CA1287194C - Installation for flocculating coagulable suspensions, in particular for cleaning the backwater from de-inking plants used for waste-paper preparation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus to flocculate coagulable substances in suspensions as are used in particular for purifying the backwaters from de-inking plants used in waste-paper preparation, has a tank (4) to which the suspension containing flocculating agent and air is supplied from a reservoir (1) through a line (2). The tank (4) contains a rotor with a vertical shaft (34), from which two arms (35, 36) at different levels extend outwards. The suspension that is to be purified is supplied through the shaft (34) and the upper arm (36) and the clear water is scooped up through the lower arm (35) that subtends an acute angle with the upper arm (36). The substances that rise to the surface and float are removed from the surface in the form of scum (8), optionally with a transport system (40) through a sludge line (18, 42).

Description

~2~71~

AN INSTALLATION FOR FLOCCULATING COAGULABLE
SUSPENSIONS, IN PARTICULAR FOR CLEANII~G T~E
BACKWATER FROM DE-INKING PLANTS USED FOR
WASTE-PAPER PREPARATION
Technical Field The present invention relates to an apparatus for flocculating coagulable substances in suspensions, in particular for purifying the backwater from de-inking installations used for waste-paper preparation, wherein chemical agents in quantities sufficient to cause flocculation, and air are added to the suspension, whereupon the floccules that are formed become attached to air bubbles and float on the surface in a tank, whereupon they can be separated in the form of scum.
Such an apparatus is required in particular for purifying the backwater from de-inking plants. Such de-inking plants are used to separate and remove printing ink from waste-paper, in order that a cleaner, lighter-coloured, and reusable paper material that can be used for new paper will result. When this is done, the printing inks are separated off in the foam of flotation plants or in the filtrate from wash plants. Part also finds its way into the filtrate of a concentrator that may also be incorporated in the system. The water from all of these process stations is either partially or completely recirculated for reasons of economy, and then reused to dissolve waste-paper.

~ ~ 144 CA/ 20/Pd -1-: . , -- , . . . -- -- .

, : - . ' . ' : ' . .
, ~ ~371~3~`~

However, this backwater is contaminated by printing ink, fine fibrous material, and other substances removed from the waste-paper during the de-inking process. As an example, the content of suspended solids may range between 500 and 3500 mg/l.
Were this water to be ræused to dissolve waste-paper before being treated, the waste-paper would be additionally soiled. For this reason, this backwater must be purified.
State of the Art It is known that this backwater purification can be undertaken by the~addition of chemicals and the foreign sub-stanees ean be floceulated in a eontainer and separated, for example, in flotation plants. In addition, air is also fed into these flotation plants and finally divided in the water. The solids then float in the tank, moved by the air to the surface, where they appear as seum, whereupon they can be scooped from the elear water with suitable deviees.
Various eationie agents and/or anionie or non-ionic chemicals ean be used either singly or in combination as such ehemieals, e.g., alum ean be used as a suitable polymer eationie agent and, for example, polyaeryl amide can be used as an additional anionie polymer, or for example, highly polymerized polyoxide produets ean be used as non-ionie agents. In order to arrive at an optimal quality of the purified backwater it is essential to add each individual chemical as precisely as possible in the quantity required to achieve optimal flocculation 71t.3 ~

of the foreign substances, i.e., the chemical addition of each individual agent may be neither under-dosed nor over-dosed. This can be achieved by the use of a regulating process, in which the effect is measured by means of suitable measuring equipment, for example, turbidity metres installed at suitable locations and with a regulating system connected thereto, by evaluating the measured degree of turbidity and of the bulk flow on the one hand, and the quantity and concentration of chemical additive on the other, so as to regulate the addition to the optimal degree of flocculation o~ turbidity. The purification effect can be greatly improved by the addition of a plurality of agents at different stations that are arranged one after the other.
In known flotation plants, however, the purification effect within the flotation tank, i.e., the flotation of the flocculated substances that adhere to air bubbles and their sepa-ration from the clear water is still optimal, and for this reason the installations must be overdimensioned in order to achieve adequate performance per unit time, so that they operate relatively uneconomically.
pescription of the Invention In order to eliminate the disadvantages found in the prior art, the present invention undertakes the task of creating an apparatus to flocculate coagulable substances in suspensions, inparticular for purifying the backwater from de-inking plants used in waste-paper preparation, in which the flocculation effect .

~ ~'r~ 3i~

and the cleaning capacity within the container are improved and an optimal value is achieved in order to permit a greater throughput and optimal economy.
The apparatus according to the present invention is characterized in that the suspension can be supplied from a reservoir through a line to a tank; in that there are addition points for flocculating agent and air ahead of the tank, and in that a rotor is provided within the tank, this being rotatable about a verticle shaft and which has two arms that extend outwards from the shaft, essentially horizontally, the suspension to which flocculating agents and air have been added being supplied through the shaft to one arm beneath the surface of the liquid or scum layer within the container, the liquid that has been cleansed of floating and flocculating substances being drawn off through the shaft by the other arm, above the bottom of the tank.
It is particularly advantageous if the arm through which the suspension is supplied is provided at a shallower depth within the tank than the other arm, through which the liquid is drawn Off.
It is particularly advantageous that the two arms are arranged at an acute angle relative to each other, this being done so that the upper supply arm trails the lower extraction arm, so that during every rotation of the rotor the clear water is drawn off shortly before fresh suspension is fed into the tank.

" .~,. :

3~7~S.~I~

It is particularly expedient to provide measuring devices within the tank, these being disposed on another co-rotating arm and which can be configured as turbidity metres, and which determine the behaviour of the flocculated substances, for example, the manner in which they rise or separate, and which by means of a control circuit make it possible to control the addition of chemicals, the supply of suspension, or the rotational speed of the rotors so as to arrive at an optimal purification effect. In addition, other measuring devices can be provided at different loca~ions ahead of the tank in order to optimize control of the addition of the chemicals.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be explained in greater detail on the basis of exemplary versions of a backwater purifi-cation plant shown in the drawings appended hereto. These drawings are as follows:
Figure 1 the layout of a backwater purification appara-tus Figure 2 a plan view of a flotation tank used in the apparatus as in Figure 1 Figure 3 the layout of another backwater purification apparatus in cross section Figure 4 a supply s~stem for scum Figure 5 a rotor with a distributor arm, in longitudinal cross section Figure 6 a cross section through this rotor on the plane VI-VI

,. ' .
.' - - ~ . ' .
.

7~9~

DESCRIRTION OF EXEMPLARY VERSIONS OF THE INVENTION
In the apparatus that is shown in Figure 1 the back-water from a de-inking plant is fed into an untreated water reservoir l; this backwater can contain solids at a concentration of approximately 500 to 1500 ppm. The reservoir 1 is connected by a line 2, in which there is a pump 3, to a tank 4, into which the backwater is introduced through an arm 36 and from which the clear water is extracted through another arm 35.
A short-chain, low molecular, strongly cationic agent 5 is added to the backwater in the reservoir 1 through a controllable pump 15 so as to effect extensive charge neutralization. This agent can be of low-molecular, strongly cationic polymer, for example, as well as combinations of such a polymer with polyvalent metal-cation compounds, e.g., aluminum chloride or aluminum oxichloride. The descrete addition of the metal-cation compounds is also possible. If there is sufficient mixing of the backwater with the agent, it is possible to dispense with diiution when the polymer is used.
A long-chain, high-molecular cationic agent 6 is fed into the line 2 after the pump 3 by a pump 16. This agent 6 causes microflocculation in the line 2.
Next, slightly ahead of the purification tank 4 another high-molecular anionic agent 7 is supplied through a pump 17.
This additional agent 7 now brings about macroflocculation in the untreated water flowing into the tank 4. Within the tank 4 the flocculated floating impurities are drawn off in the form of ~ .

.. , -' .
, r 3 ~

sludge 8 through a line 18 and the clarified backwater is also drawn off as clear water through a line 19. A portion 10 of this clear water is tapped off by means of a pump 11 and air is added to it in a mixer 13 and then passed into the feed line 2 through a saturation tank 14 at a location 12, once again saturated with air.
In order to control the optimal quanti~ies of the dif-ferent agents 5, 6 and 7 that are added there is a series of measuring devices for the characteristic properties of the back-water or of the effect achieved by the individual chemicals, said measuring devices being connected to control systems which once again control the pumps 15, 16 and 17 for the addition of the agents.
Within the untreated water reservoir 1 there is, first of all, a charge measuring device 20, this measuring the mass charge in the suspension and controlling the pump 15 for the addi-tion of the first agent 5 through the control system 30 such that extensive charge neutralization takes place in the untreated-water reservoir. This neutralization makes it possible to ensure that the flocculation process can be optimally adjusted by the addition of further different types of chemicals.
The effect of the second agent 6, which first causes microflocculation in the line 2, is determined by means of an additional measuring device 21 in the line 2 at a specific ,`' , ' : '. ` ` :
`'.''' -` ' : , ~ ~!37~

distance from the addition point used for the second agent.
This measuring device 21 can be, for example, a turbidity metre, or an apparatus to measure the bulk flow, i.e., of the volume, and of the solids content. This measuring device 21 controls the controllable pump 16 for the addition of the second agent 6 through a control system 31, and regulates this to a value that is optimal with reference to microflocculation.
The third agent 7 that causes the macroflocculation is added to the line 2 in the direction of flow after the measuring device 21, althoug~h ahead of the tank 4. The behaviour of the flocculated foreign substances as they rise in the tank 4 on account of the air being fed in is measured with at least one additional measuring device 22, which can, for example, be configured as a turbidity metre. This measuring device 22 is located at a specific distance from the inlet to the tank 4, so as to be able to measure any change in the rising behaviour of the floccules, e.g., at a place at which the separation of the solids reaches a specific value, e.g., at least 10~. This measuring device 22 controls a pump 17 through a regulating circuit 32, and provides quantitative regulation of the addition of the third agent 7 so that the clarifying action within the tank 4 can be optionally adjusted.
An additional and similarly constructed turbidity metre 23 can be provided in the tank 4 and this can be used to supply even more information concerning the behaviour of the floccules that are formed, for example, by observation of the time ,. , - , . . .
. - .

9~

curve, associated with clarification. The two turbidity metres 22 and 23 can be installed to measure the turbidity at different distances from the place where the untreated water enters the tank 4 and, in addition, to determine the degree of turbidity at different levels in the tank 4. In this way, using the regulating circuit 33 it is also possible to control the quantity of an agent, e.g., the agent 7, that is added under quantitative control by the pump 17. However, in place of this a further turbidity metre 24 in the clear water line 19 can be used such that the measured values that it provides can be compared with the m~asured values originating from the measuring device 22.
The tank 4, shown raised in Figure 1 and in plan view in Figure 2 is best configured as a cylindrical trough that is several metres in diameter, in which a rotor turns about a vertical axis 38 so slowly that the clarifying action is not restricted, e.g., by making approximately one revolution every lS
minutes. The arms 35, 36, and 37, which have openings distributed along their whole lengths from the shaft to the outer ends, extend horizontally from the shaft 34 about the axis 38. The clear water is scooped from the bottom of the tank by the arm 35 which leads in the direction of rotation whilst untreated water preferably at a somewhat shallower depth beneath the surface of the liquid or the lower edge of the sludge layer 8 is fed in through the next arm 36 that subtends an acute angle with the leading arm 35. The last arm 37, rear-most in the direction of rotation, bears the two turbidity metres 22 and 23 that measure the turbidity at different _g_ - . . . ~ .
:
.
' ' ' .

~ ~'i'71~3~1~

distances from the inlet 36 and optionally do this at different depths.
The addition of the chemica]s can be regulated quantitatively by means of the measuring devices 22, 23 and, optionally, the quantity of suspension added to the tank 4 per unit time, or the rotational speed of the total rotor assembly about the axis 38 can be controlled through the pump 3. The purification plant can be so controlled that fresh suspension containing flocculating agent and air can be first supplied ~ through the arm 36 when the purification effect at this point, i.e., flocculation and surfacing of the foreign substances that are to be separated has progressed to the point that relatively clear water can be scooped from the bottom of the tank 4 by the leading arm 35. In this connection, the supply arm 36 is arranged at most at the same depth in the tank 4 as the removal arm 35, although preferably at a somewhat lesser depth, so that no rising floccules are picked up by the removal arm. This means that the purification effect and the economy of the installation will be optimal.
Whereas in the system that is shown in Figure 1 the layer 8 of scum is removed by means of a simple overflow line 18 at the edge of the tank 4, the removal of flocculated substance from the surface can be managed with greater efficiency by additi-onal delivery systems such as paddle wheels, worm conveyors, and pressure or suction systems which move the scum towards a removal line.

.

9~

Figure 3 shows such a purification system, which is particularly advantageous, in cross section. In this, suspension that contains the flocculating agent 7 is supplied to the shaft 34 within the tank through a feed line 2 and distributed in the trailing arm 36 that is located somewhat higher. The clear water is passed to the clear water line 19 from the lower arm 35 through a drilled hole in the shaft 34. Once again, part 10 of this clear water is saturated with air in a saturator 14 and introduced into the feed line 2 through line 12. In this embodiment, the layer of scum 8 on the surface of the liquid within the tank 4 is moved inwards by means of a worm conveyor 40 that is secured to a further co-rotating arm 39 on the shaft 34 and removed to a funnel 41 in an additional central drilling 43 in the shaft 34 and then carried out of the system through the sludge line 42.
Figure 4 illustrates a particularly favourable config-uration for a conveyor system that is well-suited to removing relatively thick and stiff scum. In this, the worm conveyor 40 is arranged in a trough 44 that is semi-cylindrical in shape, within ; which the saum is moved towards the centre by means of the worm 40.
The edges of this trough 44 lie above the layer of scum 8. In order to move the scum into this trough 44 there is a paddle wheel . 45 that is parallel to the worm conveyor 40; this has a plurality of flat paddles 46 that extend across the whole width of the arm.
This paddle wheel 45 or its paddles 46 rotate within a vane 47, thereby lifting the layer of scum 8 and moving it into the trough ,~

,, --1 1-- ' .,~ - - . ~ . - . .
-'-, :: - - . . -. . .. - . :.
-, . . . .
.' . ': . :
. ~ , . ~' ' .

~2~ 9~

44. In order to be able to lift relatively stiff scum layers 8 it is expedient to provide obliquely-set paddles 48 between the paddles 46, for these will break up the scum. The scum then falls through openings between the paddle arms 49 onto the paddles 46, whereupon it is moved by these into the trough 44.
Figures 5 and 6 show a rotorwithashaft 34 and distri-butor arms 35 and 36 in both longitudinal and in cross section.
Here, within the fixed shaft 34, there is a feed channel 50 for the suspension, a removal channel 51 for the clear water and a removal trunk 52~for the sludge layer that is skimmed off. The shaft 34 is enclosed by two collars 53 and 54 to which the arms 35 and 36 are attached and which rotate together with the arms.
Thesecollars 53 and 54 are sealed onto the shaft 34 thereby leaving an annular chamber 55 or 56 free about the shaft 34 into which the clear water from the arm 35 can be removed from the arm 35 through an opening 57 in the channel 51 or the suspension can be introduced through the channel 50 through an opening 58 of the shaft 34 and distributed into the arm 36. The annular chambers 55 and 56 within the collars 53 and 54 thus permit distribution of the liquid relative to the arms 35 and 36 at any angular position. In order to ensure the even distribution in the suspension supply arm 36 at all positions, it is expedient to provide suitably formed vanes 59 within this arm. The two collars 53 and 54 can be situated close to each other or can be combined to form one mechanical unit, so that the removal arm 35 for the clear water is located somewhat deeper than the suspension : ' . .

~.~37~9 ~

feed arm 36, and thus practically no flocculated foreign sub-stances, which as a rule are rising, Will be picked up. In this manner it is possible to achieve particularly good efficiency and economy of operation for the purification installation.

~-.
~ ~. ' ' ' - .

Claims (14)

1. An apparatus for flocculating coagulable substances in suspensions, in particular for purifying the backwater from de-inking plants used in waste-paper preparation, in which connection air and chemical agents are added to the suspension in quantities sufficient to bring about flocculation, the floccules that are so formed attaching to air bubbles and rising to the surface when they are separated as sludge, characterized in that the suspension can be supplied from a reservoir through a line to a tank; in that points for flocculating agent and air are provided ahead of the tank; and in that within the tank there is a rotor, this being rotatable about the vertical shaft and which has two arms that extend essentially horizontally outwards from the shaft, in which connection the suspension that has the added flocculating agent and air can be supplied through the shaft to one arm beneath the surface of the liquid or layer of scum within the tank and the liquid freed of floating and flocculated substances can be removed by the other arm above the bottom of the tank through the shaft.

2. An apparatus according to claim 1, characterized in that the two arms are arranged at different levels in the tank such that the arm through which the suspension is supplied, is at a higher level than the arm, through which the clear water is removed.

R 144 CA/ 20/Pd

3. An apparatus according to claim 1, characterized in that on the two arms there are feed openings or removal openings along the whole length, from the shaft to the outer ends.

4. An apparatus according to one of the claims 1 to 3, characterized in that the two arms are arranged so as to subtend an acute angle with each other, so that on rotation the upper arm, through which the suspension is supplied, trails behind the lower arm, through which the clear water is removed.

5. An apparatus according to claim 1, characterized in that at least one measuring device is provided to measure one property of the flocculated substances in the tank.

6. An apparatus according to claim 5, characterized in that at least two measuring devices are provided so as to determine one property of the flocculated substances at different levels in the tank.

7. An apparatus according to claim 5, characterized in that the measuring devices are configured as turbidity metres.

8. An apparatus according to claim 5, characterized in that a regulating circuit is connected to the measuring devices, said measuring device controlling the addition of a flocculating agent.

9. An apparatus according to claim 8, characterized in that, in addition, the control circuit is able to control the quantity of suspension introduced through the line per unit time and/or the rotational speed of the rotor.

10. An apparatus according to one of the claims 1 to 3, characterized in that the tank has an overflow for the scum layer into a removal line.

11. An apparatus according to claim 1, characterized in that a transport system is provided to remove the scum layer to a removal line that passes centrally through a shaft.

12. An apparatus according to claim 11, characterized in that the transport system has a worm conveyor on an additional radial arm.

13. An apparatus according to claim 12, characterized in that the worm conveyor is arranged within a radial trough; and in that a paddle wheel is provided that is parallel to the worm conveyor, the paddles of said paddle wheel being able to move the scum layer into the trough.

14. An apparatus according to one of the claims 1 to 3, characterized in that the arms are attached to a co-rotating collar that encloses and is sealed around a fixed shaft and forms an annular chamber about the shaft in which connection the shaft has an opening in the area of the collar through which a channel to remove or supply liquid is connected with the annular chamber and the interior of the arm.