DE4206206C2 - Process for cleaning the rejects from deinking flotation - Google Patents

Description

In modern deinking plants, reject occurs at flotation levels which must be disposed of. With a consistency of 1.0 This so-called black water consists of up to 1.8% dry matter more than 98% from production water, which is reused could be det.

This dark hydrogen mixture is usually used today either led directly to the wastewater treatment plant to be together with the their operational wastewater to be cleaned, or it will by Pre-thickeners or centrifuges are thickened so that according to Pres with a dry matter content of around 50% for landfilling or burning is suitable.

The common treatment with the usual wastewater is problematic because of the high dry matter and COD Ge stop this sewage. The plant wastewater treatment plant will either overloaded very quickly or it must be very large from the start be dimensioned.

Centrifuges (see DE 26 10 581 B1) have relatively little Space requirements high investment and operating costs. The filtrate is usually loaded with solids and is not suitable for a return to production. The pre-thickening on In contrast, the sedimentation base requires a lot of space and Odor problems. Due to the long stay the water overhang is no longer fresh and can for quality reasons mostly not easily in the Altpa reprocessing.  

DE 35 25 788 A1 is for the cleaning of especially in flotation plants with selective flotation a wastewater or sludge a flotation plant described in which by means of flocculation chemicals and a Saturation tank a total float is carried out to to produce recyclable backwater that is only one more way low solids content of impurities that it contains no significant impairment of the circulation of the Waste paper processing gives more.

On the other hand, in Ullmann's encyclopedia is the technical one Chemistry, 4th ed., Vol. 6, Verlag Chemie, 1981, page 424, a Series of flotation devices described, including the so-called pressure relaxation flotation, which advantageously for cleaning waste water and sludge should be usable. Finally, DE 28 13 448 B1 describes a processing method for waste paper, at which is the one containing or from the flotation foam resulting wastewater cleaned in a flotation plant becomes.

The object of the invention is in a simple manner - without the great effort in terms of apparatus - perfect cleaning of the polluted flotation wastewater and a provision of relatively clean clear water through the here too effective depressurization flotation to effect it as To be able to use dilution water for the flotation plant.  

The discharge of this dirty water to the sewage treatment plant without return recovery and non-use as purified clear water in the Production contributes to a high specific wastewater at.

The use of pressure relief flotation for chemical-physical Kali treatment of the reject from the flotation stage does a good job by adding flocculants Cleaning the waste water with a Clear water quality that meets the requirements for Reuse in waste paper stock preparation without further fulfilled. The flotation consistency reaches one high degree of pre-thickening, and this is a direct feed to the following pressing stage (s) without further treatment or Thickening possible.

Experiences from experiments show that with an appropriate dosage of up to two components (while observing the required reaction times of the order of 30 to 60 seconds) and the addition of a compressed air / water mixture in the system (e.g. as a recycled part with a quantity from 20 to 30% of the total throughput of the system), the following values can be achieved:
Clear water: dry substance 50-300 ppm (controllable depending on the substance load of the system and the chemical dosage),
Flotate: 5-9% dry matter.

For many fabrics, it is a two-step addition of a poly To provide electrolytes, a cationi in the first stage shear and in the second stage an anionic polyelectrolyte is to be admitted. In some use cases, there is also a staged addition of a non-ionic polyelectrolyte recommended worth it.

The exact composition and amount of the polyelectrolytes must be adapted to the present case. As Substances to be flaked off always arise before Microflotation level.

The important thing here is:

• 1. If the dosage of only one polyelectrolyte meets the requirements for the purified water, the solution / the concentrate must either
  • a) are mixed directly into the pipeline in front of the flotation system so that the pipe section is sufficient for the flocculation (t = 30 · 60 seconds reaction time of the polyelectrolyte), or
  • b) be metered into a stirred reactor upstream of the flotation plant, which ensures the same reaction time as a).
• 2. If there is sufficient precipitation / flocculation with only two polyelectrolytes to be metered can be achieved can, 1a or 1b must be taken into account before finally just before the flocculated water enters the system of the second polyelectrolyte (2-5 mg / l), which in the generally responds quickly, is fed.

The air required to separate the flakes formed, which is released under pressure of 4 to 6 bar (proportion 20 to 30% of the total throughput of the plant) also occurs only at a short distance of approx. 0.5 m in front of the flotation tank into the inlet pipe.

For a better overview, only the most important parts of the system are shown in FIG. 1.

The waste paper is brought in bale into a pulper 1 , which is supplied with chemicals via a line 2 and with a container 3 with fresh water. The dissolved substance comes via pumps 4 and an intermediate container 5 into a hydrocyclone 6 , in which cleaning is carried out by centrifugal force.

From here, the fiber suspension is passed on to a cleaning and deflowering device 7 . A device such as that described in DE-OS 21 40 372 can be used for this purpose. The suspension then arrives again in a stripper 8 and a further hydrocyclone 9 .

After the hydrocyclone 9 , the fiber suspension flows into a multi-stage flotation plant 10 of a known type. In addition, 11 chemicals and a line 12 of dilution water are introduced into the flotation system 10 via a line. The fiber suspension cleaned in the flotation system 10 from dye particles and organic substances finally arrives via an intermediate bed 13 , a further hydrocyclone 14 and a pressure sorter 15 of a known type to a two-stage - also known - inclined sieve device 16 . At the same time, 17 dilution water is added via a line, so that the fiber suspension to be treated is diluted to about 0.7% consistency.

After the first dewatering stage through a sieve 18 , the fiber suspension is thickened to about 4% consistency. For this reason, an addition of dilution water is carried out again via a line 19 , so that the consistency decreases again to approximately 0.7%. Then 20 is drained on a second sieve. Depending on requirements, several such stages can be connected in series, with dilution water having to be added in an appropriate amount. Instead of the gradual addition of dilution water, the fiber suspension can also be diluted continuously. For example, several spray water pipes arranged above the screens 18 and 20 can be used for this purpose.

The fiber suspension thus freed from fillers (ash) and broken fibers then passes into an intermediate chest 21 , from where it can be conveyed to the usual treatment of the suspension.

The waste water obtained in the inclined sieve device 16 flows via lines 22 and 23 into an intermediate container 24 . The wastewater is pumped into a clarifier 28 from the intermediate tank 24 . Sedimentation takes place in the clarifier 28 , the sewage water passing through a clear water line 29 into an intermediate container 30 .

The sewage sludge is dewatered in a centrifuge 31 and the resulting clear water is fed back into the intermediate container 24 via a line 32 .

From the intermediate container 30 , the purified water is pumped back into the system via a return line 33 to the individual consumption points.

From the intermediate container 30 , other devices and secondary circuits, not shown, can also be supplied with clarified water.

As can be seen from the system described, there is a completely closed water cycle. It must only Lich the unavoidable water losses in small amounts via a fresh water line 34 , which opens into the container 3 , it is added.

The system described thus brings for the sewer sation with no burdens.

Instead of the described mechanical-chemical dissolution of the Waste paper can be used in the same way using the same inventive advantages also a purely chemical dissolving process ren be used, as it is for. B. in DE-AS 23 39 591 be is written.

In Fig. 2, an embodiment is described in which instead of the inclined sieve 16 two consecutively arranged drainage screws 35 and 36 - known construction type - for washing out fillers (ash) and broken fiber pieces from the fiber suspension are used.

The drainage screws 35 and 36 essentially consist of a screw 37 and 38, respectively, and a screen jacket 39 and 40, respectively, surrounding the screw. Via lines 17 'and 19 ' takes place in the same way as described in Fig. 1 ben, the addition of dilution water. The fiber suspension thus cleaned passes after passage through the dewatering screw 36 into an intermediate container 21 ', from where it can be passed on in the usual way for further processing of the fiber suspension. The resulting water is from lines 22 'and 23 ' in the same way as described in Fig. 1, placed in an intermediate container 24 'and then pumped to a clarifier.

The amount of waste containing the flotation foam of the flotation system 10 is processed in the system 27 which works with the gas dispersion according to the pressure release process, clear water and a small sludge fraction being obtained. So far, it was common (see DE 26 10 581 B1) to switch on a centrifuge at this point in order to largely recover the water contained in the waste amount and to obtain a thickened sludge fraction. However, the amount of wastewater represents an additional load on the sewage treatment plant 28 (see line 25 ). This line can now remain switched off by valve 42 throughout. The clear water from the system 27 is preferably reintroduced into the process via line 12 before the flotation.

It is preferably carried out in such a way that the flotation system 10 is operated with a significant overflow, so that there is a corresponding consistency of the amount of waste thereof, with which the latter can be introduced into the pressure relief flotation system 27 . By deleting the flotation foam of the system 10 , the consistency can be set exactly to the required value. The amount of waste treated generally stems from the foam of the secondary stages 10 '' of the flotation system 10 , which are switched to the primary stages 10 'of the same.

Such pressure flotation plants have a gas dispersion reactor, an example of which is given by DE 27 01 702 A1. Incidentally, such a pressure relief flotation system is a conventional, generally round flat container, from which the floated foam is removed from the surface, in particular is scooped off. Sediment can be removed from a bottom funnel, and the flotate is fed from the surface clearing device to a central discharge housing of the flotation device, from where it flows into an outlet. This is shown in FIG. 3. This is an essentially relatively flat cylindrical container, which has a central floor space 43 and an annular space 44 for supplying the amount of dirty water through the nozzle 49 . He also has an annular space 46 radially outside for draining the clear water. The flotation takes place in the inner space 45 arranged outside a central cylinder 54 . The scooped-off flotation foam is introduced into the central cylinder via a manifold 53 . It is collected by a scoop tube 51 , which rotates continuously together with a scoop 52 , the scoop device 50 rotating at the container edge on a track 56 . The drive motors for both movements are not shown here. The scoop is held by a frame construction 57 , which is mounted on an axis 58 . The arrows shown indicate the flow directions of the various material flows. Sediment can be discharged through a lock via a funnel 47 , while the clear water is drawn off via connection piece 48 .

The gas dispersion tank still required is not shown here posed. The fumigation liquid becomes the Ab to be cleaned amount of water using a relief valve in a pipeline given. Furthermore, as stated, the flocculation chemi to apply the flotation process improve, d. H. So first of all with regard to flocculation floating particles and then also with regard to the "Affini "to the gas (air) bubbles.

Claims (3)

1. A process for the treatment of waste paper that is treated in a flotation system after several pre-cleaning stages after a dissolution process, characterized by the following features:

• 1.1 the dirty water containing or resulting from the flotation foam is cleaned in a pressure relief flotation system;
• 1.2 the clear water of the pressure relaxation flotation system ( 26 ) is returned to the main flotation system ( 10 );
• 1.3 Flocculation chemicals are added to the amount of waste to be processed in the pressure relief flotation system before being introduced into the flotation tank of this system.

2. The method according to claim 1, characterized in that by means of a foam overflow of the main flotation plant ( 10 ) a wastewater quantity thereof is adjusted so that the consistency obtained is between 1.0 and 2.4%. 3. The method according to claim 1 or 2, characterized in that a two-stage addition of a polyelectrolyte, namely in the first stage of a cationic and in the second stage of an anionic, or that a one-step addition of a non-ionic polyelectrolyte he follows.