The importance of pneumatic control valve optimization in chemical control system

In automation of higher chemical control system, pneumatic control valve as the automatic regulation system of terminal execution unit, accept the control signal, realize the chemical process of continuous adjustment, runtime if failure will be directly related to the safe operation of the production plant. And according to actual statistics about 70% of the failure from the pneumatic control valve, so for the optimization of pneumatic control valve manufacturer should cause enough attention. 1 overview in a synthetic ammonia plant, a furnace is the core of the conversion, cause a furnace shut down any interlock actions will lead to the subsequent process system of parking, including a furnace hearth negative pressure control is the key. Air compressor export combustion exhaust gas turbine, as a part of the furnace combustion air, controlled by the AV - 03010 into a furnace combustion air oxygen content, within the guarantee period of furnace gas burning fully; Another part of the convection section of using waste heat to a furnace, controlled by the PV - 03048 - a/B auxiliary chamber of a stove or furnace negative pressure; Part of this is controlled by the HV - 02001 is empty. These valves control airway caliber is large, more than the same flap connecting rod drive mechanism, need power is larger, pneumatic actuator and control more complex. For precise control, PV - 03048 USES A valve ( Small valve) And B valve ( Large valve) Control, respectively, according to the working condition of need to open one or two. These valves are to participate in the interlocking TRIP03. 5 control, to ensure a safe operation under normal pressure furnace system. When the gas turbine trip or a chamber pressure is greater than 100 pa, TRIP03. 5 action: cut a furnace combustion air AV - 03010 and the convection section of the exhaust emission valve PV - 03048 - a/B, at the same time open the exhaust vent valve HV - 02001, and provide the TRIPB signal a trip. When these valves in drive or travel frequently check phenomenon action out of control, hearth negative pressure control. 2 problems of PV - 03048 - a/B is the function of stabilization from the high temperature of gas turbine exhaust gas to a furnace convection section, auxiliary hearth negative pressure control. When driving in overhaul do travel check and PV - 03048 - a/B valve action, the valve is the cylinder type pneumatic control valve, gas circuit is very complicated, a preliminary examination revealed magnetic solenoid valve coil is not enough, lead to solenoid valve output volume is small, pneumatic valve switch, the valve is not action. Still no, after replace the solenoid valve cannot control the negative pressure, negative pressure interlock switch will cause chain trip. AV - 03010 after overhaul drive without action, check the solenoid valve electricity, open air valve side road impassability, regulating valve malfunction, unable to open a furnace heating system. 3 control gas circuit transformation control chart I, II, III and IV are respectively in four gas control valve. PLT is controlled port, R is hollow, P, is A vent. The pneumatic valve type II, III, IV is FC accident shut, PLT oil-gas have spirit control valve P - When A pass, PLT airless P - A, A - R. Open type pneumatic valve Ⅰ is FO accident, PLT angry when P - A, A - When R, PLT airless P - A pass. During normal operation, the electromagnetic valve charged ventilation, gas even after solenoid valve to control the pneumatic valve of PLT pneumatic valve of gas path to four PLT side, valve Ⅱ, Ⅲ, Ⅳ open, valve I closed. I/P converter accept master 4 ~ 20 ma signal, after the transformation output to pneumatic positioner, two lines of output C1 and C2, C1 bullishness of control valve Ⅳ gas path to open valve pneumatic control valve cylinder side; C2 bullishness of close the pneumatic - valve pneumatic control valve II and III to pneumatic - valve cylinder valve side. Check valve to ensure close the valve pneumatic valve of gas can't go to the I vent. Such as master 4 ~ 20 ma signal pneumatic valves to open and close. Are to be highlighted pneumatic valve I line, it is used in electromagnetic valve power loss or lose air accident situation, forced to close the pneumatic - valve PV - 03048 - b, achieve the function of pneumatic control valve accident shut. When I open the valve, when a gas source, gas source through the check valve, valve, check valve, I close the valve to close the pneumatic - valve gas path; Without air, usually stored in a tank of gas source, the valve, check valve, I close the valve to close the pneumatic - valve gas path. The check valve to ensure that the air tank air from erosion. At the same time, the function of the pneumatic valve III is the electromagnetic valve, loss of losing electricity air accident situation close valves closed and ensure air from the vent, because of the pneumatic valve III P, A port is the reverse of PLT after the loss of air pressure P - A closed, A - R conduction, P mouth is closed valve gas side of the accident, ensure that the valve of the accident can not be empty. Comprehensive the cause of the problem, in addition to the replacement of pneumatic positioner, high temperature resistance grease to the coupling bearing regularly listed outside, other air directly to the electromagnetic valve gas all the way, and the electromagnetic valve replacement into large flux, low power consumption, improve the gas pressure control, pneumatic valve of tested four can switch normal, to get a complete solution.