Application of Intelligent Frequency Conversion Electric Control Valve in Boiler System

(A) Steam boiler automatic control system on the importance of boiler operation. According to relevant regulations, boilers with an evaporation of more than 6 tons per hour should be supplied with water from the control valve of the instrument, and water should be supplied to the boiler continuously and uniformly. Water level regulation in boiler operation should be maintained at normal water level and allowed to fluctuate within 25 mm of normal water level. The smaller the water level fluctuates, the more stable and safe the boiler operation is and the better the steam quality is. At the same time, the quality of the steam boiler automatic water supply system puts forward higher requirements. 1. Poor control endanger the safe operation of the boiler. Boiler operation, the water level changes mainly due to changes in boiler load caused. When using steam for a long time, the water level drops more; with less steam, the water level drops less. Boiler water level is too high, there will be steam with water, or even full of water accidents; water level is too low, it will lead to boiler explosion, endangering personal safety and equipment losses. In addition, due to sudden changes in load caused by false water level, but also cause misoperation adjustment system. 2 control is not steam pressure instability. Increased water supply, a direct impact on the water level rise, but the pressure drop is more sensitive. This is because the water temperature is lower than the temperature of the boiler water. When the water supply increases, more heat is absorbed in the boiler. Therefore, the heat used to evaporate the boiler water is reduced and the vapor pressure obviously drops. By the same token, water supply decreases, water level drops, and vapor pressure increases. 3 control is not good steam temperature instability. When the water supply increases, the steam pressure drops and the temperature of the boiler water drops. The radiant heat absorbed by the water wall in the hearth increases, causing the temperature of the flue gas at the outlet of the furnace to decrease, resulting in the decrease of the steam temperature. By the same token, when the water supply decreases, the temperature of the steam rises. (B) the current status of the boiler automatically Sheung Shui and difficult to control After some of our steam boiler business status of the water survey found that the flow and the drum water level to minimize the scope of fluctuations have been neglected, and some have constituted a security risk, Always threaten the safe operation of the boiler. The main problems are the following aspects: 1. Often burned electric actuator motor; 2 adjustment valve stem often curved; 3 regulating stem constantly up and down action, resulting in serious stem stem valve stem leaking; 4 Boiler water pressure gauge pointer constantly swinging, water pressure and water level fluctuations. The root cause of the electric control valve can not be adapted to the system. Boiler water supply control valve has the following four particularities: 1. Electric control valve at both ends of the pressure, the general evaporation of about 30 tons of boiler control valve inlet water pressure up to about 2MP, the outlet water pressure up to about 1.2MP, Require the electric actuator motor output torque (load) larger; 2. Deaerator tank feed water temperature up to 1000C, the regulator valve body temperature is higher, is not conducive to motor cooling, if the adjustment system shock, easy to burn electric actuator Motor; 3. Boiler drum level time constant is small, easy to adjust the process prone to oscillation system (like the electric control valve does not stop the action up and down), especially the use of three impulse regulator control, the selection of three parameters, high accuracy , The control cycle is shorter, the common "electronic" electric control valve does not adapt to the valve stem frequent movements up and down, frequent friction and wear too fast leakage; 4. Steam boiler water connection is a very important part of the requirements of electric control valve reliability Well, the failure of the boiler water can not be dangerous. At present, some boiler control valves for water supply are mostly control valves driven by "electronic servo amplifier." Such electric control valves can not change the speed of the actuator motor according to the signal deviation. Because only the direction of change, the constant speed is bound to use the system to adjust the accuracy is limited, the switch or the general slow changes in the control of the object less demanding control occasions can be used, but as large changes in steam boiler load to play on the occasion automatically Water regulating valve is difficult to achieve better automatic control effect. In addition the electric control valve uses single-phase AC motor as the control motor, and single-phase AC motor has two weaknesses: 1. The current output for use, due to the start current is almost 7 times the rated current, the motor will always be in High current working conditions, leading to motor fever, severe motor burned. Regulating system requirements Electric control valve should belong to the servo system, the input of these systems is free to change, but requires the electric control valve with a certain degree of accuracy to follow the input changes. At present, the motor action of the electric regulating valve can only be controlled by the servo amplifier at constant speed and reverse speed. Obviously, the servomotor as the actuator can not operate at low speed with the small signal. Can not be sensitive, fast, stable and reliable operation and system control coordination. (C) the solution - intelligent frequency electric actuator for the original electric actuator can not run at low speed, through the very fine trimming effect to correct minor deviations, resulting in overshoot of the adjustment system of this shortcoming, the use of intelligent variable frequency electric actuator With a variety of valve body, the use of digital technology to transform the current electric actuator, so that it has a variable speed operation, fast dynamic response, adjust the positioning accuracy, good stability, low failure rate, long life, etc., completely changed Regulating valve in some important areas can not be applied defects. We have a heating company in Tianjin Binhai New Area on a number of large-scale steam boiler water supply electric control valve used to transform, received good expectations. Multiple 35 tons of steam boilers, before the transformation of the use of "electronic" electric control valve for the water supply, the total control room instrumentation with three impulse regulators were to control the Sheung Shui electric control valve, although the hard work of professional and technical personnel to debug, the effect is not good. The water level showed a significant beating, water pressure instability, the table pointer swinging between 0.5MP-1.2MP, stem up and down the action, due to wear too fast, serious stem leaking. Frequently burned motor, affecting the normal operation of the boiler. Although professional efforts to adjust can not achieve the desired results. Now generally large and medium-sized boilers are equipped with three impulse water supply regulation instrument, which effectively overcome the drum appeared "false water level" phenomenon, which is the main control level of the drum tube object to the steam flow and water flow and the drum Liquid level three reference phase operation, go to control the control valve to change the water flow to maintain the pot liquid in a stable range. Compared with the past single impulse (only a drum level variable) water meter to adjust the high sensitivity, fast response, short control cycle. Therefore, the traditional electric control valve obviously can not adapt, so overshoot caused shock. After replacing the intelligent frequency conversion electric control valve (BPZ-40 type electric control valve), the effect is remarkable. Pressure gauge water supply is quite stable, the pointer at 1.2MP does not move, adjust the stem movement only in the range of 1 ~ 2mm slowly changes, the drum level indicates a fairly stable liquid level fluctuations of 10mm, the motor temperature is about 300C, no more burned Motor condition. In addition, intelligent inverter valve used in the computer board parameter setting functions, such as magnification, torque, stroke, the lower limit of electrical parameters, control insensitive zone settings and many other parameters according to the scene to control the object can be flexibly set set. More importantly, the servo motor adopts the frequency conversion control. The starting torque is large and the response is fast. When the action is taken, the speed of the signal changes according to the deviation signal. Therefore, the soft water is soft and soft, so the impact force of the high pressure water in the pipeline is small, which is beneficial for regulating the system stability. Now many manufacturers in the country have used this intelligent steam boiler frequency conversion valve, the original "electronic" electric control valve has been modified, the effect is very good.