CA2802885A1 - Efficient system for producing sulfuric acid using a spray tower - Google Patents
Efficient system for producing sulfuric acid using a spray tower Download PDFInfo
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- CA2802885A1 CA2802885A1 CA2802885A CA2802885A CA2802885A1 CA 2802885 A1 CA2802885 A1 CA 2802885A1 CA 2802885 A CA2802885 A CA 2802885A CA 2802885 A CA2802885 A CA 2802885A CA 2802885 A1 CA2802885 A1 CA 2802885A1
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- spray
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- 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
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/80—Apparatus
- C01B17/806—Absorbers; Heat exchangers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
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- Inorganic Chemistry (AREA)
- Gas Separation By Absorption (AREA)
- Treating Waste Gases (AREA)
Abstract
An energy efficient system is disclosed for producing sulphuric acid that employs an intermediate absorption subsystem comprising a spray tower, an energy recovery subsystem, and an intermediate absorption tower comprising a packed bed.
Description
Chemetics008-CA
EFFICIENT SYSTEM FOR PRODUCING SULFURIC ACID USING A SPRAY TOWER
Technical Field The present invention pertains to energy efficient systems for producing sulphuric acid. In particular, it relates to systems using spray tower absorption.
Background Sulfuric acid is one of the most produced commodity chemicals in the world and is widely used in the chemical industry and commercial products. Generally, production methods involve converting sulphur dioxide first to sulphur trioxide which is then later converted to sulphuric acid. In 1831, P. Phillips developed the contact process which is used to produce most of today's supply of sulphuric acid.
The basics of the contact process involve obtaining a supply of sulphur dioxide (e.g. commonly obtained by burning sulphur) and then oxidizing the sulphur dioxide with oxygen in the presence of a catalyst (typically vanadium oxide) to accelerate the reaction in order to produce sulphur trioxide. The reaction is reversible and exothermic and it is important to appropriately control the temperature of the gases over the catalyst in order to achieve the desired conversion without damaging the contact apparatus which comprises the catalyst.
Then, the produced sulphur trioxide is absorbed into a concentrated sulphuric acid solution to form oleum, which is then diluted to produce another concentrated sulphuric acid solution.
This avoids the consequences of directly dissolving sulphur trioxide into water which is a highly exothermic reaction.
While the fundamentals of the contact process are relatively simple, it is desirable to maximize the conversion of sulfur dioxide into sulphuric acid. Thus, modern plants for producing sulphuric acid often involve more than one absorption stage to improve conversion and absorption.
Commonly, a double absorption process is employed in which process gases are subjected to two contact and absorption stages in series, (i.e. a first catalytic conversion and subsequent absorption step followed by a second catalytic conversion and absorption step). Details regarding the conventional options available and preferences for sulphuric acid production and the contact process are well known and can be found for instance in "Handbook of Sulfuric Acid Manufacturing", Douglas Louie, ISBN 0-9738992-0-4, 2005, published by DKL Engineering. Inc., Ontario, Canada.
ChemeticsOO8-CA
It is also desirable to minimize the energy requirement in the industrial production of sulphuric acid. In the numerous processes involved, there are substantial sources and requirements for heat. Energy efficiency can desirably be improved with the use of complex heat exchanger arrangements to maximize energy recovery.
Many years ago in US4576813, Monsanto disclosed a method and apparatus for significantly improving the efficiency of plants that used the double absorption process. A heat recovery system was disclosed that raised the temperature at which the absorption of sulphur trioxide takes place in the intermediate adsorption stage. By operating at these higher temperatures, the heat of absorption and dilution can be used to generate useful steam instead of rejecting the heat to a cooling tower. Overall efficiency could thus be substantially improved. In the apparatus, the conventional intermediate absorption tower is replaced with a two-stage absorbing tower, a recirculating pump, a heat exchanger, and a boiler. The two-stage absorbing tower comprises two packed beds in series within the same absorption tower. However, at these higher temperatures, prior art materials of construction were subject to substantially greater corrosion rates. In order to enable the method commercially, both greater sulphuric acid concentrations and different, specially selected construction alloys had to be employed in order that the apparatus was suitably resistant to corrosion at these greater temperatures.
A disadvantage of the above approach however is that the function of the previous conventional intermediate absorption tower is integrated into the two-stage absorbing tower of the energy efficient system. In the event that a problem occurs with the heat recovery subsystem during operation, the entire plant may now need to be shutdown for repair.
Outotec has produced sulphuric acid plants that employ a similar heat recovery method but different apparatus to implement it. In the Outotec system, a combined quench venturi and packed bed absorber is employed for the intermediate absorption stage instead of a single, two-stage absorption tower. An advantage of this approach is that the quench venturi and heat exchanger subsystem can be bypassed in the event of a problem during operation. This allows the remaining packed bed absorber to operate as a conventional intermediate absorption tower (without improved heat recovery of course) and thus the sulphuric acid plant can at least continue to operate in the event of a problem with the heat recovery subsystem. A disadvantage of using a quench venturi however is that significant energy is required to operate it and provide the pressure drop therein.
EFFICIENT SYSTEM FOR PRODUCING SULFURIC ACID USING A SPRAY TOWER
Technical Field The present invention pertains to energy efficient systems for producing sulphuric acid. In particular, it relates to systems using spray tower absorption.
Background Sulfuric acid is one of the most produced commodity chemicals in the world and is widely used in the chemical industry and commercial products. Generally, production methods involve converting sulphur dioxide first to sulphur trioxide which is then later converted to sulphuric acid. In 1831, P. Phillips developed the contact process which is used to produce most of today's supply of sulphuric acid.
The basics of the contact process involve obtaining a supply of sulphur dioxide (e.g. commonly obtained by burning sulphur) and then oxidizing the sulphur dioxide with oxygen in the presence of a catalyst (typically vanadium oxide) to accelerate the reaction in order to produce sulphur trioxide. The reaction is reversible and exothermic and it is important to appropriately control the temperature of the gases over the catalyst in order to achieve the desired conversion without damaging the contact apparatus which comprises the catalyst.
Then, the produced sulphur trioxide is absorbed into a concentrated sulphuric acid solution to form oleum, which is then diluted to produce another concentrated sulphuric acid solution.
This avoids the consequences of directly dissolving sulphur trioxide into water which is a highly exothermic reaction.
While the fundamentals of the contact process are relatively simple, it is desirable to maximize the conversion of sulfur dioxide into sulphuric acid. Thus, modern plants for producing sulphuric acid often involve more than one absorption stage to improve conversion and absorption.
Commonly, a double absorption process is employed in which process gases are subjected to two contact and absorption stages in series, (i.e. a first catalytic conversion and subsequent absorption step followed by a second catalytic conversion and absorption step). Details regarding the conventional options available and preferences for sulphuric acid production and the contact process are well known and can be found for instance in "Handbook of Sulfuric Acid Manufacturing", Douglas Louie, ISBN 0-9738992-0-4, 2005, published by DKL Engineering. Inc., Ontario, Canada.
ChemeticsOO8-CA
It is also desirable to minimize the energy requirement in the industrial production of sulphuric acid. In the numerous processes involved, there are substantial sources and requirements for heat. Energy efficiency can desirably be improved with the use of complex heat exchanger arrangements to maximize energy recovery.
Many years ago in US4576813, Monsanto disclosed a method and apparatus for significantly improving the efficiency of plants that used the double absorption process. A heat recovery system was disclosed that raised the temperature at which the absorption of sulphur trioxide takes place in the intermediate adsorption stage. By operating at these higher temperatures, the heat of absorption and dilution can be used to generate useful steam instead of rejecting the heat to a cooling tower. Overall efficiency could thus be substantially improved. In the apparatus, the conventional intermediate absorption tower is replaced with a two-stage absorbing tower, a recirculating pump, a heat exchanger, and a boiler. The two-stage absorbing tower comprises two packed beds in series within the same absorption tower. However, at these higher temperatures, prior art materials of construction were subject to substantially greater corrosion rates. In order to enable the method commercially, both greater sulphuric acid concentrations and different, specially selected construction alloys had to be employed in order that the apparatus was suitably resistant to corrosion at these greater temperatures.
A disadvantage of the above approach however is that the function of the previous conventional intermediate absorption tower is integrated into the two-stage absorbing tower of the energy efficient system. In the event that a problem occurs with the heat recovery subsystem during operation, the entire plant may now need to be shutdown for repair.
Outotec has produced sulphuric acid plants that employ a similar heat recovery method but different apparatus to implement it. In the Outotec system, a combined quench venturi and packed bed absorber is employed for the intermediate absorption stage instead of a single, two-stage absorption tower. An advantage of this approach is that the quench venturi and heat exchanger subsystem can be bypassed in the event of a problem during operation. This allows the remaining packed bed absorber to operate as a conventional intermediate absorption tower (without improved heat recovery of course) and thus the sulphuric acid plant can at least continue to operate in the event of a problem with the heat recovery subsystem. A disadvantage of using a quench venturi however is that significant energy is required to operate it and provide the pressure drop therein.
Chemetics008-CA
As mentioned, specially selected metal alloys are required to provide acceptable corrosion resistance in such improved efficiency, heat recovery subsystems due to the higher temperatures and different sulphuric acid concentrations involved. Zeron 100 (UNS S32760) is an alloy promoted for use in sulphuric acid manufacturing applications at elevated temperatures up to 200 C.
There remains however a desire for yet further improvements in energy efficiency in the industrial production of sulphuric acid. The present invention addresses this desire and provides other benefits as disclosed below.
Summary The present invention provides for an energy efficient system for producing sulphuric acid using a co-current, open spray tower preferably with multiple spray levels. The absorption of SO3 is increased since each level of spray nozzles provides the same driving force for absorption (since the absorbing acid temperature and concentration is essentially the same at each level). This compares favorably to use of a packed tower or a quench venturi scrubber where SO3 absorption is diminished as the gas stream travels through the apparatus due to increasing absorbing acid temperature and concentration at the latter stages of absorption.
Specifically, the invention includes an intermediate absorption subsystem for a sulfuric acid production system which comprises a co-current open spray tower, an energy recovery subsystem, and an intermediate absorption tower. The co-current open spray tower comprises a top inlet for a gas stream comprising SO2 and SO3, a lower outlet for the gas stream after spray absorption, at least one spray inlet, at least one spray nozzle within the spray tower and connected to the spray inlet, an inlet for dilution water, and a bottom outlet for sulfuric acid liquid. The energy recovery subsystem comprises a pump and a heat exchanger arranged in series, in which the bottom outlet of the spray tower is fluidly connected to an inlet of the first side of the heat exchanger, the spray inlet of the spray tower is fluidly connected to an outlet of the first side of the heat exchanger, a water supply is fluidly connected to an inlet of the second side of the heat exchanger, and the outlet of the second side of the heat exchanger is a steam output. The energy recovery subsystem typically generates low pressure steam, for instance at about 7 barg. The intermediate absorption tower comprises a lower inlet for the gas stream connected to the spray tower lower outlet, an upper outlet for the gas stream after packed bed absorption, a distributor inlet, a liquid distributor within the intermediate absorption tower, a packed bed within the intermediate absorption Chemetics008-CA
tower and below the liquid distributor, a bottom outlet for sulfuric acid liquid, and a pump fluidly connected to the bottom outlet of the intermediate absorption tower and to the distributor inlet.
The spray tower in the intermediate absorption subsystem preferably comprises a plurality of spray nozzles on at least two levels, for example three levels. The spray nozzles desirably produce a spray less than 300 micron in average size, such that the droplets are of relatively high surface area for better SO3 absorption.
A disadvantage of employing a spray tower in such systems is the production of sub-micron mist.
However, this can be removed by high efficiency mist filter eliminators, e.g.
Brownian motion mist filters.
Thus, the intermediate absorption tower in the intermediate absorption subsystem can comprise a mist filter eliminator between the packed bed and the upper outlet for the gas stream after packed bed absorption.
As with other systems operating at higher temperatures in the intermediate adsorption stage, special corrosion resistant metal alloys are required in the heat exchanger in the energy recovery subsystem.
Suitable such corrosion resistant metal alloys include superduplex alloys such as alloys with UNS number S32760 or chromium-based austenitic alloys such as alloys with UNS number R20033.
The invention also includes complete double absorption systems for oxidizing sulfur dioxide to produce sulfuric acid. The first oxidation subsystem in such double absorption systems comprises contact catalyst, the aforementioned intermediate absorption subsystem of the invention, a second oxidation subsystem comprising contact catalyst, and a final absorption tower.
The present invention offers the advantage that it can operate in a conventional mode when the energy recovery system is not operational (by bypassing the spray tower and energy recovery subsystem or by simply turning off the energy recovery subsystem pump), and thus the double absorption system can continue to produce sulphuric acid. It also offers the advantage of a low pressure drop requirement in the spray tower and thus requires less energy (i.e. is more energy efficient) than a quench venturi apparatus.
Brief Description of the Drawings Chemetics008-CA
Figure 1 shows a schematic of an intermediate absorption subsystem of the invention comprising a spray tower, an energy recovery system, and an intermediate absorption tower for a sulphuric acid production system.
Figure 2 shows a schematic of a double absorption system for producing sulphuric acid in which the system comprises the intermediate absorption subsystem of Figure 1.
Detailed Description Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising" and the like are to be construed in an open, inclusive sense. The words "a", "an", and the like are to be considered as meaning at least one and are not limited to just one.
In a numerical context, the word "about" is to be construed as meaning plus or minus 10%.
Figure 1 shows a schematic of an intermediate absorption subsystem of the invention for use in a sulphuric acid production system. As shown, intermediate absorption subsystem 1 includes open spray tower 2, energy recovery subsystem 9, and intermediate absorption tower 14. A hot (e.g.
- 200 C) gas stream comprising SO3 and SO2 is directed into top inlet 3 of spray tower 2. Therein, SO3 is absorbed by acid spray introduced co-currently at an appropriate temperature (e.g. -120 C) and concentration (e.g. 98.5 wt %). As shown, a cooler acid supply for the spray is provided at spray inlet 5 and directed to a plurality of spray nozzles 6a, 6b, 6c. The nozzles here are located at three different levels in spray tower 2. Nozzles at the same level have been denoted with the same identifying numeral (i.e.
either 6a, 6b, or 6c). The spray nozzles desirably produce a spray less than 300 micron in average size, such that the droplets are of relatively high surface area for better SO3 absorption.
Sulfuric acid comprising the absorbed SO3 falls to the bottom of spray tower 2 at a temperature ,.. 170 C
and is diluted appropriately with dilution water provided at inlet 7. This hot acid (e.g. - 170 C) is then pumped via pump 11 from bottom outlet 8 to heat exchanger 10 in energy recovery subsystem 9. Hot acid is directed to inlet 12a of the first side of heat exchanger 10, whereupon heat is exchanged with a cold water supply provided to inlet 13a of the second side of heat exchanger 10.
The cooled acid is now ready for use as absorption media and is then directed from outlet 12b of the first side of heat exchanger 10 to spray inlet 5. The water on the second side has now been heated sufficiently to become low pressure steam and thus outlet 13b of the second side of heat exchanger 10 is a steam output which can be used Chemetics008-CA
elsewhere as desired. Heat exchanger 10 is made of a special corrosion resistant metal alloy such as superduplex alloy UNS number S32760 or chromium-based austenitic alloy UNS
number R20033.
In spray tower 2, the somewhat cooler (e.g. - 150 C) gas stream comprising SO2 and unabsorbed SO3 exits at lower outlet 4 and is directed to lower inlet 15 of intermediate absorption tower 14 and through packed bed 19 in which additional SO3 is absorbed. To accomplish this, absorbing acid is provided at distributor inlet 17 to liquid distributor 18 which distributes the acid over packed bed 19. Sulfuric acid comprising the absorbed SO3 falls to the bottom of intermediate absorption tower 14 to become the supply of absorbing acid used over the packed bed. (Dilution water can be added as necessary or desired, but is not shown in Figure 1.) This liquid acid is pumped via pump 21 from bottom outlet 20 to distributor inlet 17. A significant amount of sub-micron mist can be created when using a spray tower and so intermediate absorption tower 14 is equipped with high efficiency Brownian motion mist filter eliminator 22. After absorption, the gas stream exits intermediate absorption tower 14 at upper outlet 16.
Figure 2 shows a schematic of an exemplary double absorption system 23 for producing sulphuric acid.
Therein, system 23 comprises a first oxidation subsystem comprising contact catalyst, intermediate absorption subsystem 1 of Figure 1, a second oxidation subsystem comprising contact catalyst, and a final absorption tower. In this complex system, the first oxidation stage occurs in catalyst beds 24-26 which is followed by intermediate absorption and then the second oxidation stage occurs in bed 27 which is followed by final absorption. Hence, the first oxidation subsystem comprises catalyst beds 24-26 and the second oxidation subsystem comprises catalyst bed 27.
Double absorption system 23 in Figure 2 comprises four separate contact catalyst beds 24, 25, 26, and 27, each containing contact catalyst mass. System 23 also comprises intermediate absorption subsystem 1 (comprising spray tower 2, energy recovery subsystem 9 and intermediate absorption tower 14) and final absorption tower 28, and output stack 30. System 23 also comprises four separate heat exchangers in order to obtain a high conversion efficiency in the overall process. These heat exchangers are denoted as cold exchanger 32, hot exchanger 33, inter reheat exchanger 34, and cold reheat exchanger 35. To avoid clutter in Figure 2, the separating structures within those heat exchangers shown and their various inlets and outlets have not been called out. Instead, arrows are provided on all the interconnecting lines to show the flow of the gas stream being processed. The inlets and outlets can thus be readily inferred by the direction of the arrows.
As mentioned, specially selected metal alloys are required to provide acceptable corrosion resistance in such improved efficiency, heat recovery subsystems due to the higher temperatures and different sulphuric acid concentrations involved. Zeron 100 (UNS S32760) is an alloy promoted for use in sulphuric acid manufacturing applications at elevated temperatures up to 200 C.
There remains however a desire for yet further improvements in energy efficiency in the industrial production of sulphuric acid. The present invention addresses this desire and provides other benefits as disclosed below.
Summary The present invention provides for an energy efficient system for producing sulphuric acid using a co-current, open spray tower preferably with multiple spray levels. The absorption of SO3 is increased since each level of spray nozzles provides the same driving force for absorption (since the absorbing acid temperature and concentration is essentially the same at each level). This compares favorably to use of a packed tower or a quench venturi scrubber where SO3 absorption is diminished as the gas stream travels through the apparatus due to increasing absorbing acid temperature and concentration at the latter stages of absorption.
Specifically, the invention includes an intermediate absorption subsystem for a sulfuric acid production system which comprises a co-current open spray tower, an energy recovery subsystem, and an intermediate absorption tower. The co-current open spray tower comprises a top inlet for a gas stream comprising SO2 and SO3, a lower outlet for the gas stream after spray absorption, at least one spray inlet, at least one spray nozzle within the spray tower and connected to the spray inlet, an inlet for dilution water, and a bottom outlet for sulfuric acid liquid. The energy recovery subsystem comprises a pump and a heat exchanger arranged in series, in which the bottom outlet of the spray tower is fluidly connected to an inlet of the first side of the heat exchanger, the spray inlet of the spray tower is fluidly connected to an outlet of the first side of the heat exchanger, a water supply is fluidly connected to an inlet of the second side of the heat exchanger, and the outlet of the second side of the heat exchanger is a steam output. The energy recovery subsystem typically generates low pressure steam, for instance at about 7 barg. The intermediate absorption tower comprises a lower inlet for the gas stream connected to the spray tower lower outlet, an upper outlet for the gas stream after packed bed absorption, a distributor inlet, a liquid distributor within the intermediate absorption tower, a packed bed within the intermediate absorption Chemetics008-CA
tower and below the liquid distributor, a bottom outlet for sulfuric acid liquid, and a pump fluidly connected to the bottom outlet of the intermediate absorption tower and to the distributor inlet.
The spray tower in the intermediate absorption subsystem preferably comprises a plurality of spray nozzles on at least two levels, for example three levels. The spray nozzles desirably produce a spray less than 300 micron in average size, such that the droplets are of relatively high surface area for better SO3 absorption.
A disadvantage of employing a spray tower in such systems is the production of sub-micron mist.
However, this can be removed by high efficiency mist filter eliminators, e.g.
Brownian motion mist filters.
Thus, the intermediate absorption tower in the intermediate absorption subsystem can comprise a mist filter eliminator between the packed bed and the upper outlet for the gas stream after packed bed absorption.
As with other systems operating at higher temperatures in the intermediate adsorption stage, special corrosion resistant metal alloys are required in the heat exchanger in the energy recovery subsystem.
Suitable such corrosion resistant metal alloys include superduplex alloys such as alloys with UNS number S32760 or chromium-based austenitic alloys such as alloys with UNS number R20033.
The invention also includes complete double absorption systems for oxidizing sulfur dioxide to produce sulfuric acid. The first oxidation subsystem in such double absorption systems comprises contact catalyst, the aforementioned intermediate absorption subsystem of the invention, a second oxidation subsystem comprising contact catalyst, and a final absorption tower.
The present invention offers the advantage that it can operate in a conventional mode when the energy recovery system is not operational (by bypassing the spray tower and energy recovery subsystem or by simply turning off the energy recovery subsystem pump), and thus the double absorption system can continue to produce sulphuric acid. It also offers the advantage of a low pressure drop requirement in the spray tower and thus requires less energy (i.e. is more energy efficient) than a quench venturi apparatus.
Brief Description of the Drawings Chemetics008-CA
Figure 1 shows a schematic of an intermediate absorption subsystem of the invention comprising a spray tower, an energy recovery system, and an intermediate absorption tower for a sulphuric acid production system.
Figure 2 shows a schematic of a double absorption system for producing sulphuric acid in which the system comprises the intermediate absorption subsystem of Figure 1.
Detailed Description Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising" and the like are to be construed in an open, inclusive sense. The words "a", "an", and the like are to be considered as meaning at least one and are not limited to just one.
In a numerical context, the word "about" is to be construed as meaning plus or minus 10%.
Figure 1 shows a schematic of an intermediate absorption subsystem of the invention for use in a sulphuric acid production system. As shown, intermediate absorption subsystem 1 includes open spray tower 2, energy recovery subsystem 9, and intermediate absorption tower 14. A hot (e.g.
- 200 C) gas stream comprising SO3 and SO2 is directed into top inlet 3 of spray tower 2. Therein, SO3 is absorbed by acid spray introduced co-currently at an appropriate temperature (e.g. -120 C) and concentration (e.g. 98.5 wt %). As shown, a cooler acid supply for the spray is provided at spray inlet 5 and directed to a plurality of spray nozzles 6a, 6b, 6c. The nozzles here are located at three different levels in spray tower 2. Nozzles at the same level have been denoted with the same identifying numeral (i.e.
either 6a, 6b, or 6c). The spray nozzles desirably produce a spray less than 300 micron in average size, such that the droplets are of relatively high surface area for better SO3 absorption.
Sulfuric acid comprising the absorbed SO3 falls to the bottom of spray tower 2 at a temperature ,.. 170 C
and is diluted appropriately with dilution water provided at inlet 7. This hot acid (e.g. - 170 C) is then pumped via pump 11 from bottom outlet 8 to heat exchanger 10 in energy recovery subsystem 9. Hot acid is directed to inlet 12a of the first side of heat exchanger 10, whereupon heat is exchanged with a cold water supply provided to inlet 13a of the second side of heat exchanger 10.
The cooled acid is now ready for use as absorption media and is then directed from outlet 12b of the first side of heat exchanger 10 to spray inlet 5. The water on the second side has now been heated sufficiently to become low pressure steam and thus outlet 13b of the second side of heat exchanger 10 is a steam output which can be used Chemetics008-CA
elsewhere as desired. Heat exchanger 10 is made of a special corrosion resistant metal alloy such as superduplex alloy UNS number S32760 or chromium-based austenitic alloy UNS
number R20033.
In spray tower 2, the somewhat cooler (e.g. - 150 C) gas stream comprising SO2 and unabsorbed SO3 exits at lower outlet 4 and is directed to lower inlet 15 of intermediate absorption tower 14 and through packed bed 19 in which additional SO3 is absorbed. To accomplish this, absorbing acid is provided at distributor inlet 17 to liquid distributor 18 which distributes the acid over packed bed 19. Sulfuric acid comprising the absorbed SO3 falls to the bottom of intermediate absorption tower 14 to become the supply of absorbing acid used over the packed bed. (Dilution water can be added as necessary or desired, but is not shown in Figure 1.) This liquid acid is pumped via pump 21 from bottom outlet 20 to distributor inlet 17. A significant amount of sub-micron mist can be created when using a spray tower and so intermediate absorption tower 14 is equipped with high efficiency Brownian motion mist filter eliminator 22. After absorption, the gas stream exits intermediate absorption tower 14 at upper outlet 16.
Figure 2 shows a schematic of an exemplary double absorption system 23 for producing sulphuric acid.
Therein, system 23 comprises a first oxidation subsystem comprising contact catalyst, intermediate absorption subsystem 1 of Figure 1, a second oxidation subsystem comprising contact catalyst, and a final absorption tower. In this complex system, the first oxidation stage occurs in catalyst beds 24-26 which is followed by intermediate absorption and then the second oxidation stage occurs in bed 27 which is followed by final absorption. Hence, the first oxidation subsystem comprises catalyst beds 24-26 and the second oxidation subsystem comprises catalyst bed 27.
Double absorption system 23 in Figure 2 comprises four separate contact catalyst beds 24, 25, 26, and 27, each containing contact catalyst mass. System 23 also comprises intermediate absorption subsystem 1 (comprising spray tower 2, energy recovery subsystem 9 and intermediate absorption tower 14) and final absorption tower 28, and output stack 30. System 23 also comprises four separate heat exchangers in order to obtain a high conversion efficiency in the overall process. These heat exchangers are denoted as cold exchanger 32, hot exchanger 33, inter reheat exchanger 34, and cold reheat exchanger 35. To avoid clutter in Figure 2, the separating structures within those heat exchangers shown and their various inlets and outlets have not been called out. Instead, arrows are provided on all the interconnecting lines to show the flow of the gas stream being processed. The inlets and outlets can thus be readily inferred by the direction of the arrows.
Chemetics008-CA
In brief then, the double absorption process in Figure 2 proceeds as follows.
A gas stream comprising sulfur dioxide and oxygen is provided at a supply temperature to cold exchanger 32 where heat is exchanged with the hotter gas stream at the fourth catalyst bed outlet temperature. The gas stream exits cold exchanger 32 and is directed to hot exchanger 33 where heat is exchanged with the hotter gas stream at the first catalyst bed outlet temperature. The gas stream exits hot exchanger 33 at the first catalyst inlet temperature and is directed to first catalyst bed 24. A first oxidation of SO2 in the gas stream takes place over catalyst bed 24 and the exiting gas stream is now at the hotter first catalyst bed outlet temperature.
After exchanging heat in hot exchanger 33, the gas stream exits at the second catalyst bed inlet temperature and is directed to second catalyst bed 25. A second oxidation of SO2 in the gas stream takes place over catalyst bed 25 and the exiting gas stream is now at the hotter second catalyst bed outlet temperature.
The gas stream at the second catalyst bed outlet temperature is directed to inter reheat exchanger 34 where heat is exchanged with the colder gas stream exiting cold reheat exchanger 35.
The gas stream then exits inter reheat exchanger 34 at the third catalyst bed inlet temperature and is directed to third catalyst bed 26.
A third oxidation of SO2 in the gas stream takes place over catalyst bed 26 and the exiting gas stream is now at the hotter third catalyst bed outlet temperature.
The gas stream at the third catalyst bed outlet temperature is directed to cold reheat exchanger 35 where heat is exchanged with the colder gas stream coming from intermediate absorption subsystem 1. The gas stream then exits cold reheat exchanger 35 at the intermediate absorption subsystem inlet temperature and is directed to top inlet 3 of spray tower 2 in intermediate absorption subsystem 1 in which a first intermediate absorption of SO3 from the gas stream takes place. Absorption and energy recovery takes place as described above in Figure 1. The gas stream exits intermediate absorption tower 14 at upper outlet 16 and is then heated in two stages. The first stage involves exchanging heat with the gas stream at the third catalyst bed outlet temperature in cold reheat exchanger 35 to produce a gas stream exiting cold reheat exchanger 35. Then, the second stage involves directing the gas stream to inter reheat exchanger 34 where heat is exchanged with the hotter gas stream at the second catalyst bed outlet temperature, to produce a gas stream exiting inter reheat exchanger 34 at the fourth catalyst bed inlet temperature.
The gas stream at the fourth catalyst bed inlet temperature is next directed to fourth catalyst bed 27. A
fourth oxidation of SO2 in the gas stream takes place over catalyst bed 27 and the exiting gas stream is now at the hotter fourth catalyst bed outlet temperature.
In brief then, the double absorption process in Figure 2 proceeds as follows.
A gas stream comprising sulfur dioxide and oxygen is provided at a supply temperature to cold exchanger 32 where heat is exchanged with the hotter gas stream at the fourth catalyst bed outlet temperature. The gas stream exits cold exchanger 32 and is directed to hot exchanger 33 where heat is exchanged with the hotter gas stream at the first catalyst bed outlet temperature. The gas stream exits hot exchanger 33 at the first catalyst inlet temperature and is directed to first catalyst bed 24. A first oxidation of SO2 in the gas stream takes place over catalyst bed 24 and the exiting gas stream is now at the hotter first catalyst bed outlet temperature.
After exchanging heat in hot exchanger 33, the gas stream exits at the second catalyst bed inlet temperature and is directed to second catalyst bed 25. A second oxidation of SO2 in the gas stream takes place over catalyst bed 25 and the exiting gas stream is now at the hotter second catalyst bed outlet temperature.
The gas stream at the second catalyst bed outlet temperature is directed to inter reheat exchanger 34 where heat is exchanged with the colder gas stream exiting cold reheat exchanger 35.
The gas stream then exits inter reheat exchanger 34 at the third catalyst bed inlet temperature and is directed to third catalyst bed 26.
A third oxidation of SO2 in the gas stream takes place over catalyst bed 26 and the exiting gas stream is now at the hotter third catalyst bed outlet temperature.
The gas stream at the third catalyst bed outlet temperature is directed to cold reheat exchanger 35 where heat is exchanged with the colder gas stream coming from intermediate absorption subsystem 1. The gas stream then exits cold reheat exchanger 35 at the intermediate absorption subsystem inlet temperature and is directed to top inlet 3 of spray tower 2 in intermediate absorption subsystem 1 in which a first intermediate absorption of SO3 from the gas stream takes place. Absorption and energy recovery takes place as described above in Figure 1. The gas stream exits intermediate absorption tower 14 at upper outlet 16 and is then heated in two stages. The first stage involves exchanging heat with the gas stream at the third catalyst bed outlet temperature in cold reheat exchanger 35 to produce a gas stream exiting cold reheat exchanger 35. Then, the second stage involves directing the gas stream to inter reheat exchanger 34 where heat is exchanged with the hotter gas stream at the second catalyst bed outlet temperature, to produce a gas stream exiting inter reheat exchanger 34 at the fourth catalyst bed inlet temperature.
The gas stream at the fourth catalyst bed inlet temperature is next directed to fourth catalyst bed 27. A
fourth oxidation of SO2 in the gas stream takes place over catalyst bed 27 and the exiting gas stream is now at the hotter fourth catalyst bed outlet temperature.
Chemetics008-CA
The gas stream at the fourth catalyst bed outlet temperature is directed to cold exchanger 32 where heat is exchanged with the colder supplied gas stream. The gas stream then exits cold exchanger 32 at the final absorption inlet temperature and is directed to final absorption tower 28 in which a second and final absorption of SO2 from the gas stream takes place. The exiting gas stream is then discharged at stack 30.
The double absorption system in Figure 2 produces sulfuric acid with high conversion efficiency. And use of the inventive intermediate absorption subsystem allows for greater energy efficiency. As is apparent from Figures 1 and 2, if for some reason the energy recovery system or spray tower is not functional, they can be readily bypassed and the sulfuric acid system can operate without them (i.e. just by using intermediate absorption tower 14) and thus system 23 can operate in such circumstances in an historic conventional manner.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are to be considered within the purview and scope of the claims appended hereto.
The gas stream at the fourth catalyst bed outlet temperature is directed to cold exchanger 32 where heat is exchanged with the colder supplied gas stream. The gas stream then exits cold exchanger 32 at the final absorption inlet temperature and is directed to final absorption tower 28 in which a second and final absorption of SO2 from the gas stream takes place. The exiting gas stream is then discharged at stack 30.
The double absorption system in Figure 2 produces sulfuric acid with high conversion efficiency. And use of the inventive intermediate absorption subsystem allows for greater energy efficiency. As is apparent from Figures 1 and 2, if for some reason the energy recovery system or spray tower is not functional, they can be readily bypassed and the sulfuric acid system can operate without them (i.e. just by using intermediate absorption tower 14) and thus system 23 can operate in such circumstances in an historic conventional manner.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are to be considered within the purview and scope of the claims appended hereto.
Claims (7)
1. An intermediate absorption subsystem for a sulfuric acid production system comprising:
a co-current open spray tower comprising:
a top inlet for a gas stream comprising SO2 and SO3;
a lower outlet for the gas stream after spray absorption;
at least one spray inlet;
at least one spray nozzle within the spray tower and connected to the spray inlet;
an inlet for dilution water; and a bottom outlet for sulfuric acid liquid;
an energy recovery subsystem comprising a pump and a heat exchanger arranged in series, wherein the bottom outlet of the spray tower is fluidly connected to an inlet of the first side of the heat exchanger, the spray inlet of the spray tower is fluidly connected to an outlet of the first side of the heat exchanger, a water supply is fluidly connected to an inlet of the second side of the heat exchanger, and the outlet of the second side of the heat exchanger is a steam output; and an intermediate absorption tower comprising:
a lower inlet for the gas stream connected to the spray tower lower outlet;
an upper outlet for the gas stream after packed bed absorption;
a distributor inlet;
a liquid distributor within the intermediate absorption tower;
a packed bed within the intermediate absorption tower and below the liquid distributor;
a bottom outlet for sulfuric acid liquid; and a pump fluidly connected to the bottom outlet of the intermediate absorption tower and to the distributor inlet.
a co-current open spray tower comprising:
a top inlet for a gas stream comprising SO2 and SO3;
a lower outlet for the gas stream after spray absorption;
at least one spray inlet;
at least one spray nozzle within the spray tower and connected to the spray inlet;
an inlet for dilution water; and a bottom outlet for sulfuric acid liquid;
an energy recovery subsystem comprising a pump and a heat exchanger arranged in series, wherein the bottom outlet of the spray tower is fluidly connected to an inlet of the first side of the heat exchanger, the spray inlet of the spray tower is fluidly connected to an outlet of the first side of the heat exchanger, a water supply is fluidly connected to an inlet of the second side of the heat exchanger, and the outlet of the second side of the heat exchanger is a steam output; and an intermediate absorption tower comprising:
a lower inlet for the gas stream connected to the spray tower lower outlet;
an upper outlet for the gas stream after packed bed absorption;
a distributor inlet;
a liquid distributor within the intermediate absorption tower;
a packed bed within the intermediate absorption tower and below the liquid distributor;
a bottom outlet for sulfuric acid liquid; and a pump fluidly connected to the bottom outlet of the intermediate absorption tower and to the distributor inlet.
2. The intermediate absorption subsystem of claim 1 wherein the spray tower comprises a plurality of spray nozzles on at least two levels.
3. The intermediate absorption subsystem of claim 2 wherein the spray tower comprises a plurality of spray nozzles on three levels.
4. The intermediate absorption subsystem of claim 2 wherein the spray nozzles produce a spray less than 300 micron in average size.
5. The intermediate absorption subsystem of claim 1 wherein the intermediate absorption tower comprises a mist filter eliminator between the packed bed and the upper outlet for the gas stream after packed bed absorption.
6. The intermediate absorption subsystem of claim 1 wherein the heat exchanger in the energy recovery subsystem comprises a metal alloy with a UNS number selected from the group consisting of S32760 and R20033.
7. A double absorption system for oxidizing sulfur dioxide to produce sulfuric acid comprising a first oxidation subsystem comprising contact catalyst, the intermediate absorption subsystem of claim 1, a second oxidation subsystem comprising contact catalyst, and a final absorption tower.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2802885A CA2802885A1 (en) | 2013-01-17 | 2013-01-17 | Efficient system for producing sulfuric acid using a spray tower |
| CN2013200868072U CN203238034U (en) | 2013-01-17 | 2013-02-26 | Intermediate absorption subsystem for sulfuric acid production system and bi-absorption system for producing sulfuric acid by oxidizing sulfur dioxide |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2802885A CA2802885A1 (en) | 2013-01-17 | 2013-01-17 | Efficient system for producing sulfuric acid using a spray tower |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2802885A1 true CA2802885A1 (en) | 2013-04-01 |
Family
ID=48040636
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2802885A Abandoned CA2802885A1 (en) | 2013-01-17 | 2013-01-17 | Efficient system for producing sulfuric acid using a spray tower |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN203238034U (en) |
| CA (1) | CA2802885A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017192264A1 (en) | 2016-05-03 | 2017-11-09 | Chemetics Inc. | Energy efficient sulfuric acid system for humid environments |
| WO2022055662A1 (en) | 2020-09-09 | 2022-03-17 | Chemetics Inc. | System and method for producing sulfur dioxide and associated sulfuric acid plant |
| WO2023097389A1 (en) | 2021-12-03 | 2023-06-08 | Chemetics Inc. | Systems and methods for producing sulfuric acid or liquefied sulfur dioxide |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102016103976A1 (en) * | 2016-03-04 | 2017-09-07 | Thyssenkrupp Ag | Process and apparatus for the production of sulfuric acid |
-
2013
- 2013-01-17 CA CA2802885A patent/CA2802885A1/en not_active Abandoned
- 2013-02-26 CN CN2013200868072U patent/CN203238034U/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017192264A1 (en) | 2016-05-03 | 2017-11-09 | Chemetics Inc. | Energy efficient sulfuric acid system for humid environments |
| US10532929B2 (en) | 2016-05-03 | 2020-01-14 | Chemetics Inc. | Energy efficient sulfuric acid system for humid environments |
| WO2022055662A1 (en) | 2020-09-09 | 2022-03-17 | Chemetics Inc. | System and method for producing sulfur dioxide and associated sulfuric acid plant |
| WO2023097389A1 (en) | 2021-12-03 | 2023-06-08 | Chemetics Inc. | Systems and methods for producing sulfuric acid or liquefied sulfur dioxide |
Also Published As
| Publication number | Publication date |
|---|---|
| CN203238034U (en) | 2013-10-16 |
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| Date | Code | Title | Description |
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