FI59628C - FOERFARANDE FOER FOERBAETTRING AV AVERMEEKONOMIN AV TILLVERKNINGSPROCESSEN FOER TRAESLIPMASSA - Google Patents

Description

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C (45) Patent cyonn ·: t ty 10 09 1931 Patent meddelat V "" * (51) Kv.ik? / I »* t.ci.3 D 21 B 1/18 FINLAND —FINLAND (M) N ** hereB »» k * my «-P * t« iewetalnt 8017 (22) Hakwnltpilvl — An * eknlnt »d» | 03.θ6.θθ (23) AlkupUvt — GIM «h« cadag 03.06.80 (41) Tulhit lulklMktl - BllvK off «mJI |

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_ '(44) Date of issue of the declaration. - odl rafistarstyraiMII '' AiwMcm utlafd och utUkrifUn puMicerad 29.05.81 (32) (33) (31) ^ nrditty etuelkw · —Seglrd priority (Tl) Oy Tampella Ab, PO Box 256, 33101 Tampere 10, Suomi-Finland (FI) ( 72) Matti Aario, Pirkkala, Suomi-Finland (FI) (7M Oy Kolster Ab (5 * 0 A method for improving the thermal economy of a wood chips manufacturing process) - A method for improving the thermal economy of a wood chips manufacturing process the wood is ground with a rotary sander in a pressurized sanding chamber, hot spray water is sprayed into the sanding chamber, the ground pulp is precipitated to remove water from the pulp and the precipitated pulp is stored and / or bleached after cooling.

A method of grinding at normal atmospheric pressure using sawn and peeled wood logs to a certain extent is already known. The logs are conveyed in portions on top of the sanding pocket, from where they are dropped into the sanding pocket after the previous dose has been sanded.

The defibering itself takes place by pressing the wood portion with a hydraulic piston against the grinding stone. In this case, thanks to the friction between the wood and the grindstone, the wood heats up and the lignin that binds the fibers together softens and the 59628 fibers come off. The water sprayed on the surface of the grindstone helps the defibering process and transfers the frictional energy generated by the rotational movement of the grindstone and the trees to be sanded away from the grinding zone. In addition, the shower water removes the resulting fibers into the pulp basin under the grindstone. The study has found that the temperature of the shower water influences the defibering event in such a way that when high shower water temperatures are used, the fibers become looser and longer. Due to the long fibers, the strengths of paper made from these fibers are better than if low spray water temperatures had been used in grinding and the fiber thus produced had been made into paper. Experiments have shown that in normal grinding, the effect of warm shower water is relatively weak.

Pressure grinding is also known in advance (FI patent applications 782414, 780514 and 780515, SE patent application 7411949-6, SE patents 318178 and 336952), in which grinding takes place in a grinding space under pressure at more than one atmosphere.

The wood is fed into the overpressure sanding space, for example, by means of pressure equalization chambers built on top of the sanding pockets of the sanding machine. The grinding space delimited by the shutters and the mass basin is preferably pressurized by means of air or pressurized steam.

The defibering of the wood now takes place in the same way as in normal sanding by pressing the wooden dust against the sanding stone with the help of a hydraulic piston. The vibration and frictional heat generated by the grinding stone together with the shower water detach the fibers from the wood material.

The temperature of the jet water has been found to be more important for fiberization in overpressure grinding than in non-pressure grinding. The warmer the shower water, the longer and more complete the fibers that come off the wood and the stronger the paper made from these fibers. It is therefore advantageous for pressurized grinding the warmer the jet water is returned to the grinder.

After defibering, the pulp pulp is discharged from the grinding chamber by means of a tube in which, before adjusting the amount of pulp flow, the sticks and larger pieces of wood in the pulp pulp are comminuted with a stick crusher. The temperature of the pulp discharged from the grinding chamber is normally above 100 ° C. Depending on the temperature of the spray water and the overpressure in the grinding chamber, the temperature of the mass may rise up to 145 ° C under practical conditions. In this case, the inlet temperature of the spray water to the grinding chamber must be 130-135 ° C and the overpressure of the grinding chamber 3 bar. The thermal energy bound to the pulp stock is released in the form of steam in a cyclone where the pressure is reduced to atmospheric pressure. From the cyclone, the pulp can be fed directly to a precipitator, where the hot shower water is separated from the pulp to be returned to the grinding chamber. From the cyclone, the pulp can also be discharged to an intermediate tank, from where it can be led to various sortings: pressure sorting and vortex cleaning before being fed to a precipitator where the hot shower water is separated from the pulp. Likewise, the rejects of the sortings can be handled in the normal way: precipitated, ground and sorted before being fed to a shower water separation precipitator. The pulp is removed from the separation precipitator at a consistency of 10-33%.

The disadvantage of this known system is that 2-10% of the hot shower water leaves the system with the leaving mass. This amount must be replaced by other water, often at a much lower temperature, generally 50-60 ° C. This low temperature jet water lowers the temperature of the jet water introduced into the grinding chamber to a temperature of 2-5 ° C.

In addition, type D often has to be made large in size, so that there are plenty of cooling surfaces and thus heat loss is high. The temperature of the pulp leaving the precipitator is also harmfully high, 90-100 ° C, at which temperature the pulp tends to darken during storage and at which temperature the pulp is poorly bleachable, e.g. with peroxide bleaching.

The object of the present invention is to provide a method which eliminates the above-mentioned drawbacks and improves the thermal economy of the process of manufacturing wood chips based on pressure grinding, while at the same time making the ground pulp leaving the precipitator more suitable for storage and bleaching. This object is achieved by the method according to the invention, which is characterized in that water having a lower temperature than the temperature of the pulp is sprayed on the pulp to be precipitated and that at least part of this water is used as replacement water for the grinding space jet.

I · 4,59628

The invention is based on the idea that a heat exchange is provided between the ground pulp to be precipitated and the cold replacement water added to the spray water, so that heat can be transferred from the plum mass to the replacement water. Thus, the cold replacement water of the jet water heats up and the temperature of the jet water of the pressure grinding process remains high and at the same time the mass leaving the precipitator cools down.

In the simplest embodiment of the method, only as much water as is necessary to obtain warm replacement water can be sprayed onto the precipitated pulp, but it is preferred that enough water is sprayed on the precipitated pulp to cool the pulp to a temperature suitable for storage and / or bleaching. In this way, the ground pulp is cooled sufficiently with the same water spray for the post-treatment of the pulp.

An embodiment of the method is characterized in that the water is sprayed in two parts, the first part of which substantially corresponds to the amount of replacement water required for the jet water of the grinding chamber, and the second part corresponds to the amount of water required to cool the chippings to said temperature. In this way, the amount of replacement water required in each case for the jet water of the pressure grinding process and the amount of water required in each case for cooling the slag mass can be adjusted independently of one another.

The invention will be explained in more detail below with reference to the accompanying drawing, which schematically shows a pressure grinding process operating according to the invention.

The drawing shows a grinding machine 1 with a rotating grinding stone 2 mounted in a pressurized grinding space 3. The grinding space is associated with two grinding pockets 4, above which are arranged equal pressure chambers 5 closed by shutters. . A number of shut-off tubes 7 are arranged in the grinding space for conducting warm spray water to the surface of the grinding stone. To collect the slag mass, a mass pool 8 is arranged in the grinding space.

From the pulp pulp tank, a pipe 9 for the pulp A leads through a stick crusher 10 to a cyclone 11 provided with a steam outlet pipe 12. From the cyclone a pipe 13 leads to a depressurized pulp B 5 59628 for doped pulp C. The precipitator is provided with an outlet 19 for the precipitated ground pulp D.

The precipitator is provided with two spray pipes 20 and 21 for spraying cold water E onto the pulp web to be mixed. The precipitator has a basin 22 for both the water F leaving the ground pulp C to be precipitated and for the water E1 sprayed from the first nozzle and a second basin 23 for the water E2 sprayed from the second nozzle. From the basin 22 a pipe 24 leads to the intermediate tank 25 and from the basin 23 a pipe 26 to the cooling water tank 27. From the intermediate tank 25 a pipe 28 leads through the pump 29 to the jet pipes 7 in the grinding space for conducting hot jet water G to said jet pipes.

When preparing wood chips, the shower water is continuously circulated through a circulation system formed by pipes 9-13-24-28. Some of the spray water leaves with the precipitated ground pulp and due to other water losses in the process, escaping steam, etc., more replacement water has to be added to the circulation system than what is left from the precipitator alone with the pulp. In this case, the water E1 sprayed from the spray pipe 20 onto the ground pulp web to be doped is used as replacement water. This water heats up while cooling the pulp. In this way, the replacement water is heated by the heat of the pulp, which improves the thermal economy of the manufacturing process. The additional cooling of the ground pulp to be mixed to a temperature low enough for storage or bleaching is carried out by means of cooling water E2 discharged from the spray pipe 21.

The temperature of the ground pulp C to be precipitated on entering the precipitator is 99-100 ° C and the temperature of the precipitated mass D on leaving the precipitator is at most about 70 ° C. The temperature of the water introduced into the spray pipes 20, 21 is at most 60 ° C.

For example, if the ground pulp enters the precipitator at 99 ° C and leaves the precipitator at a consistency of 15%, the need for replacement water is 6.7% of the total shower water. If the temperature of this replacement water is 50 ° C, the total temperature of the shower water will be 0.067 * 50 ° C + 0.933 · 99 ° C = 95.7 ° C.

6,59628

If the method according to the invention is used and 50 ° C replacement water is sprayed in equal portions onto the precipitator mass path, if there are one nozzle tube, the temperature of the leaving mass and the temperature of the replacement water are: 99 ° C + 50 ° C _ co „- = 74.5 C .

2

If there are two shower pipes, the average temperature of the replacement water is:

· 50 + 0 5. 5Q

(99 + 0.5 ♦ 50 + 1.5_): 2 = 77.2 ° C 1.5 1.5 and the outlet mass temperature 71.7 ° C.

Thus, when using the method according to the invention, the total temperature of the circulating water is 0.067 · 77.2 ° C + 0.933 · 99 ° C * 97.5 ° C and the temperature of the leaving mass is 71.7 ° C.

The drawing and the related explanation are only intended to illustrate the idea of the invention. The details of the method can vary considerably within the scope of the claims.

Claims (3)

7,59628 A method for improving the thermal economy of a wood chips manufacturing process, which comprises grinding wood with a rotary sander (2) in a pressurized sanding chamber (3), spraying warm spray water (G) into the sanding chamber, compounding the ground pulp (C) to remove water (F) and precipitating the pulp (D ) is stored and / or bleached after cooling, characterized in that water (E) with a temperature lower than the temperature of the groundwood pulp is sprayed on the pulp (C) to be doped and that at least part (E1) of this water is used as replacement water for the grinding water. Method according to Claim 1, characterized in that so much water (E1, E2) is sprayed onto the pulp (C) to be precipitated that the pulp cools to a temperature suitable for storage and / or bleaching. Method according to claim 2, characterized in that the water (E) is sprayed in at least two parts (E1, E2), the first part (E1) substantially corresponding to the amount of replacement water required for the jet water (G) of the grinding chamber (3) and the second part (E2) corresponds to the amount of water required in addition to the first part (E1) to cool the ground mass (C) to said temperature.