METHOD OF COOLING HOT SYNTHESIS GAS AND SYNTHESIS GAS COOLER

Abstract: The invention is related to a method of cooling a hot synthesis gas containing solids under conditions which permit removal of solids from solid gas. The hot synthesis gas is passing at initial high temperature downwardly through a first contacting zone, thereby passing a film of cooling liquid on walls of said first contacting zone that is cooling said synthesis gas; the so cooled synthesis gas is passing a body of aqueous cooling liquid in a second contacting zone; the further cooled synthesis gas containing a decreased content of solid particles is withdrawn upwardly from said second contacting zone through a annular third contacting zone to a vapor-liquid desengagement zone with an arcuated path terminating the gas stream with a substantial downward component of velocity whereby the non-gaseous components contained therein are downwardly directed toward said body of aqueous cooled liquid thereby forming a synthesis gas stream of lower solids content; said synthesis gas stream of lower solids content is passing again upwardly. Said cooled synthesis gas will be recovered.

Description: The invention relates to a method of cooling a hot synthesis gas containing solids under conditions which permit removal of solids from gas by contacting with a body of aqueous cooling liquid and recovering a cooled synthesis gas containing a decreased content of solid particles. Such a method for cooling a hot synthesis gas and a synthesis gas cooler are know from US 2818326 and UK 2034446. A synthesis gas leaving a reaction chamber at a reaction temperatur of about 1078°C is conducted downwardly in a pipe of a quench vessel to a body of aqueous cooling liquid. The inner surface of the pipe is cooled by a falling film of a cooling liquid. The lower end portion of the pipe is provided with perforations and a sessation. The synthesis gas is discharged into intimate contact with the cooling liquid contained in the quench vessel through the perforations. It has been found to be difficult to remove small particles of solids including ash, slag, and/or char from synthesis gases. These particles, typically of particle size of as small as 0.005 mm or less, have been found to agglomerate (in the presence of water-soluble components which serve as an interparticle binder) into agglomerates which may typically contain about 1 w% of these water-soluble components. These agglomerates deposit at random locations in the apparatus typified by narrow openings in or leading to narrow conduits, exits, etc., and unless some corrective action is taken to prevent build-up, may plug the apparatus to a point at which it is necessary to shut down after an undesirably short operation period. It is an object of this invention to provide a process and apparatus for cooling hot gases and for minimizing plugging of lines. In accordance with this aspect the invention is characterized by passing said hot synthesis gas at initial high temperature downwardly through a first contacting zone, passing cooling liquid downwardly as a film on the walls of said first contacting zone and in contact with said downwardly descending synthesis gas thereby cooling said synthesis gas and forming a cooled synthesis gas; passing said synthesis gas downwardly into the body of aqueous cooling liquid in a second contacting zone thereby forming a further cooled synthesis gas containing a decreased content of solid particles; withdrawing said further cooled synthesis gas containing a decreased content of solid particles upwardly from said body of aqueous cooling liquid in said second contacting zone; passing said further cooled synthesis gas containing a decreased content of solid particles upwardly away from said body of aqueous cooling liquid through a third contacting zone to a vapor-liquid desengagement zone with a arcuate path terminating the gas stream with a substantial downward component of velocity whereby the non-gaseous components contained therein are downwardly directed toward said body of aqueous cooling liquid thereby forming a synthesis gas stream of lower solids content; passing said synthesis gas stream of lower solids content upwardly from said arcuate path as a synthesis gas containing a decreased content of solid particles, and recovering said cooled synthesis gas. The feature of terminating the upward way of the gas stream by a path with a downward arcuated component within the desengagement zone improves the decrease of liquids and solid particles within the gas by separating the directions of movements. The gas surrounds the arcuate path and streams again upwardly. The downwardly reflected liquids and solid particles fall to the aqueous cooling liquid. The method of the invention is improoved by cooling the synthesis gas from an initial high temperature of 980-1370°C, at 8-104 bar to a lower final temperature of 177-316°C, by forming a cooled synthesis gas at 760-1260°C in the first contacting zone and by forming a further cooled synthesis gas at 316-482°C in the second contacting zone. Low temperatures and low pressure at the outlet provide a effective method. The method of cooling uses a quench chamber containing a dip tube assembly characterized by an attenuated dip tube having inner and outer perimetric surfaces, and an inlet end and an outlet end; an outlet portion of said dip tube adjacent to the outlet end; a quench ring adjacent to the inner perimetric surface at the inlet end of said dip tube and adapted to direct a curtain of liquid along the inner perimetric surface of said dip tube and toward the outlet end of said dip tube; serrations on the outlet end of said outlet portion of said dip tube; a quench gas outlet; the inner part of the dip tube forming a first contacting zone containing said quench ring; adjacent to the lower extremity of the dip tube a second zone being provided containing a body of cooling liquid; an attenuated draft tube, enveloping said attenuated dip tube, having inner and outer perimetric surfaces, and outlet end adjacent to the inlet end of said attenuated dip tube, and an inlet end adjacent to the outlet end of said attenuated dip tube, said inlet end of said attenuated draft tube terminating at a distance which is further from the inlet end of said attenuated dip tube than is the outlet end of said attenuated dip tube; a circumferential baffle of arcuate cross section on a mid portion of the outer perimetric surface of said dip tube adjacent to the outlet end of said draft tube; the draft tube enveloping said dip tube enclosing a third contacting zone containing said circumferential baffle. A further embodiment of the invention is characterized by an exit baffle fitted to the inner sidewall of the quench vessel below the quench gas outlet. The invention will now be described in more details, by way of example, with reference to the drawing. The Figur is a schematic vertical section of a preferred embodiment of this invention illustrating a generator and associated there with a quench chamber. The hot synthesis gas which may be charged to the process of this invention may be a synthesis gas prepared by the gasification of coal. In the typical coal gasification process, the charge coal which has been finely ground typically to an average particle size of 0.02-0.5 mm preferably 0.03-0.3 mm, say 0.2 mm, may be slurried with an aqueous medium, typically water, to form a slurry containing 40-80 w%, preferably 50-75 w%, say 60 w% solids. The aqueous slurry may then be admitted to a combustion chamber wherin it is contacted with oxygen-containing gas, typically air or oxygen, to effect incomplete combustion. The atomic ratio of oxygen to carbon in the system may be 0.7-1.2: 1, say 0.9: 1. Typically reaction is carried out at 980-1,270°C, say 1,370°C and pressure of 8-104 bar, preferably 35-84 bar, say 63 bar. The synthesis gas may alternatively be prepared by the incomplete combustion of a hydrocarbon gas typified by methane, ethane, propane, etc. including mixtures of light hydrocarbon stocks or of a liquid hydrocarbon such as a residual fuel oil, asphalts, etc. or of a solid carbonaceous material such as coke from petroleum or from tar sands, butumen, carbonaceous residues from coal hydrogenation processes, etc. The apparatus which may be used in practice of this invention may include a gas generator such a is generally set forth in the following patents inter alia: US 2,818,326 Eastman et al US 2,896,927 Nagle et al US 3,998,609 Crouch et al US 4,218,423 Robin et al Effluent from the reaction tone in which charge is gasified to produce synthesis gas may be 980-1,370°C, say 1,370°C at 8-104 bar, preferably 35-84 bar, say 63 bar. Under these typical conditions of operation, the synthesis gas commonly contains (dry basis) 35-55 v%, say 44.7 v% carbon monoxide, 30-45 v%, say 35.7 v% hydrogen; 10-20 v% hydrogen sulfide plus COS; 0.4-0.8 v%, say 0.5 v% nitrogen+argon, and methane in amount less than about 0.1 v%. When the fuel is a solid carbonaceous material, the product synthesis gas may commonly contain solids (including ash, char, slag, etc) in amount of 0.454-4.54 kg say 1.8 kg per 26.9 Nm3 of dry product gas; and these solids may be present in particle size of less than 0.001 mm up to 3 mm. The charge coal may contain ash in amount as little as 0.5 w% or as much as 40 w% or more. This ash is found in the product synthesis gas. In accordance with practice of this invention, the hot synthesis gas at this initial temperature is passed downwardly through a first contacting zone. The upper extremity of the first contacting zone may be defined by the lower outlet portion of the reaction chamber of the gas generator. The first contacting zone may be generally defined by an upstanding preferably vertical perimeter wall forming an attenuated conduit; and the cross-section of the zone formed by the wall is in the preferred embodiment substantially cylindrical. The outlet or lower end of the attenuated conduit or dip tube at the lower extremity of the preferably cylindrical wall preferably bears a serrated edge. The first contacting zone is preferably bounded by the upper portion of a vertically extending, cylindrical dip tube which has its axis colinear with respect to the combustion chamber. At the upper extremity of the first contacting zone in the dip tube, there is mounted a quench ring through which cooling liquid, commonly water, is admitted to the first contacting zone. From the quench ring there is directed a first stream of cooling liquid along the inner surface of the dip tube on which it forms a preferably continuous downwardly descending film of cooling liquid which is in contact with the downwardly descending synthesis gas. Inlet temperature of the cooling liquid may be 38-260°C, preferably 149-249°C, say 216°C. The cooling liquid is admitted to the falling film on the wall of the dip tube in amount of 9-32, preferably 13.6-22.7, say 20.4 kg per 26.9 Nm3 of gas admitted to the first contacting zone. The cooling liquid admitted to the contacting zones, and particularly that admitted to the contacting zones, and particularly that admitted to the quench ring, may include recycled liquids which have been treated to lower their solids content. Preferably those liquids will contain less than about 0.1 w% of solids having a particle size larger than about 0.1 mm, this being effected by hydrocloning. As the falling film of cooling liquid contacts the downwardly descending hot synthesis gas, the temperatur of the latter may drop by 100-200°C, preferably 150-200°C, say 150°C because of contact with the falling film during its passage through the first contacting zone. The gas may pass through the first contacting zone for 1-8 seconds, preferably 1-5 seconds, say 3 seconds at a velocity of 6-30 (1.8-9.1), say 20 (6.1) ft/sec (m/s). Gas exiting this first zone may have a reduced solids content, and be at a temperature of 760-1,260°C, say 1,204°C. The gas leaves the lower extremity of the first contacting zone at typically 538°C-1,149°C, say 1,093°C having been cooled in the second contacting zone by typically 50-150°C, say 100°C; and passed through a second contacting zone wherein it is cooled typically by 50-150°C. Within the second contacting zone the gas contacts a body of cooling liquid. In this second contacting zone the gas passed under a serrated edge of the of the dip tube. The lower end of the dip tube is submerged in a pool of liquid formed by the collected cooling liquid which defines the second contacting zone. The liquid level, when considered as a quiescent pool, may typically be maintained at a level such that 10% ― 80%, say 50% of the second contacting zone is submerged. It will be apparent to those skilled in the art that at the high temperature and high gas velocities encountered in practice, there may of course be no identifiable liquid level during operation ― but rather a vigorously agitated body of liquid. The cooled synthesis gas passes through the said body of cooling liquid in the second contacting zone and under the lower typically serrated edge of the dip tube. The solids fall through the body of cooling liquid wherein they are retained and collected and may be drawn off from a lower portion of the body of cooling liquid. Commonly the gas leaving the second contacting zone may have had 75% or more of the solids removed there from. The further cooled gas at 316-482°C, say 427°C leaving the body of cooling liquid which constitutes the second contacting zone is preferably passed together with cooling liquid upwardly through a preferably annular passageway through a third contacting zone toward the gas outlet of the quench chamber. The annular passageway is defined by the outside surface of the dip tube forming the first cooling zone and the inside surface of the vessel or draft tube which envelops or surrounds the dip tube with a larger radius than that of the dip tube. As the mixture of cooling liquid and further cooled synthesis gas (at inlet temperature of 316-482°C, say 427°C, passes upwardly through the annular third cooling zone, the two phase flow therein effects efficient heat transfer from the hot gas to the cooling liquid: the vigorous agitation in this third cooling zone minimizes deposition of the particles on any of the contacted surfaces. Typically the cooled gas exits this annular fourth contacting zone at temperature of 177-316°C, say 260°C. The gas leaving the third contacting zone contains 45 g ― 1.13 kg, say 181 g of solids per 26.9 Nm3 of gas i.e. about 85% ― 95% of the solids will have been removed from the gas. The mixture of gas and liquid leaving the third contacting zone is directed into contact with a baffle which is placed within the path of the exiting stream as a vapor-liquid desengagement zone wherein the vapor is disengaged from the vapor-liquid mixture. Preferably this baffle is mounted on the outer surface of the dip tube at a point adjacent to that at which the stream exits the contacting zone. Typically this point is above the static liquid level and the upper terminus of the draft tube when the latter is present. The baffle is arcuate in cross-section and is curved in manner to direct the upflowing mixture of liquid and gas asay from the dip tube and downwardly toward the bottom of the quench chamber. The gas therafter passes upwardly toward the outlet of the quench chamber, as the liquid and solids are directly downwardly. The cooled product exiting synthesis gas and cooling liquid are passed (by the velocity head of the stream) toward the exit of the quench chamber and thence into the exit conduit which is preferably aligned in a direction radially with respect to the circumference of the shell which encloses the combustion chamber and quench chamber. In practice of the process according to certain of its aspects, it is preferred to introduce a directed stream or spray of cooling liquid into the stream of cooled quenched product synthesis gas, in a spray contacting zone, at the point at which it enters the exit conduit or outlet nozzle and passes from the quench chamber to a venturi scrubber through which the product synthesis gas passes. This directed stream or spray of cooling liquid is initiated at a point on the axis of the outlet nozzle and it is directed along that axis toward the nozzle and the venturi which is preferably mounted on the same axis. Although this stream will effect some additional cooling of the product synthesis gas, it is principally believed to be advantageous in that it minimizes the deposition of solids which are derived from the ash and char which originate in the synthesis gas and which may not have been completely removed by the contacting in the several contacting zones. This last directed stream of liquid at 38°C ― 260°C. say 216°C is preferably admitted in amount of 2.27 ― 11.34, say 5 kg per hour per 26.9 Nm3 of dry gas. Cooling liquid may be withdrawn from the lower portion of the quench chamber; and the withdrawn cooling liquid contains solidified ash and char in the form of small particles. If desired, additional cooling liquid may be admitted to and/or withdrawn from the body of cooling liquid in the lower portion of the quench chamber. It will be apparent that this sequence of operations is particularly characterized by the ability to remove a substantial portion of the solid (ash, slag, and char) particles which would otherwise contribute to formation of agglomerates which block and plug the equipment. The several cooling (and washing) operations remove from the gas the small quantity of water-soluble solids which may act as interparticle binder-binding together the smaller particles into undersirable larger agglomerates. The several cooling and washing steps insure that the fine particles of ash are wetted by the cooling liquid and thereby removed from the gas. The syntehesis gas cooler is provided with a reaction vessel 11 having a refractory lining 12 and inlet nozzle 13. The reaction chamber 15 has an outlet portion 14 which includes a narrow throat section 16 which feeds into opening 17. Opening 17 leads into first contacting zone 18 inside of dip tube 21. The lower extremity of dip tube 21, which bears serrations 23, is immersed in bath 22 of quench liquid. The quench chamber 19 includes, preferably at an upper portion thereof, a gas discharge conduit 20. A quench ring 24 is mounted at the upper end of dip tube 21. This quench ring may include an upper surface 26 which preferably rests against the lower protion of the lining 12 of vessel 11. A lower surface 27 of the quench ring preferably rests against the upper extremity of the dip tube 21. The inner surface 28 of the quench ring may be adjacent to the edge of opening 17. Quench ring 24 includes outlet nozzles 25 which may be in the form of a series of holes or nozzles around the periphery of quench ring 24 ― positioned immediately adjacent to the inner surface of dip tube 21. A per example aqueous liquid, entering the quench ring 24 by an inlet 36 projected through passageways or nozzles 25 and passes in a direction generally parallel to the axis of the dip tube 21. The liquid forms a thin falling film of cooling liquid which descends on the inner surface of dip tube 21. This falling film of cooling liquid forms an outer boundary of the first contacting zone. At the lower end of the first contacting zone 18, there is a second contacting zone 30 which extends downwardly toward serrations 23 and which is also bounded by that portion of the downwardly descending film of cooling liquid which is directed towards the wall on the lower portion of dip tube 21. A body of liquid 22 wherein the lower portion of the dip tube 21 is dipped is connected to an outlet 37. On the body of the quench chamber 19 an outlet 38 for solid particles is provided. The gas flows across serrations 23, through the body of liquid 22 in the second contacting zone (which is adjacent and/or below serrations 23), and thence upwardly between the outer circumference of dip tube 21 and draft tube 29, i.e. through the annulus 31 with a third contacting zone. As the gas and liquid (containing solids which have not been washed out of the gas) pass upwardly out of the upper end of the second contacting zone 30, the gas continues its way upwardly through a annular portion of the third contacting zone 31 and meats afterwards within a desengagement zone an arcuate baffle 35 fitting to the outsidewall of the dip tube. The gas-liquid mixture so exits the annular portion between dip tube 21 and draft tube 29 and is directed into the desengagement zone with the baffle 35. At this point, the liquid (including the solid suspended therein) is passed through an arcuate path toward the lower portion of quench chamber 19. The gas which passes upwardly past the edge of baffle 35 is denuded of liquid and solids. Exit baffle 32 knocks out additional liquid from the gas which exits through gas discharge conduit 20. The liquid, and the solids contained therein, fall back toward the lower portion of the quench chamber and the body of liquid 22. The cooled gas leaving through conduit 20 is found to be characterized by a decreased content of solids. In operation of the process there is admitted through inlet nozzle 13, a slurry containing 100 parts per unit time (all parts are parts by weight unless otherwise specifically stated) of charge coal and 60 parts of water: this charge is characterized as follows: There are also admitted 90 parts of oxigen of purity of 99.5 v%. Combustion in chamber 15 raises the temperature to 1,371°C at 63 bar. Product synthesis gas, passed through outlet portion 14 and throat section 16, may contain the following gaseous components: This synthesis gas may also contain about 4.1 pounds (1.86 kg) of solid (char and ash) per 1000 SCF (26.9 Nm³) dry gas. The product synthesis gas (235 parts) leaving the throat section 16 passes through the opening 17 in the quench ring 24 into first contacting zone 18. Aqueous cooling liquid at 216°C is admitted through inlet line 36 to quench ring 24 from which it exits through outlet nozzles 25 as a downwardly descending film on the inner surface of dip tube 21 which defines the outer boundary of first contacting zone 18. As synthesis gas, entering the first contacting zone at about 1,371°C, passes downwardly through the zone 18 in contact with the falling film of aqueous cooling liquid, it is cooled to about 1,177-1,204°C. The so-cooled synthesis gas is then admitted to the second contacting zone 30 and enters the second contacting zone wherein it passes under serrated edge 23 into contact with the body 22 of liquid. Although the drawing shows a static representation having a delineated "water-line", it will be apparent that in operation, the gas and the liquid in the second contacting zone will be in violent turbulence as the gas passes downwardly through the body of liquid, leaves the dip tube 21 passing serrated edge 23 thereof, and passes upwardly through the body of liquid outside the dip tube 21. The area between the outside surface of the dip tube and the inside surface of the conforming draft tube, in the preferred embodiment, defines the third contacting zone. The inlet temperature to this zone may be 427°C and the outlet temperature 260°C. The further cooled synthesis gas, during its contact with cooling liquids loses at least a portion of its solids content. Typically the further cooled synthesis gas containing a decreased content of ash particles leaving the body of liquid 22 in second contacting zone contains solids (including ash and char) in amount of about 0.27 kg per 26.9 Nm3 dry gas. The exiting gas at 260°C is withdrawn from the cooling system through gas discharge conduit 20; and it commonly passes through a venturi thereafter wherein it may be mixed with further cooling liquid for additional cooling and/or loading with water. This venturi is preferably immediately adjacent to the outlet nozzle.

Claims: 1. A method of cooling a hot synthesis gas containing solids under conditions which permit removal of solids from solid gas by contacting with a body of aqueous cooling liquid and recovering a cooled synthesis gas containing a decreased content of solid particles, characterized by passing said hot synthesis gas at initial high temperature downwardly through a first contacting zone, passing cooling liquid downwardly as a film on the walls of said first contacting zone and in contact with said downwardly descending synthesis gas thereby cooling said synthesis gas and forming a cooled synthesis gas; passing said cooled synthesis gas into the body of aqueous cooling liquid in a second contacting zone thereby forming a further cooled synthesis gas containing a decreased content of solid particles; withdrawing said further cooled synthesis gas containing a decreased content of solid particles upwardly from said body of aqueous cooling liquid in said second contacting zone; passing said further cooled synthesis gas containing a decreased content of solid particles upwardly away from said body of aqueous cooling liquid through a annular third contacting zone to a vapor-liquid desengagement zone with an arcuated path terminating the gas stream with a substantial downward component of velocity whereby the non-gaseous components contained therein are downwardly directed toward said body of aqueous cooled liquid thereby forming a synthesis gas stream of lower solids content; passing said synthesis gas stream of lower solids content upwardly from said arcuated path as a synthesis gas containing a decreased content of solid particles, and recovering said cooled synthesis gas. 2. The method as claimed in claim 1 wherein cooling of synthesis gas is accomplished from an initial high temperature of 980-1370°C, at 8-104 bar to a lower final temperature of 177-316°C, in the first contacting zone forming a cooled synthesis gas at 760-1260°C, and in the second contacting zone forming a further cooled synthesis gas at 316-482°C. 3. A quench chamber within a synthesis gas cooler containing a dip tube assembly characterized by an attenuated dip tube (21) having inner and outer perimetric surfaces, and an inlet end and an outlet end; an outlet portion of said dip tube adjacent to the outlet end; a quench ring (24) adjacent to the inner perimetric surface at the inlet end of said dip tube and adapted to direct a curtain of liquid along the inner perimetric surface of said dip tube and toward the outlet end of said dip tube; serrations (23) on the outlet end of said outlet portion of said dip tube; a quench gas outlet (20); the inner part of the dip tube forming a first contacting zone (18) containing said quench ring (24); adjacent to the lower extremity of the dip tube a second zone being provided containing a body of cooling liquid (22); an attenuated draft tube (29), enveloping said attenuated dip tube, having inner and outer perimetric surfaces, an outlet end adjacent to the inlet end of said attenuated dip tube, and an inlet end adjecent to the outlet end of said attenuated dip tube, said inlet end of said attenuated draft tube terminating at a distance which is further from the inlet end of said attenuated dip tube than is the outlet end of said attenuated dip tube; the draft tube and the dip tube enclosing a third contacting zone; a circumferential baffle (35) of arcuate cross section on a mid portion of the outer perimetric surface of said dip tube adjacent to the outlet end of said draft tube. 4. A Quench Chamber claimed in claim 3 characterized by an exit baffle (32) fitted to the inner surface of the quench chamber (19) below the quench gas outlet (20).

Inventors: REICH, EDWIN ABRAHAM
Applicants: TEXACO DEVELOPMENT CORPORATION
Application year: 1984
Main classification: C10J3
IPC codes: C01B3, C10J3