Application of the hottest PLC in water treatment

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Application of PLC in water treatment of TISCO hot continuous rolling

TISCO hot continuous rolling uses about 200000 tons of water every day, and the wastewater contains dirty oil, iron scale, sludge, etc. after treatment, the 200000 tons of wastewater is recycled, which is of far-reaching significance to our water resource deficient area. Water treatment is a complex production process, so we used PLC technology to automatically complete the whole process control of water treatment in this engineering design

1 requirements of water treatment equipment for electrical control system

(1) laminar cooling feed water pump is N1 pump set, p=132kw, ~ 380V, 4 sets, with electric valve, 3 for use and 1 for standby

(2) the laminar cooling and filtration feed water pump is N2 pump set, p=160kw, ~ 380V, 4 sets, with the order quantity of the blow molding machine and a new high electric valve, 3 in service and 1 for standby

(3) the cooling water feed pumps for rough and finish rolling are N3 pump sets, p=132kw, ~ 380V, 4 sets, with electric valves, 3 for use and 1 for standby

(4) the coarse and finish rolling filtration cooling feed water pump is N4 pump set, p=160kw, ~ 380V, 4 sets, with electric valve, 3 for use and 1 for standby

(5) the backwashing feed water pump is N5 pump set, p=75kw, ~ 380V, 2 sets, with electric valve, 1 for use and 1 for standby

(6) the medium pressure turbid circulating feed water pump is N6 pump set, p=630kw, ~ 6kV, 6 sets, with electric valve, 5 for use and 1 for standby

(7) the low-pressure turbid circulating feed water pump is N7 pump set, p=300kw, ~ 6kV, 4 sets, with electric valve, 3 for use and 1 for standby

(8) laminar flow cooling pump is N8 pump set, p=115kw, ~ 380V, 5 sets, with electric valve, 4 for use and 1 for standby

the above pump sets are operated automatically, centrally and on site

2 hardware configuration of electrical automatic control system

the electrical control system of water treatment equipment is equipped with SG-8 programmable controller. The machine has various control functions from sequence control to analog control, counting control, logic operation and so on. It is suitable for a wide range of command systems, and can freely form upper communication, PC communication, remote I/O communication and decentralized remote I/O communication networks. The hardware is an analog structure, which can be unplugged from the power template, expansion board, CPU, memory to I/O template. PLC hardware configuration is shown in Figure 1

the input is a 384 point digital signal, using a photoelectric isolated 24VDC input template g-01n, a total of 24 blocks, each of which has 16 point input. It is mainly used for the selection of operation mode and the signal input of pump operation, pressure, water level and electric valve limit

the output is 206 points. There are 16 pieces of 24VDC output template g-01t with photoelectric isolation, and each piece has 16 points of output. The start and stop of water pump, the opening and closing of electric valve, the input of standby water pump, the display of analog screen signal and accident alarm are controlled through the intermediate relay cabinet

3 application function

(1) the automatic mode is completed by PLC. First, the pump starting command is issued according to the requirements of production water. After the pump is started, when the pressure reaches the given value, the electric valve opens (if the electric valve still fails to open for more than 3min, the alarm and stop the pump, and the standby pump is automatically put into operation). When the water level of the suction well is at the lowest line (- 1.000m), the alarm will be given and the pump will be stopped one by one with a delay. After the water level rises, the water pump continues to work. If a pump fails during the operation of the water pump, the pump will be stopped, the corresponding electric valve will be closed automatically, and the standby pump will be put into operation automatically. The standby pump of each pump set can be arbitrarily specified

in addition to the above functions, the backwash water pump (N5 pump set) also meets the following requirements:

1) the backwash pump cannot be started when the water level of the mud secondary sedimentation tank is higher than the given value (+ 0.85m)

2) the backwash pump cannot be started when the water level in the suction well of the backwash pump is lower than the given value (+ 1.85M)

the interlocking operation system of laminar flow cooling pump (N8 pump set) operation and high-level stabilized pressure pool water level is as follows

when the water level of the pool L (the elevation from the bottom of the high-level stabilized pressure pool to the ground + 7.8m):

(2) centralized and on-site operation, this function is not interlocked, and is only used for debugging, maintenance and troubleshooting

4 software design

plc software is compiled with ladder diagram. In order to make the software simple and clear in the process of compilation and debugging, the electrical equipment controlled by PLC for hot rolling water treatment is divided into the following two categories according to the process requirements

class 1 composite materials other than "paper plastic" are N1 ~ N7 pump sets, and the software block diagram is shown in Figure 2. The main program controls the work of each pump group according to the input instructions and the water level of the suction well. The opening and closing mode of the electric valve of the water pump of each pump group is the same, so it is convenient to use the subroutine call method for the programming of the electric valve. Its function is to directly call the subroutine of the electric valve when controlling the water pump to meet the logic relationship of opening and closing the electric valve

the second type is N8 pump set, and the software frame is omitted. According to the water level of the high-level pool, the number of starting water pumps is compiled to improve the yield. The subroutine of the corresponding supporting electric valve of the water pump is considered in the program

in order to facilitate operation, a display and alarm program is also prepared, and each step is displayed on the simulation screen. When the step action is the same, the average wear spot diameter of the other two steel balls is measured in sequence, and it is not completed within the specified requirements, it is regarded as an accident and an alarm is given

5 Conclusion

the water treatment project of TISCO hot continuous rolling was officially put into operation on August 8, 1994. The operation of the automatic control system over the past five years shows that the economic benefits are very significant, and only energy saving is 550000 yuan per year. Moreover, the system has the advantages of reliable operation, high control accuracy, good scalability, strong anti-interference ability and convenient operation and maintenance, which provides a reliable guarantee for the normal production of hot continuous rolling

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