CN213492919U

CN213492919U - Device for purifying gases containing sulphur dioxide

Info

Publication number: CN213492919U
Application number: CN201890001472.0U
Authority: CN
Inventors: K-H·多姆; K·哈瑟旺德; U·瓦格特
Original assignee: Outotec Finland Oy
Current assignee: Meizhuo Metal Co ltd
Priority date: 2018-01-08
Filing date: 2018-01-08
Publication date: 2021-06-22
Anticipated expiration: 2028-01-08
Also published as: WO2019134752A1

Abstract

The utility model describes an equipment for purifying gas that contains sulfur dioxide. In detail, comprising at least one quench tower (10), at least one gas cooling tower (30) and at least one electrostatic precipitator (40,42), characterized in that at least one conduit (43,44,45) is foreseen to discharge the liquid phase coming from the electrostatic precipitator(s) (40,42), a pump tank (60) for the addition of the reactants and an additional packed bed tower (70), wherein the packed bed comprises silica.

Description

Device for purifying gases containing sulphur dioxide

Technical Field

The utility model relates to a device for purifying SO₂In a process and related apparatus for producing a gas of (1), wherein the gas will contain at least 1.0 wt.% SO₂Is quenched before it passes through the packed bed column and then fed to at least one electrostatic precipitator, whereby the condensate from the electrostatic precipitator is directed to a liquid effluent treatment plant. SO-containing metallurgical plants derived from the treatment or smelting of sulphidic non-iron ores are usually processed in a hot and wet gas cleaning plant consisting of a number of process steps before being sent for further processing and conversion into sulphuric acid₂The process gas of (1).

Background

Over the past few years, a steady decrease in the quality of ores and concentrates is imminent, which in turn leads to an increase in impurities in the exhaust gas. In addition to the metal compounds originating from the metallurgical process, those impurities are generally substances which are volatile during pyrometallurgical processing. Of particular interest are metal compounds containing arsenic, selenium, cadmium, mercury, and the like.

Sulfur dioxide (SO) in gases₂) And the presence of oxygen will form an amount of sulfur trioxide (SO)₃) In particular in the presence of metal oxides, which have a catalytic action at the prevailing high temperatures of about 500 to 700 ℃. SO at elevated temperature and in the presence of moisture₃Most of it is changed into gaseous sulfuric acid (H)₂SO₄) However, metal sulfates can also be formed.

The use of, for example, a dust settling chamber, cyclone separator and/or a thermal electrostatic precipitator, under control of elevated temperatures (e.g., 250 to 450 ℃) in the hot gas clean-up section is commonly used for solids removal purposes. At said temperatures, some metal compounds, e.g. As₂O₃And H₂SO₄Usually in gaseous form and therefore not removable by such devices. Similarly, halides such as chlorides and fluorinationsThe object will also pass through this device. Upon entering the wet gas clean-up section, the hot gas is quenched with a weak acid/water and cooled adiabatically. In addition to halides, the impurities will condense or sublimate and form submicron particles that must be removed from the gas by various device operations.

The halide will generally not condense but remain in the gaseous state, in particular the fluoride, and must therefore be removed by absorption in a suitable aqueous solution. While absorbed chlorides do not generally exhibit a significant vapor pressure and are therefore relatively easy to separate from the gas, absorbed fluorides dissolve in aqueous solutions and, instead, can produce a significant vapor pressure, which limits their effective removal from the gas.

Any impurities escaping through the hot and wet gas cleaning section of the plant will eventually enter the sulfuric acid plant and will be reported there as sulfuric acid produced and thus considered as impurities of product quality.

For metallurgical operations, gas purification and sulphuric acid plants lead to high investment and maintenance costs, but the need for environmental protection and avoidance of pollution is indispensable. Sulfuric acid is therefore an undesirable by-product which cannot be stored in large quantities and therefore must be easily sold or transported. While good quality acids may be marketed at a reasonable price, lower quality acids, i.e. containing higher amounts of impurities, do result in significantly lower prices and have limited use for e.g. fertilizer production.

Although the amount of impurities in metallurgical off-gases has recently increased, the demand for better quality product acids has increased at the same time, and to meet this, the gas cleaning section must be substantially more efficient.

Can separate substances such as arsenic or selenium, H well in a scrubber operated under elevated pressure drop₂SO₄-submicron particles of mist or metallic compounds. Downstream wet electrostatic precipitators (wet electrostatic precipitators) must remove residues of those substances from the gas to an extent suitable for downstream processing of the gas at the sulfuric acid plant.

All impurities separated from the gas will eventually be transferred and reported as being wetThe liquid used in the gas clean-up section is used for quenching, scrubbing, cooling. Therefore, the liquid contains a large amount of H₂SO₄. The liquid (or liquids) containing all impurities, often referred to as a weak acid or a purge acid, will ultimately be discharged from the wet gas cleanup section for further processing at the liquid effluent treatment plant.

Governed by the chemical activity of the ionic element in solution, H₂SO₄HCl and H₂F₂Are competing reaction participants and the dissolved halide may be in increased H₂SO₄Becomes less stable (less soluble) at concentration. Thus following the H of the liquid₂SO₄The higher the concentration, the more difficult it becomes to completely absorb the halide.

The chlorides are not critical and are usually separated at the gas cooling tower, which needs to reduce and meet the desired residual moisture content of the gas. However, the characteristics of the fluoride require specific and additional measures, depending on the level of fluoride concentration in the incoming gas. The present invention proposes several efficient methods for fluoride removal from metallurgical gases while minimizing the use of fresh additional process water and thus also minimizing the amount of weak acid/purge acid discharged from the wet gas clean-up section for downstream liquid effluent treatment.

Standard specifications for technical grade sulfuric acid require less than 1ppm F, which correlates to every Nm exiting the wet gas clean-up section³Less than 1mg of gas is associated with F. The hyaluronic acid requirement is generally less than 0.2 ppm F. Not only can the uncaptured fluoride contaminate the product acid, it also makes the concentrated acid very corrosive even in the presence of a few ppm, which does seriously affect the stainless steel or alloy acid coolers and piping. The fluoride escaping into the acid plant also does attack the glass fibers of the candle filter at the drying and absorption tower. It is also indeed potentially destructive for SO₂Oxidation to SO₃V of₂O₅Silica support for catalysts. There are therefore many reasons to control the F content of the gas leaving the wet gas cleaning section towards the sulphuric acid plant.

However, as indicated above, the quality of the ore is a very fluctuating parameter, which is why it is necessary to provide a flexible purification system.

SUMMERY OF THE UTILITY MODEL

Such a method for purifying SO₂The process involves purifying a gas mixture containing at least 1.0 wt.% SO₂Of the process gas stream of (a). Wherein the process gas is quenched for further cooling to typically 40 ℃ before it passes through the packed bed column. Thereafter, the process gas stream is supplied to at least one electrostatic precipitator, whereby condensate from the electrostatic precipitator is conducted into the water treatment apparatus.

The utility model is characterized in that condensate of a wet electrostatic precipitator is discharged independently, and the condensate contains most of sulfuric acid entering a wet gas purification section. The absence of said sulfuric acid at other gas purification plants thus enables operation at lower acid concentrations and thus more efficient removal of fluoride therefrom. Ultimately this results in a saving in process water requirements.

The sulfuric acid concentration of the recycle liquid at the gas cooling tower, scrubber and quench therefore remains significantly lower. As a result, the addition of process water can be reduced and thus minimize the amount of liquid effluent while still rejecting all impurities. This is based on improved fluoride solubility at the gas cooling tower and scrubber loop.

It is necessary to measure the fluoride concentration in the process gas before entering the gas cooling tower and depending on the measurement, additional steps may be taken as described below to deal with the higher fluoride content.

Depending on the measured values, for up to usually 50mg F/Nm³The addition of water in and/or after the gas cooling tower.

Higher fluoride concentrations of the process gas (typically 50-200mg F/Nm) can therefore be tolerated³). Embodiments that separately expel wet ESP condensate minimize the addition of process water and thus the volume of weak acid to be processed at the liquid effluent treatment plant.

However, an excess of, for example, water glass may cause gelation, which leads to precipitation and accumulation in acidic environments, leading to coolers, pipesClogging of the channels or packing. This risk increases with higher fluoride content. Therefore, a minimum but sub-stoichiometric amount must be given to meet the requirement of less than, for example, 1mg F/Nm at the outlet of the gas cooling tower³This can be calculated from the given operating data. Most of the fluoride will be absorbed at low acid concentration and low temperature at the gas cooling tower. A lower fraction is absorbed upstream of the scrubber at higher acid concentrations and higher temperatures.

Preferably, silicon dioxide (SiO) is used₂) Sodium silicate (Na)₂SiO₃) And/or potassium silicate (K)₂SiO₃) As a reagent, wherein Na₂SiO₃Is most preferred. This results in a so-called water glass reaction, in which stable products, such as sodium silicate, remain in solution.

Even higher fluoride concentrations in the process gas (typically 200 to 1000mg F/Nm)³) It does require an additional co-current type packed bed fluoride column between the two stages of the wet electrostatic precipitator. Preferably, it is located between two wet electrostatic precipitators so as to be able to be at H₂SO₄Operating with minimal presence. Additionally or alternatively, liquid from the packed bed column is partially drained and mixed into the quench stream. Without such an additional step, the fluoride concentration of the circulating liquid of the gas cooling tower (even with chemical dosage) would not be able to achieve near residual 1mg F/Nm at the gas outlet³The desired removal efficiency. It has been common in the past that the packing material of such columns is made of silica-containing materials that react with the fluorides contained in the gas stream and form soluble H₂SiF₆. Due to the fluoride content, such fillers must be periodically renewed or replenished. Those columns are rather large and large in scale and therefore very expensive. It was observed that the surface of the ceramic filler material was covered with other substances (e.g. soot, lead, hydrocarbons) whereby the silica was no longer accessible to the fluoride, resulting in very little or no effect of such devices.

As subject of the present invention, a separation installed between two electrostatic precipitators and using plastic packing has been foundCounter-current packed bed fluoride removal columns can handle even very high fluoride (e.g., over 2000mg F/Nm) content³) While maintaining the quality of the exiting gas as<1mg F/Nm³And simultaneously reducing the amount of chemicals and process water added and subsequently also producing less liquid effluent.

Sometimes fluoride peaks may occur. That is also conveniently to be able to add some of the reagents, e.g. Na₂SiO₃、SiO₂And/or K₂SiO₃To a gas cooling tower to cover these peaks as well. This further increases the process flexibility.

Typically, process gases are used to produce H₂SO₄Thereby enabling the production of a vendible product with minimal impurities.

Because of use in SO₂Oxidation to SO₃The catalyst of (a) is sensitive to fluoride contained in the gas, so the present invention is not only essential for constant product quality, but also extends the operating life of downstream process steps.

In a preferred embodiment, the process liquid contains between 1 and 33 wt.%, preferably between 2 and 30 wt.% of H₂SO₄. This affects the solubility of fluoride, which increases the demand for flexible fluoride control.

Preferably, a scrubber is foreseen between the quench and the packed bed column for further purification.

Additionally or alternatively, condensate from the cooling gas column and/or scrubber is used as the quench stream in the quench. Thus, the liquid effluent stream is minimized.

Such a plant comprises at least one quench tower, at least one gas cooling tower and at least one electrostatic precipitator, preferably at least two electrostatic precipitators in series. As a critical part of the present invention, condensate from the electrostatic precipitator(s) is discharged through at least one discharge conduit and guided through at least one conduit to the liquid effluent treatment apparatus, respectively.

Preferably, the apparatus further comprises a pump tank and/or a packed bed column for adding the reactive agent, wherein the packed bed comprises silica.

In summary, in combination with the fluoride column operation as described above at high fluoride uptake rates, it is the key of the present invention to send the condensate/drain of the wet ESP containing a large amount of sulfuric acid directly and separately to the liquid effluent discharge. Thus, the gas cooling tower, scrubber and quench cycle can be operated at minimum acid content and thus better fluoride absorption. As a result, residual fluoride escaping into the fluoride removal column is thus minimized and the load on the fluoride column is reduced. Finally, this also reduces the required addition of water glass.

This system is based on the separate discharge of wet ESP condensate and the use of a certain amount of water glass. Although a significant amount of fluoride is removed upstream of the first step ESP (particularly at the gas cooling tower), the evolution of fluoride does only go into the individual packed bed tower and therefore the required reagent dosage is only a fraction of the equivalent amount necessary to react with all fluoride entering the plant. When the reactive agent is added up to the stoichiometric requirement equivalent, the fluoride content of the gas leaving the wet gas scrubbing apparatus can be kept substantially just below<1mg F/Nm³And thus the production of good quality sulfuric acid can be ensured.

All process water required at the wet gas cleanup section is preferably or exclusively added to this fluoride column, not only to ensure very low sulfuric acid concentrations there (typically well below 0.5 wt.% H)₂SO₄) But also to remove dissolved and stable precipitated products (e.g. Na)₂SiF₆) Counter current to the gas flow direction towards the quench tower and the liquid effluent treatment plant. In this way, the risk of overdosing of the flocculant and thus potential clogging of the apparatus is also eliminated.

Further features, advantages and possible applications of the invention can be taken from the figures and the following description of exemplary embodiments. All features described and/or illustrated form the subject matter of the invention per se or in any combination, independent of their inclusion in the claims or their back reference.

Drawings

In the drawings:

FIG. 1 shows a SO according to the prior art₂The purification is carried out, and the water is purified,

FIG. 2 shows SO for relatively low fluoride concentration according to the present invention₂The purification is carried out, and the water is purified,

FIG. 3 shows SO for moderate fluoride concentrations according to the invention₂The purification is carried out, and the water is purified,

FIG. 4 shows SO for relatively high fluoride concentration according to the present invention₂Purifying, and

FIG. 5 shows SO for very high fluoride concentration according to the invention₂And (5) purifying.

Detailed Description

The standard wet gas cleaning process flow diagram of fig. 1 is characterized by a stepwise countercurrent flow of the aqueous phase (weak acid) with respect to the direction of the gas flow.

The process gas is fed to the quench column 10 through conduit 11. Here, a quench stream supplied via conduit 14 is used for quenching. The quench stream is partially recycled via conduit 12, pump 13 and conduit 14. The other portion of the quench stream is discharged through conduit 15.

After quenching, the cooled process gas is transported via conduit 16 to scrubber 20, where it is further purified in scrubber 20 with aqueous sulfuric acid fed via conduit 23. Part of the scrubbing liquid is recycled through conduit 21, pump 22 and conduit 23 and part is fed into conduit 24 for the quench column.

The process gas is next passed to a gas cooling tower 30 via conduit 25. The necessary fresh process water is added to the gas cooling tower 30 through conduit 38. Part of the liquid in the sump of the gas cooling tower is circulated through conduit 31, pump 32, conduit 33, heat exchanger 34 and conduit 35, while another part is discharged through conduit 36. Thus, the concentration of impurities in the liquid increases in stages until it is discharged from the quench tower through conduit 15.

The cooled process gas is then sent to a first electrostatic precipitator 40 and, if desired, to a second electrostatic precipitator 42 via a conduit 41. Thereafter, the purified sulfur dioxide may be further processed for the production of sulfuric acid. The condensate of all of the

electrostatic precipitators

40,42 is discharged through

conduits

44,45 and 46 and passed into the sump of the cooling gas column 30, the scrubber 20, to the quench column 10 from where it is discharged in the manner described herein.

The sulfuric acid in the condensate at the wet

electrostatic precipitators

40,42 has a typical 25-35% H₂SO₄And will be at typically only 1-10% H₂SO₄The concentration is fed upstream to a gas cooling tower circulation. At higher acid concentrations, the solubility of metal sulfates as well as chlorides and especially fluorides gradually disappears. To reduce the acid concentration and thus also the dissolved fluoride concentration, more process water may be added and thus the fluoride removal efficiency may be improved. This process is industrially mature and can be up to typically 50mg F/Nm³And the gas leaving the wet gas cleaning section contains less than 1mg F/Nm³. The capacity of the available fresh process water and downstream liquid effluent treatment equipment and its investment costs are determinants and limiting factors, respectively.

The present invention is characterized in that condensate from a wet electrostatic precipitator and thus a large amount of sulfuric acid is separately discharged from a wet gas cleaning section, as illustrated in fig. 2.

Condensate from all of the

electrostatic precipitators

40,42 is discharged through

conduits

44,45 and 46 and passed to a collection tank 50, respectively. From there it is pumped via pump 52 through

conduits

51 and 53 to the liquid effluent treatment plant.

Scheme 3 shows additional doses of reactive agent. The reagent remains available in the pump tank 60, from which pump tank 60 it is pumped through conduit 61, dosing pump 62 and conduit 63 to the gas cooling tower 30 for recirculation (e.g., conduit 35), or to a sump of the gas cooling tower 30.

Fig. 4 shows the use of an additional packed bed column 70. From there, the process gas from the first electrostatic precipitator 40 is supplied to this additional packed bed column 70. The packing material of this packed bed column 70 is made of a silica-containing material that reacts with fluorides contained in the gas stream and forms soluble H₂SiF₆。

Fresh water is injected into the packed bed column 70 through conduit 77. A portion of the liquid is recycled from the sump of the packed bed column 70 to the top of the packed bed column 70 through conduit 72, pump 73 and conduit 74, while another portion is discharged through conduit 76 and passed to the gas cooling column 30.

Fig. 5 shows a further flowchart in the sense of the present invention. In contrast to fig. 4, an additional duct 66 is foreseen. Through this conduit 66, additional reactant can be added from the pump tank 60 to the packed bed column 70 to capture these peaks in the fluoride concentration of the process gas.

List of reference numerals:

10 quench tower

11,12 catheters

13 Pump

14-16 catheter

20 washing device

21 catheter

22 pump

23-25 guide tube

30 gas cooling tower

31 guide tube

32 pump

33 catheter

34 heat exchanger

35-39 catheter

40 electrostatic precipitator

41 catheter

42 electrostatic precipitator

43-46 catheter

50 pump pot

51 catheter

52 pump

53 catheter

60 pump pot

61 catheter

62 dosage pump

63 catheter

70 packed bed column

71,72 catheter

73 pump

74-77 catheter

Claims

1. For purifying SO-containing substances₂The plant of gases of (1), comprising at least one quench tower (10), at least one gas cooling tower (30) and at least one electrostatic precipitator (40,42), characterized in that at least one conduit (43,44,45) is foreseen to discharge the liquid phase coming from one or more electrostatic precipitators (40,42), a pump tank (60) for the addition of reactants and an additional packed bed tower (70), wherein the packed bed comprises silica.

2. An apparatus according to claim 1, characterized in that the fluoride concentration in the gas is measured before leaving the at least one electrostatic precipitator (40,42) and that the following steps are performed depending on the measured values:

(i) for less than 50mg F/Nm³Fluoride concentration of (2), process water addition and/or

(ii) For F/Nm at 50 and 250mg³In the gas cooling tower (30) and/or after the gas cooling tower (30), a reactive agent and/or

(iii) For F/Nm at 200 and 1000mg³After the first electrostatic precipitator (40), directing the gas through an additional packed bed column (70).

3. The plant according to claim 1 or 2, characterized in that the continuous measurement of the concentration of F in the gas is used for controlling and/or adjusting the amount of reactive agent fed to the gas cooling tower (30) and/or the additional packed bed tower (70).

4. Device according to claim 1 or 2, characterized in that SiO₂、Na₂SiO₃And/or K₂SiO₃Used as a reaction reagent.

5. The apparatus according to claim 1 or 2, characterized in that a separate counter-flow packed bed fluoride removal column installed in between is foreseen between the two electrostatic precipitators (40, 42).

6. The apparatus according to claim 5, characterized in that the separate counter-current packed bed fluoride removal column has plastic packing.

7. The apparatus according to claim 1 or 2, characterized in that the apparatus comprises conduits (61,63) and a dosing pump (62) for pumping the reactants to the gas cooling tower (30).

8. The plant according to claim 1 or 2, characterized in that the purified gas is used for producing H₂SO₄。

9. The plant according to claim 1 or 2, characterized in that it is used for purifying SO-containing material from metallurgical plants for treating or smelting non-iron ore containing sulphides₂The gas of (2).

10. The plant according to claim 1 or 2, characterized by a scrubber (20) foreseen between the quench tower (10) and the gas cooling tower (30).

11. The plant according to claim 10, characterized in that it comprises a conduit (24) for the quench column (10) into which part of the liquid coming from the scrubber (20) is fed.