WO2022068983A1

WO2022068983A1 - Method and device for flue gas desulphurisation, in particular desulphurisation of exhaust gas from large-scale pyrometallurgical processes with high sulphur dioxide content

Info

Publication number: WO2022068983A1
Application number: PCT/DE2020/100851
Authority: WO
Inventors: Albin Dobersek; Andreas Gieseler; Anatolij KIRNARSKI
Original assignee: Engineering Dobersek GmbH
Priority date: 2020-10-02
Filing date: 2020-10-02
Publication date: 2022-04-07
Also published as: DE112020007643A5

Abstract

The invention relates to a method for the desulphurisation of industrial exhaust gas with an SO2 output content in the range of 12 to 30 vol.%, in particular exhaust gas from large-scale pyrometallurgical processes, the desulphurisation being achieved using a multi-stage wet absorption method with atomisation of an absorption agent, preferably a limestone-based absorption agent in the form of an aqueous solution or suspension. The exhaust gas is initially diluted, as necessary, to an SO2 content of approx. 4-10%, and then a multi-stage, in particular three-stage, wet absorption cascade is performed, with which, by means of a specific setting of deposition rates in the individual wet absorber stages (10, 12, 14), the high volume flows occurring for SO2 total deposition rates >99% can be handled while ensuring optimum FGD gypsum quality. In calcined form as an anhydrite, this FGD gypsum has also proven to be particularly advantageous for use as a binder for mine fillers, which can then be used advantageously without being transported over large distances as part of a circular concept for sulphur.

Description

Process and device for flue gas desulfurization, in particular for desulfurization of exhaust gases from large-scale pyrometallurgical processes with high sulfur dioxide contents

The present invention relates to a method and a device for flue gas desulfurization, in particular for desulfurization of exhaust gases from industrial pyrometallurgical processes with high sulfur dioxide contents, according to the preamble of claims 1 and 11.

The invention also relates to a method for extracting non-ferrous metals from a mining site with mining of sulfidic ores, including the aforementioned flue gas desulfurization method according to the preamble of patent claim 12.

Flue gas desulfurization processes with wet absorption using calcareous reagents have been in use on an industrial scale for decades, for example for flue gas cleaning in coal-fired power plants, with large quantities of so-called FGD gypsum being produced as a fundamentally reusable residue that can be used in the construction industry. The fields of application for such wet absorption desulfurization processes are usually characterized by relatively low sulfur dioxide contents in the exhaust gas of less than 1 percent by volume.

For areas of application in which waste gases with significantly higher sulfur oxide contents regularly occur, for example in certain metallurgical plants, alternative processes, for example catalytic oxidation for desulfurization, have mostly been preferred on an industrial scale in recent years. In catalysis, especially in the so-called single and double contact systems, the sulfur oxides are finally bound in sulfuric acid using a catalyst. Since sulfuric acid is relatively complex and dangerous to transport in large quantities and cannot always be used directly, the sulfuric acid is neutralized with limestone if it cannot be used locally. The gypsum formed during this neutralization is generally only suitable to a limited extent due to its structure for further processing in the construction industry and is usually landfilled. In addition to high investment and operating costs, this results in the need for landfill sites.

Theoretically, the wet absorption processes mentioned above could also be used with such high initial sulfur dioxide contents, because the exhaust gases could of course be diluted accordingly with air. However, in the case of high exhaust gas volume flows to be processed, this would lead to volume flows that could no longer be managed economically in view of the necessary dilution factors.

The object of the invention is to desulfurize exhaust gases with a high sulfur dioxide content, such as those produced in large-scale industrial pyrometallurgical processes, in an economical manner by means of a wet absorption process, with the resulting residues possibly being used further in a particularly sensible manner.

The aforementioned task is solved by means of a method or a device with the features of independent claims 1 and 11 and by means of a method with the features of patent claim 13.

Advantageous refinements of the invention are explained in the dependent patent claims.

According to a first aspect of the invention, a method for the desulfurization of industrial exhaust gases with SO ₂ -Output contents in the range between 12 and 30% by volume, in particular a method for the desulfurization of exhaust gases from large-scale pyrometallurgical processes, is proposed, the desulfurization being carried out by a Wet absorption process with atomization of an absorbent in the form of an aqueous solution or suspension, whereby an FGD gypsum suitable for further processing for construction industry applications is to be produced. This method has at least the following steps: a) if necessary, diluting the exhaust gases and increasing the oxygen content of the exhaust gases by blowing in air, so that the SO ₂ content is in a range between 4 and 10% by volume; b) Passing the exhaust gases, which may be diluted, through at least a number of m spray absorbers arranged in series and each charged with calcareous absorbent, the number of spray absorbers being m ≥ 3, and the SO ₂ separation degrees being n = 1 ... m den referred to in the direction of flow as the first/second/third etc. spray absorber through which flow occurs, from the respectively supplied gas phase by setting at least the following process parameters approximately to a predetermined target value η _{n target} : i) Setting the mass flow of supplied calcareous absorbent, and

II) adjusting the amount of suspension circulated and thus the liquid-to-gas (LG) ratio; where the degree of separation η _n is determined as ^η n = as the SO 2 concentrations

in front of or behind the respective spray absorber n, these concentrations being represented as SO ₂ gas weight per gas volume, and the separation efficiency setpoint for the first spray absorber η ₁ soII. is selected to be lower than the separation efficiency target value for the last spray absorber η _{m target. -}

Of course, the dilution step only has to be taken if the raw sulfur dioxide content of the exhaust gases is outside the capacities of the subsequent wet absorber cascade. With a range of 4 to 10% by volume, however, this capacity is significantly higher than is possible with conventional wet absorption processes.

According to a further aspect of the invention, the FGD gypsum produced above can be integrated particularly advantageously into an overall process of non-ferrous metal extraction as follows, in that the non-ferrous metal extraction is designed as follows: i) mining of the sulphide ores; ii) beneficiation of the ores with subsequent pyrometallurgical processing of the non-ferrous metal concentrates; iii) waste gas cleaning of the sulphur-containing roasting waste gases according to the process described above; iv) calcining the FGD gypsum obtained in step iii) to anhydrite; v) Use of the anhydrite obtained in step iv) as a binder for the production of a filler for the backfill; vi) Use of the filler obtained in step v) for backfilling, preferably in situ, or other use of the anhydrite, for example in the construction industry.

In one embodiment, the filler in step v) can be produced on the basis of cement with the addition of anhydrite as a binder and optionally with the addition of other residues from the metallurgical processes, such as suitable slags.

It goes without saying that the anhydrite obtained in the above steps is contained in the filler in quantitative proportions, for example with proportions by weight of at least 10%, 25% or more.

One aspect of the present invention - which can also be considered fundamentally independent of the specifically described desulfurization process - is therefore also FGD gypsum from the desulfurization of exhaust gases from pyrometallurgical processes (or other FGD gypsum obtained) by calcination To process anhydrite and then to use this anhydrite as a binder for a filler for the backfill (also referred to as backfill), which can then - especially in the event that ore mining and ore smelting take place close to each other - be transported locally with little transport effort - Can be used so that a cycle concept for the sulfur can be closed.

The absorption process according to this invention allows, through the sequential arrangement of (at least) three SO2 absorbers, designed according to the absorption and crystallization time necessary to achieve the degree of desulfurization specified for each stage, to achieve both a high degree of desulfurization of approx 99%, as well as to produce gypsum with an optimal particle size distribution and particle shape, which is optimal for its dewatering and calcination. The optimal FGD gypsum formation is achieved in particular by the fact that the SO ₂ - degrees of separation η _n are not chosen to be the same in all stages or as high as possible, but are chosen lower at least in the first stage than in the last stage, where the degrees of separation from the first to the last stage are particularly preferably chosen to increase significantly. In this way, the crystallization processes can be controlled at all stages with regard to a starting product that is optimal for the purposes of the invention.

By calcining the gypsum to form anhydrite, a salable product can then be produced that can be used in the construction industry, for example.

In addition, this product can be used as a binder in the production of mixtures for backfilling. This closes a "sulphur cycle"; i.e. the sulfur first extracted as part of an ore is finally conveyed back into the mine as part of the inert filling mixture.

Studies have shown that the use of anhydrite in the filling mixture can significantly reduce the need for cement. In this way, a double saving in operating costs is achieved when backfilling underground: Both by doing without purchased anhydrite (or costs for mining natural anhydrite) and by lower cement consumption.

In summary, it can be stated that the process and the system are able to provide a product for the mine backfill in addition to an effective exhaust gas desulfurization of the highly concentrated exhaust gases.

In a preferred embodiment of the invention, the separation efficiency target value for the first spray absorber is chosen to be rh target 75%, preferably rh target 65%, particularly preferably rh target 60% and/or the separation efficiency target value for the last spray absorber is selected with η _{m target} >80%, preferably with η _{m target} 90%, particularly preferably with η _{m target} >95%.

In one embodiment, the separation efficiency target value for the first spray absorber η ₁ target is at least 20 percentage points lower than the separation efficiency target value for the last spray absorber η _{m target.} Furthermore, it can preferably be provided that all separation efficiency target values, starting with the separation efficiency target value of the first spray absorber ili soii 'continue over the separation efficiency target values of the or the intermediate spray absorber η ₂ ... mi soii> up to the Separation efficiency target value of the last spray absorber η _{m target} are each chosen to increase.

The process is preferably designed in such a way that a total SO ₂ target degree of separation of at least 99%, preferably at least 99.5%, is achieved.

In one embodiment of the invention, the above step a) can be preceded by dedusting of the exhaust gases, in particular in an electrostatic precipitator or fabric filter.

Furthermore, in one embodiment, the first spray absorber can be followed by an additional oxidation tank, through which the absorbent that has flowed through the first spray absorber is then passed, for the purpose of increasing the oxidation and crystallization time.

Air should preferably be additionally blown into one or more of the spray absorbers.

The calcareous neutralizing agent as the main component can be selected from one or more of the substances CaCO ₃ , CaO and/or Ca(OH) ₂ .

Furthermore, in a preferred embodiment, it can be provided that the gypsum suspension obtained from the spray absorbers in one or more of the provided spray absorbers is first thickened and classified in hydrocyclone stations assigned to the respective spray absorber(s), with the coarser fraction for dewatering be routed while the finer fraction is routed back into the respective absorption process.

In the context of the invention, a device for the desulfurization of industrial exhaust gases, in particular exhaust gases with SO ₂ output contents in the range between 12 and 30% by volume and in particular from large-scale pyrometallurgical processes, is also proposed, in which the device for carrying out a method according to is formed according to one of the preceding claims. The invention is explained in more detail below by way of example with reference to the figures.

Show it:

FIG. 1 shows a block diagram of the overall concept according to the invention, including the mountain offset;

FIG. 2 shows a more detailed diagram of the flue gas cleaning according to the invention; and

FIG. 3 shows a sub-diagram for FIG. 2 with the steps of anhydrite production.

FIG. 1 shows a general scheme of an overall concept according to the invention for flue gas desulfurization in large-scale pyrometallurgical processes, in the example for use in a copper extraction plant with two furnaces.

In the example, approx. 226,000 m ³ /h flue gases with a temperature of approx. 350 °C, which contain approx. 142 t/h SO ₂ , are produced during the large-scale pyrometallurgical copper treatment under normal load. More than 99% of this sulfur dioxide should be removed from the flue gases. For this purpose, a three-stage absorber arrangement is provided with a first, a second and a third spray absorber 10, 12, 14 (also referred to as REA I, II, III in FIG. 1 or as A1, A2, A3 in FIG. 2).

A limestone suspension, which is obtained via a mill 24, the ground material being mixed with the so-called circulating water, is fed to each of these, as described in more detail below.

The FGD gypsum obtained in all three stages 10, 12, 14 is dewatered in a unit 26 and calcined in a unit 28 to form anhydrite. Finally, this anhydrite is processed in a unit 30 with various additives, such as tailings, slag and cement, to form a backfill material which can then preferably be used locally for backfilling or for backfilling at the relevant ore mines.

The flue gas cleaning according to the invention is shown in more detail in FIG. The sulphur-containing flue gases originating from the pyrometallurgy are fed in at 18 and mixed with a predetermined amount of air (in the example approx. 2 parts air to 1 part flue gas) at 20 in order to adjust the sulfur oxide content for the subsequent process control.

The flue gas is then successively passed through three spray absorbers 10, 12 and 14 or A1, A2 and A3, with the first spray absorber to achieve the required oxidation and crystallization time and thus the specified degree of desulfurization and the optimum particle size distribution in the FGD - Gypsum is an oxidation or crystallization tank 16 downstream.

According to the invention, the process control is designed in such a way that the degrees of separation of the individual stages η _n (n=1...3), which are determined as η _n = as the SO 2 concentrations before or after

the respective spray absorber n, these concentrations being represented as SO ₂ gas weight per gas volume, in each case lower in the first separator than in the last, and preferably chosen to increase overall. In the exemplary embodiment, the degrees of separation are η ₁ =57.5%, 02=67.5% and 02=98.5%, and overall a SO ₂ separation degree of >99.8% is aimed for.

For a better understanding of the further details of the method according to the invention, certain basics of flue gas cleaning are explained below:

On the chemistry of flue gas cleaning

The exhaust gases from metallurgical furnaces contain significant amounts of SO ₂ . To remove the SO ₂ , the exhaust gas is fed into a scrubbing process in which finely ground limestone is used as a neutralizing agent for the pollutant gas components that react acidically in aqueous solution. The gross chemical reaction that takes place here is the following: SO ₂ ) _g + ^1/2 O ₂ ) _g + 2 H ₂ O + CaCO ₃ ) f —> CaSO ₄ * 2 H ₂ O ) f + CO ₂ ) g

The indices g, I and f indicate that the respective components are added to or removed from the process in gaseous (g), soluble (I) or solid form (f). In fact, however, all the specified reaction steps only take place in the aqueous phase; This means that the gases SO ₂ and O2 have to be absorbed, the solid CaCOa has to dissolve and the solid CaSO4*2H2O has to be able to crystallize. The mechanical implementation of these reactions is based on the technique of handling suspensions and bulk materials.

The product component that is almost exclusively present due to the composition of the harmful gas load is CaSO ₄ *2H ₂ O ("gypsum"), so that it can be characterized as a "limestone-gypsum process".

In addition to the CaCO ₃ , limestone always contains a proportion of MgCOa. This magnesium carbonate also reacts with the absorbed noxious gas. In contrast to CaCO ₃ , MgCOa only forms soluble salts that can only be removed via a waste water discharge. The chemical reactions are: SO ₂ )g + ^1/2 O ₂ )g + MgCO ₃ )f —> MgSO ₄ )i + CO ₂ )g

The content of dissolved salts in the absorber suspension can only be influenced by discharging the waste water appropriately.

The exhaust gases from the upstream pyrometallurgical process are first freed from dust in electrostatic precipitators (not shown in the drawings). They leave the filter with an SO ₂ content of around 12 - 30% by volume and an exhaust gas temperature of 300 - 400 °C.

In the desulfurization plant, the SO ₂ content is reduced by a total of approx. 99%. The desulfurization plant (REA for short) consists of three series-connected absorbers 10, 12, 14 and an additional oxidation tank 16 for the first absorber. The downstream connection of the oxidation tank 16 ensures the required oxidation and crystallization time and thus the specified degree of desulfurization for the first absorption stage and the optimum grain size distribution in the FGD gypsum.

Since the exhaust gas temperature of 300 - 400 °C is too high for the desulfurization system, the exhaust gases are first diluted with about 515,000 Nm ³ /h of air at the point marked with the reference number 20 and thus cooled to about 150 °C. Cooling down with an evaporative cooler is not possible because the water content in the exhaust gas downstream of the evaporative cooler means that not enough water can evaporate in the FGD and the temperature in the FGD becomes too high.

The gypsum suspension obtained during the desulfurization process is first thickened in hydrocyclone stations 32a-c and temporarily stored in two gypsum suspension containers 34a, b. In addition to thickening, the FGD gypsum is classified in the hydrocyclones 32a-c, so that the coarser fraction is routed to dewatering, while the finer fraction is routed back to the absorption process, where the particles act as crystallization nuclei and thus help to form contribute to an optimal grain distribution of the gypsum produced in the absorption process.

The coarser suspension fraction discharged from the hydrocyclones 32a-c is pumped to belt filters 36a, b, where it is dewatered. The dewatered gypsum is then stored for further processing in a store with a buffer capacity of approx. 24 hours. From the store, the gypsum reaches the calcination plant 42 (cf. FIG. 3), in which anhydrite is formed from the calcium sulphate dihydrate. This anhydrite is used as a binder in the mixture for backfilling or backfilling of the excavation cavities.

The limestone absorbent required for the process is delivered as crushed limestone with a grain size of up to 60 mm (e.g. by rail) and stored in a warehouse with a storage capacity of approx. 7 days. From there, the crushed limestone reaches a total of four limestone mills (referred to collectively as 24 in FIG. 1) via dosing silos. Depending on requirements, two to three mills are in operation. The limestone is crushed in the mill and then classified in a hydrocyclone station, collectively designated 24 . The end product is a 25% by weight limestone suspension with a particle size D80 < 40 μm, which is metered into the absorbers.

flue gas scrubbing

The absorbers 10, 12, 14 as spray washers operated in countercurrent have to fulfill the following functions: In the gas-side circuit:

Cooling or saturation of the hot flue gas stream so that flue gas and scrubbing liquid coexist in common contact;

Thorough mixing of flue gas and scrubbing liquid so that strands of uncleaned flue gas are avoided; and

Separation of scrubbing liquid and scrubbed flue gas.

In the liquid side circuit:

Continuous neutralization of the noxious gases absorbed by the scrubbing liquid, so that there is always a "driving concentration gradient" from the flue gas to the scrubbing liquid; the rate-limiting step is the dissolution process of the limestone in the washing liquid;

absorption of oxygen (O ₂ ) to form gypsum; and continuous gypsum crystallization, so that the operationally difficult condition of supersaturated CaSO ₄ solutions is avoided.

The continuous neutralization of the absorbed noxious gases requires a corresponding supply of limestone suspension. The limestone suspension is produced in the limestone grinding plant 24 and initially stored in buffer tanks. From there it is pumped to the absorbers 10, 12, 14.

Because of the low rate of dissolution of the limestone, the absorbers 10, 12, 14 must be dimensioned according to the necessary residence time.

The formation of gypsum based on the SO ₂ /CaCO ₃ reaction requires oxygen. Depending on the oxygen partial pressure of the flue gas, oxygen is also absorbed. Measured against the requirements of the gypsum formation reaction, however, the amount of oxygen contained in the exhaust gas is generally not sufficient. For this reason, additional air must be supplied to the absorbers. This air is generated with four (plus one reserve unit) turbo compressors. The air is injected into the absorbers below the liquid level (via the "Oxiluff" supply 38) and is finely distributed by the agitators in the vicinity of the absorbers 10, 12, 14. According to the design, the absorbers 10, 12, 14 are operated with a suspension with a solids content of approx. 20%, so that the (initially dissolved) CaSCU arising from the chemical reaction is faced with a maximum of crystallization nuclei. In this way it is achieved that the crystallization only takes place in the absorbers 10, 12, 14, but not in the pipelines and their shut-off and control fittings.

The amount of scrubbing liquid circulated or sprayed for the SO ₂ absorption is many times that which evaporates when the flue gas stream entering the absorbers 10, 12, 14 cools down or becomes saturated. A special cooling or quenching zone in front of the actual absorbers 10, 12, 14 is therefore not required.

In the event that all circulating pumps of the first absorber 10 fail, emergency spraying is provided in the absorber inlet of the first absorber. The emergency nozzle serves to cool the exhaust gases until the exhaust gas flaps have blocked the way to the FGD and opened the way to an "emergency chimney". This ensures that the gas temperature in the absorber 10 does not rise above 80°C. In addition, the inlet channel into the absorbers 10, 12, 14 is flushed discontinuously in order to avoid caking.

To separate entrained droplets and spray mist from the flue gas flow, fine droplet separators are arranged on the absorber outlet side (not shown). The droplet eliminators consist of individual cassettes containing s-shaped PP lamellae as separating elements. Flushing the separator elements with process water prevents incrustations in this area and thus an increase in pressure loss. The last absorber 14 is equipped with two droplet separator levels in a row in order to increase the separation efficiency.

Structure / main components

flue gas routing

The waste gas to be desulfurized from the two furnaces (feed at point 18) is initially installed downstream of the furnace-side system parts, not shown, with the aid of a Booster fan promoted to a mixing chamber 20 and mixed there with fresh air to cool and dilute the exhaust gases. The fresh air pressure required is generated by a fresh air blower.

The exhaust gases behind the mixing chamber 20 are routed to the absorbers 10, 12, 14 connected in series and leave the last of the three absorbers 14 through a chimney 22 on the absorber 14. to bypass the plant and discharge the exhaust gases directly via the existing chimneys. Appropriate flue gas flaps are provided for the necessary shut-offs.

absorber

The absorbers 10, 12, 14 are designed as countercurrent spray tower scrubbers. The nozzles are distributed over six levels, with one circulating pump supplying each nozzle level.

At the absorber outlet, a droplet separator prevents droplets from being carried over into the clean gas. The droplet separator of the last absorber consists of two levels. These are arranged one above the other with a spacing of approx. 2.5 m. The drip catchers consist of plastic cassettes with S-shaped lamellae, which are rinsed with process water in sections at intervals.

limestone supply

Limestone is used as a neutralizing agent for desulfurization. In the exemplary embodiment, the limestone is delivered as crushed limestone, stored, dosed and wet-ground in ball mills. The amount of liquid required for this is taken from a circuit water tank 40 of the FGD. After the limestone suspension has been classified in a hydrocyclone station (not shown), it is temporarily stored in the limestone suspension tanks (not shown) and pumped from there to the absorbers 10, 12, 14 via a ring line.

The quantity of limestone suspension supplied to the first two absorbers 10, 12 is supplied in proportion to the incoming SCte load and as a function of the SCte degree of separation of the respective absorber. The amount of limestone fed to the last absorber 14 is also metered in proportion to the incoming SCte load. However, the pH value of the absorber suspension has a corrective effect here.

Gypsum disposal and recycling

Gypsum suspension is conveyed from the respective absorber 10, 12, 14 to the hydrocyclones 32a-c by means of gypsum extraction pumps. The number of open hydrocyclones 32a-c is constant. Depending on the amount of gypsum to be discharged, which results from the solids content in the absorber, the hydrocyclone underflow with a solids content of approx.

The hydrocyclone overflow is fed to the circuit water tank 40 as so-called circuit water. If necessary, ie if too little circulating water comes from the cyclones, process water is fed into the circulating water tank 40 . If too much circulating water is generated by the cyclones 32a-c, the hydrocyclone overflow is pumped back into the respective absorber 10, 12, 14.

The suspension is pumped from the gypsum suspension containers 34a, b to seven (plus one reserve unit) belt filters 36a, b, where it is dewatered to about 10% by weight residual moisture and then conveyed to the wet gypsum store. The wet gypsum store has a storage capacity of about 24 hours and serves as a buffer between the FGD and the calcination plant 42 (cf. FIG. 3). This consists of two calcination lines (not shown individually), which are supplied with gypsum according to the filling levels in the dosing silos there via a conveyor line assigned to the corresponding calcination line.

Anhydrite is produced by FGD gypsum calcination at a specified temperature. Studies have shown that FGD gypsum is well suited for the production of anhydrite. The calcination system 42 represents a multi-stage thermal treatment of the gypsum and consists of the following main process steps: drying 26, preheating, calcination and product cooling 44.

The chilled anhydrite is transported to a finished product warehouse with a capacity for 7 days. The loading of the gypsum on railway wagons is for 8 h/day provided, for which two lines of the same power are provided. The finished product is preferably transported to the mine, where the anhydrite is added to the backfill as a binder. This mixture can contain residues from a metallurgical plant - such as e.g. B. slag - are added, so that you get an additional advantage - Utilization of the residues.

The filtrate occurring at the belt filter 36a, b is routed to the circuit water tank 40 and, together with the water from the hydrocyclone overflow and additional process water, is used as a liquid for the wet grinding and production of the limestone suspension.

Part of the hydrocyclone overflow is collected in the plant's waste water tank and discharged from there from the process. This is necessary in order to stabilize the proportion of dissolved substances (particularly magnesium compounds) in the suspension.

process water supply

Process water is stored in a process water tank 46 . It is used for rinsing the droplet separators, as rinsing water for the suspension lines, for filling the emergency water tank and finally for level control in the circuit water tank. The process water is also used to keep the inlet channels of the absorbers 10, 12, 16 clean by rinsing and to reduce gypsum caking.

Drainage and flushing system

Permanently installed flushing connections are provided for the suspension-carrying pipelines, apart from the circulation lines of the absorbers 10, 12, 14. When a suspension-carrying line is shut down, it is flushed fully automatically with process water (exception: drain lines on the absorber and drain tank).

In order to empty one of the absorbers 10, 12, 14--eg during an inspection--the suspension content of the absorber is pumped into the so-called emptying tank by means of an emptying pump. The residue of the absorber is emptied via the pump sump assigned to each absorber. Before the plant is put back into operation, the suspension is pumped back into the relevant absorber using a recirculation pump.

Concrete pits are provided as pump sump at the absorbers 10, 12, 14, the gypsum drainage system 26 and in the limestone grinding plant 24. All pits and the discharge tank are equipped with permanently installed agitators and pumps.

process control

The control systems for the flue gas cleaning system enable safe and efficient operational management with high availability. Typical parameters of the desulfurization, which are necessary for the safe operation of the plant, are displayed, registered, reported and possibly printed out in the control room.

The following control circuits are provided:

Make-up of the limestone suspension absorber A 1 and A2:

The limestone suspension is fed back into the absorber 10, 12 in proportion to the separated SO ₂ load. The ratio of limestone to SO ₂ (stoichiometric factor) is corrected via the measured separation efficiency of the respective absorber 10, 12.

Make-up of the limestone suspension Absorber 3:

This control circuit differs slightly from the control circuit of absorbers 1 and 2. Here, the limestone suspension is fed back into this absorber 14, also in proportion to the SO ₂ load to be separated. In this absorber 14, however, the ratio of limestone to SO ₂ (stoichiometric factor) is corrected with the pH value measured in the absorber suspension.

Height control in absorbers:

In the absorbers 10, 12, 14, a fixed level is set via the discharged hydrocyclone overflow quantity. If the fill level is too high, the hydrocyclone overflow is routed to the circuit water tank 40; if the fill level is too low, the hydrocyclone overflow is routed back to the absorber. Height control in the circuit water tank:

The fill level in the circuit water tank 40 is kept constant by supplying more or less process water.

Setting the levels, in general: The levels of all containers are automatically set via valves or flaps in the inlet and outlet lines.

Density control of the absorber suspension:

The solids content in the absorbers 10, 12, 14 is controlled via the quantity of hydrocyclone underflow conveyed to the gypsum suspension tank 34a, b. If the solids content in the absorber is too high, the cyclone underflow is conveyed to the gypsum suspension tank. If the solids content in the absorber is too low, the hydrocyclone underflow is fed back into the absorber.

Level control in the gypsum slurry tanks: The level in the gypsum slurry tanks 34a,b is kept constant by the amount of suspension pumped to the belt filters 36a,b.

Reference character list

10 First spray absorber (A1 )

12 Second spray absorber (A2)

14 Third spray absorber (A3)

16 oxidation or crystallization tanks

18 flue gas supply

20 air admixture

22 chimney

24 Limestone Mill

26 FGD gypsum drainage

28 calcination unit

30 processing to mountain backfill

32a-c hydrocyclones

34a, b gypsum suspension container

36a,b bandpass filters

38 Oxi air supply

40 circuit water tank

42 calcination plant

44 Anhydrite Cooling Plant

46 process water tank

Claims

patent claims

1 . Process for the desulfurization of industrial waste gases with S02 initial contents in the range between 12 and 30% by volume, in particular processes for the desulfurization of waste gases from large-scale pyrometallurgical processes, the desulphurization by a wet absorption process with atomization of an absorbent in the form of an aqueous solution or suspension takes place, whereby a suitable FGD gypsum for further processing for construction industry applications is to be produced, characterized by the steps: a) if necessary, diluting the exhaust gases and increasing the oxygen content of the exhaust gases by air injection, so that the SO ₂ - Content is in a range between 4 to 10% by volume; b) conducting the exhaust gases, diluted as necessary, through at least a number m of spray absorbers (10, 12,14) arranged in series and each charged with calcareous absorbent, the number of spray absorbers being m ≥3, and the SO ₂ separation degrees η _n , where n=1 . . a predetermined desired value ijnsoii be regulated: i) setting the mass flow of supplied calcareous absorption medium term, and ii) setting the circulated amount of suspension and thus the liquid-to-gas (LG) ratio; where the degree of separation η _n is determined as η _n = as the SO ₂ concentration

ons in front of or behind the respective spray absorber n, where these concentrations are represented as SO ₂ gas weight per gas volume, and the separation efficiency target value for the first spray absorber (10) η _{1 SoII} is selected lower than the separation efficiency target value for the last spray absorber (14) η _{m So} II.

2. The method according to claim 1, characterized in that the desired separation efficiency value for the first spray absorber (10) is chosen to be η _{1 desired} 75%, preferably η _{1 desired ≦} 65%, particularly preferably _{1 desired} 60%, and/or that the desired degree of separation in the last spray absorber (14) is chosen to be η _{m So} II 80%, preferably η _{m So} II 90%, particularly preferably η _{m So} II ≧95%.

3. The method according to claim 1 or 2, characterized in that the separation efficiency target value for the first spray absorber (10) η _{1 target} is at least 20 percentage points smaller than the separation efficiency target value for the last spray absorber (14) η _{m target.}

4. The method according to any one of claims 1 to 3, characterized in that all separation efficiency target values, starting with the separation efficiency target value of the first spray absorber (10)η _{1 target} , further on the separation efficiency target values of the or the intermediate spray absorber ( 12) _η ₂ .

5. The method according to any one of claims 1 to 4, characterized in that the method is designed to achieve an overall SO 2 target degree of separation of at least 99%, preferably at least 99.5%.

6. The method according to claim one of claims 1 to 5, characterized in that step a) is preceded by dedusting of the exhaust gases, in particular in an electric filter or fabric filter.

7. The method according to any one of claims 1 to 6, characterized in that the first spray absorber (10) has an additional oxidation container (16) through which the through the first spray absorber (10) flowed absorption agent is then guided to increase the oxidation - and crystallization time is downstream.

8. The method according to any one of claims 1 to 7, characterized in that air is blown into one or more of the spray absorbers (10, 12, 14).

9. The method according to any one of claims 1 to 8, characterized in that the calcareous oxidizing agent is selected as the main component from one or more of the substances CaCO ₃ , CaO and/or Ca(OH) ₂ .

10. The method according to any one of claims 1 to 9, characterized in that from the spray absorbers (10, 12, 14) occurring gypsum suspension at one or more of the provided spray absorbers first in hydro cyclone stations (34a-c), the dem or assigned to the respective spray absorbers, is thickened and classified, with the coarser fraction being used dewatering, while the finer fraction is fed back into the respective absorption process.

11. Device for the desulfurization of industrial exhaust gases, in particular exhaust gases with SCte starting contents in the range between 12 and 30% by volume and in particular from large-scale pyrometallurgical processes, characterized in that the device is designed to carry out a method according to one of the preceding claims .

12. A process for the extraction of non-ferrous metals from a mining site with mining of sulfidic ores, characterized by the steps i) mining of the sulfidic ores; ii) processing of the ores with subsequent pyrometallurgical processing of the non-ferrous metal concentrates; iii) cleaning of the sulphur-containing exhaust gases by a method according to any one of the preceding claims; iv) calcination (28) of the FGD gypsum obtained in step iii) to form anhydrite; v) using the anhydrite obtained in step iv) as a binder for producing a filler for the backfill (30); vi) Use of the filler obtained in step v) for backfilling, preferably in situ, or other use of the anhydrite, for example in the construction industry.

13. The method according to claim 12, characterized in that the filler in step v) based on cement with the addition of anhydrite as a binder, and optionally with the addition of other residues of the metallurgical processes, such as suitable slags, is produced.