Improvement of PLC control system for the hottest

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Introduction to PLC control system improvement of bag type dust collector: This paper combines Siemens SPLC and Delta a series touch screen, uses matrix control method to realize the action of dust collector pulse valve, and realizes the data exchange between master station and distributed i/o equipment through PROFIBUS DP industrial bus, and obtains optimized control effect

1 introduction

industrial production and urban life will produce a large amount of flue gas and dust, such as thermal power generation, heating, etc., which will pollute the environment and endanger health

with the development of bag type dust removal technology and the increasing requirements of environmental protection, the application scope of bag type dust collector is more and more extensive. At present, bag type dust collector can be used to treat high-temperature, high humidity, adhesive, explosive, abrasive flue gas, and even filter the air containing ultra-fine dust. In the field of bag filter control, PLC occupies the main technical position. With the continuous development of control technology, PLC and touch screen are more and more widely used in the field of industrial control. Instead of the traditional intelligent operation of control panel and keyboard, touch screen can be used for parameter setting, data display and storage, and describe the automatic control process in the form of curve, animation, etc. The combined use of PLC and touch screen, on the one hand, expands the function of PLC, making it an independent system with graphical and interactive working interface, on the other hand, greatly reduces the number of switches, buttons, instruments, etc. on the operation cabinet, making the operation easier. At present, in some occasions with high control requirements, many parameter changes and hardware wiring changes, the combination of touch screen and PLC has occupied a dominant position

however, according to the traditional PLC point-to-point direct control form of the dust collector, not only the design and its field wiring are complex, but also the external signal interference makes the system unstable and expensive. In this paper, the Siemens SPLC and Delta a series touch screen are combined to realize the action of the pulse valve of the dust collector by using the matrix control method. The data exchange between the master station and the distributed i/o equipment is realized through the Profibus DP industrial bus, and the optimized control effect is achieved

2 system composition and main functions

2.1 system composition

the control system of bag filter is shown in Figure 1

Figure 1 system requirements

the bag type dust removal system is mainly composed of the dust collector body, the ash unloading system and the temperature, pressure and fault alarm of its pipeline. Among them, the dust removal control of differential pressure is mainly completed in the dust remover body. The dust remover has 6 chambers in total, 13 pulse solenoid valves in each chamber, a total of 78; And 1 outlet control valve for each chamber, 6 in total

2.2 function design

(1) ash cleaning control

control mode: differential pressure/timing, offline differential pressure/timing, manual control (for debugging or detection); Pulse interval: 1~60s continuously adjustable; Pulse width: 0.02~0.2s continuously adjustable; Timing ash cleaning cycle: 0~99 minutes continuously adjustable; Setting range of differential pressure ash cleaning: 0~3000pa, continuously adjustable; Temperature setting range: 0~300 ℃ continuously adjustable; When the dust collector of one foil rolling production line reaches the high resistance (set high pressure difference), start the pulse valve of 1; To the end of the last group of pulse valves in the 6\; dedusting room, the ash cleaning is completed; When the next high resistance arrives, the ash shall be removed in the same way

(2) ash unloading control

high and low material levels: each dust collector only sets one high and low material level on one ash hopper for alarm (high material level prompts ash unloading, and low material level prompts that ash unloading can be completed). When the material level is high or low, the sound and light alarm will be given, and the dust removal system will be automatically stopped if it is not handled after a certain time; Control room and site are used for ash unloading; Transmit signals to HMI to display system operation status

(3) temperature and pressure detection

the system needs to detect the inlet and outlet differential pressure, inlet temperature, outlet temperature and leakage detection pressure of each indoor filter bag

(4) when the control relationship (automatic mode)

flue gas temperature (refers to the inlet flue gas temperature) is normal (100~165 ℃), the inlet and outlet valves are all opened, and the bypass valve is closed; When the temperature is lower than (100 ℃) or higher than (165 ℃), the control system will give an alarm; When the temperature is higher than (170 ℃), open the bypass valve first and then close the 1~6\; outlet valve in turn; The inlet valve is manually closed on site

3 hardware configuration and software implementation

the system consists of German Siemens s series and some intermediate relays to form a matrix to detect and control the input points. The delta touch screen can be used to set the action width, interval time and timing cycle of pulse valve with poor performance of acidol and foam, and you can also view the action of pulse valve in each room. The output of PLC and intermediate relay are used to form a row and column structure, and the output control points are placed at the intersection of the row and column structure, which can greatly reduce the hardware cost of the system compared with the point-to-point output control. For example, if the point-to-point control mode is adopted for the PLC automatic control system of 13 groups/off-line injection pulse back blowing bag type dust remover in room 6 of Mingyang, Guangxi, the PLC control system needs at least 78 output points, The matrix PLC control system, which is composed of PLC output points and intermediate relays, only needs 19 output points to complete the same work

through the man-machine interface, the system can work in the room where the pulse valve is blowing at a glance. The differential pressure indication and upper and lower pressure alarm output are available. The control system can realize interlocking control with the local control box, which can facilitate the field equipment maintenance, as shown in Figure 2. The system has the advantages of stable and reliable operation, simple operation and convenient maintenance, which greatly reduces the labor intensity of operators

Figure 2 HMI main screen

6 × 13 matrix control system output is shown in Table 1

according to the schematic diagram 3 and table 1 above, the pulse valve of each chamber only needs to act through any combination of q0.0~q1.4 and q1.5~q2.2. Among them, q0.0~q1.4 and M terminals enable the intermediate relay to energize and pull in the switch to control the connection between the electromagnetic pulse valve and 24v+. Q1.5~q2.2 and M terminals enable the intermediate relay to energize and pull in the switch to control the connection between the electromagnetic pulse valve and M terminal. For example, when the e chamber 92electromagnetic pulse valve action chamber is required, only q1.0 and q2.2 need to be set to 1. At this time, q1.0 outputs 24V voltage, and the normally open point of the intermediate relay is closed, so that the e chamber 9\e electromagnetic pulse valve is connected with 24v+. Similarly, q2.2 outputs 24V voltage, and the normally open point of the intermediate relay is closed, so that the e chamber 9\e electromagnetic pulse valve is connected with M. At this time, both ends of e chamber 9ne electromagnetic pulse valve and 24v+ and M ends are connected at the same time, that is, they act. During this process, although the six electromagnetic pulse valves numbered 9y controlled by q1.0 are all connected with L1 end, only the pulse valve in chamber e controlled by q2.2 is connected with m end at this time. That is, the electromagnetic pulse valve at the intersection controlled by q1.0 and q2.2 acts, and the electromagnetic pulse valve at other points is only connected to 24v+ or m terminal. In this principle, the solenoid valve can use the 24V voltage output by PLC to realize its action. However, in order to stabilize the action of the solenoid pulse valve and reduce the load of PLC, it uses external stable DC power supply, so 19 intermediate relays are used

on the delta touch screen man-machine, the status display of the pulse valve action can be realized through the "and" operation of each pulse action signal in each room and each room. For example, the action display of the D room 5pp electromagnetic pulse valve can be realized through the following process:

a Q 1.4

a Q 2.0

= m 0.0

the touch screen can judge whether the electromagnetic pulse valve is acting by reading the contents in m0.0, If and only if q0.4 and q2.0 are both 1, then the status light on the touch screen will show that the electromagnetic pulse valve is in action, and it does not act in other cases. When the D room 5pp electromagnetic pulse valve is manually controlled on the touch screen, it only needs to set m0.1 to 1 through the touch screen. At this time, PLC can manually control the electromagnetic pulse valve in time through the following program segments:

a m0.1

= Q 1.4

= Q 2.0

it can be seen from the above that by adding 19 relays on the original basis, 59 output points are reduced, and a very satisfactory effect is achieved

Figure 3 valve matrix control principle

Figure 4 PROFIBUS DP configuration

in order to reduce the laying of control lines between the site and the control room and the transmission of external interference signals, PROFIBUS DP is adopted in the system. Only one communication line is used to connect the distributed i/o equipment with the controller CPU. The DP master station exchanges data with the distributed i/o equipment and monitors the Profibus DP data through PROFIBUS DP, as shown in Figure 4. The distributed i/o device (=dp slave) collects field sensor and actuator data so that it can be transmitted to the controller CPU through PROFIBUS DP

4 conclusion

in the pulse bag filter, the project uses the touch screen to replace the conventional digital display instrument and manual control panel to realize the setting and display of system working parameters and the Chinese display of fault alarm information, which greatly improves the interactivity of system operation and reduces the burden of on-site operators, so as to strengthen the man-machine dialogue function of the system; The matrix control circuit is improved, and the control of a large number of pulse valves of bag filter is realized (by n × M to n+m), saving a large number of PLC input/output points with year-on-year growth of 4.6%, 3.4% and 1.1% respectively, simplifying the control circuit and reducing the cost

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