2 process overview and requirements 2" with control point process flow chart (see) 2.2 process control requirements (1) pump start and stop control and overload protection (2) seal gas differential pressure control in order to ensure that chlorine does not enter the pump seal box, the seal box pressure should Higher than the intermediate tank pressure, and keep a certain difference, the difference is too low, so that the cold loses the barrier protection of the harmless gas, and the mechanical seal is quickly damaged.
28EICVol.82001No.1Welcome to order, welcome to write, welcome to release product advertising letter 1 Preface Our company's chlorine plant liquid chlorine packaging has been using pneumatic conveying liquid chlorine, because pneumatic conveying is a non-continuous production process, and the gas consumption is high, energy consumption is high . In order to reduce production costs and ensure continuous production, the company decided to carry out technical transformation. The pneumatic conveying is changed to pumping. The LS vertical liquid chlorine pump of Dalian Pumping Plant is selected because of the high pumping process control requirements and higher requirements for safe production. Therefore, automatic control must be carried out. Ensure that the safe operation of the pump and the safe process flow diagram should be maintained at a certain height to prevent cavitation and eddy currents. The intermediate tank liquid level control stabilizes the liquid level by adjusting the amount of liquid chlorine input into the intermediate tank. The two regulating valves LV-101A/B are reserved for each other, and the two intermediate tanks V102A/B are alternate with each other, and any regulating valve can be used for any. Level control of an intermediate tank. To ensure the safe and normal operation of production.
(4) The pump outlet pressure must be stable at a certain value to ensure safe production.
Limit alarm and upper limit chain start pump, lower limit chain stop pump; seal differential pressure low report; chestnut outlet pressure is high.
3 Control scheme selection and system composition The following control schemes are adopted according to process characteristics and requirements.
3.1V102A/B liquid level control system In order to facilitate the selection of the intermediate tank V102A/B liquid level signal and the regulating valve LV-101A/B, the regulator adopts the CS920 programmable regulator to realize the soft switching of the standby device. The function configuration diagram is shown in the figure.
The main features of this control system are the SSC selection control function of CS920. The regulated output signals of the two control loops A and B of the regulator are sent to two regulating valves LV-101A/B, respectively, and the intermediate tank V102A/B liquid level signal acts as the two main mode inputs of the regulator. In the regulator circuit A, the two liquid level signals are respectively used as the measured values ​​of the first control unit and the second control unit, and the output of the first control unit and the second control unit is selected as the regulator circuit A by the external selection switch to the CS920 signal. The output is such that the selected combination of LV-101A and intermediate slot V102A/B is achieved. Similarly, regulator loop B implements a selective combination of LV-101B and intermediate slot V102A/B. Therefore, in the production, according to the condition of the regulating valve LV-101A/B, the regulator circuit A or B is selected, and then the SSC selection control function part of the intermediate tank V102A/B.CS920 is selected by the external selection switch. The procedure of the circuit A is as follows: DIO For the A loop, select the intermediate slot switch signal P4 for ACNT2 switching parameter P4=2 P3 for ACNT1 switching parameter P3=l H2 for ACNT2 switching register A loop selection control to Y output 16 subsequent procedure 3.2 出 出 pressure control through pressure transmitter The pressure signal is measured and sent to the CS920 programmable regulator. The output control signal adjusts the opening of the regulating valve on the return pipe, that is, adjusts the return flow to keep the pump outlet pressure stable. 3.3 dense differential pressure control The differential pressure signal is measured by the differential pressure transmitter and sent to the CS920 programmable regulator. The output control signal is adjusted to supplement the opening of the sealed gas regulating valve, that is, the supplementary sealing air volume is adjusted. Keep the differential pressure stable.
3.4 Chestnut's start-stop control and interlocking and signal reporting pump start and stop by the button on the instrument panel, the liquid level is interlocked by the upper and lower limit alarm signals of the programmable regulator, and the AC contact in the motor switchboard is controlled by PLC. The motor controls the motor to start and stop. PLC selects FX (M4MR. Pump local control or instrument interlock is selected by the switch on the instrument panel. Pump motor overload protection is realized by thermal relay. Control ladder diagram and motor control diagram are shown.
Each regulator inputs the upper and lower limit alarm signals into the flash signal alarm.
H Bu XI is open to X5 for irrigation: from åœ into YO, 丫 1 for electric M M C phase secret electricity 4 system installation and operation (1) liquid level, pressure and differential pressure transmitter installation with chlorine The isolation tank must be added to the source point, and the solution is treated with aldehyde fluorotributylamine.
(2) In the production process, first select the LV-101A/B from the process pipeline through the process valve selection control chart and motor control, so as to determine the A or B circuit of the regulator, and then use the selection switch on the instrument panel to select through CS920. The level transmitter of the intermediate tank V102A/B.
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