Process for determining the conditions needed in controllably obtaining sulfate pulp having a predetermined kappa number

Claim 2

A PROCESS FOR DETERMINING THE CONDITIONS NEEDED IN CONTROLLABLY OBTAINING A PREDETERMINED DEGREE OF DELIGNIFICATION AND THEREFORE A PREDETERMINED KAPPA NUMBER IN THE MANUFACTURE OF SULFATE PULP FROM WOOD, AND THEN PULPING THE WOOD UNDER THE CONDITIONS THEREBY DETERMINED, USING AN ALKALINE PULPING LIQUOR COMPRISING AN ALKALI METAL HYDROXIDE AND AN ALKALI METAL SULFIDE, WHICH COMPRISES TAKING A SAMPLE OF ALKALINE PULPING LIQUOR AT AN EARLY STAGE IN THE PULPING OF THE WOOD TO BE PULPED AT WHICH FROM AT LEAST 20 PERCENT UP TO ABOUT 85 PERCENT OF THE ALKALI ADDED INITIALLY HAS BEEN CONSUMED, TITRATING THE SAMPLE WITH AN ACID TO THE END POINT AT WHICH THE CONDUCTIVITY OF THE SAMPLE HAS DECREASED TO A RELATIVELY CONSTANT VALUE, DETERMINING FROM THE AMOUNT OF ACID ADDED DURING THE TITRATION THE ALKALI CONCENTRATION AT THE END POINT, AND FROM THIS ALKALI CONCENTRATION DETERMINING THE "H" FACTOR AT THE DESIRED KAPPA VALUE IN THE FINISHED SULFATE PULP, AND FROM THE "H" FACTOR DETERMINING THE PULPING TIME AND TEMPERATURE RELATIONSHIP NEEDED TO OBTAIN PULP OF THIS KAPPA VALUE, AND THEN PULPING THE WOOD AT THE DETERMINED TIME AND TEMPERATURES TO OBTAIN PULP OF THIS KAPPA VALUE.

Claim 3

A process according to claim 1, in which the sample is prepared by mixing wood chips and alkaline sulfate puLping liquor.

Claim 4

A process according to claim 1, in which the pulping is carried out in the early stage at a rising temperature within the range from about 0.1* to about 25*C per minute.

Claim 5

A process according to claim 1, in which the acid employed in the titration is a strong inorganic acid which is nonoxidizing under the titration conditions.

Claim 6

A process according to claim 1, in which the acid is used in dilute aqueous solution whose normality is within the range from about 0.1 to about 6 N.

Claim 7

A process according to claim 1, in which the alkaline pulping liquor is brought to a temperature within the range from about 110*C to about 180*C, and then the sample is taken.

Claim 8

A process according to claim 1, in which the titration is effected with a strong inorganic acid.

Claim 9

A process according to claim 7, in which the acid is selected from the group consisting of sulfuric acid and hydrochloric acid.

Claim 10

A process according to claim 1, in which the pulping is carried out batchwise.

Claim 11

A process according to claim 1, in which the pulping is carried out continuously.

Claim 12

A process according to claim 1, in which the alkali metal hydroxide is sodium hydroxide.

Claim 13

A process for determining the alkali concentration of an alkaline pulping liquor comprising an alkali metal hydroxide and an alkali metal sulfide, which comprises taking a sample of the alkaline pulping liquor at a stage at which from at least 20% up to about 85% of the alkali added initially has been consumed, titrating the sample with an acid to the end point at which the conductivity of the sample has decreased to a relatively constant value, and determining the alkali concentration at the end point from the amount of titrating acid added to the end point.

Claim 14

A process for determining the alkali concentration of an alkaline pulping liquor comprising an alkali metal hydroxide and an alkali metal sulfide, which comprises taking a sample of the alkaline pulping liquor at a stage at which from at least 20% up to about 85% of the alkali added initially has been consumed, titrating the sample with an acid to the end point at which the conductivity of the sample has decreased to a relatively constant value, and determining the alkali concentration at the end point from the amount of titrating acid added to the end point.

Claim 15

A process according to claim 12, in which the alkali metal hydroxide is sodium hydroxide, and the alkali metal sulfide is sodium sulfide.

Claim 16

A process for preparing sulfate pulps of relatively uniform quality having a desired Kappa number which comprises pulping wood using an alkaline pulping liquor comprising alkali metal hydroxide and alkali metal sulfide at a pulping temperature and for a pulping time established by taking a sample of alkaline pulping liquor at an early stage in the pulping of the wood to be pulped at which from at least 20 percent up to about 85 percent of the alkali added initially has been consumed, titrating the sample with an acid to the end point at which the conductivity of the sample has decreased to a relatively constant value, determining from the amount of acid added during the titration the alkali concentration at this end point, and from this alkali concentration determining the ''''H'''' factor at the desired Kappa value in the finished sulfate pulp, and from the ''''H'''' factor determining the pulping time and temperature relationship needed to obtain pulp of this Kappa value.

Claim 17

A process for preparing sulfate pulps of relatively uniform quality having a desired Kappa number which comprises pulping wood using an alkaline pulping liquor comprising alkali metal hydroxide and alkali metal sulfide at a pulping temperature and for a pulping time established by taking a sample of alkaline pulping liquor at an early stage in the pulping of the wood to be pulped at which from at least 20 percent up to about 85 percent of the alkali added initially has been consumed, titrating the sample with an acid to the end point at which the conductivity of the sample has decreased to a relatively constant value, determining from the amount of acid added during the titration the alkali concentration at this end point, and from this alkali concentration determining the ''''H'''' factor at the desired Kappa value in the finished sulfate pulp, and from the ''''H'''' factor determining the pulping time and temperature relationship needed to obtain pulp of this Kappa value.

Claim 18

A process according to claim 14, in which the alkali concentration of one or more samples taken at an early pulping stage from the alkaline pulping liquor is determined by titration with an acid to an end point corresponding to the limiting relatively constant value of the conductivity of the sample that is reached as conductivity decreases during the acid titration.

Claim 19

A process according to claim 14, in which to obtain a sample of alkaline liquor for the ''''H'''' factor determination, the sulfate pulping is begun by charging and mixing wood chips and alkaline pulping liquor in a digester, the pulping is then begun, using an increasing temperature, and allowed to continue for an initial pulping period during which from at least 20 percent up to about 85 percent of the alkali added initially has been consumed, after which a sample of the pulping liquor is taken, and titrated with an acid to the end point, and then the pulping is carried out at approximately the same rate of temperature increase duriNg the initial stages until the final pulping temperature is reached.

Claim 20

A process according to claim 16, in which the rate of temperature increase during the initial pulping stages is within the range from about 0.1*C/minute to about 25*C/minute.

Claim 21

A process according to claim 17 in which the rate of temperature increase during the initial pulping stages is within the range from about 0.5* to about 10*C/minute.

Claim 22

Apparatus for the continuous preparation of sulfate pulps of relatively uniform quality having a desired Kappa number, comprising, in positive flow connection and in combination, a digester arranged for the through passage of particulate wood while converting the wood in transit to pulp by pulping with alkaline sulfate pulping liquor, means in fluid flow communication with the digester for introducing wood and alkaline pulping liquor at one end of the digester, means in fluid flow communication with the digester for withdrawing wood pulp at another end of the digester, means for heating the digester, means in fluid flow communication with the digester for withdrawing a sample of pulping liquor at a position along the digester corresponding to an early stage of pulping at which from at least 20 percent up to about 85 percent of the alkali added initially has been consumed, means in fluid flow communication with the digester for measuring the conductivity of the sample, means in fluid flow communication with the digester for titrating the sample with acid to an end point at which conductivity has been decreased to a relatively constant value, and means connected with the digester for controlling the temperature of the digester and the rate of the transit of the digesting wood therethrough according to the alkali concentration of the sample, and an ''''H'''' factor at that alkali concentration.

Claim 23

Apparatus for the continuous preparation of sulfate pulps of relatively uniform quality having a desired Kappa number, comprising, in positive flow connection and in combination, a digester arranged for the through passage of particulate wood while converting the wood in transit to pulp by pulping with alkaline sulfate pulping liquor, means in fluid flow communication with the digester for introducing wood and alkaline pulping liquor at one end of the digester, means in fluid flow communication with the digester for withdrawing wood pulp at another end of the digester, means for heating the digester, means in fluid flow communication with the digester for withdrawing a sample of pulping liquor at a position along the digester corresponding to an early stage of pulping at which from at least 20 percent up to about 85 percent of the alkali added initially has been consumed, means in fluid flow communication with the digester for measuring the conductivity of the sample, means in fluid flow communication with the digester for titrating the sample with acid to an end point at which conductivity has been decreased to a relatively constant value, and means connected with the digester for controlling the temperature of the digester and the rate of the transit of the digesting wood therethrough according to the alkali concentration of the sample, and an ''''H'''' factor at that alkali concentration.

Claim 24

Apparatus according to claim 19, including a preheater for heating the particulate wood prior to passage through the digester.

Claim 25

Apparatus according to claim 19, including a gas evaporator for concentrating spent alkaline liquor, and means for recycling hot gases from the evaporator to a preheater for the particulate wood.

Claim 26

Apparatus according to claim 19, in which the means for determining conductivity is a conductivity meter.

Claim 27

Apparatus according to claim 19, including means for adding alkali to the liquor in the digester at a position along the digester corresponding to a later stage of the digestion.