SE435075B - Process for the emptying of pulp from the boiler of a batchwise cellulose boiler - Google Patents

Abstract

A process for the emptying of pulp from the boiler of a batchwise cellulose boiler, in which the boiling fluid in the final stage of the boiling cycle is passed to a settling vessel under pressure, and the boiler is subsequently de- gassed in essentially the same way until it attains atmospheric pressure or negligibly higher. This process is especially noteworthy in that, during the said de-gassing, the washing liquid, preferably filtrate from filter washing, is transferred to the boiler for pre-washing of the pulp at a relatively low temperature, preferably such that the temperature in the mixture of wash liquid and pulp is 105 degrees Celsius or lower, whereupon a flow of steam is taken from the settling vessel to the boiler in order to blow out its pulp content at a temperature of 90 - 105 degrees Celsius, which amounts to so-called cold blowing. <IMAGE>

Description

79065140-5 is to provide a process of the kind mentioned in the introduction, which is characterized by good heat economy, and which allows blowing of the pulp at a relatively low temperature, preferably in the range 90 - 10500, which means so-called cold blowing, and whereby the mass can be pre-washed in the boiler.

According to the invention, a process of the initially mentioned kind is characterized in that during the said degassing washing liquid, preferably filtrate from filter wash, is added to the digester for pre-washing the pulp at a relatively low temperature, preferably such that the temperature in the mixture of washing liquid and pulp becomes 105 ° C or lower, whereupon an angelic flux is passed from the equalization tank to the digester to blow out its pulp content at a temperature of 90 - 105 ° C, which means so-called cold blowing.

From the equalization tank, the hot cooking liquid is led to one or more relaxation cyclones. These are under lower pressure than the equalization tank for cooking liquid. The steam generated in the cyclones can to some extent be used in the coker at the beginning of the next cooking cycle and in separate auxiliary processes. In this case, fresh steam is saved in comparison with a conventional system. The rest of the relaxed steam is led to surface condensers, ie. a heat recovery unit in which hot water is produced. Due to the fact that the flow is regulated via a well-known multi-stage condenser process, the odor gases released by the relaxed steam and the steam vapors can be led to the odor gas purification system.

After emptying the cooking liquid, the secondary heat of the liquid remaining in the chips is utilized by a degassing technique known per se. The pressure in the boiler is thereby lowered to slightly above atmospheric pressure. The generated steam flow is fed to a heat meter recovery unit together with or instead of a meadow flow, coming from a relaxation cyclone, to which liquid is fed from the equalization tank, which latter steam flow is regulated so that the combined steam flow is kept substantially constant. The free liquid in the boiler is sucked out through a strainer in the bottom of the boiler.

The boiler is then filled with the filter from the pulp laundry and blown empty with the help of steam relaxed from the equalization tank. This produces a prewashed FJV maSSafh 7906540 - 5 filtrate, ie. the washing liquid is suitably fed to the charcoal with a relatively low temperature, i.e. preferably such that the temperature of the mixture is washing liquid and pulp. becomes 105 ° 0 or lower. The boiling content can then be blown at a temperature of preferably 90 - 105%, which means cold blowing.

It is advantageous for washing liquid to be supplied to the boiler through an eyelet located in the bottom of the boiler in order to distribute washing liquid evenly in the boiler bottom.

It may also be appropriate to supply a regulated flow of laundry detergent. through a strainer located in the bottom of the cooker under the blow nozzle into the bottom cone of the cooker. in order to reduce the friction in the flow through this part of the coke reindeer and thereby facilitate the boiler drying.

In such cases. then, disturbances occur in a mssea factory, for example at a boiler, so that the steam combustion occasionally decreases, 'according to the invention there is a possibility in conducting external high-pressure steam, i.e. steam coming from the steam boiler. to the equalization tank to recover this steam instead of blowing it out in 11.11 'ten.

The new process has several advantages, regarding the factory's steam zone, the process, the maize quality. the washing power and the environmental value, which is shown in the table below.

Advantages regarding the factory 'steam consumption Theoretically, 100 9% of the boiler's are latent. heat available in the form of a controlled six-axis axial flow. Compared with a conventional heat recovery system, greater freedom of choice in the utilization of eekundär heat has been created throughout.

In addition, the secondary heat is utilized at a higher energy level. than before. tn ions in the primary flow to the coker can be reduced.

Process exhausts In general, it can be said that the best properties of the continuous and satevisa. kokprooeesen combined.

The secondary. the heat flow from the boiler can with greater certainty than before be connected to various auxiliary processes, since the flows are not affected by disturbances in the main process. 7906540-5 Improved maize quality Mefeaen meager: collection of congenital temperature (90 - 1o5 ° c). Namely, cold blue means that the risk of breakage of the fiber wall through violent expansion of liquid bound in the fiber is reduced compared with what is the case with conventional blowing. This improves the strength properties of the msssan.

The variation of the kappa number decreases because it is more economical than before to use a: high water to wood content when cooking.

If problems in operation arise in the further treatment of pulp (washing-ri, bleaching), this method opens up an opportunity to sound. a finished cook wait 1 boiler without causing reduction of kappa's. The descent of the boiler to near. atmospheric pressure as well as the supply of the filter from the laundromat lowers the temperature of the pulp, which leads to a lower reaction of the cooking proeese below a level which does not affect the kee-pa number.

Improved washing effect The free. the cooking liquid with a high concentration of cooking chemicals and components dissolved from the wood are removed from the cooker and replaced with a washing liquid with a lower concentration of the above-mentioned. substances. Dmblandxxing of washing liquid ooh mass. takes place partly in the boiler, partly in the blue line and the blow tank. In the bladder tank, there is also a diffusion of possible chemicals from concentrated cooking liquid absorbed in the fiber to the weaker washing liquid. This achieves a dilution and thereby a washing effect.

It is possible to raise the temperature. the washing liquid in the filter wash without any major risk of boiling in the suction leg is present: The temperature of the base liquid to the filters is lower than before.

Improved environmental odor Odor gases from the boiler can be led to treatment as a smooth, controlled flow. The method according to the invention will be described in more detail in the following with reference to the attached three figures, of which. Figure 1 shows the temperature / time diagram of a batch of sulphate pulp soak with conventional heat recovery; Figure 2 shows the corresponding for the method according to the invention; Figure 3 schematically shows a plant for carrying out the method according to the invention.

The conventional procedure consists of the following steps: 1 A - B chip filling 2 B - C basing 3 C - D cooking liquid filling 4 l) - E heating with low pressure steam 5 E - F turning with high pressure steam 6 F - G boiling 7 G - H top blowing 8 H - In bottom blowing A - A 500 minutes incl. 40 min. in the meantime.

Figure 2 shows how the new procedure can be carried out in a plant of the type shown in figure 5. The plant consists of a number of boilers, usually about 8 - 12, of which only one digester with the designation 1 is shown. Circulation heating is arranged by means of the heat exchanger 2, which is equipped with a circulation pump 3. External steam is supplied to the heat exchanger 2 through the line 4. The circulating carbon liquid is returned to the boiler 1 through a line 5 with a valve 6. The line 5 is via a line 7, provided with a valve B, in connection with a leveling tank 9, from which a line 10, provided with a valve 11, leads back to the boiler 1. From the boiler 1 a line 12, provided with a valve 15, leads , out of the boiler to the blue system, which is not shown.

The line 10 communicates with a line 14 for supplying new cooking liquid.

This line is provided with a valve 15. A line 16, provided with a valve 17, is connected to the circulation line through the heat exchanger 2 and to a strainer in the boiler bottom. The bottom of the equalization tank 9 is connected via a line 18 partly, via a line 19 in connection with a first relaxation cycle 20 and partly, via a line 21 in connection with a tensioning cyclone 22. The bottom of the expansion cyclone 20 is connected via a line 25 to the tensioning cycle 22. the inlet of the cyclone 20 is connected via a line 24 to a steam line 25, coming from the top of the boiler 1. The lines 24, 25 are also connected to the other boilers, which are not shown. The steam drain c 7906540-5 of the relaxation cyclone 22 communicates via a line 27 with a line 28, coming from the top of the boiler 1, and is provided with a valve 29. The line 28 leads to the heat recovery unit 30, from which odor gases depart due to reason 31 From the flushing drain of the cyclone, a line 32 leads to a black liquor system. from the top of the equalization tank 9 a line 34 with valve 26 leads to the top of the cooker.

The kettle top is connected to line 28 through a valve 35. Line 36, provided with a valve 37 is connected to line 16. Line 19 is provided with a valve 38. Line 23 is provided with a valve 39. Line 21 is provided with a valve m u ..

The system works as follows: In E11 chip filling basing cooking liquid filling - heating with low-pressure steam and steam from the relaxation cyclone heating with high-pressure saxing kolming emptying of cooking liquid. top blowing to the recovery system degassing to heat recovery unit supply of washing liquid pressure oil for blowing sv boil-a cold blow final degassing cc zzc-'wf-swmøwtfitdo 1 2 5 4 5 6 7 8 9 Hïli flfi tä fifi wï »I 10 J- 13 M- AA- 12 300 minutes incl. 35 min intermediate ..

A-B The chip filling is started by opening the boiler valve and the chip filler valve and starting the chip supply. Fresh or secondary waste from line 24 is fed to the chip packer. When the right chip level. in the boiler has been reached, the valves are closed.

BC During the basing, the chips in the digester are preheated by a supply of relief vapor from the release cyclone 20 through valve 33. At the same time, the air in the digester is expelled through a valve 37 in line 36. Preheating with steam from release cycle 20 is continued until the desired temperature or the desired pressure in the digester is reached, after which the valve 33 in the line between the digester and the cyclone is closed. A temperature control closes the evacuation valve 37 when the steam flow z2zlz 'control iniítpm fl ct in line 36.

C-D .TJ-E E-F 7906540-5 Boiling liquid is supplied through the bottom strainer into the cooker. To increase the rate of saturation, boiling hydrogen vapor can also be added through a center nail. Charging of black liquor to the cooking liquid can advantageously take place directly through a line 10 with flow control from the equalization tank for cooking liquid. measure means a saving of fresh produce.

When a sufficient amount of cooking hydrogen has been invested. line 14 and line 10, close the supply valves 11 and 15. the valve 17 is closed.

The circulating pump 5 for cooking liquid is started. The indirect heating of fresh liquid cooking liquid is started with a temperature control which senses the outlet temperature temperature of the cooking liquid from the chelator 2. valve 6 is open and valve 8 is closed.

At the same time, steam is added directly to the boiler. from line 24 through valve 33.

The supply is stopped automatically when the boiler pressure has risen to a pressure close to that in the relaxation cyclone.

The inert gas shaft, which accompanies the evens voltage shaft from line 24 to the digester, is vented out of the digester via the texent vent degassing line, while valve 55 is kept slightly open during heating.

The rest of the heating to boiling temperature takes place indirectly in the calorie atom with the help of fresh steam.

Boiling.

Pumping of the digester on free cooking liquid (part of the cooking liquid is bound in the liquid) is done during the current cooking time with the help of the circulating pump for cooking liquid. Valves: 6 in the carbon liquid non-circulation line are closed and the valve in the line from the heat exchanger 2 to the equalization tank for cooking liquid and the valve 17 on the suction side of pump 3 are opened. 'Pömningen is interrupted autemausxt when a level naikster at a suitable high 1 came; closes the valve 8 in the line to the equalization tank and stops the circulation pump.

The cake pressure is lowered by opening the valve 53 in the line 25 from the cooker to line 24. The steam valve 35 is controlled by a pressure control. which primarily closes the valve 58 in the liquid supply pipeline from 7906540-5 I I-J J-K K-L L-M M-N the equalization system to cyclone 20. This compensates for the load peak caused by the steam supply from the digester.

When the boiler pressure has been lowered to the level of the pressure in cyclone 20, the rod automatically closes the valve 35 in the line 25 from the boiler and cyclone 20 is fed again with liquid, from the equalization properties.

The remaining pressure drop in the boiler is effected by discharging with valve 29 to the heat recovery unit for hot water production. The load change of the emission from the boiler is measured with a flow meter in line 28. The variation in this vapor flow is compensated primarily by changing the hydrogen vapor flow to relaxation Bovision 22 with valve 40, from which thereby: some vapor is produced, so that the vapor flows in the wires. 27 and 28 become substantially constant. The meadow stream to the heat recovery unit for hot water production is measured with a flow meter.

If throttling of valve 40 is not sufficient, secondary throttle 29 is throttled to reach constant sum flow to unit 10. If for tideekäl so. required. the blowing can take place simultaneously through the valves 35 and 29. In this case the valve 53 is controlled by the pressure in line 24. the valve 29 is controlled by the desired sum flow in the lines 27 and 28. During the degassing, the boiler is supplied with washing liquid (the filter from the wash ) through valve 15. valve 17 is closed. The washing water is pumped in through the bottom nail and the flow is controlled by a level controller, placed at the appropriate level. Also the valves 55 and 29 in the line for degassing to the heat recovery unit atäng fl.

The boiler is pressurized by opening. valve 26 for the equalization tank for cooking liquid.

Boiled bladder from the boiler-one to the blow tank. When the whole boiler has been blown away, valves 13 and 26 in the bldsledxiing and line from the equalization tank are closed automatically. The boiler is degassed once more to the heat recovery unit with valve 29. At atmospheric pressure in the boiler, the boiler lid is opened and the boiler is ready for a m 'cooking cycle. 7906540 -5 Release cyclone 20 acts as an integral part of the cooking system. It enables the return of degassing vapors and compensates for the currently occurring degassing sensations and heating requirements in the boiler.

Outgoing energy flows from the basic system are measured by three flow meters, located in lines 28, 21 and 23. Data from the flow measurement are fed to a control system that primarily controls valve 40 and secondarily controls the degassing valves 29 and 35.

Claims (3)

vsóesao-s 10 Patentkrav 1. A process for boiling batches of cellulose in a digester for emptying pulp from a digester, wherein the cooking liquid in the final stage of the cooking cycle is led to an equalization cistern below and the digester thereon, degassed until there is substantially atmospheric pressure therein or slightly above it känne - drawn e. v that under the said. the degassing wash liquid, preferably filtered from filter wash, is fed to the digester for pre-washing the pulp at a relatively low temperature, preferably such that the temperature in the mixture of wash liquor and pulp becomes 105 ° C or lower, whereupon a vapor stream is passed from the equalizer to the digester for to blow from there its pulp content at a temperature of 90 - 10500, which means so-called cold blowing. 2. A method according to claim 1, characterized in that after the completion of the cooking cycle a free liquid of a kettle is sucked out through a strainer located in the bottom of the kettle. Method according to claim 1 or 2, characterized in that after the free liquid has been sucked out of a digester washing liquid, a smoker is supplied through a sieve located in the bottom of the digester in order to distribute the washing liquid evenly in the digester bottom.