The CTMP processes provide excellent bulk properties of paper at a high production capacity. The key sub-processes in CTMP pulping cover all the way from chip preparation, high-consistency refining, steam recovery, fractionation, treatment of long fiber fraction, bleaching and dewatering to pulp storage prior to papermaking process or drying and baling for market pulp. The use of CTMP pulps is continuously spreading into new end-use applications and combinations. At the same time, new and better process technologies and equipment for Bleached Chemi-ThermoMechanical Pulp (BCTMP) applications are being developed.
HT-CTMP, is a further development of the traditional CTMP production process. In the CTMP production process, wood chips are first impregnated with chemicals (sulfite and/or sodium hydroxide) and preheated at 90 to 150 °C to help soften the adhesive material (lignin) between the fibers. The chips are then refined mechanically in the pressurized refiner to produce pulp. The HT-CTMP process uses higher temperatures of 150 to 180 °C during this stage. This softens the lignin even more, allowing the fibers to be separated more easily. The result is a pulp with fibers that are more intact and have a very low shive content (fewer bundles of fibers). The binding quality of the pulp is slightly reduced, but the bulk is greatly increased. As it is easier to separate the fibers, the total energy consumption of the refining process is reduced.
TMP (thermomechanical) pulping processes provide excellent strength related properties of paper at a high production capacity. The key sub-processes in TMP cover all the way from chip preparation, high-consistency refining, steam recovery, fractionation, treatment of long fiber fraction, bleaching and dewatering to pulp storage prior to papermaking process or drying and baling for market pulp. TMP process can consist of single stage, two or three refiners in a series in one production line supplying paper machine, and the TMP pulp is dewatered and stored before papermaking.
NSSC (Neutral Sulfite Semi Chemical) pulping is a type of semi-chemical pulping process to produce unbleached pulp at yields of around 80%. Hardwoods are normally used as raw material and the produced pulp is mainly used for production of corrugating medium (fluting). Chips are impregnated with sulfite and carbonate at neutral pH, cooked for about 30 minutes at around 170-180 °C, defibrated to coarse pulp in a refiner, washed and finally refined to obtain an optimum combination of strength and stiffness. The total specific energy consumption in defibration and refining is normally less than 200 kWh/t. The spent liquor is normally sent to a kraft mill for recovery of chemicals and heat (cross-recovery).