WO2017220656A1 - Integrated process for the production of concentrated sulphuric acid - Google Patents

Integrated process for the production of concentrated sulphuric acid Download PDF

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Publication number
WO2017220656A1
WO2017220656A1 PCT/EP2017/065246 EP2017065246W WO2017220656A1 WO 2017220656 A1 WO2017220656 A1 WO 2017220656A1 EP 2017065246 W EP2017065246 W EP 2017065246W WO 2017220656 A1 WO2017220656 A1 WO 2017220656A1
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WO
WIPO (PCT)
Prior art keywords
sulphuric acid
sulphur
section
sulphur dioxide
production
Prior art date
Application number
PCT/EP2017/065246
Other languages
French (fr)
Inventor
Lorenzo BRUNO
Original Assignee
Saipem S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Saipem S.P.A. filed Critical Saipem S.P.A.
Priority to EP17732408.4A priority Critical patent/EP3472097A1/en
Publication of WO2017220656A1 publication Critical patent/WO2017220656A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • 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
    • C01B17/48—Sulfur dioxide; Sulfurous acid
    • C01B17/50—Preparation of sulfur dioxide
    • C01B17/54—Preparation of sulfur dioxide by burning elemental sulfur
    • 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
    • C01B17/775—Liquid phase contacting processes or wet catalysis processes
    • 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

Definitions

  • the present invention finds application in the field of filtration of gases produced by boilers in thermal power plants . Such thermal power plants are particularly integrated into refinery plants . Alternatively, the present invention is applied to the filtration of off- gases from various combustion processes .
  • a refinery plant is a very complex structure, within which heavy crude processing systems for the production of hydrocarbons and important by-products for the petrochemical industry are located, and several facilities providing auxiliary services .
  • the SNOX/WSA system is used for the removal of sulphur dioxide contained in the flue gas from boilers or from off gas from the combustion of hydrogen sulphide, from FCC (Fluid Catalytic Cracking) , exhausted hydrogen sulphide incineration, etc .
  • the system essentially comprises a reaction section, a gas cooling section and a condensation section, as schematically shown in figure 1.
  • the sulphur dioxide reacts catalytically with oxygen to give sulphur trioxide .
  • the reaction conducted at about 400 °C, is as follows :
  • the reactor may optionally be associated with a reactor for NOx removal .
  • the off gas from the catalytic reaction section is cooled down to a temperature of about 260 °C .
  • a part of sulphur trioxide is combined with water vapour, yielding sulphuric acid vapours , as shown hereinafter :
  • Sulphuric acid stripping techniques with hot gases at about 400 °C are a possible alternative, but they suffer ma or problems of flexibility and the operating temperatures limit the use of materials .
  • a sulphuric acid production system generally comprises three sections : combustion, reaction, absorption .
  • elemental sulphur is sent at the liquid state to a burner where it is burnt with air to give :
  • the liquefied sulphur at a temperature of about 140-150 °C is sprayed through an atomizer to generate very fine droplets, characterized by a high contact surface to promote combustion with air.
  • the reaction reaches temperatures of about 1000 ⁇ -1600°C and a significant amount of heat is recovered in a steam generator, such as WHB with fume tubes .
  • sulphur dioxide is made reacting catalytically with the oxygen contained in the gas to give sulphur trioxide :
  • reaction is hindered by temperatures higher than 430 °C and, therefore, multiple catalytic beds must be used, from 2 to 3 , with an intercooler therebetween .
  • gases containing sulphur trioxide are suitably cooled to about 250 °C .
  • sulphur trioxide is absorbed by the water contained in a recirculating solution of sulphuric acid :
  • Concentrated sulphuric acid (about 98% by weight ) is obtained in this way, in an azeotropic solution and gases which, after being properly treated, are released to the atmosphere .
  • off gases containing unreacted SO2 are obtained from the absorption section, normally also released to the atmosphere.
  • the concentration of acid is maintained around 98% by adding water.
  • Figure 3 shows a diagram of such a system, in which the gas is treated passing through two catalytic beds and then treated in a first absorption column, where sulphur trioxide is converted to sulphuric acid .
  • the gases containing the residual sulphur dioxide are again heated up to 420 °C and sent to the third bed, where part of the SO2 is converted to SO3.
  • the gases leaving the third bed are cooled and sent to the second absorption tower, where sulphur trioxide is converted to sulphuric acid .
  • This process is able to recover 99.7% of sulphur dioxide (the residual SO2 is ⁇ 2 Kg per ton of sulphuric acid produced) .
  • EP 844211 it is disclosed sulphuric acid obtained from the condensation tower, which is sent to a stripping column at a temperature of 400-600 °C; in the column, part of the water is evaporated .
  • an integrated system for the production of sulphuric acid is described .
  • a solution of non-concentrated sulphuric acid is described, obtained from a SNOX/WSA process for the production of concentrated sulphuric acid in the absorption section of a system for the production of sulphuric acid from sulphur .
  • the present invention describes the use of off gases rich in sulphur dioxide from the absorption section of a system for the production of sulphuric acid from sulphur, in the reaction section of a SNOX/WSA system.
  • Figure 1 shows the diagram of a typical SNOX/WSA system
  • Figure 2 shows a schematization of a single contact sulphuric acid production system
  • Figure 3 shows a schematization of a double contact sulphuric acid production system
  • Figure 4 shows a typical SNOX/WSA system (A) and for the production of sulphuric acid from sulphur (B) ;
  • Figure 5 is a block diagram of a system according to the present invention, with a three-phase catalytic section;
  • Figure 6 is a block diagram of a system according to the present invention, with a two-phase catalytic section;
  • Figure 7 is a schematization of a system according to the present invention.
  • concentrated sulphuric acid refers to sulphuric acid at the concentration of about 98% by weight, corresponding to the azeotropic concentration .
  • sulphur dioxide or “sulphur trioxide” are to be construed as equivalent to "a gas rich in ... " or "a gas comprising ... "
  • a process is described for the preparation of concentrated sulphuric acid from a gas containing sulphur dioxide .
  • such a process comprises the steps of a) sub ecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain a gas comprising sulphuric anhydride ; b) sub ecting the gas comprising sulphuric anhydride to a cooling step in the presence of water so as to obtain an aqueous solution of non-concentrated sulphuric acid; c) sub ecting the solution obtained from step b) to an absorption step in the presence of sulphuric anhydride, wherein the sulphuric anhydride of step c) comprises sulphuric anhydride obtained from an oxidation step of the sulphur dioxide obtained in a process for preparing concentrated sulphuric acid from sulphur .
  • such a process comprises the steps of :
  • step d ' subject the sulphur dioxide obtained from step c ' ) to a catalytic oxidation in the presence of oxygen, thus obtaining sulphur trioxide ;
  • steps c') r d ' ) and e ' ) are carried out separately from steps a') and b ' ) , but in integration therewith .
  • steps a') and b ' ) are steps of a SNOX/ SA process for the production of sulphuric acid from sulphur dioxide .
  • steps c ' ) , d ' ) and e ' ) are carried out in a process for the production of sulphuric acid from sulphur .
  • the sulphuric acid obtained in a SNOX/WSA process is sent to the absorption step of a process for the production of sulphuric acid from sulphur .
  • such a process comprises the steps of :
  • sulphur dioxide of step f) comprises sulphur dioxide from the absorption step in a process for the production of concentrated sulphuric acid from sulphur.
  • such a process comprises the steps of :
  • step h' subjecting the sulphur trioxide of step g ' ) to an absorption step, thus obtaining concentrated sulphuric acid and an off gas rich in sulphur dioxide ;
  • step j ' subjecting sulphuric anhydride obtained from step i ' ) to a cooling and condensation step in the presence of water so as to obtain a solution of non TM concentrated sulphuric acid
  • gas containing sulphur dioxide of step i ' comprises the off gas of step h' ) .
  • steps f ' ) , g ' ) and h ' ) are carried out in (are part of) a process for the production of concentrated sulphuric acid from sulphur, while steps i ' ) and j ' ) (as well as the above steps f) and g) ) are carried out in (are part of) a SNOX/WSA process .
  • steps f ' ) , g ' ) and h ' ) are carried out separately from steps i ' ) and j') f but in integration therewith .
  • the off gas rich in sulphur dioxide obtained from the absorption step of a process for the production of sulphuric acid from sulphur is sent to the reaction step of a SNOX/WSA process .
  • Suitable catalysts known to the man skilled in the art are used in the catalytic oxidation steps .
  • the embodiment of the invention above described therefore allows to eliminate the treatment step of off gases resulting from a process for the production of sulphuric acid from sulphur and from the structural point of view, it allows to eliminate a gas emission point to the atmosphere from the system.
  • a process for the production of concentrated sulphuric acid comprising the steps of :
  • step 11 sub ecting the sulphur dioxide of step I ) to catalytic oxidation, thus obtaining sulphur trioxide ;
  • step V) subjecting the sulphuric anhydride of step IV) to a cooling and condensation step in the presence of water so as to obtain a solution of non-concentrated sulphuric acid
  • step III) is carried out in the presence of non- concentrated sulphuric acid obtained from step V) , and wherein
  • step IV) is carried out in the presence of the sulphur dioxide of the off gas produced in step III.
  • steps I), I I ) and III) are carried out in (are part of) a process for the production of sulphuric acid from sulphur .
  • steps IV) and V) are carried out in (are part of) a SNOX/WSA process .
  • an integrated system for the production of concentrated sulphuric acid is described .
  • such a system comprises:
  • condensation section is functionally connected to the absorption section (ASS2 ) of a system for the production of concentrated sulphuric acid from sulphur .
  • the oxidation (0X1), cooling (RAFF1 ) and condensation (CONDI ) sections are parts of a SNOX/WSA system.
  • such a system comprises:
  • absorption section (ASS2 ) is operatively connected to the catalytic oxidation section (0X1 ) of a system for the production of non-concentrated sulphuric acid from sulphur dioxide .
  • such a catalytic oxidation section (0X1 ) is part of a SNOX/WSA system.
  • an integrated system for the production of concentrated sulphuric acid comprising a SNOX/WSA system and a system for the production of sulphuric acid from sulphur, wherein both systems are structurally modified with respect to traditional ones .
  • the modifications comprise the functional connection of the cooling (RAFF1) and the condensation (CONDI ) section of the SNOX/WSA system, so that it is functionally connected to the absorption section (ASS2 ) a system for the production of sulphuric acid from sulphur and the functional connection of the absorption section (ASS2 ) of a system for the production of sulphuric acid from sulphur with the catalytic oxidation section (0X1 ) of a SNOX/WSA system.
  • RAFF1 cooling
  • CONDI condensation
  • such a system comprises:
  • a plant for the production of non-concentrated sulphuric acid from sulphur dioxide comprising:
  • RAFF1 a section for cooling the gases obtained from the non-concentrated sulphuric acid oxidation section in the form of steam;
  • a plant for the production of concentrated sulphuric acid from sulphur comprising:
  • condensation section 3 (CONDI ) is functionally connected to the absorption section 6) (ASS2 ) in a system for the production of sulphuric acid from sulphur; and in that
  • said absorption section 6) (ASS2 ) is operatively connected to the catalytic oxidation section 1 ) (0X1 ) .
  • sulphuric acid produced by the SNOX/WSA system is sent directly to the section of a system for the production of sulphuric acid from sulphur, and that the off gases from the absorption section of a system for the production of sulphuric acid from sulphur are sent directly to the catalytic oxidation section of the SNOX/WSA system.
  • a solution of non-concentrated sulphuric acid is described, obtained by a SNOX/WSA process in the absorption section of a system for the production of sulphuric acid from sulphur to obtain concentrated sulphuric acid .
  • the invention describes the use of off gases rich in sulphur dioxide from the absorption section of a system for the production of sulphuric acid from sulphur, in the catalytic reaction section of a SNOX/ SA system.
  • this ratio increases as the dilution of sulphuric acid from SNOX/WSA increases .
  • ⁇ 1 ⁇ 2 ⁇ 0.3 corresponding to a concentration of sulphuric acid of about 93% (by weight) .
  • the process of the present invention operates in conditions in which R > 0.1, i.e. corresponding to a concentration of about 98% by weight of sulphuric acid.
  • a sulphuric acid system of about 100 MTPD must be associated to it .
  • construction of a system for sulphuric acid associated with another system according to the present invention has a lower cost than a standard sulphuric acid system with the same capacity .
  • the impact on the CAPEX for the construction of the system for sulphuric acid is estimated in the order of about 5-10% of the SNOX system.
  • the integrated process described allows to use a low efficiency system for sulphuric acid, such as represented by a single contact process , thus resulting in a reduction in the manufacturing costs (CAPEX) .
  • the integrated system of the present invention does not increase the emission points , indeed, it eliminates at least one emission point .

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  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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Abstract

The present invention relates to a process for the production of concentrated sulphuric acid.

Description

Description
"Integrated process for the production of concentrated sulphuric acid"
Technical field of the invention
The present invention finds application in the field of filtration of gases produced by boilers in thermal power plants . Such thermal power plants are particularly integrated into refinery plants . Alternatively, the present invention is applied to the filtration of off- gases from various combustion processes .
Background art
A refinery plant is a very complex structure, within which heavy crude processing systems for the production of hydrocarbons and important by-products for the petrochemical industry are located, and several facilities providing auxiliary services .
Among these, we may mention in particular a system for the filtration of flue gases produced by boilers (SNOX/WSA) .
SNOX/WSA system
The SNOX/WSA system is used for the removal of sulphur dioxide contained in the flue gas from boilers or from off gas from the combustion of hydrogen sulphide, from FCC (Fluid Catalytic Cracking) , exhausted hydrogen sulphide incineration, etc . The system essentially comprises a reaction section, a gas cooling section and a condensation section, as schematically shown in figure 1.
1 ) reaction section
In this section, the sulphur dioxide reacts catalytically with oxygen to give sulphur trioxide . The reaction, conducted at about 400 °C, is as follows :
so2 + H o2- so3
The reactor may optionally be associated with a reactor for NOx removal .
2 ) cooling section
The off gas from the catalytic reaction section is cooled down to a temperature of about 260 °C . A part of sulphur trioxide is combined with water vapour, yielding sulphuric acid vapours , as shown hereinafter :
S03 + H20 (v) -> H2SO4 (v)
3 ) condensation section
In a glass tube heat exchanger, gas is cooled with air, thus completing the condensation of sulphuric acid :
H2SO4 (v) ->H2S04 (i)
Sulphuric acid thus condensed, once cooled, is stored to be then used as a by-product .
The drawback resulting from the use of this process is associated with the production of sulphuric acid at a concentration of 93-96%, which has a lower market value than concentrated sulphuric acid (about 98%) and which is more difficult to carry (especially by ship) as it is more corrosive and aggressive, especially for concentrations around 94
The methods currently used for the concentration of sulphuric acid by distillation have limits , as they require glass equipment , adapted to handle small volumes , and which are costly and delicate to assemble and maintain .
Sulphuric acid stripping techniques with hot gases at about 400 °C are a possible alternative, but they suffer ma or problems of flexibility and the operating temperatures limit the use of materials .
System for the production of sulphuric acid from sulphur
The production of concentrated sulphuric acid (about 98%) is normally obtained from sulphur .
A sulphuric acid production system generally comprises three sections : combustion, reaction, absorption .
In the combustion zone, elemental sulphur is sent at the liquid state to a burner where it is burnt with air to give :
S + 02-> S02 (ΔΗ= -297 kJ/mol) In particular, the liquefied sulphur at a temperature of about 140-150 °C is sprayed through an atomizer to generate very fine droplets, characterized by a high contact surface to promote combustion with air. The reaction reaches temperatures of about 1000~-1600°C and a significant amount of heat is recovered in a steam generator, such as WHB with fume tubes .
In the reaction zone, sulphur dioxide is made reacting catalytically with the oxygen contained in the gas to give sulphur trioxide :
S02 + ½ 02 * S03 (ΔΗ= -99 kJ/mol)
The reaction is hindered by temperatures higher than 430 °C and, therefore, multiple catalytic beds must be used, from 2 to 3 , with an intercooler therebetween .
In the absorption zone, instead, gases containing sulphur trioxide are suitably cooled to about 250 °C .
In particular, sulphur trioxide is absorbed by the water contained in a recirculating solution of sulphuric acid :
S02 + H02 ·* H2SO4 (ΔΗ= -101 kJ/raol)
Figure imgf000005_0001
Concentrated sulphuric acid (about 98% by weight ) is obtained in this way, in an azeotropic solution and gases which, after being properly treated, are released to the atmosphere . In addition, off gases containing unreacted SO2 are obtained from the absorption section, normally also released to the atmosphere.
The concentration of acid is maintained around 98% by adding water.
The recovery of sulphur in the form of sulphuric acid is 97-98%; the remainder is lost into the atmosphere as off gas rich in sulphur dioxide .
In order to reduce the concentration of sulphur dioxide in off gases , suitable methods may be adopted; one of these is the "Double Contact ----- Double Absorption (DC/DA) System" , far more efficient than the Single Contact Process (see figure 3 ) , allowing the recovery of 97-98%.
Figure 3 shows a diagram of such a system, in which the gas is treated passing through two catalytic beds and then treated in a first absorption column, where sulphur trioxide is converted to sulphuric acid . The gases containing the residual sulphur dioxide are again heated up to 420 °C and sent to the third bed, where part of the SO2 is converted to SO3. The gases leaving the third bed are cooled and sent to the second absorption tower, where sulphur trioxide is converted to sulphuric acid .
This process is able to recover 99.7% of sulphur dioxide (the residual SO2 is <2 Kg per ton of sulphuric acid produced) .
In prior-art document EP 2760566 there is disclosed a process for the preparation of sulphuric acid wherein the conversion of SO2 to SO3 and of SO3 to sulphuric acid are performed with two steps , with the purpose of increasing the conversion to sulphuric acid .
In EP 844211 it is disclosed sulphuric acid obtained from the condensation tower, which is sent to a stripping column at a temperature of 400-600 °C; in the column, part of the water is evaporated .
Summary of the invention
The authors of the present invention have surprisingly found that it is possible to produce concentrated sulphuric acid in a SNOX/WSA integrated with a system for the production of sulphuric acid from sulphur .
Ob ect of the invention
According to a first ob ect of the invention, a process for the production of concentrated sulphuric acid is described .
According to a second object of the invention, a process for the production of non-concentrated sulphuric acid is described .
According to a further object , a process for the production of sulphuric acid is described .
According to a further aspect of the invention, an integrated system for the production of sulphuric acid is described .
According to a further object, the use of a solution of non-concentrated sulphuric acid is described, obtained from a SNOX/WSA process for the production of concentrated sulphuric acid in the absorption section of a system for the production of sulphuric acid from sulphur .
According to yet another ob ect , the present invention describes the use of off gases rich in sulphur dioxide from the absorption section of a system for the production of sulphuric acid from sulphur, in the reaction section of a SNOX/WSA system.
Brief description of the drawings
Figure 1 shows the diagram of a typical SNOX/WSA system;
Figure 2 shows a schematization of a single contact sulphuric acid production system;
Figure 3 shows a schematization of a double contact sulphuric acid production system;
Figure 4 shows a typical SNOX/WSA system (A) and for the production of sulphuric acid from sulphur (B) ;
Figure 5 is a block diagram of a system according to the present invention, with a three-phase catalytic section;
Figure 6 is a block diagram of a system according to the present invention, with a two-phase catalytic section;
Figure 7 is a schematization of a system according to the present invention.
Detailed description of the invention
For the purposes of the present invention, concentrated sulphuric acid refers to sulphuric acid at the concentration of about 98% by weight, corresponding to the azeotropic concentration .
In the following description, reference can be made to sulphuric acid also when referring to an aqueous solution of sulphuric acid .
In the following description, "sulphur dioxide" or "sulphur trioxide" are to be construed as equivalent to "a gas rich in ... " or "a gas comprising ... "
The terms "a gas rich in ... " and "a gas comprising ... " are to be construed as equivalent to each other .
According to a first object of the invention, a process is described for the preparation of concentrated sulphuric acid from a gas containing sulphur dioxide .
In particular, such a process comprises the steps of a) sub ecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain a gas comprising sulphuric anhydride ; b) sub ecting the gas comprising sulphuric anhydride to a cooling step in the presence of water so as to obtain an aqueous solution of non-concentrated sulphuric acid; c) sub ecting the solution obtained from step b) to an absorption step in the presence of sulphuric anhydride, wherein the sulphuric anhydride of step c) comprises sulphuric anhydride obtained from an oxidation step of the sulphur dioxide obtained in a process for preparing concentrated sulphuric acid from sulphur .
According to a preferred aspect , such a process comprises the steps of :
a') subjecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain a gas comprising sulphuric anhydride ;
b ' ) subjecting the gas comprising sulphuric anhydride to a cooling and condensation step in the presence of water so as to obtain an aqueous solution of non-concentrated sulphuric acid; and the steps of :
c ' ) subjecting sulphur to combustion in the presence of oxygen, thus obtaining sulphur dioxide ;
d ' ) subject the sulphur dioxide obtained from step c ' ) to a catalytic oxidation in the presence of oxygen, thus obtaining sulphur trioxide ;
e' ) subjecting said sulphuric anhydride to an absorption step in the presence of the solution of sulphuric acid obtained from step b' ) . More in particular, steps c')r d ' ) and e ' ) are carried out separately from steps a') and b ' ) , but in integration therewith .
In a preferred aspect of the invention, steps a') and b ' ) are steps of a SNOX/ SA process for the production of sulphuric acid from sulphur dioxide .
In a preferred aspect , steps c ' ) , d ' ) and e ' ) are carried out in a process for the production of sulphuric acid from sulphur .
An off gas rich in sulphur dioxide is also obtained from the above step e ' ) ·
In practice, in the process described above, the sulphuric acid obtained in a SNOX/WSA process is sent to the absorption step of a process for the production of sulphuric acid from sulphur .
According to a second ob ect of the invention, an alternative process for the production of non- concentrated sulphuric acid is described .
In particular, such a process comprises the steps of :
f ) catalyt ically oxidizing a gas rich in sulphur dioxide so to obtain a gas rich in sulphur trioxide ;
g) cooling and condensing the sulphur trioxide obtained from the previous step in the presence of water so as to obtain liquid sulphuric acid,
wherein the sulphur dioxide of step f) comprises sulphur dioxide from the absorption step in a process for the production of concentrated sulphuric acid from sulphur.
According to a particular aspect , such a process comprises the steps of :
f ' ) sub ecting sulphur to a combustion step in the presence of oxygen, thus obtaining a gas rich in sulphur dioxide ;
g ' ) sub ecting the sulphur dioxide of step f ' ) to a catalytic oxidation step, thus obtaining sulphur trioxide ;
h' ) subjecting the sulphur trioxide of step g ' ) to an absorption step, thus obtaining concentrated sulphuric acid and an off gas rich in sulphur dioxide ;
and the steps of :
i ' ) subjecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain sulphuric anhydride ;
j ' ) subjecting sulphuric anhydride obtained from step i ' ) to a cooling and condensation step in the presence of water so as to obtain a solution of non™concentrated sulphuric acid,
wherein the gas containing sulphur dioxide of step i ' ) comprises the off gas of step h' ) .
According to a preferred aspect , steps f ' ) , g ' ) and h ' ) are carried out in (are part of) a process for the production of concentrated sulphuric acid from sulphur, while steps i ' ) and j ' ) (as well as the above steps f) and g) ) are carried out in (are part of) a SNOX/WSA process .
More in particular, steps f ' ) , g ' ) and h ' ) are carried out separately from steps i ' ) and j')f but in integration therewith .
In practice, in the above process , the off gas rich in sulphur dioxide obtained from the absorption step of a process for the production of sulphuric acid from sulphur is sent to the reaction step of a SNOX/WSA process .
Suitable catalysts known to the man skilled in the art are used in the catalytic oxidation steps .
The embodiment of the invention above described therefore allows to eliminate the treatment step of off gases resulting from a process for the production of sulphuric acid from sulphur and from the structural point of view, it allows to eliminate a gas emission point to the atmosphere from the system.
In a preferred aspect of the invention, it is possible to implement a process which therefore comprises one or both of the following aspects :
1 ) carrying out the absorption step in a process for the production of sulphuric acid from sulphur using non- concentrated sulphuric acid obtained from a SNOX/WSA process ;
2 ) carrying out the oxidation reaction of sulphur dioxide in a SNOX/WSA process , wherein such a sulphur dioxide comprises the sulphur dioxide produced from a process for the production of concentrated sulphuric acid from sulphur (and contained in the off gases of the absorption step) .
A process for the production of concentrated sulphuric acid is therefore described, comprising the steps of :
I ) sub ecting sulphur to combustion in the presence of oxygen, thus obtaining a gas rich in sulphur dioxide ;
11 ) sub ecting the sulphur dioxide of step I ) to catalytic oxidation, thus obtaining sulphur trioxide ;
III) carrying out a step for absorbing sulphuric anhydride in the presence of non-concentrated sulphuric acid thus obtaining concentrated sulphuric acid and an off gas comprising sulphur dioxide ;
and separately :
IV) carrying out a catalytic oxidation step of a gas comprising sulphur dioxide in the presence of oxygen so as to obtain sulphuric anhydride ;
V) subjecting the sulphuric anhydride of step IV) to a cooling and condensation step in the presence of water so as to obtain a solution of non-concentrated sulphuric acid,
wherein
step III) is carried out in the presence of non- concentrated sulphuric acid obtained from step V) , and wherein
step IV) is carried out in the presence of the sulphur dioxide of the off gas produced in step III.
According to an even more preferred aspect of the invention, steps I), I I ) and III) are carried out in (are part of) a process for the production of sulphuric acid from sulphur .
According to an even more preferred aspect of the invention, steps IV) and V) are carried out in (are part of) a SNOX/WSA process .
According to another object of the present invention, an integrated system for the production of concentrated sulphuric acid is described .
In particular, such a system comprises :
- a section for the catalytic oxidation (0X1 ) of sulphur dioxide contained in a gas into sulphur trioxide ; a section for cooling (RAFF1 ) said sulphur trioxide so as to obtain non-concentrated sulphuric acid not in the form of steam;
■- a condensation section (CONDI ) of sulphuric acid into steam to obtain liquid non-concentrated sulphuric acid;
wherein said condensation section (CONDI ) is functionally connected to the absorption section (ASS2 ) of a system for the production of concentrated sulphuric acid from sulphur . According to a preferred aspect, the oxidation (0X1), cooling (RAFF1 ) and condensation (CONDI ) sections are parts of a SNOX/WSA system.
According to another o ect of the present invention, an integrated system for the production of sulphuric acid is described .
In particular, such a system comprises :
- a section for the combustion (C0MB2 ) of sulphur in the presence of oxygen to obtain sulphur dioxide ;
~ a section for the catalytic oxidation (0X2 ) of sulphur dioxide to obtain sulphur trioxide ;
a section for absorbing (ASS2 ) the sulphuric anhydride, thus obtaining concentrated liquid sulphuric acid and an off gas rich in sulphur dioxide ;
wherein said absorption section (ASS2 ) is operatively connected to the catalytic oxidation section (0X1 ) of a system for the production of non-concentrated sulphuric acid from sulphur dioxide .
According to a preferred aspect , such a catalytic oxidation section (0X1 ) is part of a SNOX/WSA system.
According to a further ob ect of the present invention, an integrated system for the production of concentrated sulphuric acid is described, comprising a SNOX/WSA system and a system for the production of sulphuric acid from sulphur, wherein both systems are structurally modified with respect to traditional ones . More in detail, the modifications comprise the functional connection of the cooling (RAFF1) and the condensation (CONDI ) section of the SNOX/WSA system, so that it is functionally connected to the absorption section (ASS2 ) a system for the production of sulphuric acid from sulphur and the functional connection of the absorption section (ASS2 ) of a system for the production of sulphuric acid from sulphur with the catalytic oxidation section (0X1 ) of a SNOX/WSA system.
According to a preferred aspect of the invention, such a system comprises :
a) a plant for the production of non-concentrated sulphuric acid from sulphur dioxide , comprising :
1 ) a section for the catalytic oxidation (0X1 ) of sulphur dioxide into sulphur trioxide ;
2 ) a section for cooling (RAFF1 ) the gases obtained from the non-concentrated sulphuric acid oxidation section in the form of steam;
3 ) a condensation section (CONDI ) of sulphuric acid into steam to obtain liquid non-concentrated sulphuric said integrated system further comprising :
b) a plant for the production of concentrated sulphuric acid from sulphur, comprising :
4 ) a section for the combustion of sulphur (C0MB2 ) in the presence of oxygen to obtain sulphur dioxide ; 5) a section for the catalytic oxidation of sulphur dioxide (0X2 ) to obtain sulphur trioxide ;
6) a section for absorbing (ASS2 ) sulphuric anhydride in order to obtain liquid sulphuric acid and an off gas rich in sulphur dioxide ;
and being characterized in that :
said condensation section 3 ) (CONDI ) is functionally connected to the absorption section 6) (ASS2 ) in a system for the production of sulphuric acid from sulphur; and in that
said absorption section 6) (ASS2 ) is operatively connected to the catalytic oxidation section 1 ) (0X1 ) .
By "functional connection" it is meant that the sulphuric acid produced by the SNOX/WSA system is sent directly to the section of a system for the production of sulphuric acid from sulphur, and that the off gases from the absorption section of a system for the production of sulphuric acid from sulphur are sent directly to the catalytic oxidation section of the SNOX/WSA system.
A structural integration between the two systems is thus created .
According to another ob ect of the invention, the use of a solution of non-concentrated sulphuric acid is described, obtained by a SNOX/WSA process in the absorption section of a system for the production of sulphuric acid from sulphur to obtain concentrated sulphuric acid .
According to yet another object, the invention describes the use of off gases rich in sulphur dioxide from the absorption section of a system for the production of sulphuric acid from sulphur, in the catalytic reaction section of a SNOX/ SA system.
An important parameter for assessing the feasibility of the integration described in the present invention is :
Figure imgf000019_0001
which allows to size the sulphuric acid system with respect to the SNOX/WSA system.
In particular, this ratio increases as the dilution of sulphuric acid from SNOX/WSA increases .
Other parameters (in moles , unless otherwise stated) are represented by :
Figure imgf000019_0002
Generally, ϊ½<0.3 , corresponding to a concentration of sulphuric acid of about 93% (by weight) .
The process of the present invention operates in conditions in which R > 0.1, i.e. corresponding to a concentration of about 98% by weight of sulphuric acid.
In a typical limit case, R2=0.3 and if we consider that
Figure imgf000020_0001
should be obtained, we consider as the only source of water that from the sulphuric acid of the SNOX system (deeming irrelevant the water from the combustion air) we will obtain typical ratios of
Figure imgf000020_0002
If we consider the conversion of 97% of sulphuric acid in the system (higher conversion values have often been achieved) :
Figure imgf000020_0003
and R3-0.2.
For example, if the SNOX system produces 500 MTPD (very high productions for a boiler fume SNOX) ,
a sulphuric acid system of about 100 MTPD must be associated to it .
Such systems are much smaller than the size of traditional systems .
In addition, the construction of a system for sulphuric acid associated with another system according to the present invention has a lower cost than a standard sulphuric acid system with the same capacity .
For the SNOX system employing fumes from boiler comprising diluted SO2, the impact on the CAPEX for the construction of the system for sulphuric acid is estimated in the order of about 5-10% of the SNOX system.
The man skilled in the art will be able to understand the several advantages offered by the process of the present invention from the above description.
In particular, it will be possible to obtain concentrated sulphuric acid (concentration of about 98%) using the non-concentrated sulphuric acid produced by a SNOX/WSA system; such a concentration at 98% increases the commercial value of sulphuric acid, which can be more easily stored and transported, due to the lower risk and corrosive power .
The possibility of using the SNOX/WSA system is another advantage linked to the fact that its technology is well established and does not comprise equipment with particular criticalities.
The integrated process described allows to use a low efficiency system for sulphuric acid, such as represented by a single contact process , thus resulting in a reduction in the manufacturing costs (CAPEX) .
A further saving on cost results from the possibility of avoiding the insertion of ceramic filters in the absorption section of the system for sulphuric acid, as the fumes can be sent directly to the SNOX/WSA .
In addition, the process described does not have the typical capacity limits of the traditional systems for the production of concentrated sulphuric acid nor the limits in the use of materials .
The integrated system of the present invention does not increase the emission points , indeed, it eliminates at least one emission point .

Claims

CLAIMS :
1. Process for preparing concentrated sulphuric acid comprising the steps of :
a) su jecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain a gas comprising sulphuric anhydride ;
b) subjecting the gas comprising sulphuric anhydride obtained from step a) to a cooling and condensation step in the presence of water so as to obtain an aqueous solution of non-concentrated sulphuric acid;
c) subjecting the solution obtained from step b) to an absorption step in the presence of sulphuric anhydride, wherein the sulphuric anhydride of step c) comprises sulphuric anhydride obtained in a process for preparing concentrated sulphuric acid from sulphur .
2. Process for preparing concentrated sulphuric acid according to claim 1 comprising the steps of :
a') subjecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain a gas comprising sulphuric anhydride ;
h' ) subjecting the gas comprising sulphuric anhydride obtained from step a' ) to a cooling and condensation step in the presence of water so as to obtain an aqueous solution of non-concentrated sulphuric acid; and the steps of : c' ) subjecting sulphur to combustion in the presence of oxygen so as to obtain sulphur dioxide;
d' ) sub ecting the sulphur dioxide obtained from step c' ) to a catalytic oxidation in the presence of oxygen so as to obtain sulphuric anhydride ;
e' ) subjecting the sulphuric anhydride obtained from step d' ) to an absorption step in the presence of the solution of non-concentrated sulphuric acid obtained from step b' ) .
3. Process according to claim 1 or 2, wherein the steps a) and b) or, a' ) and b' ) , respectively, are steps of a
SNOX/WSA process .
4. Process according to claim 2 or 3 , wherein said step c' ) , d' ) and e' ) are steps of a process for the production of sulphuric acid from sulphur .
5. Process for the production of non-concentrated sulphuric acid comprising the steps of :
f) catalytically oxidating a gas rich in sulphur dioxide thus obtaining a gas rich in sulphuric anhydride ;
g) cooling and condensing the sulphur trioxide obtained from the previous step in the presence of water so as to obtain liquid sulphuric acid,
wherein the sulphur dioxide of step f) comprises the sulphur dioxide obtained from the absorption step of a process for the production of concentrated sulphuric acid from sulphur .
6. Process for the production of non-concentrated sulphuric acid according to claim 5, comprising the steps of :
f ' ) subjecting sulphur to a combustion step in the presence of oxygen, thus obtaining a gas rich in sulphur dioxide ;
g' ) sub ecting the sulphur dioxide obtained from step f ' ) to a catalytic oxidation step thus obtaining sulphuric anhydride ;
hf ) subjecting the sulphuric anhydride obtained from the preceding step to an absorption step so as to obtain concentrated sulphuric acid and an off gas rich in sulphur dioxide ; and the steps of :
i ' ) subjecting a gas containing sulphur dioxide to a catalytic oxidation step in the presence of oxygen so as to obtain sulphuric anhydride ;
j ' ) subjecting sulphuric anhydride obtained from step i ' ) to a cooling and condensation step in the presence of water so as to obtain a solution of non-concentrated sulphuric acid,
wherein the gas containing sulphur dioxide of step i ' ) comprises the off gas of step h' ) .
7. Process according to claim 5 or 6, wherein the steps f) and g) or, i' ) and j ' ) , respectively, are steps of a SNOX/WSA process .
8. Process according to claim 6 or 7, wherein the steps f' ) , g' ) and h' ) are steps of a process for the production of sulphuric acid from sulphur .
9. Process for the production of concentrated sulphuric acid and of non-concentrated sulphuric acid, comprising the steps of :
I ) su jecting sulphur to combustion in the presence of oxygen, thus obtaining a gas rich in sulphur dioxide ;
I I ) sub ecting the sulphur dioxide of step I ) to catalytic oxidation, thus obtaining sulphur trioxide ;
III) carrying out a step for absorbing sulphuric anhydride in the presence of non-concentrated sulphuric acid thus obtaining concentrated sulphuric acid and an off gas comprising sulphur dioxide ;
and separately
IV) carrying out a catalytic oxidation step of a gas comprising sulphur dioxide in the presence of oxygen so as to obtain sulphuric anhydride ;
V) subjecting the sulphuric anhydride of step IV) to a cooling and condensation step so as to obtain a solution of non-concentrated sulphuric acid,
wherein
step III) is carried out in the presence of non- concentrated sulphuric acid obtained from step V) ; and wherein step IV) is carried out in the presence of the sulphur dioxide of the off gas obtained from step III.
10. Process according to claim 8, wherein steps I), 11 ) and III) are steps of a process for the production of concentrated sulphuric acid from sulphur and steps IV) and V) are steps of a SNOX/WSA process .
11. Integrated plant for the production of sulphuric acid comprising :
a section for the catalytic oxidation (0X1 ) of the sulphur dioxide contained in a gas so as to obtain sulphuric anhydride ;
- a section for cooling (RAFF1 ) said sulphur trioxide so as to obtain non-concentrated sulphuric acid not in the form of steam;
- a condensation section (CONDI ) of sulphuric acid into steam to obtain liquid non-concentrated sulphuric acid; wherein said condensation section (CONDI ) is functionally connected to the absorption section (ASS2 ) of a plant for the production of concentrated sulphuric acid from sulphur .
12. Integrated plant for the production of sulphuric acid comprising :
a section for the combustion of sulphur (COMB2 ) in the presence of oxygen so as to obtain sulphur dioxide ;
- a section for the catalytic oxidation (0X2 ) of the sulphur dioxide so as to obtain sulphuric anhydride;
----- a section for absorbing (ASS2 ) sulphuric anhydride in order to obtain concentrated liquid sulphuric acid and an off gas rich in sulphur dioxide ;
wherein said absorption section (ASS2 ) is operatively connected to the catalytic oxidation section (0X1 ) of the sulphur dioxide of a plant for the production of sulphuric acid from sulphur dioxide .
13. Integrated plant for the production of sulphuric acid comprising :
a) a plant for the production of non-concentrated sulphuric acid from sulphur dioxide , comprising :
1 ) a section for the catalytic oxidation (0X1 ) of sulphur dioxide into sulphur trioxide ;
2 ) a section for cooling (RAFF1 ) the gases obtained from the non-concentrated sulphuric acid oxidation section in the form of steam;
3 ) a section for condensing (CONDI ) the sulphuric acid into vapour in order to obtain liquid non-concentrated sulphuric acid;
said integrated plant further comprising :
b) a plant for the production of concentrated sulphuric acid from sulphur, comprising :
4 ) a section for the combustion (C0MB2) of sulphur in the presence of oxygen so as to obtain sulphur dioxide ; 5) a section for the catalytic oxidation (0X2) of the sulphur dioxide so as to obtain sulphuric anhydride ;
6) a section for absorbing (ASS2 ) sulphuric anhydride in order to obtain liquid sulphuric acid and an off gas rich in sulphur dioxide ;
and being characterized in that :
- said condensation section 3 ) (CONDI ) is operatively connected to the absorption section 6) (ASS2 ) of a plant for the production of sulphuric acid from sulphur; and in that
- said absorption section (ASS2 ) is operatively connected to the oxidation section 1 ) (0X1 ) .
14. Use of a solution of non-concentrated sulphuric acid obtained by a SNOX/WSA process for the production of concentrated sulphuric acid in an absorption section of a plant for the production of sulphuric acid from sulphur .
15. Use of off gases rich in sulphur dioxide coming from the absorption section of a plant for the production of sulphuric acid from sulphur, in a reaction section of a SNOX/WSA plant .
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CN113666342A (en) * 2021-07-13 2021-11-19 南通醋酸化工股份有限公司 Waste acid treatment method and system for producing acesulfame potassium

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