Abstract It is an indisputable fact that the online analysis system has broken through and surpassed the online analyzer. The failure of the online analysis system in the engineering application has more extensive, more complicated and richer technical connotations than the failure of the analyzer. This article begins with the definition of online analysis system engineering application failure, standing in the engineering user's technical perspective, classification of failures and a more in-depth technical analysis.
Key words On-line analysis system Sample gas processing system Sample gas processing parts Engineering Application Accuracy Failure
1 Online analysis system engineering application status
The application of on-line gas analysis engineering in China's specialization began in 1985, and the 24 years of experience in engineering application practice is worthy of careful summarization and full use. Based on the indisputable fact that the on-line analysis system has broken through and surpassed the on-line analysis system, the on-line analysis system has become the main format of the dominant market, and the on-line analysis engineering technology must highly lock the orientation of the engineering application. Today's online analytical systems have the strength, adaptability, and scale of engineering applications, and are expanding into a wider range of applications.
The main purpose of on-line analysis system engineering application is optimization of process control and safe production as well as energy conservation, pollution control, and emission reduction. A more intuitive technical expression is the pursuit of timely, continuous measurement accuracy of material component information. "Discontinuity" and "inaccuracy" will become two technical standards for judging the "broad" failures of online analytical systems.
2 On-line analysis of system engineering application fault definition
The failure of the on-line analysis system engineering application discussed in this paper is not merely the damage of the system or the instrument. It may disable the narrow but classical failure of retirement, but it is a "broad" failure.
Causes the operation of the online analysis system to seriously deviate from the normal state of engineering applications, so that the output signal of the material component detection of the online analysis system seriously deviates from any abnormal state or fault of the correct detection value, and is defined as the engineering application failure of the online analysis system (hereinafter referred to as failure ). Naturally, it also includes failures where the on-line analysis system or on-line analyzer is damaged and the consequences of deactivation or even retirement are extremely serious.
3 On-line analysis system engineering application fault classification technology analysis
This article takes the wide field of view of the online analysis system engineering application perspective, carries on the classification assessment and the technical analysis to the engineering application fault of the online analysis system, in order to be able to prepare the emergency plan of the fault handling, and improve the efficiency and effect of the troubleshooting.
The engineering application faults of the on-line analysis system can be roughly classified into the following ten categories, and the following classification statements will be made:
(1) Misdirected Design Mistakes
(2) Failure of technology transfer
(3) Poor environmental adaptability
(4) The response is too slow
(5) Deterioration or interruption of sample flow
(6) Sample gas dusting failure
(7) Sample gas dehumidification failure
(8) No detection signal
(9) Low accuracy of analysis
(10) Poor security
3.1 targeted design errors
The most important feature of the on-line analysis system is the targeted design for sample gas conditions, engineering application requirements and environmental conditions. This targeted design is mainly based on the technical agreement of the project (the effective attachment of the contract), and of course, the order contract is also based. Only it is far less accurate and comprehensive than the technical agreement.
(1) The analyzer's measurement range does not meet the engineering application requirements, which in turn leads to a serious reduction in the accuracy of the test;
(2) The selection and specifications of the analyzer dissatisfied the use and maintenance of the equipment;
(3) The on-line analysis system does not adapt well to the sample gas conditions and environmental conditions of the unusual state of the project. It is very detrimental to know and communicate with the “abnormal†lack of gas.
Strengthen the internal coordination of the project users and strengthen the in-depth technical exchanges between the parties before and after the ordering of the supply and demand. Generally, such failures can be avoided.
3.2 Failure of technology transfer
Once the on-line analysis enters the engineering application site, the system-specific design of product technology, installation technology, use and maintenance technology, and general maintenance technology must be accurately transferred to the hands of professional users of engineering users. The method of rapid and effective transfer is mainly the installation and operation instructions of the system, the system installation specifications or guidance documents, the targeted training of the operators, and the supply of spare parts.
The outstanding performance of technology transfer failure is reflected in the user's "do not use" and "will not maintain." The serious consequence is that it will trigger failures that should not have occurred, even if the system is out of service or damaged.
(1) Poor instruction in installation instructions;
(2) Technical training is not in place;
(3) The user's management is not standardized.
The responsibility of the supplier is: Installation instructions should be accurate, easy to understand and guide the user to install, use, and maintain the equipment; training users should follow the procedures to improve training quality. Demand side should also have standardized management so that professionals can receive training and avoid blind movement of operators.
3.3 Poor environmental adaptability
The application environment of the on-line analysis system is difficult to control, and sometimes it is very difficult to choose a suitable installation location.
(1) The maximum temperature of the environment is the highest and the lowest temperature can easily cause system failure. When the maximum temperature is ≥45°C, the analyzer with a working temperature of 40°C must be tampered with. It is necessary to add air conditioners for cooling. The lowest temperature ≤ +5 °C is absolutely not allowed, and the analyzer and some sample gas processing components cannot be adapted. It is necessary to control the room temperature ≥ 10 °C.
(2) The smaller the distance between the sampling point of the system and the analysis cabinet is, the better is <15m. It is beneficial to improve the speed of response of the system.
(3) Install the control room or analysis cabinet away from high-power electrical equipment or strong electromagnetic field equipment to avoid electrical interference and high-frequency electromagnetic interference. Electrical interference will cause the analysis instrument signal to be inconsistent with the DCS signal in the upper stage, which can be eliminated by adding a signal isolator. The high-frequency interference signal will reduce the safety performance of the system, and even make the analyzer with poor quality appear the trouble of the liquid crystal display or the black screen.
Once electrical interference and high-frequency electromagnetic interference appear, troubleshooting is generally difficult.
3.4 The reaction is too slow
The timely display of on-line analysis is necessary, and safety monitoring programs are particularly important. Generally, the requirement for the total system delay time (T10) is <60s. The system with fast bypass flow design and the system for short-distance transmission of sample gas will be much smaller than 60s.
(1) The sample gas transmission line is too long (for example ≥ 30 meters), too thick (preferably φ6x1), the inner wall is too dirty and rough;
(2) Excessive sample processing components and excessive dead volume;
(3) Sample gas flow rate is too small (analyzer flow rate is selected as 1L/min as possible).
The analysis system of the positive pressure sample gas is particularly important for decompression of the high pressure sample gas to about 0.1 MPa in the decompression tank at the sampling point. The higher the transmission pressure, the slower the system's reaction speed (total lag time).
3.5 Sample gas flow drop or interruption
The drop or interruption of the sample flow rate is the most intuitive display of sample gas processing performance deterioration or failure of the sample gas processing system, and it is also an important observation content in the daily maintenance of the system.
(1) Sampling probe filters, membrane filters have serious dust accumulation or clogging;
(2) There is a blockage of the accumulated dust in the air path, and the most serious is the clogged failure of the condensate caused by the sample gas condenser due to the set temperature being too low;
(3) Severe gas leakage will also cause a serious drop in sample gas flow. If the pressure of the source flow of the process sample is too low, it is the system's adaptability problem. If necessary, the sample gas treatment system (such as adding an air pump) must be properly changed to eliminate it.
3.6 Sample gas dusting failure
Sample gas dust removal is one of the most difficult tasks of the sample gas processing system. The stringent requirement of the analyzer is < 0.3um.
<10ug/m3. With the development of technology and advances in system design, it should be said that sample gas dust removal is a very mature technology.
Sample gas dusting has three technical links:
(1) Sampling probe's heated backflush filtration technology, the high-efficiency filter element used can filter 99% of 0.3um dust, and continuously collect dust on the filter element, with the help of PLC control solenoid valve group to achieve the heating blowback under 0.6MPa pressure Sweeping can completely realize maintenance-free and high-reliability clogging prevention continuous sampling.
(2) The failure of the post-stage membrane filter should be vigilant except that the filter membrane is heavily contaminated or dust needs to be replaced, and that the air flow resistance is increased or the diaphragm is damaged. The filter membrane with hydrophobic characteristics can effectively adapt to occasional "escape" and liquid mist in the sample gas.
(3) The positive pressure type on-line analysis system still needs to set a certain principle of the pre-stage filter, such as the filter with the accuracy of 1um 99% and the liquid mist trap. The combined design of dust, droplet filter and liquid mist trap is the best, and Chongqing Lingka Analytical Instrument Co., Ltd. has this patented product.
All filters, unless the filter element and the filter membrane have hydrophobic properties, will be easily clogged or broken due to sample gas or liquid mist. The targeted design of the sample gas processing system should prevent this potential failure.
3.7 Sample gas dehumidification failure
The dehumidification (including removal of water) of the sample gas treatment system is also the most difficult task of the sample gas treatment system, and there is still a great deal of room for optimization and improvement.
(1) The water separator is used to remove water from the sample. The most classic and most reliable method of draining condensate is to use a peristaltic pump. However, a peristaltic pump drain failure (such as a drain tube sticking) can cause serious failure of the condensed water into the downstream flowmeter.
(2) To reduce the humidity of the sample gas, that is, to dehumidify, a sample gas condenser must be used. The most classic and effective compressor-type gas condenser, better two-way. The greatest advantage of the vortex-type sample gas condenser is the intrinsically safe explosion protection, but the sample gas temperature can only be reduced within 25°C. The advantage of the semiconductor refrigeration sample gas condenser is its low cost, and the sample inlet temperature can only reach about 60°C.
(3) The biggest problem with the use of sample condenser is that the set-point temperature of the outlet sample gas should not be too low, generally about +4°C. If <+2°C is set, local ice blocking is most likely to occur. Condensate is poured back into the analyzer, causing more serious consequences.
The temperature of the outlet sample gas after the sample gas condenser treatment described above is all at +4°C, and the absolute limit of 0°C cannot be reached. Because of the influence of sample pressure and other conditions, the dew point of the sample gas at this time is not +4°C, but it may be much higher, causing serious failure of the liquid water thereafter.
Nafion Polymer Separator Dryer from Perma Fure of the United States can make the sample gas dew point below -10°C. The Baldwin thermoelectric condenser can also reduce the sample gas dew point to -7°C. This is a great leap in sample gas processing system technology and can provide more effective protection for online analyzers.
3.8 No detection signal
The most unacceptable failure of the on-line analysis system is that the analyzer has no display value, ie no output signal.
(1) The sample gas is interrupted, and the sample gas flow rate is not displayed. Mainly sample gas processing system due to blockage or suction pump damage and other serious faults should be targeted inspection and exclusion. Sample gas with liquid water can also easily cause damage to the suction pump.
(2) There is an error in the electrical connection of the system or analyzer. In particular, if the output signal is open, it should be carefully checked and confirmed.
(3) Analyzer failure; if the receiver and other components are damaged. Instrument fuse protection should not be neglected.
3.9 Low Accuracy of Analysis Values
The essential purpose or ultimate purpose of using on-line analyzers and on-line analysis systems in engineering is accurate, reliable, and timely on-line inspection, providing accurate information on the amount of material components for industrial processes to achieve optimal control of the process.
Whether the analytical value is accurate can be confirmed only by correctly using the qualified standard gas and rigorously calibrating the zero point and range of the analyzer.
The reason why the analytical values ​​are inaccurate has been thoroughly discussed in the "Online Analytical System Generalized Anti-Jamming Study" [1] paper, which can be divided into the following categories;
(1) Analyzer: The instrument principle and its range selection are inappropriate, and the interference error of the interference components is too large.
(2) Sample gas processing system: Various subtle changes and effects of the process sample gas during sampling, sample gas transmission and sample gas processing. For example, the sample gas condenser of flue gas desulphurization (CEMS) system is an indispensable sample gas treatment component of the sample gas treatment system. SO2 will lose 3-5% from the condensate water, that is, in this technical step, the analytical value is accurate. The degree dropped by 3-5%.
(3) Application environment: mainly electrical interference and RF electromagnetic interference, as described above. A low-quality analyzer, with a cell phone next to it, can make the display of the instrument "chaotic."
There are many influencing factors in this aspect, involving many principles and many subtle factors, which can only be specifically analyzed on specific issues. The experience of engineering applications plays a decisive role.
3.10 Poor security
The technical problems involved in the safety analysis of online analytical systems are many and they are very professional. They can be summarized as follows:
(1) The electrical safety indicators of analyzers and online analyzers are qualified, but the original electrical safety performance will be degraded due to high humidity due to transportation, storage, and installation.
(2) The on-line analysis system with certain explosion-proof requirements and the on-line analysis system with the specification design, in the process of on-site installation or reassembly, the explosion protection function of the original design is degraded due to installation negligence or failure of inspection and confirmation.
(3) When the system is installed and operated, the discharge of condensate and exhaust gas does not meet the requirements, and it is not unblocked or discharged to a safe or contaminated place.
(4) Leakage of sample gas processing system is absolutely not allowed, and it is a great source of safety hazards and failures.
4 Online Analysis System Engineering Application Troubleshooting
On-line analysis system is a large-scale, sophisticated complete set of equipment, and it should pursue a 100% success rate of engineering application. Therefore, a thorough and in-depth technical analysis of its engineering application faults is of great practical significance, and it also has certain guiding significance for the elimination of faults.
The following comments were made on the troubleshooting of the application of online analytical system engineering:
4.1 Strengthen the full-process technical service of a professional factory
The professional factory has targeted and standardized professional design, which is the biggest guarantee for the successful application of the analysis system. The system's installation and operation instructions, technical training, spare parts supply, etc. shall also be required to effectively protect the product's design technology, application maintenance technology, and general maintenance technology, and be fully understood, mastered, and proficient by the engineering user's professional operators. use.
4.2 Guided by professional and technical knowledge
On-line analysis of engineering technology is a very special new profession. To repair and repair its engineering application failures, it is difficult to imagine without good professional and technical knowledge and considerable theoretical knowledge. Therefore, further study and technical exchanges become necessary.
4.3 Empirically Solve Real Problems
The professional application of on-line analysis system also has 24 years of arduous process. After all, it has accumulated a wealth of experience in engineering applications, which is certainly useful in the use and maintenance of the system. Some kind of failure will be eliminated or its negative impact will be reduced. Even if we don't know why, we know how to do it according to the procedures and we can certainly achieve good results.
4.4 Do more in-depth analysis of the current state of production process conditions and field conditions
It should be sobering to realize that the production process conditions in industrial production are dynamically changing, and of course, they are very stable. The biggest reason for the change is the adjustment of the product or the improvement of the production process. At this time, it is still stubborn that the analysis value is different from the original, and the big change is that the analysis system is faulty. It is obviously a misunderstanding or misunderstanding. Unexpected undesired disturbances or abnormalities may also occur in the production process, resulting in huge changes in sample conditions, and inevitably such potential failures should also arouse our great concern.
4.5 pay attention to details and focus on the process
On-line analysis of the industry's online analytical system engineering applications, "details determine the success or failure" of the concept is very popular, and indeed so. What is difficult is any time or any technical aspect. We pay close attention to the details and have no negligence or loopholes.
The engineering application of the on-line analysis system can control all the details only if the entire process is controlled.
Therefore, our final advice and suggestions are:
Effectively control the entire process, grasp all the details, eliminate failures before they occur, and strive for the complete success of the online analytical system engineering application.
references
Jin Yizhong, Cao Yigang, Online Analysis System Generalized Anti-jamming Research, Analytical Instruments, 2009,(6):
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