RU2256680C1 - Method of control of water-stream soot granulation process - Google Patents

Abstract

FIELD: automation of chemical technological processes; control of water-stream soot granulation process.

SUBSTANCE: proposed method includes stabilization of power consumed by electric motor of granulator rotor drive by change of flow rate of water to granulator and stabilization of smoothed present magnitude of water flow rate through change of revolutions of sluice-type feeder supplying soot to granulator.

EFFECT: improved quality of soot granulation; enhanced stability of temperature conditions in drying moist granules.

3 dwg, 1 tbl, 2 ex

Description

The invention relates to the automation of chemical-technological processes and can be used to control the wet granulation process.

The process of soot granule formation is carried out by intensively mixing dusty soot with water in a granulator, followed by drying of the wet granules in a dryer drum with high-temperature flue gases generated during fuel combustion. Providing the required particle size distribution of the granules is achieved with a certain ratio of the mass flow rates of dusting soot and wetting agent (moisture content of the granules), which in the general case is determined by their physicochemical properties [1].

A known method of automatically controlling the weight ratio of dusty carbon black and water, in which the flow rate of dusty carbon black is determined using continuous belt scales, and the water flow rate is automatically adjusted to maintain a given ratio [2].

The disadvantage of this method of regulation is the significant technical difficulties not only to accurately measure the weight of dusty soot, but simply to transport it stably using a conveyor belt equipped with weight measuring sensors. Problems associated with the transportation, weighing and dosing of dusty soot are the main reasons that necessitate the granulation of soot.

Another disadvantage of this method is that it does not take into account the change in the physicochemical parameters of soot and wetting agent, which does not provide the required quality of the finished product.

Closest to the proposed method is a method of controlling the process of wet granulation of soot, which consists in stabilizing the power consumed by the granulator rotor drive motor [3].

We accept this method as a prototype.

This method proposes 2 options for stabilizing the power consumption consumed by the granulator rotor drive electric motor.

According to the first option, the power is regulated by changing the flow rate of the water (wetting agent), and the number of revolutions of the sluice feeder supplying soot to the granulator is kept constant at a given level.

This control method does not allow to obtain the required quality of granulation and thermal regime of drying wet granules due to the following circumstances. The volumetric supply of dusty soot by a lock feeder at a constant speed of rotation does not ensure its constant weight flow. At the same time, there are both high-frequency fluctuations in the mass flow rate of dusty soot and low-frequency oscillations of significant amplitude. This is due to the fact that the bulk density varies significantly. In addition to the main soot stream from the reactors, soot from the after-treatment filter after cleaning the gases passing through the drying drum and from the aspiration system of the process equipment also enters the compactor hopper located in front of the granulator, in addition to the main soot stream from the reactors. The last two streams carry soot, which has already passed granulation (dust and small fragments of destroyed granules) and has a higher bulk density. Therefore, for example, when packaging products, the soot flow from the aspiration system increases sharply, changing the bulk density of the entire mass of soot in the hopper in front of the granulator. Higher-frequency changes in soot supply occur during the periodic formation and collapse of soot arches on the conical surface of the hopper, its sticking to the walls of the hopper and the blades of the airlock feeder due to its high adhesion to metal surfaces. Therefore, in the known method, when the motor power is stabilized by changing the water flow rate at a constant number of revolutions of the gateway feeder, the weight consumption of soot in the granulator can vary significantly, which causes an almost equivalent change in the water flow rate, and hence the flow rate of wet granules, equal to the total mass of the components included in the granulator. This leads to a significant change in temperature in the dryer drum, the restoration of which is complicated by the large inertia of the drying process. As a result, the overdrying of the granules leads to their intense destruction, and when underdrying, they get rejected by moisture.

It should be noted that in this embodiment, the stabilization of electric motor power, and hence the moisture content of the granules, is satisfactory.

When implementing the second control option according to this method, namely, when regulating the power of the granulator rotor drive electric motor by changing the speed of the lock feeder when the water flow is kept constant, it is not possible to achieve power stabilization within the specified limits, which causes fluctuations in the moisture content of the granules, and hence sizes. This is due to the fact that the regulatory body itself - the gateway feeder is a source of disturbance in the mass flow rate of soot when its apparent density and other factors mentioned above change.

Since the amount of water is constant, the temperature regime in this control variant is more stable, however, in this embodiment, temperature fluctuations at the drum outlet are caused by fluctuations in the initial moisture content of the granules.

The aim of the present invention is to improve the quality of granulation and the stability of the thermal regime of the drying process.

This goal is achieved by the fact that in the known method, including stabilization of the power consumed by the granulator rotor drive electric motor, by changing the granulation water flow rate, the smoothed current value of the water flow rate is further adjusted by changing the number of revolutions of the lock feeder.

The essence of the proposed control method is illustrated by the following experimental data.

Figure 1 shows the time diagrams of the power N, the flow rate of the granulation Qв and the soot temperature at the outlet of the drying drum Tc obtained by stabilizing the power by changing the flow rate of the prototype [3]. Since stabilization of the N power ensures a constant ratio of soot and water (approximately 50:50), the water consumption graph almost unambiguously reflects both the consumption of dusty soot and wet granules. As can be seen in figure 1, the fluctuation diagram of the supply of dusty soot includes both high-frequency and low-frequency components, and only the low-frequency components of the flow of wet granules affect the temperature of the granulated soot at the outlet of the drying drum Tc.

The dynamic differences in the granulation and drying parameters are explained by different speeds of the processes: the soot dwell time in the granulator is 10-20 seconds, and in the dryer drum - 10-20 minutes. Therefore, the high-frequency vibrations of the wet granules are leveled in the drying drum, as can be seen when comparing the diagrams TC and QB in figure 1. In addition, it is seen that the soot temperature diagram is shifted in time by a value of τ relative to the water flow rate Qв, which also indicates the inertia of the drying process. A closer relationship between the temperature Tc is observed for low-frequency fluctuations in the values of water flow Qv.

A dryer drum equipped with blades on the inner surface in order to intensify heat and mass transfer of a wet granule layer with hot flue gases is a control object with pronounced mixing, which leads to leveling of high-frequency disturbances in the consumption of wet granules, therefore, it affects the temperature regime in mainly only low-frequency fluctuations in the flow of dusty soot, which at constant power cause adequate fluctuations in water and wet granules.

In the proposed method for controlling the process of wet granulation of soot, including stabilizing the power consumed by the granulator rotor drive motor, changing the flow rate of water to granulation, additionally changing the number of revolutions of the airlock feeder supplying dusting soot to the granulator, the smoothed current value of the water flow rate is maintained (in Fig. 1, the smoothed the current value of the water flow is shown by a dashed line).

A significant difference of the proposed method, which ensures the stability of the moisture content of the granules and the temperature regime of drying, is that a more dynamic process of formation of granules is controlled using a water flow control loop that provides higher performance, and stabilization of the temperature of the drying, characterized by significant inertia, is achieved by adjusting the smoothed current water consumption. When controlling a rapidly changing power consumption by changing the water flow rate, the value of this control parameter itself should oscillate around a given value by changing the number of revolutions of the airlock feeder supplying dusty soot to the granulator. Only such control of the wet granulation process with the existing nature of disturbances in the consumption of dusty soot can, unlike both versions of the prototype, simultaneously ensure stabilization of the moisture content of the granules and the temperature regime of drying.

Figure 2 shows a diagram of the implementation of this method.

The dusting soot from the tank 1 is supplied to the granulator 4 by means of a gate feeder 2 controlled by an electric motor 3. The flow rate of the granulator to the granulator is controlled by a flow meter 5 and is automatically changed by the regulator 6 by acting on the control valve 7, comparing the set power value with the measured sensor 8 from the drive motor granulator rotor 9. The signal from the flowmeter 5 enters through the filter 10 to the regulator 11, from which it is supplied to a frequency-controlled drive 12, which controls the frequency of the supply voltage of the electric motor 3.

The operation of the circuit is as follows.

For example, let the bulk density of dusty soot increase, and with a constant number of revolutions of the airlock feeder, its mass flow rate will increase. In this case, the humidity of the soot will decrease and, accordingly, the power consumption of the electric motor 9 will decrease. This upsets the balance of the regulator 6, which, acting on the control valve 7, will increase the water flow until the set value of the power of the electric motor 9 is restored.

The control loop smoothed current water flow works as follows. The water flow signal is measured by the sensor 5 and passes through a filter 10, in which high-frequency oscillations are suppressed, as shown in Fig. 1 in the graphs of water flow and its smoothed current value. As long as the smoothed current value of the water flow is constant and corresponds to the set value, the number of revolutions remains unchanged. Let, for example, the water flow signal measured by the sensor 5 and passed through the filter 10, suppressing high-frequency oscillations, exceed a predetermined value. In this case, the regulator 11 will generate a signal to the variable frequency drive 12 to lower the frequency of the supply voltage of the electric motor 3. A decrease in the number of revolutions of the airlock feeder reduces the supply of dusty soot, restoring the set value of the water flow.

Example 1

The control method was tested in industrial conditions of OJSC “Yaroslavl carbon black”.

The power control loops were controlled by changing the water flow rate and water flow rate by changing the number of revolutions of the gateway feeder using the “Remicont-130” small-channel controller. The water flow signal was supplied to the PI controller through a filter with the transfer function of the aperiodic link:

where s, T is the Laplace operator and the time constant, respectively.

The command signal about the change in the number of revolutions of the gateway feeder from the Remicont-130 controller was supplied to a frequency-controlled drive that controls the frequency of the supply voltage of the gateway feeder electric motor.

The filter time constant T was determined empirically, firstly, from the condition of minimizing the influence of changes in the number of revolutions of the gateway feeder on the stability of maintaining power consumption by changing the water flow rate, and secondly, ensuring a stable value of the smoothed current water flow rate and, consequently, the temperature of granular soot at the outlet of the dryer drum. In the process of adjusting the control loops, the filter time constant varied within 0.5–3 min. The best value of the time constant was about 1 minute, which corresponds to the suppression of the amplitude of the harmonic signal with a frequency of 2π rad / min up to 15%, and with a frequency of 1 rad / min - only up to 70%. For a harmonic signal, the maximum value is reached after 1/4 of the period, which for a frequency of 1 rad / min is approximately 1.5 minutes or 10% of the soot's residence time in the dryer drum.

Figure 3 shows the time diagrams of the power consumption of the electric drive motor of the rotor of the granulator N, the water flow Qв (smoothed current water flow is shown by a dashed line), the number of revolutions of the airlock feeder n, the temperature of the granulated soot at the outlet of the drying drum Tc. Figure 1 shows that until the 6th minute the regulator of the smoothed current flow rate of water was in equilibrium and the number of revolutions of the gateway feeder n remained practically unchanged. Starting from the 6th minute, the number of revolutions n increased, keeping constant the average mass flow rate of dusty soot. Subsequently, there was a gradual decrease in the number of revolutions n to close to the initial value. At the same time, high-frequency fluctuations in water flow Qw, caused by the operation of the power regulator N, fluctuated around a predetermined value without significantly affecting the temperature of granular soot Tc at the outlet of the drying drum.

The results of comparative tests of the control method of the prototype and variants of the proposed method are shown in the table.

Table Experience number Water consumption, kg / h The moisture content of the granules,% Dust soot consumption,% Consumption of wet granules, kg / h Power consumption kW Speed of airlock feeder The temperature of the dry granules, ° C Dust content,% By a known method Experience 1 3550 50.1 3536 7086 72 16 160 2.9 Experience 2 4000 48.3 4280 8282 72 16 103 2.1 According to the proposed method Example 1 Experience 3 3560 50.6 3617 7035 72 fifteen 120 1.6 Experience 4 3480 50.3 3440 6840 72 19 125 0.8 Example 2 Experience 5 3500 50.6 3416 6917 72 17 122 1.4 Experience 6 3540 49.7 3482 7122 72 14 118 1.7

In experiment 2, it was shown that the flow rate of dusty soot at a constant number of revolutions of the airlock feeder reached 4280 kg / h in comparison with 3536 kg / h in experiment 1 at a constant number of revolutions - 16 rpm. Low-frequency fluctuations in the mass flow rate of dusty soot at a constant number of revolutions caused an increase in the consumption of wet granules from 7086 to 8282 kg / h. The temperature of the granules at the outlet of the dryer drum decreased from 160 to 103 ° C, that is, close to critical, when moisture may appear in the finished product, therefore, the known control method involves an increased temperature regime, which in turn leads to an increase in the dust content in the finished products.

In experiment 4, a decrease in the consumption of dusty soot is compensated by an increase in the number of revolutions up to 19 rpm from 15 rpm in experiment 3. At constant humidity of the granules, stabilization of their mass flow rate allowed to keep the temperature at the outlet of the drying drum within 120 ÷ 125 ° C. In addition, higher stability of the temperature regime in the drying drum allowed to reduce fuel consumption in experiments 3, 4 in comparison with the known control method by 3-5%.

Example 2

In experiments 5, 6, instead of a filter and a PI controller, an integral controller was used in the control loop of the smoothed current water flow by changing the speed of the gateway feeder, which has the ability to smooth out high-frequency oscillations. The isodrome time varied within 1–4 min, and the best results were obtained at a value close to 1.5 min. In experiment 6, data are presented illustrating the operation of the control circuit under conditions of reducing the number of revolutions of the gateway feeder to 14 rpm from 17 rpm in experiment 5.

In experiments 3, 4 and 5, 6, an almost equivalent result was obtained: the deviation of the mass flow rate of wet granules from 16% in the known method was reduced in the proposed method due to stabilization of the smoothed current flow rate of the water by changing the speed of the lock feeder to 3%.

The technological cycle of the finished product preparation process is completed by aspiration of dust generated as a result of the destruction of part of the granules and its recycling for re-granulation, therefore, the technical and economic advantages of the proposed method include how to reduce the energy costs of drying by reducing the maximum allowable temperature of granular soot at the outlet of the drying drum , and reducing the amount of soot destroyed during the drying process and returned to the repeated granulation. In general, both of these factors create the prerequisites for increasing the productivity of the entire production line, since the productivity of the granulation and drying processes limits the volume of finished products of this installation.

Sources of information:

1. V.Yu. Orlov, A.M. Komarov, L.A. Lyapina, Production and use of carbon black for rubbers. Yaroslavl, ed. AR, 2002, p. 314.

2. USA patent 3337907, 1967.

3. US patent 3266873, 1966.

Claims (1)

A method for controlling the process of wet granulation of soot, including stabilization of the power consumed by the granulator rotor drive electric motor, by changing the flow rate of water to granulation, characterized in that in addition to changing the number of revolutions of the airlock feeder supplying dusting soot to the granulator, the smoothed current value of the water flow rate is stabilized.

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