Of practical reasons each type of bleaching stage has got a special letter, Table 10.1. By combining
these letters according to some special rules it is easy to understand how the bleaching sequence
is designed. Thus, a sequence using chlorine in the first stage, alkaline extraction in the
second and chlorine dioxide in the third stage the sequence will be: CED. However, if two chemicals
are used together in the same stage the two letters from the table are written together within
parenthesis and in some cases with a plus between. If for example both chlorine and chlorine dioxide
are used in the same stage and if they are charged at the same time the stage is denoted as(C + D). The chemical that is charged in highest quantity is written as the first one. Thus, in the
example above the chlorine charge is larger than the chlorine dioxide charge. If on the other hand
one chemical is charged ahead of the other the two symbols are written after each other and in
some cases with a comma between. Thus, if chlorine dioxide is charged before chlorine the stage
will be denoted as (DC). Although there are strict rules which have been specified by Tappi (The
Technical Association of the Pulp and Paper Industry) simplifications are often used. One example
is the plus sign that in most cases is eliminated for example in (EOP)- and (PO)-stages thus it
can be difficult to know if a sequential or simultaneous charge is used.
Of practical reasons each type of bleaching stage has got a special letter, Table 10.1. By combiningthese letters according to some special rules it is easy to understand how the bleaching sequenceis designed. Thus, a sequence using chlorine in the first stage, alkaline extraction in thesecond and chlorine dioxide in the third stage the sequence will be: CED. However, if two chemicalsare used together in the same stage the two letters from the table are written together withinparenthesis and in some cases with a plus between. If for example both chlorine and chlorine dioxideare used in the same stage and if they are charged at the same time the stage is denoted as(C + D). The chemical that is charged in highest quantity is written as the first one. Thus, in theexample above the chlorine charge is larger than the chlorine dioxide charge. If on the other handone chemical is charged ahead of the other the two symbols are written after each other and insome cases with a comma between. Thus, if chlorine dioxide is charged before chlorine the stagewill be denoted as (DC). Although there are strict rules which have been specified by Tappi (TheTechnical Association of the Pulp and Paper Industry) simplifications are often used. One exampleis the plus sign that in most cases is eliminated for example in (EOP)- and (PO)-stages thus itcan be difficult to know if a sequential or simultaneous charge is used.
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