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There are described individual technological knots in the stock preparation line for the production of deinked pulp „DIP“ usable at the production of printing or sanitary papers. Waste papers ONP, OMG or OFW are mostly used as the raw material but it is also possible to process untraditional pulps as papers with increased wet strength and laminated papers of Tetrapack type. The line comprises pulping, cleaning and screening - removing of all kinds of impurities, flotation and wash deinking, wash water purification and sludge thickening. The block diagram shows clearly the arrangement of the line:
Fig. 1: Pulping and coarse pre-screening of waste paper
Waste paper in bales free from wires is fed into the vertical pulper VV, where is pulped periodically at a consistency of 8 % up to 12 % in the circulating water from the boiler. The pulper VV is also dosed with auxiliary chemical agents for a flotation deinking. The impurities from the pulper are discharged into the dewatering drum OBN and liquidated.
Coarse pre-screening at a consistency of 4 % in high-density stock cleaners VS and a two-stage screening in separators VDT and VSV combined with an efficient deflaking and rejects washing. The rejects are dewatered in the vibrating screen VP and liquidated.
Line characteristic
- automated operation of the line when the operator only controls pulping and liquidates the waste
- high flexibility of possibilities of the raw material furnish
- environmentally sensitive process when only very clean rejects nearly without fibres are discharged
Fig. 2: Desanding and fine stock pre-screening
Two-stage desanding of the stock at a consistency of 2 % and 1 % in cleaners HL and VU. Slotted pressure screens STU follow when the accepts from the 1st stage are directed into the thickener OK for washing meanwhile the accepts of the 2nd stage recirculate. The rejects of the fine screening are removed into a common chest of rejects and sludges. The polluted wash water of the thickener OK is led into the microflotation purifying plant. The installation of a dispersing refiner DD we recommend only for stocks with a high content of heavy pulpable pieces of paper and when we want to minimize the volume of rejects. The thickened stock is storaged and homogenized in the chest with a feeding capacity of minimum of two hours. In this way the continuous running of the following technological equipment is guaranteed even at short downtime of the preceding line.
Line characteristic
- fully automated operation of the line with a programmed control of the technological parameters
- efficient removal of all kinds of larger impurities (more than 0,25 mm)
- washing of printing inks, filling agents and zero fibres together with the thickening of accept
Fig. 3: Flotation deinking station
A precize parameters control and homogenization of the stock pumped at a consistency of nearly 1 % into the 1st stage flotation cells FC at a parallely dosing of additional flotation chemical agents. In the 1st stage of cells FCa multiple deinking is performed. The deinked stock flows from the 1st stage into the accept collecting chest, the sludge separated by flotation is led into the 2nd stage of cells FC. Here it is distributed into the accept recycling in front of the 1st stage and into the concentrated sludge being removed into the sludge and rejects tank (on the filter press).
Line characteristic
- fully automated operation of the line
- simple but precise control of the operating parameters
- efficient separation of printing inks
Fig. 4: Final fine cleaning and screening, washing and thickening of stock
About 1 % consistency of the accept after the flotation deinking is optimal also for the following line: the fine cleaning and screening takes place firstly in the cleaners MOVI VO (1st stage) where heavy and light impurities are removed at the same time as well as the residual air from the flotation. The rejects are end-cleaned in the 2nd stage cleaners: heavy impurities are removed in the cleaners VU, the light one in the reverse cleaners VTV. Both rejects from the 2nd stage are led into the sludges and rejects chest. The accept from the cleaners MOVI VO is led into the pressure screens STU working mostly in a three-stage arrangement. The accept from 1st and 2ndstage screens STU flows for washing and thickening into the thickener OK and further into the accepted stock (DIP) storage chest. The accept from the 3rd stage screen STU recirculates back in front of the 2nd stage, the rejects flow into the sludges and rejects chest.
Line characteristic
- fully automated operation of the line
- efficient separation of all sorts of residual impurities inclusive of the problematic stickies
- washing of printing inks, filling agents and microstickies together with the thickening of accepts
- high effectivity also at a relative low volume of rejects
Fig. 5: Purifying of wash waters, thickening of sludges and rejects
Wash waters of both thickeners OK and the filter press VX are entrapped in a chest from where they are fed into the microflotation purifying station MF. The purified water is returned into the technological line, the sludge separated by flotation is led into the sludges and rejects chest. The water balance in the stock preparation line is of gentle deficit so that the purified water chest must be refilled with a volume of nearly5 - 10 l/kg of product by complementary water (e.g. of the PM). The purified water chest should have a volume adequate to at least a two-hour capacity to enable a temporary assistance in case of short timedown of some stock preparation knots and their running before start of the PM without demands on refilling of the missing water or discharging of the water excess. All sludges and fine rejects from the line are collected in the homogenizing chest and from there they are fed with addition of the flocculantion agents in the wireband filter press VX, where they are thickened to a dry substance of about 45 - 50 %.
Line characteristic
- fully automated operation of the line
- module unit-built construction of the microflotation station MF
- highly environmentally sensitive operation
- minimum consumption of flocculantion agents