METHOD FOR FLOCCULATING SOLID PARTICLES CONTAINED IN A SUSPENSION, AND SYSTEM FOR CARRYING OUT THE METHOD

Abstract

Methods for flocculating solid particles in a provided suspension including specifying a target charge density of the suspension at which the solid particles flocculate; providing a flocculant having a charge density; determining, at a plurality of measuring times, the suspension charge density present in the suspension in the course of a titrimetric analysis, measuring the flow potential; determining, at respective of the measuring times, a quantity of the flocculant needing to be added to ensure optimal flocculation based on the target charge density, the flocculant charge density, and the suspension charge density present at the respective measuring time; and subsequently adding the determined quantity of flocculant into the suspension; and systems therefor. The methods and systems can provide the actual demand of flocculant needed for efficient flocculation in a continuous flocculation method of a suspension.

Claims

1. A method for flocculating solid particles (2) contained in a suspension, comprising the following steps: a. preparing a suspension and specifying a target charge density (dEqz) for the suspension, wherein the target charge density (dEq.sub.z) defines a charge density of the suspension at which the solid particles (2) flocculate; b. at a plurality of measurement times: determining a suspension charge density (dEq.sub.M) in the suspension using of a titrimetric analysis with measurement of streaming potential of the suspension; c. each respective measurement time of the plurality of measurement times, determining a required quantity (D.sub.p) of a flocculating agent defining a flocculating agent charge density (dEq.sub.p) to be added to the suspension to optimize flocculation based on the target charge density (dEq.sub.Z), the flocculating agent charge density (dEq.sub.p) and the suspension charge density (dEq.sub.M) at said each respective measurement time; and d. e. subsequent to said each respective measurement time, adding to the suspension the determined quantity (Dp) of flocculating agent to be added.

2. The method as claimed in claim 1, wherein the step of specifying the target charge density (dEqZ) includes determining the target charge density (dEqZ) using a separate laboratory test.

3. The method as claimed in claim 2, wherein the step of determining the target charge density (dEq.sub.Z) includes determining the target charge density (dEqZ) of a specific suspension once or in a repeated manner.

4. The method as claimed in claim 1, further including determining the flocculating agent charge density (dEq.sub.p) from empirical data in a separate investigation.

5. The method as claimed in claim 3, further including monitoring the flocculating agent charge density (dEq.sub.p) at defined chronological intervals.

6. The method as claimed in claim 1, wherein the flocculating agent is a charged polymer.

7. The method as claimed in 6, wherein the flocculating agent is an anionic or a cationic polymer.

8. The method as claimed in claim 1, wherein the step of determining the suspension charge density (dEq.sub.M) includes determining the suspension charge density (dEq.sub.M) at regular or irregular chronological intervals determined manually or automatically.

9. The method as claimed in claim 1, wherein the step of determining the suspension charge density (dEq.sub.M) includes automatically supplying a defined sample volume of the suspension to a streaming potential measuring cell, and determining the suspension charge density (dEqM) in the streaming potential measuring cell.

10. The method as claimed in claim 1, including performing at least the steps b. and c. automatically using a processing and control unit (9).

11. The method as claimed in claim 1, wherein the steps of determining and adding the required quantity (Dp) of flocculating agent to be added include using quantitatively proportional control, load-proportional control, proportional regulation or PID regulation.

12. The method as claimed in claim 1, including performing steps a.-d. in a continuous dewatering process for solid-liquid suspensions.

13. The method as claimed in claim 1, including performing steps a.-d. in a process for dewatering sewage sludge.

14. The method as claimed in claim 13, wherein said process for dewatering sewage sludge includes filtration, sedimentation, flotation, thickening and/or dewatering of sewage sludge.

15. A system configured for flocculating solid particles (2) contained in a suspension, comprising: a processing and control unit (9), a measuring cell (13) and a dosing unit (10), wherein the processing and control unit (9) is operatively connected to the measuring cell (13) and the dosing unit (10) for signal transmission therebetween, wherein: the measuring cell (13) is configured to determine a suspension charge density (dEq.sub.M) in the suspension at a plurality of measurement times using a titrimetric analysis with measurement of streaming potential of the suspension, and to transfer data obtained thereby to the processing and control unit (9); the processing and control unit (9) is configured to: a. calculate, at each respective measurement time of the plurality of measurement times, a quantity (Dp) of flocculating agent required to be added to the suspension to optimize flocculation based on the suspension charge density (dEqM) determined at said each respective measurement time, a specified target charge density (dEqZ) for the suspension, and a flocculating agent charge density (dEqp) of the flocculating agent, and b. transmit to the dosing unit a dosing signal based on the required quantity (Dp) of the flocculating agent to be added to the suspension; and the dosing unit (10) is configured, based on of the dosing signal, to add to the suspension the required quantity (D.sub.p) of the flocculating agent to be added.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Further embodiments and developments will now be explained in more detail with the aid of the exemplary embodiments described below. These are intended to illustrate embodiments of the invention to the person skilled in the art so that the invention can be carried out by the person skilled in the art, but are not intended to limit the invention. In connection with the description of said exemplary embodiments, reference is made to the following figures with the aid of which the embodiments are described in more detail. In the drawings:

[0059] FIG. 1 shows a diagrammatic overview of the system for use in a decanter centrifuge as an exemplary dewatering assembly, in respect of quantitatively proportional regulation, proportional regulation and PID regulation;

[0060] FIG. 2 shows a diagrammatic overview of the system for use in a decanter centrifuge as an exemplary dewatering assembly, in respect of load-proportional regulation, proportional regulation and PID regulation; and

[0061] FIG. 3 shows a diagrammatic view of the sequence of a method.

DETAILED DESCRIPTION OF EMBODIMENTS

[0062] FIGS. 1 and 2 show the system for use in connection with a decanter centrifuge 1 as an exemplary dewatering assembly. It should be expressly stated at this juncture that this is merely an exemplary representation with the aid of which a system or method can be illustrated. Equally, the system or method may also be used in other types of dewatering assemblies.

[0063] With a decanter centrifuge 1 of this type, a phase separation of a suspension can be carried out, for example in the context of a sewage sludge dewatering process. In this regard, the solid particles 2 contained in the suspension (for example sewage sludge) are separated from the liquid phase (for example water) and eliminated. To this end, in the centrifuge, gravitational acceleration is replaced by the substantially higher centrifugal acceleration. Because of their higher density, the solid particles 2 collect at the wall of the bowl 4 and are transported with the aid of a screw conveyor 5 to corresponding outlet openings 6. At the same time, the clarified liquid 3 flows along the screw conveyor 5 into the liquid outlet zone 6.

[0064] FIG. 1 illustrates the diagrammatic sequence of quantitatively proportional regulation of the addition of flocculating agent. By means of an infeed stream 8, the decanter centrifuge 1 is supplied with the suspension to be dewatered (the sewage sludge). This may be continuous or discontinuous. The term “continuous supply” in this regard should be understood to mean a supply with a continuous volumetric flow of the suspension. The term “discontinuous supply” means that the decanter centrifuge 1 is fed with a fixed volume of a suspension; in this case, the supply is not continuous, but batchwise. Prior to the start of the dewatering process occurring in the centrifuge 1, the target charge density dEqZ of the suspension is specified, i.e. a target value at which an optimal flocculation occurs which is aimed for during dewatering. In at least one embodiment, the target charge density dEqZ corresponds to that charge density at the isoelectric point of the suspension. The target charge density dEqZ may, for example, be determined in the context of a separate laboratory test. In addition, a sample may be removed from the infeed stream 8 and analysed. The target charge density dEqZ determined in this manner can be provided to a processing and control unit 9 for further implementation of the method, for example by manual inputting by a user. Furthermore, said procedure (sample removal from the suspension, determination of the target charge density dEqZ) may also proceed in an automated manner. Other types of methods for the determination or for specifying the target charge density may be used in the context. The method is controlled and regulated in the processing and control unit 9.

[0065] As can also be seen in FIG. 1, the processing and control unit 9 regulates the addition of the flocculating agent required for flocculation or dewatering, for example by means of a dosing unit 10 provided for that purpose. In the context, the charge density dEqp of the flocculating agent used is known and the method uses it as an input parameter. The processing and control unit 9 uses the flocculating agent charge density dEqp when executing the method. In this regard, the flocculating agent charge density dEqp can be specified by a manufacturer or provider of the flocculating agent, or in fact be determined by the user per se (whether that is a consumer such as a client or the marketer such as a merchant or service provider), for example in the context of a laboratory test. The flocculating agent charge density dEqp may be monitored at a plurality of time points in the method or the dewatering process. Previously determined values are then replaced by the prevailing determined values.

[0066] After supplying the decanter centrifuge 1 with the suspension to be dewatered, the suspension charge density dEqM in the suspension (at the respective time points) is determined at a plurality of measurement time points. In addition, a sample is removed (for example from the liquid discharge zone 7 of the decanter centrifuge 1) and the suspension charge density dEqM is determined by way of a titrimetric analysis by measuring the streaming potential. Sampling may, for example, be carried out by means of a sampling unit 11 provided especially for sample removal. The sampling unit 11 in this regard may be controlled by the processing and control unit 9 and be commanded to take samples at the respective measurement time points. The sampling unit 11 may also have a microcontroller in which the appropriate time points for taking samples are specified or programmed. The actual determination of the suspension charge density is carried out in a measuring cell 13. The sample removal together with the subsequent titrimetric analysis are part of the routine of the method. The measured suspension charge density dEqM is transmitted to the processing and control unit 9—as indicated by the path of the arrows.

[0067] The processing and control unit 9 determines the required quantity Dp of flocculating agent to be added at the respective measurement time points in order to guarantee continuous optimized flocculation. The quantity Dp of the flocculating agent to be added in this regard is determined on the basis of the target charge density dEqZ, the flocculating agent charge density dEqp and the suspension charge density dEqM at the respective measurement time point.

[0068] Following the respective measurement time points, the required quantity of flocculating agent is added to the dewatering assembly or the decanter centrifuge 1 via a dosing unit 10. If at a specified time point no further addition of flocculating agent is required, the processing and control unit 9 does not transmit an “add” command to the dosing unit 10.

[0069] The protocol of the method which has been described enables an appropriate addition of a flocculating agent to be provided, avoiding under-dosing and over-dosing.

[0070] FIG. 2 shows a diagrammatic representation of the system or method under load-proportional regulation. Compared with quantitatively proportional regulation (see FIG. 1), the processing and control unit 9 uses additional information at the initial time point (i.e. prior to the dewatering). The solids content may, for example, be determined by means of a solids probe 12 which is installed in the suspension feed line for the separation assembly (in this case the decanter centrifuge 1). The other components shown in FIG. 2 correspond to those in the view of FIG. 1 and the system components described above. For details of the regulation used in the context (for example quantitatively proportional regulation, load-proportional regulation, proportional regulation, PID regulation), reference should be made to the section of the description above pertaining to the description of the figures.

[0071] As has already been described, the present invention also comprises a system for carrying out the method. The essential components of the system are the processing and control unit 9, the measuring cell 13, and the dosing unit 10.

[0072] FIG. 3 highly diagrammatically shows the individual steps of the exemplary method.

[0073] Thus, in a step a. of the method, a suspension is provided and a target charge density dEqZ for the suspension is specified, but with the proviso that the target charge density dEqZ is that charge density of the suspension at which the solid particles flocculate. In a step b. of the method, a flocculating agent is provided, wherein the flocculating agent has a flocculating agent charge density dEqp. According to a step c. of the method, the suspension charge density dEqM in the suspension is determined at a plurality of measurement time points by way of a titrimetric analysis with measurement of the streaming potential. In a subsequent step d. of the method, a quantity Dp of the flocculating agent to be added in order to guarantee an optimal flocculation is calculated at the respective measurement time points, namely based on the target charge density dEqZ, the flocculating agent charge density dEqp and the suspension charge density dEqM at the respective measurement time point. According to a step e. of the method, following the respective measurement time points, the determined quantity Dp of the flocculating agent to be added to the suspension is specified.

[0074] Depending on the number of measurement time points, steps c. to e. are repeated by the number of times which corresponds to the number of measurement time points.

[0075] While the above describes certain embodiments, those skilled in the art should understand that the foregoing description is not intended to limit the spirit or scope of the present disclosure. It should also be understood that the embodiments of the present disclosure described herein are merely exemplary and that a person skilled in the art may make any variations and modification without departing from the spirit and scope of the disclosure. All such variations and modifications, including those discussed above, are intended to be included within the scope of the disclosure.