SimplyOne concept in details
Design bases
Jouko Hautala’s design bases from long experience which is entirely benefitted in SimplyOne concept is in details as follows:
1. The cardboard needs time for desintergration
Everyone who makes cardboard from recycled fiber wants the coarse reject from pulping, most of which is plastic, to be clean and fiber-free. OCC, MOW, UBC, CUPSTOCK and TETRAPAK raw materials contains a wide range of cardboard that is either easily degradable or difficult to degrade, which requires a long time to degrade. In the conventional fiberline, the disintegration time is usually too short for wet-strength cardboard, which means that non-disintegrating pieces of cardboard with the plastic end up in the reject washing. In reject washing, generally in a reject drum, these cartons do not disintegrate but come through as such. In SimplyOne concept pulping, the board is given enough time to disintegrate (up to one hour), so the coarse reject is obtained clean out. In addition, the disintegration of the board is ensured by a rotor rotating at the bottom of the reject washer.
2. Less pumps and energy
The conventional line uses a lot of pumping energy to transfer this coarse reject from the first pulper to the secondary pulper and from there on to the high reject drum. There are special reject pumps on the market and / or a closed secondary pulper has enough power to lift this reject into the reject drum. In SimplyOne concept pulping, this coarse reject transfer forward with free gravity energy.
3. Less wearing and maintenance
With the coarse reject, a lot of sand, metal and glass also flows into the reject drum. The holes in the reject drum are usually 8-15 mm in diameter. From these openings, those small wearing particles are returned back to the pulper to wearing the rotor and screen plate. In the SimplyOne reject washer, the screen plate has slots of 2 mm, so only small particles can get back into the pulper in addition to the fiber. That screen plate is kept clean by a rotating rotor, as in pulpers.
4. Less machinery and investment costs
In the screen plates of the primary- and secondary pulpers of the OCC line, the holes are usually 10 mm or even 20 mm. From these openings, a lot of heavy reject enters the pulp, which is usually removed with HC cleaners that require pumping energy. There are also so many impurities in the pulp that coarse screening is required so that the pulp is clean enough for cleaning and fine screening. In SimplyOne pulper, the openings in the screen plate have slots width of about 2.5 mm. This narrow slots handle the functions of HC cleaners and coarse screening. This way, the SimplyOne line does not need separate HC cleners or coarse screening at all. As such, the pulp from the pulpers is suitable for cleaning and fine screenng.
This lack of HC cleaners and coarse screening in the SimplyOne concept brings the greatest investment, energy and maintenance savings to the OCC line.
5. Improved pulp quality
The biggest impurity in OCC raw material is plastic, which comes in various forms. There are small and large pieces as well as long and short pieces. The unfortunate feature of pulper is that those larger and longer plastics tend to rotate near the rotor according to the laws of physics, and the long plastics form ropes into the pulper. The reject pipe into the secondary pulper starts from the wall of the primary pulper. So the plastic content of coarse reject flow is slightly less than in the primary pulper. Due to these factors, the pulper has to be emptied of plastics from time to time. In SimplyOne pulpers, we have strived for a solution where the reject leaving the pulpers contains at least as much plastic as the pulper enters. This reduces the need to empty pulper.
6. Worse raw materials can also be utilized
The volume of the secondary pulper of the conventional OCC line is small relative to the primary pulper. As a result, the raw material can contain only about 5% coarse reject. In the Simply One Concept, as the number of rejects increases, the volume of the secondary pulper and the reject washer is increased. The proportion of material thus rejected can be up to 50%.