Cellulose refining lines

We offer a description of two varieties of basic types of cellulose refining lines - a refining line for cyclic refining and a refining line for continuous refining.

1. Pulping in a vertical pulper working usually periodically.
2. Continuous refining line with screening of heavy impurities and consequent refining in single and double disc refiners.
3. Cyclic refining line with a laminar refining chest and with refining in single or double disc refiners.

Pic. 1: Continuous refining line

Continuous refining line - characteristics

• we recommend continuous refining for refining with a high flow capacity and for relatively low demands on the required increase of refining grade,
• reliable failure-free operation in an automatic mode when the operators only provide sufficient amount of the pulp; everything else is done automatically,
• a wide scale of refining fillings enables to achieve desired refining characteristics (shortening, fibrillation, dispersion, etc.) with a relatively low power consumption.

Continuous refining process automation

• LIA level-indicator inform the operators about the level condition in the chests,
• NIC consistency indicator measures the pulp consistency and maintains it on a constant level that is the best for consequent refining (usually 3,5 to 5 %),
• FIC flow-meter with a control valve for constant flow setting,
• °SRI refining grade indicator measures ºSR of the refined material.

The automatic control ADAM-K controls each refiner with regards to ºSRI or keeps a constant load of each refiner that was chosen by the operator.

Cyclic refining line - characteristics

• we recommend the periodical refining with a low flow capacity and for relatively high demands on the required increase of refining grade,
• reliable failure-free operation in automatic mode when the operators only provide sufficient amount of the pulp; everything else is done automatically,
• a wide scale of refining fillings enables to achieve desired refining characteristics (shortening, fibrillation, dispersion, etc.) with a relatively low power consumption.

Cyclic refining process automation

• LIA level-indicators inform the operators about the level condition in the chests, LIA in C2 chest controls the automatic filling and emptying (by controlling pneumatic gate valves).

The automatic control controls the duration of the refining cycle and facilitates the load setting of each refiner with a possibility of its gradual automatic lowering during each cycle.

Liner production from 100 % OCC/OMP, 500 t/day

Pic. 3: Pulping

Pulping line - characteristics

• automatic operation with minimal operational requirements,
• efficient separation of all types of impurities,
• possibility to pulp paper that is pulpable with difficulty and unpulped bales up to 1 t,
• reliable failure-free operation with low operation and machine requirements,
• very clean rejects with almost no fiber loss, dryness around 50 %
• specific energy consumption is between 25 and 26 kWh/t, pumps and agitators included.

Pulping operation

The operators place the bales onto a conveyor one after the other (no gaps) and cuts the wires.

• LICA level-indicator maintains the constant stock level in the pulper by releasing water through the control valve,
• NICA consistency indicator measures the pulped stock consistency and keeps it constant by controlling the waste paper bales conveyor speed,
• SIC frequency converter of the conveyor motor speed.

Cleaning system = Periodical reject separator (PSN-30), Reject dewatering drum (OBN-10), Reject dewatering press (OLV-600), pneumatic gate valves, pump of C2 chest and rejects conveyors work in an automatic unattended mode.

During the cleaning of the whole Low-consistency vertical pulper (LCV) chest, the operator starts with watering and washing down the impurities in LCV and then they let the impurities out through pneumatic gate valve DN-300 into C1 chest. A possible big tangle of impurities is taken out of the LCV by a Motor polyp grab (MPD-06-150). The impurities from C1 are automatically released through the pneumatic gate valve DN-400 into Reject dewatering drum (OBN-100). The whole cleaning process lasts approximately 15 to 20 minutes.

Discharging of the pulp is continuous, through HD-cleaner
VS-50-A cleaner into C3 chest. Heavy impurities from cleaner VS are released periodically into a sand trap (SP-250-10) which makes them thicker and takes them into a reject container.

Primary coarse screening of fine and heavy impurities

Heavy impurities screening line – characteristics

• two-level arrangement of HD-cleaners SVS-25 with the sand trap OP-25,
• I° HD-cleaner SVS-25-O works at usual consistency from 4 to 4,5% that is necessary for following screens,
• high efficiency is provided by a continual outlet of 8 to 12% of the rejects into II°,
• II° HD-cleaner SVS-25-A works at consistency up to 2% which ensures its high efficiency,
• II° HD-cleaner SVS-25-A and its pump are protected from heavy impurities by the sand trap OP-25,
• SVS cleaners work with a very low pressure loss from 50 to 100 kPa, the consequence of which is a low energy input of pre-arranged pumps and long service life of all parts of the line,
• the heavy rejects are centrally dewatered in a sand trap SP-250.

Advantages when compared to the classical one-level HD-cleaners arrangement

• considerably higher sorting efficiency,
• longer service life and lower maintenance requirements for the line.

Fine impurities screening line – characteristics

• combined screening in a pressure screen STU-201 and in separators VDT-40 and VSV-30 with the Papcsreen with bores of a 2,2 mm diameter links the advantages of both concepts,
• installation of the STU pressure screen in I° ensures a high flow input with a low energy consumption,
• VDT and VSV separators' high deflaking efficiency in II° and III° enables a reliable line operation with no stuffing even when processing considerably coarse pulped materials,
• fully automatic operation; possible to program a deflaking and washing effect in the final separator VSV; minimal fiber loss - clean rejects,
• the vibration screen or drum separator just dewaters a clean reject with almost no fiber, the reject then goes to a final thickening in a worm press OLV-600,
• environmentally friendly operation (the line rejects are thickened to approx. 50 % together with the pulper rejects, the rejects are clean with out fiber),
• low specific energy consumption (approx. 26 to 27 kWh/t) including the pumps and agitators,
• thanks to a wise LC-1 and 2 level chest system, the level regulation is not necessary; therefore constant pump flows are secured,
• all line nodes work with constant flow and pressure conditions thus the consequent parameter regulation is not necessary; the line works continuously and the parameters are settled constantly and indicated only for control reasons (PI, FI),
• in case of an STU or VDT screen blockage, the pressure difference raises which switches on the emergency automatics; in 30 to 40 seconds it ensures the screen regeneration and continuous separator operation without any line operation failures or necessary intervention from an operator.

Fine slot stock screening

Pic. 5: Fine slot stock screening

Fine screening line – characteristics

• a slot screening of a middle consistency; two fractions out of one raw material: the stock for a top layer = excellent purity and homogeneity; the stock for a bottom layer = sufficient purity and homogeneity; both fractions have approximately the same fiber length and refining grade. It is not necessary to thicken a bigger part of the stock,
• an alternative for a long fraction refining (Russian or American OCC processing),
• during the last screening in pressure screen (STU-081-L), the stock is released from sand in LD-cleaner SVU-25-M; the sand is dewatered in the central sand trap SP-250-10,
• adjustable deflaking of the reject from STU-201 in D30-D ensures a reject minimization and reliable operation of the last STU-081-L step even when processing the problematic (wet-strength) OCC papers,
• environmentally friendly operation - the STU-081-L reject is pressed in a belt press VX-15 for approx. 35% of a dryness and the fiber loss is 1% at most out of the resulting line capacity (500 t per day),
• low specific energy consumption:
• 29 to 30 kWh/t including pumps and agitators,
• 20 to 22 kWh/t refining - when installed.

Fine screening process automation

• no consistency regulation is necessary in the line as the stock comes out of a pre-screened stock chest with a relatively stable consistency 3,2 to 3,4% and the following technology is due to the consistency self-regulated, since the line is designed so that all chests and piping lines have the best consistency when the line is set up,
• all line nodes run with practically constant flow and pressure conditions, therefore it is not necessary to “post-regulate” the parameters during operation - the line runs with a constant parameter set-up which is indicated only for control reasons (PI, FI),
• in case of any STU screen blockage, there is an increase in a pressure loss (PdIA) that switches on the emergency automatics; in 30 to 40 seconds it ensures the screen regeneration and continuous separator operation without any line operation failures or necessary intervention from an operator.
  

Note: refiners DD are installed only for the raw materials that need to increase the degree of grinding (AOCC, Rocc).

Mixing and approach flow system of PM

Pic. 6 - Mixing and approach flow system of PM

Line charasteristics

• approach flow system for a top and bottom layer share
• a double step blending concept. The first mixing pump pumps the stock through a multi-step cleaner system SVO-25 and SVU-25-MK, the second one pumps the stock through the pressure screen STU into the headbox.
• cleaner SVU-25-MK rejects are dewatered in the sand trap SP-250-15 in the bottom layer. The rejects from the pressure screen that have a guarding function only (the stock is screened perfectly in the stock preparation line) go to the bottom layer as well. There they are screened on the secondary pressure screen STU-081. STU-081 reject recycles back to the SPL for the bottom layer together with the paper machine broke.
• specific energy consumption is approx. 51 kWh/t including the pumps and agitators.

Ecological and energetic line evaluation

According to various OCC and OMP norms the content of impurities should not overreach 2%; however, the practice shows us that it is better to draw up the reject management for at least a double contamination. The frame of the described line and the subsequent waste balance come from this realistic assumption.

Ecological characteristics of the line

• compactness and a high level of the dryness in the waste, low fiber loss,
• elimination of unsolved waste disposal (into the sewage) and of waste that is not thickened properly (liquid waste), all types of waste can be transported in a normal container,
• insignificant fresh water consumption (for sealings only), fully closed technological wastewater recirculation.

Energy characteristics of the line

• low energy consumption, a detailed overview follows.

Beverage packagess processing

Beverage containers, a TetraPak type, with no additions of other waste paper or other contaminations serve as a raw material. The containers are made of polyethylene and aluminium foils (30 to 40 %) and of cardboard from good primary fibers. The line output is high quality screened stock that is usable for a paper production, and clean foils mixture with fiber content approx. 1 %. The foils are raw material suitable for PET+AL recycling.
When the material is contaminated by other waste paper, the line output is formed again by clean primary fiber; however, the foil mixture is contaminated by materials disabling easy recycling. Consequently, those used as energy source or cement addition. The line is easily modifiable for 15 to 100 t per day capacity.

Line characteristics

• pulping in a primary HD-pulper MCV-30-T with high tearing effect,
• washing (pulped stock and foils separation) in a secondary pulper LCV-14-T,
• final washing and foil dewatering from the pulper in a drum OBN-10,
• heavy impurities screening in HD-cleaner SVS-25-M,
• rest of the foils separation in VSV-30 separator and their dewatering,
• refining of the slightest impurities in slot screens STU-081 and their dewatering,
• screened stock dewatering in FOK-1500 filter,
• recycled water in two circuits: contaminated (diluting) and filtered (washing and operating),
• pulping, raw material manipulation, products and wastes are handled by an operator, other parts of the line are fully automatic under operator's supervision,
• the mass yield is approx. 98%, 1 to 2% of the reject leaves the line (from SVS and STU)
• energy consumption (SEC) is from 270 to 280 kWh/t (including pumps and agitators).