EP1232794A1 - Method for separating of a multi-phase mixture and decanter centrifuge system for carrying out this method - Google Patents

Abstract

An assembly separates a multi-phase mixture into liquid (54) and dry (52) phases and employs a decanting centrifuge (100) with an annular immersion disc (14). A liquor weir is located on the end-face of the centrifuge drum (20). An Independent claim is also included for a separation process in which after starting the centrifuge drum (20) and setting an initial tank depth, the mixture (50) is introduced into the drum. The liquid and dry phases are drawn off. The tank depth and centrifuge fluid level are regulated by the liquor weir until a pre-determined dry substance concentration is reached. The tank depth is continually compared with a tolerance range. During the process the weir is so positioned that a reaction to feed concentration changes is possible in both directions. As the process progresses, the centrifuge speed is lowered in steps and the weir position adjusted so that the dry phase remains constant.

Description

• eine ringförmige Tauchscheibe, die an ihrem inneren Umfang mit einer Welle verbunden ist und deren Außendurchmesser kleiner ist als der Innendurchmesser einer Zentrifugentrommel; und
• wenigstens ein endseitig an der Zentrifugentrommel angeordnetes Flüssigkeitswehr mit einem Wehrspalt, durch den die Flüssigkeitsphase aus der Zentrifugentrommel ableitbar ist, und mit einer Teichtiefeneinstellvorrichtung, mit der die Teichtiefe x_T der in der Zentrifugentrommel rotierenden Flüssigkeitsphase einstellbar ist,

mit folgenden Schritten:

a) Anlaufen der Zentrifugentrommel auf eine Starttrommeldrehzahl n_Z,1 und Einstellen der Teichtiefe x_T auf eine Startteichtiefe x_T,1 ;

b) Einleiten des Mehrphasengemisches in die rotierende Zentrifugentrommel;

c) Abzug der Trockenphase durch die wenigstens eine Trockensubstanzaustragsausnehmung und Abzug der Flüssigkeitsphase durch den Wehrspalt;

d) Regeln der Teichtiefe X_T mittels der Teichtiefeneinstellvorrichtung in Abhängigkeit von der Trockensubstanzkonzentration C_TS in der abgezogenen Trockenphase bis zum Erreichen einer vorgegebenen Soll-Trockensubstanzkonzentration C_TS,1.

The invention relates to a method for separating a multiphase mixture into at least one liquid phase and a dry phase with a predetermined dry substance concentration c _TS , by means of a decanter centrifuge which comprises:

• an annular immersion disk which is connected on its inner circumference to a shaft and whose outer diameter is smaller than the inner diameter of a centrifuge drum; and
• at least one liquid weir arranged at the end of the centrifuge drum with a weir gap through which the liquid phase can be derived from the centrifuge drum and with a pond depth setting device with which the pond depth x _{T of} the liquid phase rotating in the centrifuge drum can be set,

with the following steps:

a) starting the centrifuge drum to a starting drum speed n _{Z, 1} and setting the pond depth x _T to a starting pond depth x _{T, 1} ;

b) introducing the multiphase mixture into the rotating centrifuge drum;

c) deduction of the dry phase through the at least one dry matter discharge recess and withdrawal of the liquid phase through the weir gap;

d) regulating the pond depth X _T by means of the pond depth setting device as a function of the dry matter concentration C _TS in the subtracted drying phase until a predetermined desired dry matter concentration C _{TS, 1} .

The pond depth is defined as the difference between external and inner diameter of the rotating in the centrifuge drum Liquid ring.

A decanter centrifuge with at least partial hydraulic Promote how you perform the procedure is assumed is known from DE 43 20 265 C2. Here, a liquid ring is placed in the rotating centrifuge drum between the submersible and the liquid weir certain fill level, the so-called pond depth and thus a hydrostatic due to the liquid phase Generates pressure that contributes to the discharge of the dry phase. The hydraulic delivery can be in addition to or instead of the discharge with a rotatable with differential speed Snail done.

The weir is essentially in two parts. A Weir plate closes the cylindrical shell of the centrifuge drum and rotates with it. At least she is a passage for draining a liquid the centrifuge drum. The weir plate is a parallel one Throttle disc associated with the axially displaceable the stationary storage of the rotatable centrifuge drum is arranged. Between the rotating weir plate and the stationary throttle disc forms a gap that extends in the radial direction and through which the liquid phase flung out of the centrifuge drum becomes. The axial displacement of the throttle disc can Weir gap width can be varied. By reducing the The width of the weir gap becomes a pressure increase in the liquid phase causes that this increases the dry phase pushes out of the centrifuge drum. The liquid phase partially penetrates into the dry phase and reduces its concentration of dry matter. Vice versa an expansion of the weir gap causes a reduction in pressure, reduced hydraulic delivery and finally an increase in dry matter concentration in the dry phase.

This liquid weir has for a decanter centrifuge has proven itself as it is with a rotating centrifuge drum is adjustable and so a regulation of the dry matter concentration allowed over the weir gap. By means of the Regulation of the weir gap width can be based on concentration and Amount changes in the supplied multi-phase mixture in ongoing process.

However, it has been shown that the regulation of the dry matter concentration via the adjustable liquid weir an unchanged high use of energy at high speed rotating decanter centrifuge required. The high energy consumption is based in particular on the fact that the Drum fed amount of the multi-phase mixture continuously must be accelerated from a rest position until it the high angular velocity impressed by means of the centrifuge drum reached.

In the course of the procedure, the defense position can change into a Move to the edge, in which the throttle plate of the weir is no longer adjustable. In case of major changes from Concentration and / or amount of the multi-phase mixture applied can then no regulation of the dry matter concentration done more. The process must be stopped and with approached an empirically determined drum speed become.

A pneumatic liquid weir is known from DE 195 00 600, by blowing compressed gas into the weir gap the flow resistance of the liquid phase in the weir is increased, which increases the pond depth. Also with this training of the liquid weir is a regulation the dry matter concentration through a weir adjustment possible during operation.

Various methods are proposed in EP 1 044 723 A1 in order to influence the properties of the separated phases with machine parameters such as the drum speed or the differential speed. However, the composition of the liquid or dry phase is always the focus of the considerations. However, the disclosed regulation of the dry matter concentration by varying the drum speed requires an increased use of energy. In addition to the already high energy consumption at a high basic speed, the frequent braking and acceleration of the drum is also very energy-intensive due to the high mass moments of inertia of a loaded decanter centrifuge and the high angular speeds.
A method that would be suitable for operating a decanter centrifuge with an adjustable liquid weir is not disclosed.

It is therefore the task of a process of the beginning to develop the type mentioned so that on the one hand a Optimization of energy consumption in base load operation Decanter centrifuge takes place and that, on the other hand, the decanter centrifuge is operated so that even with sudden Changes in the type and quantity of the incoming product Regulation of the process with regard to a predetermined Dry matter concentration of the separated dry phase is guaranteed.

e) Festlegen eines Teichtiefentoleranzbereichs mit einer unteren Teichtiefe x_T,U und einer oberen Teichtiefe x_T,O;

f) Vergleichen der eingeregelten Teichtiefe x_W mit dem Teichtiefentoleranzbereich und fortwährende Durchführung der Schritte b) bis f) bei einer innerhalb des Teichtiefentoleranzbereiches liegenden Teichtiefe x_T;

g) Erhöhen der Zentrifugentrommeldrehzahl n_Z um einen Drehzahlstufenwert Δn_Z bei einer Teichtiefe x_T, die kleiner ist als die untere Teichtiefe x_T,U, oder Absenken der Zentrifugentrommeldrehzahl n_Z um einen Drehzahlstufenwert Δn_Z bei einer Teichtiefe x_T, die größer ist als die obere Teichtiefe x_T,O;

h) Nachregeln der Teichtiefe x_T in Abhängigkeit von der Trockensubstanzkonzentration c_TS in der abgezogenen Trockenphase bis zum Erreichen einer vorgegebenen Soll-Trockensubstanzkonzentration c_TS,0;

i) Vergleich der nachgeregelten Teichtiefe x_T mit einem vorgegebenen Teichtiefentoleranzbereich und Wiederholung der Schritte f) bis i) bei einer außerhalb des Teichtiefentoleranzbereiches liegenden Teichtiefe x_T unter fortwährender Einleitung des Mehrphasengemisches in die rotierende Zentrifugentrommel und Abzug der Flüssigkeits- und Trockenphase.

This problem is solved with a method of the type mentioned at the outset, which is characterized by the following further steps:

e) defining a pond depth tolerance range with a lower pond depth x _{T, U} and an upper pond depth x _{T, O} ;

f) comparing the adjusted pond depth x _W with the pond depth tolerance range and continuously carrying out steps b) to f) at a pond depth x _T lying within the pond depth tolerance range;

g) Increase the centrifuge drum speed n _Z by a speed step value Δn _Z at a pond depth x _T that is smaller than the lower pond depth x _{T, U} , or decrease the centrifuge drum speed n _Z by a speed step value Δn _Z at a pond depth x _T that is greater than the upper pond depth x _{T, O} ;

h) readjusting the pond depth x _T as a function of the dry matter concentration c _TS in the deducted drying phase until a predetermined target dry matter concentration c _{TS, 0} ;

i) Comparison of the readjusted pond depth x _T with a predetermined pond depth tolerance range and repetition of steps f) to i) at a pond depth x _T lying outside the pond depth tolerance range while continuously introducing the multiphase mixture into the rotating centrifuge drum and subtracting the liquid and dry phases.

The advantages achieved with the method of the invention exist in particular that a decanter with to operate a plunger and a liquid weir is that in a base load operation with largely constant Amount and concentration of the feed an optimization can be made in terms of energy consumption and that at the same time a willingness to react to sudden Changes in the inflow is given by the fact that the weir in returned a middle position defined by the tolerance range from which it becomes both the dry phase thicken more than it can further dilute.

In a particularly preferred embodiment of the method, a decanter centrifuge is used, the liquid weir of which consists of a weir plate with at least one liquid recess and a throttle plate, which is mounted in a stationary manner with a weir gap opposite the weir plate and is axially displaceable. The pond depth x _T must be reduced by increasing the weir gap width x _W and increasing by reducing the weir gap width x _W. A corresponding weir gap width tolerance range with a lower weir gap width x _{W, U} and an upper weir gap width x _{W, O is} assigned to the pond depth tolerance range. As an increase in the weir gap reduces the back pressure on the weir, the pond depth consequently decreases. With the lower weir gap width x _{W, U of} the weir gap width tolerance range, the upper pond depth x _{T, U is} reached and vice versa.

A further embodiment of the method provides that a decanter centrifuge is used, the liquid weir of which has at least one axially extending, U-shaped liquid channel, the inlet and outlet openings of which are arranged towards the outer periphery of the liquid weir and in the region of a U-shaped bend of the liquid channel, a compressed gas can be introduced to form a hydrohermetic pressure chamber. The pond depth x _T can thus be increased by increasing the gas pressure and reduced by lowering the gas pressure. A corresponding gas pressure tolerance range with a lower gas pressure p _U and an upper gas pressure p _{O is} assigned to the pond depth tolerance range.

Further advantageous refinements of the method are Subclaims and the following description of a Embodiment with reference to the drawing.

• einer Dekantierzentrifuge umfassend:
  • eine Hohlwelle, die wenigstens ein innenliegendes Einlaufrohr aufweist;
  • eine um die Hohlwelle rotierbare Zentrifugentrommel, welche mit wenigstens einer in ihren Trommelmantel eingebrachten Trockensubstanzaustragsausnehmung versehen ist;
  • eine ringförmigen Tauchscheibe, die an ihrem inneren Umfang mit der Hohlwelle verbunden ist und deren Außendurchmesser kleiner ist als der Innendurchmesser des Trommelmantels;
  • wenigstens ein endseitig an der Zentrifugentrommel angeordnetes Flüssigkeitswehr mit einem Wehrspalt, durch den die Flüssigkeitsphase aus der Zentrifugentrommel ableitbar ist, und mit einer Teichtiefeneinstellvorrichtung, mit der die Teichtiefe x_T der in der Zentrifugentrommel rotierenden Flüssigkeitsphase einstellbar ist,
• einer Sensoreinrichtung zur Messung der Trockensubstanzkonzentration c_TS in der abgezogenen Trockenphase;
• eine Wehrregeleinrichtung zur Regelung der Teichtiefe x_T in Abhängigkeit von der Trockensubstanzkonzentration c_TS.

The invention also relates to a decanter centrifuge system for carrying out the method, with at least the following individual parts:

• a decanter centrifuge comprising:
  • a hollow shaft which has at least one internal inlet pipe;
  • a centrifuge drum which is rotatable about the hollow shaft and which is provided with at least one dry substance discharge recess made in its drum shell;
  • an annular plunger which is connected on its inner circumference to the hollow shaft and whose outer diameter is smaller than the inner diameter of the drum shell;
  • at least one liquid weir arranged at the end of the centrifuge drum with a weir gap through which the liquid phase can be derived from the centrifuge drum and with a pond depth setting device with which the pond depth x _{T of} the liquid phase rotating in the centrifuge drum can be set,
• a sensor device for measuring the dry substance concentration c _TS in the extracted dry phase;
• a weir control device for controlling the pond depth x _T as a function of the dry matter concentration c _TS .

A decanter centrifuge system with the features of the preamble of claim 17 is from the publication "Intelligent measurement and control technology for optimized process control in wastewater treatment" (DR. H.-J. BEYER / M. FLEUTER, Westfalia Separator Industry GmbH in: 4. Mersebuger Conference automation, measuring methods and experiments in mechanical process engineering, November 1999). With the help of a weir control device, the pond depth x _{T is} adjusted depending on the dry matter concentration c _TS . This enables extensive automation of the phase separation process. However, operator intervention is still required if there are major changes in the type, quantity and / or concentration of the incoming product and the weir has reached a limit position from which it can no longer react to the changes that have occurred. In addition, high energy consumption can be determined in the ongoing process due to the high drum speeds.

It is therefore the task of a decanter centrifuge system to evolve so that energy consumption when separating a multi-phase mixture using a decanter centrifuge is reduced and also changes with quantity and composition of the incoming product can be compensated without user intervention.

This object is achieved in a decanter centrifuge system of the type mentioned above, which is characterized by a speed control device for controlling the drum speed n _Z as a function of the pond depth x _T and the dry matter concentration c _TS , with a concentration signal input (221), a pond depth signal input (222) and a speed control signal output (224).

With this decanter centrifuge system it is possible to have two Control variables, namely pond depth and speed, automatically influence. The speed control device is subordinate. The weir control device maintains priority in the system for the regulation of the pond depth depending on the Dry matter concentration. So that comes the speed control device a role as a supplementary system to that in Optimization of energy consumption during times of base load operation can effect or the position of the weir in the Regarding system reactions to changes in the inflow can optimize.

In the event of a failure of the weir control system can also the dry matter concentration by changing the drum speed regulated or at least reduced to the extent that the dry matter remains flowable and clogging the discharge lines is prevented.

Further advantageous configurations of the decanter centrifuge system can be found in subclaims 18 to 24.

Fig. 1

eine erste Ausführungsform eines Dekantierzentrifugensystems in schematischer Übersicht;

Fig. 2

eine zweite Ausführungsform eines Dekantierzentrifugensystems in schematischer Übersicht,

Fig. 3

den inneren Aufbau einer Dekantierzentrifuge mit mechanischem Flüssigkeitswehr in Schnittansicht;

Fig. 4a bis 4c

den Verlauf verschiedener Parameter während des Verfahrens, jeweils aufgetragen in einem Diagramm über der Zeitachse;

Fig. 5a,b

die ausströmende Flüssigkeit bei verschiedenen Stellungen eines mechanischen Flüssigkeitswehrs in Schnittansicht;

Fig. 6

eine Dekantierzentrifuge mit pneumatische, Flüssigkeitswehr in Schnittansicht; und

Fig. 7

den Ablauf des Verfahrens in einem Flussdiagramm.

The invention is explained in more detail below with reference to the drawings. The figures show in detail:

Fig. 1

a first embodiment of a decanter centrifuge system in a schematic overview;

Fig. 2

a second embodiment of a decanter centrifuge system in a schematic overview,

Fig. 3

the internal structure of a decanter centrifuge with mechanical liquid weir in a sectional view;

4a to 4c

the course of various parameters during the procedure, each plotted in a diagram over the time axis;

5a, b

the outflowing liquid at different positions of a mechanical liquid weir in a sectional view;

Fig. 6

a decanter centrifuge with pneumatic, liquid weir in a sectional view; and

Fig. 7

the flow of the method in a flow chart.

Figure 1 shows a first embodiment of a decanter centrifuge system according to the invention. A decanter centrifuge 100 is with an inlet pipe 11, a liquid line 36 and a dry substance discharge line 27 are connected. The decanter centrifuge 100 has a drum drive device 25 for driving a centrifuge drum 20 on and a worm drive device 45 for driving a screw conveyor 40. In addition, the decanter centrifuge 100 provided with a liquid weir that is adjustable via a weir adjustment device 35.

A sensor device 60 is arranged on the dry substance discharge line 27, with which a dry substance concentration c _TS can be measured in the dry phase drawn off there. The measurement signal from the sensor device 60 is applied to the concentration signal input 211 of a weir control device 210. In the first embodiment shown here, a weir gap width control signal, with which the weir adjustment device 35 is acted on, is output at its control output 214. The design of the weir control device 210 as a PI controller has proven to be particularly suitable. Due to a high integrating component, control deviations can initially be averaged over a period of time, so that the decanting centrifuge system does not swing up.

The measurement signal of the sensor device 60 is also based on the Concentration signal input 221 of a speed control device 220 activated. At a weir gap signal input 222 a signal is applied, which is the current Weir gap width transmitted. This weir gap signal can directly from the control output 214 of the weir control system 210 be removed so that there is a target value of the weir gap represents.

However, the actual weir gap width is preferred determined by distance measurement directly on the weir and the Weir gap width signal input 222 of the speed control device 220 activated. The speed control device 220 is designed as a step controller.

The preferred embodiment shown in FIG. 2 differs from the first from FIG. 1 in that it has a deactivation device 215, which only unlocks the speed control device 220 when the start-up phase of the process has ended and the weir gap width x _W provisionally by the weir control device 210 has been settled. Furthermore, the deactivation device 215 deactivates the speed control device 220 after a change in the drum speed until the associated influence on the dry substance concentration c _TS to be measured on the sensor device 60 has been compensated for again by the weir control device 210. The speed control device 220 is then enabled again, so that it can, if necessary, carry out a further change in the drum speed.

3 shows the internal structure of a decanter centrifuge 1 shown, consisting essentially of a centrifuge drum 20, a hollow shaft 20, a liquid weir 30 and there is a screw conveyor 40.

The centrifuge drum 20 is rotatable at bearings 23, 24 stored and can via a drum drive device 25th (see Fig. 1) are rotated. Inside the centrifuge bowl 20, a hollow shaft 10 is arranged, which via bearings 15, 16 is rotatably mounted on the drum jacket 21. In an axial A stationary inlet pipe 11 projects through the bore of the hollow shaft 10 into, which opens at least one inlet recess 12. Through this is a connection from the inner hole to External circumference of the hollow shaft 10 created.

On the outer periphery of the hollow shaft 10 is a screw conveyor 40 attached, which rotates via a worm drive device 45 is. The worm drive device 45 can also Be part of the drum drive device 25, for example be formed by a separate gear stage. hollow shaft 10 and drum jacket 21 are arranged concentrically, so that between the hollow shaft 10 and the drum jacket 21 an annular space 26 is formed. The hollow shaft 10 has one Immersion disc 14 on the one shown in Figure 1 Embodiment near a cross-sectional taper of hollow shaft 10 and drum shell 21 is arranged. The Exchange disc 14 is attached to the hollow shaft 10 and closes the annular space 26 towards the hollow shaft. The outer The circumference of the exchange disk 14 is spaced from the inner circumference of the centrifuge jacket 21, so that there is a passage of liquid or dry substance is possible. At the The end of the conical area includes the drum jacket 21 provided at least one dry matter discharge recess 22.

At the opposite axial end of the centrifuge drum 20 a liquid weir 30 is arranged. The centrifuge drum 20 is completed with a weir plate 32, which has individual recesses, the leakage of liquid allow. The weir plate 32 is opposite Throttle plate 34 arranged on a stationary part the housing of the decanter centrifuge 1 is attached and does not rotate with the cylinder drum 20. The throttle plate 34 is displaceable parallel to the axis of rotation of the cylinder drum 20. The width of one between weir plate 32 and Throttle plate 34 forming weir gap 33 is thus also variable with rotating cylinder drum 20.

The adjustment of the throttle plate 34 can be via electrical or pneumatic adjustment devices that are made via a gap width signal are controllable, which from the control output 214 of a weir control device 210 is output.

FIG. 6 shows a section of a decanter centrifuge with a pneumatic liquid weir 330. This has a U-shaped liquid channel with an inlet opening 331 directed towards the centrifuge drum 20, a U-shaped bend 333 and an outlet opening 332. It closes in FIG Embodiment shown another U-shaped channel deflection, so that a labyrinth seal is formed with 4 deflections. A compressed gas line 334 can be used to blow compressed gas into the liquid channel in the region of the U-shaped bend 333, where a hydrohermetic pressure chamber is formed. The pressurized gas introduced into the bend 333 increases the flow resistance for the liquid phase 54 and thus increases the dynamic pressure at the liquid weir 330, so that the pond depth X _T increases and the dry substance concentration of the discharged sludge phase 52 decreases. If the gas pressure is chosen too high, the gas phase breaks out of the bend 333 of the channel and either collects in the centrifuge drum 20 or flows outwards. At a gas pressure, which is approximately the pressure of the rotating liquid phase in the bend 333, no more gas passes into the liquid phase 54, so that it can emerge unhindered. If these pressure values are exceeded or fallen below, the pond depth x _{T is} no longer influenced. If the gas pressure lies between the limit pressures mentioned, the method of the invention can be used in the same way as previously stated for a decanter centrifuge with a mechanically adjustable liquid weir 30. The previously described decanter centrifuge system with its sensors 60 and control devices 210, 220 can also be operated together with a decanter centrifuge with a pneumatically adjustable liquid weir 330.

The method according to the invention is described below with reference explained on the drawing.

The product to be processed is a Multi-phase mixture containing at least one liquid phase and has an insoluble solid phase. In the here training of the method presented is the aim of Separation process, the solid phase with the lowest possible Separate residual liquid, nevertheless the dry phase consisting of solid and residual liquid still be conveyable through pipelines, so that it must remain fluid. This objective arises for example in the processing of sewage sludge in municipal Sewage treatment plants.

The cylinder drum 20 is accelerated to a high nominal speed n _Z0 , and the product is introduced. The nominal speed n _Z0 is limited by the design of the decanter centrifuge 100. At a high nominal speed n _Z0 at the beginning of the process, the drying phase 52 which separates out in the centrifuge drum 20 has a high dry substance concentration c _TS .

If there is a large difference in density between the solid and liquid phases, solids are easier to sediment. In these cases, the nominal speed n _{Z0 can be} lower than the design-related maximum speed n _{z, max} . The process can then be started at a starting speed that is 0.5 to 0.7 times the maximum speed. As a result, the dry phase initially has an increased amount of residual water. To compensate for this, the process is started with a weir wide open so that as much liquid as possible can flow off.

In any case, however, the nominal speed n _{Z0 is} chosen so high at the beginning of the process that a strong phase separation is achieved and that fine dust is not washed out with the separated liquid phase.

In order to ensure the conveyability of the drying phase 52 and to discharge such a high volume already in the start-up phase of the process that the pipelines are filled on the discharge side and a measurement of the dry substance concentration c _TS with the aid of the sensor device 60 is made possible at a high rated speed separated dry matter mixed with liquid. For this purpose, the weir gap width x _{W of} the weir gap 33 is initially set to a starting value when the process is started, which is approximately 0.5% to 5% of the maximum adjustable weir gap width x _{W, max} . The pressure in the annular space 26 rises through the narrow weir gap 33, so that liquid 54 presses into the centrifuged drying phase 52. The dry phase 52 thus diluted again is conveyed past the immersion disk 14 to the dry substance discharge recess 22.

The width ratios on the weir are shown schematically in FIGS. 5a and 5b. After exiting the weir plate 32, the liquid phase 54 is flung radially outwards due to the high centrifugal forces. With a very wide opening of the weir gap 33 shown in FIG. 5b, the liquid phase throws away and no longer wets the throttle plate 34. The gap width x _W is then without influence on the hydraulic conveyance of the drying phase 52 in the centrifuge drum 20. The maximum adjustable weir gap width x _{W, max} is thus the width of the weir gap 33 at which the throttle plate 34 is just still being wetted by the emerging liquid phase 54 takes place and thus a regulation of the dynamic pressure of the liquid phase can take place.

The weir gap width x _W is then regulated as a function of the dry matter concentration c _TS in the subtracted drying phase 52 until a predetermined target dry matter concentration c _{TS, 0 is reached} .

A weir gap width is defined as the desired working point, which is determined taking into account machine-technical and product-specific data and, if necessary, determined by preliminary tests. Furthermore, a weir gap width tolerance range, designated 37 in FIG. 4b, around the working point and a starting weir gap width x _{W, 1 are} defined. The width of the weir gap width tolerance range 37 is preferably 0.5% to 5% of the maximum weir gap width x _{W, max.}

The operating point can also be in the middle of the process effective travel range of the throttle plate 34 set so that there are equally large reserves for the Travel path of the throttle plate in both directions.

After the process has been started up in this way, the optimization of the method according to the invention begins with a view to saving energy, provided that the regulated weir gap width x _{W is} not within the weir gap width tolerance range 37.

If the weir gap width lies within the weir gap width tolerance range 37, the process is continued without optimizing energy consumption by continuously feeding in the product and subtracting the liquid and dry phases. A regulation of the weir gap width is used to react to changes in concentration or quantity in the feed, so that the dry matter concentration c _TS again corresponds to a predetermined target value after a short period of time.

If the weir gap width cannot be increased further, since it is close to the maximum weir gap width x _{W, max} , the drum speed n _Z is increased so that the dry matter concentration c _TS tends to be increased in the dry phase. This is counteracted by an increase in pressure in the liquid phase, which is brought about by reducing the weir gap width x _W. Through the steps of increasing the speed and readjusting the weir gap width, if necessary after a repetition, the throttle plate of the weir is again positioned in the weir gap width tolerance range 37.

If, however, the weir gap width x _W is below the predetermined weir gap width tolerance range 37, the centrifuge drum speed n _Z is reduced by a speed step value Δn _Z , which is preferably 2% of the maximum nominal speed. It is also possible to carry out the method with speed step values Δn _Z of 30 to 70 rpm. It has been shown that, on the one hand, this preferred value for the speed step values is large enough to bring about energy savings in the shortest possible time and in the fewest steps. On the other hand, the amount of change imposed on the process does not cause the system to swing up or have any other negative effects.

After the speed change, the weir gap width x _W is readjusted as a function of the dry matter concentration c _TS in the subtracted drying phase 52 until a predetermined desired dry matter concentration c _{TS, 0 is reached} .

• Drehzahlabsenkung,
• Nachregelung des Wehrspaltes 33 und
• Überprüfung der Wehrspaltweite

wiederholt.The regulated weir gap width x _W is again compared with the predetermined weir gap width tolerance range 37. As long as the weir gap width x _W lies outside the weir gap tolerance range 37, the steps are:

• Speed reduction,
• Readjustment of weir gap 33 and
• Checking the weir gap width

repeated.

Otherwise the energy optimization is canceled. The weir 30 is then in a position in which there are still sufficient reserves to move the throttle valve 34 in the process-technically effective range and thus to change the weir gap width x _W if a change in the quantity and / or composition of the product added so requires ,

The process according to the invention is finally carried out on a Example and with reference to FIGS. 7 and 4a to Fig. 4c explained again.

In a municipal sewage treatment plant, the decanting system of the invention is used for drying, thickening or reducing the volume flow of sewage sludge, which is a mixture of liquid and solids with a dry matter content of 0.1-50 g / l. The aim is to dewater to a dry matter concentration c _TS of 60 g / l.

4 shows the time course of the drum speed n _Z (FIG. 4a), the weir gap width x _W (FIG. 4b) and the volume flow of the product supplied (FIG. 4c) in the method according to the invention.

In the phase labeled "I" the centrifuge drum 20 accelerated to a high drum speed, which in Range of design-related, maximum permissible in operation Speed is.

As shown in Fig. 4b, the weir gap width x _W , starting from an almost closed weir gap 33, is increased in a ramp function until the drum is completely filled with the volume of the multi-phase mixture provided during operation, the predetermined drum speed is reached and a constant volume throughput in the decanter centrifuge is available.

At the end of phase "I", which comprises steps a) to d) of the method according to the invention, the weir gap width x _W is readjusted until a predefined dry substance concentration c _{TS is reached} in the removed drying phase 52.

Subsequent to the readjustment, a check is carried out at the beginning of phase “II” as to whether the weir gap width x _{W is} already within the weir gap width tolerance range 37, which is shown in FIG. 4b between the dashed lines.

Since the weir gap width x _{W is} still outside the tolerance band, the drum speed n _Z can be reduced by a speed step value Δn _z , thereby saving energy. The lower dry matter concentration c _TS due to the reduction of the drum speed in the carried out drying phase is compensated for by increasing the weir gap width x _W.

The above steps are repeated in phases "III" and "IV". At the end of phase "IV", the weir gap width x _W after the readjustment has been carried out is within the weir gap width tolerance range 37.

Therefore, the speed control device 220 is deactivated, and there is no further reduction in the drum speed. The weir 30 is now in a position from which out the decanter centrifuge system of the invention Changes in the product feed react in both directions can. The weir gap 33 can be opened further to the Withdrawal of fluid from a product with a lower dry matter concentration to increase. But he can continue be closed, which makes a more concentrated Product a certain residual moisture in the carried out drying phase remains what clogging the discharge side Pipe systems prevented.

In phase "V" of FIG. 4c, an increase in the inflow amount, for example due to a rain shower, is recorded. At the same time, the solids content is lower. In order to keep the dry matter concentration c _{TS of} the discharge constant, the weir gap width x _{W is} greatly increased out of the tolerance range 37 in order to be able to draw off more and more liquid.

The process flow is also in the flow chart of FIG Fig. 7 shows graphically: First the centrifuge drum start and the weir to a starting weir gap can be set. It then becomes the feed of the multiphase mixture opened in the rotating decanter centrifuge, which is gradually filled with it. The liquid phase and the drying phase is deducted continuously.

The weir control device 210 (cf. FIGS. 1, 2) is used for the weir position the discharge concentration to the desired Setpoint adjusted. During this time the function is the speed control device 220 is still bridged. After this this bridging period has ended, the scheme Approved. For the specific application is considered of machine-technical and plant-specific Data of the optimal working point of the weir control system 210 set. From this operating point the Area in which the decanter centrifuge is procedural and works optimally in terms of energy consumption. The center and width of this area become the definition of a weir gap width tolerance range.

The current position of the weir is then determined and with compared to the weir gap tolerance range.

The control valve's control value is below of this area, the decanter is underutilized and the drum speed, which is related to the energy consumption of the Separation process is directly related to one Speed level value can be reduced.

The control output value leaves the range in positive Direction, the drum speed is too low and must be raised the weir position in the weir gap width tolerance range due.

If one of the conditions for the adjustment of the drum speed is given, a check is carried out to determine whether the weir control device is corrected, ie whether the discharge concentration corresponds to the setpoint. If this is the case, the drum speed is adjusted. If the control difference is too large, the dry matter concentration c _TS must first be readjusted and the drum speed is only changed in a later step.

If the drum speed was changed, the result is for Weir control equipment that is constantly active may be a new one Operating point. This operating point must be determined by the control and be approached. This will be a recovery time started for the scheme. After this time begins again the cycle that defines the weir gap tolerance range and a new comparison of the weir position with the tolerance range.

Claims (24)

Method for separating a multi-phase mixture (50) into at least one liquid phase (54) and a dry phase (52) with a predetermined dry substance concentration c _TS ,
by means of a decanter centrifuge (100) which has: an annular immersion disk (14) which is connected on its inner circumference to a shaft (10) and whose outer diameter is smaller than the inner diameter of a centrifuge drum (20); and at least one liquid weir arranged at the end of the centrifuge drum (20) with a weir gap through which the liquid phase (54) can be derived from the centrifuge drum (20), and with a pond depth setting device with which the pond depth x _{T of} the rotating in the centrifuge drum (20) Liquid phase is adjustable, with the following steps: a) starting the centrifuge drum (20) to a starting drum speed n _{Z, 1} and setting the pond depth x _T to a starting pond depth x _{T, 1} ; b) introducing the multiphase mixture (50) into the rotating centrifuge drum (20); c) withdrawing the dry phase (52) through the at least one dry matter discharge recess (22) and withdrawing the liquid phase (54) through the weir gap (33); d) regulating the pond depth x _T by means of the pond depth setting device as a function of the dry matter concentration c _TS in the extracted drying phase (52) until a predetermined desired dry matter concentration c _{TS, 1} ;
characterized by the following steps e) defining a pond depth tolerance range with a lower pond depth x _{T, U} and an upper pond depth x _{T, O} ; f) comparing the adjusted pond depth x _W with the pond depth tolerance range and continuously carrying out steps b) to f) at a pond depth x _T lying within the pond depth tolerance range; g) Increase the centrifuge drum speed n _Z by a speed step value Δn _Z at a pond depth x _T that is smaller than the lower pond depth x _{T, U} , or decrease the centrifuge drum speed n _Z by a speed step value Δn _Z at a pond depth x _T that is greater than the upper pond depth x _{T, O} ; h) readjusting the pond depth x _T as a function of the dry matter concentration c _TS in the extracted drying phase (52) until a predetermined target dry matter concentration c _{TS, 0} ; i) Comparison of the readjusted pond depth x _T with a predetermined pond depth tolerance range and repetition of steps f) to i) for a pond depth x _T lying outside the pond depth tolerance range while continuously introducing the multi-phase mixture (50) into the rotating centrifuge drum (20) and subtracting the liquid and dry phase (54, 52). Method according to Claim 1, characterized in that a decanter centrifuge (100) is used, the liquid weir (30) of which consists of a weir plate (32) with at least one liquid recess and a throttle plate (34) which is stationary with the formation of a weir gap (33) is mounted and axially displaceable relative to the weir plate (32) and that the pond depth X _{T is} to be lowered by increasing the weir gap width x _W and increasing by reducing the weir gap width x _W , the pond depth tolerance range being correspondingly corresponding to a weir gap width tolerance range with a lower weir gap width X _{W, U} and an upper weir gap width x _{W, O is} assigned. Method according to Claim 2, characterized in that half of the maximum weir gap width x _{W, max is} selected as the center point of the weir gap tolerance range (37), at which the throttle plate (34) is currently not wetted by the liquid phase (54) emerging from the weir gap (33) ) more takes place. Method according to Claim 2, characterized in that the weir gap width x _W regulated in step d) is selected as the center point of the weir gap tolerance range (37). Method according to one of claims 2 to 4, characterized in that in step a) a start weir gap width x _{W, 1} corresponding to 0.5% to 5% of the maximum weir gap width x _{W, max is} selected for setting the starting pond depth x _{T, 1} . Method according to one of claims 2 to 5, characterized in that the width of the weir gap width tolerance range (37) between a lower weir gap width x _{W, U} and an upper weir gap width x _{W, O} 0.5% to 5% of the maximum weir gap width x _{W, max} is. Method according to one of claims 2 to 6, characterized in that in step d) the weir gap width x _{W is increased} as a linear function of time, as long as a control deviation of the measured dry matter concentration c _TS from the desired dry matter concentration c _{TS, 1} more than 10% is. Method according to claim 1, characterized in that a decanter centrifuge is used, the liquid weir of which has at least one axially extending, U-shaped liquid channel, the inlet and outlet openings of which are arranged towards the outer circumference of the liquid weir and in which a compressed gas is located in the region of the U-shaped bend can be introduced with the formation of a hydrohermetic pressure chamber and that the pond depth x _T can be increased by increasing the gas pressure and reduced by lowering the gas pressure, the pond depth tolerance range being assigned a corresponding gas pressure tolerance range with a lower gas pressure p _U and an upper gas pressure p ₀ . A method according to claim 8, characterized in that the pond depth x _W regulated in step d) is selected as the center of the pond depth tolerance range. Method according to one of claims 8 or 9, characterized in that a starting gas pressure p ₁ corresponding to 95% to 99.5% of a maximum gas pressure p _{max is} selected in step a) to set the starting pond depth x _{T, 1} . Method according to one of claims 8 to 10, characterized in that the width of the gas pressure tolerance range between a lower gas pressure p _U and an upper gas pressure p _{0 is} 0.5% to 5% of the maximum gas pressure p _max . Method according to one of claims 8 to 11, characterized in that in step d) the gas pressure is reduced as a linear function of time, as long as a control deviation of the measured dry substance concentration c _TS from the target dry substance concentration c _{TS, 1 is} more than 10%. Method according to one of claims 1 to 12, characterized in that the maximum permissible, design-related nominal speed n _{Z, max of} the decanter centrifuge (100) is selected as the starting drum speed n _{Z, 1} . Method according to one of claims 1 to 12, characterized in that the starting drum speed n _{Z, 1} 0.5 times to 0.7 times the maximum permissible, design-related nominal speed n _{Z, max of} the decanter centrifuge (100) is selected. Method according to one of claims 1 to 14, characterized in that the speed step value Δn _Z corresponds to 1% to 3% of the maximum permissible, design-related nominal speed n _{Z, max} . Method according to one of claims 1 to 15, characterized in that the speed step value Δn _{Z is} 30 ... 70 revolutions per minute. Decanter centrifuge system for carrying out the method according to one of claims 1 to 16, with at least the following individual parts: a decanter centrifuge (100) comprising: a hollow shaft (10) which has at least one internal inlet pipe (11); a centrifuge drum (20) which is rotatable about the hollow shaft (10) and which is provided with at least one dry substance discharge recess (22) made in its drum shell (21); an annular immersion disk (14) which is connected on its inner periphery to the hollow shaft (10) and whose outer diameter is smaller than the inner diameter of the drum shell (21); at least one liquid weir arranged at the end of the centrifuge drum (20) with a weir gap through which the liquid phase (54) can be derived from the centrifuge drum (20), and with a pond depth setting device with which the pond depth x _{T of} the rotating in the centrifuge drum (20) Liquid phase is adjustable, a sensor device (200) for measuring the dry substance concentration c _TS in the extracted dry phase (52); a weir control device (210) for controlling the pond depth x _T as a function of the dry matter concentration c _TS ; marked by a speed control device (220) for controlling the drum speed n _Z depending on the pond depth x _T and on the dry matter concentration c _TS , with a concentration signal input (221), a pond depth signal input (222) and a speed control signal output (224). Decanting centrifuge system according to Claim 17, characterized in that the decanting centrifuge (100) has a screw conveyor (40) which is arranged in the annular space (26) formed between the hollow shaft (10) and the centrifuge drum (20) and which is connected to the hollow shaft (10) with a Screw speed n _{S is} rotatable, which can be increased by a differential speed Δn _S compared to the drum speed n _Z. Decanting centrifuge system according to claim 17 or 18, characterized in that the liquid weir (30) consists of a weir plate (32) with at least one liquid recess and a throttle plate (34) which is stationary with a weir gap (33) opposite the weir plate (32) stored and axially displaceable. Decanting centrifuge system according to claim 17 or 18, characterized in that the liquid weir (330) has at least one axially extending, U-shaped liquid channel, the inlet and outlet openings (331, 332) of which are arranged towards the outer circumference of the liquid weir (330) and at which can be introduced in the area of a U-shaped bend (333) with the formation of a hydrohermetic pressure chamber via a compressed gas line (334). Decanting centrifuge system according to one of Claims 17 to 20, characterized in that the speed control device (220) can be deactivated by means of a deactivation device (215) during the control of the pond depth x _T by the weir control device (210) until a predetermined dry matter concentration c _TS is reached. Decanting centrifuge system (100) according to one of claims 17 to 21, characterized in that the weir control device (210) is a PI controller or a PID controller. Decanting centrifuge (100) according to one of Claims 17 to 22, characterized in that the speed control device (220) is a step controller which has a pond depth signal input (222), a concentration signal input (221) and a speed control signal output (224). Decanter centrifuge (100) according to one of Claims 17 to 23, characterized in that the pond depth signal input (221) of the speed control device (220) and the weir control signal output (214) of the weir control device (210) are connected directly to one another.

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