FI68687B - FOERFARANDE VID LUTAOTERVINNING EFTER SODAHUSPANNAN VID SULFATPROCESSER - Google Patents

Description

ΓΤ75 £ ΞΓΤ1 ΓΒ, .... KU U LUTUSJ U LK ΑΙSU / η / ο π 6 11 UTLÄGGNIN GSSKRIFT 6 8 687 («) (51) Kv.lk. '/ Int.CI.4 D 21 C 11/0 * 4 FINLAND - FINLAND Patent application - Patentaniöknlng 79389 * 4 (22) Application date - Ansöknlngsdag 12.12.79 (23) Starting date - Giltlghetsdag 12 12 79 (41) Has become public - Blivlt offentllg ^ q £ gg

National Board of Patents and Registration / 44) Date of publication of the notice and publication. -, β

Patent-och registerstyrelsen '' Ansökan utlagd och utl.skriften publlcerad /0.1)0.op (32) (33) (31) Privilege requested — Begärd prloritet 12.12.78 28.02.79 Swedish-Swedish (SE) 78l27 * 40- * 4 7901820-6 Proven-Styrkt (71) (72) Runar Ingvald Lindroos, Granstigen 22, S-710 * 40 Frövi, Sweden-Sver ige (SE) (7 **) Berggren Oy Ab (5 **) Method for liquor in recovery after 1 boat in the soda boiler of the process - Förfarande vid lutltervinning efter sodahus-pannan vid su 1fatprocesser

The invention relates to a process developed in comparison with the prior art for the recovery of sulphate or lye after the boiler of the soda compartment of sulphate processes.

The lye melt obtained from the boiler of the soda compartment is discharged into the melt dissolution tank, where the melt is dissolved in a dilute caustic strength from the causticizing plant to a strength of about 22 ° Be. The resulting green liquor is further pumped to a causticizing plant for calcination. The dilute lye formed in the washing of the lime obtained in the causticization plant is passed to a dilute liquor clarifier, from which the dilute lye is pumped to the melt dissolution tank. The effluents are led to the atmosphere via a steam pipe in which a heat exchanger and a condensate separator are arranged in parallel. The flap allows the outlets to either flow directly into the atmosphere or through a heat exchanger and separator. The heat exchanger and the separator are intended to recover the heat from the exhaust gases, and the vapors and dust they contain are to be condensed or separated.

2 68687 This makes the outlet to the atmosphere as clean as possible. Said effluents from the melt dissolution tank consist of e.g. dust, SC ^ and I ^ Sr.

In practice, it has proved impossible to clean the exhaust gases from the melt dissolution tank in this way, because the heat exchanger unit and the condensate separator "grow out" quickly and become inoperable. Through the flap, the exhaust gases are therefore passed through the steam pipe as impurities directly into the atmosphere. This has a strong impact on the paper mill environment.

In a sub-step of the sulphate process in the pulp industry, the melt from the boiler of the soda compartment is dissolved in the dilute lye of the causticizing plant during the recovery of sulphate or lye. Dissolution takes place in melt dissolution tanks and the solution, the so-called green liquor, is pumped to the clarifier of the green liquor and further to the causticizing plant for further processing and conversion to white liquor. By clarifying, a suitable amount of quicklime is added to the purified green liquor in a lime extinguisher, whereby the green liquor turns into white liquor. The process is called causticization.

This type of method, to which the invention relates, has heretofore been considered to work satisfactorily. However, as energy costs rise and the demands on environmental cleanliness become higher, these known methods and associated facilities are no longer economically viable and do not meet the environmental requirements of society.

The temperature of the green liquor coming from the melt dissolution tank is about 90 ° C, and the temperature rises to about 10-15 ° C when lime is added in the lime extinguisher. The high temperature of the lime extinguisher has been detrimental because of the high steam generation, which in turn results in a high gas flow through the steam pipe and the lime tank and from the sorter and the subsequent causticizing vessel (large impure effluents) and high heat losses due to exhaust losses. there has been no possibility of heat recovery. Process temperatures have therefore hitherto been kept low.

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The process according to the present invention, as set out in the claims, has made it possible to keep the temperature of the causticizing plant high, at about 106-108 ° C, i.e. close to the boiling temperature, but nevertheless it has been possible to limit gas leakage. While the removed gas is also efficiently cleaned, the thermal energy it contains is recovered. When the temperature of the liquor is kept higher in the causticizing plant and the heat of the effluent vapors is recovered, a much better efficiency is obtained when applying the patented method than in the known method. When the vapors leaving the chimneys or steam pipes are effectively cooled, a vacuum develops in the respective treatment chambers (lime extinguisher with sorter, causticizing vessel and intermediate vessel), whereby the leakage of gas and steam in the plant is eliminated. The vacuum can be strengthened so that the cooling water jets can be directed in the outflow direction of the exhaust gases, whereby the flow of these gases is accelerated, resulting in an ever-increasing vacuum in the vessel.

By means of the invention, it is possible to purify the exhaust gases in the steam pipe from SO 2 and to recover the dust contained in the gases (sodium sulphate). By means of the invention, it is possible to continuously pass the exhaust gases through a heat exchanger and a separator, whereby the heat content of the gas can be efficiently utilized, which substantially improves the thermal efficiency of the plant. When the washing liquid (dilute lye) is returned from the scrubber to the suction side of the dilute liquor pump for feeding to the melt solution tank, the adjustment of the dilute liquor in the dilute liquor clarifier is not disturbed. As the washing liquid raises the temperature of the dilute lye fed to the melt leach tank by about 4 °, the temperature of the green liquor in the melt leach vessel is raised, which is advantageous for further processing, calcination, in the calcination plant.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a flow chart of lye recovery and soda boiler, Figure 2 shows schematically a side section of a scrubber according to the invention, Figure 3 shows a scrubber in cross-section along line 4 68687 III-III; gives an example of a causticizing plant.

The plant after the boiler of the soda compartment (not shown) comprises a melt dissolution tank 1 into which the sulphate melt coming from the boiler is discharged. The melt is dissolved by stirring with stirrers 2 into dilute lye, which is pumped by pump 3 from dilute liquor clarifier 4 via line 5 with a four-way valve 6 from which line 7 leaves. The green liquor obtained in the melt dissolution vessel 1 is pumped by a pump 8 through line 9 to a four-way valve 6 and from there through line 10 to a green liquor clarifier 11. From the green liquor clarifier 11, green liquor is pumped through a pump 12 and line 13 to a causticizing plant (not shown). By adjusting the four-way valve 6 and keeping the lines 7 and 8 clean, the flow of these lines can be changed so that dilute lye flows through line 9 to the melt dissolution tank 1, from where it is pumped via line 7 by pump 14.

From the melt dissolution vessel 1, a steam pipe 15 leaves for removing the effluents of said vessel 1. These removals, as mentioned, consist mainly of dust, SO 2 and H 2 S. In parallel with the steam pipe 15, a heat exchanger or steam condenser 16 and a condensate separator 17, which in principle consists of a cyclone, are connected in series. The fan 18 blows the exhaust gases back into the steam pipe 15. The heat exchanger is cooled by the water which flows in at 19 and has a temperature of e.g. about 45 ° C and out at 20, where the water temperature is about 75 ° C. The flap 21 is used to adjust the flow path of the outlets either through the instrument panel and the steam condenser or directly out into the atmosphere.

A washer 22 is arranged in the steam pipe between the melt dissolution tank 1 and the temperature device. The purpose of the scrubber, which will be described in more detail below, is to wash off and condense the effluents of the melt dissolution tank 1. As the washing liquid, dilute lye is used, which is discharged via line 23 from line 5. The pressure of the dilute lye is increased by means of a pump 24, and the lye is sprayed through a riser and branch lines through nozzles 25-30 arranged in a certain way in the scrubber.

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The liquid accumulating at the bottom of the scrubber, which consists of the scrubbed substances from the exhaust gases as well as the scrubbing liquor, is led through the line 31 to the suction side of the pump 3. Also connected to the line 31 are the drain lines from the heat exchanger 16, the condensate separator 17 and the fan 18. Since the return liquid is pumped from the line 31 directly through the pump 3 to the melt dissolution tank, dust (soot, etc.) in the liquid is pumped from the melt dissolution tank to the green liquor clarifier 11. slurry.

The scrubber 22 is shown in more detail in Figures 2 and 3. As can be seen, the scrubber consists of a cylindrical rod 32 with a base 33 and an inlet 34 of a steam pipe 15 concentrically fitted thereto. The inlet extends somewhat up above the base 33, as shown in the figure. The jacket 32 terminates at the top in a cone which turns into an outlet 35 of the extension of the steam pipe 15. Inside the scrubber, a downwardly open, conical cover 36 with a slightly larger diameter than the inlet is arranged above the inlet 34. A corresponding cover 37 is arranged below the outlet opening 35. The aforementioned nozzles 25-29 are arranged along the longitudinal axis of the scrubber at regular intervals and facing upwards. The nozzles spray the washing liquid (dilute lye) conically upwards, as shown in the drawing. The nozzle 30 is arranged in the inlet opening, also turned upwards, so that the jet moves in the flow direction of the exhaust gases and reaches the mouth of the inlet opening. Nozzles 25-30 are supported in the scrubber by inlet wires (shown in dashed lines in the drawing). Due to the kinetic energy and direction of the jets, flushing of the exhaust gases is achieved as well as accelerated traction in the steam crease. Cover 37 prevents liquid from entraining through the outlet, and cover 36 prevents liquid from penetrating down into the inlet. Due to the substances contained in the exhaust gases, deposits can accumulate in the parts of the scrubber, in particular on the cover 36. To prevent this, two tangentially oriented wires 38 terminate on the inside of the cover 36. The nozzles have two nozzles 39 directed obliquely upwards towards the same side of the cover. The two wires 40 may further be adapted to terminate tangentially to the inlet 34 for the same purpose. Warm water is supplied to these lines and nozzles. ____ 6 68687 under the relevant for rinsing parts if necessary.

Warm water is supplied to lines 38, 40 and nozzles 39 through a manifold 43 surrounding the scrubber. The lines are suitably provided with valves as shown in the drawing.

For intermittent flushing of the bottom of the scrubber, a line 41 (see Fig. 1) is provided, which is connected to the dilute liquor line 23. In order not to become obscure in Fig. 2, this line is not drawn therein, but may be suitably provided with one or more diagonally bases. 33 with nozzles directed towards.

Through the drain pipe 42 (Fig. 2), the washing liquid with the washed outlets is led back to the suction side of the pump 3 via the above-mentioned line 31.

Numeral 44 denotes a nozzle fitted in the outlet 35 and into which water is fed. The intention is that if the dilute lye supply is interrupted, the exhaust gases can be washed with water, which is a better option than not washing them at all. Of course, several suitably placed water nozzles can be used.

The downwardly sloping flange 45 is further attached to the inner surface of the jacket so that the jets from the upper nozzle 25 reach the upper surface of the flange and the jets from the nozzle 26 reach the lower surface of the flange. This flange leads water flowing along the inner surface of the jacket towards the center of the scrubber.

From the melt dissolution tank 1, which receives the liquor from the soda boiler, the green liquor is pumped to the green liquor clarifier 2, see Fig. 4. The green liquor clarified here is further pumped through line 19 and distributor 20 to to the lime extinguisher 3, where the lime is mixed with green liquor.

This may have a temperature of about 94 ° C as it enters the lime extinguisher, where the temperature rises to about 106-108 ° C when the lime is fed, partly due to the temperature of the lime and partly due to the reaction that takes place. The lime extinguisher is provided with a sorter 6, 7 68687 to which green liquor is also fed from the distributor 20 and into which the contents of the lime extinguisher drain. As usual, the sorter has a scraper that constantly transports away sand and so on.

The mixture of lye and lime is passed through a sorter 6 through two causticization vessels 7, 8, in which the causticization reaction takes place with vigorous stirring of the mixture. From the causticization vessel 8, the mixture flows into an intermediate vessel 9, from where it is further pumped to a white liquor clarifier, screen or filter, where the mesa is separated from the liquor. Clear lye and lime are further passed from the white liquor clarifier to further processing.

Such a system has a scrubber 12 and 13, respectively, placed in the steam pipe 10 leading to the lime extinguisher 3 and in the pipe 11 leading to the sorter 6. The nozzles 14 arranged in the scrubber and located along its central axis provide a plate-like jet pattern (marked with broken lines) which can be changed upwards by changing nozzles. from a directed cone shape to a flat or even downwardly directed cone shape. Cold water is supplied to the nozzles 14 via line 15. Above the scrubber and steam pipe there may also be one or more cold water nozzles 16. The scrubber 12 is further provided from below with a nozzle system for periodically rinsing the scrubber base with hot water from the hot water tank 33. Likewise, the nozzle 17 is fitted to the mouth of the steam pipe in the scrubber. This nozzle 17, like other nozzles, can be adjustable with respect to the spray pattern. However, either hot water or green liquor is continuously fed to the nozzle 17 from the green-liquor clarifier 2 via lines 19 and 21. This is to keep the washer precipitates in solution. With the aid of suitable valves, in the latter case it is also possible to periodically spray hot water through the nozzle 17 in order to clean it of the deposits formed by the lime sludge and the like.

The causticizing vessels 7, 8 and the steam pipes 22, 23, 24 leading to the intermediate vessel 9 are likewise fitted with scrubbers 25, 26 and 27, respectively, which are of the same type fitted to the steam pipe of the sorter 6. However, in the example shown, the intermediate dish washer 27 is provided with four nozzles.

The shower and coolant of these scrubbers is likewise the cold water coming from the line 15.

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The washing liquid accumulating at the bottom of the scrubber 12, which contains large amounts of lime sludge, is led via line 28 to a collecting vessel 29, where the sludge is separated and the liquid is led to a re-causticization vessel 30 from which the slurry is pumped to wash the sludge. The washing water from the scrubbers 13, 25, 26, which mainly consists of now heated cooling water, is led via a line 31 to a second collecting vessel 32, where the sludge quantities are separated and the water is led to a hot water tank or accumulator 33. hot water can be discharged into the nozzles of the scrubber 12 and the nozzle 17. The washing liquid from the scrubber 27 to the intermediate vessel 9, which is relatively "clean", is led directly through the line 34 to the tank 33. The water temperature here is n.

70 ° C, and water can be used for various purposes in the process.

In addition to the pumps marked with the letter P, the system also includes several valves in connection with the nozzles and nozzles. These valves are not separately marked, but are only shown in the drawing by conventional symbols. The letter O denotes mixers fitted to those vessels.

It will also be apparent from the invention described above that it has now become possible for the first time to recover the heat from the exhaust gases from the components belonging to the causticizing plant, in particular from the lime extinguisher. Exhaust gases or vapors from the extinguisher contain, as mentioned, e.g. large amounts of dust and lime. When the exhaust gases are cooled, a further vacuum is created in the steam pipe (s) and thus in the lime nozzle or similar vessel, whereby gas leakage through the lime tank and other openings and hatches as well as from the sorter is eliminated. When a vacuum is maintained in the lime extinguisher, it is also automatically possible to raise its temperature without increasing the gas leakage. The temperature of the green liquor and the lime added to it is therefore not very critical, and the working temperature can also be kept as close as possible to the boiling point. Said vacuum can be amplified by directing the cooling water sprayed from the scrubber nozzles in the direction of steam outflow, which accelerates the removal of exhaust gases.

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The number of washer nozzles is determined by the temperature of the available cooling water as well as, of course, other operating data of the plant. The collecting vessels 29 and 32 can also be considered to be replaced by a single vessel for separating the sludge, from which vessel the liquid is led to the hot water tank 33.

As mentioned at the outset, the present invention achieves significantly better and more efficient purification of the exhaust gases from the melt dissolution tank compared to the prior art, while improving the thermal efficiency of the plant. This is possible because the heat exchanger series and the steam condenser, which according to the invention only needs to condense water vapor and very small amounts of exhaust gas, can be used continuously without very much contamination, as well as because the dilute lye introduced into the melt dissolution tank the temperature can be kept higher by adding heated washing liquid from the scrubber.

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Claims (15)

1. A method for recovering lye after a boiler in a soda compartment and for causticizing in a continuous causticizing plant of a sulphate process, comprising e.g. a lime nut-nut fed with green liquor from a green liquor clarifier and likewise lime and for which a disposer is fitted, one or more causticizing vessels and an intermediate vessel, the liquor from the soda boiler and from which a steam pipe with connected heat exchanger systems leads therefrom, characterized in that the steam leaving the melt dissolution tank, consisting mainly of dust, SC 2 and i 2 St, is passed before the heat exchanger system through a scrubber where the steam is washed with dilute lye and sprayed the substances washed from the steam in the scrubber together with the dilute lye fed are collected in the scrubber and passed to the suction side of the pump to pump the dilute lye into the melt dissolution tank. A method according to claim 1, characterized in that the dilute lye from the dilute liquor clarifier is pumped with the same pump partly into the melt dissolution tank and partly into the scrubber, whereby the dilute lye is sprayed here by means of a pressure-increasing pump. Method according to Claim 1 or 2, characterized in that any substances condensed and accumulated in the heat exchanger system and in the condensate separator are collected and discharged together with the substances collected in the scrubber. Method according to one of the preceding claims, characterized in that the steam after the heat exchange system is passed through a condensate separator, which is suitably a cyclone. A method according to claim 1, characterized in that the steam leaving the lime extinguisher and the steam leaving the sorter are cooled and washed with a cold water jet, whereby the substance contained in the washing liquid is recovered. li 68687 A method according to claim 5, characterized in that the steam leaving the lime extinguisher is passed through a first scrubber and cooled and washed with cold water jets, and that the steam leaving the sorter is passed through a second scrubber and cooled and washed with cold water jets, whereby the washing liquid accumulates in the second scrubber. a hot water system from which hot water is supplied to the first scrubber for its intermittent washing. A method according to claim 6, characterized in that the washing liquid accumulating in the first scrubber is passed to a re-causticization vessel. Method according to one of Claims 5 to 7, characterized in that the steam from the causticizing vessel is passed through a third scrubber and cooled and washed therein with cold water jets, the washing liquid accumulating in the third scrubber being fed to the hot water system. Method according to one of Claims 5 to 8, characterized in that the steam from the intermediate vessel is passed through a fourth scrubber and cooled and washed therein by cold water jets, the washing liquid accumulating in the fourth scrubber being fed to the hot water system. Method according to one of Claims 5 to 9, characterized in that the cold water jets can be directed by a movement component in the direction of steam flow through the respective scrubber. 10 68687 Method according to one of Claims 5 to 10, characterized in that the cooling and washing cold-water jets are sprayed out in the form of a plate-like spray pattern along the steam flow path from nozzles arranged in the middle of the scrubbers. A method according to claim 6, characterized in that the jet pattern is conical with the tip directed against the direction of steam flow. 68687 Method according to one of Claims 5 to 12, characterized in that green liquor is sprayed from the green liquor clarifier in connection with its inlet to the first scrubber. Method according to one of Claims 5 to 13, characterized in that hot water is sprayed into the first scrubber in connection with its inlet. An apparatus for carrying out a process for recovering lye after a soda boiler in sulphate processes according to claim 1, wherein the liquor from the soda boiler is fed to a melt dissolution tank (1) pumped with a first pump (3) dilute liquor from a dilute liquor clarifier (4) and a second pump (8); green liquor to a green liquor clarifier (11) and from which a steam pipe (15) with connected heat exchanger systems (16) leads, characterized in that a gas scrubber (22) is arranged in the steam pipe (15) between the melt dissolution tank and the heat exchanger system for washing steam, consists essentially of dust, SC 2 and I 2, the scrubber consisting of a cylindrical jacket (32) provided at the bottom with an inlet (34) arranged concentric with the jacket for the steam pipe (15) and at the top with an inlet concentric outlet (35) for the steam pipe extension for the heat exchanger system to the scrubber (22) is arranged along the axis of the jacket with a row of spray nozzles (25-30, 44) each of which is directed to spray dilute lye in a plate-like spray pattern, and that the first cover (26) formed by a cone with the tip facing upwards is fitted between the spray nozzle rows and the inlet.