APMP is short for Alkaline peroxide mechanical pulp. It uses alkaline peroxide as an oxidizing agent to carbonylate lignin. As a result of carbonylation, lignin with a carbonyl group can be combined with hydrogen bonding to enhance the bonding force between fibers. When the chips are treated with an oxide, the lignin is softened, and fibers are easy to be separated. In the refining process, the alkaline peroxide is simultaneously subjected to a bleaching reaction.
APMP pulping is a clean pulp production process with high yield, low pollution, and no sulfide production. Although the APMP pulping process is developed from the BCTMP and CTMP pulping processes, the APMP process and the CTMP process are different in various aspects, such as the pulping mechanism, so the production process, the impregnation conditions, the chemicals, the severity of the reaction, the refining method, etc.
As a paper pulper machine manufacturer with 20 years’ experience, CNBM can supplies various paper pulp making machines, such as digester, twin roll press, blow tank, disc filter, single screw press, and etc.
APMP pulping principle
he most important feature of APMP pulping is the combination of pulping and bleaching, and the bleaching process is completed while pulping. The pulping principle of APMP is the result of the interaction of hydrogen peroxide and sodium hydroxide. The chemical reaction mainly occurs in the pretreatment process, and the alkali reacts with the hemicellulose of the wood chips, and the fibers are separated from the primary wall and the secondary wall. A large number of studies have shown that sodium hydroxide plays many roles in the pre-impregnation process. It ensures that the pretreatment liquid has certain alkalinity to promote the hydrogen peroxide to remove the oxygen ions, fully exert the bleaching effect of hydrogen peroxide, dissolves certain extracts and hemicellulose in wood, and dissolves small molecular weight lignin.
How to optimize APMP pulping?
- Improve the yield of wood chips
In the APMP pulping process, large and thick slices contain more knots, which will change the density of wood and increase the energy consumption of extrusion. The smaller wood chips contain more impurity and extracts. The content of unground material is high and the whiteness is lowered. For this purpose, the chip preparation system has been modified, focus on the chipper, the crusher and the chip screen. After the transformation, the large pieces, thick pieces and small pieces of the wood chips were greatly reduced, and the pass rate of the wood chips was increased from 81% to over 90%.
- Improve the compression ratio of wood chips and screw extrusion
The penetration of the chemical solution largely depends on the air content and the content of harmful substances in the wood chips during the immersion, at the same time, cracking caused by the extrusion and pressure release of the wood chips and the degree of cracking are also related. The effect is related to the compression ratio and the number of extrusions. Studies have shown that the compression ratio of the wood chip extruder is increased from 4:1 to 6:1, and the running load is increased from 70%-80% to 75%-85%, which improves the extrusion effect and thus effectively Improved impregnation efficiency.
- Optimize the screening process to improve the screening efficiency
Reduce the width of the screen from 0.45mm to 0.30mm; appropriately reduce the slope of the corrugated surface in the screen and optimize the gap between the rotors; optimize the screening parameters, including pulp concentration and flow, pressure difference between inlet and outlet, load, slagging rate, etc.; master the dilution of white water in the intermediate washing tank and the submerged pulp pool, obtain a balanced and uniform pulp concentration and make the pulp throughput of the second-stage mill and the pressure screen under conditions of equilibrium, the fiber bundle content in the pulp is reduced, and the screening efficiency is improved.
The presence of fiber bundles in high-yield pulp can cause many paper diseases, such as coating scratches, bright spots, fish eyes, etc. These factors previously limited the high yield pulp to be applied in a wide range of high-grade papers. In the past few years, the increase in high-yield pulp quality mainly profits from advances in screening technology, resulting in a reduction in fiber bundles in a high-yield pulp. The pressure screen is one of the most important equipment in high-yield pulp quality control. For high-yield hardwood pulp, it is possible to use a 0.15mm or even 0.1mm refined seam screen.
- Strengthen the pulp washing
Since the high-yield pulp contains a large amount of anionic trash, the pulp washing process before papermaking is very important to reduce the negative effects of the anionic garbage for a paper machine, and the bad effects from residual additives, such as poor sizing effect and cation retention, the amount of filter aid is increased. Adding a concentrating squeeze after rinsing is very effective in reducing anionic trash and saving water.
Through the above measures, the optical index and physical strength index of poplar APMP pulp have been greatly improved. The consumption of chemicals has decreased from 8%-9% in the initial period before optimization to 5%, and H2O2 has decreased from 8% to 4.5%. The APMP pulp quality can meet a variety of requirement of medium and high-grade paper.