DD141431A5 - METHOD FOR THE TREATMENT OF EXPRESSIONS OF CELLULOSE MANUFACTURE - Google Patents

Abstract

The invention relates to a process for treating waste liquors from cellulose production by pyrolysis. The aim of the invention is to improve the recovery of heat and chemicals. According to the invention, the pyrolysis is carried out in a two-stage process, after which the waste liquor has been evaporated to 40% dry matter, in such a way that in a first reaction vessel the waste liquor, which has an average particle size of 50 to 100 μm, is heated to 650 to 800 °C and the substantial portion of the sulfur is converted into hydrogen sulfide. The heat content of the product, consisting of gas, in particular hydrogen sulfide, and dust, is recovered by heat exchange, optionally with simultaneous steam generation. The cooled gas/dust mixture is separated. The dust, consisting in particular of coal dust and sodium carbonate, is treated in a second reaction vessel, the gasified coal is burned to recover heat and the separated sodium carbonate is used as caustic soda to recover pulping liquor for cellulose production after sulphur dioxide, obtained from the combustion of hydrogen sulphide, has been absorbed therein. e«e« ec«,« * iS] * ceee Fig.1 - 20 pages of the •»«4 ·*»» SIEV.“ c isq. ©

Description

Berlin, 28 · 5. 1979 AP D21 G / 210 396 54 706 la

Process for the treatment of waste liquors of cellulose production. .

Application of the invention

The present invention relates to a process for the treatment of waste liquors of cellulosis production, namely a process in the context of the pyrolysis of waste liquors, which have been evaporated to a content of dry matter suitable for pyrolysis.

Character istik of the known technical solutions

The pyrolysis process, when applied to sulphite liquors, is currently carried out in the manner that the evaporated waste liquor is injected through special nozzles into the reaction vessel. " To carry out the pyrolysis, a carrier oil, a necessary amount of air and possibly also steam are also supplied. The reaction products, which partly consist of a gas which u. a carbon monoxide, hydrogen sulphide and hydrogen, and partly of a dust containing carbon and chemicals for digestion, mainly sodium, essentially in the form of the carbonate, are sent to a heat exchanger or boiler for the recovery of the heat content; possibly by the generation of steam. The gas / dust mixture is then fed to a recycling stage, where the major part of the total solids content is. Itatrium recovery is macerated, with the sodium essentially as sodium carbonate

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and the carbon residue is removed from the process, and the caustic soda brine is fed to an absorber due to the maceration, to be used after the absorption of the sulfur dioxide to produce new cooking acid.

This process has become known under the name SCA-Biillerud process and is used to a great extent for the recovery of sulphite waste liquors. However, a thorough investigation of the process and the various parameters "has been made which are critical to the reaction process to explore the possibility of improving the recovery of chemicals and heat. The process and the equipment used in the process, in particular the reaction vessel, are very sensitive to changes. If the temperatures are too high, deposits of solids on the walls of the reaction vessel occur. "In this respect, the content of chlorides in the waste liquor is of great importance.

A factor of great importance is also the particle size during the pyrolysis in the reaction vessel. From the pure technical point of view of pyrolysis, it is desirable to get as fine a dust as possible, but such a desire brings with it great problems of dust separation »The optimum average particle size is between 50 / U and 100> u. This particle size is achieved by atomizing the waste liquor, either by steam atomization at low pressure or by pressure atomization at high pressure, but with a certain addition of a protective steam with respect to the discharge nozzles

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can be made use of the ultrasonic atomization.

A disadvantage of the currently used method is the relatively large amounts of wet carbon _T having a dry matter content of etv / a 20 %. Regardless of whether the carbon is burned externally or recycled to evaporation, the water must be gasified in the carbon requiring a large amount of energy. The external combustion of the carbon also implies the loss of the chemicals (both of the sodium hydroxide) · Also of sulfur),

The aim of the invent clothes

¹ . ι

The aim of the invention is to provide a simple and economical process by which an improvement in the recovery of heat and chemicals can be achieved in the processing of waste liquors from the cellulose production,

Explanation of the essence of the invention

The invention has for its object to find suitable process steps so that the processing of waste liquors from the cellulose production can be carried out under conditions which substantially improves the recovery of heat and chemicals.

According to the invention, the process is carried out in two stages at specific reaction vessel temperatures and corresponding particle sizes mid in such a way that during the first stage the essential part of the suspension

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Felgehaltes the waste liquor is converted into hydrogen sulfide. The first stage dry dust containing essentially carbon and sodium compounds may then be subjected to carbon gasification in a second stage to give a relatively pure sodium carbonate. It is essential that gas and dust from the first stage be cooled before the separation of the dust and the dust is supplied to the carburetor under controlled conditions.

In particular, the process of improving the recovery of heat and chemicals in the pyrolysis of cellulose production leaching is carried out by carrying out the pyrolysis in a two-stage process with a waste liquor evaporating to a dry matter content of at least 40 % in such a way that pyrolysis is carried out in the first stage under supply of a carrier oil at a temperature of 650 ⁰ C to 800 ⁰ C in a first pyrolysis reaction vessel that the waste liquor is atomized in its supply to the reaction vessel to an average particle size of 50 - 100 / u, that during the first stage the substantial part of the sulfur content in the spent liquor is converted to hydrogen sulphide, that the heat content in the resulting product, consisting of a mixture of gas and finely divided dust, is recovered by heat exchange in a boiler, possibly under simultaneous Steam generation that d The gas / dust mixture is cooled before it is separated in gas, including the hydrogen sulfide, and dust, that the dust consists essentially of carbon and sodium carbonate and fed via feeders (preferably 'Y / ash feeders) to a second reaction vessel is, preferably a cyclone carburetor for gasification of Kohlen ™

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by air and possibly also with steam in certain amounts in such a manner that the temperature in the reaction vessel or the carburetor both below and above the melting point of the sodium. Carbonates can be adjusted by a suitable process engineering development, but that the carbon gasification preferably takes place under the conditions of a reducing atmosphere.

It is particularly advantageous that "the hydrogen sulfide formed in the first reaction vessel after the dust separation and cleaning burned in a scrubber and absorbed the resulting sulfur dioxide in sodium hydroxide in a sulfur dioxide and used for the production of cooking liquor." that the hydrogen sulfide formed in the first reaction vessel is absorbed in sodium hydroxide solution in a hydrogen sulfide absorber following the dust separation to obtain the so-called green liquor, which is caustified in a manner known per se for the production of cooking liquor.

It is an essential feature of the invention that the second reaction vessel can operate both below and above the melting point of sodium carbonate and that the gas obtained is fed to a separate boiler / dust collector for heat recovery and dust separation, the gas being subsequently separated by a separate wet and condenser scrubber for the purpose of additional dust separation and the gas is subsequently fed to a gas boiler for combustion and heat recovery together with the gas from the first reaction vessel ·

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Furthermore, it is also possible to proceed in such a way that the second reaction vessel operates above the melting point of the sodium carbonate and the gas obtained following the separation of the molten sodium carbonate is mixed with the gas from the reaction vessel and the two gases are sent to a common boiler for recovering the heat and then via a common dust separation in the sulphate liquors are fed to a common HpS absorber, a common condenser scrubber, a common gas boiler and in the case of the sulphite waste liquors a common SO 2 absorber »

The separated sodium carbonate can be used according to the invention for the preparation of the cooking liquor for digesting the wood feedstock.

Execution s p ice e1

The invention will be explained in more detail using an exemplary embodiment. In the attached drawing show:

Pig. 1: a schematic representation of erfindungsge-. The process for the treatment of waste liquors, the cellulose production by the sulphite process; , '' ·

FIG. 2: a schematic representation of the process according to the invention for the treatment of waste liquors of cellulose production by the sulphate process:

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Pig. 3ί is a schematic representation of another embodiment of the method of the invention according to Pig. 1;

Pig. 4: a schematic representation of another embodiment of the method according to the invention, according to Pig. Second

After Pig · T, the waste liquor 2 is discharged from the wood pulp according to the sulphite process after evaporation to a content of dry matter of at least 40 % to a reaction vessel 1. Injection takes place with the aid of nozzles attached to the reaction vessel 1 at the upper part thereof. In the lid of the reaction vessel 1, a burner is provided (not shown), are fed through the air, steam and carrier oil 3 in such amounts, which are set exactly to the amount and properties of the particular waste liquor 2 to be pyrolyzed.

According to the invention, it is possible to allow maximum sulfur separation in the first reaction vessel 1. This implies that the pyrolysis is to be carried out in such a way that the substantial part of the sulfur content in the waste liquor 2 is converted to hydrogen sulphide in the gaseous phase. In the course of the pyrolysis, a gas is thus formed which contains carbon monoxide, carbon dioxide, hydrogen sulphide, hydrogen, nitrogen and small amounts of hydrocarbons The organic substance in the waste liquor 2 forms a carbon dust during the pyrolysis, which together with the digestion chemicals and the other inorganic material forms the solid pyrolysis products.

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The gas / dust mixture 4 from the reaction vessel 1 is fed in a manner known per se to a boiler 5 for the recovery of the heat content in the form of vapor 6 and subsequently to a cyclone 7 for the separation of dust. 'that gas and dust are cooled before the actual dust separation. From the cyclone 7, a gas 8 is obtained, which contains hydrogen sulfide. This gas 8 still contains a certain amount of dust and is therefore a Faßabscheider 9 and then fed via a pipe 10 a condenser scrubber 11, from where the gas 8 is supplied via the pipe 12 to a gas boiler 13 for combustion, possibly together with the carrier oil 3 » which is fed to the boiler 13 via the pipe 14. The exhaust gas 15 from the boiler 13 ", which contains sulfur dioxide, is supplied to a sulfur dioxide absorber 16, from which the purified exhaust gas 17 can be discharged into the environment, and the sulfur dioxide solution 18 formed can be used for the production of a new cooking liquor. "

According to the present invention, it is important that the dust 19 from the cyclone 7, which consists essentially of carbon and sodium carbonate, be fed via feeders to a second reaction vessel 20 for carbon gasification and sodium carbonate separation. Air and possibly a certain amount of steam are fed to the gasification. It may be necessary to also feed carrier oil 21 to this reaction vessel 20, which is basically intended to serve as a cyclone carburetor. The gas 22 from the reaction vessel 20 is fed to a boiler 23 and possibly a dry separator for vapor formation 24 and possibly for dust separation. This dust 25 as well

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also the dust 26 from the reaction vessel 20 consist essentially of sodium bicarbonate and v / earth together collected at 27 and fed via a filter 28 for the carbon to the aforementioned sulfur dioxide absorber 16 in the form of soda cooking liquor 29. The remaining carbon 30 from the carbon filter 28 can be returned to the evaporated waste liquor 2 and together with it the reaction vessel 1. The gas 31 from the boiler 23 v / ird fed via a condenser scrubber 32 to the gas boiler 13. The carbon carburetor in this case can operate both below and above the melting point of the sodium carbonate.

The process also includes heat exchangers and other technical equipment, but these are immaterial to the present invention and therefore Mer are not specified.

Pig * 2 is another embodiment of the process according to the invention for pyrolysis of waste liquors of cellulose production according to the sulphate process.

In the same manner as in the above embodiment of treatment of waste liquors by the sulfite process, the evaporated waste liquor 2 is fed to a first reaction vessel 1 together with the carrier oil 3. The resulting gas / dust mixture 4 v / ird is fed to a boiler 5 for heat recovery and then a dry separator 7, from where the gas 8 is fed with small amounts of residual dust to a Haßabscheider 9. In a manner analogous to the liquor extraction process, the carbon dust 19 (which also contains sodium carbonate) is gasified in a wide reaction vessel 20 and the resulting gas 22 is gasified to a vessel 23 and possibly a subsequent dry run.

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supplied to separators. With the sodium carbonate 25; 26 from the second reaction vessel 20 and the kettle 23 is obtained Uatronkochlauge, which is freed by means of a so-called police filter 33 of possibly existing residual carbon.

According to the one in Pig. 2 reproduced for the pyrolysis of sulfate liquors process, the gas 10 from the Uaßabscheider 9 with a content of hydrogen sulfide a hydrogen sulfide absorber 34 and the purified gas 35 via a scrubber 36 a gas boiler 13 fed. The. Soda cooking liquor 37 from the police filter 33 may be used to absorb the hydrogen sulfide in the absorber 34. The solution 38 obtained in the absorber is used for the production of green liquor, which is used after the usual caustification (not shown) for digestion according to the sulphate process.

The steam generated in the gas boiler 13 in Figure 2 is designated 39. In addition, the possibility of purifying the exhaust gas 40 from the gas boiler by means of a scrubber 41 has also been reproduced. The purified gas 42 from the condenser 32 is supplied to the gas boiler 13 for combustion.

In Pig. 3, another process for the recovery of sulfite blues is presented. This method differs from that described above with reference to Pig. 1 described method as follows:

The gas 22 from the reaction vessel 20 is returned to the boiler 5 after the separation of the sodium carbonate 2b for heat recovery.

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The deposition of the sodium carbonate 26 is carried out in the most appropriate manner by the reaction vessel 20 is operated at a temperature of 850 - 1000 ⁰ C, so that the sodium carbonate melts and can be discharged in the liquid state * The condensate of the Naßabscheider 9 and 11 can then serve to dissolve the sodium carbonate 26, after which the purified soda cooking liquor 29 can be used to prepare new cooking liquor 18 analogously to the earlier scheme *

In Pig. 4 we are dealing with a process analogous to that in Fig. 3, but in this case the application is for the purpose of recovering the sulphate liquors.

The methods according to Figures 3 and 4 thus differ from the above-mentioned methods (corresponding to Figure 1 and Figure 2) in that no separate kettle 25 and no separate dust separation are required, nor do they require a separate wet and condensate washer 32 can be significantly reduced.

In all cases, it is in some sense more advantageous to operate the carbon gasifier under reducing conditions for the following reasons. The plant costs are lower. In addition, the carbon contains sulfur, which is completely converted into inactive chemicals under oxidizing conditions. By operating in a reducing atmosphere, part of the sulfur in the carbon can be degassed as H ₂ S, which can then be recovered in the form of active chemicals. Despite the reducing conditions in the carbon gasifier, much of the sulfur in the carbon becomes

;

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be converted into inactive chemicals and the effect is therefore low. It is therefore important that the sulfur deposition in the reaction vessel 1 be maximized, so that the sulfur content in the carbon is as low as possible.

The present invention is not limited to the described embodiments but can be varied within the scope of the inventive concept. The present invention thus encompasses processes for recovering chemicals in waste liquors from the production of so-called modified mechanical pulps, for example the production of modified thermomechanical pulp. Since the content of dry matter in such waste liquors is relatively high, a larger amount of carrier oil must be supplied as part of the pyrolysis. In addition, the reaction vessel temperature can be increased to improve the sulfate reduction.

Claims (6)

- 13 - 28. 5. 1979 54 706 18 Invention claim 1". Process for improving the recovery of heat and chemicals during the pyrolysis of cellulose production leaching by carrying out the pyrolysis in a two-stage process with a waste liquor evaporating to a dry matter content of at least 40%, characterized in that the pyrolysis in the first stage is below Feed of a carrier oil (3) at a temperature of 650 ⁰ C to 800 ⁰ C in a first pyrolysis reaction vessel (1) is carried out that the Abauge (2) in its supply to the reaction vessel (1) to an average particle size of 50 - 100 / U is atomized, that during the first stage, the substantial part of the Schwefelgshaltes in the waste liquor (2) is converted into hydrogen sulfide, that the heat content "in the resulting product, consisting of a mixture (4) of gas and finely divided Dust recovered by Y / heat exchange in a boiler (5), possibly under simultaneous steam generation (6) in that the gas / dust mixture (4) is cooled before it is separated into gas (8), containing the hydrogen sulphide and dust (19); that the dust (19) consists essentially of carbon and sodium carbonate and is fed via feeders (preferably wash feeders) to a second reaction vessel (20), preferably a cyclone gasifier for gasification of the carbon by air and possibly with steaming in certain amounts in such a way that the temperature in the reaction vessel (20) or the gasifier both below and above the melting point of the sodium carbonate by a suitable procedural - 14 - 28. 5. 1979 .54 706 18 Development can be adjusted, but that the carbon gasification preferably takes place under the conditions of a reducing atmosphere 2. The method according to item 1, characterized in that the hydrogen sulfide formed in the first reaction vessel (1) after the dust separation (7; 9) and the cleaning in a scrubber (11) burned and the resulting sulfur dioxide in Hatronkochlauge in a Sulfur dioxide absorber (16) is absorbed and used for the preparation of the cooking liquor · Method according to item 1, characterized in that the hydrogen sulphide formed in the first reaction vessel (1) is absorbed in hatron cooking liquor in a hydrogen sulphide absorber (34) following the dust separation (7; 9) to obtain the so-called green liquor which is in one is caustified in a manner known per se for the production of cooking liquor, Method according to points 1 - 3 »characterized in that the second reaction vessel (20) can operate both below and above the melting point of sodium carbonate and that the obtained gas (22) is a separate boiler / dust collector (23) for heat recovery and for dust separation, the gas (31) is subsequently passed through a separate hiss and condenser scrubber (32) for the purpose of additional dust separation and the gas is subsequently sent to a gas boiler (13) for combustion and heat recovery together with the Gas from the first - 15 - 28. 5. 1979 54 706 18 Reaction vessel (1) is supplied · Process according to points 1-3, characterized in that the second reaction vessel (20) operates above the melting point of the sodium carbonate and the gas (22) recovered following the separation of the molten sodium carbonate (26) with the gas (4) from the reaction vessel (1) is mixed and the two gases a common boiler (5) for 'heat recovery and then via a common dust separation (7i 9) in the sulfate liquors a common HpS absorber (34) »a common condenser scrubber (11; 36), a common gas boiler (13) and in the Suifitablaugen a common SO ^ -Absorber (16) are fed. 6. The method according to the items 1-5, characterized in that the separated sodium carbonate (25; 26) is used to prepare the cooking liquor for digesting the wood feed. For this 4 pages drawings