Device for effecting continuous gravimetric dosing

Description of the invention

The present invention relates to a continuous gravimetric dosing device used in particular for the gravimetric transport and dosing of bulk materials.

Such a system for continuous gravimetric transport and / or dosing of bulk materials is known from WO 99/13302, preferably a balance with a dosing rotor is used. The dosing device downstream of the bulk material feed is situated in the closed pneumatic conveying section and is supported on dynamometric chambers. A computer-controlled central dosing control system is used for the appropriate adjustment of the required quantity transferred per time unit (flow rate), the weighing-out signal of the weighing chambers serves as an input signal, and at the same time the rotational speed of the dosing rotor and possibly the lock with the drum are regulated. with baffles for feeding loose material.

Thus, in the case of this control system, the bulk material mass is detected in the balance with the dosing rotor, which is temporarily acting in the rotor weighing section, which, by multiplying by the angular velocity of the dosing rotor, the bulk material mass throughput is obtained. In this case, the electronic weighing system delays the transmission of the respective value of the weight of the bulk material (load) temporarily located on the rotor weighing section (measuring section) up to a predetermined pre-control point, so that just before unloading the bulk material into the pneumatic conveying line, corresponding to the predetermined specified flow rate, angular velocity or rotational speed can be changed, thus the metering rotor is accelerated or retarded. As a result, a relatively high dosing accuracy is achieved, which has proven itself well in practice when dosing bulk pulverulent materials, for example when dosing pulverized coal in cement rotary tubular kilns or for dosing additives in waste gas treatment.

Until now, a separate dosing control computer was used to control continuously operating gravimetric dosing devices of this kind, such as belt dosing scales, rotor dosing scales or gravimetric batch systems. This computer analyzes the weight and speed measurement or similar parameters. A separate frequency converter is usually used to control the speed of the drive. The frequency converter controls the rotational speed of the dosing drive, the predetermined speed being performed by the dosing control computer. The transmission of the set speed to the frequency converter takes place via serial or parallel data lines in an analogue or binary manner. This design corresponds to that of a divided control system for communication, so that due to the use of cabling, standard connectors and the like, the laboriousness of the installation and commissioning is correspondingly high.

The present invention relates to a device for continuous gravimetric dosing and determination of the mass flow of liquid materials, with a dosing device, with the determination of the instantaneous mass flow upstream of the receiving station by means of the dosing control device. The discharge is controlled by changing the rotational speed of the metering device drive device by means of the motor control.

The essence of the invention consists in the fact that the dosing control device and the motor control device, including the frequency converter or the thyristor control device, are combined in one subassembly, which subassembly is located in the switch cabinet or inside the dosing device.

Preferably, the above-mentioned subassembly is coupled to the metering device drive and has a rotational speed meter, preferably a tacho generator for measuring the actual rotational speed, the rotational speed meter being connected to the metering device, or the metering device having a separate rotational speed meter, preferably a friction wheel or generator. pulses.

The dosing control device according to the invention has at least one integral circuit which detects any deviation possibly present at or immediately after the receiving station and accordingly corrects the set value of the dosing control device, in which an adder unit for changing the position of the pre-control point is arranged.

PL 207 330 B1

The drive of the dosing device is an asynchronous, synchronous, vector or reluctance motor.

According to the invention, in contrast to the conventional design of the dispensing electronics, the function of the dispensing control computer or dispensing control circuit is transferred to the motor control device (frequency converter). Thus, the analysis of the process-relevant measured values, the calculation of the setpoint speeds of the metering drive and the control of the metering drive are preferably performed in one sub-assembly. As a result, the work on cabling, standard connectors or the sealing of the individual housings is significantly reduced, since such dosing devices are mostly located in a very dusty environment.

The following configurations are possible for the components consisting of a dosing control unit and a motor control unit in one device. For example, this structure can be placed in a common switch cabinet, where the measuring system with a separate measuring variable amplifier is connected to a combined motor control unit - dosing control unit. Preferably, the construction or installation of the subassembly consisting of the dosing control unit and the motor control unit is carried out directly on the dosing device, whereby the measuring system can also be connected to a combined motor control unit - dosing control unit, also with a separate measuring variable amplifier. Preferably, the sub-assembly of the combined motor control unit - dosing control unit is integrated directly into the drive motor, this measuring system with a separate measured value amplifier being connected to the motor control unit of the dosing control unit. The installation is preferably carried out again directly on the dosing device.

The subject of the invention is shown in the embodiment in the drawing, in which fig. 1 shows schematically a device for continuous, gravimetric dosing of bulk material with a dosing rotor as dosing device, fig. 2 - schematically a tape dosing scale, as a dosing device, FIG. 3 shows a different embodiment of the belt dosing weigher according to FIG. 2, and FIG. 4 shows a further embodiment of the dosing device.

1 shows a device 1 for continuous gravimetric dosing and mass flow determination, wherein the conveyed material, dosed in accordance with a predetermined flow rate, in particular loose bulk material, is fed from the hopper or tank 2 via a feed 3. The conveyed material thereby arrives at a dosing device 4 which is arranged inside the housing 5 and thus defines a weighing distance with an angle of rotation of approximately 300 [deg.] As far as the receiving station. The dosing device 4 is preferably designed as a dosing rotor 4a. In this case, the metering rotor 4a is mounted on a pivot axis AA which is guided from the side of the housing 5 and is driven by a drive 6 in the form of a speed-controlled electric motor. The housing 5 of the dosing rotor 4a rests on a dynamometer chamber 7 with a limited pivoting movement. The support moment on the dynamometer chamber 7, at a distance from the oscillation axis AA, is directly proportional to the mass flow transported through the weighing section of the dosing rotor 4a from the point lead 3 to the collection point 8.

At the lower end of the housing 5, an exhaust conduit 9 opens towards the receiving station 8. The dynamometer chamber 7 and the tachometer 6a of the drive 6 are connected to an electronic metering control device, which thus determines the instantaneous mass flow X by multiplying the instantaneous load and the rotational speed / angular velocity, and is set with respect to the set, given flow rate W, as also via a PI controller, a control line 15 and a motor control device 20, in particular via a frequency converter, it controls the drive motor 6 of the metering rotor 4a in order to change the rotational speed or angular velocity. Generally, it is the control and the regulation to keep the set flow rate constant. If there is a negative deviation in the metering device 4 (for example -0.2%), then in order to keep the flow rate X constant, the angular velocity of the metering rotor 4a is increased by a predetermined amount, i.e. + 0.2% in the present case, as indicated known by the control path in FIG. 1. A similar dispensing control device 10 is shown in further embodiments according to the invention, corresponding to FIG. 2 - 4, however according to the invention it is a device

The dosing control 10 is connected directly to the motor control device 20 to form sub-assembly G.

It is important here that by connecting or coupling the dosing control device 10 with the motor control device 20 (usually a frequency converter), the wiring and sealing workload can be significantly reduced, so that the overall design effort for the dosing device 4, hereinafter, can be significantly reduced. case on the dosing scales shown schematically in Figures 2-4. In this way, it is also possible to speed up the data exchange in the dosing device 4, in particular the signal stream with parameters such as rotational speed, rotational speed, weighing signals from the dynamometer chamber 7 and the like. Thus, by coupling the dosing control device 10 to the motor control device 20 into a single unit, it is possible to adjust the rotational speed with almost no idle time, practically eliminating the signal line 15 shown in Fig. 1. As is known, for this purpose also in the embodiment according to the invention, in order to minimize control deviations, adder units or integration circuitry, as indicated in FIG. 1, are used. If, for example, sent to the pre-control point P (cf. FIG. 1 and the aforementioned description 99/13302 of the Applicant) the setting value of the drive motor 6 was not sufficient due to the total inertia for the desired flow rate, then due to the initial displacement of the control point P with respect to the receiving station 8, the necessary period can be created in order to accelerate / deceleration of the dosing device 4 with the timely achievement of the controlled speed at the receiving station 8, thus, the preset mass flow W can be controlled or regulated by means of a dosing device. The pre-control point P should therefore be as close as possible to the receiving point 8, so that it is expedient to arrange accelerating / braking drives 6 and fast-responding frequency converters as a control device. engine 20.

Figure 3 shows a preferred embodiment of a device for continuous gravimetric dosing and mass flow determination, the subassembly G with the combined dosing control / motor controller 10/20 being connected directly to the drive motor 6 of the dosing device 4 while maintaining the remaining structure as this is shown in Fig. 1 and Fig. 2. Thus, depending on the momentary loading of the dosing belt, also the start or starting point of the regulation of the rotational speed of the drive motor 6 may be different, taking into account the respective moment of inertia, in order to maintain the given flow rate W. Here, too, structurally predetermined geometrical parameters, such as the dead weight and the length of the dosing belt, can be structurally stored in the dosing control device 10, so that in the case of the actual angular velocity measured by the tachymeter 6a or the pulse generator, it is possible to obtain precise information when the load has been determined. reaches the receiving station 8 via the dosing device 4 by means of the dynamometer chamber 7, and thus, when secondary adjustment can be carried out by accelerating / reducing the transport speed.

Although in this case a dosing rotor and a belt dosing weigher have been described as the dosing device 4, the described control and regulating device can be used in the case of a dosing screw conveyor or similar dosing devices to increase the short-term dosing accuracy at the receiving or discharge station, since here too, significant moments of inertia can occur. In this case, the subassembly G can also be integrated or built into the dosing device 4, as is indicated in FIG. 4 in the example of an intermediate chamber between the strings of a belt dosing balance. As a result, a particularly compact design of the device can be achieved.