H2O2 single stage bleaching of the hottest waste n

Single stage H2O2 bleaching of waste pulp and SGW mixed pulp

Keywords: waste pulp; SGW； H2O2 bleaching

the treatment capacity of waste paper in our factory is not large, so there is no need to add a bleaching production line. We tried to send the waste paper pulp to the mechanical pulp workshop, mix it with ordinary ground wood pulp for H2O2 single-stage bleaching, and then send it to the paper workshop for paper making. After several months of production practice, the bleaching effect is good, which can fully meet the requirements of paper production, and the production cost is low, the process flow is simple, and the operation is simple. Now the bleaching process is briefly discussed, and its bleaching effect and influencing factors are discussed

1 production process

1.1 raw materials

waste paper that has not been printed has a low whiteness, about 46% ZBD. It is broken up by a hydraulic pulper, then by a high-frequency disintegrator, then screened, and finally mixed with SGW. The proportioning ratio of the two pulps is about 1:4, that is, the amount of SGW pulp is about 4 times that of waste pulp

1.2 bleaching process conditions

h2o ericliedtke, member of adidas Group Implementation Committee, said: "it is a good thing for global leaders to gather together to discuss the climate conference. 2. The dosage is 1.5% - 3.0% (for absolutely dry pulp) The dosage of NaOH is 1% - 2%, and the dosage of Na2SiO3 is 2.0% - 3.0%; The concentration of bleached pulp is 18% - 25%, the bleaching temperature is 50 ~ 60 ℃, and the bleaching time is 1 ~ 1.5h; The pH value of the bleaching solution is 10 ~ 11

1.3 main process flow

waste paper → shredding → dredging → screening → mixing with SGW → purification → concentration → H2O2 bleaching → papermaking

2 factors affecting H2O2 bleaching of mixed pulp

2.1 H2O2 dosage

production practice shows that within a certain range, the greater the H2O2 dosage, the more whiteness will be improved, but the production cost will also increase. In order to explore the most suitable amount of H2O2, a concept is introduced first: whiteness increase ratio, that is, the whiteness increased by the unit amount of H2O2. Its calculation formula is as follows:

whiteness increase ratio = (whiteness after bleaching - whiteness before bleaching) × 100/H2O2 dosage

the greater the whiteness increase ratio, the more whiteness will be increased by the unit H2O2 dosage. At this time, the H2O2 dosage is the most appropriate

the test shows that with the increase of H2O2 dosage, the whiteness increase shows an upward trend, but the whiteness increase ratio first increases and then decreases. When the H2O2 dosage is 2.0% - 2.4%, the whiteness of mixed pulp with unit H2O2 dosage increases the most. Therefore, the most suitable H2O2 dosage for H2O2 bleaching of waste pulp and SGW mixed pulp is 2.0% - 2.4%

2.2 before bleaching, make sure to make the alkali ratio of the marking solution

alkali ratio, that is, the ratio of NaOH to H2O2 in the bleaching solution. When the H2O2 dosage is the same (2.2%), with the increase of alkali ratio, the whiteness of mixed pulp increases first and then decreases. When the alkali ratio is 0.5 ~ 0.8, the whiteness increases the most. Therefore, the H2O2 bleaching ratio of waste pulp and SGW mixed pulp is 0.5 ~ 0.8

2.3 bleach pulp concentration

the higher the bleach pulp concentration, the more the whiteness of the mixed pulp is improved after bleaching, and the less H2O2 remains after bleaching. Due to the low beating degree and fast water filtration of waste pulp, the concentration after dehydration by double thickener is relatively high, which can basically reach about 20%, which is beneficial to bleaching

2.4 bleaching temperature and time

like H2O2 bleaching of mechanical pulp, high bleaching temperature can shorten the bleaching time, but too high temperature is detrimental to bleaching. From the production practice in recent months, when the bleaching temperature is lower than 50 ℃, the bleaching speed is slow, and the whiteness cannot meet the process requirements within the specified time. When the temperature is higher than 65 ℃, the bleaching effect is not ideal, and the pulp is easy to turn yellow. The bleaching temperature of mixed pulp is appropriate at 50 ~ 60 ℃, but we generally control it at 55 ~ 60 ℃, because the bleaching time is 1 ~ 1.5h, and the output should be increased, so the temperature of the future trend of China's plastic market should be slightly higher from a professional perspective, so as to improve the bleaching speed

3 conclusion

several months of production practice has proved that it is feasible to mix waste paper and ground wood pulp for H2O2 bleaching. The mixed pulp has good bleachability, the whiteness can be increased by more than 10 degrees, and the whiteness is also easy to control. The whiteness qualification rate in a few months reaches about 95%. We have disposed of nearly a thousand tons of waste paper, all of which are sent to the mechanical pulp workshop and bleached with ground wood pulp. The effect is good, which can meet the needs of papermaking

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