FI63268C - Procedures for emptying a batch cellulose cooker. - Google Patents

Description

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Patent · och raflstarttyralMn '' AiwMun utlafd «h utl ^ rtan publlnrad 31.01.83 (32) (33) (31) company name -Sverige (SE) (72) Rauno Juhani Salmi, Vantaa, Finland-Finland (FI) (74) Berggren Oy Ab (54) Procedure for emptying a pulp batch digester - Förfaringssätt for end of the cellulose batch

The invention relates to a procedure for emptying a pulp batch digester using a heat recovery method in which free broth is transferred from the digester to a separate accumulator corresponding to the cooking pressure during the cooking cycle.

Secondary heat recovery methods are already known, which are based on the so-called for the recovery of bulb heat from the effluent vapor from the buffer tank or from the material streams taken directly from the digester. The disadvantage of these methods is the periodicity of the material and heat streams fed to the recovery equipment, which makes it difficult to control the process and that the secondary heat is only available as hot water, which is often generated in excess of the process needs. In addition, the known methods have to equalize the amounts of odorous gas periodically released before continuous treatment with an intermediate storage tank or by introducing leaking air into the system when no odorous gas is released from the process.

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The main features of the invention appear from the appended claim.

At the end of the cooking process, the broth in the digester, to which most of the heat used for cooking and the odors generated in the cooking reactions are bound, is thus transferred under pressure to a separate broth surge tank. The broth used from this tank is directed as a controlled process stream to lower pressure expansion cyclones, which may be one or more. The expansion steam released in the expansion cyclones can be used in the early stages of the cooking process instead of fresh steam, and the excess leads to surface condensers where hot water is produced by its heat. Depending on the expansion-vapor stream, the released odorous gases and methanol vapor can be fed directly to the odorous gas treatment through a known multi-stage surface condensing process due to the flow controllability. After emptying the broth, the secondary heat contained in the broth remaining in the chips in the digester is recovered by a known degassing technique and fed back to the main process or to the heat recoverers. The kettle is filled with washing liquid and the kettle is emptied using the pressure energy of the broth surge tank.

The method according to the invention saves fresh steam in so far as the expansion steam is used instead and the secondary heat flows of the pulp batch soup and the released odorous gas streams can be equalized compared to the prior art. In addition, one washing step must be performed in the digester and the digester is emptied in the so-called a cold buffer, which is known to have a healing effect on the strength properties of the pulp.

The accompanying drawing illustrates a schematic diagram of a pulp digester and a secondary heat recovery apparatus implemented in accordance with the invention. When the cooking is complete, the functions are as follows: 1. Close the cooking circulation valve 3 and open the valve 4 of the pipe leading to the broth surge tank 2.

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3 63268 2. Drain the kettle 1 with a cooking circulation pump of 5 broths. The pressures and temperatures at this stage are approximately the same in both pressure vessels.

3. When the digester has emptied of free broth, close valve 4 and stop the cooking pump 5.

4. Deaerate the digester to the expansion steam recovery line by opening valve 6 and the rest of the gasification through valve 7 to the heat exchangers. At the same time, the broth is fed into the kettle by opening the valve 8.

5. When the kettle is approximately depressurized and almost full of washing broth, close valves 7 and 8.

6. Raise the pressure of the digester to the buffer pressure by opening the valve 9 and empty the digester by opening the buffer valve 10.

7. When the digester is empty, close valves 9 and 10 and degas the digester by opening valve 7. The digester is filled with chips and chemicals using known techniques and a new digestion is started with direct expansion steam from expansion cyclone 12 by opening valve 18.

8. The high-pressure cooking broth which is periodically fed to the broth surge tank 2 is directed in a continuous flow, controlled by a valve 11, to an expansion cyclone 12, where the expansion steam generated is used instead of fresh steam at different stages of cooking. The height of the broth surface of the expansion tank varies according to the cooking rhythm of the digesters.

9. Controlled by valve 13, the partially expanded broth is directed to a second expansion cyclone 14 where the pressure is reduced to normal. The broth is passed through the valve 15 past the first expansion stage so that the steam flow to the surface condensing process 16 is as even as possible.

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