US1819963A - Process for treatment of wood pulp by percolation - Google Patents

Description

Aug. 18, 1931. I E. MORTERUD 5 PROCESS FOR TREATMENT OF WOOD PULP BY PERCOLATION Filed Nov. 10, 1950 lll lli'll Patented Aug. 18, 1931 UNITED STATES EINAR MORTERUD, OF TORDEROD, NEAR MOSS, NORWAY PROCESS FOR TREATMENT OF WOOD PULP BY PERCOLATION Application filed In wood pulp digesters it is well known to circulate liquor or washing liquid through the digester for the purpose of dissolving the chemical compounds which are to be removed from the pulp or for washing away the remains of the liquor after the digesting process has been terminated.

According to the process which has been in use for this purpose the percolating liquid is allowed to pass in a continuous flow through the wood pulp to be digested or washed.

In accordance with the present invention the supply of percolating liquid to the top of the digester takes place with interruptions so as to cause an intermittent flow of liquid through the wood pulp to be treated.

Thereby a kind of pulsation is caused to take place in the material to be treated, as the latter will be exposed to a pressure each time an amount of li uid is supplied to the top of the digester an to a decrease of pressure when the particular quantity of liquid has passed.

The process is particularly adapted for the purpose of washing digested pulp, but may also with advantage be utilized in connection with the digesting process proper.

As it will be understood the comression above referred to of the wet pulp wil cause a certain amount of liquid to be pressed out of the same, and this expelled liquid will be car ried along with the percolating liquid.

After the particular amount of liquid has passed the fibres will again expand so as to absorb an amount of -fresh liquid every time an amount of liquid passes through the pulp.

The variation of pressure caused by the intermittently supplied percolating liquid may be further accentuated by means of as pressure in the digester, said gas pressure eing supplied every time a quantity of percolating liquid is being introduced, the pressure being again relieved after the particular 5 quantity of liquid has passed. The said pressure relief may be carried so far as to cause a boiling of the liquid absorbed by thepulp, which has the efiect of giving a more efiicient digestion. In case the treatment takes place at a temperature above the boiling point of November 10, 193( Serial No. 494,756, and in Norway November 20, 1929.

the liquid the said pressure release may be caused simply by letting out steam.

Another effect which tends to increase the efficiency of the treatment is the higher velocity with which the liquid is now passing the pulp particles, whereby liquid to take adhering particles of old away is increased.

'It has also been found that when the percolating liquid is supplied intermittently in separate quantities and in accordance with the present process, the percolating liquid is less liable to form paths through the pulp to be digested, and all parts of the liquid supplied to the top of the digester will pass through the digester on approximately vertical paths.

Further, according to the present process it is possible to gradually increase the speliquid cific weight of the liquid supplied to the diester from each quantity to the next, for instance, by supplying quantities of liquid with successively decreasing temperature, which cannot be done in case of a continuous supply of liquid, as in that case the liquid with higher specific weight will overtake and be mixed with the other liquid in the digester.

If a single digester is used the process may be carried out by means of the arrangement illustrated on Fig. 1, where 1 is the digester, 2 the circulating ump and 3 a collectin vessel provided with a siphon outlet 4. when the liquid in the collecting vessel has reached a level corresponding to the highest point of the siphon outlet, the vessel will be emptied by means of the siphon tube and a certain quantity of liquid is then supplied to the top of the digester through the distributing sieve 5. When the collecting vessel has been emptied as far as .to the lowest point of the siphon tube the current of liquid is interrupted in a known manner until the vessel has again been filled up to the top level. I

According to the-arrangement illustrated on Fig. 2 two digesters 1 and 6 are provided, having their outlets connected with a common collecting tank 7. In this tank a pump 2 leads the circulating liquid to a distributing valve or cock 8, by means of which the current of liquid may be conducted either to dithe ability of the caused automatically or by stance a top distributing sieve may be used,

which is divided into several concentric or sector shaped parts, and the circulating liquid may be turned on to one section after the pjiiier by means of a distributing valve or the It is also feasible to use a rotating distributing member, having approximately the form ofa sector and by means of which the circulating liquid is successively conducted to the various parts of the surface area. of the digester. In that case it will be understood that the-circulating liquid will take the form of a helical layer of liquid moving axially throu h the digester.

Alt ough the process above described is particularly adapted for being used in connection with digesting and washing of wood 821p, it will be understood that it may also utilized in connection with other materials which are to be treated by means of a current of liquid for extracting or washing pur ses.

C aims:

1. In a process for treating materials, such as wood pulp, with a current of liquid for the purpose of extracting, washing etc. supplying the liquid in such a manner to the vessel containing the material in question, that the liquid is caused to pass the various particles of said material in an intermittent current.

said vessel and means for periodically interruptmg the connection between the pressure side of said circulation pump and'the intake 1; to said vessel.

6. In an apparatus for carrying out the process according to claim 1 the combination w1t h two or more vessels containing the materlal to be treated and a continuously operating circulation pump for supplying liquid to the top of said vessels of means for alternately connecting said circulation pump with the several vessels.

In testimony whereof I afiix my signature.

EINAR MORTERUD.

2. In a process as claimed in claim 1 supplying quantities of liquid at determined intervals to the upper part of the vessel containing the material.

3. In a process as claimed in claim 1 exposing the material to an increase of pressure simultaneously with each quantity of liquid and a pressure decrease during each interval between two quantities of liquid.

4. In an apparatus for carrying out the process according to claim 1 the combination with a vessel containing the material to be treated and a continuously operating circulation pump of a collecting vessel for circulating liquid separate from said first named vessel and connected with the latter as well as with the circulating pump.

5. In an apparatus for carrying out the process according to claim 1 the combination with a vessel containing the material to be treated, a continuously operating circulation pump for supplying liquid to the top of

Images