Process and plant for the production of liquid acid

Abstract

A process for the production of liquid acid, comprising the steps of: feeding liquid acid with a first concentration into a gas purification; passing a gas through the gas purification such that a second concentration of the liquid acid is reached; withdrawing the liquid acid from the sump of the gas purification, where in the gas purification sump is divided by a partition wall into a first and a second section. The concentration of the liquid acid collected in the first section is adjusted to the first concentration. The liquid acid with the first concentration from the first section is at least partially fed back into step and the liquid acid with the second concentration collected in the second section is at least partially withdrawn as product.

Claims

1. A process for the production of sulfuric acid, comprising the steps of: (i) feeding liquid acid with a first concentration into a gas purification in form of a packed bed absorber or a packed bed drying tower; (ii) passing a gas through the gas purification such that a second concentration of the liquid acid is reached; (iii) withdrawing the liquid acid from the sump of the gas purification, wherein the gas purification sump is divided by a partition wall into a first and a second section, wherein the concentration of the liquid acid collected in the first section is adjusted to the first concentration, the liquid acid with the first concentration from the first section is at least partially fed back into step (i), and the liquid acid with the second concentration collected in the second section is at least partially withdrawn as product, and the concentration of the liquid acid in the first section is adjusted with acid or water.

2. The process according to claim 1, wherein the gas in step (ii) is conducted through the gas purification in counter-flow or in co-current flow to the liquid acid.

3. The process according to claim 1, wherein the first and/or the second section is level controlled.

4. The process according to claim 1, wherein the volume of down coming acid introduced into the second section is greater than the amount of product withdrawn from the second section.

5. The process according to claim 1, wherein the liquid acid is sulfuric acid or oleum and that the gas comprises SO.sub.3.

6. A plant for the production of sulfuric acid, by a process according to claim 1, comprising a gas purifier in form of a packed bed absorber or a packed bed drying tower containing a supply system for liquid acid, a gas inlet, and a gas purifier sump, wherein the gas purifier sump is divided by a partition wall into a first section and a second section, that separate outlets are provided for the first and second sections, respectively, and that the first section is connected with the acid supply system via a recycling line, wherein an inlet for an adjusting liquid is provided in the first section.

7. The plant according to claim 6, wherein a lance is provided for introducing the adjusting liquid into the first section.

8. The plant according to claim 6, wherein the partition wall is made of bricks or carbon steel or stainless steel.

9. The plant according to claim 6, wherein the top level of the partition wall is located below the lowest point of the gas inlet.

10. The plant according to claim 6, wherein an overflow is provided between the first and second sections.

11. The plant according to claim 6, wherein a level control is provided in the first and/or second section.

Description

(1) In the drawings:

(2) FIG. 1 shows schematically a suitable absorber for carrying out the method of the invention for the production of oleum with a certain maximum concentration;

(3) FIG. 2 shows the lower section of an absorber or a drying tower used in the process and plant of the invention;

(4) FIG. 3 is a schematic cross section along line A-A in FIG. 2;

(5) FIG. 4 shows schematically the method of the invention for the production of sulfuric acid in an absorber;

(6) FIG. 5 shows schematically the method of the invention for the production of oleum in an absorber;

(7) FIG. 6 shows schematically the method of the invention for the production of sulfuric acid with a certain minimum concentration in a drying tower.

(8) The invention is first illustrated by way of example with reference to the FIGS. 1 to 3.

(9) In FIG. 1 an absorber 1 is depicted as a packed bed absorption tower comprising a packed bed 2 located above an absorber sump 3. An acid supply system 4 in the form of an irrigation system known in the art is provided above the packed bed 2 to introduce liquid acid, in particular sulfuric acid or oleum, that then trickles through the packed bed 2 and is collected in the absorber sump 3. A gas inlet 5 is provided below the packed bed 2 to introduce a gas containing sulfur trioxide (SO.sub.3) and possibly containing sulfur dioxide (SO.sub.2), which then flows upwardly in counter current flow through the packed bed 2. By the contact with the down coming sulfuric acid sulfur trioxide is absorbed in the acid thereby increasing the acid concentration.

(10) In the case of oleum production, non-absorbed sulfur trioxide may be recycled to the gas inlet 5 through recycling line 6. Alternatively, the gas containing sulfur trioxide and possibly sulfur dioxide may be bypassed via line 6 to the gas outlet 7 and the amount of gas bypassed can be adjusted via gas valve 8.

(11) The absorber sump 3 is divided into a first section 3a and a second section 3b by a partition wall 9.

(12) A diluting medium, in particular water or dilution acid, is introduced into the first section 3a through line 10 to reduce the acid concentration in said section 3a to a desired value. The amount of diluting medium may be adjusted by valve 11. In case of the diluting medium being sulfuric acid, the dilution acid may be removed from a drying tower (not shown) and introduced to the absorber 1 via lines 12 and 10. The liquid acid is withdrawn from the first section 3a through outlet nozzle 13 (FIG. 2) and line 14, 15 via pumps 16, 17 and then recycled to the acid supply system 4 via recycling line 18. The temperature of the acid may be adjusted by heat exchangers (coolers) 19, 20 prior to the recycling to the absorber 1.

(13) Obviously, it is possible to use only one outlet nozzle 13, line 14, pump 16 and heat exchanger 19, respectively. Dilution may also be performed outside the absorber sump 3 after withdrawing the acid from the first section 3a.

(14) From the second section 3b of the absorber sump 3, the acid/oleum is withdrawn as product acid/oleum through an outlet nozzle 21 (FIG. 2) and line 22 via pump 23 and heat exchanger (cooler) 24 and then withdrawn through line 25 and/or partially recycled to the second section 3b through line 26. The amount of acid/oleum recycled can be controlled via valve 27, wherein the amount of product acid/oleum withdrawn from the process is controlled via valves 28. If necessary, the concentration of the product acid/oleum may be adapted to the desired value by introducing a dilution medium such as water or dilution acid, which is shown in FIGS. 4 and 5, wherein water (FIG. 4) or acid (FIG. 5) is introduced to tank 29, respectively.

(15) FIG. 2 shows the lower part of the absorber 1 with the packed bed 2 (partially) and the absorber sump 3. As can be seen in FIG. 2 the partition wall 9 is made of brick but may also consist of other suitable materials such as carbon steel, stainless steel, etc.

(16) In case of the depicted counter-current flow setup the gas inlet 5 for the SO.sub.3-containing gas is located below the packed bed 2 and its lowest point is at a predetermined distance h, preferably 100-300 mm, above the top level of the partition wall 9 to ensure that the SO.sub.3-containing gas does not flow through the product acid in the second section 3b.

(17) In the first section 3a of the absorber sump 3 the dilution medium is introduced preferably through a lance 30 directly into the first section 3a. Other means of introducing the dilution medium can be envisaged, such as a nozzle above the acid level in the first section 3a. The diluted acid is withdrawn for the first section 3a through nozzle 13. The acid level in the first section 3a is level controlled to ensure that no diluted acid enters into the second section across the partition wall 9.

(18) The liquid level in the second section 3b is defined by the height of the partition wall and the relation between the acid trickling into the first section 3a from the packed bed 2 and the acid flow withdrawn through outlet nozzle 21. While the acid level in the second section 3b may be level controlled similar to the first section 3a, it is preferred that the second section 3b (product section) is designed such the amount of down coming liquid is greater than the production rate, i.e. the acid flow withdrawn through nozzle 21. Thereby there is always an overflow of acid from the second section 3b into the first section 3a. The overflow may be over the top level of the partition wall 9 or through a specific overflow conduit (not shown). The calculation for the minimum area of the second section 3b (product section) is based on:
desired production rate (m.sup.3/h) divided by irrigation rate (m.sup.3/m.sup.2h)

(19) In accordance with the invention, the sulfuric acid production inside the drying tower 31 is schematically shown in FIG. 6. The drying tower 31 is depicted as a packed bed drying tower comprising a packed bed 32 located above an drying tower sump 33.

(20) An acid supply system (not shown) known in the art is provided above the packed bed 32 to introduce liquid acid, in particular sulfuric acid or oleum, that then trickles through the packed bed 32 and is collected in the drying tower sump 33. A gas inlet 34 is provided below the packed bed 32 to introduce a gas containing water, e.g. air, and possibly containing oxygen and sulfur dioxide (SO.sub.2), which then flows upwardly in counter current flow through the packed bed 32 and is removed via gas outlet 35. Water is absorbed by the contact with the down coming sulfuric acid thereby reducing the acid concentration.

(21) The drying tower sump 33 is divided by partition wall 9 into a first section 33a and a second section 33b. Diluted acid in the first section 33a is concentrated by introduction of highly concentrated sulfuric acid via line 36. The concentrated acid is recycled via line 37 to the top of the drying tower. From the second section 33b diluted acid is withdrawn via line 38 and pump 39.

EXAMPLE 1 (PRODUCTION OF SULFURIC ACID IN THE ABSORBER)

(22) As shown in FIG. 4, liquid sulfuric acid (H.sub.2SO.sub.4) at a temperature of 70 to 90 C., preferred 80 C. is directed from the absorber 1 plus cross flow acid from the drying tower via conduit 12, wherein the absorber 1 is made from stainless steel or brick lined carbon steel. Apart from having the specified concentration and temperature, the liquid H.sub.2SO.sub.4 is virtually free of contaminating compounds like sulfur dioxide (SO.sub.2) and nitrous oxides (NO.sub.x). The liquid H.sub.2SO.sub.4 is injected in a volume regarding irrigation rates between 10 to 40 m.sup.3/m.sup.2 h and runs down over a packed bed 2 made of ceramic saddles into the absorber sump 3 and is simultaneously being flowed through with a sulfur trioxide (SO.sub.3) containing gas in counter-current flow via gas inlet 5 into the absorber 1. The inlet for the SO.sub.3-containing gas is located below the packed bed 2 and above the top level of the partition wall 9. The SO.sub.3-containing gas enters the absorber at a temperature of 160 to 240 C., a volume fraction of SO.sub.3 of 5 to 35 wt-%. Due to the reaction of SO.sub.3 with the water contained in the sulfuric acid, the concentration of the sulfuric acid is increased to 99.4 wt-%. Any unabsorbed SO.sub.3 leaves the absorber 1 through line 7 located at the top of the absorber 1 and can optionally be recycled. Typically, the volume fraction of SO.sub.3 is reduced to far less than 1 wt-% upon exiting the absorber 1.

(23) The sulfuric acid with a concentration of 99.4 wt-% and a temperature of 90 to 140 C. collects in the sump 3 of the absorber 1. The sump 3 is divided by partition wall 9 made of acid resistant bricks, carbon steel or stainless steel into two sections 3a, 3b. The liquid level in the first section 3a is controlled so that there is no overflow of liquid from the first section 3a into the second section 3b. Undiluted sulfuric acid from the second section 3b is withdrawn through line 22 and a pump 23 and is fed first into a heat exchanger 24 where it is cooled to a temperature of 70 to 90 C. and then into an optional diluter 29. In the diluter 29 the concentration of the sulfuric acid is adjusted with water to the desired final concentration of 99.1 wt-%, which then is withdrawn as end product

(24) The sulfuric acid in the first section 3a of the absorber sump 3 is diluted to a concentration of 98.5 wt-% by supplying water through line 10 while preferably the concentration of the sulfuric acid is constantly monitored. The diluted sulfuric acid is removed from the absorber 1 through line 14 and at least partially recycled to the acid supply system 4 of the absorber 1 via line 18.

EXAMPLE 2 (PRODUCTION OF OLEUM)

(25) As shown in FIG. 5, liquid oleum (H.sub.2S.sub.2O.sub.7) at a concentration of 34 wt-% of free SO.sub.3 and a temperature of 40 to 70 C. C., preferably 50 C., is directed in a closed loop into the head of an absorber 1 made from carbon steel or stainless steel or brick lined carbon steel. The liquid oleum is fed to the top of the tower and runs down over a packed bed 2 made of ceramic packings, e.g. Intalox saddles, into the absorber sump 3 and is simultaneously being contacted with a sulfur trioxide (SO.sub.3) containing gas in counter-current flow which is passed via gas inlet 5 into the absorber 1. The inlet for the SO.sub.3-containing gas is located below the packed bed 2 and above the top level of the partition wall 9. The SO.sub.3-containing gas enters the absorber at a temperature of 160 to 240 C. and a volume fraction of 5 to 35 wt-%. Due to the reaction of SO.sub.3 with the acid contained in the oleum, the concentration of the free SO.sub.3 in the oleum is increased to 35.5 wt-%. Any unabsorbed SO.sub.3 leaves the absorber 1 through line 7 located at the top of the absorber 1 and can optionally be recycled.

(26) The oleum with a concentration of 35.5 wt-% of free SO.sub.3 and an increased temperature collects in the sump 3 of the absorber 1. The sump 3 is divided by partition wall 9 into two sections 3a, 3b. The liquid level in the first section 3a is controlled so that there is no overflow of liquid from the first section 3a into the second section 3b. Undiluted oleum from the second section 3b is withdrawn through line 22 and a pump 23 and is fed first into a heat exchanger 24 and then into an optional diluter 29. In the diluter 29 the concentration of the oleum is adjusted with acid to the desired final concentration of 35.1 wt-% of free SO.sub.3 and withdrawn as an end product.

(27) The oleum in the first section 3a of the absorber sump 3 is diluted to a concentration of 34 wt-% of free SO.sub.3 by supplying sulfuric acid having a concentration of 98 to 99 wt-% through line 10 while preferably the concentration of the sulfuric acid is constantly monitored and controlled. The diluted oleum is removed from the absorber 1 through line 14 and at least partially recycled to the top of the absorber 1.

EXAMPLE 3 (PRODUCTION OF SULFURIC ACID IN THE DRYING TOWER)

(28) As shown in FIG. 6, liquid sulfuric acid (H.sub.2SO.sub.4) at a concentration of 94 wt-% and a temperature of 70 to 90 C. is directed from the drying tower 31, which is made from stainless steel or brick lined carbon steel and injected in a volume regarding irrigation rates between 10 to 40 m.sup.3/m.sup.2 h and runs down over a packed bed 32 made of ceramic saddles into the drying tower sump 33. At the same time air as a water containing gas, is introduced via gas inlet 34 into the drying tower 31. The inlet for the gas is located below the packed bed 32 and above the top level of the partition wall 9. The water containing gas enters the drying tower at a temperature of 5 to 40 C. Due to the hygroscopic properties of sulfuric acid the water contained in the air is absorbed in the acid and the concentration of the sulfuric acid is reduced to 93 wt-%. Dried air with a water content of less than 50 mg (H.sub.2O)/Nm.sup.3 leaves the drying tower 31 through line 35 located at the top of the drying tower 31 and may be used for elemental sulfur combustion. In a further embodiment, exhaust gas from the overall sulfuric acid production process is recycled to the drying tower, since this exhaust gas contains unreacted sulfuric dioxide.

(29) The sulfuric acid with a concentration of 93 wt-% and a temperature of 80 to 100 C. is collected in the sump 33 of the drying tower 31. The sump 33 is divided by partition wall 9 made of acid resistant bricks, carbon steel or stainless steel into two sections 33a, 33b. The liquid level in the first section 33a is controlled so there is no overflow of liquid from the first section 33a into the second section 33b. Sulfuric acid from the second section 33b is withdrawn through line 38 and a pump 39 is withdrawn as end product.

(30) The sulfuric acid in the first section 3a of the absorber sump 3 is concentrated to a concentration of 94 wt-% by supplying sulfuric acid with a concentration of at least 98 wt-% through line 36 while preferably the concentration of the sulfuric acid is constantly monitored. The concentrated sulfuric acid is removed from the drying tower 31 through line 37 and at least partially recycled to the top of the drying tower 31.

LIST OF REFERENCE NUMERALS

(31) 1 absorber 2 packed bed 3 absorber sump 3a first section 3b second section 4 acid supply system 5 gas inlet (for SO.sub.3-containing gas) 6 recycling line 7 gas outlet 8 gas valve 9 partition wall 10 line 11 valve 12 cross flow line 13 outlet nozzle 14, 15 acid effluent line 16, 17 pump 18 recycling line 19, 20 heat exchanger 21 outlet nozzle 22 line 23 pump 24 heat exchanger 25 line 26 line 27, 28 valves 29 diluter 30 lance 31 drying tower 32 packed bed of the drying tower 33 drying tower sump 34 gas inlet 35 gas outlet 36 line 37 recycling line 38 line 39 pump h distance top level of partition wall 9 to gas inlet 5