A method for reducing the amount of hydrogen peroxide in chemical mechanical pulp

Abstract

A method for saving hydrogen peroxide in chemical mechanical pulping, the invention relates to the technical field of papermaking, and comprises pre-steaming, one-stage wood chip washing, two-stage wood chip washing, spiral dehydration, steam bin retention, MSD, pre-preg, reaction bin retention, high-concentration grinding, chemical mixing, bleaching, one-stage spiral pressing, two-stage spiral pressing, low-concentration grinding, pressure screening, multi-disc filtration and three-stage spiral pressing steps; wherein, the bleaching filtrate of the one-stage spiral pressing and the two-stage spiral pressing enters the clear / turbid filtrate pool; fresh alkali solution is added in the pre-preg step; the characteristic is that the clear / turbid filtrate pool is connected to the water inlet pipe of the pre-preg section, that is, the bleaching filtrate in the clear / turbid filtrate pool is reused in the pre-preg section. The bleaching filtrate is reused in the pre-preg section, and the supplemented fresh alkali solution is used to fully utilize the hydrogen peroxide residue in the bleaching filtrate and the remaining NaOH, Na2SiO3 and DTPA and other chemicals in the filtrate, thereby reducing the chemical consumption in the bleaching section and reducing the cost.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a method for reducing hydrogen peroxide in chemical mechanical pulp. Background Art

[0002] The comprehensive water consumption per ton of pulp and paper in my country's papermaking enterprises is relatively high. According to the requirements of the clean production standards, the comprehensive water intake per ton of pulp and paper is required to be less than 50 tons. At present, except for a few enterprises or some production lines in my country that have reached the international advanced level, the average comprehensive water intake per ton of pulp and paper in most enterprises is still at a high level of 103 tons. Reducing water resource consumption is a need for clean production in my country's papermaking industry and a need to achieve my country's strategic goals of energy conservation and emission reduction. The key production part for paper mills to reduce the use of fresh water is the bleaching section. At present, the filtrate of the bleaching section mainly returns to the bottom of the bleaching tower, and the other part goes to the wood chip washing group and is discharged after washing, which reduces the utilization rate of the bleaching filtrate. Summary of the invention

[0003] The purpose of the present invention is to provide a method for reducing hydrogen peroxide in chemical mechanical pulping in view of the defects and shortcomings of the prior art, and to reuse the bleaching filtrate in the pre-preg stage, and to make full use of the residual hydrogen peroxide in the bleaching filtrate and the remaining NaOH and Na 2 SiO 3 And DTPA and other chemicals, reduce the chemical consumption in the bleaching stage and reduce costs.

[0004] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: it includes pre-steaming, one-stage wood chip cleaning, two-stage wood chip cleaning, spiral dehydration, steam bin retention, MSD, pre-preg, reaction bin retention, high-concentration grinding, chemical mixing, bleaching, one-stage spiral pressing, two-stage spiral pressing, low-concentration grinding, pressure screening, multi-disc filtration and three-stage spiral pressing steps; wherein, the bleaching filtrate of the one-stage spiral pressing and the two-stage spiral pressing enters the clear / turbid filtrate pool; fresh alkali solution is added in the pre-preg step; the clear / turbid filtrate pool is connected to the water inlet pipe of the pre-preg section, that is, the bleaching filtrate in the clear / turbid filtrate pool is recycled to the pre-preg section.

[0005] Preferably, after the spiral dehydration, the wood chips enter the steam bin, the water suspension is intercepted by the arc screen, the water enters the washing tank for cleaning, and then is transported to a wood chip cleaning section for recycling.

[0006] Preferably, the pressure-screened sludge is concentrated by a curved surface concentrator and then enters a sludge tank. The concentrated sludge is then pumped into a sludge mill for refining by a sludge pump and enters a sludge tank. The sludge is then pumped into a sludge screen by a sludge pump, and the good sludge is sent to a multi-disc filter. The sludge is returned to the curved surface concentrator, mixed with the pressure-screened sludge and concentrated again.

[0007] Preferably, the pulp produced by the three-stage screw pressing enters the pulp tower.

[0008] Preferably, the residence time of the reaction chamber is 20-30 min.

[0009] Preferably, the temperature of the reaction chamber is 50-80 degrees Celsius.

[0010] Preferably, the steam bin residence time is 20-30 min.

[0011] Preferably, the temperature of the steam bin is 90-95 degrees Celsius.

[0012] Compared with the prior art, the invention has the following beneficial effects: the invention provides a method for reducing hydrogen peroxide in chemical mechanical pulp, reusing the bleaching filtrate to the pre-preg stage, using the supplemented fresh alkali solution, and making full use of the residual hydrogen peroxide in the bleaching filtrate and the remaining NaOH and Na 2 SiO 3 And DTPA and other chemicals, reduce the chemical consumption in the bleaching stage and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of the present invention.

[0014] Figure 2 This is a test data table showing the effect of recycling the white filtrate to the pre-preg stage on whiteness in the feasibility experiment of the present invention.

[0015] Figure 3 This is an experimental data table showing the effect of recycling the white filtrate to the pre-preg stage on the performance of the slurry in the feasibility experiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. The preferred embodiments in the description are only used as examples, and all other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, this specific implementation adopts the following technical scheme: it includes pre-steaming, one-stage wood chip washing, two-stage wood chip washing, spiral dehydration, steam chamber residence for 20 minutes, temperature is 90 degrees Celsius, MSD, pre-preg, reaction chamber residence for 30 minutes, temperature is 55 degrees Celsius, high-concentration grinding, chemical mixing, bleaching, one-stage spiral pressing, two-stage spiral pressing, low-concentration grinding, pressure screening, multi-disc filtration and three-stage spiral pressing steps, and finally the pulp enters the pulp tower; wherein, the bleaching filtrate of the one-stage spiral pressing and the two-stage spiral pressing enters the clear / turbid filtrate pool; fresh alkali solution is added in the pre-preg step; the clear / turbid filtrate pool is connected to the water inlet pipe of the pre-preg section, that is, the bleaching filtrate in the clear / turbid filtrate pool is reused in the pre-preg section;

[0018] After spiral dehydration, the wood chips enter the steam bin, the water suspension is intercepted by the curved screen, the water enters the washing tank for cleaning, and then is transported to a wood chip cleaning section for recycling;

[0019] The sludge from pressure screening is concentrated by the curved surface concentrator and enters the sludge tank. The concentrated sludge is then pumped into the sludge mill for grinding by a sludge pump and enters the sludge tank. The sludge is then pumped into the sludge screen by a sludge pump. The good sludge is sent to the multi-disc filter and the sludge is returned to the curved surface concentrator to be mixed with the sludge from pressure screening and concentrated again.

[0020] Compared with the prior art, the invention has the following beneficial effects: the invention provides a method for reducing hydrogen peroxide in chemical mechanical pulp, reusing the bleaching filtrate to the pre-preg stage, using the supplemented fresh alkali solution, and making full use of the residual hydrogen peroxide in the bleaching filtrate and the remaining NaOH and Na 2 SiO 3 And DTPA and other chemicals, reduce the chemical consumption in the bleaching stage and reduce costs.

[0021] Feasibility experiment:

[0022] 1. Comparison of chemical consumption before and after the white filtrate is recycled to the pre-preg stage Figure 1 ,from Figure 1 It can be seen that after being recycled to the pre-impregnation stage, the amount of hydrogen peroxide used was reduced by an average of 15.1%, the amount of pre-impregnation alkali used was reduced by an average of 8.26%, the bleaching chelating agent decreased slightly, and no adjustment was made to other auxiliary chemicals.

[0023] 2. After the white filtrate is recycled to the pre-preg stage, the test data on the effect on whiteness are as follows: Figure 2 , it can be seen from the test data that the whiteness of the bleaching tower outlet after reuse is significantly improved, with an increase of 6.12%, and the pulp is also improved. The specific whiteness test method is as follows: weigh 4 concentrations of pulp, put it into a 1000ml measuring cylinder to loosen it; pour the loosened pulp into an 80-mesh sieve and stir it evenly by hand; take the sieve frame out of the water steadily, put wood pulp paper underneath, and then take another piece of wood pulp paper and press it on the paper sheet from above, press it with your hand, take out the paper sheet, bake it in an oven at 150℃ for 30 minutes, and take the pulp paper off the wood pulp paper; use the ZB-B whiteness meter to fold the prepared sample in half, put it in the test area, press the measurement, display the measurement results, test the four sides, and take the average value.

[0024] 3. After the white filtrate is recycled to the pre-preg stage, the experimental data on the effect on the performance of the pulp are as follows: Figure 3 According to the tracking data, it can be seen that after reuse, there is little impact on the slurry tensile index, bulk, PCD, and COD. The bulk decreases slightly. This is due to the impregnation effect of NaOH in the reuse filtrate. Overall, there is no obvious adverse effect on the quality of the slurry.

[0025] For those skilled in the art, they can modify the technical solutions described in the aforementioned embodiments and make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reducing hydrogen peroxide in chemical mechanical pulp, comprising the steps of pre-steaming, one-stage wood chip washing, two-stage wood chip washing, spiral dehydration, steam chamber retention, MSD, pre-soaking, reaction chamber retention, high-concentration grinding, chemical mixing, bleaching, one-stage spiral pressing, two-stage spiral pressing, low-concentration grinding, pressure screening, multi-disc filtration and three-stage spiral pressing; wherein: The bleaching filtrate from the first and second stage screw pressing enters the clear / turbid filtrate pool; fresh alkali solution is added in the pre-preg step; the characteristic is that the clear / turbid filtrate pool is connected to the water inlet pipe of the pre-preg section, that is, the bleaching filtrate in the clear / turbid filtrate pool is recycled to the pre-preg section; after the spiral dehydration, the wood chips enter the steam bin, the water suspended matter is intercepted by the arc screen, the water enters the washing water tank for cleaning, and then is transported to the first wood chip cleaning section for recycling; the pulp residue screened by the pressure is concentrated by the curved concentrator and then enters The pulp enters the pulp residue tank, and then the pulp residue pump is used to pump the concentrated pulp residue into the residue mill for grinding, and then enters the pulp residue tank, and then is pumped into the residue screen by the pulp residue pump. The good residue is sent to the multi-disc filter, and the pulp residue is returned to the curved surface concentrator, mixed with the pressure-screened pulp residue for re-concentration; the pulp from the three-stage spiral pressing enters the pulp tower; the residence time in the reaction bin is 20-30min; the temperature of the reaction bin is 50-80 degrees Celsius; the residence time in the steam bin is 20-30min; the temperature of the steam bin is 90-95 degrees Celsius.

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