. In some cases these improvements may make possible significant savings in the overall cost of the process in which the transfer-line burner is used.

To obtain maximum combustion efficiency in the transfer-line burner, sufficient air or other oxygencontaining gas should be injected near the top of the burner so that essentially all of the carbon monoxide will be burned to carbon dioxide, the heat of combustion being absorbed by the solids. The solid particles should be separated from the gas stream before significant additional conversion of carbon dioxide to carbon monoxide occurs. This can be accomplished by injecting sufficient air to burn all of the carbon monoxide, plus a small excess, so that the solids are discharged from the gas stream while some oxygen is still present in the gas. The amount of air or other oxygencontaining gas required for the generation of sufficient heat to raise the temperature of the solids in the gas stream to the desired level and the amount of gas required to convert the carbon monoxide to carbon dioxide can be readily calculated for any particular set of transfer-line burner operating conditions.

EXAMPLE 2 This example summarizes a calculated material balance for a gasification operation in which bituminous coal is converted into a methane-rich gas in a gasifier of the type shown in the drawing, heat for the process is provided by circulating char solids through a transfer-line burner as disclosed herein, and the operation of the burner is controlled in accordance with the invention by injecting combustion air into the burner at a first point near the lower end of the burner and injecting additional oxygen-containing gas into the burner downstream from the first point. The operating conditions for the process are set forth in the following table.

TABLE IV Thousands of Pounds] Hour CH 38 CO 1 55 C0 1 19 H 1) H 0 1 12 Other 28 Total 47 1 The steam rate to the reactor is 219,000 pounds per hour and the amount of char recycled into the reactor through line 17 is 8,224,000 pounds per hour.

Char is continuously withdrawn from the reactor and fed through line 22 to the transfer-line burner at the Gasification Process Operating Conditions Broad Range Preferred Range Specific Example Item (All Coals) (Bituminous Coals) (Bituminous Coal) Gasifier Temperature, "F. 1450-1800 1500-1700 1600 Pressure. psig 50-1000 100-500 180 Steam Rate/Coal Feed Rate. Lbs/Lb. 0.2-2.0 0.51.5 1.0 Steam Superficial Velocity, Ft./Sec."' 0.2-2.0 0.5-1.5 0.53 Char Solids Holdup in Bed/Coal Feed Rate, Hrs. 0.2-5.0 0.5-3.0 0.64 Product Gas Elfluent Rate/Coal Feed Rate.

SCF/Lh. 15-40 -30 25 Product Gas Composition, Mole "/1 CH, 0-20 5-10 8.7 CO 5-40 1 5-25 20.6 C0: 0- 5-15 10.0 H, 10-50 30-40 35.5 H,O 5-50 1 5-30 22.9 other 0-10 0-5 2.3 Transfer-Line Burner Char Solids Inlet Temperature, F. 1450-1800 1500-1700 1600 Outlet Temperature. F. 1500-1950 1600-1900 1800 Outlet Pressure. psig -1000 100-500 180 Char Circulation Rate/Coal Feed Rate, LhsJLb. 10-100 10-30 20 Combustion Air Rate/Char Circulation Rate.

l.hs./Lh. 0.02-0.2 0.05-0.15 0.1 Solids Residence Time. Sec. 0.1-5.0 0.5-1.5 1.0 Gas Superficial Velocity, FtJSec. 30-300 50-150 I 10 Flue Gas Rate/Coal Feed Rate, SCF/Lb. 28 Flue Gas Composition, Mole '4 C0 0-10 0-2 1.7 CO, 10-25 15-22 17.2 11,0 0-20 10-15 11.6 0, 0-5 0-2 Nil N, 50-90 60-80 66. 1 Other l-l0 1-5 3.4

"'At lluidind bed temperature and pressure.

In an operation carried out under the conditions listed for the specific example in the above table, the feed rate is 410,000 pounds of bituminous coal per hour. The ultimate analysis of the coal feed is:

Thousands of Pounds/Hour Carbon 270 Hydrogen 19 Oxygen 67 Nitrogen 4 Sulphur 2 Ash 32 Water 1 6 Total 4 10 rate of 8,364,000 pounds per hour. To promote combustion of the char solids in the burner, combustion air is introduced into the burner system through line 26 and valve 27 at the rate of 747,000 pounds per hour. A portion of this air is injected through each of the four air inlet lines as shown. The distribution of air between the uppermost inlet line 35 and lower inlet lines 30, 33 and 34 is varied by valve 39 and controller 40 as necessary to maintain the carbon monoxide content of the flue gas at the low level indicated in Table IV above. The flue gas taken off overhead from the burner is discharged at the rate of 883,400 pounds per hour. This gas has the composition shown in Table IV and contains the listed constituents in the following amounts:

Hot char solids separated from the flue gas stream in separation zone 32 are recycled to the gasifier through line 33 at the rate of 8,322,000 pounds per hour.

What is claimed is:

1. In a process wherein a solids stream consisting esgases containing carbon monoxide are withdrawn overhead from said transfer line burner, and wherein said heated particles are separated from said combustion gases and returned to said fluidized bed reactor; the improvement which comprises introducing a first stream of oxygen-containing gas into said transfer line burner at a point near the lower end thereof in a quantity sufficient to initiate the combustion of carbon in said particles, introducing additional oxygen-containing gas into said burner at a second point near the upper end of said burner in a quantityisufficient to burn carbon monoxide present in the combustion gases reaching said second point and generate additional heat, monitoring the carbon monoxide content of the combustion gases withdrawn from said burner, regulating the relative quantities of oxygen-containing gas introduced into said burner at said first point and said second point in response to changes in the carbon monoxide content of said combustion gases withdrawn from said burner, and

'controlling the total amount of oxygen-containing gas introduced into said burner in response to changes in the temperature in said fluidized bed reactor.

2. A process as defined by claim 1 wherein said carbon monoxide conten of said combustion gases is monitored by continually sampling said gases and analyzing the gas samples for carbon monoxide and wherein the relative amounts of oxygen-containing gas introduced at said first and said second points are regulated by varying the amount of oxygen-containing gas supplied to said burner at said second point in response to changes in the carbon monoxide content of said gas samples.

3. A process as defined by claim 1 wherein oxygencontaining gas is also introduced into said burner at at least one point intermediate said first and said second points.

4. A process as defined by claim 1 wherein said oxygen-containing gas is introduced into said burner at said second point in a quantity in excess of that required to burn essentially all of the carbon monoxide reaching said second point.

5. A process as defined by claim 1 wherein said oxygen-containing gas is introduced into said burner at each of said points through a plurality of nozzles spaced about the periphery of said burner.

Claims (5)

1. IN A PROCESS WHEREIN A SOLIDS STREAM CONSISTING ESSENTIALLY OF CARBONACEOUS PARTICLES WITHDRW FROM A FLUIDIZED BED REACTORS IS CONTACTED WITH AN OXYGEN-CONTAINING GAS IN A TRANSFER LINE BURNER TO BURN CARBON PRESENT IN SAID PARTICLES AND RAISE THE TEMPERATURE OF SAID STREAM, WHEREIN HEATED PARTICLES AND COMBUSTION GASES CONTAINING CARBON MONOXIDE ARE WITHDRAW OVERHEAD FROM SAID TRANSFER LINE BURNER, AND WHEREIN SAID HEATED PARICLES ARE SEPARATED FROM SAID COMBUSTION GASES AND RETURNED TO SAID FLUIDIZED BED REACTOR; THE IMPROVEMENT WHICH COMPRISES INTRODUCING A FIRST STREAM OF OXYGEN-CONTAINING GAS INTO SAID TRANSFER LINE BURNER AT A POINT NEAR THE LOWER END THEREOF IN A QUANTITY SUFFICIENT TO INITATE THE COMBUSTION OF CARBON IN SAID PARTICLES INTRODUCING ADDITIONAL OXYGEN-CONTAINING GAS INTO SAID BURNER AT A SECOND POINT NEAR THE LOWER END OF SAID BURNER IN A QUANTITY SUFFICIENT TO BURN CARBON MONOXIDE PRESENT IN THE COMBUSTION GASES REACHING SAID SECOND POINT AND GENERATE ADDITIONAL HEAT, MONITORING THE CARBON MONOXIDE CONTENT OF THE COMBUSTION GASES WITHDRAWN FROM SAID BURNER, REGULATING THE RELATIVE QUANTITIES OF OXYGEN-CONTAINING GAS INTRODUCED INTO SAID BURNER AT SAID FIRST POINT AND SAID SECOND POINT IN RESPONSE TO CHANGES IN THE CARBON MONOXIDE CONTENT OF SAID COMBUSTION GASES WITHDRAWN FROM SAID BURNER, AND CONTROLLING THE TOTAL AMOUNT OF OXYGEN-CONTAINING GAS INTRODUCED INTO SAID BURNER IN RESPONSE TO CHANGES IN THE TEMPERATURE IN SAID FLUIDIZED BED REACTOR.

2. A process as defined by claim 1 wherein said carbon monoxide content of said combustion gases is monitored by continually sampling said gases and analyzing the gas samples for carbon monoxide and wherein the relative amounts of oxygen-containing gas introduced at said first and said second points are regulated by varying the amount of oxygen-containing gas supplied to said burner at said second point in response to changes in the carbon monoxide content of said gas samples.

3. A process as defined by claim 1 wherein oxygen-containing gas is also introduced into said burner at at least one point intermediate said first and said second points.

4. A process as defined by claim 1 wherein said oxygen-containing gas is introduced into said burner at said second point in a quantity in excess of that required to burn essentially all of the carbon monoxide reaching said second point.

5. A process as defined by claim 1 wherein said oxygen-containing gas is introduced into said burner at each of said points through a plurality of nozzles spaced about the periphery of said burner.

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