CN109594386A - A kind of method of bleached pulp - Google Patents

Abstract

A kind of method of bleached pulp wherein the paper pulp is made successively to be subjected to the effect of ozone and chlorine dioxide, or is subjected to both effects in reverse order.The method is characterized in that handled paper pulp is " low concentration paper pulp " of the consistency less than or equal to about 5% (weight), ozone and paper pulp are mixed in Stirring device, wherein paper pulp is stirred at low speed when ozone is injected paper pulp, to obtain fluid paper pulp, less than or equal to about 12 meter per seconds but about 2 meter per seconds are greater than or equal in the tangent peripheral speed of Stirring wall paper pulp, time of contact between ozone and paper pulp is between 1 to 20 minute, the amount of ozone in injection Stirring device is calculated as 1 kilogram to 20 kilograms with dry paper pulp per ton, paper pulp, which is maintained at, can substantially be extended to the fluid state reacted completely with ozone.

Description

A kind of method of bleached pulp

Technical field

The present invention relates to a kind of methods of bleached pulp, wherein the paper pulp is successively subjected to the work of ozone and chlorine dioxide With, or it is subjected to both effects in reverse order.

Background technique

Past, the chlorine as one of bleaching agent are widely used in bleached pulp, especially so-called chemical pulp.Chlorine dioxide Or hypochlorite is also known the lignin that can not only remove in cellulose but also the bleaching agent that can improve cellulose whiteness.It is general and The selection of speech, bleaching agent is mainly determined according to the paper type made from handled paper pulp is wished.For example, so-called when using Kraft pulp come when preparing extra white writing paper, it is necessary to using a large amount of bleaching agent and must from those effects faster and more It is selected in the bleaching agent of selectivity.No matter what type of Chlorinated Bleaching agent is used, is all generated in bleaching process organic Chlorine products, they are almost insoluble in the aqueous solution for cleaning paper pulp, have largely in each stage of paper pulp bleaching Organic chlorides are taken away or are extracted with waste liquid from paper pulp.There are the organic chlorides of low amount in paper pulp.In general, When use chlorine and when it is intended that obtaining very white product, compared with the slightly lower method of the whiteness of gained paper pulp, it is necessary to make With apparent larger number chlorine.

Since the discharge of chlorination waste liquid has extremely harmful influence to environment, so, it has made laws rule in many countries If fixed without total ban, also it is limited in using chlorine and its derivative in paper pulp bleaching, so that limitation must be located thereafter The content containing organochlorine compound in water lotion of reason.What the lower limit value of organic chloride material discharge was defined as, with t (ton) table Show the quantity of absorbable halogenated organic substance or AOX in terms of paper pulp per ton.Currently, the maximum quantity of paper pulp per ton is limited to 1 Or 2t, it is specifically respectively determined by country variant, still, in a few years from now on, in terms of prepared paper pulp per ton, by the row of requirement AOX content in radioactive waste liquid is lower than 0.5 ton.

During bleached pulp, organic chlorides are reduced or removed using some solutions.

Simplest method is with the chemicals of non-chlorinated, such as oxygen, peroxide, such as hydrogen peroxide, ozone, peracetic acid And the like replace used chlorination chemicals.Unfortunately, these use the method for bleaching of non-chlorinated product not The characteristic of paper pulp, such as whiteness or viscosity may be made to assign desired value in reasonable price.

It is other that the use that initial bleaching stage reduces chlorine is that typically in for a possibility that reducing organochlorine compound content Amount.Various solutions have been proposed, such as increase the removing of lignin in the cooking of pulp stage, and wooden with oxygen removal Element.Before carrying out the suitably extraction stage, these processing are possible to reduce the content of lignin in the paper pulp for being sent to bleach plant. However, these processing can not efficiently reduce the concentration of organochlorine compound in bleached pulp and the amount of residue cannot be made to reach To sufficiently low numerical value.

Other possibilities are to replace chlorine with chlorine dioxide, and chlorine dioxide is strong oxidizer compared with chlorine, then with respect to chlorine and Speech is possible to that lignin can be removed with less amount (fewer than half).This kind of method is abbreviated as DE, and preferably DEDED is in document In be it is known, the D stage is the stage with chlorine dioxide treatment, and E-stage is the traditional extraction stage.

These related different disposals are described more fully, can refer to by written by J.B.Casey " paper pulp and paper, chemistry and Chemical technology ", the third edition first volume, 1980, JohnWiley&Son, New York, page 694 to 696.

The experimental method of " sulphite " type bleached pulp is also published in March, 1984 " paper pulp and paper science " periodical In, it is " the shadow that bleaching chemical and bleaching sequence generate some characteristics of sulfite pulp by the topic written by F.Granum Ring ", the J.25 or J.29 page, which describe many experiments sequences, especially using the sequence of oxygen or ozone, followed by making With the sequence of chlorine dioxide.

A kind of method for bleaching of kraft pulp for paper manufacture, this method packet are disclosed in European patent EP 464157 The process with pure or mixed ClO 2 bleaching is included, followed by the stage bleached with ozone, extracts rank without centre Section, takes followed by the alkali carries as the phase III, and the final fourth stage for using ClO 2 bleaching, which is by this The final stage for the method for bleaching that sequence carries out.

Canadian Patent CA2031850 also discloses a kind of method that the paper pulp according to so-called DZ sequence is bleached, i.e., first Chlorine dioxide treatment is first used, ozone treatment is then used, without the centre extraction stage between two stages, makes two in the method Kind chemicals injection when being separated from each other in bleaching process.It is believed that this method can reduce the generation of AOX.So And all these known embodiments are all to being carried out first on the paper pulp of oxygen removal lignin.

Canadian Patent CA2031848 also discloses a kind of method similar with above-mentioned Canadian Patent CA2031850, but It is that its sequence is arbitrary, that is, actually depicts the sequence of ZD or DZ.As disclosed in all embodiments, here The initial period of necessary useful oxygen removal lignin again.

In the two Canadian Patents and in above-mentioned European patent, all these embodiments are all the paper with medium consistency It is counted on the basis of slurry.

Those skilled in the art have been generally acknowledged that the consistency of paper pulp is got over if mixed in the mixer of very high speed Height, the efficiency with the chemical treatments of D and Z-type are then better.This is why up to now, these methods are not all low thick Degree paper pulp is that the paper pulp aspect for containing more water than medium or high-consistency paper pulp is developed.

However, currently being faced with the pulp mill of low consistency pulping operations, there are many problems.Current many factories CD sequence It is operated, i.e., the stage of chlorine bleaching is used first, followed by what is bleached with chlorine dioxide (the above-mentioned intermediate solution having been mentioned) Second stage, wherein method as described above is unsatisfactory in terms of the AOX discharge standard that will be come into force.Current In these factories with low consistency pulping operations, all devices used are exclusively used in low consistency paper pulp, especially mixer, conveying The size and general all process units of pipeline and intermediate storage equipment.Prevent AOX product in waste liquid dense with regard to currently known It spends for high method, in order to change these factories, needs to equip these factories with medium or high-consistency device to reach To standard as above.This means that all existing equipment must be replaced with new equipment in these factories, this means that on Million dollars of investment.

Therefore there is currently no the AOX that one kind had both generated low amount, i.e., paper pulp per ton contains the AOX less than 0.5 ton, again The method handled using the paper pulp of low consistency, the i.e. paper pulp of consistency≤5%.

Summary of the invention

It is an object of the present invention to provide a kind of solutions of above problem.

The method is characterized in that handled paper pulp is " low concentration of the consistency less than or equal to about 5% (weight) Paper pulp " mixes ozone and paper pulp in Stirring device, wherein paper pulp is stirred at low speed when ozone is injected paper pulp, to obtain Paper pulp must be fluidized, is less than or equal to about 12 meter per seconds in the tangent peripheral speed of Stirring wall paper pulp, but be greater than or wait In about 2 meter per seconds, the time of contact between ozone and paper pulp between 1 to 20 minute, injects the ozone amount in Stirring device It is calculated as 1 to 20 kilogram with butt paper pulp per ton, paper pulp almost keeps fluidized state during the entire process of with ozone reaction.

It is preferred that ozone and oxygen mix are injected, it is preferably in a proportion of the ozone for containing 3 to 20% (volumes) in oxygen, oxygen Also it is contacted with paper pulp, time of contact is substantially identical as the duration of ozone and generates supplement and going of carrying out simultaneously is wooden Effect and/or bleaching action.

Oxygen is recycled in agitation phases finish time, filters out undesirable impurity, and depending on the circumstances return to The inlet of ozone generator.

It is preferably used in the ozone generator for being higher than and inputting oxygen under atmospheric pressure, on the one hand make ozone generator Yield highest, and on the other hand since the pressure of the latter declines, thus in the case where being higher than atmospheric pressure but lower than 15 bars absolute pressures (preferably 1.3 bars to 2.5 bars of absolute pressures) obtain the mixing of oxygen and ozone usually under 1 to 3 bar of absolute pressure Object.Admixture of gas can be introduced directly into paper pulp in this way, without pressurizeing before injection.

It is preferred that the tangent peripheral speed of paper pulp is lower than 9 meter per seconds and even more preferably below 6 meter per seconds, it is about 1 in diameter In the case where the cylindric blender of rice, it indicates approximately less than 120 revs/min of rotation speed.

When using duration of ozone treatment preferably at 2 to 10 minutes in stirred reactor, needed for dry pulp per ton Ozone amount preferably between 2 to 10 kilograms.For chlorine dioxide, with dry pulp count number per ton 1 to 20 kilogram it Between change, preferably with dry pulp count number per ton between 2 to 10 kilograms.

Therefore, by using method of the invention, the amount for being easily obtained the AOX in terms of prepared dry pulp per ton is 0.1 To 0.2 kilogram of sewage.Do not change design or the factory using CD or DC sequence, it can be simply with the above-mentioned dosage ozone of input Factory replaces the factory of input chlorine.The present invention is other obvious advantage is that keeping the mechanical performance for even strengthening paper pulp.

Stirring device or stirred reactor refer to containing one or more blades, the blender of preferably drum type, in cylinder It is measured at the circumference of certain a part, the blade can be such that whole liquid (low consistency paper pulp) rotate with tangential velocity, by this It is defined as the tangential peripheral speed of paper pulp.

" (chemical engineering ", on October 11st, 1976, page 141 to 143, entitled " the mixing speed of blender stirred tank The common feature of stirred reactor is described in the article of rate ".

Further advantage of the invention be need not to use intermediate storage or flash tank (such as: Canadian Patent CA2031848), which is used in mixer pour into paper pulp after mixing paper pulp and reactant to continue to make paper pulp and smelly It is reacted between oxygen, so as to improve paper pulp bleaching effect.In the entitled " KvaernerMC of Kvaerner pulp technology AB company Think to carry out fluidisation appropriate only using the paper pulp of the mixer designed exclusively for paper pulp in the pamphlet second page of type mixer " The paper pulp (thus keeping the rheological behavior of paper pulp substantially same with water phase) that consistency is about 10% or more can be obtained.Due to this original Cause, rotation speed are necessarily greater than about 1800 revs/min, i.e., for diameter is about the industrial mixer of 30cm, tangent circle Circular velocity is about in 30m/s.Most 10 seconds of time of contact in mixer between paper pulp and ozone.In addition, according to the invention Method, the step of need not being carried out before DZ sequence of the invention with oxygen removal lignin.

The step of ozone treatment is carried out before and after with chlorine dioxide treatment.

Certainly, method of the invention can be used for wherein injection of ozone, and the case where be not injected into chlorine dioxide, or it is available Before and after the stage or sequence bleached in any one using above-mentioned any known bleaching agent the step of injection of ozone, packet Include it is other from the present invention it is similar or it is different with ozone inject stages.

In addition, being described by this, it is assumed that the rotation speed of mixing arm and the rotation speed of paper pulp are not much different, especially Refer to the speed (tangential peripheral speed) on wall, in practice it can be found that the interior difference due to caused by internal turbulence of paper pulp.

Specific embodiment

Embodiment 1

In this embodiment, the cork of the unused oxygen removing lignin of low consistency is handled in mixer according to the present invention The sample of kraft pulp.The lignin in paper pulp is removed by the ClO2 of addition 2% chlorine dioxide first.Then by the sample It is divided into two parts；By first part-sample A-, handled after the washing according to following condition in the Ep stage:

NaOH feeding quantity: 1.5%

H2O2 feeding quantity: 0.25%

Temperature: 75 DEG C

Time: 120 minutes

Consistency: 10%

By second part _ sample B_, before any cleaning, directly handled under following operating condition with O3:

Temperature: 50 DEG C

Pressure: atmospheric pressure

Pulp thickness: 2.5%

O3 concentration in O2: 10 weight %

Incorporation time: 6 minutes

The rotation speed of periphery mixer: 4.1m/s

Inject the amount of O3: 5kg/t or 0.5% in paper pulp

The degree of O3 consumption: 95%

After reacting, identical as sample A, sample B is cleaned, the Ep stage is then carried out.

Compared with the Kappa value of the sample A after DZEp is handled is 5.6, the kappa value of the sample B after DEp processing It is then 3.4, this demonstrate the effects for carrying out O3 processing under this condition.

Embodiment 2

In this embodiment, with the ox-hide eucalyptus pulps-Kappa9.0, transparency 45.8%ISO of O2 removing lignin For being used by the O3 carried out under medium consistency with conventional high shear mixing (sample A) according to DZ sequence processing and under low consistency The O3 processing that low shear mixing (sample B) carries out compares.As reference, according to DEoD sequential processes first part paper pulp. Operating condition as reference are as follows:

The D stage

Temperature: 55 DEG C

Residence time: 45 minutes

ClO2 additional amount: 1.3% (pure ClO2)

Consistency: 11%

The Eo stage

Temperature: 70 DEG C

Residence time: 125 minutes

NaOH additional amount: 1.3%

Consistency；12%

The pressure of oxygen: 2 bars

The last D stage

Temperature: 70 DEG C

Residence time: 90 minutes

ClO2 additional amount: 0.6% (pure ClO2)

Consistency: 11%

The acquired results of reference sample are:

Kappa:0.9 after DEo sequence

Whiteness after DEo sequence: 73.8%ISO

Whiteness after DEoD sequence: 88.1%ISO

The sequence of DZEoD

In both cases, ClO2 and O3 is added in order, before carrying out any cleaning, is run out of in first step O3 is added after ClO2.

For sample A, other than making the amount of ClO2 be reduced to 0.48%, condition and the reference operation condition phase of D step Together.Then the O3 of 0.4% (or 4kg/t is calculated as with paper pulp) is added under the conditions of following high shear mixing:

The pressure of O3: 9 bars

The concentration of O3 in O2: 9.5 weight %

Pulp thickness: 11%

Temperature: 55 DEG C

Periphery mixer rotation speed: 78m/s

Other than amount in addition to making ClO2 in the last D stage is reduced to 0.4%, according to item identical with reference operation condition Part carries out subsequent step.Acquired results are as follows:

Kappa:0.9 after DZEo

Whiteness after DZEo: 79.2%ISO

Whiteness after DZEoD: 88.5%ISO

Sample B is handled with ClO2 and O3 under low consistency；Amount in addition to making ClO2 be reduced to 0.45% and pulp thickness subtract Lack to except 2.5%, the condition in other D stages is identical as reference operation condition.Then add under the conditions of following low shear mixing Enter the O3 of 0.4% (or 4kg/t is calculated as with paper pulp):

The pressure of O3: 2 bars

The concentration of O3 in O2: 9.5 weight %

Pulp thickness: 2.5%

Temperature: 55 DEG C

Periphery mixer rotation speed: 11m/s

Other than amount in addition to making ClO2 in the last D stage is reduced to 0.4%, according to item identical with reference operation condition Part carries out subsequent step.Acquired results are as follows:

Kappa:0.9 after DZEo

Whiteness after DZEo: 79.0%ISO

Whiteness after DZEoD: 88.3%ISO

These embodiments are clearly illustrated using the suitable fluidisation item at least identical as having effects that in medium consistency Under part when low consistency, according to DZ sequence, O3 processing can be used for ClO2 step.This is used to obtain 88%ISO whiteness by comparing Different ClO2 amount when ClO2 amount reduction and reflect.DzEoD sequence carries out processing point with medium and low consistency respectively Other need 0.88% and 0.85%ClO2, and reference operation condition then needs 1.9% ClO2.

Claims (8)

1. a kind of method of bleached pulp, wherein the successively paper pulp described in ozone and chlorine dioxide treatment, or with opposite time Sequence carries out both processing, the method is characterized in that institute of the handled paper pulp for consistency less than or equal to about 5% (weight) It calls " low concentration paper pulp ", ozone and paper pulp is mixed in Stirring device, wherein stirring at low speed paper when ozone is injected paper pulp Slurry is less than or equal to about 12 meter per seconds still in the tangent peripheral speed of Stirring wall paper pulp to obtain fluid paper pulp More than or equal to about 2 meter per seconds, the time of contact between ozone and paper pulp between 1 to 20 minute, injects in Stirring device The amount of ozone be calculated as 1 kilogram to 20 kilograms with dry paper pulp per ton, during the entire process of making paper pulp and ozone react, Fluid state should be kept it in.

2. a kind of method of bleached pulp described in accordance with the claim 1, it is characterised in that the gaseous mixture of input ozone and oxygen Body, preferably ratio are the ozone for containing 3 to 20% (volumes) in oxygen, and oxygen is also contacted with paper pulp, and time of contact is basic It goes up identical as ozone duration and generates delignification that is additional and carrying out simultaneously and/or bleaching action.

3. a kind of method of bleached pulp according to claim 2, it is characterised in that recycle oxygen to regard concrete condition Depending on for recycling.

4. according to a kind of method of bleached pulp described in any claim in claims 1 to 3, it is characterised in that introduce paper The pressure of ozone and oxygen in slurry is between 1 to 15 bar of absolute pressure.

5. a kind of method of bleached pulp according to claim 4, it is characterised in that introduce the ozone and oxygen in paper pulp Pressure be between 1 to 3 bar of absolute pressure, preferably between 1.3 bars to 2.5 bars absolute pressures.

6. according to a kind of method of bleached pulp described in any claim in claim 1 to 5, it is characterised in that tangent circle Circular velocity is less than or equal to 9m/s, preferably 6m/s.

7. according to a kind of method of bleached pulp described in any claim in claim 1 to 6, it is characterised in that per ton dry The content of ozone is 2 to 10 kilograms in paper pulp.

8. according to a kind of method of bleached pulp described in any claim in claim 1 to 7, it is characterised in that introduce paper The content of chlorine dioxide is calculated as 1 to 20 kilogram with dry pulp per ton in slurry, is preferably calculated as 2 to 10 kilograms with dry pulp per ton.