US 3657064 A
Process for simultaneously producing sulfite pulping chemical from a spent pulping medium by the exothermic oxidative conversion of sodium sulfide to sodium sulfite and for the control of the temperature in exothermic reaction and also for employing the exothermic reaction heat to make steam to be mixed with air for use in said oxidation process. Ground particles of a spent pulping smelt are treated in a fluidized bed reactor in intimate contact with moving air enriched with steam for about 10 seconds to 2 hours, wherein the weight ratio of steam to air ranges from about 0.2 to 1 to 1.2 to 1. The temperature in the reactor is adiabatically controlled and the heat of reaction generated in the reactor is absorbed by adiabatic cooling to form the steam used in the reactor.
Claims available in
Description (OCR text may contain errors)
United States Patent Shick [151 3,657,064 [451 Apr. 18, 1972  DIRECT OXIDATIVE CONVERSION OF SODIUM SULFIDE TO SODIUM SULFITE BY ABSORBING THE HEAT OF REACTION IN A FLUIDIZED BED SYSTEM USING ADIABATIC COOLING FOREIGN PATENTS OR APPLICATIONS 614,478 2/1961 Canada ..l59/DIG. 3
OTHER PUBLICATIONS Perry s Chemical Engineers Handbook 4th Edition Mc- Graw-Hill 1963 pp. 20- 51 8t 20- 52 Priestley, R. J., Chemical Engineering Vol. No. July 9, 1962 pp. 125- 127 Primary Examiner-S. Leon Bashore Assistant Examiner-Alfred DAndrea, Jr. Attorney-Paul L. Sabatine and E. J. Holler [5 7] ABSTRACT Process for simultaneously producing sulfite pulping chemical from a spent pulping medium by the exothermic oxidative conversion of sodium sulfide to sodium sulfite and for the control of the temperature in exothermic reaction and also for employing the exothermic reaction heat to make steam to be mixed with air for use in said oxidation process. Ground particles of a spent pulping smelt are treated in a fluidized bed reactor in intimate contact with moving air enriched with steam for about 10 seconds to 2 hours, wherein the weight ratio of steam to air ranges from about 0.2 to 1 to 1.2 to 1. The temperature in the reactor is adiabatically controlled and the heat of reaction generated in the reactor is absorbed by adiabatic cooling to form the steam used in the reactor.
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PWWQQS PATENTEDAPR 18 m2 SHEET 8 BF 9 m OE a.) M ATroRUE S DIRECT OXIDATIVE CONVERSION OF SODIUM SULFIDE TO SODIUM SULFITE BY ABSORBING THE HEAT OF REACTION IN A FLUIDIZED BED SYSTEM USING ADIABATIC COOLING BACKGROUND OF THE INVENTION The present invention generally relates to an improved means for the production of sulfur values from a spent pulping liquor as produced in a neutral sulfite pulping process. In particular, the subject invention concerns an improved process and an improved apparatus for the direct oxidation conversion of alkali sulfide into an alkali monosulfite in regeneration of fresh cooking liquor from a spent neutral sulfite pulping liquor. Specifically, the patentable invention provides an improved process and apparatus for controlling the direct oxidative reaction between sodium sulfide and oxygen to form sodium sulfite by regulation of the reaction temperature of the reaction while simultaneously generating steam, which is employed as a catalyst for the reaction and as a reaction moderator for the direct oxidation process, and while preheating air which is introduced into the reaction chamber as the oxidative agent.
The manufacture of paper from pulp which is produced from various cellulosic materials, such as wood, straw and the like requires a continuous and related stream of processing steps. For example, in the fabrication of pulp from wood, it is first necessary that the wood chips be digested or cooked in the immediate presence of suitable pulping chemicals like sodium hydroxide and sodium sulfide, sodium sulphite or sodium acid sulphite to effectively remove the constituents which hold or firmly bind the cellulose materials together that form the wood. The binding components generally comprise various organic materials, such as lignins and resins and they are present in the cooking liquor. Next, the spent cooking or digestion liquor, that is, the liquor that has lost essentially most of its wood digestive properties due to its chemical activity on the wood chips, is mechanically separated from the pulp. The separated spent liquor is generally called black liquor. The black liquor contains the lignins and resins and other organic materials in addition to the spent digestive inorganic pulping chemicals. The black liquor is next subjected to a series of process steps designed to recover the economically important sodium and sulfur values contained therein. The first step in the recovery process is the removal or evaporation of excess water to give a concentrated black liquor. Then, the black liquor is burned in a conventional recovery furnace to bum-off the organic and other combustible matter contained therein and also to produce a process workable molten ash or smelt. The just produced smelt usually contains inorganic chemicals like sodium carbonate, caustic soda, sodium sulfide and other inorganic salts. For use in sulfite pulping, it is necessary that the sodium sulfide present in the smelt be converted to sodium sulfite. One way is to oxidize the sodium sulfide to sodium sulfite. An apparatus which may be employed for the direct oxidation conversion of sodium sulfide to sodium sulfite is the fluidized bed reactor.
Conventionally, the fluidized bed reactor entails a fluidized system. In a fluidized system, air or a preselected gas is moved upwards through a mass of powdered solid to make the particles float in a moving gas stream. The floating particle mass appears to resemble a boiling liquid. The purpose of the floating particle technique is usually to react the gas and the solid or to react gaseous components in the presence of a solid catalyst. While the fluidized bed has in the past been employed in other arts, it has also found employment in the pulping art as an apparatus for the recovery of sulfur values.
In Czechoslovakia Pat. No. 95,701 patentee Hojnos describes a fluidized bed process in which a coarsely pulverized smelt was treated in a conventional fluidized bed with a mixture of superheated steam and air at temperatures from 212 F. to 660 F. for conversion of the sodium sulfide to sodiurn sulfite, using approximately 1.8 to 6 pounds of steam per pound of sodium sulfide, or approximately 0.6 to 2.0 pounds of steam per pound of smelt. Inventors Shick and Chari in US. Pat. No. 3,420,626 describe another process in which a finely pulverized smelt was treated in a specialized fluidized bed apparatus at temperatures from 350 F. to l 1 10 F. with a mixture of steam and air to convert sulfide to sulfite, with a preferred volumetric ratio range of steam to air of from 0.1 to 2, corresponding to a preferred weight ratio range of about 0.06 to 1.2 pounds of steam per pound of air. In both processes the presence of the steam is essential to preferentially promote the formation of sulfite and to inhibit the formation of sulfate.
Heretofore, the recovery of sodium and sulfur values was carried out in a single system fluidized bed reactor by moving the smelt into the reactor, preheating the necessary air, mixing it with steam, and then conveying the mixture into the reactor to contact the smelt and produce the desired single stage fluidized reaction with the oxidation of the oxidizable components present in the smelt and with an accompanying generation of excessive heat, because of the exothermic reaction between the smelt and the oxygen taking place in said fluidized system. Reaction temperatures could be controlled only by uses of large excess of air and steam or by limiting the rate of reaction to correspond to the heat losses to the environment. The general type of prior art fluidized bed described supra for its utilization in a smelt treating process was usually characterized by some inherent disadvantages, for example, the lack of any predetermined system to absorb the heat of reaction for temperature control, the need for a separate means for generating steam, the physical demand for an independent source for preheating the air, as well as the requirements of excessive quantities of air and steam and/or low operating rates, which seriously hindered the effective utilization of the prior art fluidized bed oxidation systems.
Accordingly, it is a primary purpose of this invention to make available to the art means and processes for overcoming the serious drawbacks associated with the prior art systems.
It is a further object of the present invention to provide a fluidized bed system that simultaneously generates the necessary steam required for the reaction process and also has means for controlling the temperature of the process.
It is an additional object of this invention to provide a direct oxidation conversion system that possesses in addition to temperature control means a high degree of self-sufficiency with regard to the heat and steam by controlled direct addition of water to the system to absorb heat and generate steam and by the indirect cooling to generate steam with fire or water tube construction and with either controlled water addition or boiler pressure control.
It is yet another purpose of the invention to provide uniform temperature distribution, high heat transfer and intimate contact between gas and solid of a fluidized bed of a direct oxidation conversion system.
Yet still a further purpose of the invention lies in one aspect for providing a vertical tube type heat exchanger surface in which the temperature would be controlled by the amount of water present with the reaction air around said tubes; and in another aspect with horizontal or pendant vertical coils immersed in a fluid bed for temperature control and the like.
It is still another object of the present invention to provide a novel means for conduct of fluidized bed operations therein which is characterized by operation conditions that lend themselves to an economically operative result. Other objects, features and advantages of the present invention will become clear to those skilled in the art from the following description, the accompanying drawings and the appended claims.
SUMMARY OF THE INVENTION This patentable invention concerns a dual process for controlling the temperature and utilizing the heat of a direct oxidation reaction of smelt wherein the sodium sulfide present in the smelt is oxidized to sodium sulfite. The invention further concerns a means for controlling the exothermic heat of the oxidation process by circulating confined water at elevated temperatures throughout the reaction bed or alternatively mixing water at ambient temperatures or at an elevated temperature with air entering the fluidized reaction area.
DESCRIPTION OF THE INVENTION In attaining the objects, features and advantages of the present invention it has now been unexpectedly found that such temperature control and steam formation may be balanced to give the desired ratio of steam to air in the recovery of sodium and sulfur values from smelt by introducing the ground or granulated smelt into a single fluidized bed reactor designed with a lower air plenum, a distributor plate, and a fluidized bed section for either batch or continuous operation, or a number of fluidized bed reactors, in spaced apart relation and arranged in series for a continuous operation. These reactors are further provided with a heat transfer source, such as a horizontal or vertical tube means immersed in the fluidized bed. One embodiment of the invention uses the fluidized smelt particles juxtaposed on one side of the heat transfer tubes and water, or in another embodiment for some heat transfer tubes reaction air, is on the other side to provide heat exchange between the two. In operation of the fluidized bed part of the heat of reaction serves to heat the smelt feed and the reaction air to maintain the temperature of the bed at the desired level while the excess is used to generate steam in the submerged tubes. The temperature of these tubes and of the reactor is controlled either by the amount of water introduced into the tubes or by the pressure maintained on the water in the tubes. The steam produced is mixed with reaction air, which is introduced into the lower plenum of the reactor and which then passes up through the fluidized bed promoting the desired reactions within the bed. At the end of the reaction, the product is continuously discharged from the last reactor while it is transferred from one reactor to another and fed continuously into the first reactor by means known in the technology of fluid beds. To start a reactor, steam may be supplied to the water side of the submerged cooling surface to heat the fluidized bed and/or the air for the reaction may be preheated with steam or by direct firing to preheat the bed. The incoming air passes upwards throughout the ground smelt and produces violent agitation or a fluidization state wherein the particles in contact with the onrushing air are subjected to direct oxidation conversion. The fluidization process is exothermic, and quantities of energy in the form of heat are generated by the reaction. Into this heat is placed a regulating coil which serves the dual function of generating steam that can be mixed with the incoming fluidization producing air, or the coils can be used to control the reaction temperature by flowing water at various degrees of temperature through the coils to carry-off excessive reaction heat. The just oxidized particles are next separated from the fluidized bed exhaust gas in a cyclone where entrained particulate solids are led to an exhaust station, or they can be conveyed back to the fluidized bed if the need arises.
The invention will be further disclosed with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic sheet illustrating a single fluidized bed system with temperature control means and a multicyclone means suitable for practicing the present invention.
FIG. 2 is a diagram representing a fluidized bed reactor with a temperature coil and its control apparatus for practicing the present invention.
FIG. 3 is a fluidized bed reactor with heat exchangers for performing the direct oxidation conversion of the invention.
FIG. 3A is a multistage fluidized bed reactor with separate heat exchangers for performing the direct oxidation conversion ofthe invention.
FIG. 4 is a schematic depiction of a multistage fluid bed with cooling and steam generating means place in the multivertical bed system.
FIG. 5 is a multistage spouted fluid bed with control means for the direct addition of water for the process and temperature control for the direct oxidation of smelt.
FIG. 6 shows a transport type fluidized reactor with direct injection of tempering water.
FIG. 7 shows a transport type fluidized reactor with recirculation of coarse solids and with direct injection of tempering water.
FIG. 8 is a diagram showing the approximate equilibrium temperature rise in the reactor above the average feed temperatures as a function of mol percentage of sodium sulfide in the smelt and the amount of tempering water used, when operating with percent of the air theoretically required to oxidize the sodium sulfide to sodium sulfite.
FIG. 9 is a diagram showing the approximate temperature rise in the reactor as a function of the percentage of sodium sulfide in the smelt and the amount of tempering water vaporized, when operating with 200 percent of the theoretical air.
In the following disclosure the drawings will be further described in detail according to the mode and the manner of the invention.
DETAILED DESCRIPTION OF THE INVENTION Referring now more specifically to the drawings and by way of introduction, there is shown in FIG. I a block outline flow diagram generally illustrating the temperature control and steam producing systems of the invention. At the top left of FIG. 1, it can be seen that ground smelt particles 12 are introduced into the system through standpipe 10. The finely divided smelt falls by gravity to the bottom of standpipe 10 into tubular screw conveyor 16 which transports the smelt particles laterally to the base of fluidized bed reactor 18. The screw conveyor is the typical screw conveyor containing an internal screw rotating on a shaft driven by power source 14, usually a variable speed electric gear motor for control of feed rate of the smelt. The vertical fluidized bed 18 is also connected at its base to a conduit 21 for introducing air alone or in regular operation air enriched with steam into the vertical fluidized bed 18, or upstanding reactor suitable for operation under expanded bed or transport conditions. The upstanding reactor has an outlet at its top 7 which connects to a cyclone separator 26, where the now oxidized product proceeds through bottom outlet 6 which extends downwardly, then laterally and to the right driven by an internal screw 24 with a pitch that moves the product rightwardly to the extended outlet 22. The internal screw also has at its opposite end a reverse pitch blade to move the product for the series of cyclones, which feature will be discussed below, leftwardly to outlet 22. Rotation screw 24 is driven by a conventional power source, 20, usually an electric motor and gear reducer. Cyclone separator 26 has an upper outlet 8 arising into a curving conduit 28 which extends laterally to the right to a plurality of cyclones 30 in spaced apart parallel relation. The base of each of the cyclones is connected to internal screw conveyor 24 with blades pitched to carry the oxidized particles to the left and downwardly and outwardly through outlet 22. The series of cyclones terminates in a single air filtering means 32, usually a bag, with an outlet at its downward base 23 where the additional finest oxidized product is easily collected by a suitable means, to free the excess process gases of objectionable dust before their release to the atmosphere. The multicyclones are connected to common conduit 19 at their uppermost end which conduit returns a major portion of the gases and fine particles to conduit 21 for re-entry into the fluidized bed reactor 18. The temperature of the reaction in the reactor bed and the amount of water mixed with the incoming air and recirculated gases is governed by a temperature control system and computer 13. Air supplied by blower 17 is carried by conduit 21 with the recirculated gases through blower 15 to obtain sufiicient force to drive the mixed gases into the reactor bed. The temperature of the mixed gases is measured at station 9 by a conventional temperature sensing means, which temperature is conveyed to temperature control box 13 by wire 4. The temperature measuring devices suitable for the present purpose are generally based on thermocouples. However, suitable conventional temperature measuring apparatus also includes a bimetallic thermometer, resistance thermometers, and the like. Also, the temperature could be measured if the need arose by measuring devices based on physical phenomena such as liquid-in-glass thermometers, pressure filled expansion thermometers, liquid pressure thermometers and the like. Thus, as the reaction temperature in the fluidized bed exceeds a predetermined level, water at ambient temperature is introduced into conduit 21 through water feed line 11, to mix with and vaporize in and cool the circulating gases prior to their entrance into the fluidized bed 18. The valve could be of a conventional mannually operated type but is best of a design that responds automatically to electrical stimuli or the like from the central computer 13. Representative of conventional valves that may be employed herein are the gate, slide or butterfly type, the gas control diaphram type, thermostatic expansion or the like. The amount of water entering from the outside line 5 passing through the valve into conduit 11 is monitored and controlled by the electrical or pneumatic connection 3 that relays the signal or response to temperature control box 13. The temperature of the air-recirculated gas-vaporized water mixture in conduit 21 is easily measured as it moves laterally to the left by thermocouple 27, which relays the data through wire 2 to the temperature control box 13. The temperature of the reaction bed is determined by a heat measuring means 25 which conveys the detected temperature to temperature control box 13 through wire 1. Thus, if the temperature is in excess of the desired temperature the temperature control system will permit valved water inlet 11 to deliver more metered water to the air and other gases moving laterally to the reactor, thus to provide the system with an air-steam rate control for temperature and the oxidizing air for the operation of the fluidized bed reactor.
Another embodiment for performing the invention is set forth in FIG. 2 which shows a fluidized bed reactor with an internally disposed cooling and steam generation system in an exothermic fluidized reaction process. In FIG. 2 ground smelt containing sodium sulfide which is to be oxidized to sodium sulfite is introduced by a gravimetric feeder (not shown) into a particle conveying means 34 and through a rotary feed control mechanism 47 into a fluidized bed reactor 35. The fluidized bed reactor is made of a plenum 38 for spreading laterally and upwardly the incoming oxidizing air and steam which enters the base of plenum 38 through fluid communicating means 36, usually a conventional pipe or the like. Next, the conveyed air passes upward through a perforated deck plate 39 which contains a plurality of orifices in spaced apart relation to permit the air to pass into the bottom of fluidized bed 40. The air as it passes upwardly through the fluidized bed 40 produces violent action and agitation with the ground smelt particles introduced into fluidized bed 40. The fluidized bed reaction generally occurs between the perforated deck plate 39 and the fluid bed level 51. The upper portion of the fluidized bed apparatus is continuous and expands into a freeboard chamber 35 with conventional steel or ceramic lining as is used by the art in fluidized bed reactors. The apparatus expands upwardly, then narrows inwardly and connects with a conveying conduit 50 that extends laterally to the side of the reactor for carrying off the exhaust gases into a conventional cyclone, not shown, to separate entrained particulate solids from the exhaust gases. The desired height 51 of the fluidized bed 40 is automatically controlled at the desired level by the discharge of the oxidized product through the overflow conduit 48 which passes downwardly and outwardly through the fluidized bed to the exterior environment. A rotary valve, of the types disclosed supra, is positioned in the discharge conduit 48 as a gas seal. The space juxtaposed immediately upwardly from the fluidized bed level reaction area is the fluid bed freeboard 49 of the reactor. Most of the entrained solids from the bed are separated from the gases in this freeboard region and fall back into the fluidized bed 40. The exhaust gases are conducted from the freeboard 49 through outlet 50 to a cyclone, not shown, for removal of the remaining particulate matter which may be returned to the fluidized bed or combined with the product from the bed as desired. The temperature control of the fluidized bed reactor and the generation of steam is effected by means of internally disposed boiler tube 42. The in-- ternally disposed boiler tubes are connected to a steam drum 43 and a distribution header 41. The distribution header 4] is connected to a feed waterline 44 through the control valve 33. The rate of flow of water into header 4] is controlled by valve 33 to maintain the water level in drum 43 sensed through connection 45. The steam reservoir 43 has a fluid communicating conduit 37 which feeds into air conduit 36. Thus, in operation, steam generated by the heat of the fluidized bed reaction and maintained at a predetermined pressure in steam reservoir 43 can be fed into the incoming air 36 for entrance into the plenum chamber 38 and then into fluidized bed reactor 40. The pressure in the steam drum 43 and the boiler tubes 42 is controlled by valve 46 which is operated automatically through the pressure sensing connection 46a. In the present disclosure, the expression ambient temperature is meant to mean a room temperature of about 70 to 72 F. Also, the phrase tempering water means water at a temperature of from 50 to 212 F. inclusive. This valve 46 may be a conventional spring-loaded diaphram pressure regulating valve, or a pilot operated regulating valve controlled by a pressure sensing and transmitting line represented by 46a. Hence, in operation, the temperature in the fluidized bed is controlled by the temperature of the immersed boiler tubes, the temperature of which is in turn controlled by generation of steam at the pressure selected for their operation, while water is supplied to make up that removed in the form of steam; and the steam from this temperature control boiler portion of the apparatus is mixed with the reaction air to moderate and control the oxidation reaction, as has been found necessary for best results in the conversion of the sulfide to sulflte.
FIG. 3 and FIG. 3A diagrammatically illustrate additional aspects for performing the mode and the manner of the invention. Turning first to FIG. 3, there is set forth therein a vertical type fluidized reactor 52. The fluidized reactor consists of an external shell 58 made of steel or ceramic lined steel and the like and it has openings to bring its internal area in fluid communication with the exterior environment. At the bottommost end of the reactor is located an air, water and steam inlet 63 which is in fluid communication with the bottom of the fluidized reactor tube area 57. Entering the reactor laterally and proximate to the uppermost end is an air feed and water inlet 61 for permitting air and water at ambient temperatures to become energized with heat for eventual use in the fluidized bed and also for controlling the reactor temperature. The amount of water entering the reactor is easily controlled by any conventional means, such as a conventional area meter, a pressure drop meter, a rotameter or the like. The air and water entering the reactor 52 at 61 come into intimate contact with the outermost portion of the fluidized reactor tubes 57 which extend vertically from lower tube sheet 59 at the top of the fluidized bed 56 to upper tube sheet also numbered 59 near the top of the fluidized reactor 52. The shell surrounding the internally housed vertical fluidized reactor tubes also has suitable baffles 60 to direct the flow of air and water or steam back and forth across the fluidized reactor tubes to promote heat exchange. At the top of the reactor, that is, at its uppermost end and at right angles to the air and water inlet is an outlet 64. This outlet permits gases and oxidized smelt to leave the reactor and be conveyed to a suitable particle separating means, for example, a cyclone, not shown. Entering the reactor laterally and above the bottommost inlet is a smelt inlet 54. The smelt, to be oxidized is fed into the fluidized reaction bed 56 where it comes into immediate contact with air and steam entering at 63 and moving upwardly through perforated deck plate 55 to contact the smelt and produce a fluidized state. Thus, in operation, smelt is fed into the reactor at 54 onto the perforated deck plate 55 where it comes into contact with air and steam entering through the bottommost inlet 63. The entering air and steam were heated by their contact with reactor tubes 57 after they entered the vertical reactor at 61 and left this immediate area at 65 to be conveyed by a conduit to reactor inlet 63. Further in operation, the oxidized particles and hot gases produced in the fluidized reaction 56 pass upward within the fluidized reactor tubes 57 and ultimately to the uppermost outlet 64, for eventual conveyance to a particle separator, for example a cyclone.
The spirit of the invention is further illustrated by FIG. 3A wherein a multiphase fluidized reactor 53 is schematically depicted by setting forth a vertical fluidized reactor. The fluidized reactor 53 consists of an outer shell 58, which is made of steel or steel lined with ceramic and the like. The reactor has openings for either entering the internal area of the reactor or to bring the internal area of the reactor into communication with the external environment. Entering the reactor laterally and proximate to its uppermost end is an air feed and water feed inlet 61 for permitting the air and water at ambient temperatures to enter the reactor and to become energized with heat for subsequent use in the fluidized bed reaction and also for simultaneously regulating the temperature of the reaction medium. The air and water entering the reactor 53 at inlet 61 come into intimate contact with the outermost surfaces of fluidized reactor tubes 57 and 57a, which tubes extend along the axis of the reactor in two courses between the tube sheets 59 at the top of the reactor and at the top of the second phase fluidized bed 56a, as well as at the bottom of bed 56a and at the top of the lower fluidized bed 56. The air and steam leave the area of the uppermost reactor via outlet 65a through a conduit extending downwardly and inwardly through opening 62 into the lower reactor and into immediate contact with the lower fluidized reactor tubes 57. The air and steam leave the lower heat exchanger section surrounding the fluidized reactor tubes 57 through outlet 65 by a conduit that extends outwardly and bends downwardly, then inwardly and upwardly into a bottom connection 63 for permitting air and steam to enter the bottommost fluidized bed 56. The air and water or water vapor are directed across the fluidized reactor tubes in the heat exchanger sections by means of the baffles 60. At the uppermost top of the reactor 53 is disposed an outlet 64. The outlet 64 lets hot gases and smelt particles containing sodium sulfite derived from the direct oxidation conversion of sodium sulfide be conveyed to a conventional particle separator, for example a cyclone not presently shown. At the opposite end of the reactor, on a vertical axis from the outlet is a bottom inlet 63 for permitting air and steam into the lower fluidized bed 56. Entering the reactor laterally and proximate the bottommost inlet is a smelt inlet 54. The smelt to be oxidized is fed into the fluidized reaction bed 56 where it comes into contact with the air and steam entering at 63 and moving upwardly through perforated deck plate 55 to contact the smelt and to produce a fluidized state. Hence, in operation, ground smelt particles enter the reactor 58 at inlet 54 and move onto perforated deck plate 55 where they come into immediate contact with air and steam entering through inlet 63. The entering air and steam were previously energized by their contact with fluidized reactor tubes 57a as they entered the upper reactor at 61 and passed outwardly at 65a and then around the lower reactor tubes 57 by entering through inlet 62 and leaving at outlet on 65, as part of their journey into inlet 63. The oxidized particles and hot gases produced in the first or bottom fluidized bed 56 pass upwards through the fluidized reactor tubes 57 to the uppermost fluidized bed 56a where the oxidation of those particles not previously oxidized takes place, and then, they proceed through the fluidized reactor tubes 57a to the uppermost outlet 64 for conveyance to a particle separator. By controlled addition of water at 61 the reactor temperature is controlled and the steam required for moderation of the oxidation reaction is generated.
The embodiment as set forth in the drawing labeled FIG. 4 illustrates the invention as performable in another type of temperature controllable multifluidized solid reactor depicted as number 66. The multifluidized solid reactor 66 is generally of the vertical type with the starting product entering at the top and the final product leaving at the bottom. The present reactor has a temperature control system consisting in part of a steam and water drum 75. The drum has a water inlet 78a for permitting ambient temperature water to enter the drum to maintain the desired water level and, the drum also has a pressure or steam relief pipe 78 to draw off the steam generated at the desired pressure. This steam may be conveyed by a steam line, not shown, for admixture with the reaction air in the inlet duct 73. Leading from the drum is a series of fluid conveying ducts 76 which carry water from drum 75 into the heat exchange coils 74 in the fluidized beds 71. In the fluidized beds 71, 71a etc., coils 74 remove excessive energy from the reaction and return hot water and steam through returning fluid conveying ducts 77 back to the steam drum 75, where the steam is separated from the water. Now, turning to the upper right portion of the apparatus it can be seen that the reactor has a smelt feed means 67 leading into a tubular screw conveyor 67a for carrying the ground smelt particles in the upper fluidized bed 71a. in each fluidized bed 71 the ground smelt particles come into contact with air and steam that enters the reactor through inlet 73 and passes upwardly through perforated deck plate 70 to oxidize the smelt particles in the fluidized bed 71. The oxidized particles and other particles leave the uppermost fluidized bed 71a through down spout 68 that conveys them into the deck plate area of the fluidized bed immediately below. A repeat of this process occurs in the series set forth in reactor 66, with a final discharge of the particles at downward overflow outlet 69, provided with a rotary valve gas seal. The hot gases produced in the fluidized bed reaction are permitted to escape to the exterior through exit duct 72. Thus, in operation the smelt enters the uppermost fluidized bed where oxidation starts and, due to the violent action of the bed, some of the particles spill over into the downspout that carries the particles to the bed immediately below, where the oxidation reaction continues. The process is repeated until the final product is discharged from the bottommost fluidized bed. The temperature of the reaction is maintained by the circulation of water into coils positioned in the beds and with the conveyance of steam out of the coils into a suitable steam boiler drum. The gases produced in the process are conveyed from the fluidized beds to a conventional scrubber before they are discharged into the atmosphere.
The direct oxidation conversion of coarsely ground or granular smelt in a multistage spouted fluidized bed with the controlled direct addition of water for process and temperature control is illustrated in accompanying FIG. 5, wherein there is shown a plurality of vertical, columnar, in-line fluidizing apparatus 79 suitable for the direct oxidation conversion of smelt particles. The columnar fluidizing apparatus 79 is composed of single apparatus designated as 93 and each single apparatus is connected with a passageway 92 between the adjacent columnar fluidizing apparatus, in the lower portion of said column through which the transfer of particles is made from one column to another column. Each of the passageways is provided with a valve, labeled on the drawing V, permitting the movement of particles from one fluidized bed 94 to the next adjacent fluidized bed. The top of each vertical column leads into a common duct 89 that carries exhaust gases to the scrubber before they are discharged into the atmosphere. Each of the plurality of in-line fluidized beds is further designed with a tapered bottom 95 connected to the inlet throat 87, which is characteristic of a spouted bed. The ground smelt is introduced into the fluidized vertical reactor by gravimetric feed through feed control valve 81. It falls into the reactor where it is supported and turbulently mixed by the jet of air issuing from the throat 87. At the narrowed end of tapered column where it merges into throat 87 is internally mounted a water spray nozzle 86. The water spray nozzle receives water at ambient temperatures or if desired in a heated or superheated state, from tempering water feed conduit 83. A temperature sensing means, 97c, of the type described above like a thermocouple, measures the temperature of the fluidized reaction in the fluidizing bed 94 and through conventional control means permits water to be electrically monitored by a proportioned control diaphram valve or the like or by a manual valve 84 for admitting the tempering water into the system. The necessary oxidizing air enters the fluidizing apparatus 79 laterally through the air header 82 and then upwardly through throat 87 wherein the air, water and/or steam mix and then proceed upwardly into the fluidized bed 94 for oxidizing the ground smelt. In the extreme turbulence at the throat and in the rising central spout of the fluidized bed, heat is rapidly exchanged between the bed contents and the fluidizing gases so that all of the tempering water is flashed into steam before it can reach the walls of the apparatus 93, which would cause sticking. The flashing of this tempering water absorbs the heat of the oxidation reaction and this controls the temperature in the fluidized bed and also provides the steam necessary for moderation of the reaction for production of sulfite. As the quantity of fluidized solids in the apparatus 93 increases in volume, and in view of its turbulent fluidized state, these solids start to overflow through the downward directed connecting passage 92 to the next columnar apparatus. The process is repeated until in the last fluidized bed in the series, the passageway 91 leads externally and carries the now oxidized particles 90 through valve V to a conventional collecting station, that is, a cyclone or the like. Thus, in operation as just described the temperature of the fluidizing reaction is maintained at a desired predetermined level by regulating the water injected into each fluidizing bed as needed for control of the direct oxidation conversion of the smelt.
Direct oxidation conversion of ground smelt in a fluidized state is further illustrated in the process diagram of FIG. 6. Flaked smelt obtained by chilling molten smelt on a suitable cooler and flaker is fed through the hopper and screw feeder 96 into a gas-swept grinding mill, such as the commercially available Sturtevant vertical mill sold under the trade name Pulver Mill," 97b. The finely ground smelt is conveyed with circulating gases through duct 98 to the special mixing eductor 99, where it is mixed with reaction air from line 100 supplied by the variable discharge air compresser 101 and with tempering water from line 102 as measured by rotameter 103 and controlled by a water valve, not shown. The water is flashed into steam in the presence of the hot gases and reacting smelt as the mixture moves down through the reactor 104, and is finally conveyed through duct 105 to a second special mixing eductor 106, where further air and tempering water are added from lines 100 and 102 respectively and the reaction is continued in the reactor 107. The mixture of gases and solids is conveyed from reactor 107 through line 108 to the hot cyclone 109, in which the solids are centrifically separated and discharged with the excess gases through duct 110 and through a wet scrubber, such as a commercially available Schneible Multiwash scrubber 111. Water is introduced through line 112 and metered by rotameter 113 into the scrubber 111 to collect the solid product and to wash the excess gases. This scrubbing action is enhanced by recirculation of the product solution through line 114 by pump and motor combination 115. The product solution is discharged from the discharge line 116 and contains the oxidized smelt in solution. The major portion of the gases entering the cyclone 109 are discharged relatively free from solids through the recirculation gas duct 117, which returns them to the base of the vertical mill 97b, where they serve as the sweeping gas in that mill and also to condition the finely ground smelt for the direct oxidation reaction. The clean excess spent gases are discharged to the atmosphere from the system through the gas discharged duct 118.
A similar but alternative arrangement of a transport type reactor, in this case with recirculation of the coarser solids, is illustrated in the process flow diagram of FIG. 7. Items 96-A through 107-A correspond to 96 through 107, as discussed for FIG. 6. Also items 111-A through 116-A, as well as item 118-A, serve the same functions as the corresponding items described for FIG. 6. However, duct 108-A discharges the product from the second reactor 107-A into a centrifical flow splitter ll09-A, which returns the coarse solids through the gas recycle line 117-A with the recirculation gases to the Sturtevant mill, where these coarser solids are further comminuted and are recycled. The excess gases and the finer product are conveyed through duct -A to the scrubber 111-A, where they are collected and finally discharged as a solution at 116-A. In the operation of the processes illustrated by FIGS. 6 and 7, the temperature of the reactors 104-A and 107-A are monitored by thermocouples, not shown, and are controlled by the controlled addition of the tempering water, adding more water if the temperature rises or reducing the addition of water if the temperature falls.
The above disclosure and the following description and examples are merely representative of the spirit of the invention and they are not to be construed as limiting the invention as these and other methods will be obvious from the instant disclosure and accompanying examples to those skilled in the art.
EXAMPLE 1 The mode and manner of performing the invention herein described is further illustrated by the following example. In
. this example, a run was made employing an apparatus as is illustrated in FIG. 6, as fully described supra. In the apparatus a 15-inch Sturtevant Pulver Mill was used for grinding and for gas circulation. The various ducts of the apparatus were approximately 6 inches in diameter, and the reactors were approximately 26 inches in diameter by 22 feet in overall heighth. A run was made under the following conditions: the feed rate of smelt was 230 pounds per hour, an air rate of 250 pounds per hour, which air rate corresponds to approximately 137 percent of the theoretical requirement for the oxidation reaction, and a water rate of approximately 0.1 gpm, or 50 pounds per hour, which water rate corresponds to approximately 0.2 pounds of water per pound of smelt or 0.2 pounds of water per pound of air. In operation, the temperature in the first reactor was controlled at approximately 480 F. and the temperature in the second reactor was at about 420 F. The chemical composition of the smelt feed and the oxidized product are set forth in Table 1 below. The analysis of the smelt feed and the oxidized product are expressed as percent on a Na O basis.
TABLE 1 Analyses Na,0) Feed Product Na,S 37.3 8.3 w sp, 1.3 2.1 Na SO 1.6 23.5 M1 50, 1.4 6.5 Na CO 58.4 59.6
Total 100.0 100.0
The results obtained for the run under the described conditions indicate a 60 percent conversion of sodium sulfide to sodium sulfite. If a more complete conversion is described, more water would be required to maintain the stated temperatures.
EXAMPLE 2 The spirit of the invention can be further illustrated by the present example. The apparatus employed for this run is illus trated according to FIG. 7 supra with its dimensions as set forth in Example 1. In operation, flaked smelt was fed at room temperature, about 70 to 72 F. into the apparatus at a smelt feed rate of 310 pounds per hour. The air rate feed for the oxidation reaction was 585 pounds per hour, which corresponds to approximately 268 percent of the theoretical air. The water feed rate was varied from 200 to 400 pounds per hour. The water rate corresponds approximately to 0.34 to 0.68 pounds of water per pound of air, or 0.65 to 1.3 pounds of water per pound of smelt. The chemical composition of the smelt feed and the oxidized product had an analysis expressed as percent of Na O as set forth in Table 2.
TABLE 2 Analyses (7cNa,O) Feed Product Na,S 33.5 4.8 Na,S,O;, 1.6 3.5 Na,50 1.1 24.0 Na,SO 3.1 8.4 Na CO, 60.7 59.3
Total 100.0 100.0
The results for the run correspond to approximately 66 percent oxidation conversion of the sodium sulfide to the sodium sulfite. The results demonstrated that the tempering water has a two-fold purpose, first, to control the temperature of the reaction, and secondly, to supply steam for moderation of the oxidation conversion reaction.
EXAMPLE 3 A further suitable apparatus for carrying out the oxidation of sodium sulfide to sodium sulfite has been illustrated in the diagram for FIG. 2. This diagram shows a conventional fluidized bed reactor with an immersed heat exchange coil suitable for indirect generation of steam by heat transfer from the reacting smelt containing 50 mol percent of sodium sulfide which was fed into the reactor through line 34 at a rate of 1,000 pounds per hour. When this smelt was reacted with l ,685 pounds of air per hour (corresponding to 150 percent of the theoretical requirements) supplied through line 36 to 1,300 pounds of steam per hour generated in the coils 42 in the bed and conducted by line 37 to be mixed with the air to give essentially complete oxidation of the sulfide content, the temperature in the bed increased approximately 330 F. above that of the temperatures of the smelt, water, and air, flowing into the system to give a reaction temperature of approximately 400 F. in the bed, at which temperature an equilibrium was established between the exothermic reaction and the steam generation in the coils 42. The tempering water supplied indirectly through the immersed coils in which it is converted into steam corresponds in this case to approximately 1.3 pounds of water per pound of smelt and 0.78 pounds per pound of air. In this manner, the temperature of the reaction is controlled and the steam for moderating the reaction is formed.
The following figures further illustrate the spirit of the invention.
FIG. 8 illustrates the relationship at adiabatic equilibrium conditions between the average temperature rise of the smelt, water and air in such a fluidized reactor system as a function of the sulfide content of the smelt expressed as mol percent and the pounds of tempering water used per pound of smelt when using 100 percent of the air theoretically required for the desired oxidation reaction. Additionally, the corresponding pounds of water per pound of air are shown.
1n FIG. 9 the corresponding adiabatic equilibrium temperature rises as a function of the percent sulfide in the smelt and the pounds of tempering water applied per pound of smelt or per pound of air are shown when operating with 200 percent of the air theoretically required for the desired reaction.
These examples and these figures illustrate that the steam generated under these adiabatic conditions corresponds to that required for proper control of the course of the oxidation reaction; i.e., from approximately 0.2 to 1.2 pounds of water per pound of air or from approximately 0.5 to 2.0 pounds of water per pound of smelt.
While specific details of the spirit of the invention including constructive and process details have been disclosed herein, it should be appreciated that such disclosure is done in compliance with the provisions of the patent statutes and that all obvious embodiments and equivalents in the light of this disclosure are intended to be included within the scope of the patentable invention.
1. 1n an improved process for simultaneously controlling the temperature and for producing steam in the direct oxidation of sodium sulfide to sodium sulfite contained in ground particles of a spent pulping smelt wherein said process comprises the following steps:
a. introducing the ground smelt particles into a fluidized bed reactor wherein the particles are in intimate contact with moving air enriched with steam to form a gaseous mixture to produce a fluidized reaction,
b. maintaining the smelt particles in the air enriched with steam for about 10 seconds at elevated temperatures to about 2 hours at lower temperatures and wherein the weight ratio of steam to air is about 0.2 to l to 1.2 to 1, and
. controlling the temperature of the fluidized bed reaction during the direct oxidation of the sodium sulfide to sodium sulfite in the smelt particles at about 212 to l,200 F.; the improvement comprising absorbing the heat of reaction in the fluidized reactor while simultaneously forming the steam for step (a) from water thereby to control the temperature of the reaction, and circulating the water used to generate the steam for step (a) through a heat exchange element disposed in the fluidized bed and in intimate contact with the gaseous mixture to thereby adiabatically limit the temperature of the reaction, the step of absorbing the heat of reaction further characterized by a balance between the steam required for moderation of the reaction and that formed by the adiabatic cooling of the reactor.
2. A process for controlling the temperature of the exothermic reaction employed for the direct oxidation conversion of sodium sulfide contained in a pulping smelt to sodium sulfite in a fluidized bed reactor system and forming the necessary steam for moderation of the reaction, the process comprising the steps of:
l. reacting smelt particles in a fluidized condition with a gas stream containing oxygen and steam formed from water; and
2. absorbing the heat of reaction by adiabatic cooling to form the steam for the reaction in the reactor system at a temperature of about 212 F. to about 1,200 F. to thereby produce the temperature controlled oxidation reaction and sodium sulfite, the process further characterized by a balance between the steam required for moderation of the reaction and that formed by the adiabatic cooling of the reactor.
3. A process as defined in claim 2 in which the temperature ofstep (2) is about 350 to l,l00 F.
4. A process as defined in claim 2 in which the steps l and (2) are repeated step-wise at least once, and the water is introduced into a fluid reactor of the reactor system.
5. A process as defined in claim 2 in which the steps l and (2) are repeated step-wise at least once, and water is introduced into a transport-type reactor of the reactor system.
6. A process as defined in claim 2 in which the steps l and (2) are repeated step-wise at least once, and water is introduced into a multistage spouted bed reactor of the reactor system.
7. A process as defined in claim 2 in which the temperature of the water in step (1 is about 50 to 2 l 2 F.
8. A process as defined in claim 2 in which 0.2 to 1.2 pounds of water of step l is employed for each pound of the gas containing oxygen in the gas stream.
9. A process as defined in claim 2 in which in step (1) 0.5 to 2.0 pounds of water is used for each pound of smelt particles.
10. A process as defined in claim 1 in which the generated steam is conveyed to the outside of the fluidized reactor and mixed with air to produce a gaseous air stream mixture before the mixture enters the fluidized bed direct oxidation reaction for the conversion of sodium sulfide to sodium sulfite.
11. A process as defined in claim 1 in which generated steam is introduced into the fluidized reactor.