Paper pulp high density bleaching method

Abstract

The invention provides a paper pulp high density bleaching method which comprises the following steps: condensing unleached paper pulp after washing and carrying out extruding dehydration on the condensed paper pulp with a double-screw extruder so as to obtain a high density slurry; pumping mixed liquor of hydrogen peroxide and a bleaching auxiliary agent into the high density slurry to obtain a mixture of materials and reagents; inputting the mixture into a high density bleaching warehouse with feeding spirals and carrying out bleaching at elevated temperature and pressure so as to obtain a bleached slurry; directly inputting the bleached slurry into a high density pulping machine with feeding spirals without washing, and adding sodium hydrosulphite into the high density pulping machine with metering screws during the process of feeding so as to obtain a mixture of materials and reagents; inputting the mixture into the high density bleaching warehouse with feeding spirals after the mixture comes out from the high density pulping machine, discharging the mixture after bleaching at elevated temperature and carrying out fiber dispersion and washing to obtain high beating degree bleaching paper pulp. According to the invention, slurries are delivered by spirals and concentration of the delivered slurries is high, which enables energy consumption in delivery to be reduced, heat energy consumption in the chemical reaction of bleaching to be effectively reduced and economic benefits to be increased.

Description

technical field [0001] The invention relates to a pulp bleaching process, in particular to a pulp high-concentration bleaching method. Background technique [0002] Pulping and papermaking is a heavy polluting industry. In order to reduce environmental pollution and improve pulp bleaching efficiency, pulping and bleaching technology is developing towards medium consistency (>7%) and high consistency (>25%) bleaching technology. Experiments have proved that increasing pulp bleaching concentration can increase bleaching efficiency, reduce bleaching chemical consumption, and reduce environmental pollution; especially in the case of increasingly tight coal resources, increasing bleaching concentration can effectively reduce heat energy consumption and improve economic benefits. [0003] When the pulp concentration is higher than 7%, as the flow carrier water decreases, the slurry changes from a suspension state to a pseudoplastic state, forming a network package with highe...

AI Technical Summary

Problems solved by technology

With the discovery of pulp turbulence and the advancement of medium-consistency pump technology, pulp medium-consistency bleaching technology has been widely used. However, if the pulp concentration is greater than 17%, the pumping efficiency of the medium-consistency pump will be greatly reduced, and the pulp bleaching concentration is difficult to exceed 17%; when the pulp concentration is greater than 25%, the free water in the pulp is basically removed, part of the contained water is tightly wrapped on the surface of the fiber, and is tightly combined with the microfibers of the primary wall layer of the fiber cells, and the other part exists in the inner cavity of the fiber cells. There is no water that can be used as a flow carrier, so it is difficult for the high-consistency pump to transport the pulp concentration to exceed 25%. Some domestic experts have produced a high-consistency pump, but the transmission efficiency is not high and it is difficult to match it with the existing mechanical mixer. Pulp high-consistency bleaching is difficult to be popularized and applied in engineering

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