Technical Standard and Application of Power Station Boiler Safety Valve

Power station safety valve verification standards related to the provisions of the State Quality Supervision Bureau Boiler and Pressure Vessel Inspection Bureau promulgated the "steam boiler safety technology supervision regulations:" in the boiler safety valve should be checked at least once a year ";" power boiler pressure (DL612-1996) 9.1.13) stipulates: "After the installation and overhaul of the boiler and the safety valve shall be checked, the pressure of the safety valve shall be checked" (and clearly stipulates the scope of the regulation: f) Thermal system pressure vessels: high and low pressure heaters, deaerators, various types of expansion vessels, etc. "The State Power Corporation promulgated the" 25 key requirements for preventing major accidents in power generation "states:" All kinds of pressure vessels Safety valve should be regularly checked and discharge test. " These provisions are very clear on the regular inspection of power station safety valve. Electricity Industry Standard Electric Power Industry Boiler and Pressure Vessel Supervision Order (DL612-1996) 9.1.13 There are clear provisions on the safety valve of the instrument calibration: "The pure mechanical spring-type safety valve can be calibrated and adjusted by the hydraulic device, generally at 75% ~ 80% of the rated pressure.After adjusting the hydraulic valve safety valve, at least the minimum starting value of the safety valve from the actual seat review. "1 Safety valve testing methods At present, the power system safety valve calibration is generally The methods used are offline measurement and online measurement of two. Off-line measurement requires the removal of the safety valve to the test bench when the equipment is stopped, which is time-consuming and laborious. And this kind of measurement method can not solve the influence of temperature on the safety valve opening pressure, but for some non-removable safety valves Valve, etc.) is powerless. Online measurement is divided into real jump measurement and measurement of two instruments. The actual jump measurement will cause unnecessary damage to the safety valve, and noise pollution and safety issues in measurement have drawn more and more attention. On July 9, 1999, Jinzhou Power Plant in Liaoning Province, Five traumatic experience of tragedies should not be forgotten. Instrument measurement methods are currently more advanced and commonly used methods, such as the British FURMANITE company in the eighties developed TREVITEST practical products. The instrument uses a hydraulic motor driven hydraulic pump as the power source, using two-channel pen recorder with the sensor as a measurement recording unit. The recorded safety valve opening process of the force curve, the operator manually determine the feature points, by hand to calculate the final result of the entire measurement process need to be involved, so the consistency of the measurement results are greatly affected by human factors, the measurement accuracy can not Guarantee. In addition, the high cost of such instruments (quoted in 2000 amounted to 1.25 million) is difficult to promote in the country. Safety valve manufacturers in Japan, the United States and other countries also developed similar products in succession in the 1990s, but such products can only be used in safety valves manufactured by their own manufacturers, which are powerless to domestic and other manufacturers' safety valves. Since the nineties, there have also been some imitations in China. There is not much breakthrough in technology and there are still some shortcomings of poor measurement consistency and low measurement accuracy. NSH series of on-line pressure relief valve safety valve system by the Beijing State Mechanical and Electrical Technology Co., Ltd. and Beijing Labor Safety Technology and Equipment Center developed a new type of portable instruments, the basic working principle is the same as the British FURMANITE TREVITEST safety valve detection system, and in the design process There are major breakthroughs. NSH safety valve on-line constant pressure meter is a new type of patented product to check the safety valve of power station, Boiler & Pressure Vessel Bureau of Labor Ministry, Recommended Products of Power Station Valve Standard Committee. This product has passed the test of China Academy of Metrology. At present, the instrument has been in the country more than 50 power plant safety valve calibration application, the practice proved that this instrument set NSH safety valve on-line calibrator can be stopped or running in the case of the unit, only 2-5 Sec open time to complete on-line performance testing of safety valves and operating parameters of the test, but also failed to detect the safety valve on-line setting can measure and record the safety valve opening pressure and the safety valve where the system media pressure and other parameters . 2 Design Principle Spring safety valve opening and closing action is dependent on the pressure changes at the inlet of the media and spring preload to make the valve automatically open and close. When the medium pressure (internal pressure) rises to enhance the lifting force than the spring preload force, the valve spring to open automatically against the spring preload to release excess media, so that the pressure drop, but also due to the spring force, Pressure drop to safety, the valve automatically shut down, stop bleeding. According to this principle, it is conceivable that when an on-line (also known as hot) measurement or adjustment safety valve provides an upward additional force from the outside, when the sum of the medium pressure and this additional force just overcomes the spring preload, the valve The core will also be opened, even in the absence of medium effect offline (also known as cold) conditions, alone by the external force to overcome spring preload, the valve core can also be opened, a clearly shows that the force Balance the relationship. Obviously, we can see that the spool open condition is: FT = FW + PL × S Where: FT - spring preload FW - external additional force PL - medium pressure S - safety valve sealing surface area The opening pressure P is: P = PL + FW / S When cold, P = FW / S Obviously, if the additional external force FW can be accurately measured, it can be easily calculated based on the known spool area S and system operating pressure The safety valve opening pressure P. This is the safety valve on-line test technology design basis and principle. 3 Technical Basis According to the analysis of the spring safety valve opening action characteristics, we can draw: Under the action of external force FW, a safety valve from closed to open, and then from open to close the whole process, the external force FW changes Law, when the additional force increases gradually from zero, and the internal pressure PL × S just happens to spring preload, the valve micro-Kai, increasing the role of medium area S, so that the spring pressure to overcome the internal pressure of the role of preload The force increases dramatically, which results in an instant reduction in external appendages. The first characteristic peak A appears. When the external additive force decreases to reach the close point, the external force will appear instantaneous rebound due to the sudden decrease of the medium acting area in order to maintain the balance of force. The above two characteristic peaks A and B are the technical basis for detecting the opening pressure of the safety valve and the pressure of the seatback under the on-line condition. When the valve is not open, the external force to overcome the static rigidity of the valve core, when it reaches the opening point, the external force to overcome the spring elastic force, the slope of the two changes over time, resulting in the first inflection point C, In the same way, another inflection point D appears when the valve is closed. The two inflection points corresponding to the valve opening and back seat, it is cold test valve open, back seat pressure technical basis. From the above analysis is not difficult to see that the key to safety valve on-line test technology is how to quickly and correctly find the corresponding open feature points. 4 System Configuration Online testing system consists of mechanical fixtures, hydraulic power unit and data acquisition and processing unit composed of three parts, relatively independent of each other by two 10-meter-long hydraulic hose and two 10-meter long five-core shielded cable interconnection Into a complete safety valve test system. It has small size, light weight, modular components, equipment, computerized, simple operation, stable and reliable, and other notable features, performance in many ways than the same level of foreign instruments. 4.1 Fixture: to ensure that the measured safety valve clamping position, for the hydraulic power unit to provide external environment, the use of modular structure, demolition is very convenient. 4.2 Hydraulic Power Unit: Provides adjustable hydraulic output and flow, the maximum output of 10MPa, the maximum lifting force of 50KN, used to control the additional lifting force and speed. 4.3 data processing unit: it is the heart of the test system, directly determine the reliability and accuracy of the system. Among them, the force sensor with spoke structure, high sensitivity, accuracy can reach 0.05%, the pressure sensor using high temperature sensor, the working temperature up to 200 ~ 250 degrees. Both sensors are high-output, built-in amplifier, its linearity, repeatability and anti-interference ability. Test system uses a two-channel low-gain, high-precision amplifier circuit, intelligent A / D conversion and data acquisition circuit, which can capture both force and pressure parameters, the core part of the selection of the current market

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