The straw ammonium sulfite pulp is completely free from chlorine-based bleaching agents
(3) Conservation of papermaking fiber raw materials. The ammonium hydroxide pulping process causes less damage to fiber raw materials during the cooking stage compared to the sodium hydroxide pulping method; this makes it more suitable for straw-based pulps, as it helps increase the crude pulp yield, conserve raw materials, and reduce costs.
(4) The slurry exhibits good strength. Within the high-yield range (70%), the ammonium hydroxide process slurry has significantly higher strength than the alkali process slurry at the same harvest rate. When the hardness of the raw slurry is comparable, the ammonium hydroxide process slurry has slightly higher strength than the sulfate process slurry.
1.2.4 Challenges associated with ammonium-based pulping process
Currently, the sub-ammonium pulping process faces several challenges: the yield per unit volume of pulp is lower (i.e., the ball charging rate is reduced); at the same cooking pressure, the cooking time is longer; and it is more difficult to achieve high-whiteness pulp. Additionally, this method causes more severe equipment corrosion compared to the alkali pulping process; it is classified as Level V, "Moderately Corrosion-Resistant Category." When steam boilers fabricated from Type A3 steel are used in the ammonium pulping process, they corrode by approximately 0.3–0.5 mm per year. Numerous measures have been implemented to mitigate the corrosion caused by the sub-ammonium process on the steam boilers. These include: installing reinforcing pins inside the steam boilers; maintaining the pH value above 7 (at the endpoint); reducing steam release rates; adding quinone; injecting ammonia water into the shaft ends; adding urea at the spiral pre-soaking machine (at a dosage of 2% relative to the cellulose content); and successfully applying various buffering agents—such as caustic soda, lime, ammonium bicarbonate, magnesium oxide, and ammonium phosphate—to the sub-ammonium pulping process.
