Recently mainstream of chlorine dioxide plant in overseas is of R 8 process which practically dose not generate chlorine as by-product, however there arises problems in treating sesquisulphate which is a by product from R 8 plant as the usage of chlorine dioxide rises. For this circumstance. in order to decrease by product sulphate. R 10 process was developed to become operational. Furthermore, R 12 process was developed and is now in test run for practical use. Also R 13 process which produces no by product is under study.
In Japan. however, major pulp bleach sequences use chlorine, hypochlorite and chlorine dioxide, therefore R 2 H process which matches this sequence is the leading one for chlorine dioxide plants. As the circumstance is such that hypochlorite which forms large amount of chloroform in the bleach sequence might not be used in the future, transfer to R 8 process would be accelerated. Also in Japan, the required amount of chlorine dioxide is smaller than the amount in overseas, R 2 P process would be another choice.
Following conditions would be required for future pulp mills in selecting a chlorine dioxide plant :
1) Matching of bleach sequence with kind and amount of by-products, and ClO
2 production capacity
2) Higher safety of the plant including environmental issues
3) Flexibility of the plant to correspond with pulp capacity increase and new technology
4) Lower cost of chlorine dioxide production totaling raw materials cost. operational cost including operation and maintenance, and facility amortizement
The shift to ECF is unavoidable for the pulp bleach in Japan from the present situation, therefore the usage of chlorine dioxide is estimated to increase by 2 to 3 times.
In view of above circumstances. R 2 P process would be a kind of provisional one, while R 8 process is expected to be one of the best options for a future chlorine dioxide plant.
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