CA2262265A1 - Apparatus for concentrating and purifying sulfuric acid - Google Patents
Apparatus for concentrating and purifying sulfuric acid Download PDFInfo
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- CA2262265A1 CA2262265A1 CA002262265A CA2262265A CA2262265A1 CA 2262265 A1 CA2262265 A1 CA 2262265A1 CA 002262265 A CA002262265 A CA 002262265A CA 2262265 A CA2262265 A CA 2262265A CA 2262265 A1 CA2262265 A1 CA 2262265A1
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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
- C01B17/88—Concentration of sulfuric acid
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0053—Details of the reactor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0053—Details of the reactor
- B01J19/0073—Sealings
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/02—Apparatus characterised by being constructed of material selected for its chemically-resistant properties
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
- F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
- F28F21/081—Heat exchange elements made from metals or metal alloys
- F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
- F28F21/083—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys from stainless steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/00049—Controlling or regulating processes
- B01J2219/00051—Controlling the temperature
- B01J2219/00074—Controlling the temperature by indirect heating or cooling employing heat exchange fluids
- B01J2219/00087—Controlling the temperature by indirect heating or cooling employing heat exchange fluids with heat exchange elements outside the reactor
- B01J2219/00101—Reflux columns
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/00049—Controlling or regulating processes
- B01J2219/00051—Controlling the temperature
- B01J2219/00074—Controlling the temperature by indirect heating or cooling employing heat exchange fluids
- B01J2219/00087—Controlling the temperature by indirect heating or cooling employing heat exchange fluids with heat exchange elements outside the reactor
- B01J2219/00103—Controlling the temperature by indirect heating or cooling employing heat exchange fluids with heat exchange elements outside the reactor in a heat exchanger separate from the reactor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/00049—Controlling or regulating processes
- B01J2219/00051—Controlling the temperature
- B01J2219/00074—Controlling the temperature by indirect heating or cooling employing heat exchange fluids
- B01J2219/00105—Controlling the temperature by indirect heating or cooling employing heat exchange fluids part or all of the reactants being heated or cooled outside the reactor while recycling
- B01J2219/0011—Controlling the temperature by indirect heating or cooling employing heat exchange fluids part or all of the reactants being heated or cooled outside the reactor while recycling involving reactant liquids
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/02—Apparatus characterised by their chemically-resistant properties
- B01J2219/025—Apparatus characterised by their chemically-resistant properties characterised by the construction materials of the reactor vessel proper
- B01J2219/0259—Enamel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/02—Apparatus characterised by their chemically-resistant properties
- B01J2219/025—Apparatus characterised by their chemically-resistant properties characterised by the construction materials of the reactor vessel proper
- B01J2219/0277—Metal based
- B01J2219/0286—Steel
-
- 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
- Y02P20/141—Feedstock
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
An apparatus and process for concentrating sulfuric acid to an H2SO4 content of 95 to 98% and optionally for purifying the sulfuric acid at a temperature of 270 to 340°C are described. The apparatus consists at least of a naturally circulating evaporator system (4, 5; 6: 7; 1; 13) comprising a two-part vapour hood (4, 5), a heat exchanger (1), in particular a shell-and-tube heat exchanger, a circulating line (6, 7) and a distillation column (13), wherein the parts of the apparatus conveying the liquid sulfuric acid at a temperature of 270 to 340°C comprising the lower part of the vapour hood (4), heat exchanger (1) and circulating line (6, 7) consist of an austenitic/ferritic iron alloy containing silicon of a specific composition.
Description
Le A 32 737 BW/FC
Apparatus for concentrating and purifying sulfuric acid This invention relates to an apparatus for concentrating and purifying sulfuric acid which allows sulfuric acid to be concentrated at 270-340°C to an H,S04 content of 95-98%. The parts of the apparatus which convey sulfuric acid consist of austenitic or austenitic/ferritic steels.
It is known to concentrate waste sulfuric acid to approx. 96% under slightly reduced pressure and temperatures in the range from 300 to 320°C (Winnacker, Kiichler, Chemische Technologie, volume 2, 4'h edition 1982, pp. 67-70).
In the so-called Pauling process, waste sulfuric acid is evaporated from an HZSO~
content of 70-85% to 95-96% in cast iron boilers indirectly heated with flue gases and equipped with a distillation column. Considerable corrosive losses must always 1 S be allowed for in the production of the boilers by means of large wall thicknesses.
The ratio of heat transfer surface to boiler volume in such apparatus is highly unfavourable. Such plants consequently constitute a considerable safety hazard because, in the event of boiler failure, approx. 10 m3 of boiling 96% sulfuric acid could flow into the combustion chamber, which is at a temperature of approx.
750°C. In the drum concentrator, the sulfuric acid is concentrated by direct contact with hot flue gases. The exhaust gases are contaminated with SO~, sulfuric acid vapour, nitrogen oxides and optionally organic compounds, so entailing considerable purification costs due to the large specific exhaust gas volume.
Achieving a high degree of concentration in a falling film evaporator made from silica glass (EP-A 22 473) has only been possible to implement in small units.
The same applies to the high degree of concentration described in DE-A 2 909 029 which is achieved by means of IR heat sources made from silica glass immersed in the sulfuric acid.
LeA32737 _2_ Vacuum evaporators having heat exchangers made from tantalum (cf. for example EP-A 156 199) are restricted to a temperature range of below 200°C.
At such temperatures, sulfuric acid may only be evaporated to 95-96% under extremely reduced pressures, so entailing specifically large plant size per unit evaporating output and high costs for producing the vacuum and condensing the vapours.
Moreover, the conditions for oxidative degradation of organic impurities are also very unfavourable due to the low acid temperature.
The object was accordingly to develop an apparatus which makes it possible to achieve highly efficient water evaporation with a low sulfuric acid content at temperatures in the range above 250°C and optionally to permit oxidative purification.
The object was achieved according to the invention by an apparatus for concentrating sulfuric acid to an HZSOa content of 95-98% and optionally for purifying the sulfuric acid at a temperature of 270 to 340°C, consisting of at least a naturally circulating evaporator system comprising a two-part vapour hood, a heat exchanger, in particular a shell-and-tube heat exchanger, circulating line and distillation column, characterised in that the parts of the apparatus conveying the liquid sulfuric acid at a temperature of 270 to 340°C comprising the lower part of the vapour hood, heat exchanger and circulating line consist of an austenitic/ferritic iron alloy containing silicon of the following composition from 13 to 32 wt.% of chromium from 5 to 25 wt.% of nickel from 4 to 9 wt.% of silicon max. 0.07 wt.% of carbon max. 0.03 wt.% of sulfur max. 0.03 wt.% of phosphorus max. 8 wt.% of manganese max_ 3 wt.% of molybdenum T _ A 11 rl ~1 ~7 max. 4 wt.% of copper max. 20 wt.% of cobalt max. 4 wt.% of tungsten max. 2 wt.% of niobium and tantalum max. 0.2 wt.% of nitrogen and a remainder to make up to 100 wt.% of iron with a structure having a delta ferrite fraction of between 10 and 65%, preferable containing at least 20 percent by weight Fe, or of austenitic iron alloys comprising from 10 to 12 wt.% of chromium from 15.5 to 17.5 wt.% of nickel from 5.7 to 6.5 wt.% of silicon max. 0.06 wt.% of carbon max. 0.03 wt.% of phosphorus max. 0.03 wt.% of sulfur max. 1.5 wt.% of manganese max. 0.15 wt.% of titanium max. 0.8 wt.% of zirconium max. 0.2 wt.% of nitrogen max. 0.3 wt.% of molybdenum max. 0.01 wt.% of boron max. 0.25 wt.% of rare earth metals max. 1 wt.% of magnesium, aluminium and calcium and a remainder to to make up 100 wt.%
of iron or from 8 to 16 wt.% of chromium from 20 to 30 wt.% of nickel from >6.5 to 7.4 wt.% of silicon max. 0.03 wt.% of carbon max. 0.03 wt.% of phosphorus Le A 32 737 max. 0.01 wt.% of sulfur max. I wt.% of magnesium, aluminium and calcium and a remainder up to 100 wt.% of iron, and in which the upper part of the vapour hood and the distillation column consist of enamelled steel.
The lower part of the vapour hood is preferably provided with a discharge pipe made from an iron alloy containing silicon which ends with an outlet in an immersion vessel made from iron alloy containing silicon or enamelled steel.
In a preferred embodiment, the circulating line has an additional discharge port and/or a port for introducing gases, for example air or inert gas, in order to increase the acid circulation speed and/or for introducing oxidising agents, for example sulfuric acid, hydrogen peroxide, ozone, nitrosylsulfuric acid.
The heat exchanger of the apparatus is in particular a shell-and-tube heat exchanger, through the tubes of which the circulating sulfuric acid flows, and which is heated by flue gas or electricity.
The tubes of the heat exchanger preferably comprise bimetallic tubes, wherein the inner tube consists of the same iron alloy containing silicon as the lower part of the vapour hood and the outer tube consists of heat-resistant steel.
In another preferred embodiment, the lower part and upper part of the vapour hood are joined together by a pair of flanges, wherein the flange of the lower part consists of the same iron alloy containing silicon as the lower part of the vapour hood.
In a preferred embodiment of the invention, the flange of the lower part of the vapour hood has at least two annular grooves to accommodate seals.
LeA32737 _5_ In a particularly preferred embodiment of the invention, the parts of the apparatus which consist of iron alloys containing silicon are provided with a superficial passivating layer which is produced by at least 24 hours treatment with 95 to 98%
sulfuric acid at 290 to 340°C, preferably by at least 12 hours treatment with 95 to 98% sulfuric acid, which contains at least 350 ppm of nitrosylsulfuric acid, at a temperature of 250 to 340°C, or with 95 to 100% nitric acid at a temperature of 70 to 90°C, wherein the pressure selected is suff=iciently high that the liquid does not boil.
The packing of the distillation column is in particular made from glass, cast silicon iron or ceramics.
The present invention also provides a process for concentrating sulfuric acid to a concentration of 95 to 98% using the apparatus according to the invention, which process is characterised in that the apparatus is charged with sulfuric acid of a concentration of 70 to 93% and the sulfuric acid is distilled at a pressure of 0.3 to 1.2 bar (abs.), preferably of 0.8 to 0.99 bar (abs.) and a temperature of 270 to 340°C, preferably of 280 to 320°C.
Purification of the sulfuric acid is in particular achieved by introducing oxidising agents such as nitrosylsulfuric acid, nitric acid, hydrogen peroxide. ozone or others into the circulating sulfuric acid. If the introduction is made beneath the heat exchanger, the circulation speed of the liquid acid is advantageously increased by the resultant reaction gases.
The present invention also provides the use of the apparatus according to the invention for concentrating and optionally purifying sulfuric acid.
One disadvantage of known sulfuric acid evaporating plants made from enamelled steel is the numerous flange connections which cause problems, especially at relatively high operating temperatures. In the apparatus according to the invention, LeA32737 flange connections may be entirely avoided in those parts of the plant containing hot liquid sulfuric acid, as the alloys used according to the invention are weldable.
It is, however, preferred to use flange connections wherever appropriate for plant design or processing reasons, in particular with regard to cleaning requirements.
Particularly preferred flange connections are those of the groove and spring designs.
Compensators, which are required to offset the thermal expansion of plant components made from the same iron alloy containing silicon as the lower part of the vapour hood, may also be used.
The apparatus components made from iron alloys containing silicon are preferably subjected to a passivating surface treatment before the intended commissioning thereof for concentrating sulfuric acid. The preferred treatment is for at least 24 I S hours with 95 to 98% sulfuric acid at 250 to 340°C, preferably for at least 12 hours with 95 to 98% sulfuric acid which contains at least 350 ppm of nitrosylsulfuric acid at a temperature of 250 to 340°C or with 95 to 100% nitric acid for at least 12 hours at a temperature of 70 to 90°C and under a pressure at which the liquid does not boil.
The apparatus according to the invention for concentrating and optionally purifying sulfuric acid provides various advantages in comparison with prior art apparatus:
The materials and heating media used allow the apparatus to be operated at 270 to 340°C and a pressure of 0.3 to I.2 bar (abs.), preferably of 0.8 to 0.99 bar (abs.).
In comparison with plants having tantalum heat exchangers, which may be operated at a maximum of 200°C, the apparatus according to the invention permits the optimum operating conditions for destroying organic impurities in the sulfuric acid while simultaneously minimising vapour condensation costs.
LeA32737 _7_ The comparatively high operating pressure moreover permits small apparatus dimensions, so reducing the capital costs for the plant.
In comparison with known Pauling plants, the specific acid content (relative to water evaporating output) is only 10 to 20%. It is particularly advantageous that in the event of leakage, the released acid may straightforwardly be retained in a bund, whereas leaks from Pauling boilers pass into the boiler furnace chamber and thus cause considerable S03 emissions.
Due to the possible large temperature difference between heating medium and sulfuric acid. the specific heat exchange surface required is very small in comparison with plants which must be heated with steam or heat-transfer oil.
The parts made from iron alloy containing silicon are preferably all covered with liquid sulfuric acid during operation. This ensures that no corrosive sulfuric acid of a lower concentration can cause corrosion damage to the apparatus by condensation at cold points.
Producing the upper part of the vapour hood from enamelled steel has the advantage that the condensates containing dilute sulfuric acid which occur in this part may readily be processed according to the invention without leaving corrosion damage on the walls of the upper part of the vapour hood. Other corrosion processes accordingly proceed in this section of the apparatus than in the area of the lower part of the vapour hood or in the naturally circulating portion.
Since all parts of the apparatus which contain liquid sulfuric acid at a temperature of above 270°C may be joined together by welds or groove and spring flanges, the apparatus according to the invention suffers no sealing problems.
The invention is illustrated in greater detail below by the figures, without the invention consequently being limited by specific details.
LeA32737 _g_ The figures show Figure 1 a schematic representation of one embodiment of the apparatus according to the invention Figure 2 an magnified representation of the flange connection between the lower part (4) and upper part (5) of the vapour hood of the apparatus according figure 1.
Le A 32 737 Example Figure I shows the schematic structure of the concentration apparatus. The apparatus consists of a two part vapour hood 4, 5, a shell-and-tube heat exchanger I, a circulating line 6, 7 and a distillation column 13, which together form a naturally circulating evaporator system.
The parts of the heat exchanger I which come into contact with sulfuric acid consist of iron alloy containing silicon with 5.94% Si, 17.49% Ni, I 1.34% Cr, 62.7%
Fe and comprise bimetallic tubes 16 with an inner tube 17 consisting of the iron alloy containing silicon and an outer tube 18 made from heat-resistant steel I
.4593.
The circulating line 6 is provided with a discharge port I I and with a port 12 for introducing air or oxidising agents (65% HN03; sulfuric acid saturated with nitrosylsulfuric acid) for destroying organic compounds.
An overflow tube 8 passes through the wall of the lower part 4 of the vapour hood, through which tube the hot concentrated sulfuric acid is discharged into the immersion vessel 9, from which it flows through the port 10 into a receiver or an acid condenser. All the parts of the apparatus hitherto described, which come into contact with liquid 95-98% sulfuric acid at a temperature of 270-340°C, are made from the above-stated iron alloy containing silicon and are joined together by welded joints.
The size of the immersion vessel 9 is adapted to the operating pressure of the apparatus and to the residence time required for complete oxidation of organic impurities. For the intended operating temperature of 320°C and the production of 6 t/h of 96% acid, the volume is 1.5 m~ and the immersion depth 50 cm.
The lower part 4 of the vapour hood is connected to the upper part 5 by a flange connection (see detail in figure 2), which is made from enamelled steel. A
column 13 is placed upon the upper part 5, the column being made from enamelled steel and filled with glass packing. Above the column is located the feed line 15 for the 70 to LeA32737 93% sulfuric acid, which is distributed by a suitable distribution system, for example a nozzle 26, over the column packing 24. The aqueous vapours are discharged through the port 14 to a condensing system which is not shown.
The heat exchanger 1 is designed for heating with flue gas (cf. figure 1 ), which is introduced through a gas inlet port 2 into the space around the tubes 16 and discharged through a gas outlet port 3. The flue gas is passed repeatedly through the tube bundle by means of a false bottom. The outer shell of the heat exchanger 1 and the ports 2, 3 consist of heat-resistant steel.
Figure 2 shows the pair of flanges with which the lower part 4 and upper part 5 of the vapour hood are connected. Grooves 23 to accommodate seals 22 made from glass- or porcelain-filled PTFE are provided in the lower part flange 21) which is made from the iron alloy containing silicon. The mating flange 20 consists of enamelled steel. For safety reasons, the width of the flange is at least 100 mm, such that the outer seal is not heated above approx. 150°C and remains fully fianctional in order to provide a reliable outward seal. The flanges are compressed and fastened together by means of autoclave clamps.
Apparatus for concentrating and purifying sulfuric acid This invention relates to an apparatus for concentrating and purifying sulfuric acid which allows sulfuric acid to be concentrated at 270-340°C to an H,S04 content of 95-98%. The parts of the apparatus which convey sulfuric acid consist of austenitic or austenitic/ferritic steels.
It is known to concentrate waste sulfuric acid to approx. 96% under slightly reduced pressure and temperatures in the range from 300 to 320°C (Winnacker, Kiichler, Chemische Technologie, volume 2, 4'h edition 1982, pp. 67-70).
In the so-called Pauling process, waste sulfuric acid is evaporated from an HZSO~
content of 70-85% to 95-96% in cast iron boilers indirectly heated with flue gases and equipped with a distillation column. Considerable corrosive losses must always 1 S be allowed for in the production of the boilers by means of large wall thicknesses.
The ratio of heat transfer surface to boiler volume in such apparatus is highly unfavourable. Such plants consequently constitute a considerable safety hazard because, in the event of boiler failure, approx. 10 m3 of boiling 96% sulfuric acid could flow into the combustion chamber, which is at a temperature of approx.
750°C. In the drum concentrator, the sulfuric acid is concentrated by direct contact with hot flue gases. The exhaust gases are contaminated with SO~, sulfuric acid vapour, nitrogen oxides and optionally organic compounds, so entailing considerable purification costs due to the large specific exhaust gas volume.
Achieving a high degree of concentration in a falling film evaporator made from silica glass (EP-A 22 473) has only been possible to implement in small units.
The same applies to the high degree of concentration described in DE-A 2 909 029 which is achieved by means of IR heat sources made from silica glass immersed in the sulfuric acid.
LeA32737 _2_ Vacuum evaporators having heat exchangers made from tantalum (cf. for example EP-A 156 199) are restricted to a temperature range of below 200°C.
At such temperatures, sulfuric acid may only be evaporated to 95-96% under extremely reduced pressures, so entailing specifically large plant size per unit evaporating output and high costs for producing the vacuum and condensing the vapours.
Moreover, the conditions for oxidative degradation of organic impurities are also very unfavourable due to the low acid temperature.
The object was accordingly to develop an apparatus which makes it possible to achieve highly efficient water evaporation with a low sulfuric acid content at temperatures in the range above 250°C and optionally to permit oxidative purification.
The object was achieved according to the invention by an apparatus for concentrating sulfuric acid to an HZSOa content of 95-98% and optionally for purifying the sulfuric acid at a temperature of 270 to 340°C, consisting of at least a naturally circulating evaporator system comprising a two-part vapour hood, a heat exchanger, in particular a shell-and-tube heat exchanger, circulating line and distillation column, characterised in that the parts of the apparatus conveying the liquid sulfuric acid at a temperature of 270 to 340°C comprising the lower part of the vapour hood, heat exchanger and circulating line consist of an austenitic/ferritic iron alloy containing silicon of the following composition from 13 to 32 wt.% of chromium from 5 to 25 wt.% of nickel from 4 to 9 wt.% of silicon max. 0.07 wt.% of carbon max. 0.03 wt.% of sulfur max. 0.03 wt.% of phosphorus max. 8 wt.% of manganese max_ 3 wt.% of molybdenum T _ A 11 rl ~1 ~7 max. 4 wt.% of copper max. 20 wt.% of cobalt max. 4 wt.% of tungsten max. 2 wt.% of niobium and tantalum max. 0.2 wt.% of nitrogen and a remainder to make up to 100 wt.% of iron with a structure having a delta ferrite fraction of between 10 and 65%, preferable containing at least 20 percent by weight Fe, or of austenitic iron alloys comprising from 10 to 12 wt.% of chromium from 15.5 to 17.5 wt.% of nickel from 5.7 to 6.5 wt.% of silicon max. 0.06 wt.% of carbon max. 0.03 wt.% of phosphorus max. 0.03 wt.% of sulfur max. 1.5 wt.% of manganese max. 0.15 wt.% of titanium max. 0.8 wt.% of zirconium max. 0.2 wt.% of nitrogen max. 0.3 wt.% of molybdenum max. 0.01 wt.% of boron max. 0.25 wt.% of rare earth metals max. 1 wt.% of magnesium, aluminium and calcium and a remainder to to make up 100 wt.%
of iron or from 8 to 16 wt.% of chromium from 20 to 30 wt.% of nickel from >6.5 to 7.4 wt.% of silicon max. 0.03 wt.% of carbon max. 0.03 wt.% of phosphorus Le A 32 737 max. 0.01 wt.% of sulfur max. I wt.% of magnesium, aluminium and calcium and a remainder up to 100 wt.% of iron, and in which the upper part of the vapour hood and the distillation column consist of enamelled steel.
The lower part of the vapour hood is preferably provided with a discharge pipe made from an iron alloy containing silicon which ends with an outlet in an immersion vessel made from iron alloy containing silicon or enamelled steel.
In a preferred embodiment, the circulating line has an additional discharge port and/or a port for introducing gases, for example air or inert gas, in order to increase the acid circulation speed and/or for introducing oxidising agents, for example sulfuric acid, hydrogen peroxide, ozone, nitrosylsulfuric acid.
The heat exchanger of the apparatus is in particular a shell-and-tube heat exchanger, through the tubes of which the circulating sulfuric acid flows, and which is heated by flue gas or electricity.
The tubes of the heat exchanger preferably comprise bimetallic tubes, wherein the inner tube consists of the same iron alloy containing silicon as the lower part of the vapour hood and the outer tube consists of heat-resistant steel.
In another preferred embodiment, the lower part and upper part of the vapour hood are joined together by a pair of flanges, wherein the flange of the lower part consists of the same iron alloy containing silicon as the lower part of the vapour hood.
In a preferred embodiment of the invention, the flange of the lower part of the vapour hood has at least two annular grooves to accommodate seals.
LeA32737 _5_ In a particularly preferred embodiment of the invention, the parts of the apparatus which consist of iron alloys containing silicon are provided with a superficial passivating layer which is produced by at least 24 hours treatment with 95 to 98%
sulfuric acid at 290 to 340°C, preferably by at least 12 hours treatment with 95 to 98% sulfuric acid, which contains at least 350 ppm of nitrosylsulfuric acid, at a temperature of 250 to 340°C, or with 95 to 100% nitric acid at a temperature of 70 to 90°C, wherein the pressure selected is suff=iciently high that the liquid does not boil.
The packing of the distillation column is in particular made from glass, cast silicon iron or ceramics.
The present invention also provides a process for concentrating sulfuric acid to a concentration of 95 to 98% using the apparatus according to the invention, which process is characterised in that the apparatus is charged with sulfuric acid of a concentration of 70 to 93% and the sulfuric acid is distilled at a pressure of 0.3 to 1.2 bar (abs.), preferably of 0.8 to 0.99 bar (abs.) and a temperature of 270 to 340°C, preferably of 280 to 320°C.
Purification of the sulfuric acid is in particular achieved by introducing oxidising agents such as nitrosylsulfuric acid, nitric acid, hydrogen peroxide. ozone or others into the circulating sulfuric acid. If the introduction is made beneath the heat exchanger, the circulation speed of the liquid acid is advantageously increased by the resultant reaction gases.
The present invention also provides the use of the apparatus according to the invention for concentrating and optionally purifying sulfuric acid.
One disadvantage of known sulfuric acid evaporating plants made from enamelled steel is the numerous flange connections which cause problems, especially at relatively high operating temperatures. In the apparatus according to the invention, LeA32737 flange connections may be entirely avoided in those parts of the plant containing hot liquid sulfuric acid, as the alloys used according to the invention are weldable.
It is, however, preferred to use flange connections wherever appropriate for plant design or processing reasons, in particular with regard to cleaning requirements.
Particularly preferred flange connections are those of the groove and spring designs.
Compensators, which are required to offset the thermal expansion of plant components made from the same iron alloy containing silicon as the lower part of the vapour hood, may also be used.
The apparatus components made from iron alloys containing silicon are preferably subjected to a passivating surface treatment before the intended commissioning thereof for concentrating sulfuric acid. The preferred treatment is for at least 24 I S hours with 95 to 98% sulfuric acid at 250 to 340°C, preferably for at least 12 hours with 95 to 98% sulfuric acid which contains at least 350 ppm of nitrosylsulfuric acid at a temperature of 250 to 340°C or with 95 to 100% nitric acid for at least 12 hours at a temperature of 70 to 90°C and under a pressure at which the liquid does not boil.
The apparatus according to the invention for concentrating and optionally purifying sulfuric acid provides various advantages in comparison with prior art apparatus:
The materials and heating media used allow the apparatus to be operated at 270 to 340°C and a pressure of 0.3 to I.2 bar (abs.), preferably of 0.8 to 0.99 bar (abs.).
In comparison with plants having tantalum heat exchangers, which may be operated at a maximum of 200°C, the apparatus according to the invention permits the optimum operating conditions for destroying organic impurities in the sulfuric acid while simultaneously minimising vapour condensation costs.
LeA32737 _7_ The comparatively high operating pressure moreover permits small apparatus dimensions, so reducing the capital costs for the plant.
In comparison with known Pauling plants, the specific acid content (relative to water evaporating output) is only 10 to 20%. It is particularly advantageous that in the event of leakage, the released acid may straightforwardly be retained in a bund, whereas leaks from Pauling boilers pass into the boiler furnace chamber and thus cause considerable S03 emissions.
Due to the possible large temperature difference between heating medium and sulfuric acid. the specific heat exchange surface required is very small in comparison with plants which must be heated with steam or heat-transfer oil.
The parts made from iron alloy containing silicon are preferably all covered with liquid sulfuric acid during operation. This ensures that no corrosive sulfuric acid of a lower concentration can cause corrosion damage to the apparatus by condensation at cold points.
Producing the upper part of the vapour hood from enamelled steel has the advantage that the condensates containing dilute sulfuric acid which occur in this part may readily be processed according to the invention without leaving corrosion damage on the walls of the upper part of the vapour hood. Other corrosion processes accordingly proceed in this section of the apparatus than in the area of the lower part of the vapour hood or in the naturally circulating portion.
Since all parts of the apparatus which contain liquid sulfuric acid at a temperature of above 270°C may be joined together by welds or groove and spring flanges, the apparatus according to the invention suffers no sealing problems.
The invention is illustrated in greater detail below by the figures, without the invention consequently being limited by specific details.
LeA32737 _g_ The figures show Figure 1 a schematic representation of one embodiment of the apparatus according to the invention Figure 2 an magnified representation of the flange connection between the lower part (4) and upper part (5) of the vapour hood of the apparatus according figure 1.
Le A 32 737 Example Figure I shows the schematic structure of the concentration apparatus. The apparatus consists of a two part vapour hood 4, 5, a shell-and-tube heat exchanger I, a circulating line 6, 7 and a distillation column 13, which together form a naturally circulating evaporator system.
The parts of the heat exchanger I which come into contact with sulfuric acid consist of iron alloy containing silicon with 5.94% Si, 17.49% Ni, I 1.34% Cr, 62.7%
Fe and comprise bimetallic tubes 16 with an inner tube 17 consisting of the iron alloy containing silicon and an outer tube 18 made from heat-resistant steel I
.4593.
The circulating line 6 is provided with a discharge port I I and with a port 12 for introducing air or oxidising agents (65% HN03; sulfuric acid saturated with nitrosylsulfuric acid) for destroying organic compounds.
An overflow tube 8 passes through the wall of the lower part 4 of the vapour hood, through which tube the hot concentrated sulfuric acid is discharged into the immersion vessel 9, from which it flows through the port 10 into a receiver or an acid condenser. All the parts of the apparatus hitherto described, which come into contact with liquid 95-98% sulfuric acid at a temperature of 270-340°C, are made from the above-stated iron alloy containing silicon and are joined together by welded joints.
The size of the immersion vessel 9 is adapted to the operating pressure of the apparatus and to the residence time required for complete oxidation of organic impurities. For the intended operating temperature of 320°C and the production of 6 t/h of 96% acid, the volume is 1.5 m~ and the immersion depth 50 cm.
The lower part 4 of the vapour hood is connected to the upper part 5 by a flange connection (see detail in figure 2), which is made from enamelled steel. A
column 13 is placed upon the upper part 5, the column being made from enamelled steel and filled with glass packing. Above the column is located the feed line 15 for the 70 to LeA32737 93% sulfuric acid, which is distributed by a suitable distribution system, for example a nozzle 26, over the column packing 24. The aqueous vapours are discharged through the port 14 to a condensing system which is not shown.
The heat exchanger 1 is designed for heating with flue gas (cf. figure 1 ), which is introduced through a gas inlet port 2 into the space around the tubes 16 and discharged through a gas outlet port 3. The flue gas is passed repeatedly through the tube bundle by means of a false bottom. The outer shell of the heat exchanger 1 and the ports 2, 3 consist of heat-resistant steel.
Figure 2 shows the pair of flanges with which the lower part 4 and upper part 5 of the vapour hood are connected. Grooves 23 to accommodate seals 22 made from glass- or porcelain-filled PTFE are provided in the lower part flange 21) which is made from the iron alloy containing silicon. The mating flange 20 consists of enamelled steel. For safety reasons, the width of the flange is at least 100 mm, such that the outer seal is not heated above approx. 150°C and remains fully fianctional in order to provide a reliable outward seal. The flanges are compressed and fastened together by means of autoclave clamps.
Claims (13)
1. Apparatus for concentrating sulfuric acid to an H2SO4 content of 95-98% or for purifying sulfuric acid at a temperature of 270 to 340°C, comprising at least a naturally circulating evaporator system comprising a two-part vapour hood, a heat exchanger, a circulating line and a distillation column, wherein the parts of the apparatus for conveying liquid sulfuric acid at a temperature of 270 to 340°C comprising the lower part of the vapour hood, the heat exchanger and the circulating line comprise an austenitic/ferritic iron alloy containing silicon of the following composition from 13 to 32 wt.% of chromium from 5 to 25 wt.% of nickel from 4 to 9 wt.% of silicon max. 0.07 wt.% of carbon max. 0.03 wt.% of sulfur max. 0.03 wt.% of phosphorus max. 8 wt.% of manganese max. 3 wt.% of molybdenum max. 4 wt.% of copper max. 20 wt.% of cobalt max. 4 wt.% of tungsten max. 2 wt.% of niobium and tantalum max. 0.2 wt.% of nitrogen and a remainder to make up to 100 wt.% of iron with a structure having a delta ferrite fraction of between 10 65%, or of an austenitic iron alloy comprising from 10 to 12 wt.% of chromium from 15.5 to 17.5 wt.% of nickel from 5.7 to 6.5 wt.% of silicon max. 0.06 wt.% of carbon max. 0.03 wt.% of phosphorus max. 0.03 wt.% of sulfur max. 1.5 wt.% of manganese max. 0.15 wt.% of titanium max. 0.8 wt.% of zirconium max. 0.2 wt.% of nitrogen max. 0.3 wt.% of molybdenum max. 0.01 wt.% of boron max. 0.25 wt.% of a rare earth metal max. 1 wt.% of magnesium, aluminium or calcium and a remainder to make up to 100 wt. of iron or from 8 to 16 wt.% of chromium from 20 to 30 wt.% of nickel from >6.5 to 7.4 wt.% of silicon max. 0.03 wt.% of carbon max. 0.03 wt.% of phosphorus max. 0.01 wt.% of sulfur max. 1 wt.% of magnesium, aluminium or calcium and a remainder up to 100 wt.% of iron, and in which the upper part of the vapour hood and the distillation column comprises an enamelled steel.
2. Apparatus according to claim 1, wherein the lower part of the vapour hood is provided with a discharge tube made from an iron alloy containing silicon which ends with an outlet in an immersion vessel made from iron alloy containing silicon or enamelled steel.
3. Apparatus according to claim 1 or 2, wherein the circulating line has an additional discharge port or a port for introducing a gas or an oxidising agent.
4. Apparatus according to one of claims 1 to 3, wherein the heat exchanger is a shell-and-tube heat exchanger, through the tubes of which the circulating sulfuric acid flows, and which is heated by flue gas or electricity.
5. Apparatus according to claim 4, characterised in that the tubes of the heat exchanger comprise bimetallic tubes, wherein the inner tubes comprise an iron alloy containing silicon, which is selected from the iron alloys suitable for the lower part of the vapour hood, and the outer tubes comprise a heat-resistant steel.
6. Apparatus according to one of claims 1 to 5, wherein the lower part and upper part of the vapour hood are connected by a flange connection, wherein the flange of the lower part comprises the same iron alloy containing silicon as the lower part of the vapour hood.
7. Apparatus according to one of claims 1 to 6, wherein the flange of the lower part has at least two annular grooves to accommodate seals.
8. Apparatus according to one of claims 1 to 7, wherein the parts of the apparatus which comprise an iron alloy containing silicon are provided with a superficial passivating layer which is produced by at least 24 hours treatment with 95 to 98% sulfuric acid at 250 to 340°C, which contains at least 350 ppm of nitrosylsulfuric acid, at a temperature of 250 to 340°C, or with 95 to 100 nitric acid at a temperature of 70 to 90°C and at a pressure such that the acid does not boil.
9. Apparatus according to one of claims 1 to 7, wherein the parts of the apparatus which comprise an iron alloy containing silicon are provided with a superficial passivating layer which is produced by at least 12 hours treatment with 95 to 98% sulfuric acid at 250 to 340°C, which contains at least 350 ppm of nitrosylsulfuric acid, at a temperature of 250 to 340°C, or with 95 to 100 nitric acid at a temperature of 70 to 90°C and at a pressure such that the acid does not boil.
10. Apparatus according to one of claims 1 to 9, wherein the packing of the distillation column comprises glass, cast silicon iron or ceramics.
11. Process for concentrating sulfuric acid to a concentration of 95 to 98%, comprising charging an apparatus according to one of claims 1 to 10, with sulfuric acid of a concentration of 70 to 93% and distilling the sulfuric acid at a pressure of 0.3 to 1.2 bar (abs.), and a temperature of 270 to 340°C.
12. Process for concentrating sulfuric acid to a concentration of 95 to 98%, comprising charging an apparatus according to one of claims 1 to 10, with sulfuric acid of a concentration of 70 to 93% and distilling the sulfuric acid at a pressure of 0.8 to 0.99 bar (abs.), and a temperature of 270 to 340°C.
13. Use of an apparatus according to one of claims 1 to 10, for concentrating or purifying sulfuric acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19807632A DE19807632A1 (en) | 1998-02-23 | 1998-02-23 | Device for concentrating and purifying sulfuric acid |
| DE19807632.0 | 1998-02-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2262265A1 true CA2262265A1 (en) | 1999-08-23 |
Family
ID=7858691
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002262265A Abandoned CA2262265A1 (en) | 1998-02-23 | 1999-02-19 | Apparatus for concentrating and purifying sulfuric acid |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0937680A1 (en) |
| JP (1) | JPH11314906A (en) |
| CA (1) | CA2262265A1 (en) |
| DE (1) | DE19807632A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107574375A (en) * | 2017-08-31 | 2018-01-12 | 武汉钢铁有限公司 | Counterenamel hot rolling acid-cleaning steel plate and its manufacture method with excellent application of slip performance |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10128032A1 (en) * | 2001-06-08 | 2002-12-12 | Outokumpu Oy | Process for protecting steel part of apparatus against corrosion comprises using anodic protection, in which an anode, cathode and reference electrode are connected together |
| DE10360707A1 (en) | 2002-12-19 | 2004-07-08 | Hawera Probst Gmbh | Rock drill used e.g. in hammer drills for drilling rock comprises a drill head having at its end a trapezoidal or X-shaped receiving groove for a cutting element |
| PL2011566T3 (en) * | 2007-07-06 | 2011-05-31 | Plinke Gmbh | Apparatus for cleaning waste sulphuric acid |
| CN101798659B (en) * | 2010-04-07 | 2012-01-04 | 朝阳鸿翔冶炼有限公司 | Low-carbon low-phosphorus nickel-chromium-iron alloy used for stainless acid resistant steel and preparation method thereof |
| JP5759011B2 (en) * | 2010-11-22 | 2015-08-05 | テイジン・アラミド・ビー．ブイ． | Method for increasing sulfuric acid concentration in sulfuric acid solution |
| CN102872759A (en) * | 2012-09-14 | 2013-01-16 | 横店集团浙江英洛华硅材料有限公司 | Heat energy recycling system for alkalization kettle |
| CN105246589B (en) * | 2013-03-15 | 2017-09-08 | 因温斯特技术公司 | Thermal siphon is esterified device |
| CN106795605B (en) | 2014-10-01 | 2019-09-20 | 日本制铁株式会社 | Stainless steel steel |
| DE102018217955B4 (en) * | 2018-10-19 | 2020-06-04 | Plinke Gmbh | Process for working up mixed acid and waste water from the nitration of aromatics and device for carrying out the process |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1420707A (en) | 1920-08-06 | 1922-06-27 | Johnson Charles Morris | Alloy steel |
| IT1061126B (en) | 1975-06-24 | 1982-10-20 | Sandvik Ab | STAINLESS STEEL |
| EP0022473B1 (en) * | 1979-06-13 | 1983-10-19 | Bayer Ag | Process and apparatus for regenerating sulphuric acid |
| CA1181569A (en) | 1982-06-11 | 1985-01-29 | Frank Smith | Apparatus and process |
| CH654282A5 (en) | 1983-02-09 | 1986-02-14 | Bertrams Ag | METHOD AND DEVICE FOR CONCENTRATING AND PURIFYING SULFURIC ACID CONTAINING ORGANIC IMPURITIES. |
| DE4213324A1 (en) * | 1992-04-23 | 1993-10-28 | Bayer Ag | Process for concentrating and purifying sulfuric acid |
| DE4308151C2 (en) * | 1993-03-15 | 1995-01-19 | Bayer Ag | Use of kneading and casting materials as well as welding filler materials made of austenitic steel for components exposed to hot concentrated sulfuric acid or oleum |
-
1998
- 1998-02-23 DE DE19807632A patent/DE19807632A1/en not_active Withdrawn
-
1999
- 1999-02-10 EP EP99102513A patent/EP0937680A1/en not_active Withdrawn
- 1999-02-18 JP JP11039982A patent/JPH11314906A/en active Pending
- 1999-02-19 CA CA002262265A patent/CA2262265A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107574375A (en) * | 2017-08-31 | 2018-01-12 | 武汉钢铁有限公司 | Counterenamel hot rolling acid-cleaning steel plate and its manufacture method with excellent application of slip performance |
| CN107574375B (en) * | 2017-08-31 | 2019-06-07 | 武汉钢铁有限公司 | Counterenamel hot rolling acid-cleaning steel plate and its manufacturing method with excellent application of slip performance |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11314906A (en) | 1999-11-16 |
| EP0937680A1 (en) | 1999-08-25 |
| DE19807632A1 (en) | 1999-09-02 |
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