1: Introduction of tail tensioning system of boiler bottom dry slag machine in thermal power plant
The slag dryer at the bottom of boiler in thermal power plant is a very important equipment in thermal power plant. If the slag dryer can not discharge slag normally, the boiler will not be able to operate normally, which will directly affect the efficiency of power plant. The tail tension system directly affects the operation of the slag dryer and is an important part of the slag dryer. Power plant boiler
See Fig. 1 for the system diagram of bottom slag dryer
2: Composition and control requirements of tensioning system
(1) System composition
The tension system is powered by the hydraulic station. Two hydraulic cylinders (piston diameter 90mm, cylinder rod diameter 70mm, stroke 630mm) provide relatively stable tension for the chain plate machine (the tension pressure can be adjusted at any time according to the length and working conditions of the chain plate machine). See (Fig. 2) for hydraulic system diagram
(2) Control and alarm requirements
Control requirements: the system adopts PLC control, and realizes the functions of equipment start, stop, data modification, status monitoring, fault alarm and so on through man-machine interface. After the equipment is started, the oil pump should start and stop automatically according to the needs. After starting, the oil pump will start to run automatically. The two hydraulic cylinders need to extend out synchronously. The displacement difference during the stretching process should not exceed 5mm. The displacement value is determined by the magnetostriction installed in the two hydraulic cylinders Displacement sensor Provide. ( Displacement sensor The transmission range is 0-630mm, and the signal is 0-10V). When any hydraulic cylinder reaches the set maximum tension pressure, it will stop extending automatically. When both hydraulic cylinders reach the set maximum tension pressure (the tension pressure feedback is provided by the pressure transmitter installed on the rod less chamber of each oil cylinder, The transmission range is 0-10mpa and the signal is 4-20mA). The oil cylinder stops extending and the oil pump stops running automatically. Enter the monitoring operation state. When the tension pressure of any hydraulic cylinder is lower than the set minimum tension pressure, the oil pump starts automatically, and the solenoid valve is powered on to supplement the pressure until the set maximum tension pressure is reached. Because the movement of the chain plate machine may cause the change of displacement, when the displacement difference exceeds 15mm after entering the monitoring state, travel compensation is needed. But priority should be given to ensure that the pressure is within the normal range Displacement sensor The measured displacement value is within the effective range.
Alarm requirements: after alarm 1 enters the monitoring state, when the displacement difference exceeds 15mm, travel compensation is required. Due to various reasons, the displacement difference can not be eliminated. When the difference reaches 50 mm, an alarm is required to stop the machine and upload the alarm value to the central control room.
Alarm 2 in order to protect the hydraulic cylinder, when magnetostrictive displacement sensor When the displacement value is more than 620mm, an alarm is required to stop the machine and upload the alarm value to the central control room.
After alarm 3 enters the monitoring state, when the tension pressure is lower than 10 bar of the lower limit pressure suddenly, it is necessary to alarm and stop the machine and upload the alarm value to the central control room.
Other fault alarms (such as motor overload, oil filter blockage, low liquid level) need to be uploaded to the central control room for comprehensive alarm signals. Alarm information and alarm history display are required on the screen.
3: Process requirements
The layout of the control box is reasonable and the wiring meets the requirements of the regulations. There is margin for PLC I / o point.
4: Design scheme
According to the control requirements and the importance of the equipment, in order to avoid the loss of the system when the system can not run due to PLC or touch screen failure, a set of completely manual control mechanism is added on the basis of meeting the control requirements. (it is proved that this set of mechanism also plays an indispensable role in the initial commissioning.)