FI119915B - Removal of sulfur from the smell gases of a cellulose factory - Google Patents

Description

The present invention relates to a process for removing sulfur 5 from the chemical cycle of a sulphate pulp mill according to the preamble of claim 1.

Desulphurisation of Sulfur Gases in a Pulp Mill In such a process, concentrated odor gases containing sulfur compounds in process streams of the sulfate process are collected and these odor gases are burned to oxidize the sulfur compounds.

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The invention also relates to the use according to claim 15 and the hardware arrangement according to the preamble of claim 16.

The modern pulp mill is so closed that, although sulfur-containing fresh chemicals are replaced by sulfur-free, the cycle needs to be desulphurized to prevent uncontrolled sulfur emissions. The combustion of concentrated odor gases in either a recovery boiler, a lime kiln or a separate odor gas boiler or back-flame is used in all modern sulphate pulp mills.

20 When strong odor gases are burned in a recovery boiler, the sulfur is removed either as flue gas (sulfur dioxide) or as fly ash. Fly ash is usually removed from the system by discharge into waterways. Flue gas emissions containing sulfur dioxide cause soil acidification, damage to trees and building materials and other environmental damage. Ash, on the other hand, is rich in heavy metals of wood origin, so it is likely 25 that fly ash will be banned for future environmental reasons. Another significant disadvantage of fly ash removal is that the sulfur in the ash removes sodium in a molar ratio Na / S 2/1, which must be added to the system.

When the strong odorous gases are burned in the lime kiln, sulfur is eliminated either as flue gas emissions 30 (sulfur dioxide and TRS = total reduced sulfur compounds) or in lime / waste manure. In addition to the above-mentioned disadvantages, sulfur causes driving disturbances (including tires) in the lime kiln.

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When the concentrated odorous gases are burned in a separate odorous gas boiler, either sodium bisulphite or a low sulfur dioxide solution is obtained. In sodium bisulfite, sodium in the ratio of Na / S = 1/1 leaves the system with sulfur.

S During combustion of strong odor gases in the spare flame, all sulfur is eliminated as air emissions in the form of sulfur dioxide.

Any desulphurisation process in use will have one or more of the following disadvantages: air emissions will increase, sodium losses will increase, resulting in higher operating costs due to the replacement chemical needed, or the desulphurisation end product will be unusable at the factory.

The object of the present invention is to eliminate the problems of the prior art and to provide a completely novel solution for the recovery of sulfur from the process streams of the sulphate process.

The present invention is based on the idea that sulfur contained in concentrated odor gases is recovered as elemental sulfur, which can be recycled to the process or recycled.

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Selective oxidation of sulfur compounds to elemental sulfur is well known in the art.

Thus, FI102250 discloses a catalyst for the selective oxidation of sulfur compounds to elemental sulfur, a process for preparing the catalyst, and a process for selective oxidation of sulfur compounds to elemental sulfur. Application application FI 25 903673, for its part, proposes monolithic catalysts for the treatment of gases containing sulfur compounds in industry.

GB 2117749 describes a method and apparatus for burning sulfur-containing gases into elemental sulfur.

None of the above solutions have proposed the treatment of concentrated odorous gases, nor do they contain any proposal for the recovery of the sulfur thus obtained.

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According to the invention, the odorous gases collected from the process streams of a sulphate cellulose mill are burned at a low air coefficient such that at least a substantial portion of the sulfur compounds are oxidized to the elemental residue which is removed from the system. This solution allows controlled sulfur removal from pulp mill waste gases. The process 5 for oxidizing sulfur compounds used in the invention is based on the so-called Claus process.

The invention also provides an apparatus arrangement for desulphurizing a chemical cycle of a sulphate pulp mill comprising an odorous gas combustion unit provided with an inlet connected to a source of concentrated odorous gases, and an outlet means through which the oxidized sulfur effluent may be removed from the apparatus. The combustion unit according to the invention comprises at least one combustion unit of a Claus rigid system.

More specifically, the method of the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The use of the Claus process according to the invention is disclosed in claim 15.

The apparatus arrangement according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 16.

The invention provides considerable advantages. Thus, the process can be used to remove sulfur, in particular from the waste gases of a sulphate pulp mill. Sulfur gas sulfur is recovered in a form that can be utilized in one or another process. 25

The prior art methods do not disclose a solution in which the desulphurisation method according to the invention is integrated as part of the deodorizing system for the sulphate cellulose mill.

The combustion of the odorous gases can be carried out in one or more stages to optimize the removal of elemental sulfur in different temperature ranges. This can be followed by sequentially matching one or more Claus firing units. Different driving conditions can be used.

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On the other hand, the invention provides sulfur in such a form that it can be utilized, for example, as sulfur dioxide for bleaching and as sulfuric acid, either for the production of bleaching chemicals or for tall oil extraction. At the same time, the mill's sodium losses can be minimized.

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As a process connection, the solution can be placed in connection with the existing combustion of concentrated odorous gases. tail gas can be burned in existing equipment such as a recovery boiler, a smell gas boiler, a lime kiln or a flame.

In the process of the invention, it is preferable to use, for example, cooling water or boiler water from a pulp mill for the condensation of sulfur.

In the apparatus arrangement according to the invention, the combustion apparatus of the Claus ice system, i.e. the reactor, and the corresponding steam boiler are coupled from its feed inlet to the smell gas line of the sulfate process boiler or 1S evaporator or the corresponding smell gas source. In order to condense the oxidation products obtained from the incinerator, the arrangement further comprises a condenser by which the products, particularly the elemental sulfur, can be condensed into liquid or solid form. The burner is provided with an outlet connected to a condenser 20 to discharge these liquid or solid materials. In addition, the unit still has a gaseous (non-condensed) material removal unit which can remove light oxidation products as well as inert and unreacted compounds (TRS and SO2). As will be more fully understood from the following, at least some of the sulfur compounds of the concentrated odor gases from the Claus combustion are conducted to conventional odor gas combustion in a recovery boiler, odor gas boiler, lime kiln, or more. Therefore, the gaseous compound outlet of the hardware arrangement is preferably connected via pipelines to a sump or sludge furnace feed or similar after-treatment device.

As a process coupling, the solution can be placed in connection with the existing combustion of concentrated odorous gases. tail gas can be burned in existing equipment such as a recovery boiler or lime kiln or similar and the required sulfur condenser from the cooling water side can be integrated as part of the mill's water circulation / heat recovery. This reduces the hardware solution to a simple and economically advantageous one. The solution according to the invention is applicable to both existing and new plants.

As a simple addition, the solution is particularly well suited to the factory concept where the soda-5 boiler is the primary combustion site for concentrated odor gases.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below with reference to the detailed description and with reference to the accompanying drawings.

Figure 1 is a flow diagram illustrating the collection of odorous gases.

Figure 2 shows, also by means of a flow chart, a prior art method for treating odor gases.

Figure 3 shows the sulfur recovery according to the invention by the Claus process. Fig. 4 is a flow diagram of an alternative embodiment of the invention in which several combustion devices of the Claus rigid system are connected in parallel.

Figure 5 shows a sulfur recovery by Claus process and a flow diagram of the post-treatment of gases from the Claus system.

A special feature of the invention is that the so-called 20 Claus process is used to bind sulfur from concentrated odor gases, the following reactions taking place in the Claus process: H2S + 3/2 O2 <-> S02 + H2O 1/3 (I) 2 H2S + S02 <-> 3 S + 2 H2O 2/3 (II) 25 The strong odor gases are burned with air or oxygen, so that some of the sulfur in the strong odors remains in the elemental sulfur and some in the sulfur dioxide. The elemental sulfur remains in the range of 50 to 90 mol, typically 70 to 85 mol%.

30 Concentrated odoriferous gases are herein defined as those odorous gases in a pulp mill whose content exceeds the so-called. upper explosion limit. These gases consist of e.g. hydrogen sulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide.

6 The reduced sulfur in concentrated odorous gases is quite concentrated and is also sodium-free and rich in heat. By burning with a suitable air factor, most of the sulfur is oxidized to elemental sulfur, as happens in the traditional Claus process described above. Sulfur can be condensed and separated separately as liquid sulfur, an inert element with its own market value. By "air ratio" is meant herein the molar ratio of oxygen in air (O2) to sulfur (S) in the gas being treated. The air factor is one when the amount of oxygen in the air is in stoichiometric to its sulfur content of the gas being treated to convert all sulfur into sulfur dioxide. "Under-air", in turn, means that the air coefficient is less than one.

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In the present invention, the combustion of concentrated odorous gases is carried out under air or under air, typically with an air factor of 0.4 to 0.9, whereby the adiabatic combustion temperature is about 1400 to 1800 ° C. In one gas mixture, the combustion was carried out with an air factor of about 0.6, whereby the adiabatic combustion temperature was about 1600 ° C.

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In accordance with the method of the invention, a stream of scent gases collected from a source of concentrated odorous gases is incinerated in the first combustion unit through suitable pipelines and through a suitable pipeline of gases from the first combustion unit to a second combustion unit, such as a lime or Optionally, a portion of the stream of concentrated odor gases may be passed directly past the second combustion unit of the first combustion unit.

According to the invention, at least 10 mol% of the collected odorous gases are degassed in the first combustion unit by the Claus process. Preferably 30 to 90 mol%, typically 50 to 90 mol%, are passed through the Claus process. The remainder of the collected odorous gases can be led directly to incineration in existing plants.

The strong odorous gases are burned in the first combustion unit with vacuum. The sulfur oxidized to elemental 30 is condensed on a condenser and removed from the bottom of the odor gas combustion unit in a molten state. The liquid elemental sulfur is introduced into the collector and further transported to the conveyor. As it cools, liquid sulfur solidifies, but especially for short-term storage for new use, it is advisable to make it in liquid form.

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The exhaust or tail gas is routed, if necessary, to another Claus stiffener to maximize sulfur removal. The second burner, if necessary, uses different driving conditions than the first burner.

Exhaust or tail gases, such as sulfur dioxide and TRS, from the Claus ice system are routed for disposal to at least one combustion unit of another combustion unit, such as an odor gas boiler, a recovery boiler, a lime kiln or a flame. The Claus waste system in this process does not aim at complete sulfur recovery as elemental sulfur, but at least 10 mole% of the sulfur compounds passed through the Claus waste system are incinerated in a second fuel incinerator. Of the sulfur compounds of concentrated odor gases from Claus combustion, typically at least 10 mole%, up to about 50 mole%, preferably about 15 to 30 mole%, are sent for incineration in conventional combustion systems such as a recovery boiler or a lime kiln.

15 The Claus fluidized bed system utilizes, where appropriate, technologies developed in connection with the Claus combustion of hydrogen sulphide, such as catalysts. Examples of suitable catalysts are disclosed in patent application FI904949 or patent application FI102250.

The elemental sulfur obtained according to the process can be stored in liquid or solid form and transported in liquid or solid form, for example, to a sulfuric acid mill or another pulp mill. It can also be fed back into the process, for example, by adding it appropriately to the white liquor (making a polysulfide solution) or feeding it in a combination burner or other suitable means to adjust the sulphide upward if necessary. Recovery of sulfur in liquid or solid form is advantageous because it is then easily stored and transported.

According to an alternative solution, the odorous gases can be burned in a Claus reactor using oxygen instead of air.

According to another alternative solution, the elemental sulfur can be further burned to sulfur dioxide or processed into sulfuric acid. However, even in this case, the elemental sulfur can first be recovered by the Claus process combustion unit.

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According to a third alternative solution of the invention, the amount of concentrated odorous gases is increased, for example, by heat treatment of black liquor.

The method according to the invention will now be described with reference to the accompanying figures. 5

Figure 1 illustrates, by means of a flow chart, the collection of concentrated odor gases into the collectors of the cooking plant 1 or the evaporator 2 from known sources of concentrated odor gases either individually or in combination in generally known ways.

Figure 2 also shows, by means of a flow chart, a prior art method of treating odorous gases in which the concentrated odorous gases are introduced into the odorous gas boiler 3 (with condenser 7), the recovery boiler 4, the lime kiln 5, the flame 6 or more.

Figure 3 shows an apparatus arrangement 15 suitable for burning odor gases according to the invention. The apparatus arrangement of the invention comprises at least one odorous gas combustion unit 10 (first combustion unit) into which a stream of concentrated odorous gases can be collected and conducted from a source of concentrated odorous gases and wherein the reduced sulfur contained in the concentrated odorous gases is incinerable. The combustion unit comprises at least one combustion unit 10 of the Claus rigid system, and a condenser 11 connected thereto, together with an air supply 20 to 18. The combustion unit is provided with an inlet 14 connected to a source of strong odor gases and an outlet 15 for removing oxidized and condensed sulfur compounds in liquid or solid form as elemental sulfur. The elemental sulfur can be introduced into the collector 12 and further transported 13. The combustion unit also comprises an outlet 16 through which the gaseous non-condensed sulfur compounds from the first 25 fuel units can be fed to the second combustion unit for combustion. In addition, the feed unit 14 of the first combustion unit may be connected to a manifold 17 such that some of the concentrated odorous gases may be passed through the manifold past the first combustion unit for direct combustion to the second combustion unit 30.

The second combustion unit comprises at least one combustion device, such as an odor gas boiler, a recovery boiler, a lime kiln and / or a flame.

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Figure 4 illustrates an apparatus arrangement in which the first combustion unit comprises at least two Claus ice-burner units 20,21 connected in parallel and condensers 22,23 connected thereto and an air supply conduit 33, 34. The combustion unit is provided with an inlet 26 connected to a source of concentrated odor gases; and a discharge connection 27, 5 through which the oxidized and condensed sulfur compounds of the concentrated odorous gases can be removed from the device in liquid or solid form as elemental sulfur. Elemental sulfur may be introduced into the collector 24 and further transported 25. The combustion unit also comprises an outlet 28 through which gaseous, non-condensed sulfur compounds from the first combustion unit may be fed to a second Claus stiff combustor 21 10 through an inlet 29. The latter combustor 21 is stolen by an outlet 32 through which the oxidized and condensed sulfur compounds can be removed from the device in liquid or solid elemental sulfur form. The elemental sulfur can be introduced into the collector 24 and further transported 25. The second Claus wastewater burner is further stolen by an outlet 30 through which the gaseous non-condensed sulfur compounds from the Claus wastewater burner can be fed to another combustion unit.

The feed line 26 of the first combustion unit may be connected to the manifold 31 such that some of the concentrated odorous gases may be passed through the manifold past the first fuel unit for direct combustion to the second fuel unit. Alternatively, the outlet of the first Claus burner 28 of the Claus-20 rigid system may also be connected to a manifold through which part of the gas stream from the first Claus burner can be led directly to the second combustion unit for combustion.

Figure 5 shows a sulfur recovery by a Claus process with several Claus-25 combustion units connected in series and a flow diagram of the post-treatment of gases from the Claus system. The apparatus assembly comprises a first combustion unit having at least two parallel Claus ice burner units 40.41 and associated evaporators 42.43 and air feed lines 58.59. The first burner of the Claus ice system is provided with an inlet port 46 connected to a source of concentrated odor gases and an outlet port 47 through which the oxidized and condensed sulfur compounds of the high odor gas can be discharged from the apparatus in liquid or solid elemental sulfur. The elemental sulfur may be introduced into the collector 44 and further transported 45. The combustion apparatus also comprises an outlet 48 through which the gaseous, non-condensable sulfur compounds from the first Claus solid fuel combustion apparatus may be conducted to the second 10.

To the Claus ice burner 41 via the inlet 49. The latter combustor 41 is provided with a discharge connection 57 through which the oxidized and condensed sulfur compounds can be removed from the apparatus in liquid or solid elemental sulfur form. The elemental sulfur may be introduced into the collector 44 and further transported 45. The second Claus-5 waste system incinerator is further provided with an outlet 50 through which the gaseous, non-condensed sulfur compounds from the Claus system incinerator may be fed to another combustion unit.

As described in connection with Figure 4, the feed unit 46 of the first combustion unit may be connected to a manifold 51 such that a portion of the concentrated odorous gases may be passed through the manifold past the first combustion unit for direct combustion to the second combustion unit. Alternatively, the off-line assembly 48 of the first Claus burner of the Claus rigid system may also be connected to a manifold through which a portion of the gas stream from the first Claus burner can be led directly to the second burner unit 15 for combustion.

Exhaust or tail gas from the Claus rigid system combustor 41 of the first combustion unit, such as sulfur dioxide and TRS, is led to at least one combustion unit of the second combustion unit, such as a smell gas boiler 53 (equipped with condenser 20 56.

Claims (20)

1. A process for removing sulfur from the chemical circulation of a sulfate cellulose plant, in which process 5. concentrated odorous gases containing sulfur compounds are collected, and - they are combusted to oxidize the sulfur compounds, characterized by - combustion unit by means of a Claus process in such a way that at least a substantial portion of the sulfur compounds are oxidized to elemental sulfur, however, that at least 10 mole% of the sulfur compounds led by a Claus system are incinerated in a second combustion unit combustion device. and - the elemental sulfur is used in liquid or solid form. 2. A method according to claim 1, characterized in that the air factor during combustion runs up to about 0.4 - 0.9. Process according to Claim 1 or 2, characterized in that the desulphurisation 20 is integrated as part of the cellulose plant's odor removal system. Process according to claim 1, 2 or 3, characterized in that the sulfur is condensed from the flue gases after the combustion of the gases. 25 Process according to any of the preceding claims, characterized in that water from the boiler or cooling water circulation of the cellulose factory is used to condense the sulfur. Method according to any of the preceding claims, characterized in that a portion of the concentrated odor gases is directed to the first combustion unit, which comprises one or more Claus system combustion devices (10; 20; 21; 40; 41) and a part to the second combustion unit, which comprises combustion in a soda boiler (3; 53), odor gas boiler (4; 54), a blast furnace (5; 55) or a bed (6; 56) or in a plurality of these systems. Process according to any of the preceding claims, characterized in that at least 10 mole%, preferably 30-90 mole% of the collected odor gases are fed to one or more Claus system combustion devices (10; 20; 21; 40 ; 41) to be incinerated. Method according to any of the preceding claims, characterized in that the collected odor gases are combusted in the first combustion unit's Claus system combustion devices (10; 20; 21; 40; 41) and the remaining end gases are fed to the second combustion unit for combustion in the boiler (3; 53), the odor gas boiler (4; 54), the blast furnace (5; 55) or the flame (6; 56), or in several of these systems. Method according to any of the preceding claims, characterized in that the odor gas produced by the tila Claus process is burnt to elemental sulfur 50 - 90 15 mole%, typically 70 - 85 mole%. Process according to any of the preceding claims, characterized in that air, oxygen or a mixture thereof is used in the combustion of the odorous gases. 20 11. A process according to any of the preceding claims, characterized in that the elemental sulfur obtained from the Claus process is further incinerated to sulfur dioxide or processed to sulfuric acid. Method according to any of the preceding claims, characterized in that at least part of the elemental sulfur is measured back in the process, e.g. by adding sulfur in viilut or by feeding sulfur in the boiler. Method according to any of the preceding claims, characterized in that the odor gases are collected from a boiler or evaporator (1; 2) source of concentrated odor gases separately or in combination. Process according to any of the preceding claims, characterized in that the amount of concentrated odor gas is increased by any suitable method, such as heat treatment of black liquor. 15. The use of a Claus process for desulphurizing a sulfate cellulose plant's chemical circulation in such a way that concentrated odor gases are combusted in one or a plurality of Claus system combustion devices at lower air to the elemental sulfur and at least 5 mole% of the sulfur through a Claus system. may be incinerated into at least one incinerator's combustion device, such as a soda boiler (3; 53), odor gas boiler (4; 54), blast furnace (5; 55) or bed (6; 56), or to a plurality of these systems. An arrangement for removing sulfur from the chemical circulation of a sulfate cellulose plant, comprising: at least one odor gas combustion unit (10; 20; 21; 40; 41), where a flow of concentrated odor gas can be collected and conducted from a source (1,2). of concentrated odor gases and in which the reduced sulfur containing the concentrated odor gases can be combusted, characterized in that the combustion unit comprises a first combustion unit (10; 20; 21; 40; 41) having at least one Claus system combustion device (10; 20; 21; 40; 41), which is provided with an inlet (14; 26; 29; 46; 49) connected to the source (1,2) of concentrated odor gases (1, 2), and an outlet (15). ; 27; 32; 47; 57), through which the oxidized and condensed sulfur compounds of the concentrated odor gas can be removed from the device as liquid or solid elemental sulfur, and a second combustion unit, the first unit has an outlet (16; 30; 50) for gaseous, uncondensed sulfur compounds connected to the second combustion unit. 25 Arrangement according to claim 16, characterized in that the combustion unit comprises at least two Claus system combustion devices (20; 21; 40; 41) connected in series, the first combustion device having an outlet (28; 48) for gaseous, uncondensed sulfur compounds. connected to the inlet (29; 49) of the second combustion device. Arrangement according to claim 16 or 17, characterized in that the first combustion unit comprises a Claus system combustion device (10; 20; 21; 40; 41) and herein a capacitor (11; 22; 23; 42; 43). 19. Arrangement according to the patent claims 16-18, characterized in that the second combustion unit comprises an odor gas boiler (53), a boiler (54), a blast furnace (55) and / or a location (56). 5 Arrangement according to any of claims 16-19, characterized in that the inlet (14; 26; 46) of the first combustion unit is connected to a distribution piece (17; 31; 51) in such a way that some of the concentrated odor gases can be passed through the distribution piece past the first combustion unit to the second combustion unit. 10