Moderate-thick paper pulp pressure stabilizing dual flow-lift tower oxygen bleaching method

Abstract

The invention relates to a medium-concentration paper pulp stable-pressure double- upflow tower bleaching method, comprising: feeding the paper pulp from a medium- concentration pump into a medium- concentration mixer, adding in medium-pressure steam and oxygen gas and mixing uniformly, entering in the upflow towers, passing through tower-bottom distributor and upflowing at the same speed, discharging the paper pulp from the tower top, entering in a pressurizer and obtaining the same pressure as the outlet pressure of the medium-concentration pulp pump , then entering in the other medium-concentration mixer and mixing with the charged medium- pressure steam and oxygen gas, then entering from the tower bottom into the other upflow tower, passing through the other tower- bottom distributor and upflowing at the same speed, diluting by the tower- top diluting water, spraying into a spray pot, and pumping by pulp pump into a vacuum pulp washer for washing. And it adopts a pressurizing pump to connect two upflow towers in series, largely raising the lignin eliminating ratio in the oxygen gas bleaching stage and reducing the production cost. And it is especially applied to the oxygen gas-bleaching production of medium-concentration nonwood paper pulp.

Description

technical field [0001] The invention relates to a pulp bleaching method in the pulp and paper industry, in particular to a medium-consistency pulp oxygen bleaching method for wood and non-wood pulp with stable pressure and double upflow towers, which can be applied to the production of pulp oxygen bleaching with a daily output of more than 50 tons system. Background technique [0002] The existing medium-consistency pulp oxygen bleaching method in my country mainly uses a single upflow tower bleaching method, and can only be used for wood pulp. The delignification efficiency of this method is low, no more than 38%, but the proportion of oxygen consumption is large, resulting in the following problems in the pulp bleaching production system of my country's pulp and paper mills: [0003] (1) Due to the low delignification rate, in order to bleach the pulp to a certain degree of brightness, more bleaching agents and bleaching aids must be added in the subsequent bleaching stag...

AI Technical Summary

Problems solved by technology

The delignification efficiency of this method is low, no more than 38%, but the proportion of oxygen consumption is large, resulting in the following problems in the pulp bleaching production system of my country's pulp and paper mills:

In addition, chlorine dioxide bleaching will also produce a small amount of toxic and harmful organic chlorides, which will increase the degree of environmental pollution. At the same time, the high cost of chlorine dioxide production will greatly increase the cost of bleaching.

[0005] (3) Due to the insufficient mixing and reaction of oxygen and pulp, and the upflow velocity of oxygen is greater than the upflow velocity of pulp, oxygen is easy to accumulate at the top of the tower and remains in the pulp, which not only wastes oxygen, but also makes the subsequent medium-concentration pump run Unstable, even turbidity, affecting the bleaching effect of subsequent bleaching stages

[0006] (4) The use of single tower bleaching increases the relevant size of the tower equipment, increases the building area and height of the plant, and increases the investment cost

[0008] (1) Higher requirements are put forward for the outlet pressure of the medium-consistency pump, which must reach more than 1.2Mpa, which increases the design difficulty and investment of the medium-consistency pump

[0009] (2) In order to guarantee 2 # To increase the drift pressure of the flow tower, it must be increased by 1 # The drift pressure of the upflow tower makes 1 # The upflow tower and its delivery pipeline are in a higher pressure state, which puts forward higher requirements for its strength and airtightness, increases investment, and is also unfavorable to operation

[0010] (3)1 # The bleaching pressure of the upflow tower often exceeds the normal bleaching pressure of pulp, and the pressure fluctuation of the two towers also affects the process stability of the bleaching process, making it difficult to ensure the stable strength of pulp fibers, especially not suitable for non-wood pulp bleaching