Improved pulp wash with carbon dioxide by steepslope9876


									Improved pulp wash
with carbon dioxide
Linde and the Pulp and Paper Industry
Linde is a major supplier of industrial gases to the pulp and paper industry. The countries of
Northern Europe have vital national resources in their vast forests, and consequently forest
products continue to be a major earner of export income.
   Being the leading gas supplier in this region, Linde has dedicated itself to serve this cross-
border forest industry. The development of the pulp and paper industry in Northern Europe has
accelerated in the last few decades, in particular due to advances in more sophisticated
technology. One of the driving forces for this development has been new market demands
– demands that have often been enveloped in environmental terms. These days, every mill and

                                                                                                                                           ® ADALKA, CODIP and GRAFICO are registered trademarks of the Linde Group
every process calls for special consideration, and this is why developing practical and profitable
applications for them also calls for special experience.

This is where Linde’s specialized know-      oxygen delignification and ozone bleaching     CO2 has been extensively used in the
ledge of gas application technology and      as well as various CO2 applications for       pulping process since the beginning of
its fundamental knowledge of pulp and        both pulp and paper processes.                the 1990s. Today, CO2 addition to pulp
paper processing comes to the aid of the        Linde offers a number of specific           washing is a patented, established tech-
industry in reaching its goal.               applications for paper production. In order   nology that is used in more than 30 fiber
   At Linde, our aim has always been to      to control pH, alkalinity and calcium hard-   lines worldwide – in both unbleached and
use this specialized knowledge to design     ness in the stock preparation process for     bleached fiber lines. The technology has
and develop systems that will not only im-   papermaking, for example, we have devel-      been specifically designed to improve
prove overall process efficiency, but will    oped the ADALKA® process stabilizer,          washing performance, which is of particular
also help the industry reduce environ-       the CODIP® process improver and the           importance from an economical as well
mentally negative effluents.                  GRAFICO® calcium carbonate saver, not         as an environmental viewpoint.
   We have extensive experience and          to mention a number of other tailor-made
knowledge, for example, in the areas of      solutions.

CO2 pulp wash technology
Whatever the pulp mill, pulp washing is      economical benefits. It is important to        fully carried out not only on old limited
one of the most important process stages.    note that CO2 can be added in many            washlines, but also on new washlines.
Poor washing conditions lead to higher       different ways and positions – depending      The prime reason that investment costs
water and chemical consumption. It also      on your specific needs – with a minimum        are low is that the CO2 pulp wash process
reduces the effectiveness of water treat-    of investment.                                calls for no design modification whatsoever.
ment and chemical recovery operations.          Linde has witnessed positive effects of    This means that you will find it is both quick
All these factors tend to magnify plant      CO2 in various types and brands of            and easy to start using carbon dioxide in
costs or effluent problems. Our CO2 wash      washers, e.g. screw washers, vacuum and       pulp washing.
technology will help you significantly im-    pressure washers, displacement washers
prove your wash results with substantial     and belt washers. This has been success-

                            CO2 is used in more than 30 washlines in various ways,
                            depending on specific needs.

                                                                                Wash liquor


                                                                                                           Fig.1. Schematic drawing
                                                                                                           of a simplified washline
                                                                                                           with a filter and a press.
Benefits of the
Linde CO2 pulp
wash process                                           Capacity                                     Defoamers



                                         Fig. 2. Reduced fiber swelling                 Fig. 3. The addition of CO2 reduces
                                         improves dewatering and leads to              the need for defoamers.
                                         an increased capacity.

 Adding CO2 to the alkaline
                                      Quick response when                           Cleaner equipment
wash liquor – where it is rapidly
                                      applying CO2                                  with CO2 addition
  dissolved – accomplishes            An effect of our process is related to pH     The increase in carbonate concentration
                                      and ion exchange, which reduces fiber          influences the process in two specific
         two things:
                                      swelling. An immediate result is that de-     ways. Carbonate reacts with the nearly
  First, the pH level is reduced at   watering capability is notably improved.      insoluble calcium soaps, converting them
  the point of addition, causing a    This benefit has shown to be of significant     into soluble soaps. This noticeably reduces
  significant reduction in fiber        importance in fiber lines running high-        the level of resin deposits on the washing
  swelling.                           kappa pulps – where washing capacity is       equipment.
                                      often limited. Such limited capacity often       Second, the soluble soaps that are
                                      results in excessively low consistency, or    produced will act as surface-tension-
                                      it may even cause some pulp to be by-         reducing detergents. This improves the
                                      passed. But the addition of CO2 has           removal of dissolved organics while
                   CO2                clearly been shown to improve capacity        reducing the foaming tendency of the
                                      considerably. The increased removal of        liquor. A noted result has been a cut in
  And, second, there is a formation   dirty filtrate has also produced positive      defoamer usage of up to 50%.
  of both carbonate and hydro-        results in the paper mill in the form of
  carbonate ions.                     reduced carryover and a far more stable
                                      pH level for the pulp. There are also fewer
                                      instances of insufficiently washed pulp.
                              COD                                      Na loss                  Wash water usage
         COD in washed pulp

                                                   Na in washed pulp

                                                                                                      Wash water
                                    CO2                                     CO2                                         CO2

    Fig. 4. The addition of CO2                Fig. 5. CO2 addition reduces Na                   Fig. 6. CO2 addition reduces wash
    reduces COD in washed pulp.                loss.                                             water usage.

Economical                                                                                    CO2 pulp wash – a versatile
benefits                                                                                       tool in the right hands
Objectives for the use of CO2 pulp wash:    However, we have succeeded in boosting            The experience we have gained from
•   increased production rate               washing capacity by up to 15% in a num-           extensive commercial operation has
•   reduced carryover from the wash plant   ber of washlines. We have also been able          shown that the CO2 amount and the opti-
                                            to see reductions of COD and Na levels            mal point of addition tend to be specific
•   reduced consumption of required
                                            in washed pulp of up to 20–30%, which             to each fiber line. This is why – after a
                                            in some cases has lead to a notable               technical estimation of the potential of CO2
•   reduced wash-water volumes
                                            reduction in the consumption of required          wash technology – our specialists always
•   savings in steam consumption            chemicals.                                        perform a mill trial in order to determine
•   reduced effluent load                       An economical option, on the other             maximum efficiency.
•   reduced maintenance costs               hand, might preferably be to use the                 All credit to sound technical planning,
                                            improved washing efficiency to reduce the          but nothing can beat hands-on work at
The results may vary somewhat, since        amount of water consumed. It has been             the site. That’s why our experienced
washing conditions and the demands of       possible to reduce wash-water flows by             specialists will be there on your site to
process improvement vary from mill to       20%. This will, in turn, lead to a cut in steam   give you a hand in reaching the best
mill.                                       consumption, which may well be of impor-          possible CO2 pulp washing results.
                                            tance especially when the evaporation plant
                                            represents a bottle-neck in the process.
   – a showcase of successful CO2 addition

                                                                                                             Photo: Lars Bygdemark

Korsnäs produces board, paper, and fluff pulp for             runnability and washing that Korsnäs had set as its
hygienic products. It has been a proven leader in            priority targets. The process has, of course, now
pulp and paper technology for many years. Today,             been in commercial operation for a number of years
annual pulp production at its highly efficient process-       in both bleached and unbleached washlines, and
ing plant amounts to approximately 660,000 tonnes,           with continued process improvements. The success
360,000 tonnes of which represent bleached pulp.             of this CO2 technology means that Korsnäs has
   When contact was first made between Linde and              successively strengthened its position as a techno-
Korsnäs with regard to the addition of CO2 to the            logical leader in the industry. Another prime reason
pulp wash process, it was not long before a process-         for its leading position, however, is that Korsnäs is,
trial agreement had been reached. The experience             and always has been, a company that is open to
gained in those initial trials made it possible to opti-     concepts and proposals intended to strengthen
mize the process and achieve the improvements in             improvements in its processing systems.

                                       How efficient is your pulp washing?
                                       Pulp washing is one of the most important process stages in any mill. Less than satis-
                                       factory washing conditions will quite likely cause a higher consumption of wash water
                                       and an increased use of defoamers and required chemicals. Everyone of these repre-
                                       sents a factor that leads to increased cost and greater effluent problems.
                                         Take a good look at the benefits of our process as presented. We sincerely believe
                                       that you will come to the conclusion that more in-depth discussions are called for.
                                       Contact us for specific facts about your specific conditions. We have a team of
                                       specialist standing ready.
                                       Linde Gas & Engineering
                                       SDP – Pulp & Paper
                                       Phone: +46 8 731 10 00
                                                                   Linde Gas –
                                                                   Making the difference

                                                                   Linde Gas is in the business of making a       Created through forward thinking, a
                                                                   difference in everything we do. For the    close customer relationship and a sound
                                                                   benefit of our customers. Through           business sense, the Linde Gas combination
                                                                   innovative solutions within manufac-       of gas products and support services, in-
                                                                   turing industry, metallurgy, chemistry,    novative hardware, customized solutions
                                                                   food processing, medicine, specialty       and on-site supply systems generates
                                                                   gases, alternative fuel technologies       new and profitable opportunities.
 Subject to alteration. Printed on chlorine-free bleached paper.

                                                                   and the environment. This difference           Linde Gas technology daily drives
                                                                   is reflected in our position as a leading   entrepreneurship the world over with our
                                                                   company in Europe and as a major           employees all working concertedly to
                                                                   driving force world-wide.                  keep making that difference.

                                                                   Gas technology that works for you
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                                                                                                                                   Linde AG

                                                                                                                                   Linde Gas Division
                                                                                                                                   Phone: +49 89 7446-0
                                                                                                                                   Fax: +49 89 7446-1230

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