DE2529709C3 - Process for the production of sulfuric acid - Google Patents

Description

The invention relates to a process for the production of sulfuric acid by catalytic conversion from SO, to SO, in gases with an SO, content above Vol.'Cr with cooling, cleaning and drying of SO, -containing gases before use in the contact system, heating of purified SO. -containing Gases to the working temperature of the first contact tray in heat exchange with hot SO, -containing Gases between contact plates under equilibrium

Cooling of the SO, -containing gases to the working temperature the next contact tray, intermediate absorption of the after several contact trays in one first contact stage formed SO, in sulfuric acid at elevated temperature, two-stage cooling of the SO, -containing gases emerging from the first contact stage prior to intermediate absorption with reheating the gases emerging from the intermediate absorption to the working temperature of the next Contact tray in the first cooling stage, cooling of the gases fully catalyzed in the second contact stage in a final heat exchanger with the recovery of heat not required in the contact system, and absorption of the SO generated in the second contact stage in an end absorber.

Many chemical processes produce dilute sulfuric acids, which also contain impurities can. For reasons of environmental protection, this acid must be released into rivers or coastal waters turning more and more restricted; In addition, the levy involves considerable costs tied together. Step into the sea when making a delivery even higher transport costs.

These dilute acids must therefore be processed in a suitable manner to make them reusable or to produce harmless products or to reduce the transport weight and transport volume. This work-up is also becoming more and more urgent for reasons of the recovery of raw materials.

The diluted substances are processed in generally by concentration and possibly by thermal cleavage. In both cases must be larger Quantities of water are driven out of the dilute acids, which requires large amounts of heat are. These required amounts of heat cause considerable operating costs, in particular when expensive primary energy or thermal energy at a high temperature level has to be used. which can also be used economically for other purposes, e.g. B. for steam generation could be used.

From DE-AS 11 86 838 a method is known in which SCVhalti ^ e gases with an entry SO ₁ content above 9 *> after cleaning and drying and catalysis in a first contact stage in a hot rubbed intermediate absorption of SO, freed, fully catalyzed in a second contact stage and then the remaining SO _{1 is} removed in the final absorption. After the first contact stage, the SO, -containing gases are cooled in two stages, with the gases emerging from the intermediate absorption being heated to the working temperature of the next contact tray in the second cooling stage. In the second cooling stage or in the final heat exchanger, heat cannot be dissipated for the contact system.

From DE-PS 15 67 67: it is known to _{produce hot gases with an SO 1} gel of 8-11 "" before the intermediate absorption, also in two stages: / u cooling, whereby in the first cooling stage and in the final WtiinieaiiMauschT after the let / ien contact tray heat can be obtained which is not required in the contact star.

From DE-OS 23 07 ^{ > 73 it is known to mix a partial flow of the gases with oxygen-containing gases in the case of high-percentage SO. -Containing gases in such a way that the mixture can be converted to equilibrium in the first contact tray without the for the catalyst's maximum permissible temperature is exceeded, and the SO ₃ -containing gas stream emerging from the first contact tray is mixed with the remaining SO 3 -containing gas upstream of the second contact tray. Due to the SO2 content in the mixture, equilibrium in the second contact tray is also reached before a harmful temperature is reached.

From DE-OS 21 45 546 it is known to remove the end gases with dilute sulfuric acid to treat in of SO, and sulfuric acid mist being the diluted sulfuric acid can be concentrated and the end gases can be heated. The invention is based on the object of concentrating dilute sulfuric acids to gain as much excess heat as possible from the contact system in an economical manner.

This object is achieved according to the invention by combining the following steps:

a) Combination of sulfuric acid production with: o a concentration / on dilute

Sulfuric acid,

b) adding oxygen-containing gases to a partial flow of the SO2 -containing gases in an amount, a conversion of the gas mixture in at least

: 5 suns of a first contact horde until the equilibrium of the reaction SO, + ^! , O, * ^ SO, without exceeding the maximum permissible temperature for the catalytic converter.

c) Heating of the gas mixture on the Arbeitsjo temperature of the first contact tray in heat exchange with hot SO, -containing gases between Contact hordes.

d) Mixing the SO2 -containing gas from at least the first contact tray with the remaining one

r> SO, -containing gas in front of a further contact tray the first contact stage.

e) Adjustment of the amount of the in the first contact tray conducted partial flow of the SO.-hJtigen gases in such a way that the generated in step (b |

4 ,, amount of SO, after mixing according to step (d) a ratio of SO,: SO, results in a conversion in the further contact trays to to equilibrium without exceeding the maximum permissible temperature for the catalytic converter

4. enables.

f) Implementation of the intermediate and final absorption of the SO from the contact gases of the catalysis as hot absorption at working temperatures such as 100-200 ° Γ, preferably 110-160 ° C.

g) Carrying out the catalysis in the second contact stage in at least two contact trays with Cooling the gases' wipe the contact plates.

h) Expulsion of water from the dilute sulfuric acids by direct contact with hot gases, three consist of end gas of the catalysis after the end absorption and / or inert gases with little water.

i) Heating of the expulsion gases with at least one part of that in the end heat exchanger heat generated after the second contact stage,

k) heating of the expulsion gases with at least a portion of the cooling of the catalytic gases according to step (g) accumulating heat and / or with at least part of the in the second cooling stage after the first contact stage and before the intermediate absorption Warmth, and

I) indirect transfer of thermal energy from the acid circuits of drying and / or intermediate absorption and / or final absorption for concentrating and / or heating the dilute sulfuric acid. The gas mixture of the oxygen-containing gas and the SO _: -containing partial stream can be passed to the remaining SO ₂ -containing gas before being mixed with one or more contact trays connected one behind the other. If it is passed through several contact trays, cooling takes place between the contact trays by exchanging heat with gases containing SO2 or a mixture of gases containing SO2 and added oxygen-containing gases. Air or oxygen-enriched air are generally used as the oxygen-containing gases. The oxygen required for the total conversion is preferably added to the partial flow of the SO2 -containing gases upstream of the first contact tray. However, it is also possible to add only the amount necessary to control the conversion in the first contact tray and the remainder at a later point in the contact system. The first contact stage consists of two to three contact trays, the second contact stage generally consists of two contact trays. An increase in the number of contact trays is possible, but does not bring any advantages. If the end heat exchanger is designed in one stage after the last contact tray, the entire heat exchanger is used to heat the expulsion gases; if it is designed in two stages one behind the other or in parallel, one of the two stages is used to heat the expulsion gases. The expulsion gases are further heated either in the second cooling stage after the first contact stage and before the intermediate absorption or in the heat exchanger between the contact trays of the second contact stage, whereby, depending on the mode of operation, the other heat exchanger is used to heat a mixture of gases containing SO oxygen-containing gases is used. The cooling of the SO ₃ -containing gases from

the intermediate absorption is preferably carried out at 130 to 200 ° C. The cooling of the SO ₃ -containing gases after the second contacting step prior to the entry into the final absorber is preferably carried out also at 13O-2OO ^c C.

A preferred embodiment consists in the fact that the amount of the admixed according to step (d) remaining SO, -containing gas is dimensioned so that there is a gas temperature after mixing that corresponds to the working temperature of the next contact tray. This allows a heat exchanger to work this point can be saved.

A preferred embodiment consists in that the oxygen-containing gases are dried separately with sulfuric acid before being used in the contact vessel. This makes it possible to dissipate the heat generated during the drying of the oxygen-containing gases inTien gases and to operate the acid circuit of the dryer without cooling. Furthermore, the heat dissipated in the gas is introduced into the contact system. It is also possible to add the partial flow of SO ₂ -containing gases to the oxygen-containing gases before entering the dryer. In this case, however, the advantage described above does not apply.

A preferred embodiment consists in this.

that the drying of the oxygen-containing gases and or the SE-containing is "conducted as a hot drying gases and the gases emerge at a temperature of 60-80 ° C, preferably 65-70 ° C, from the Trock- ■■> drying. This If heat is conducted with the gases into the contact system, the acidic heat accumulates at an increased temperature level and can be used profitably.

A preferred embodiment consists in

in that the addition of the oxygen-containing gases to the partial _{flow of the SO 2} -containing gases according to step (b) takes place upstream of a blower which promotes the gas mixture. As a result, the fan conveying the remaining partial flow of the SO. -Containing gas can be kept small > una can be operated at low pressure, which increases the operating costs for conveying the gases lower in the contact system.

A preferred embodiment is that the addition of the oxygen-containing gases to the

: o Partial flow of the SOy-containing gases according to step (b) takes place after a fan promoting the oxygen-containing gases. In this case, the advantage described above does not apply, but both can On the pressure side, the blower must be designed approximately the same.

: i This reduces the effort for the blower, only one spare fan is required and the need for spare parts is reduced. This design davm is chosen if the operating costs are lower than the savings described.

ju Another preferred embodiment exists in that the drying and / or intermediate absorption and / or final absorption at least partially in Venturi absorbers are carried out in direct current. This results in high outlet temperatures for the gases and the

π acid reached.

The invention is illustrated by means of the examples. example 1

The contact system shown in Fig. 1 is calculated for a line of approx. 1000 tpd SO ₃ , with

Fission gases with a composition of approx. To .4 7 υ _Λ ι ot. co », im \ /" i ot. r \ n ~. » χι ι <- / - \

was taken as a basis.

About 40830 NmVh SO ₂ gas,

4. which contains approx. 56 g / Nm 'of water, sucked with the fan 12a via the venturi 2, line 3, sprinkler tower 3b, spray separator 4, dried there using approx. 96% strength by weight H ₂ SO ₄ and via line 11 with a temperature of approx. 65 ° C. the

in drying acid is circulated via line 5, cooler 6, line 7, pump 8, line 9, line 9y to nozzle 10, line 9x to nozzle 10 /.

About 5417ONmVh atmosphere are over line la. Air, which contains approx. 20 g / Nm ³ water, with

-, s sucked in by the fan 12 via the venturi 2α, line 3α, spray separator Aa , dried there by means of approx. 96% strength by weight H ₂ SO ₄ and discharged via the line live at a temperature of approx. 65 ° C. The drying acid is via line 5c, pump 8c, Le? -

M, device 9c, line 9n to nozzle 10c in the circuit. 27180 NmVh of 28.43% by volume SO ₂ gas are added to the total amount of air via the He line. 81350 NmVh of gas with approx. 9.5% by volume SO ₂ and approx. 15.14% by volume O _{2 are transferred via line Hc}

_r , the fan 12 via the line 13,14,15,16.17. 18 and 20 required for the first contact tray 21a of the contact vessel 21. The gases are in heat exchange with the SO, gases in the heat exchanger 27

preheated from approx. 90 ° C to approx. 200 ° C and in the two heat exchangers 23a and 23 from approx. 200 ° C to approx. 435 ° C. 13650 NmVh high-percentage SO ₂ gas (approx. 28.43 vol.% SO ₂ , approx. 3.86 vol.% O _2, remainder N, + CO,) is at a temperature of approx. 85 ° C via line We with the fan 12a, line 19 (z r-ach of the contact tray 21a mixed with the precatalyzed gases. The temperature of the SO.-containing gases after the contact tray 21a is thereby reduced from about 6 to 7 ° C to about 540 "C. The · SO, -containing gases are passed via line 22, heat exchanger 23, line 24 into the contact shelf lib at a temperature of approx. 450 "C. The further catalyzed gases leave the contact shelf Hb via line 22a at a temperature of approx. 570 ° C, are cooled to approx. 460 ° C. in the heat exchanger 23a and passed via line 24a to the contact tray 21c.

It will be headed by IB . 89 930 NmVh SO -containing gases with a temperature of approx. 507 "C passed into the intermediate heat exchanger 26, there in heat exchange with the absorbed gases to approx. 280 ° C (point 26a) and then in the heat exchanger 27 to approx. 190 ° C The intermediate absorption system was cooled down and passed through line 28 into the Venturi intermediate absorber 29. Approximately 79100 NmVh of SO, gases largely freed from it leave the intermediate absorption system via line 30, spray separator 31, line 32 at a temperature of approximately 140 ° C.

The highly concentrated absorber acid (ca. 98 ^e -99.0 wt.% H ₂ SO ₄₎ is conducted via line 5a, 6a cooler, line 7, pump 8, line 9 to the nozzle TOA in the circulation.

Via line 33 the gases are passed at a temperature of about 440 ° C to the contacting tray IXd, leave via line 34 having a temperature of about 482 ° C, the contacting tray lid. In the heat exchanger 35, the further catalyzed gases are cooled to approx. 420 ° C and passed via line 36 to the contact tray He , via line 37 approx. 78590 NmVh of fully catalysed gases at a temperature of approx. 422 ° C leave the contact boiler 21 and are in the Wäiincausiausther 4v cooled to about 10 ° C. and passed via line 41 to venturi end absorber 42. Approx. 77485 NmVh end gases leave end absorber 42 via line 43, spray separator 44, line 45.

The highly concentrated absorber acid (approx. 98.5-99.0% by weight H ₂ SO ₄ ) is fed via line Sb, cooler 6b, line Ib, pump Bb, line ffc, line 9; led to the nozzle 1Od in the circuit. ¹ acid is exchanged via lines 9e, 9k, 9d and 9 / to set the optimum acid concentrations required in the acid circuits, and the necessary dilution water is added via line 9 / Tind 9h. The production is released via line 9g with a concentration of approx. 96% by weight H ₂ SO ₄ .

The end gases, which are practically free of steam, are heated at approx. 110 ° C via line 45, heat exchanger 40, line 46, heat exchanger 35 preheated to approx. 420 ° C. and passed via line 46a into a dilute acid concentration plant, not shown, where the heat content of the gases is used to concentrate dilute acid.

Example 2

The contact system shown in Fig. 2 differs, for example 1, Fig. 1 by:

a) Laying the gas line 1 la from the suction side of the fan 12 to the pressure side of the fan 12a, so that the fan 12 only 54170NmVh dried air instead of 81350NmVh mixed gas,

and the fan 12a must deliver 40830 NmVh of highly concentrated SO ₂ gas instead of 13650 NmVh of highly concentrated gas;

b) only the heat exchanger 40 is used to preheat the end gases. The end gases will be

ίο in heat exchanger 40 from approx. 110 "C to approx.

Preheated to 340 ° C. and then passed via line 46 into a dilute acid concentration stage (not shown);

c) the heat exchanger 35 is used to preheat the atmosphere. Uses air. As a water vapor carrier for a non-illustrated thin Acid concentration level required Luftmann « χ, πη / - <· Al IB« M _m '/ U ... 1, A ;; U-, I ": ...""

■ ■■ »■■ Q«. Wff · * · «. "SO. CU. ' I «III I Il TW Il \ M UlS ^ II ^ VIIUIIg 47 is fed into the heat exchanger 35 at a temperature of approx. 30 ° C, where it is heated to approx. 115 ° C and in passed a dilute acid concentration (not shown).

2s example 3

The contact system shown in FIG. 3 is _{calculated for an output of approx. 1000 tpd SO 1} , with fission gases with a composition of approx. 17.0% _{by volume SO 2} , approx. 1.50% _{by volume O 2} , the remainder being N. ₂ + CO,

were taken as a basis.

Approx. 67430 NmVh of dried SO ₂ gas with a concentration of approx. 17.0% by volume and a temperature of approx. 65 ° C. are sucked in with the fan 12 via line lic. Be over wire Hey

about 63,570 NMVH dried air sucked in at a temperature of about 65 ° C with the fan 12a, 53900NmVh about 17.0 sodium SO via line 11a about vol.% added ₂ gas to the total amount of air, so that a total of 117 470 NmVh gas with a

SO ₂ concentration of approx. 9.2 vol.% SO ,, approx. 12.0 vol.% O ₂ via lines 13, 14, 15, 1 * 6, 17, ie and 2u to the first contact tray Ha of the ivomakt boiler 21 are directed. These gases are in heat exchange with the SO gases in heat exchanger 40 from approx. 90 ° C to approx. 260 ° C and into the two heat exchangers 23 and 35 preheated from approx. 260 ° C to approx. 440 ° C.

13520 NmVh approx. 17.0% by _{volume SO 2} gas is supplied at a temperature of approx. 90 ° C. via line 13a

so mixed with the precatalyzed gases after the contact tray 21a. The temperature of the SOy-containing Gas is thereby reduced from 610 ° C to approx. 550 ° C. The SOj-containing gases are via pipe 22, heat exchanger 23, line 24 in the contact

horde Hb passed at a temperature of about 450 ° C.

Via line 25 approx. 126 240 NmVh SO, -containing gases with a temperature of approx. 527 ° C are released passed into the intermediate heat exchanger 26, there in heat exchange with the absorbed gases to approximately 277 ° C (point 26) and then cooled in heat exchanger 27 to about 185 ° C lind passed via line 28 into the venturi intermediate absorber 29 where fiber line 9g and nozzle 1Od the absorbers

acid is injected. Approx. 116 570 NmVh from the SO, Most largely freed gases leave via line 30, spray separator 31, line 32 at a temperature of approx. 140 ° C the intermediate absorption system and

are then passed via line 33 at a temperature of about 430 ° C. to the contact tray Hd . The gases leave the contact tray lld via line 34 at a temperature of approximately 470 ° C. and are cooled to approximately 420 ° C. in the heat exchanger 3S and passed via line 36 to the contact tray . Leave Übet Leitung37 about 113820NmVh fertigkatalysierte area with a temperature of about 422 ° C the contact reactor 21 are cooled in heat exchanger 40 to about 255 ° C, passed via line Ma to the heat exchanger 40a, where the gases to about 180 ° C be cooled down. The gases are conveyed to the end absorber via line 41.

About 50,000 NmVh of atmospheric air from approx. 30 ° C preheated to approx. 210 ° C

and passed via line 46 into a thin, acidic concentration, not shown. About 100,000 NmVh atm. Air is preheated from about 30 ° C to about I60 ³ C and passed via line 46 in an unillustrated Dünnsäureaufkonzentrierstufe.

The advantages of the invention are mainly that it is possible to remove excess heat the contact system, including such heat that occurs at a relatively low temperature level, to be used economically for the concentration of dilute sulfuric acids. This can reduce the consumption of expensive primary energy or the use of heat with a high temperature can be avoided or reduced.

3 Biaii drawings

Claims (7)

Claims: I. Process for the production of sulfuric acid by catalytic conversion of SO, to SO3 in gases with an SO, content over 10% by volume with cooling, cleaning "and drying of the SOv-containing gases before use in the contact system, heating of the cleaned SO, -containing gases to the working temperature of the "first contact tray in heat exchange with hot SO3-containing gases between contact trays with simultaneous cooling of the SO3 -containing gases to the working temperature of the next contact tray, intermediate absorption of the SO formed after several contact trays in a first contact stage, in Sulfuric acid at elevated temperature, two-stage cooling of the SO, -containing gases exiting from the first contact stage before intermediate absorption with reheating of the gases exiting from the intermediate absorption to the working temperature of the next contact tray in the first cooling stage, cooling of the gases fully catalyzed in the second contact stage in one Endwä Heat exchanger with recovery of heat not required in the contact system, and absorption of the SO1 generated in the second contact stage in an end absorber, characterized by the following steps: a) Combination of sulfuric acid production with a concentration of dilute sulfuric acid. b) Addition of oxygen-containing gases to a partial flow of the SO, -containing gases in an amount that a conversion of the gas mixture in at least one first contact tray to the equilibrium of the reaction SO, + ', O, * ± SO, without exceeding the Catalyst allows maximum allowable temperature. c) Heating of the gas mixture to the working temperature of the first contact tray in heat exchange with hot SO, -containing gases between contact trays. d) Mixing the SO, -containing gas from at least the first contact tray with the remaining SO, -containing gas upstream of a further contact tray of the first contact stage. e) Adjustment of the amount of the partial flow of SO2 -containing gases passed into the first contact tray in such a way that the amount of SO2 produced in step (b) has a ratio of SO2: SO2 after mixing according to step (d). shows that a conversion in d: n further contact trays to equilibrium without exceeding the maximum permissible temperature for the catalyst <-i possible. f) Implementation of the intermediate and land absorption of the SO. from the contact gases of the catalysis as hot absorption at working temperatures of 100-200 ° C. preferably 110-160 ° C. g) Carrying out the catalysis in the second contact stage in at least two contact trays with cooling of the gases between the contact trays. Expulsion of water from the diluted sulfuric acid through direct contact with hot gases, which consist of end gas from the catalysis after the final absorption and / or inert, water-poor gases, i) heating of the expulsion gases with at least part of the heat generated in the final heat exchanger after the second contact stage , k) heating the expulsion gases with at least part of the heat produced during the cooling of the catalytic gases according to step (g) and / or with at least part of the heat produced in the second cooling stage after the first contact stage and before the intermediate absorption, and 1) indirect transfer of thermal energy from the acid circuits of drying and / or intermediate absorption and / or end absorption for concentrating and 'or preheating the dilute sulfuric acid. 2. The method according to claim 1, characterized in that the amount of according to step (D) mixed remaining SO, -containing gas is dimensioned so that after the mixing Gas temperature is present, which corresponds to the working temperature of the next contact tray. 3. Process according to claims I and 2, characterized in that the oxygen-containing Gases are dried separately with sulfuric acid before use in the contact vessel. 4. Process according to claims 1 to 3, characterized in that the drying of the oxygen-containing gases and / or the SO, -containing gases is carried out as hot drying and the gases exit the drying process at a temperature of 60-80 ° C., preferably 65-70 ° C. 5. Procedure according to the. Claims 1 to 4, characterized in that the addition of the oxygen-containing gases to the Teüstrom of SO.-containing gases according to step (b) before a die Gas mixture promoting blower takes place. 6. The method according to claims 1 to 4, characterized in that the addition of the oxygen-containing gases to the substream of the SO, -containing gases according to step (b) after a die Oxygen-containing gases promoting blower takes place. 7. The method according to claims 1 to 6, characterized in that the drying and or intermediate absorption and / or end absorption at least partially in Venturi absorbers in the Direct current takes place.