CA1085583A - Process of concentrating dilute phosphoric acid - Google Patents
Process of concentrating dilute phosphoric acidInfo
- Publication number
- CA1085583A CA1085583A CA294,197A CA294197A CA1085583A CA 1085583 A CA1085583 A CA 1085583A CA 294197 A CA294197 A CA 294197A CA 1085583 A CA1085583 A CA 1085583A
- Authority
- CA
- Canada
- Prior art keywords
- stage
- acid
- concentrating
- heated
- phosphoric acid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/08—Compounds containing halogen
- C01B33/10—Compounds containing silicon, fluorine, and other elements
- C01B33/103—Fluosilicic acid; Salts thereof
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/765—Multi-stage SO3-conversion
- C01B17/7655—Multi-stage SO3-conversion with intermediate absorption
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/18—Phosphoric acid
- C01B25/234—Purification; Stabilisation; Concentration
- C01B25/2343—Concentration concomitant with purification, e.g. elimination of fluorine
Abstract
ABSTRACT OF THE DISCLOSURE
A process for concentrating dilute phosphoric acid, in which dilute phosphoric acid is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas. The process is characterized in that the dilute phosphoric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circu-lated through two successive concentrating stages and in said stages is sprayed and directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to SO3 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating-stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption.
The process of the invention avoids the use of primary energy or steam for producing the hot gases and also enables one to minimize the operating costs as well as the acid fume content of the exhaust gas.
A process for concentrating dilute phosphoric acid, in which dilute phosphoric acid is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas. The process is characterized in that the dilute phosphoric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circu-lated through two successive concentrating stages and in said stages is sprayed and directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to SO3 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating-stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption.
The process of the invention avoids the use of primary energy or steam for producing the hot gases and also enables one to minimize the operating costs as well as the acid fume content of the exhaust gas.
Description
~ - ~
1~855~3 The invention relates to a process for concentrat-ing dilute phosphoric acid, which is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas.
- The treatment of raw phosphates with sulfuric acid in a wet process often results in a dilute phosphoric acid, 10which contains about 26 to 32% P2O5 and must be concentrated to a P2O5 content above about 45~ for the production of fertilizer. The phosphoric acid is concentrated by an evaporation of water in direct contact with hot gases or by an indirect supply of heat in a vacuum and this may be accom-panied by crystallization (A.V. Slack, "Phosphoric Acid", Vol.
II, 1968, Marcel Dekker, Inc., New York, pages 581-634). When he phosphoric acid is concentrated by an indirect supply of heat in a vacuum, expensive equipment is required to produce the vacuum, the boiling may be delayed because the operation must be performed in the boiling range, and primary energy or steam is required. When the phosphoric acid is concentrated by a direct contact with hot gases, primary energy at considerable cost is required in the known processes for producing the hot gases. Steam is also used in part for indirectly heating the acid before it is contacted with the hot gases. The use of submerged burners results in the production of acid fumes at a considcrable ratc, and these fumes can be scparatcd only with difficulty and are withdrawn with the exhaust gascs.
It is an object of the invention to avoid the use of primàry energy or steam in a concentrating process which involves a direct contact with hot gases and also to minimize the operating costs as well as the acid fume content of the exhaust gas.
`` 1085583 This object is accomplished according to the inven-tion in that the dilute phosphoric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circulated through two successive concen-trating stages and in said stages is directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to S03 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption.
To heat the gas mixture by an indirect heat exchange with the surplus gas heat of the gases which have left the first contacting stage and have been partly converted to S03, the end gas may be heated and may be mixed with air before entering the concentrating unit, or the air may be properly heated and may subsequently be mixed with the end gas. The gas mixture is suitably heated in the second heat exchange stage in the flow path of the S03-containing gases. In the operation of the interstage absorption system of the sulfuric acid contact process plant, the gas phase and the sulfuric ; acid flow concurrently and the gas exit temperature of the S02-containing gases is approximately as high as the temperature of the draining sulfuric acid and the temperature of thP draining sulfuric acid and the temperature of the draining sulfuric acid is at least 95C. The first and second concentrating stages succeed one another in the direction of flow of the hot gases. The phosphoric acid is generally concentrated to a P2O5 content of 45 to 60~.
According to a preferred feature, the dilute phos-phoric acid is circulated, the fresh dilute phosphoric acid is fed to the second concentrating stage, the circulating acid is heated by the heat which is to be withdrawn from the sulfuric acid circulating through the interstage absorption system of the sulfuric acid contact process plant, the circulating phosphoric acid is sprayed into the second concentrating stage in a countercurrent to the rising gas mixture, part of the circulating acid is fed from the sump of the second concentrating stage into the sump of the first concentrating stage, the remaining part of the circulating acid is fed from the sump of the second concentrating stage to the acid circulating through the secondconcentrating stage, the acid circulating through the first concentrating stage is heated behind the sump thereof by means of the heat which is to be removed from the sulfuric acid circulating in the final absorption system and is then sprayed into the first concen-trating stage concurrently to the descending gases, and phosphoric acid of higher concentration is withdrawn from the ac`id which circulates through the first concentrating stage.
This operation results in a favorable transfer and supply of the heat which is required for the concentrating treatment whereas a formation of deposits in the concentrating unit is avoided because heat at a higher temperature is supplied through the gas phase to the first concentrating stage and only heat at a relatively low temperature is supplied by the heated acid .~
to the second stage. Generally, the heating of the acid circulating through the phosphoric acid-concentrating stages 1085~83 in the interstage and final absorption systems may be interchanged.
According to a preferred feature, the acid is concentrated in the first concentrating stage in a vertical Venturi tube. In that case, a favorable and fast transfer of heat and mass is effected in a small unit because the gas and liquid phases are intimately mixed. Because all walls are constantly flushed with acid, the solids which are formed as the concentration of the acid is increased cannot deposit but remain in suspension. Besides, the pressure loss in the gas is low.
According to a preferred feature, the acid circulat-ing through the first concentrating stage is heated by heat to be removed from the sulfuric acid which circulates in a high-temperature final absorption system. In the final absorber of the sulfuric acid contact process plant, the gas phase and the sulfuric acid flow concurrently at least in a first absorption stage. The second stage may be operated with uncooled sulfuric acid, which flows in a countercurrent to the gas so that the exit ~emperature of the end gas corresponds to the temperature of the draining sulfuric acid, which is at least 95C. This -~
operation results in a removal of heat at a higher rate by the gases leaving the two absorption systems of the sulfuric acid contact process plant so that heat at a correspondingly lower rate must be removed from the acids which circulate in said -absorption systems. As a result, the area of the heat exchangers for cooling the sulfuric acid can be reduced and ~` the surplus heat from the absorption systems of the contact ~ .
process plant is utilized in a desirable manner to concentrate ~;~ 30 the phosphoric acid.
:~
.: :. - : ;~ .: . .
. : , .
1085~83 According to a preferred feature, the tail gas from the final absorption system of th~ sulfuric acid contact process plant is heated with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant, said heating is effected in a second heat exchange stage in the gas flow path, and the air is admixed to the heated tail gas. This operation avoids a temperature drop of the S03-containing gases at the heat-exchange surfaces of the heat exchanger below the dew point.
According to a preferred feature, gases which have a high SO2 content and become available at a low temperature are processed in the sulfuric acid contact process plant and part of the gas mixture is heated in the final heat exchanger succeeding the last contacting tray. That operation will afford advantages particularly when the SO2-containing gases which are processed in the sulfuric acid contact process plant come from metallurgical plants and contain more than 8.5% SO2 and surplus heat is available for thermally self-sufficient operation of the contact process plant. The final heat exchanger has preferably two stages, the first stage in the flow path of the hot gases serves to preheat gases for the contact process plant and the second stage serves to heat the gas mixture. Either the air or the tail gas may be heated.
According to a preferred feature, the hot gases are fed to the first concentrating stage at a temperature of 70 to 250C, preferably 80 to 220C. This results in a good heat supply to the first stage without a formation of crusts.
According to a preferred feature, the hot gases are fed to the first concentrating stage at a temperature of 100 to 280C, preferably 120 to 250C. When gases having a high So2 content are processed in the contact process plant, this feature results in a very good heat supply to the first stage without a formation of crusts.
According to a preferred feature, the phosphoric acid is sprayed into the first concentrating stage at a temperature of 60 to 100C, preferably 75 to 90C. As a result, additional heat at a relatively low temeprature is fed to the first stage as heat of the acid, and a good evapo-ration of water in the first stage is accomplished whereas there is no danger of a formation of crusts.
According to a preferred feature, the fluorine constituents are absorbed in an absorption unit in two successive stages, fluosilicic acid is injected in the first stage of the absorption unit into a vertical Venturi tube absorber to flow concurrently with the gases, fluosilicic acid ; is injected in the second stage into an empty tower to flow in a countercurrent to the gases, and a considerable part of the inside surfaces of the absorption unit is contacted by the injected fluosilicic acid. To contact the inside surfaces r with fluosilicic acid, the latter is injected with turbulence so that separated SiO2, which is formed by the hydrolysis of SiF4, cannot deposit on the wall. Besides, an optimum phase boundary surface between the gas and liquid is formed and results in a good absorption.
According to a preferred feature, the fluorine constituents are absorbed in two series-connected absorption units, water is continuously fed to the acid which circulates ` in the second stage of the second absorption unit, acid from the sump of the second stage of the second absorption unit flows over into the sump of the second stage thereof, acid from the sump of the first stage of the second absorption unit flows over into the sump of the second stage of the first absorption unit, acid from the sump of the second stage of the first absorption unit flows over into the sump of the first . . .
stage thereof, and fluosilicic acid is withdrawn as product from the sump of the first stage of the first absorption unit.
The overflow rates are controlled so that a continuous equilibrium of flow is achieved and the steady-state concen-trations of the fluosilicic acid circulating in the several absorption stages decrease from the first stage to the last.
This results in constant optimum conditions for the absorption of fluorine. Besides, the adjustment of a continuous equi-librium of flow minimizes the residence times of the acid in the several sumps so that an increased aging accompanied by a deposition of the separated SiO2 is avoided and a large propor-tion of the SiO2 is discharged with the product from the absorption units.
According to a preferred feature, the continuous feeding of water to the second stage of the second absorption unit is controlled so that the product acid withdrawn from the first stage of the first absorption unit has the desired fluo-silicic acid concentration. This enables a simple adjustment of the desired fluosilicic acid concentration in the product which is discharged.
According to the preferred feature, the bottoms of the sumps slope toward the inlets of the suction conduits leading to the acid-circulating pumps so that the silica gel and/or SiO2 which is separated during the formation of fluosilicic acid is kept in suspension and flows with the acid through all stages of the absorption units and is continuously discharged from the absorption system together with the fluosilicic acid product. In that case there is a turbulent flow of acid in the sumps and regions of stagnant liquid are avoided so that the deposition of SiO2 suspended in the liquid phase is further opposed.
:; :
, . .
.
1085~83 The invention will be described more fully and by way of examples with reference to the drawings.
The drawings are flow schemes of processes of concentrating dilute phosphoric acid in conjunction with a sulfuric acid contact process plant, which is fed in FIG. 1 with SO2-containing gases produced by the burning of sulfur, in FIG. 2 with SO2-containing gases from a roasting - plant and in FIG. 3 with gases having a high SO2 content and formed in a pyrometallurgical plant.
Raw phosphate is fed in conduit 1 and sulfuric acid is fed in conduit 2 to a wet-process plant 3. Dilute phosphoric acid is fed from a filter unit 4 in conduit 5 to an agitating vessel 6 and in a conduit 7 to the second concentrating stage %, which consists of an empty tower.
From the sump 9 of the second concentrating stage 8, phosphoric acid is fed by means of a pump 10 through conduit 11 into the heat exchanger 12 and is heated there and sprayed from conduit 13 into the second concentrating stage 8. Part of the phosphoric acid which has been collected in the sump 9 flows in conduit 14 into the sump 15 of the first concentrating stage 16, which consists of a vertical Venturi tube. Phospho-ric acid from the sump 15 is fed via conduit 17, pump 18, and conduit 19 into the heat exchanger 20 and is heated there and then sprayed from conduit 21 into the first concentrating `~ stage 16. Concentrated phosphoric acid is fed in conduit 22 to the agitating vessel 23.
The SO2-containing gases are fed in conduits 24 and 24a into the contact process tower 25, in which the gases are catalytically reacted in known manner. From the first contacting stage, the partly converted gases, which contain iO85583 S03, are fed in conduit 26 to the first heat exc~ange stage 27 and in conduit 28 into the second heat exchange stage 29. The cooled gases which contain S03 are fed in conduit 30 to the interstage absorber 31, in which a large part of the S03 is removed by a treatment with sulfuric acid. The gases which contain the residual S02 are fed in conduit 32 to the first heat exchange stage 27 and are heated there to the operating temperature of the next contacting stage and are then fed in conduit 33 to the second contacting stage of the contact process tower 25, in which their conversion is completed in known manner. The converted gases which contain S03 are fed in conduit 34 to a heat exchanger 35 and are cooled therein and are then fed in conduit 36 to the final absorber 37, in which the S03 is removed from the gases by a treatment with sulfuric acid. The end gases from the contact process plant are fed in conduit 38 to the second heat exchange stage 29, in which they are heated by a heat exchange with the S03-contain-ing gases, and are then fed in conduit 39 to a blower 40, which is supplied with air through filter 41 and conduit 42.
In accordance with Fig. 3, filtered air is first heated in the second heat exchange stage 35a in a heat exchange with the S03-containing gases which are fed to the final absorber 37. The heated gas mixture is fed in conduit 43 to the first concentrating stage 16 in which the gas mixture and the concurrently sprayed phosphoric acid are cooled by an adiabatic evaporation of water and most of the concentrated phosphoric acid is collected in the sump 15 whereas the qas which has been enriched with water vapor is ~ed to the second concentrating stage 8, in which it rises in a countercurrent to the sprayed phosphoric acid. This results in a further adiabatic evaporation of water to cool the phosphoric acid which is then collected in the sump 9.
_ g _ The exhaust gas from the concentrating unit contains water vapor and fluorine compounds and is fed in conduit 44 to the first absorption unit 45 and in said unit is treated in the first stage 45a, consisting of a vertical Venturi tube, with concurrently flowing fluosilicic acid and in the second stage 45b with countercurrently flowing fluosilicic acid.
These treatments are correspondingly repeated in the second absorption unit 46. After the removal of most of the fluorine compounds, the gas is fed into the atmosphere through conduit 47.
Water is fed in conduit 48 to the acid which circulates in the second stage 46b of the second absorption unit 46. In conduit 49, the fluosilicic acid which has been formed is withdrawn from the acid circulated in the first stage 46a of the second absorption unit 46 and is then added to the acid which circu-lates in the second stage 45b of the first absorption unit 45.
The entire fluosilicic acid product is withdrawn in conduit 50 from the acid circulating in the first absorption stage 45a of the first absorption unit 45.
The phosphoric acid is heated in the heat exchangers 12 and 20 by the sulfuric acid which is fed to the heat exchan-gers 12 and 20 in conduits 51 and 52, respectively, and when cooled by the heat exchange is returned to the absorbers 31 and 37 in conduits 53 and 54, respectively.
The SO2-containing gases are produced in a sulfur-burning furnace 55a, a fluidized-bed roasting furnace 55b or a flame cyclone reactor 55c. The hot gases which contain SO2 are cooled in a waste heat boiler 56. The heat which has been removed is used to produce steam. In accordance with Fig. 1, the cooled gases which contain SO2 are directly fed to the contact process tower 25 in conduit 24. In accordance with Figs. 2 and 3, the cooled gas which contains SO2 is purified and dried in known manner and is then heated to the operating ~085583 temperature of the first contacting tray by the heat which is released in the contact process tower as a result of the cata-lytic oxidation of SO2 to SO3. This heat is used to produce steam in accordance with Fig. 1. In all cases, the air required to burn sulfur and to oxidize SO2 is dried before.
Examples In all cases, the sulfuric acid contact process plant is designed for a production capacity of 1500 (metric) tons of H2SO4, calculated as 100% H2SO4, per day.
; 10 The conditions which are obtained at the positions indicated by the reference numbers of Figs. 1 to 3 will now be indicated.
;' .
Position Unit Fig.l Fig.2 Fig.3 1 Raw phosphate feed rate t/h 70.4 70-4 70-4 P2O5 content % by weight 34 34 34 1~ . . . _
1~855~3 The invention relates to a process for concentrat-ing dilute phosphoric acid, which is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas.
- The treatment of raw phosphates with sulfuric acid in a wet process often results in a dilute phosphoric acid, 10which contains about 26 to 32% P2O5 and must be concentrated to a P2O5 content above about 45~ for the production of fertilizer. The phosphoric acid is concentrated by an evaporation of water in direct contact with hot gases or by an indirect supply of heat in a vacuum and this may be accom-panied by crystallization (A.V. Slack, "Phosphoric Acid", Vol.
II, 1968, Marcel Dekker, Inc., New York, pages 581-634). When he phosphoric acid is concentrated by an indirect supply of heat in a vacuum, expensive equipment is required to produce the vacuum, the boiling may be delayed because the operation must be performed in the boiling range, and primary energy or steam is required. When the phosphoric acid is concentrated by a direct contact with hot gases, primary energy at considerable cost is required in the known processes for producing the hot gases. Steam is also used in part for indirectly heating the acid before it is contacted with the hot gases. The use of submerged burners results in the production of acid fumes at a considcrable ratc, and these fumes can be scparatcd only with difficulty and are withdrawn with the exhaust gascs.
It is an object of the invention to avoid the use of primàry energy or steam in a concentrating process which involves a direct contact with hot gases and also to minimize the operating costs as well as the acid fume content of the exhaust gas.
`` 1085583 This object is accomplished according to the inven-tion in that the dilute phosphoric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circulated through two successive concen-trating stages and in said stages is directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to S03 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption.
To heat the gas mixture by an indirect heat exchange with the surplus gas heat of the gases which have left the first contacting stage and have been partly converted to S03, the end gas may be heated and may be mixed with air before entering the concentrating unit, or the air may be properly heated and may subsequently be mixed with the end gas. The gas mixture is suitably heated in the second heat exchange stage in the flow path of the S03-containing gases. In the operation of the interstage absorption system of the sulfuric acid contact process plant, the gas phase and the sulfuric ; acid flow concurrently and the gas exit temperature of the S02-containing gases is approximately as high as the temperature of the draining sulfuric acid and the temperature of thP draining sulfuric acid and the temperature of the draining sulfuric acid is at least 95C. The first and second concentrating stages succeed one another in the direction of flow of the hot gases. The phosphoric acid is generally concentrated to a P2O5 content of 45 to 60~.
According to a preferred feature, the dilute phos-phoric acid is circulated, the fresh dilute phosphoric acid is fed to the second concentrating stage, the circulating acid is heated by the heat which is to be withdrawn from the sulfuric acid circulating through the interstage absorption system of the sulfuric acid contact process plant, the circulating phosphoric acid is sprayed into the second concentrating stage in a countercurrent to the rising gas mixture, part of the circulating acid is fed from the sump of the second concentrating stage into the sump of the first concentrating stage, the remaining part of the circulating acid is fed from the sump of the second concentrating stage to the acid circulating through the secondconcentrating stage, the acid circulating through the first concentrating stage is heated behind the sump thereof by means of the heat which is to be removed from the sulfuric acid circulating in the final absorption system and is then sprayed into the first concen-trating stage concurrently to the descending gases, and phosphoric acid of higher concentration is withdrawn from the ac`id which circulates through the first concentrating stage.
This operation results in a favorable transfer and supply of the heat which is required for the concentrating treatment whereas a formation of deposits in the concentrating unit is avoided because heat at a higher temperature is supplied through the gas phase to the first concentrating stage and only heat at a relatively low temperature is supplied by the heated acid .~
to the second stage. Generally, the heating of the acid circulating through the phosphoric acid-concentrating stages 1085~83 in the interstage and final absorption systems may be interchanged.
According to a preferred feature, the acid is concentrated in the first concentrating stage in a vertical Venturi tube. In that case, a favorable and fast transfer of heat and mass is effected in a small unit because the gas and liquid phases are intimately mixed. Because all walls are constantly flushed with acid, the solids which are formed as the concentration of the acid is increased cannot deposit but remain in suspension. Besides, the pressure loss in the gas is low.
According to a preferred feature, the acid circulat-ing through the first concentrating stage is heated by heat to be removed from the sulfuric acid which circulates in a high-temperature final absorption system. In the final absorber of the sulfuric acid contact process plant, the gas phase and the sulfuric acid flow concurrently at least in a first absorption stage. The second stage may be operated with uncooled sulfuric acid, which flows in a countercurrent to the gas so that the exit ~emperature of the end gas corresponds to the temperature of the draining sulfuric acid, which is at least 95C. This -~
operation results in a removal of heat at a higher rate by the gases leaving the two absorption systems of the sulfuric acid contact process plant so that heat at a correspondingly lower rate must be removed from the acids which circulate in said -absorption systems. As a result, the area of the heat exchangers for cooling the sulfuric acid can be reduced and ~` the surplus heat from the absorption systems of the contact ~ .
process plant is utilized in a desirable manner to concentrate ~;~ 30 the phosphoric acid.
:~
.: :. - : ;~ .: . .
. : , .
1085~83 According to a preferred feature, the tail gas from the final absorption system of th~ sulfuric acid contact process plant is heated with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant, said heating is effected in a second heat exchange stage in the gas flow path, and the air is admixed to the heated tail gas. This operation avoids a temperature drop of the S03-containing gases at the heat-exchange surfaces of the heat exchanger below the dew point.
According to a preferred feature, gases which have a high SO2 content and become available at a low temperature are processed in the sulfuric acid contact process plant and part of the gas mixture is heated in the final heat exchanger succeeding the last contacting tray. That operation will afford advantages particularly when the SO2-containing gases which are processed in the sulfuric acid contact process plant come from metallurgical plants and contain more than 8.5% SO2 and surplus heat is available for thermally self-sufficient operation of the contact process plant. The final heat exchanger has preferably two stages, the first stage in the flow path of the hot gases serves to preheat gases for the contact process plant and the second stage serves to heat the gas mixture. Either the air or the tail gas may be heated.
According to a preferred feature, the hot gases are fed to the first concentrating stage at a temperature of 70 to 250C, preferably 80 to 220C. This results in a good heat supply to the first stage without a formation of crusts.
According to a preferred feature, the hot gases are fed to the first concentrating stage at a temperature of 100 to 280C, preferably 120 to 250C. When gases having a high So2 content are processed in the contact process plant, this feature results in a very good heat supply to the first stage without a formation of crusts.
According to a preferred feature, the phosphoric acid is sprayed into the first concentrating stage at a temperature of 60 to 100C, preferably 75 to 90C. As a result, additional heat at a relatively low temeprature is fed to the first stage as heat of the acid, and a good evapo-ration of water in the first stage is accomplished whereas there is no danger of a formation of crusts.
According to a preferred feature, the fluorine constituents are absorbed in an absorption unit in two successive stages, fluosilicic acid is injected in the first stage of the absorption unit into a vertical Venturi tube absorber to flow concurrently with the gases, fluosilicic acid ; is injected in the second stage into an empty tower to flow in a countercurrent to the gases, and a considerable part of the inside surfaces of the absorption unit is contacted by the injected fluosilicic acid. To contact the inside surfaces r with fluosilicic acid, the latter is injected with turbulence so that separated SiO2, which is formed by the hydrolysis of SiF4, cannot deposit on the wall. Besides, an optimum phase boundary surface between the gas and liquid is formed and results in a good absorption.
According to a preferred feature, the fluorine constituents are absorbed in two series-connected absorption units, water is continuously fed to the acid which circulates ` in the second stage of the second absorption unit, acid from the sump of the second stage of the second absorption unit flows over into the sump of the second stage thereof, acid from the sump of the first stage of the second absorption unit flows over into the sump of the second stage of the first absorption unit, acid from the sump of the second stage of the first absorption unit flows over into the sump of the first . . .
stage thereof, and fluosilicic acid is withdrawn as product from the sump of the first stage of the first absorption unit.
The overflow rates are controlled so that a continuous equilibrium of flow is achieved and the steady-state concen-trations of the fluosilicic acid circulating in the several absorption stages decrease from the first stage to the last.
This results in constant optimum conditions for the absorption of fluorine. Besides, the adjustment of a continuous equi-librium of flow minimizes the residence times of the acid in the several sumps so that an increased aging accompanied by a deposition of the separated SiO2 is avoided and a large propor-tion of the SiO2 is discharged with the product from the absorption units.
According to a preferred feature, the continuous feeding of water to the second stage of the second absorption unit is controlled so that the product acid withdrawn from the first stage of the first absorption unit has the desired fluo-silicic acid concentration. This enables a simple adjustment of the desired fluosilicic acid concentration in the product which is discharged.
According to the preferred feature, the bottoms of the sumps slope toward the inlets of the suction conduits leading to the acid-circulating pumps so that the silica gel and/or SiO2 which is separated during the formation of fluosilicic acid is kept in suspension and flows with the acid through all stages of the absorption units and is continuously discharged from the absorption system together with the fluosilicic acid product. In that case there is a turbulent flow of acid in the sumps and regions of stagnant liquid are avoided so that the deposition of SiO2 suspended in the liquid phase is further opposed.
:; :
, . .
.
1085~83 The invention will be described more fully and by way of examples with reference to the drawings.
The drawings are flow schemes of processes of concentrating dilute phosphoric acid in conjunction with a sulfuric acid contact process plant, which is fed in FIG. 1 with SO2-containing gases produced by the burning of sulfur, in FIG. 2 with SO2-containing gases from a roasting - plant and in FIG. 3 with gases having a high SO2 content and formed in a pyrometallurgical plant.
Raw phosphate is fed in conduit 1 and sulfuric acid is fed in conduit 2 to a wet-process plant 3. Dilute phosphoric acid is fed from a filter unit 4 in conduit 5 to an agitating vessel 6 and in a conduit 7 to the second concentrating stage %, which consists of an empty tower.
From the sump 9 of the second concentrating stage 8, phosphoric acid is fed by means of a pump 10 through conduit 11 into the heat exchanger 12 and is heated there and sprayed from conduit 13 into the second concentrating stage 8. Part of the phosphoric acid which has been collected in the sump 9 flows in conduit 14 into the sump 15 of the first concentrating stage 16, which consists of a vertical Venturi tube. Phospho-ric acid from the sump 15 is fed via conduit 17, pump 18, and conduit 19 into the heat exchanger 20 and is heated there and then sprayed from conduit 21 into the first concentrating `~ stage 16. Concentrated phosphoric acid is fed in conduit 22 to the agitating vessel 23.
The SO2-containing gases are fed in conduits 24 and 24a into the contact process tower 25, in which the gases are catalytically reacted in known manner. From the first contacting stage, the partly converted gases, which contain iO85583 S03, are fed in conduit 26 to the first heat exc~ange stage 27 and in conduit 28 into the second heat exchange stage 29. The cooled gases which contain S03 are fed in conduit 30 to the interstage absorber 31, in which a large part of the S03 is removed by a treatment with sulfuric acid. The gases which contain the residual S02 are fed in conduit 32 to the first heat exchange stage 27 and are heated there to the operating temperature of the next contacting stage and are then fed in conduit 33 to the second contacting stage of the contact process tower 25, in which their conversion is completed in known manner. The converted gases which contain S03 are fed in conduit 34 to a heat exchanger 35 and are cooled therein and are then fed in conduit 36 to the final absorber 37, in which the S03 is removed from the gases by a treatment with sulfuric acid. The end gases from the contact process plant are fed in conduit 38 to the second heat exchange stage 29, in which they are heated by a heat exchange with the S03-contain-ing gases, and are then fed in conduit 39 to a blower 40, which is supplied with air through filter 41 and conduit 42.
In accordance with Fig. 3, filtered air is first heated in the second heat exchange stage 35a in a heat exchange with the S03-containing gases which are fed to the final absorber 37. The heated gas mixture is fed in conduit 43 to the first concentrating stage 16 in which the gas mixture and the concurrently sprayed phosphoric acid are cooled by an adiabatic evaporation of water and most of the concentrated phosphoric acid is collected in the sump 15 whereas the qas which has been enriched with water vapor is ~ed to the second concentrating stage 8, in which it rises in a countercurrent to the sprayed phosphoric acid. This results in a further adiabatic evaporation of water to cool the phosphoric acid which is then collected in the sump 9.
_ g _ The exhaust gas from the concentrating unit contains water vapor and fluorine compounds and is fed in conduit 44 to the first absorption unit 45 and in said unit is treated in the first stage 45a, consisting of a vertical Venturi tube, with concurrently flowing fluosilicic acid and in the second stage 45b with countercurrently flowing fluosilicic acid.
These treatments are correspondingly repeated in the second absorption unit 46. After the removal of most of the fluorine compounds, the gas is fed into the atmosphere through conduit 47.
Water is fed in conduit 48 to the acid which circulates in the second stage 46b of the second absorption unit 46. In conduit 49, the fluosilicic acid which has been formed is withdrawn from the acid circulated in the first stage 46a of the second absorption unit 46 and is then added to the acid which circu-lates in the second stage 45b of the first absorption unit 45.
The entire fluosilicic acid product is withdrawn in conduit 50 from the acid circulating in the first absorption stage 45a of the first absorption unit 45.
The phosphoric acid is heated in the heat exchangers 12 and 20 by the sulfuric acid which is fed to the heat exchan-gers 12 and 20 in conduits 51 and 52, respectively, and when cooled by the heat exchange is returned to the absorbers 31 and 37 in conduits 53 and 54, respectively.
The SO2-containing gases are produced in a sulfur-burning furnace 55a, a fluidized-bed roasting furnace 55b or a flame cyclone reactor 55c. The hot gases which contain SO2 are cooled in a waste heat boiler 56. The heat which has been removed is used to produce steam. In accordance with Fig. 1, the cooled gases which contain SO2 are directly fed to the contact process tower 25 in conduit 24. In accordance with Figs. 2 and 3, the cooled gas which contains SO2 is purified and dried in known manner and is then heated to the operating ~085583 temperature of the first contacting tray by the heat which is released in the contact process tower as a result of the cata-lytic oxidation of SO2 to SO3. This heat is used to produce steam in accordance with Fig. 1. In all cases, the air required to burn sulfur and to oxidize SO2 is dried before.
Examples In all cases, the sulfuric acid contact process plant is designed for a production capacity of 1500 (metric) tons of H2SO4, calculated as 100% H2SO4, per day.
; 10 The conditions which are obtained at the positions indicated by the reference numbers of Figs. 1 to 3 will now be indicated.
;' .
Position Unit Fig.l Fig.2 Fig.3 1 Raw phosphate feed rate t/h 70.4 70-4 70-4 P2O5 content % by weight 34 34 34 1~ . . . _
2 Sulfuric acid (calculated as 100~ H2SO4 t/h 62.5 62.5 62.5 7 Fresh dilute ~ phosphoric acid t/h 77.6 83.3 80.4 Z P2O5 content % by weight 29 27 28 22 Concentrated phosphoric acid rate t/h 41.7 41.7 41.7 P2O5 content % by weight 54 54 54 . ~
H2SiF discharge rate 6 t/h 33.4 33-4 33-4 l~2Si~6 contcnt % by weight 20 20 20 48 Water feed rate t/h 29 29 29 .:
24 Gas flow rate standard 145484 175500 102000 m /h S2 content % by vol. 10 8 14 Position ~nit Fig.l Fig.2 Fig.3 38 Gas flow rate standard 124375 154416 80453 m3/h Gas temperature C 140 140 140 39 Gas temperature C 254 235 305 _ 42 Air flow rate standard (calculated as 3 dry air) m /h 50866 15590 89548 Air temperature C 20 20 165 . 43 Gas flow rate standard 170000 170000 170000 (calculated as 2 dry gas) m /h Gas temperature C 184 215 231 . .
I 44 Gas temperature C 75 75 75 Water vapor3g/standard content m of dry gas 188 224 209 44 Fluorine 3g/standard 5.2 5.2 5.2 content m of dry gas 47 Gas flow ratestandard m3 170000 170000 170000 (calculated as 3 dry gas) m /h Gas temperature C 63 63 63 Water vapor3g/standard 240 240 240 contentm of dry gas 21 P2O5 content % by weight 54 54 54 TemperatureC. 85 85 85 - ,:
19 Phosphoric acid O
temperature C 75 75 75 :
13 P2O5 content % by weight 41 39 40 :~ Temperature C 80 80 80 '.
Position Unit Fig.l Fig.2 Fig.3 - 11 Phosphoric acid C 71 71 71 temperature 51 H2SO4 content % by weight 98.5 98.5 98.5 Temperature C 140 140 140 53 Temperature C 111 111 111 52 H2O4 content % by weight 98.5 98.5 98.5 Temperature C 140 140 140 54 Temperature C 121 121 121 -The advantages afforded by the invention reside mainly in that dilute phosphoric acid can be concentrated without a need for primary energy or steam and in such a manner that surplus heat from a sulfuric acid contact process plant can be economically utilized with a low expenditure.
The operating costs of the combined system are low because primary energy or expensive steam is not required for concen-trating the dilute phosphoric acid and costs involved in theextraction of surplus heat from the absorption systems of the contact process plant are saved. Besides, the end gas from the contact process plant is purified once more without an additional expenditure. The fluorine constituents of the raw phosphoric acid which is to be concentrated are removed to a very high degree in the course-of the concentrating treatment and are recovered as a usable fluosilicic acid in a succeeding unit for absorbing the fluorine compounds. Whereas the high-temperature heat which becomes available in the production of the SO2-containing gases and in the catalytic reaction in the contact process plant is usually employed to produce steam for use in the process of concentrating the phosphoric acid which --becomes available, said heat is now freely available for a production of energy in as much as the heat is not required for heating initially cold gases which contain S02 to the operating temperature of the first contacting tray.
:
i : .
H2SiF discharge rate 6 t/h 33.4 33-4 33-4 l~2Si~6 contcnt % by weight 20 20 20 48 Water feed rate t/h 29 29 29 .:
24 Gas flow rate standard 145484 175500 102000 m /h S2 content % by vol. 10 8 14 Position ~nit Fig.l Fig.2 Fig.3 38 Gas flow rate standard 124375 154416 80453 m3/h Gas temperature C 140 140 140 39 Gas temperature C 254 235 305 _ 42 Air flow rate standard (calculated as 3 dry air) m /h 50866 15590 89548 Air temperature C 20 20 165 . 43 Gas flow rate standard 170000 170000 170000 (calculated as 2 dry gas) m /h Gas temperature C 184 215 231 . .
I 44 Gas temperature C 75 75 75 Water vapor3g/standard content m of dry gas 188 224 209 44 Fluorine 3g/standard 5.2 5.2 5.2 content m of dry gas 47 Gas flow ratestandard m3 170000 170000 170000 (calculated as 3 dry gas) m /h Gas temperature C 63 63 63 Water vapor3g/standard 240 240 240 contentm of dry gas 21 P2O5 content % by weight 54 54 54 TemperatureC. 85 85 85 - ,:
19 Phosphoric acid O
temperature C 75 75 75 :
13 P2O5 content % by weight 41 39 40 :~ Temperature C 80 80 80 '.
Position Unit Fig.l Fig.2 Fig.3 - 11 Phosphoric acid C 71 71 71 temperature 51 H2SO4 content % by weight 98.5 98.5 98.5 Temperature C 140 140 140 53 Temperature C 111 111 111 52 H2O4 content % by weight 98.5 98.5 98.5 Temperature C 140 140 140 54 Temperature C 121 121 121 -The advantages afforded by the invention reside mainly in that dilute phosphoric acid can be concentrated without a need for primary energy or steam and in such a manner that surplus heat from a sulfuric acid contact process plant can be economically utilized with a low expenditure.
The operating costs of the combined system are low because primary energy or expensive steam is not required for concen-trating the dilute phosphoric acid and costs involved in theextraction of surplus heat from the absorption systems of the contact process plant are saved. Besides, the end gas from the contact process plant is purified once more without an additional expenditure. The fluorine constituents of the raw phosphoric acid which is to be concentrated are removed to a very high degree in the course-of the concentrating treatment and are recovered as a usable fluosilicic acid in a succeeding unit for absorbing the fluorine compounds. Whereas the high-temperature heat which becomes available in the production of the SO2-containing gases and in the catalytic reaction in the contact process plant is usually employed to produce steam for use in the process of concentrating the phosphoric acid which --becomes available, said heat is now freely available for a production of energy in as much as the heat is not required for heating initially cold gases which contain S02 to the operating temperature of the first contacting tray.
:
i : .
Claims (16)
1. A process for concentrating dilute phosphoric acid, in which dilute phosphoric acid is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas, characterized in that the dilute phospho-ric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circulated through two successive concentrating stages and in said stages is sprayed and directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to SO3 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption.
2. A process according to claim 1, characterized in that the dilute phosphoric acid is circulated, the fresh dilute phosphoric acid is fed to the second concentrating stage, the circulating acid is heated by the heat which is to be withdrawn from the sulfuric acid circulating through the interstage absorption system of the sulfuric acid contact process plant, the circulating phosphoric acid is sprayed into the second concentrating stage in a countercurrent to the rising gas mixture, part of the circulating acid is fed from the sump of the second concentrating stage into the sump of the first concentrating stage, the remaining part of the circulating acid is fed from the sump of the second concentrating stage to the acid circulating through the second concentrating stage, the acid circulating through the first concentrating stage is heated behind the sump thereof by means of the heat which is to be removed from the sulfuric acid circulating in the final absorption system and is then sprayed into the first concen-trating stage concurrently to the descending gases, and phosphoric acid of higher concentration is withdrawn from the acid which circulates through the first concentrating stage.
3. A process according to claim 1, characterized in that the acid is concentrated in the first concentrating stage in a vertical Venturi tube.
4. A process according to claims 1, 2 or 3, character-ized in that the acid circulating through the first concen-trating stage is heated by heat to be removed from the sulfuric acid which circulates in a high-temperature final absorption system.
5. A process according to claim 1, characterized in that the tail gas from the final absorption system of the sulfuric acid contact process plant is heated with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant, said heating being effected in a second heat exchange stage in the gas flow path, and air being admixed to the heated tail gas.
6. A process according to claim 1, characterized in that gases which have a high SO2 content and become available at a low temperature are processed in the sulfuric acid contact process plant and part of the gas mixture is heated in the final heat exchanger succeeding the last contacting tray.
7. A process according to claim 5, characterized in that the hot gases are fed to the first concentrating stage at a temperature of 70 to 250°C.
8. A process according to claim 7, characterized in that the hot gases are fed to the first concentrating stage at a temperature of 80 to 220°C.
9. A process according to claim 6, characterized in that the hot gases are fed to the first concentrating stage at a temperature of 100 to 280°C.
10. A process according to claim 9, characterized in that the hot gases are fed to the first concentrating stage at a temperature of 120 to 250°C.
11. A process according to claim 1, characterized in that the phosphoric acid is sprayed into the first concen-trating stage at a temperature of 60 to 100°C.
12. A process according to claim 11, characterized in that the phosphoric acid is sprayed into the first concen-trating stage at a temperature of 75 to 90°C.
13. A process according to claim 1, characterized in that the fluorine constituents are absorbed in an absorption unit in two successive stages, fluosilicic acid is injected in the first stage of the absorption unit into a vertical Venturi tube absorber to flow concurrently with the gases, fluosilicic acid is injected in the second stage into an empty tower to flow in a countercurrent to the gases, and a considerable part of the inside surfaces of the absorption unit is contacted by the injected fluosilicic acid.
14. A process according to claim 13, characterized in that the fluorine constituents are absorbed in two series-connected absorption units, water is continuously fed to the acid which circulates in the second stage of the second absorp-tion unit, acid from the sump of the second stage of the second absorption unit flows over into the sump of the second stage thereof, acid from the sump of the first stage of the second absorption unit flows over into the sump of the second stage of the first absorption unit, acid from the sump of the second stage of the first absorption unit flows over into the sump of the first stage thereof, and fluosilicic acid is withdrawn as product from the sump of the first stage of the first absorption unit.
15. A process according to claim 14, characterized in that the continuous feeding of water to the second stage of the second absorption unit is controlled so that the product acid withdrawn from the first stage of the first absorption unit has the desired fluosilicic acid concentration.
16. A process according to claims 14 or 15, character-ized in that the bottoms of the sumps slope toward the inlets of the suction conduits leading to the acid-circulating pumps so that the silica gel and/or SiO2 which is separated during the formation of fluosilicic acid is kept in suspension and flows with the acid through all stages of the absorption units and is continuously discharged from the absorption system together with the fluosilicic acid product.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2700009.5 | 1977-01-03 | ||
| DE2700009A DE2700009C3 (en) | 1977-01-03 | 1977-01-03 | Process for the concentration of dilute phosphoric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1085583A true CA1085583A (en) | 1980-09-16 |
Family
ID=5998041
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,197A Expired CA1085583A (en) | 1977-01-03 | 1977-12-30 | Process of concentrating dilute phosphoric acid |
Country Status (15)
| Country | Link |
|---|---|
| JP (1) | JPS5385797A (en) |
| AU (1) | AU513920B2 (en) |
| BE (1) | BE862580A (en) |
| BR (1) | BR7800006A (en) |
| CA (1) | CA1085583A (en) |
| DE (1) | DE2700009C3 (en) |
| ES (1) | ES465669A1 (en) |
| FI (1) | FI773907A (en) |
| FR (1) | FR2376071A1 (en) |
| GB (1) | GB1589945A (en) |
| IT (1) | IT1090383B (en) |
| NO (1) | NO774454L (en) |
| PL (1) | PL203780A1 (en) |
| SE (1) | SE7800045L (en) |
| ZA (1) | ZA777069B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2824010A1 (en) * | 1978-06-01 | 1979-12-13 | Metallgesellschaft Ag | METHOD FOR CONCENTRATING DILUSED PHOSPHORIC ACID |
| CA1146722A (en) * | 1981-04-10 | 1983-05-24 | Gordon M. Cameron | Energy recovery method and system for combined sulphuric and phosphoric acid manufacturing plant |
| DE3232446A1 (en) * | 1982-08-12 | 1984-02-16 | Metallgesellschaft Ag, 6000 Frankfurt | METHOD FOR PRODUCING SULFURIC ACID |
| US4576813A (en) * | 1983-07-05 | 1986-03-18 | Monsanto Company | Heat recovery from concentrated sulfuric acid |
| US4670242A (en) * | 1984-11-09 | 1987-06-02 | Monsanto Company | Heat recovery from concentrated sulfuric acid |
| CN103523763B (en) * | 2013-10-11 | 2017-04-05 | 徐州天正活性炭厂 | A kind of energy saver and method of rapid concentration of dilute phosphoric acid |
| CN104445118B (en) * | 2014-12-01 | 2016-08-31 | 四川玖长科技有限公司 | Technique for phosphoric acid processed from the kiln discharge flue gas of kiln-process phosphoric acid technique |
| CN109941979A (en) * | 2019-04-30 | 2019-06-28 | 舒爱桦 | A kind of technique of concentrated fertilizer phosphoric acid food grade phosphoric acid |
-
1977
- 1977-01-03 DE DE2700009A patent/DE2700009C3/en not_active Expired
- 1977-11-28 ZA ZA00777069A patent/ZA777069B/en unknown
- 1977-12-13 AU AU31501/77A patent/AU513920B2/en not_active Expired
- 1977-12-13 GB GB51891/77A patent/GB1589945A/en not_active Expired
- 1977-12-21 FR FR7738599A patent/FR2376071A1/en not_active Withdrawn
- 1977-12-22 FI FI773907A patent/FI773907A/en not_active Application Discontinuation
- 1977-12-23 NO NO774454A patent/NO774454L/en unknown
- 1977-12-29 JP JP15861077A patent/JPS5385797A/en active Pending
- 1977-12-29 IT IT31377/77A patent/IT1090383B/en active
- 1977-12-30 BE BE6046295A patent/BE862580A/en unknown
- 1977-12-30 CA CA294,197A patent/CA1085583A/en not_active Expired
-
1978
- 1978-01-02 ES ES465669A patent/ES465669A1/en not_active Expired
- 1978-01-02 BR BR7800006A patent/BR7800006A/en unknown
- 1978-01-02 SE SE7800045A patent/SE7800045L/en unknown
- 1978-01-02 PL PL20378078A patent/PL203780A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU3150177A (en) | 1979-06-21 |
| BE862580A (en) | 1978-06-30 |
| ES465669A1 (en) | 1978-09-16 |
| GB1589945A (en) | 1981-05-20 |
| FR2376071A1 (en) | 1978-07-28 |
| PL203780A1 (en) | 1978-08-14 |
| NO774454L (en) | 1978-07-04 |
| DE2700009C3 (en) | 1979-11-15 |
| BR7800006A (en) | 1978-08-15 |
| AU513920B2 (en) | 1981-01-15 |
| SE7800045L (en) | 1978-07-04 |
| DE2700009A1 (en) | 1978-07-06 |
| DE2700009B2 (en) | 1979-03-29 |
| IT1090383B (en) | 1985-06-26 |
| ZA777069B (en) | 1978-09-27 |
| JPS5385797A (en) | 1978-07-28 |
| FI773907A (en) | 1978-07-04 |
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