JPS641677B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a control device for preventing surging of a variable speed blower. [Prior Art] In an air blower, when the air flow rate decreases to a flow rate below the apex of the flow rate-pressure characteristic line, the air pressure and air volume vibrate, causing a phenomenon that generates noise, the so-called surging phenomenon. If the air flow rate of the blower drops below the flow rate at which surging occurs, the opening of the suction valve or damper can be reduced to lower the blower's discharge pressure, which will change the flow rate-pressure characteristics of the blower and prevent surging from occurring. can be prevented. According to this method, a surging prevention control device has been proposed that continuously adjusts the opening of the air blower's suction valve according to the air flow rate, but in this device, the air flow rate constantly fluctuates. In this case, the frequency of operation of the suction valve increases, which increases the wear of the mechanically rotating portion of the suction valve, resulting in a disadvantage that the life of the suction valve is shortened. In order to eliminate this drawback, a device has also been proposed in which the opening degree of the suction valve is adjusted in stages according to the amount of air blown by the blower. With such a device, the frequency of operation is lower than with a device that continuously adjusts the opening of the suction valve, but the stepwise opening of the suction valve means that the amount of air blown by the blower changes at each opening. This is determined by whether the flow rate is larger or smaller than the set flow rate, so if the air flow rate fluctuates around a certain flow rate set value, the suction valve will repeatedly open and close, resulting in unstable operation. . In order to eliminate these drawbacks, the opening degree of the suction valve is adjusted in stages according to the air flow rate of the blower, and the set value of the air flow rate with respect to the switching point of the suction valve opening degree has a predetermined hysteresis. Accordingly, the present applicant has already proposed a surging prevention control device that can reduce the frequency of operation of the suction valve and stabilize its operation (see Japanese Patent Laid-Open No. 54-99207). but,
The above-mentioned surging prevention control device proposed by the present applicant was based on the premise that the rotational speed of the blower was constant. Conventionally, the induced blower used in the waste gas treatment equipment of oxygen converters was operated at a constant speed of full speed during blowing, but from the viewpoint of energy saving and dust collection efficiency, it has been changed to variable speed. It is more advantageous to reduce the speed. The circumstances during this time will be explained below with reference to FIG. FIG. 1 is a schematic diagram showing an outline of the configuration of an oxygen converter waste gas treatment device. In the same figure, oxygen converter 1
The waste gas generated by blowing is induced by the induced blower 6, so it passes through the hood 2 and is cooled by the cooler 3. After that, coarse dust is removed in the primary dust collector 4, and then the secondary Fine dust is finally removed in the dust collector 5, and the thus purified waste gas is released from the chimney 8 depending on the case by switching the three-way switching valve 7, or is collected as a valuable gas in the gas holder 9. be done. In such waste gas treatment equipment, the induced blower 6 is conventionally driven by a variable speed motor (not shown), but during blowing, it is operated at full speed, and the suction damper 10 on the suction side of the induced blower 6 is throttled. The company was operating at a sufficiently reduced capacity. However, instead of always operating the induced fan 6 at full speed using the motor, if the motor speed is reduced depending on the situation, energy can be saved in the sense that less power is required, and if the rotation speed of the induced fan 6 is reduced, , the opening degree of the suction damper 10 can be increased by loosening the throttle of the suction damper 10 accordingly. Increasing the opening degree of the suction damper 10 means that pressure loss (hereinafter simply referred to as pressure loss) in the suction damper 10 is reduced. Since the total pressure loss in the flue through which the waste gas flows is a constant value determined by the capacity of the induced blower 6, the pressure loss reduced in the suction damper 10 is directed to the primary precipitator 4 or the secondary precipitator 5. I can do it. The dust collection efficiency of each dust collector is
Since the pressure loss is roughly proportional to the magnitude of the pressure loss, the dust collection efficiency can be increased by allocating the pressure loss reduced by the suction damper 10. According to the above, the induced blower is used during blowing.
It is preferable to operate at a variable speed rather than a constant speed in terms of energy saving and dust collection efficiency. [Problems to be Solved by the Invention] However, as mentioned above, the surging prevention control device for a blower proposed earlier by the present applicant was based on the assumption that the blower would be operated at a constant speed. It became necessary to improve the system so that it could be applied to blowers operated at variable speeds. This invention was made based on the above-mentioned technical background, and therefore the purpose of this invention is to:
By adjusting the opening degree of the suction valve (or damper and the like) in stages according to the airflow rate of the blower, and by giving a predetermined width of hysteresis to the set value of the airflow rate with respect to the switching point of the suction valve opening degree, An object of the present invention is to provide a surging prevention control device for a variable speed blower that can reduce the frequency of operation of a suction valve and stabilize its operation.

[Means to solve the problem]

In order to achieve such an object, the present invention provides a stepwise variable speed blower, a suction valve or damper provided on the suction side of the blower, and an opening degree of the suction valve or damper. an operating device, an opening command device that switches and provides a plurality of opening command values stepwise to the operating device, a flow rate transmitter that detects the air flow rate of the blower and transmits it as an actual value of the air blow amount; The air blowing volume setting value corresponding to the point at which the opening command value is changed is set, and the air blowing volume setting value at the point at which the opening command value is changed to an increasing direction is different from the air blowing volume setting value at the point at which the opening command value is changed to a decreasing direction. It is composed of a plurality of comparators each having a predetermined width of hysteresis between them, and each comparator compares the set air flow rate with the actual air flow rate detected by the flow rate transmitter. a switching command generating means for giving an opening command value corresponding to the actual value of the air blowing amount to the opening command device; and a speed detection transmitter for detecting the rotational speed of the blower; A plurality of switches are provided corresponding to each stepwise different rotational speed of the blower, and the actual value of the air blowing amount is changed to the rotational speed of the blower at that time through a switch means that can be switched based on the output signal of the speed detection transmitter. It is characterized in that it is given to the switching command generation means corresponding to the switching command.

[Effect]

When the speed of the blower changes, the characteristic curve of air volume vs. wind pressure changes accordingly. Therefore, each time the speed of the blower changes, a plurality of switching command generation means provided in advance are used to change the speed of the blower to different speeds in stages. It is used by switching depending on the situation.

【Example】

Next, embodiments of the invention will be described in detail. Before explaining one embodiment of the present invention, first, an outline of a surging prevention control device previously proposed by the applicant of the present invention will be explained. FIG. 2 is a block diagram showing the configuration of a surging prevention control device for a blower previously proposed by the applicant. In the figure, 11 is a blower that blows air in the direction of the arrow, and 12 is a suction damper (sometimes called a suction valve) for adjusting the amount of air sucked into this blower 11. 14 is an opening command device that gives an opening command value to the operating machine 13; 15 is a damper operating device for adjusting the opening command value;
16 1 to 16 o are flow rate transmitters that detect the amount of air blown by the blower 11 and generate a signal F proportional to the amount of air blown, and 16 ₁ to 16 _o are settings that indicate the flow rate at the point at which the opening degree of the damper is switched, respectively. This is a comparator that compares the level and generates an output signal depending on whether it is large or small. Reference numeral 16 denotes a switching command generating means constituted by these comparators 16 ₁ to 16 _o . The opening command device 14 has a plurality of input terminals θ ₁ corresponding to each command value.
~θ _o , and the outputs of the corresponding comparators 16 ₁ to 16 _o are connected to each input terminal. It is now assumed that the blower 11 has flow rate-pressure characteristics as shown in FIG. Characteristic curves A to E in Fig. 3 each have a damper 12 opening of 100%.
-20% of each characteristic. F ₁ to _{F 8} in Figure 3
is the air flow rate indicating the opening switching point of the damper 12, of which F ₁ , F ₃ , F ₅ , and F ₇ are the air flow amount at the opening switching point in the decreasing direction of the air flow amount F, F ₂ , F ₄ , _F6 , _F8
is the air flow rate at the opening switching point in the increasing direction of the air flow rate F. In the apparatus shown in FIG. 2, when the opening degree of the damper 12 is adjusted in steps of 20% in the range of 100% to 20% as shown in FIG. 3, the comparator 16 ₁
〜16 _o are provided, and the set values for each are damper opening switching point airflow volume F ₁・F ₂ , F ₃・F ₄ ,
F ₅ , F ₆ and F ₇ , F ₈ are set. In addition, the opening command device 14 has 20%, 40%, 60%, 80% and
An opening command value of 100% is set corresponding to each input terminal θ ₁ to _{θ o} . The comparators 16 ₁ to 16 _o generate output signals only when the output signal F of the flow rate transmitter 15 is larger than two set values respectively set, and
The output signal is stopped when the output signal becomes smaller than the set value. And the opening command device 14 is
The input terminal corresponding to the maximum opening command value is selected from among the input terminals θ ₁ to _{θ o} to which output signals are given from 16 ₁ to 16 _o , and the corresponding opening command value is sent to the damper operating device 13. give. A specific example of the configuration of the opening degree command device 14 and the switching command generation means 16 is shown in FIG. In FIG. 4, H ₁ , H ₂ to _{H 7} , H ₈ are connected to comparators 16 ₁ to 16, respectively.
16 ₄ output contacts, X ₁ to X ₄ are output relays, A ₁ to _{A 4}
are the self-holding contacts of relays X ₁ to _{X 4} , respectively, and c ₁
~ _c4 are switching output contacts of relays _X1 ~ _X4 , respectively. The switching contacts c ₁ to c ₄ connect the terminal b to each input θ 1 to θ ₄ of each command value setter _{14 1} to 14 ₄ of the opening command device, and the terminal a to the common terminal c of the next stage switching contact. , and connect terminal a of the final stage switching contact c ₄ to setter 1.
Connect to input θ ₅ of 4 ₅ . Relays X ₁ to X ₄ turn on contacts A ₁ to _{A 4} , which are off in the non-operating state, and switching contacts C ₁ to _{C 4} , which are closed to the terminal B side, respectively, when in the operating state, and close them to the terminal A side. Switch to Each output contact H ₁ , H ₂ of each comparator 16 ₁ to 16 ₄
~ _H7 , _H8 are turned off while the signal F given from the flow rate transmitter is smaller than the respective set values _F1 , _F2 ~ _F7 , _F8 , and turned on when the set values are exceeded. Setting values for each output contact H ₁ -H ₈ are selected as F ₁ -F ₈ shown in FIG. 3, respectively. If the air flow rate F is larger than the set value _F8 , the contacts of all comparators
Since H ₁ to _{H 8} are all on, relays X ₁ to _{X 4}
operates, contacts A ₁ to _{A 4} turn on, and switching contacts C ₁ to C ₄ turn on.
is closed to the terminal a side, so the input terminal θ ₅ connected to the setting device 14 ₅ of the opening degree command device 14 is selected.
As a result, from the opening command device 14, the setting device 14 ₅
A command value of 100% opening is output and given to the damper operating device 13 shown in FIG. The damper operating device 13 operates the damper 12 according to this command value so that the opening degree becomes 100%. In this way,
When the blower 11 is operated with the damper opening degree at 100%, the blower 11 takes a flow rate-pressure characteristic shown by characteristic line A in FIG. In this state, when the air flow rate F decreases below _F8 , contact _H8 of comparator ₁₆₄ turns off, but since self-holding contact _A4 of relay _X4 itself is on, the relay
Since _X4 maintains its operating state, the command value is not changed. When the air flow rate F further decreases below _F7 , the contact _H7 of the comparator ₁₆₄ is turned off. As a result, relay X ₄ becomes inoperable, contact a ₄ turns off, and changeover contact c ₄ switches to terminal b side, and this time,
Since the setting device ₁₄₄ is selected, the opening command value of 80% is output from the opening command device 14. According to this command value, the operating device 13 adjusts the damper 12 to 80% opening. As a result, the flow rate of the blower 11 -
Since the pressure characteristics shift from the characteristic curve A to B in FIG. 3, the peak of the characteristic line where surging occurs also shifts from _S1 to _S2 on the low flow rate side. Therefore, surging is less likely to occur and stable operation can be continued. In the same way, in the process of decreasing the air flow rate F, the lower setting value of the two setting values set in the comparator, for example, for comparator ₁₆₄ , the opening degree is changed at the point of setting value _F7 . The command value is switched. In addition, in the process of increasing the air flow rate F, the opening command is adjusted at the higher level setting value of the two setting values set for each comparator, for example, for comparator 16 ₄ , the opening command is set at the setting value F ₈ . By performing the switching, for example, for the comparator ₁₆₄ , switching of the opening degree command is realized with a hysteresis width of F ₈ -F ₇ =ΔF. This concludes the general description of the surging prevention control device previously proposed by the present applicant, and next, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 5 is a block diagram showing one embodiment of the present invention. In the figure, the blower 11 is coupled to a drive motor 20 via a coupling 19 and is driven by the motor. The motor 20 is a variable speed motor, and its speed can be changed by any suitable means (preferably in a manner that is energy efficient). The speed detection transmitter 21 detects the rotational speed of the blower 11, and when the rotational speed is at a certain first speed, it sends a command to the switches 17 and 18 that are interlocked with each other, so that the switches contact contact a. When it is detected that the blower 11 is at a certain second speed, a command is sent so that the switches 17 and 18 are switched to contact b, and in the same manner, the blower 11 is set to the nth speed ( (n is any integer), switches 17 and 18 are switched to terminal n. Furthermore, as explained earlier with reference to FIGS. 2 and 4, if the combination of the switching command generating means 16 and the opening command device 14 is S ₀ , it corresponds to n types of rotational speeds that the blower 11 can take. For each of the n types of characteristic curves of air volume vs. wind pressure, n combinations of comparator groups and opening command devices were set in the same manner as described above with reference to FIGS. 3 and 4. (S ₀ -S _o ) are prepared, and as shown in the figure, the comparator group is connected to each terminal of the switch 17, and the opening command device is connected to each terminal of the switch 18. Figure 6 is a characteristic diagram showing the characteristic curve of air volume versus wind pressure at the top when the rotation speed of the fan is 100%, and the same characteristic curve at the bottom when the rotation speed is 50%. It is. The rotation speed of the blower is
When there are n types instead of 100% and 50%,
There are n groups of characteristic curves, and each of them has n combinations S ₀ to _{S o} of settings with hysteresis, as explained with reference to FIGS. 2, 3, and 4. This is done in each case. From the above, it is believed that the explanation of the operation of the embodiment of the present invention shown in FIG. 5 is already clear. In addition,
In FIG. 5, the opening command device 14 is shown to be switched to a different one each time the rotational speed of the blower changes, but one opening command device 14 is commonly used for all, and the switching It goes without saying that it is sufficient to provide only the command generating means 16 for each speed and use it selectively. [Effect of the Invention] As explained above, according to the present invention, in a variable speed blower, no matter what speed the blower is switched to, the suction valve or damper is adjusted in stages according to the air flow rate of the blower at that speed. The frequency of operation of the suction valve or damper is reduced compared to continuous operation of the suction valve or damper, and/or the opening degree of the suction valve or damper is switched in an increasing direction. Since there is a predetermined width of hysteresis between the flow rate at the point where the flow rate is switched to the decreasing direction, even if there is a slight fluctuation in the air flow rate near the set flow rate at the switching point, the suction valve or damper will not be operated due to this. This has the effect that the suction valve or damper can be operated stably, and the initial objective can be achieved. Moreover, if the present invention is applied to an induced fan in an oxygen converter waste gas treatment device, there is an advantage that surging can be prevented stably as described above while saving energy and improving dust collection efficiency. Although the embodiment of the present invention has been described as using an analog meter, it goes without saying that this can be realized using a microcomputer.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the configuration of an oxygen converter waste gas treatment device, Fig. 2 is a block diagram showing the configuration of a blower surging prevention control device proposed earlier by the applicant, and Fig. 3 is a blower 4 is an electric circuit diagram showing a specific configuration example of the opening command device 14 and comparator 16 in FIG. 2, and FIG. FIG. 6 is a block diagram showing the configuration of an embodiment of the invention, and a characteristic diagram showing the relationship between air volume and air pressure when the rotational speed of the blower changes. In the figure, 1 is an oxygen converter, 2 is a hood, 3 is a cooler, 4 is a primary dust collector, 5 is a secondary dust collector, 6 is an induced draft equipment, 7 is a three-way switching valve, 8 is a chimney, 9 is a gas holder, 10 is a suction damper, 11 is a blower, 12 is a suction damper, 13 is a damper operating device, 14 is an opening command device, 15 is a flow rate transmitter, 16
are switching command generating means, 16 ₁ to 16 _o are respective comparators, 17 and 18 are respective interlocking switches,
19 is a coupling, 20 is a motor, and 21 is a speed detection transmitter.

Claims (1)

[Claims] 1. A blower 11 whose speed is variable in steps, a suction valve or damper 12 provided on the suction side of this blower, and an operating device 13 that operates the opening degree of this suction valve or damper; An opening command device 14 that switches and gives a plurality of opening command values to the operating device in stages; a flow rate transmitter 15 that detects the amount of air blown by the blower and transmits it as an actual value of the amount of air blown; and the opening command. The air blow rate setting value corresponding to the point where the value is changed is set, and there is a difference between the air blow rate setting value at the point where each opening command value is changed in the increasing direction and the air blow rate setting value at the point where the opening command value is changed in the decreasing direction. It is composed of a plurality of comparators 16 ₁ to 16 _o , each having a hysteresis of a predetermined width, and each comparator calculates the air flow rate set value and the air flow rate actual value detected by the flow rate transmitter, respectively. a switching command generating means 16 that compares and gives an opening command value to the opening command device according to the actual value of air blowing amount; and a speed detection transmitter 21 that detects the rotational speed of the blower, and the switching command A plurality of generating means are provided corresponding to each stepwise different rotational speed of the blower, and a switch means 17 is configured to switch the actual value of the air blow amount based on the output signal of the speed detection transmitter.
A surging prevention control device for a variable speed blower, characterized in that the surging prevention control device for a variable speed blower is applied to a switching command generation means corresponding to the rotational speed of the blower at that time.