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Short sequence bleaching without penalties - options for Eucalyptus pulp


Bleaching with a low number of stages is very attractive from the point of investment cost. The downside is easily described with: potentially higher chemical cost, a limited brightness gain, lower flexibility, poorer quality and more difficulties in daily operation. Therefore, despite of all positive messages from equipment or chemical suppliers so far mostly integrated pulp and paper producers have accepted a three stages concept for their bleach plant. Recently detected and implemented modifications of ECF bleaching technology have created the potential to re-evaluate the impact of shorter sequences. Based on a comparison of chemical input and effluent load with organic compounds it is possible to directly connect stages and decrease the number of washers. Another possibility is to use temperature to lower retention time. Thus, depending on the chemicals used in bleaching, short sequences with a low number of washing steps can be applied without losing flexibility in brightness control and consequently chemical addition. An even shorter two stages approach allows brightness at about 88 %ISO, however it is very difficult to obtain a brightness above 90 %ISO in just two stages. Sequential addition of ClO_2 or higher amounts of chemical do not continuously permit top quality. The importance of washing and thus the use of more stages becomes obvious in the comparison of the different options. Two sequences are compared. The first approach analyzes the potential options with high temperature in the first D stage. The second analyzes the potential to apply ozone. Starting with a hot D_0 stage gives a low Kappa number after the extraction and a rather high brightness. This permits a very low demand for chlorine dioxide in D_1 and its combination with a short final P stage. There is no need to operate a washer between D_1 and P. This can be realized with the simple addition of a mixer on top of the up-flow D tower and a down-flow tube for the peroxide reaction. With a counter-current water flow from the P washer to the Ep washer only two effluents currents are discharged. The acidic effluent of the D_0 stage washer and the alkaline effluent of the Ep washer. Temperature profile in this set-up is very constant throughout the bleaching process in this _(hot)D_0-Ep-(D_1P) sequence. The alternative uses the direct combination of ozone with hydrogen peroxide and an extraction. The abbreviation would be (ZpE). This can be similarly followed with a D_1/P combination. However, controlling such a process becomes complicated as a Kappa number too high after the first combination cannot be lowered sufficiently in the second step. The answer is the use of three short stages. A moderate input of ClO_2 ahead of the Z/E combination gives the flexibility required to make the process viable. This sequences allows small towers, retention time can stay short. It can be abbreviated with d-(ZE)-(DP). As brightness and Kappa can be monitored easily between the towers, process control is not difficult and swings in incoming Kappa can be compensated.......

【作者名称】: HANS U. SUESS, KURT SCHMIDT, BERND HOPf
【作者单位】: Degussa AG, Germany
【关 键 词】: Short sequence bleaching without penalties - options for Eucalyptus pulp
【会议名称】: Appita Annual Conference and Exhibition incorporating the ISWFPC(International Symposium on Wood, Fibre and Pulping Chemistry) vol.1: Appita Conference Sessions; 20050516-19; Auckland(NZ)
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 101,709,470
【摘要长度】: 3,077
【会议地点】: Auckland(NZ)
【会议组织】: Degussa AG, Germany
【会议时间】: 2005
【上篇论文】: 外文会议 - Application Research on Sealing Technologies of CO2 MA Granary and MA Grain Storage Technologies
【下篇论文】: 外文会议 - INFLUENCE OF SURFACTANTS ON THE HOMOGENEOUS AND HETEROGENEOUS OXIDATION OF AZO DYES

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