AU624540B2

AU624540B2 - Process and apparatus for concentrating a liquid which contains sulfuric acid and water

Info

Publication number: AU624540B2
Application number: AU64992/90A
Authority: AU
Inventors: Heinz Dittmar; Klaus Hohmann; Ramiro Serrano-Velarde
Original assignee: Metallgesellschaft AG
Current assignee: Outokumpu Oyj
Priority date: 1989-10-27
Filing date: 1990-10-26
Publication date: 1992-06-11
Anticipated expiration: 2010-10-26
Also published as: DE3935892A1; EP0425000B2; DE3935892C2; JPH03146408A; DE59003963D1; EP0425000B1; CA2024547A1; EP0425000A1; MY106697A; ES2047829T3; ES2047829T5; AU6499290A; BR9005114A

Description

624540 Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number:

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9 0 4 o 00 0990 0 I 0* 0 Lodged: o t r 0omplete Specification Lodged: I t r "Accepted: Published: 'riority Related Art 00*0e Ii Name of Applicant v Address of Applicant: Actual Inventor Address for Service METALLGESELLSCHAFT AKTIENGESELLSCHAFT Reuterweg 14, D-6000 Frankfurt/Main, Federal Republic of Germany KLAUS HOHMANN, HEINZ DITTMAR and RAMIRO SERRANO-VELARDE WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Complete Specification for the invention entitled: PROCESS AND APPARATUS FOR CONCENTRATIN- LIQUID WHICH CONTAINS SULFURIC ACID AND WATER The following statement is a full description of this invention, including the best method of performing it known to us 1.

-2- PROCESS AND APPARATUS FOR CONCENTRATING A LIQUID WHICH CONTAINS SULFURIC ACID AND WATER

DESCRIPTION

This invention relates to a process of concentrating a liquid which contains sulfuric acid and water and in which the concentration of H 2

SO

4 calculated without solids, is about 15 to 30% by weight, and an apparatus for carrying out that process.

In that process it is important to minimise the 06 10 demand for live steam, to avoid a formation of disturbing o crusts for the longest possible time, and to achieve high S throughput rates. In order to accomplish that object it is a o proposed in accordance with the invention that the 1 .1 lid is .tO circulated in a first heated processing stage at highest 15 temperatures of 50 to 70°C through a first heat exchange zone, iw.hich is indirectly heated with water vapour, and through a first evaporating zone, vapours and a liquid stream which contains sulfuric acid, water and dissolved salts and has an H SO 4 content of about 25 to 40% by weight, 20 calculated without solids, are separately withdrawn from the first evaporating zone and fed to a second heated processing stage, the liquid is circulated in the second heated processing stage at highest temperatures of 130 to 160QC and under a pressure which is higher than in the first 25 processing stage in at least one circuit through at least one heat exchange zone, which is heated with live steam, and through at least one evaporating zone, the vapours from the evaporating zone or zones are fed to the first heat exchange zone as a heating fluid, partly concentrated liquid having an H2 SO content of 55 to 70% by weight, calculated without solids, is withdrawn from an evaporating zone of the second processing stage and is fed to a flashing zone, in which the liquid is flashed with a reduction of the temperature of the liquid to a value which is lower by 20 to 70°C than the highest temperature in the second processing stage and concentrated liquid having an H2 SO 4 content of 60 to 80% by weight, calculated without solids, is withdrawn from the flashing zone. In the calculation of the H2 SO4 concentration wihtout solids, dissolved salts are also not taken into account.

That process is also particularly desirable for a processing of dilute sulfuric acid, which becomes available in the production of TiO 2 pigments. Such dilute sulfuric acid conains 5 to 20% by weight dissolved salts, particularly sulfates of iron, manganese, aluminum and 1 0 calcium.

It is important for the process that the final "tII concentration after the second heated processing ztage is achieved only by flashing without a use of heating surfaces.

As a result, the risk of incrustation, which is particularly *a 15 high owing to the high concentration of H 2

SO

4 and salts, is minimised. A thermal heating is effected only in the first and second processing stages, in which the acid flows countercurrently to the vapours. In the first processing stage the concentrating treatment is controlled to keep the 20 H 2 SO4 content at or below 40% by weight, calculated without 2t 4 solids, because a higher content might result in a higher tendency toward a precipitation and formation of crusts.

In accordance with a further feature of the I invention, the second processing stage comprises two liquid circuits, each of which includes a heat exchange zone, and K the two evaporating zones are operated under the same pressure. In that case the two partial stages may be designed to permit of a changeover of their connections or can individually be shut down. As a result, any crusts formed in the partial stage which contains the more highly concentrated liquid can be eliminated at least in part or a further growth of such crusts can be prevented if a changeover is effected so that said partial stage is now supplied with less highly concentrated liquid. In this manner the time for which the plant can be operated before it must be shut down and the heating surfaces must be cleaned can considerably be prolonged.

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-4- It is not necessary in the process to effect a preconcentraing, at a higher or lower expense, of the liquid which is to be supplied to the first processing stage. But it may be desirable to preheat such liquid by means of waste heat, by means of condensate obtained from vapours and/or live steam.

The apparatus for carrying out the process described first hereinbefore comprises a first heated processing stage, which is provided with a supply line for 10 the liquid to be concentrated, a first evaporating vessel, a first indirect heat exchanger, a first circulating line, a pump incorporated in said first circulating line, and a o liquid discharge line, which leads to a second heated io o processing stage, which comprises at least one evaporating 15 vessel and at least one indirect heat exchanger provided with means for supplying live steam. The second stage also comprises a vapour line leading from the evaporating vessel 'o the indirect heat exchanger of the first processing stage and a liquid line leading from the second processing stage 20 to a flashing vessel. The plant in accordance with the invention is operated without a need for complicated •9 .evaporator units and particularly without a need for ,A falling-film or rising-film evaporators.

Owing to the aggressive nature of the fluids to be processed, the materials used in the plant must be carefully selected. It is desirable to use steel which is lined with lead and stone. In that case the circulating lines and even the evaporating vessels may be durably protected against an attack by acid. The tubes of the heat exchanger may consist, of grahite.

Embodiments of the process and of the apparatus will be explained with reference to the drawings.

Figure 1 shows a first variant; Figure 2 shows a variant in which the second processing stage consists of two parts.

In accordance with Figure i, the liquid which is to be concentrated and which contains sulfuric acid, water and dissolved salt is supplied in line i. The H2 SO4 content lies in the range of about 15 to 25% by weight, calculated without solids. The first thermal processing stage comprises the circulating indirect heat line 2, the circulating pump 3 incorporated in the line 2, the first indirect heat exchanger 4 and the first evaporating vessel The heat exchanger 4 is heated with vapours from line 7.

10 Condensate obtained from the vapours is drained in line 8.

o The evaporating vessel is filled with liquid only in part o and vapours are withdrawn in line 9. The highest temperatures of the liquid in the first processing stage *9 S 1 occur at the outlet of the heat exchanger 4 and in the 15 vessel 5 and lie in the range from 50 to 70'C. In that stage the H2 SO 4 content of the liquid will be about 25 to by weight, calculated without solids.

That liquid is withdrawn in line 10 and is fed to 9 IO- the second thermal processing stage. The second thermal 20 processing stage comprises the circulating line 12, the circulating pump 13, the indirect heat exchanger 14 and the r9.1 evaporating vessel 15. That second stage is heated with live steam, which is fed in line 17 to the heat exchanger 14. Condensate is drained in line 18. The evaporating vessel 15 is also filled with liquid only in part and the 5 vapours withdrawn from it flow in line 7 to the heat exchanger 4.

At the outlet of the heat exchanger 14 and in the evaporating vessel 15 the temperatures of the liquid lie in the range from 130 to 160 0 C and the liquid has an H2 SO 4 content of 55 to 70% by weight, calculated without solids.

The pressure in the evaporating vessel 15 is higher by 0.2 to 1 bar than in the evaporating vessel 5. In order to overcome that pressure difference and the inevitable friction losses without a need for a feed pump in line the evaporating vessel 5 of the first processing stage is disposed on a level which is higher by several metres, /1 .i~Q' j I

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particularly by 2 to 10 metres, than the level of the evaporating vessel 15 of the second processing stage so that the higher hydrostatic pressure in the container 5 is sufficient for effecting a flow of the liquid through line 10 into the circulating line 12.

Partly concentrated liquid is withdrawn from the evaporating vessel 15 in line 19 and is delivered to a circulating line 22, which belongs to a flashing vessel and in which a circulating pump 23 is incorporated. The 10 flashing vessel 25 is filled with liquid in part. The concentrated liquid is withdrawn from the flashing vessel through line 26. The final concentration corresponds to an H2SO 4 content of 60 to 80% by weight, preferably at least 65% by weight, calculated without solids. The pressure in the flashing vessel 25 is lower by 0.2 to 1 bar than in the evaporating vessel 15. Vapours leave the flashing vessel in line 27 and in a manifold 28 are fed together with the vapours from line 9 to a condenser 21, which is connected to a vacuum source 29.

In the variant shown in Figure 2 the process comprises a second thermal processing stage, which consists of two parts, and the two partial stages can be changed over and are so designed that their connections can be changed over and each of them can be shut off. The first processing 25 stage comprises the supply line i, the circulating line 2 and the evaporating vessel 5 and is designed exactly as has been explained with reference to Figure i. In Figure 2 the pumps in the circulating lines have not been shown, for the sake of clearness, also the condenser 21 and the associated vacuum source 29 shown in Figure i.

Liquid which leaves the first thermal processing stage in line 10 enters through line 11 and the opened valve Ila the circulating line 12a, which extends through the heat exchanger 14a is heated by live steam from line 17a.

Vapours are withdrawn from the vessel 15a in line 7a. The valve 20 in line 19a is open and the valve 30 in line 31 is 'a i; k Ai i~ii i:.

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Irt -7closed. The partly concentrated liquid flows in line 19a to the other partial stage of the second thermal processing stage. That other partial stage comprises the circulating line 12b, the heat exchanger 14b, the evaporating vessel 15b, the line 17b for feeding live steam and the line 7 for withdrawing vapours. The pressure in the two vessels and 15b is the same and the vapours from said two vessels serve to heat the heat exchanger 4 of the first thermal processing stage.

Partly concentrated liquid is withdrawn in line 19b from the second thermal processing stage and is delivered through the open valve 32 to the circulating line 22, which leads to the flashing vessel 25. The valve 34 in line 35 is closed. Liquid having the final concentration is withdrawn in line 26. The vapours are conducted in lines 27 and 28 to the condenser, not shown.

In the arrangement shown in Figure 2 it may be desired to shut down the second partial stage of the second thermal processing stage. That second partial stage 20 comprises the evaporating vessel 15b. That shutdown can be effected in that the valve 20 is closed and the valve 34 is opened so that liquid is flowing to the circulating line 22 from the vessel 15a through line 35. On the other hand, it may be desired to shut down only the first partial stage, which comprises the evaporating vessel 15a. In that case the valves 1la and 20 are closed and liquid flows from line fhrough line 31 and the now open valve 30 to the circulating line 12b. Owing to these changes of the connections, the second processing stage remains operable but has a lower capacity.

In another desirable variant the connections of the two partial stages of the second thermal processing stage shown in Figure 2 may be changed so that that partial stage which is first flown through by the liquid and comprises the evaporating vessel 15a is now flown through after the other partial stage, which comprises the evaporating vessel ii U1

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Bi L. F 1 I -8ij; For that purpose the valve lla is closed and liquid is conducted from line 10 through line 31 and the now open valve 30 to the circulating line 12b. When the valve 32 is S 5 through the now open valve 36 and the line 37 to the circulating line 12a. The liquid drained from the evaporating vessel 15a flows through the now open valve 34 and the line 35 to the circulating line 22. That change of S t connections will be desirable, when crusts have been 10 formed in that partial stage which was initially supplied ij with more highly concentrated liquid and it is desired now S' to supply that partial stage with less highly concentrated {liquid from line 10 so that the crusts are dissolved or at least are prevented from growing further.

Examples In each of the two following Examples a watercontaining preheated sulfuric acid is concentrated which has become available in the production of TiO 2 pigments. In the first Example, the processing is in accordance with Figure I 20 1; corresponding values are stated in the Tables in columns j provided with the letter beside the reference numerals I Example, the processing is in accordance with Figure 2 and the corresponding values are stated in columns provided with the letter beside the reference numerals for the line.

S1 1 10 10 (B) Rate (kg/h) 22,000 20,000 15,500 14,000

H

2 S0 4 by weight) 19.4 19.4 27.4 27.4 Salts by weight) 14.4 14.4 20.4 20.4 Water by weight) 66.2 66.2 52.2 52.2

H

2 SO4 content by weight, without solids) 23.0 23.0 34.5 34.5 Temperature 76 76 56 56 i i -9- 19 19a 19b 26(A) 26(B) Rate (kg/h) 9,600. 9,950 8,650 9,350 8,420 H SO 4 by weight) 44.4 39.0 44.4 45.6 45.6 Salts by weight) 33.0 28.9 33.0 35.2 35.2 H SO 4 content by STemperature (OC) 142 120 142 115 115 Supply of live steam through lines 17, 17a and 17b: 17 17a 17b i Rate (kg/h) 8,800 5,900 2,100 S Temperature 170 155 155 S, Pressure (bars) 8 5.5 SVapours from vessels 5, 15, 15a, 15b and 15 5 5 15 15a 15b 25(A) Rate (kg/h) 6,450 5,800 5,950 4,050 1,300 250 230 Temp. 42 42 79 79 79 42 42 The pressure in each of the vessels 15, 15a and j 15b is 0.47 bars. Owing to the vacuum source 29, the pressure in the vessels 5 and 25 is about 0.08 bar in both Examples.

S i ft 35 i

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Claims

1. A process of concentrating a liquid which contains sulfuric acid and water an.d in which the concentration of H SO calculated without solids, is about 15 to 30% by 2 4 weight, characterised in that the liquid is circulated in a first heated processing stage at highest temperatures of to 70°C through a first heat exchange zone, which is indirectly heated with water vapour, and through a first evaporating zone, vapours and a liquid streamn which contains sulfuric acid, water and dissolved salts and has an H2 SO 4 content of about 25 to 40% by weight, calculated without solids, are separately withdrawn from the first evaporating zone and fed to a second heated processing stage, the liquid is circulated in the second heated processing stage at highest temperatures of 130 to 160 0 C and under a pressure i which is higher than in the first processing stage in at least one circuit through at least one heat exchange zone, which is heated with live steam, and through at least one evaporating zone, the vapours from the evaporating zone or zones are fed to the first heat exchange zone as a heating fluid, partly concentrated liquid having an H 2 SO 4 content of to 70% by weight, calculated without solids, is withdrawr from an evaporating zone of the second processing stage and is fed to a flashing zone, in which the liquid is flashed with a reduction of the temperature of the liquid to a value S which is lower by 20 to 70 0 C than the highest temperature in the second processing stage and concentrated liquid having an H 2 SO 4 content of 60 to 80% by weight, calculated without solids, is withdrawn from the flashing zone.

2. A process according to claim i, characterised in that the second processing stage comprises two liquid circuits, each of which includes a heat exchange zone, which is heated with live steam, and an evaporating zone, and the two evaporating zones are operated under the same pressure. otI -11-

3. A process according to claim 2, characterised in that each of the two liquid circuits of the second processing stage is adapted to be selectively supplied first with liquid from the first processing stage.

4. A process according to claim 1 or any of the following claims, characterised in that the liquid supplied to the first processing stage has been obtained in the production of TiO, 2 pigments and contains 5 to 20% by weight t" dissolved salts.

5. An apparatus for concentrating a liquic which contains sulfuric acid and water and in which the Sro .3141 45~ V ~t1. A S II concentration of H 2SO, calculated without solids, is about 15 to 30% by weight, characterised by a first heated processing stage, which is provided with a supply line for the liquid to be concentrated, a first evaporating vessel, a first indirect heat exchanger, a first circulating line, a pump incorporated in said first circulating line, and a liquid discharge line, which leads to a second heated processing stage, which comprises at least one evaporating vessel and at least one indirect heat exchanger provided with means for sup'.'ing live steam, and also a vapour line leading from the evaporating vessel to the indirect heat exchanger of the first processing stage and a liquid line leading from the second processing stage to a flashing vessel.

6. An apparatus according to claim 5, characterised in that the evaporating vessel of the first processing stage is disposed on a level which is 2 to 10 metres above the level of the evaporating vessel or vessels of the second processing stage. LI -12-

7. An apparatus according to claim 5 or 6, characterised in that at least one evaporating vessel and one circulating line are internally provided with a lining of lead and a lining of stone. DATED this 10th day of August, 1990. i t tt METALLGESELLSCHAFT AKTIENGESELLSHAFT WATERMARK PATENT ATTORNEYS 2ND FLOOR "THE ATRIUM", 290 BURWOOD ROAD, HAWTHORN, VIC. 3122. n AUSTRALIA Se r SMELB DISK /I 4 MG i i. i 1 *1 i* 1