PLC control system and configuration of boiler mak

2022-10-15
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PLC control system and configuration of boiler make-up water treatment in power plant introduction

make-up water treatment in power plant boilers requires the use of corresponding treatment technologies in combination with different water quality conditions. Untreated water contains a variety of solid and liquid impurities, forming water scale and a large number of sediments, affecting the service life of the boiler. Therefore, impurities must be removed by physical, chemical, physical and biochemical methods. Standardizing the treatment of boiler make-up water in power plants can not only effectively prevent and reduce boiler scaling and corrosion 8 The accident caused by the erosion of the ball disk test machine and the deterioration of its steam quality is also conducive to promoting the safety, economy, energy conservation and environmental protection of the boiler operation in power plants. The cleaning treatment of boiler make-up water in power plant plays a vital role in the overall operation of the boiler

2 PLC application design of ControlLogix series

boiler make-up water monitoring system is composed of power cabinet, PLC control cabinet and operator station

the boiler make-up water system adopts Rockwell's ControlLogix series PLC. All modules communicating through the backplane are based on the producer/consumer mode. Each module occupies a separate slot, and the module can be inserted in any slot of various 1756 frames. There is no need to disconnect the wiring when replacing the module. When wiring, the user connects the connecting wire to the removable terminal strip (rtbs) and inserts the terminal strip into the front of the module. All modules can be plugged in and out with power. Photoelectric isolation and digital filtering can effectively reduce signal interference. As a fault diagnosis aid, a status indicator is also set in front of the module to indicate input or output and fault status. The i/o module can directly report the fault condition to the processor. The digital i/o module covers the range from 10V to 265vac and 10V to 146vdc, and the provided relay contact output module ranges from 10V to 265vac or 5V to 150VDC. The voltage range of analog signal includes standard analog input and output, as well as direct thermocouple and RTD temperature input signals. The optional features of the analog module include digital filtering suitable for interference sources and interference environments, as well as the range selection of each i/o channel, so as to increase the flexibility of users. The comprehensive self diagnosis function of the analog module can monitor: input open-circuit/open-loop monitoring, board level fault monitoring, two alarm levels for the upper limit (HI and HI HI) plus an over physical range alarm, and two alarm levels for the lower limit (LO and Lo Lo) plus a low physical range alarm. Engineering unit conversion makes input and output analog signals easier to use. User configured output response (final value or any user-defined value) for analog module failure to ensure safety. The status area of the analog module can provide information for the processor for alarm and fault diagnosis. The mechanical key lock of each module for RTB can prevent improper voltage from being applied to the module. The electronic key lock between each module and logix5555 processor can prevent the user from inserting the wrong module type or different versions of modules into the slot. The channel configuration of the module is carried out through software with a inflation of 3.50%, rather than through a dial switch or jumper. The data precision of analog quantity template can reach ieee32-bit floating-point or 16 bit integer data format

the composition of redundant control system based on Rockwell's ControlLogix series PLC is shown in Figure 1, so there is no problem that cannot be solved

Figure 1 control system with redundant architecture

3 system process flow interface design

3.1 process flow

process system adopts pretreatment system, which is composed of chemical demineralization system and dosing system. In addition, the control of pretreatment dosing system and ammonia dosing system is also included in the boiler make-up water treatment control system

pretreatment system process flow: raw water from the main plant → mechanical mixing clarifier → raw water tank → raw water pump → high efficiency fiber filter → activated carbon filter

process flow of chemical desalination system: pretreated clean water → strong acid cation floating bed → carbon dioxide remover → intermediate water tank → strong alkali anion floating bed → mixed ion exchanger → demineralized water tank → demineralized water pump → main plant

dosing system dosing system refers to the storage and metering equipment of acid and alkali for regeneration of each ion exchanger in the chemical demineralization system. The process of dosing system is: low acid tank → high acid tank → acid metering tank → acid ejector → strong acid cation floating bed (and mixed ion exchanger); Low level alkali tank → high level alkali tank → alkali metering tank → alkali ejector → strong alkali anion floating bed (and mixed ion exchanger)

3.2 the confirmation criteria of process control standard methods are: equipment used, environmental conditions, personnel technology, etc.

(1) valve control logic: the valve control logic is shown in Figure 2

Figure 2 valve control logic

(2) control of cation exchange inlet regulating valve: the regulating valve adopts PID negative feedback closed-loop automatic control. When the water level of the intermediate water tank is higher than the set value, reduce the valve opening, and when the water level of the intermediate water tank is lower than the set value, increase the valve opening, as shown in Figure 3

Figure 3 cation exchange inlet regulating circuit

(3) water pump control logic: the water pump control logic is shown in Figure 4

Figure 4 pump control logic

3.3 process interface

before the automatic/manual transfer switch on the local valve control box changes from manual position to automatic position, the on/off transfer switch of the valve must be placed in the middle position. The main screen includes real-time data display screen, alarm screen, report screen and historical curve screen

(1) filter control interface

filter control interface is shown in Figure 5. On the left side of each filter inlet valve on the screen, the instantaneous flow when the filter is working is displayed in real time. Turn the change-over switch of the local operation box to the local position, and the solenoid valve of the corresponding filter cannot be operated on the computer. If it is hit far away, the solenoid valve of the corresponding filter can be operated on the computer

Figure 5 filter control interface

(2) dosing control screen

dosing control screen is shown in Figure 6. Coagulant and coagulant aid dosing: click the dosing control mode button to pop up the control screen and select the working mode. Manual dosing: click the manual button to dosing according to the set frequency. Automatic dosing: click the automatic button to automatically add drugs according to the flow. Close the screen, click the motor icon, pop up the motor control screen, and start the motor. Dosing pump works. Chlorine dioxide dosing: Motor chlorine dioxide dosing machine icon, pop up the control screen, start the dosing machine, and the manufacturer's equipment will work automatically

Figure 6 dosing control interface

4 conclusion

the boiler make-up water monitoring system adopts the combination of upper computer and programmable controller (PLC). The boiler make-up water monitoring system has an operator station as the man-machine interface during system debugging and operation. The operator station is set in the control room of the chemical water workshop. The operator station also has the function of engineer station. The control of the boiler make-up water monitoring system is realized by PLC. The PLC controller is dual computer redundant hot standby, that is, the programmable controller (PLC) is equipped with dual computer hot standby central processing unit (CPU), redundant power module and redundant communication module. The whole chemical water treatment system can be controlled automatically, semi automatically, remotely or locally by PLC. (end)

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