CA3021202A1 - Sulphuric acid plant - Google Patents
Sulphuric acid plant Download PDFInfo
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- CA3021202A1 CA3021202A1 CA3021202A CA3021202A CA3021202A1 CA 3021202 A1 CA3021202 A1 CA 3021202A1 CA 3021202 A CA3021202 A CA 3021202A CA 3021202 A CA3021202 A CA 3021202A CA 3021202 A1 CA3021202 A1 CA 3021202A1
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- sulphuric acid
- sulphur
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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
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Abstract
A novel sulphuric acid plant design has been developed that allows for capacities in excess of 10,000 mtpd. In the plant, sulphur is combusted to sulphur dioxide using oxygen instead of air and using submerged combustion to manage the heat which is generated. The design offers lower capital expenditure as well as enhanced energy recovery.
Description
Docket No Chemetics020-CA
SULPHURIC ACID PLANT
Technical Field The present invention pertains to improved sulphuric acid plants and processes for operation.
Background Sulphuric 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.
The absorbing of the sulphur trioxide is usually done in one or more absorption towers.
Distributors are used in the absorption towers to distribute strong sulphuric acid solution across the top of a packed bed within the tower. Sulphur trioxide gas flows through the tower in generally counter-current flow to the solution, but it can also flow co-currently. The strong sulphuric acid solution is used to absorb the flowing sulphur trioxide. In CA2802885, an improved 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. This improved system is commercially available under the trade-mark ALPHATM.
In W02008/052649, a process is disclosed for the continuous catalytic complete or partial oxidation of a starting gas containing from 0.1 to 66% by volume of sulphur dioxide plus oxygen, in which the catalyst is Docket No Chemetics020-CA
kept active by means of pseudoisothermal process conditions with introduction or removal of energy. The related apparatus is for the continuous catalytic complete or partial oxidation of a starting gas containing sulphur dioxide and oxygen, and is characterized by at least one tube contact apparatus which is an upright heat exchanger composed of at least one double-walled tube whose catalyst-filled inner tube forms a reaction tube, with heat being transferred cocurrently around the reaction tube and an absorber for separating off SO3 being installed downstream of the tube contact apparatus.
The reactivity of the catalyst is preset by mixing with inert material. This process and apparatus are commercially available under the trade-mark CORETM.
The ever growing global need for phosphate based fertilizer has led to the existence of several large companies in the industry. These companies are located in areas with an abundance of phosphate rock allowing them to have large integrated fertilizer complexes that demand large volumes of sulphuric acid.
This has led to ever larger sulphuric acid plants with outputs between 4000 and 5000 MTPD. As the plants have become larger, the economic and technical maximums are approached as the converters, absorbing towers and gas-gas exchangers involved are getting too large to be economically fabricated. The result is that multiple sulphuric acid plants are required to meet the downstream demand.
Commercial sulphur burning sulphuric acid plants have always used ambient air as the source of the oxygen required in the process. The use of ambient air is inexpensive (air is available anywhere) and the conventional process operating at approximately 12 vol% SO2 into the converter perfectly balances the 02:
SO2 ratio required for high conversion and the maximum allowable temperature in the first catalyst bed.
The obvious disadvantage of using air is that each required molecule of oxygen also comes with approximately four molecules of inert gas (mainly N2 and CO2) which must also flow through the plant, therefore requiring very large equipment to handle to entire gas flow.
The use of oxygen as an alternative for some or all of the air has long been considered. In EP2330075 for instance, it is suggested that oxygen be used to combust sulphur to sulphur dioxide. Therein, it suggests that preferably a tube contact apparatus as exemplified in W020081052649 is used. Nonetheless, the use of oxygen in conventional commercial sulphuric acid plants was not warranted because the following process issues could not be overcome:
1) The burning of Sulphur with oxygen or oxygen enriched air creates extremely high furnace temperatures which exceed the limits of available refractory materials.
SULPHURIC ACID PLANT
Technical Field The present invention pertains to improved sulphuric acid plants and processes for operation.
Background Sulphuric 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.
The absorbing of the sulphur trioxide is usually done in one or more absorption towers.
Distributors are used in the absorption towers to distribute strong sulphuric acid solution across the top of a packed bed within the tower. Sulphur trioxide gas flows through the tower in generally counter-current flow to the solution, but it can also flow co-currently. The strong sulphuric acid solution is used to absorb the flowing sulphur trioxide. In CA2802885, an improved 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. This improved system is commercially available under the trade-mark ALPHATM.
In W02008/052649, a process is disclosed for the continuous catalytic complete or partial oxidation of a starting gas containing from 0.1 to 66% by volume of sulphur dioxide plus oxygen, in which the catalyst is Docket No Chemetics020-CA
kept active by means of pseudoisothermal process conditions with introduction or removal of energy. The related apparatus is for the continuous catalytic complete or partial oxidation of a starting gas containing sulphur dioxide and oxygen, and is characterized by at least one tube contact apparatus which is an upright heat exchanger composed of at least one double-walled tube whose catalyst-filled inner tube forms a reaction tube, with heat being transferred cocurrently around the reaction tube and an absorber for separating off SO3 being installed downstream of the tube contact apparatus.
The reactivity of the catalyst is preset by mixing with inert material. This process and apparatus are commercially available under the trade-mark CORETM.
The ever growing global need for phosphate based fertilizer has led to the existence of several large companies in the industry. These companies are located in areas with an abundance of phosphate rock allowing them to have large integrated fertilizer complexes that demand large volumes of sulphuric acid.
This has led to ever larger sulphuric acid plants with outputs between 4000 and 5000 MTPD. As the plants have become larger, the economic and technical maximums are approached as the converters, absorbing towers and gas-gas exchangers involved are getting too large to be economically fabricated. The result is that multiple sulphuric acid plants are required to meet the downstream demand.
Commercial sulphur burning sulphuric acid plants have always used ambient air as the source of the oxygen required in the process. The use of ambient air is inexpensive (air is available anywhere) and the conventional process operating at approximately 12 vol% SO2 into the converter perfectly balances the 02:
SO2 ratio required for high conversion and the maximum allowable temperature in the first catalyst bed.
The obvious disadvantage of using air is that each required molecule of oxygen also comes with approximately four molecules of inert gas (mainly N2 and CO2) which must also flow through the plant, therefore requiring very large equipment to handle to entire gas flow.
The use of oxygen as an alternative for some or all of the air has long been considered. In EP2330075 for instance, it is suggested that oxygen be used to combust sulphur to sulphur dioxide. Therein, it suggests that preferably a tube contact apparatus as exemplified in W020081052649 is used. Nonetheless, the use of oxygen in conventional commercial sulphuric acid plants was not warranted because the following process issues could not be overcome:
1) The burning of Sulphur with oxygen or oxygen enriched air creates extremely high furnace temperatures which exceed the limits of available refractory materials.
2) When oxygen is used ideally an 02: SO2 ratio close to 0.5 should be used to minimize the oxygen cost. However, this results in SO2 concentrations well above 60% which cannot be Docket No.: Chemetics020-CA
handled using vanadium catalyst in a conventional adiabatic converter because the resulting process gas temperature would exceed the upper temperature limit of the catalyst.
Submerged combustion is well known for various applications. For instance, an article titled "S0xClean:
an alternative to burning sulphur in air", Sulphur 348 Sept-Oct 2013, discloses the SO2CleanTM process in which high purity sulphur dioxide is produced by burning sulphur using oxygen rather than air in a submerged combustion process, whereby cooling of the combustion apparatus is achieved by evaporation of part of the liquid sulfur. Further, the SO3CleanTM process can be used to produce gas/liquid SO3, oleum and sulphuric acid. The process can be tailored to produce SO3 derivatives including oleum and sulphuric acid in varying strengths and quantities. The various SOxCleanTM processes were suggested for the production of sulphuric acid. The main disadvantage of the SOxCleanTM process is the requirement to cool the combustion products to effectively condense all sulfur vapor from the SO2 gas to prevent downstream blockages or process upsets.
Secondary combustion techniques for the combustion of sulphur to sulphur dioxide have also long been known to those skilled in the art; e.g. as disclosed in US3803298.
There exists a desire for improvements in sulphuric acid plant design and operation to efficiently and cost effectively produce large volumes of sulphuric acid. The present invention addresses this desire and provides other benefits as disclosed below.
Summary A new process and associated apparatus for sulphuric acid production have now been developed that overcome the aforementioned hurdles thereby providing for the first time a design that can take full advantage of the benefits offered by using pure oxygen.
Specifically, the new process is for the production of sulphuric acid in a single contact, single absorption sulphuric acid plant. The process comprises the steps of: employing oxygen or oxygen enriched air for the combustion of sulphur to sulfur dioxide, employing submerged combustion for the combustion of sulphur to sulphur dioxide, employing a secondary combustion step after the submerged combustion for the combustion of residual sulphur to sulphur dioxide, employing oxygen or oxygen enriched air for the conversion of sulphur dioxide to sulphur trioxide, and converting sulphur dioxide to sulphur trioxide in a contact apparatus containing a conversion catalyst.
handled using vanadium catalyst in a conventional adiabatic converter because the resulting process gas temperature would exceed the upper temperature limit of the catalyst.
Submerged combustion is well known for various applications. For instance, an article titled "S0xClean:
an alternative to burning sulphur in air", Sulphur 348 Sept-Oct 2013, discloses the SO2CleanTM process in which high purity sulphur dioxide is produced by burning sulphur using oxygen rather than air in a submerged combustion process, whereby cooling of the combustion apparatus is achieved by evaporation of part of the liquid sulfur. Further, the SO3CleanTM process can be used to produce gas/liquid SO3, oleum and sulphuric acid. The process can be tailored to produce SO3 derivatives including oleum and sulphuric acid in varying strengths and quantities. The various SOxCleanTM processes were suggested for the production of sulphuric acid. The main disadvantage of the SOxCleanTM process is the requirement to cool the combustion products to effectively condense all sulfur vapor from the SO2 gas to prevent downstream blockages or process upsets.
Secondary combustion techniques for the combustion of sulphur to sulphur dioxide have also long been known to those skilled in the art; e.g. as disclosed in US3803298.
There exists a desire for improvements in sulphuric acid plant design and operation to efficiently and cost effectively produce large volumes of sulphuric acid. The present invention addresses this desire and provides other benefits as disclosed below.
Summary A new process and associated apparatus for sulphuric acid production have now been developed that overcome the aforementioned hurdles thereby providing for the first time a design that can take full advantage of the benefits offered by using pure oxygen.
Specifically, the new process is for the production of sulphuric acid in a single contact, single absorption sulphuric acid plant. The process comprises the steps of: employing oxygen or oxygen enriched air for the combustion of sulphur to sulfur dioxide, employing submerged combustion for the combustion of sulphur to sulphur dioxide, employing a secondary combustion step after the submerged combustion for the combustion of residual sulphur to sulphur dioxide, employing oxygen or oxygen enriched air for the conversion of sulphur dioxide to sulphur trioxide, and converting sulphur dioxide to sulphur trioxide in a contact apparatus containing a conversion catalyst.
3 Docket No.: Chemetics020-CA
The new process is particularly suited for use with the process of the invention in which the sulphuric acid plant comprises a contact apparatus that is an upright heat exchanger comprising at least one double-walled tube whose catalyst-filled interior tube forms a reaction tube or that is a tubular heat exchanger comprising at least one single-walled tube whose catalyst-filled interior forms a reaction tube, and the process is characterized in that energy is introduced to the catalyst or is removed from the catalyst via an intermediate circuit in order to establish a temperature profile over the length of the reaction tube, at which the catalyst is kept active. Further, the new process can desirably comprise a secondary combustion step for the combustion of sulphur to sulphur dioxide to create a process gas at the inlet of the contact apparatus essentially free of sulfur without the need for cooling beyond the dewpoint of sulfur vapor.
The sulphuric acid plant associated with the new process can comprise an intermediate circuit comprising a molten salt. In the process, unconverted sulphur dioxide may be recycled to the secondary combustion step. Further, the ratio of oxygen to sulphur dioxide employed in the converting step can be less than or equal to 1.0, preferably between 0.4 and 0.8, and more preferably between 0.45 and 0.55.
The new apparatus of the invention is a single contact, single absorption sulphuric acid plant for the production of sulphuric acid according to the aforementioned process.
Desirably, the sulphuric acid plant can be of all-metal construction and uses oxygen with a purity exceeding 95 vol% 02. Further, the plant desirably can be absent a main blower, a drying tower system. a reheat exchanger, and a secondary conversion and absorption system.
Brief Description of the Drawings Figure 1 shows a representative schematic of a conventional DCDA (double conversion, double absorption) sulphuric acid plant using ambient air.
Figure 2 shows a schematic of a SCSA (single contact, single absorption) sulphuric acid plant of the invention using oxygen and the process of the invention.
Figure 3 shows a schematic of a reactor used in an embodiment of the invention.
Detailed Description
The new process is particularly suited for use with the process of the invention in which the sulphuric acid plant comprises a contact apparatus that is an upright heat exchanger comprising at least one double-walled tube whose catalyst-filled interior tube forms a reaction tube or that is a tubular heat exchanger comprising at least one single-walled tube whose catalyst-filled interior forms a reaction tube, and the process is characterized in that energy is introduced to the catalyst or is removed from the catalyst via an intermediate circuit in order to establish a temperature profile over the length of the reaction tube, at which the catalyst is kept active. Further, the new process can desirably comprise a secondary combustion step for the combustion of sulphur to sulphur dioxide to create a process gas at the inlet of the contact apparatus essentially free of sulfur without the need for cooling beyond the dewpoint of sulfur vapor.
The sulphuric acid plant associated with the new process can comprise an intermediate circuit comprising a molten salt. In the process, unconverted sulphur dioxide may be recycled to the secondary combustion step. Further, the ratio of oxygen to sulphur dioxide employed in the converting step can be less than or equal to 1.0, preferably between 0.4 and 0.8, and more preferably between 0.45 and 0.55.
The new apparatus of the invention is a single contact, single absorption sulphuric acid plant for the production of sulphuric acid according to the aforementioned process.
Desirably, the sulphuric acid plant can be of all-metal construction and uses oxygen with a purity exceeding 95 vol% 02. Further, the plant desirably can be absent a main blower, a drying tower system. a reheat exchanger, and a secondary conversion and absorption system.
Brief Description of the Drawings Figure 1 shows a representative schematic of a conventional DCDA (double conversion, double absorption) sulphuric acid plant using ambient air.
Figure 2 shows a schematic of a SCSA (single contact, single absorption) sulphuric acid plant of the invention using oxygen and the process of the invention.
Figure 3 shows a schematic of a reactor used in an embodiment of the invention.
Detailed Description
4 Docket No.: Chemetics020-CA
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.
The words "oxygen" or "pure oxygen" are to be considered as meaning oxygen in concentrations exceeding 90% by volume.
The trade-marks CORESTM and CORESO2TM refer to molten salt cooled and molten salt cooled using oxygen processes and apparatus of the invention respectively.
Major fertilizer producers of the world create ever increasing demand for sulphuric acid in order to keep pace with their phosphate fertilizer production capacity expansions. A novel sulphuric acid plant design has been developed that allows single train capacities in excess of 10,000 mtpd. The design offers lower capital expenditure as well as enhanced energy recovery.
For comparison, Figure 1 shows a representative schematic of a conventional DCDA (double conversion, double absorption) sulphuric acid plant using ambient air for combustion.
People skilled in the art will recognize that this schematic represents only one of several similar embodiments that are in industrial use today. Figure 2 however shows a schematic of a SCSA (single contact, single absorption) sulphuric acid plant of the invention using pure oxygen for combustion and the CORESO2TM
process.
The process of the invention is designed to take full advantage of the benefits of using pure oxygen instead of air. The process has the following features:
= Pure oxygen reduces the gas volume involved and hence the equipment size by more than 70%
= The main blower not required since oxygen is received under pressure, thereby saving power = The drying tower system is eliminated since the supplied oxygen contains no moisture = Low temperature submerged combustion allows for all-metal construction = High conversion is achieved in a single pass in the molten salt cooled CORESTM system = Being a single absorption design, no reheat exchangers nor secondary absorption system are required = Enhanced energy recovery is obtained thereby producing more steam
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.
The words "oxygen" or "pure oxygen" are to be considered as meaning oxygen in concentrations exceeding 90% by volume.
The trade-marks CORESTM and CORESO2TM refer to molten salt cooled and molten salt cooled using oxygen processes and apparatus of the invention respectively.
Major fertilizer producers of the world create ever increasing demand for sulphuric acid in order to keep pace with their phosphate fertilizer production capacity expansions. A novel sulphuric acid plant design has been developed that allows single train capacities in excess of 10,000 mtpd. The design offers lower capital expenditure as well as enhanced energy recovery.
For comparison, Figure 1 shows a representative schematic of a conventional DCDA (double conversion, double absorption) sulphuric acid plant using ambient air for combustion.
People skilled in the art will recognize that this schematic represents only one of several similar embodiments that are in industrial use today. Figure 2 however shows a schematic of a SCSA (single contact, single absorption) sulphuric acid plant of the invention using pure oxygen for combustion and the CORESO2TM
process.
The process of the invention is designed to take full advantage of the benefits of using pure oxygen instead of air. The process has the following features:
= Pure oxygen reduces the gas volume involved and hence the equipment size by more than 70%
= The main blower not required since oxygen is received under pressure, thereby saving power = The drying tower system is eliminated since the supplied oxygen contains no moisture = Low temperature submerged combustion allows for all-metal construction = High conversion is achieved in a single pass in the molten salt cooled CORESTM system = Being a single absorption design, no reheat exchangers nor secondary absorption system are required = Enhanced energy recovery is obtained thereby producing more steam
5 Docket No = Chemetics020-CA
In the present invention, the major problem of high temperatures during the combustion of sulphur in pure oxygen is solved by using a submerged combustion system where the oxygen is sparged into molten sulphur. Combustion energy is transferred to the liquid sulphur allowing part of the liquid sulphur to evaporate thus maintaining a constant temperature in the combustion system.
The resulting process gas leaving the combustion system is therefore a mixture of gaseous sulphur and SO2 at approx. 460 C which is the boiling point of sulphur at the operating pressure. The majority of the sulphur contained in the process gas is condensed in the sulphur condenser at approximately 350 C to produce high pressure steam and returned to the combustion system.
The process gas containing all the SO2 and a small amount of residual sulphur is then transferred to the secondary combustion chamber where the process gas is mixed with additional oxygen and recycled process gas from the absorber tower to convert any remaining sulphur to SO2.
This raises the temperature to approx. 750 C allowing the process gas to be cooled in a superheater to adjust the temperature before entering the CORESTM Reactor.
The relatively cool temperatures in the entire combustion system allows for either all-metal construction or the use of cost effective thin refractory linings. Because a smaller volume of gas leaves the combustion area to flow to the converter compared to a conventionally designed sulphur burning acid plant, there is more combustion energy available for production of steam as the energy previously used to warm up the nitrogen present in the air to the converter inlet temperature is no longer required. Together with other process changes, this increases the total high pressure steam production by 7.5%
The 02 : SO2 ratio of the process gas leaving the secondary combustion system is controlled at 0.5 resulting in a process gas containing up to 66 vol% SO2. In the illustrated embodiment of the invention, this process gas enters the C0RESTM reactor in a C0RESTM system (see Figure 3) where approximately 70% of the SO2 is converted to S03. The molten salt coolant maintains the process gas temperature below 630 C to prevent catalyst damage. A specially developed catalyst mixture with high heat transfer capability is used to prevent hot spots in the centre of the catalyst. In the reactor, more than 90% of the reaction energy is transferred to the molten salt. The molten salt flow is designed to operate below 450 C
therefore no special materials are required in the C0RESTM System. Cooling of the molten salt is achieved by superheating steam from the sulphur condensers. The superheated steam is exported to battery limit or used for power generation.
In the present invention, the major problem of high temperatures during the combustion of sulphur in pure oxygen is solved by using a submerged combustion system where the oxygen is sparged into molten sulphur. Combustion energy is transferred to the liquid sulphur allowing part of the liquid sulphur to evaporate thus maintaining a constant temperature in the combustion system.
The resulting process gas leaving the combustion system is therefore a mixture of gaseous sulphur and SO2 at approx. 460 C which is the boiling point of sulphur at the operating pressure. The majority of the sulphur contained in the process gas is condensed in the sulphur condenser at approximately 350 C to produce high pressure steam and returned to the combustion system.
The process gas containing all the SO2 and a small amount of residual sulphur is then transferred to the secondary combustion chamber where the process gas is mixed with additional oxygen and recycled process gas from the absorber tower to convert any remaining sulphur to SO2.
This raises the temperature to approx. 750 C allowing the process gas to be cooled in a superheater to adjust the temperature before entering the CORESTM Reactor.
The relatively cool temperatures in the entire combustion system allows for either all-metal construction or the use of cost effective thin refractory linings. Because a smaller volume of gas leaves the combustion area to flow to the converter compared to a conventionally designed sulphur burning acid plant, there is more combustion energy available for production of steam as the energy previously used to warm up the nitrogen present in the air to the converter inlet temperature is no longer required. Together with other process changes, this increases the total high pressure steam production by 7.5%
The 02 : SO2 ratio of the process gas leaving the secondary combustion system is controlled at 0.5 resulting in a process gas containing up to 66 vol% SO2. In the illustrated embodiment of the invention, this process gas enters the C0RESTM reactor in a C0RESTM system (see Figure 3) where approximately 70% of the SO2 is converted to S03. The molten salt coolant maintains the process gas temperature below 630 C to prevent catalyst damage. A specially developed catalyst mixture with high heat transfer capability is used to prevent hot spots in the centre of the catalyst. In the reactor, more than 90% of the reaction energy is transferred to the molten salt. The molten salt flow is designed to operate below 450 C
therefore no special materials are required in the C0RESTM System. Cooling of the molten salt is achieved by superheating steam from the sulphur condensers. The superheated steam is exported to battery limit or used for power generation.
6 Docket No Chemetics020-CA
After leaving the CORESTM reactor, the process gas is cooled in the economizer where boiler feed water from the deaerator is preheated before entering the sulphur condensers. The cooled gas from the economizer is directed to the absorption system where the SO3 is converted to sulphuric acid.
The SO3 formed in the CORESTM reactor is preferably absorbed in an ALPHATM hot absorption system to produce hot concentrated acid and medium pressure steam at pressures up to 10 barg. The ALPHATM
system is constructed from specially selected alloys (proprietary SARAMET
HT/HT+ alloys) for long and reliable service life. These materials are more tolerant of process upsets than any other known materials in the market, thus providing best in class on-stream time.
The high SO3 concentration of the process gas requires a large circulating flow of acid to limit the operating temperature. The hot acid leaving the ALPHATM hot absorption system is used to produce medium pressure (up to 15 barg) steam which is also exported. Approximately 99% of the SO3 is absorbed in the ALPHATM tower which is significantly higher than for a conventional plant and is due to the higher inlet SO3 concentration, thus producing more medium pressure steam. For maximum energy efficiency, the process gas leaving the ALPHATM tower can be directly recycled to the secondary combustion (after mist removal) without the need to remove the remaining S03. In this option, no cold absorption system is required and no cooling water is necessary in the absorption section except for cooling of the final product acid. If maximum energy efficiency is not required a cold absorber section is used to absorb the remaining SO3 and cool the process gas. Alternatively, when production of medium pressure steam is not desired, only a cold absorption system can be used.
Water is added to the ALPHATM pump tank and cold absorber pump tank to maintain a constant sulfuric acid concentration. Because the incoming oxygen does not contain any moisture as is the case when using .. ambient air, the medium pressure steam production in the ALPHATM system stays at maximum level regardless of the ambient humidity of the plant site and no reduction in steam production is encountered compared to a conventional acid plants using air in high humidity locations.
Almost all the process gas leaving the absorption system is recycled to the secondary combustion system, preferably using a small blower which is the only gas moving equipment in the plant. The entire plant is highly energy efficient and the pressure drop through the entire plant is less than 50% of a conventional double absorption design. Because the oxygen is received at 0.5 barg, there is no need to provide a main blower. The amount of acid circulated through the plant is also significantly reduced as the dry tower and final absorber tower of a DCDA are no longer required, thus further reducing power consumption.
After leaving the CORESTM reactor, the process gas is cooled in the economizer where boiler feed water from the deaerator is preheated before entering the sulphur condensers. The cooled gas from the economizer is directed to the absorption system where the SO3 is converted to sulphuric acid.
The SO3 formed in the CORESTM reactor is preferably absorbed in an ALPHATM hot absorption system to produce hot concentrated acid and medium pressure steam at pressures up to 10 barg. The ALPHATM
system is constructed from specially selected alloys (proprietary SARAMET
HT/HT+ alloys) for long and reliable service life. These materials are more tolerant of process upsets than any other known materials in the market, thus providing best in class on-stream time.
The high SO3 concentration of the process gas requires a large circulating flow of acid to limit the operating temperature. The hot acid leaving the ALPHATM hot absorption system is used to produce medium pressure (up to 15 barg) steam which is also exported. Approximately 99% of the SO3 is absorbed in the ALPHATM tower which is significantly higher than for a conventional plant and is due to the higher inlet SO3 concentration, thus producing more medium pressure steam. For maximum energy efficiency, the process gas leaving the ALPHATM tower can be directly recycled to the secondary combustion (after mist removal) without the need to remove the remaining S03. In this option, no cold absorption system is required and no cooling water is necessary in the absorption section except for cooling of the final product acid. If maximum energy efficiency is not required a cold absorber section is used to absorb the remaining SO3 and cool the process gas. Alternatively, when production of medium pressure steam is not desired, only a cold absorption system can be used.
Water is added to the ALPHATM pump tank and cold absorber pump tank to maintain a constant sulfuric acid concentration. Because the incoming oxygen does not contain any moisture as is the case when using .. ambient air, the medium pressure steam production in the ALPHATM system stays at maximum level regardless of the ambient humidity of the plant site and no reduction in steam production is encountered compared to a conventional acid plants using air in high humidity locations.
Almost all the process gas leaving the absorption system is recycled to the secondary combustion system, preferably using a small blower which is the only gas moving equipment in the plant. The entire plant is highly energy efficient and the pressure drop through the entire plant is less than 50% of a conventional double absorption design. Because the oxygen is received at 0.5 barg, there is no need to provide a main blower. The amount of acid circulated through the plant is also significantly reduced as the dry tower and final absorber tower of a DCDA are no longer required, thus further reducing power consumption.
7 Docket No.: Chemetics020-CA
A small purge stream from the absorber tower is required since the incoming oxygen contains generally less than 100 vol% 02 and therefore the relatively small amount of inert gases must be removed to prevent accumulation in the system. For the preferred system using oxygen purity above 99 vol% the purge flow is less than 1% of the gas leaving the absorber tower. The purge flow is treated in a tail gas system. Several options exist for this tail gas treatment, the simplest being either a low temperature (ambient) catalytic system or a wet scrubber using peroxide since both options produce a weak sulphuric acid that can be used as dilution water.
SO2 emissions below 10 ppm are easily achieved. In addition, because the purge stream emitted to atmosphere is extremely small (-1000 Nm3/hr), the total mass of SO2 or acid mist emissions from the C0RES02TM system is virtually zero.
It is easy to understand that an acid plant using oxygen is significantly cheaper to build and operate compared to a conventional plant using air. However, the production of oxygen requires a significant capital investment (or long term supply agreement) and consumes energy. The required flow of oxygen for a large sulphuric acid plant can practically only be provided by an air separation type oxygen plant.
This type of plant uses refrigeration and compression to liquify ambient air followed by cryogenic distillation to separate the air into almost pure oxygen, nitrogen and argon.
Air Separation plants are commercially available from numerous suppliers such as Messer Group GmbH, Linde AG or Air Products & Chemicals Inc. In such an oxygen plant, the main compressor and refrigeration system are the main power users that must be included in any comparison. The oxygen plant can also produce nitrogen and argon as valuable by-products that can be sold into the local market for additional revenue streams.
The process of the invention offers a compelling alternative for production of sulphuric acid. It offers the most value in remote regions where the excess power produced from the sulphuric acid plant has a relatively low value or cannot be exported as well as in industrial locations where nitrogen from the oxygen plant can be sold or where low cost oxygen is available as a by-product from a nearby nitrogen producer.
The present process offers the following advantages over conventional sulphuric acid plant designs including:
= Smaller footprint with lower investment cost = Simplified process with fewer rotating equipment components
A small purge stream from the absorber tower is required since the incoming oxygen contains generally less than 100 vol% 02 and therefore the relatively small amount of inert gases must be removed to prevent accumulation in the system. For the preferred system using oxygen purity above 99 vol% the purge flow is less than 1% of the gas leaving the absorber tower. The purge flow is treated in a tail gas system. Several options exist for this tail gas treatment, the simplest being either a low temperature (ambient) catalytic system or a wet scrubber using peroxide since both options produce a weak sulphuric acid that can be used as dilution water.
SO2 emissions below 10 ppm are easily achieved. In addition, because the purge stream emitted to atmosphere is extremely small (-1000 Nm3/hr), the total mass of SO2 or acid mist emissions from the C0RES02TM system is virtually zero.
It is easy to understand that an acid plant using oxygen is significantly cheaper to build and operate compared to a conventional plant using air. However, the production of oxygen requires a significant capital investment (or long term supply agreement) and consumes energy. The required flow of oxygen for a large sulphuric acid plant can practically only be provided by an air separation type oxygen plant.
This type of plant uses refrigeration and compression to liquify ambient air followed by cryogenic distillation to separate the air into almost pure oxygen, nitrogen and argon.
Air Separation plants are commercially available from numerous suppliers such as Messer Group GmbH, Linde AG or Air Products & Chemicals Inc. In such an oxygen plant, the main compressor and refrigeration system are the main power users that must be included in any comparison. The oxygen plant can also produce nitrogen and argon as valuable by-products that can be sold into the local market for additional revenue streams.
The process of the invention offers a compelling alternative for production of sulphuric acid. It offers the most value in remote regions where the excess power produced from the sulphuric acid plant has a relatively low value or cannot be exported as well as in industrial locations where nitrogen from the oxygen plant can be sold or where low cost oxygen is available as a by-product from a nearby nitrogen producer.
The present process offers the following advantages over conventional sulphuric acid plant designs including:
= Smaller footprint with lower investment cost = Simplified process with fewer rotating equipment components
8 Docket No Chemetics020-CA
= Utilizes only proven technologies in a new process configuration.
= Virtually no emissions = Low operating expenditure In addition, if a market can be found for the nitrogen (and/or Argon) that is co-produced in the oxygen plant, then this would more than offset the additional power used in the associated oxygen plant and significantly improve the economics of the sulphuric acid production.
It should be clear that although the aforementioned description has focussed on sulfuric acid plants with large capacity, the same process and economic benefits exist for smaller plants and the invention therefore has applicability for any plant capacity.
The following Examples have been included to illustrate certain aspects of the invention but should not be construed as limiting in any way.
Examples A case study was done for sulphuric acid plants with 10,000 mtpd capacity in which an embodiment of the invention using oxygen for sulphur combustion was compared to that of a conventional sulphur burning sulphuric acid plant using ambient air. The study assumed 6,000 mtpd as the largest practical single train capacity for conventional sulphuric acid technology and hence a dual train design was required for the conventional embodiment. The comparison was done on investment cost, steam production, and utility consumption. It was further assumed that all steam was used to produce power.
Further, only the investment cost for the sulphuric acid plant itself and the oxygen plant were considered. Any investments required for sulphur melting and/or power generation were therefore not included. Costs were based on a US gulf coast location. Further still, any revenue generated from the sale of by-product nitrogen and argon (while potentially very significant on the basis of approximately 40 million USD/yr at a nitrogen price of 50 USD/MT) was also not included since these revenues are highly location dependent.
Table 1 shows the results of the case study. The results are all normalized in that for each parameter, the performance of the conventional sulphuric acid plant is taken as 100 and the performance of the inventive system is shown relative to those numbers.
= Utilizes only proven technologies in a new process configuration.
= Virtually no emissions = Low operating expenditure In addition, if a market can be found for the nitrogen (and/or Argon) that is co-produced in the oxygen plant, then this would more than offset the additional power used in the associated oxygen plant and significantly improve the economics of the sulphuric acid production.
It should be clear that although the aforementioned description has focussed on sulfuric acid plants with large capacity, the same process and economic benefits exist for smaller plants and the invention therefore has applicability for any plant capacity.
The following Examples have been included to illustrate certain aspects of the invention but should not be construed as limiting in any way.
Examples A case study was done for sulphuric acid plants with 10,000 mtpd capacity in which an embodiment of the invention using oxygen for sulphur combustion was compared to that of a conventional sulphur burning sulphuric acid plant using ambient air. The study assumed 6,000 mtpd as the largest practical single train capacity for conventional sulphuric acid technology and hence a dual train design was required for the conventional embodiment. The comparison was done on investment cost, steam production, and utility consumption. It was further assumed that all steam was used to produce power.
Further, only the investment cost for the sulphuric acid plant itself and the oxygen plant were considered. Any investments required for sulphur melting and/or power generation were therefore not included. Costs were based on a US gulf coast location. Further still, any revenue generated from the sale of by-product nitrogen and argon (while potentially very significant on the basis of approximately 40 million USD/yr at a nitrogen price of 50 USD/MT) was also not included since these revenues are highly location dependent.
Table 1 shows the results of the case study. The results are all normalized in that for each parameter, the performance of the conventional sulphuric acid plant is taken as 100 and the performance of the inventive system is shown relative to those numbers.
9 Docket No.: Chemetics020-CA
Table 1: Comparison of inventive to conventional sulphuric acid plant Conventional plant Inventive plant using ambient air using oxygen Acid plant alone Investment cost 100 35 Plot area 100 55 Maintenance cost (@2.5 /o per year) 100 35 High pressure steam production (60 barg/500 C) 100 107 Medium pressure steam production (10 barg/200 C) 100 110 Power consumption 100 17 Cooling water (@ 10 C AT) 100 20 Emissions (standard design) 100 ppm <10 ppm Power production (gross) 100 107 Power production (net) 100 124 Acid plant + oxygen plant Capital expenditure 100 78 Maintenance cost 100 56 Power production (net) 100 86 Cooling water consumption (@ 10 C AT) 100 108 It is clear from Table 1 that the capital expenditure for the inventive acid plant plus the associated oxygen plant is more than 20% lower than a conventional sulphuric acid plant using ambient air. The simplified plant design with significantly lower equipment count and lower temperatures also reduces operating staffing, reduces maintenance, and improves plant reliability.
On the other hand, the combined inventive acid plant and oxygen plant consume more power than a conventional plant. However, because the inventive acid plant produces more steam and therefore can also produce more power than a conventional plant, the overall difference is not that significant.
For this assumed location, the major reduction in investment cost (and thus financing costs) made the inventive process a clear winner as long as the sell price of excess power was below 100 USD/MWh. This analysis was based on a 10 year amortization of the investment cost.
Table 1: Comparison of inventive to conventional sulphuric acid plant Conventional plant Inventive plant using ambient air using oxygen Acid plant alone Investment cost 100 35 Plot area 100 55 Maintenance cost (@2.5 /o per year) 100 35 High pressure steam production (60 barg/500 C) 100 107 Medium pressure steam production (10 barg/200 C) 100 110 Power consumption 100 17 Cooling water (@ 10 C AT) 100 20 Emissions (standard design) 100 ppm <10 ppm Power production (gross) 100 107 Power production (net) 100 124 Acid plant + oxygen plant Capital expenditure 100 78 Maintenance cost 100 56 Power production (net) 100 86 Cooling water consumption (@ 10 C AT) 100 108 It is clear from Table 1 that the capital expenditure for the inventive acid plant plus the associated oxygen plant is more than 20% lower than a conventional sulphuric acid plant using ambient air. The simplified plant design with significantly lower equipment count and lower temperatures also reduces operating staffing, reduces maintenance, and improves plant reliability.
On the other hand, the combined inventive acid plant and oxygen plant consume more power than a conventional plant. However, because the inventive acid plant produces more steam and therefore can also produce more power than a conventional plant, the overall difference is not that significant.
For this assumed location, the major reduction in investment cost (and thus financing costs) made the inventive process a clear winner as long as the sell price of excess power was below 100 USD/MWh. This analysis was based on a 10 year amortization of the investment cost.
10 Docket No.: Chemetics020-CA
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.
II
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.
II
Claims (12)
1. A process for the production of sulphuric acid in a single contact, single absorption sulphuric acid plant comprising:
employing oxygen or oxygen enriched air for the combustion of sulphur to sulfur dioxide;
employing submerged combustion for the combustion of sulphur to sulphur dioxide;
employing a secondary combustion step after the submerged combustion for the combustion of residual sulphur to sulphur dioxide;
employing oxygen or oxygen enriched air for the conversion of sulphur dioxide to sulphur trioxide; and converting sulphur dioxide to sulphur trioxide in a contact apparatus containing a conversion catalyst.
employing oxygen or oxygen enriched air for the combustion of sulphur to sulfur dioxide;
employing submerged combustion for the combustion of sulphur to sulphur dioxide;
employing a secondary combustion step after the submerged combustion for the combustion of residual sulphur to sulphur dioxide;
employing oxygen or oxygen enriched air for the conversion of sulphur dioxide to sulphur trioxide; and converting sulphur dioxide to sulphur trioxide in a contact apparatus containing a conversion catalyst.
2. The process of claim 1 wherein the sulphuric acid plant comprises a contact apparatus that is an upright heat exchanger comprising at least one double-walled tube whose catalyst-filled interior tube forms a reaction tube, characterized in that energy is introduced to the catalyst or is removed from the catalyst via an intermediate circuit in order to establish a temperature profile over the length of the reaction tube, at which the catalyst is kept active.
3. The process of claim 1 wherein sulphuric acid plant comprises a contact apparatus that is a tubular heat exchanger comprising at least one single-walled tube whose catalyst-filled interior forms a reaction tube, characterized in that energy is introduced to the catalyst or is removed from the catalyst via an intermediate circuit in order to establish a temperature profile over the length of the reaction tube, at which the catalyst is kept active.
4. The process of claim 2 wherein the sulphuric acid plant comprises an intermediate circuit comprising a molten salt.
5. The process of claim 3 wherein the sulphuric acid plant comprises an intermediate circuit comprising a molten salt.
6. The process of claim 1 wherein unconverted sulphur dioxide is recycled to the secondary combustion step.
7. The process of claim 1 where the ratio of oxygen to sulphur dioxide employed in the converting step is less than or equal to 1Ø
8. The process of claim 7 where the ratio of oxygen to sulphur dioxide employed in the converting step is between 0.4 and 0.8.
9. The process of claim 8 where the ratio of oxygen to sulphur dioxide employed in the converting step is between 0.45 and 0.55.
10. A single contact, single absorption sulphuric acid plant for the production of sulphuric acid according to the process of claim 1.
11. The sulphuric acid plant of claim 10 characterized in that the plant is of all-metal construction.
12. The sulphuric acid plant of claim 10 characterized in that the plant is absent a main blower, a drying tower system, a reheat exchanger, and a secondary conversion and absorption system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA3021202A CA3021202A1 (en) | 2018-10-17 | 2018-10-17 | Sulphuric acid plant |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA3021202A CA3021202A1 (en) | 2018-10-17 | 2018-10-17 | Sulphuric acid plant |
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| CA3021202A1 true CA3021202A1 (en) | 2018-12-24 |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110316704A (en) * | 2019-04-11 | 2019-10-11 | 湖北锦泽环保科技有限公司 | A kind of acid production with sulphur industrial tail gas technique of zero discharge |
| WO2021118599A1 (en) | 2019-12-13 | 2021-06-17 | Chemetics Inc. | Integrated ammonia and sulfuric acid production plant and process |
| WO2022055662A1 (en) | 2020-09-09 | 2022-03-17 | Chemetics Inc. | System and method for producing sulfur dioxide and associated sulfuric acid plant |
| CN114534641A (en) * | 2022-03-17 | 2022-05-27 | 广东韶钢松山股份有限公司 | Acid making equipment and steam boiler method |
| WO2023097389A1 (en) | 2021-12-03 | 2023-06-08 | Chemetics Inc. | Systems and methods for producing sulfuric acid or liquefied sulfur dioxide |
| WO2023225742A1 (en) * | 2022-05-27 | 2023-11-30 | Chemetics Inc. | Tail gas treatment system and method for a sulfuric acid production plant |
-
2018
- 2018-10-17 CA CA3021202A patent/CA3021202A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110316704A (en) * | 2019-04-11 | 2019-10-11 | 湖北锦泽环保科技有限公司 | A kind of acid production with sulphur industrial tail gas technique of zero discharge |
| WO2021118599A1 (en) | 2019-12-13 | 2021-06-17 | Chemetics Inc. | Integrated ammonia and sulfuric acid production plant and process |
| WO2022055662A1 (en) | 2020-09-09 | 2022-03-17 | Chemetics Inc. | System and method for producing sulfur dioxide and associated sulfuric acid plant |
| CN116113598A (en) * | 2020-09-09 | 2023-05-12 | 凯密迪公司 | System and method for producing sulfur dioxide and related sulfuric acid plant |
| WO2023097389A1 (en) | 2021-12-03 | 2023-06-08 | Chemetics Inc. | Systems and methods for producing sulfuric acid or liquefied sulfur dioxide |
| CN114534641A (en) * | 2022-03-17 | 2022-05-27 | 广东韶钢松山股份有限公司 | Acid making equipment and steam boiler method |
| WO2023225742A1 (en) * | 2022-05-27 | 2023-11-30 | Chemetics Inc. | Tail gas treatment system and method for a sulfuric acid production plant |
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