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Keywords: liquid level monitoring, interlocking, level switch, float ball, photoelectric, ultrasonic, external level switch, octanol tank, variable frequency ultrasonic technology, variable frequency amplitude, micro vibration analysis The Application of External Liquid Level Switch in the?Butanol and Octanol Tank
Zhanghongfei,Liangdong
(PetroChina DAQING Petrochemical Pompany, Heilongjiangg, Daqing)
Abstract: This paper briefly describes the measuring principle and characteristics of the external liquid level switch, and introduces the installation method according to the actual conditions on site, which has a certain significance of application.
Keywords: external liquid level switch,butanol and octanol tank,frequency conversion ultrasonic technology
I. INTRODUCTION Safety work is the basis for the survival and development of an enterprise, and it is also the fundamental guarantee for the health and safety of the country’s property and the people. The petrochemical industry is characterized by complex production processes, high temperature and high pressure equipment, and raw materials and products that are flammable and explosive. Therefore, safety work is at the forefront of all aspects of petrochemical enterprises. There are four most important monitoring data in petrochemical enterprises, including liquid level, pressure, temperature and flow, and liquid level as one of the four most important data. Its monitoring plays a decisive role in the safety production of petrochemical enterprises.
In recent years, with the continuous development of China's petrochemical industry, the safety production of petrochemical enterprises is facing a lot of new situations, especially the frequent occurrence of major accidents in recent years, which has made the country and all sectors of the society raise the safety of petrochemical companies. The request. The SIS system (safety instrumentation system) has been used more and more widely in petrochemical enterprises. It can not only achieve alarms for liquid level arrival monitoring, but also chain related equipment, which in turn will affect the reliability and stability of liquid level switches. Accuracy and simplicity make higher demands.
Daqing Petrochemical Company's butyl octanol plant was completed and put into operation on June 18th, 1986. The plant uses propylene and synthesis gas as raw materials, and Davy/DOW low-pressure carbonyl synthesis technology is used to produce 2-ethylhexanol and n-butanol. Butanol. In 2012, the plant was expanded and expanded. The carbonyl synthesis system was changed from gas-phase circulation to liquid-phase cycle. The rear system of the original plant was changed to a butanol production line and a octanol production line was added.
In the production of octyl alcohol, its final product and intermediate products are all liquids, many of which are flammable, explosive, volatile, toxic, and pungent. The device is provided with a tank area. In order to prevent empty cans and spilled cans, the company has used several liquid level switches, float ball type, and photoelectric type liquid level switches since it was put into operation. Since these two liquid level switches are plug-in type, holes need to be opened in the cans to create cans. There is a long-standing odor around the area. Due to their limitations, sometimes the switches are falsely reported, which leads to chain movement errors. Afterwards, Xi'an Dinghua's ELL frequency conversion ultrasonic liquid level switch was selected.
Second, the working principle of several switches 2.1, the working principle of the float level switch The magnetic float float level switch with the liquid level rise or fall, so that the sensor detects the set position of the reed switch chip action, issued Contact open (close) conversion signal.
In a closed non-magnetic tube, one or more reed switches are installed, and then the tube is passed through one or more hollow floating balls with ring-shaped magnets. The rising or falling of the liquid will move the floats up and down together. Thus, the reed switch in the non-magnetic tube generates a pull-in or break-out action, thereby outputting a switch signal.
2.2. The working principle of the photoelectric level switch The photoelectric level switch uses infrared detection. Using the principle of light refraction and reflection, light will reflect or refract at the interface of two different media. When the liquid to be measured is in a high position, the liquid to be measured and the photoelectric switch form an interface. When the liquid to be measured is in a low position, the air and the photoelectric switch form another interface. These two interfaces make the internal light of the photoelectric switch. The intensity of the reflected light received by the receiving crystal is different, which corresponds to two different switching states.
2.3, ELL-SA frequency conversion ultrasonic level switch working principle (Figure 1)
Xi'an Dinghua shares EL-SAL frequency conversion ultrasonic liquid level switch is a patented adaptive "frequency change amplitude ultrasonic technology", which means that the instrument can automatically adjust the transmission signal according to the received signal frequency, wave strength or wavelength Wave frequency, wave strength or wavelength.
1. A monitoring point uses two probes attached to the outer tank wall to achieve monitoring. One is a transmitting probe and the other is a receiving probe.
2. The transmitting probe can be frequency-converted and amplitude-amplified to emit ultrasonic waves, and the receiving probe receives the after-thaw signal transmitted along the tank wall;
3. When there is liquid at the monitored point, the ultrasonic signal emitted by the transmitting probe will be transmitted to the liquid part, and the residual vibration signal received by the receiving probe will be greatly attenuated and the amplitude will become smaller;
4. When the monitored point has no liquid, the ultrasonic signal emitted by the transmitting probe will not be transmitted in the air, and the attenuation of the residual signal received by the receiving probe will be very small, and the amplitude will become large;
5. The receiving probe transmits the received signal to the host. The host will automatically determine whether the monitored point has liquid or no liquid according to the characteristics such as the amplitude of the signal.
6, according to the liquid or no liquid output a switch for interlocking related equipment or sound and light alarm.
Figure I. The working principle of variable frequency ultrasonic liquid level switch 
Third, the advantages and disadvantages of several liquid level switches 3.1, Float level switch advantages:
1, the float switch does not contain easily lead to failure and bellows, springs, seals and other components, but the use of direct-float drive internal switch magnet;
2, float level switch is a simple structure, easy to use, safe and reliable liquid level controller. It is faster than normal mechanical switches and has a long working life. Compared with electronic switches, it has the characteristics of strong resistance to load and impact. A product can realize multi-point control;
3, application of a wide range of shortcomings:
1. The float switch is a simple passive device, and it does not have a self-checking function. It needs regular inspection and maintenance.
2. The float or float level gauge is a moving part and will be contaminated when used in thicker or thicker liquids. Poor measurement accuracy, viscosity does not work when <0.8mpa*s. The pressure, density and dielectric constant of the container are required, and the installation must be stopped, clear, open, and hot.
3, the installation location is relatively high, maintenance and inspection must be erected scaffolding, personnel work at heights;
4. The valves, flanges and other supporting parts of the float level switch belong to the sealing point. Once there is leakage, it is difficult to repair. If the shutoff valve is not strict, the liquid level switch cannot be cut out;
5. The inside of the switch communicates with the tank body and is filled with medium. In winter, the outside needs heat insulation and heat tracing, and the maintenance of the meter is large. In addition, the heat tracing pipeline is complex, and the integrity of the on-site tank is not coordinated.
3.2, photoelectric level switch advantages:
1, no mechanical moving parts, high reliability;
? 2, small size, cost-effective;
3, liquid level control, high accuracy, repeatability.
Disadvantages: Not suitable for frozen liquids and crystalline liquids.
3.3, ELL-SA frequency conversion ultrasonic level switch advantages:
1. Leading technology: The product adopts Xi'an Dinghua's "micro-vibration analysis" signal processing technology to ensure reliability and accuracy;
2. Safety: When measuring toxic, corrosive, pressure, flammable, volatile, and easily leaking liquids, do not use valves, connecting pipes, joints, no leakage points, no contact with the liquid and gas inside the tank, very safe. Even if the instrument is damaged or repaired, it will never cause leakage, poisoning or explosion.
3, installation and maintenance convenience: installation and maintenance do not move the fire, do not clear the tank, does not affect the production.
4. Reliable and durable: There are no mechanical moving parts in the sensors and meters, and they are strictly sealed and isolated from the outside. They will not wear or corrode.
5. Widely applicable: It has nothing to do with the pressure, temperature, density, dielectric constant, viscosity, and non-corrosiveness of the measured medium. It can be widely used in petrochemical, chemical, oil depot, petroleum, electric power, liquid storage, transportation, and pharmaceutical industries.
Disadvantages: The material requirement for the can body is not non-hard material. The installation requirements are relatively high. The installation spacing of the measuring probe is about 1 meter. The two probes cannot have a weld between them (ie, on the same steel plate).
Fourth, ELL-SA frequency conversion ultrasonic installation requirements ELL-SA external measurement level switch by the instrument host (transmitter) and probe components, vertical tank single-point instrument installation shown in Figure 2. 
4.1 Installation requirements of the instrument host 1. Select the position near the alarm point of the tank, and install the low alarm point near the alarm point; the high position can be installed near the alarm point in the tank top to minimize the distance from the probe to the transmitter;
2. The transmitter is installed with a 2-inch riser fixed or instrument protection box. The riser height is 1.2~1.5 meters. The transmitter installation location should be as easy as possible for operation, observation, and easy access to personnel;
3, to avoid direct sunlight 4.2, the probe installation requirements ELL-SA external measurement level switch can reliably work, depends to a large extent on the correct installation of the measuring head, for carbon steel tank, the measuring head is generally used magnetic force Magnetic rings are directly adsorbed; for stainless steel tanks, glued or welded connection bases are used.
1, according to the alarm point on the wall to select the measuring head installation position, the two measuring head spacing 1000mm, not across the weld, the distance from the horizontal weld more than 100mm, the distance from the vertical weld greater than 300mm, try to stay away from the weld;
2. The surface of the tank wall measuring head shall be polished. The dimensions of the mounting surface on the container wall shall be guaranteed to be no less than φ80mm, the surface flatness shall reach 0.15mm, and the surface roughness shall reach 1.6. The installation surface should be free of welding slag and paint blocks so that the measuring head can be completely and closely attached to the container wall;
3. The cable length between the probe and the host during calibration of the instrument must be the same as the length of the final cable;
4. After the probe is installed, seal it with sealant.
Fifth, the actual use of the effect of testing 5.1, companies use ELL-SA frequency conversion ultrasonic liquid level switch purpose of anti-leakage, eliminate odors around the tank area, liquid level switch high monitoring, reliable chain into the pump, anti-rising tank.
5.2 Functions to be Accomplished The company has reconstructed seven of its storage tanks, from original atmospheric tanks to floating-top tanks, and simultaneously updated and modified the supporting instruments. The first application of Xi'an Dinghua new type ELL-SA external measurement level switch.
The octanol storage tank has a diameter of 12m, a height of 15.7m, a wall thickness of 11mm, and a high reporting point (alarm level above this position) of 12m.
When it exceeds the high reporting point, the sound and light alarm of the DCS room will alarm, and the chain feed pump will be turned off to stop feeding.
5.3, the actual use of the effect of the tank feed pump starts, starting from the low level feed, ELL-SA frequency conversion ultrasonic level switch relay output long closed, the instrument shows LO (non-liquid state), when the tank feed to 12m, The meter display changes from LO to HI (liquid state), the relay output is changed from normally closed to normally open, the chain feed pump is turned off, the feed is stopped, the red light of the DCS room sound and light alarm is on, and the alarm sounds. Seven ELL-SA frequency conversion ultrasonic liquid level switches have all been tested, and they all achieve the expected results. Conclusion, the use of ELL-SA frequency conversion ultrasonic level switch can fully meet the requirements of enterprises.
VI. Concluding remarks Through the installation and testing of ELL-SA frequency conversion ultrasonic liquid level switch under actual working conditions, the effect is very satisfactory. ELL frequency conversion ultrasonic liquid level switch also has the features of explosion-proof grade and high protection level. It has flameproof type (EXd) And intrinsic safety type (EXia); IP67 and IP65, so ELL frequency conversion ultrasonic level switch is suitable for fixed point level measurement and alarm linkage of various liquids in various containers. It can be widely used in petrochemical, chemical, oil depot, petroleum, electric power The liquid storage and transportation industries have significant advantages in the field of fixed-point liquid level measurement and alarm for pressure vessels, hazardous chemical liquids, inflammable and explosive liquids, etc., and have broad prospects for development.
references:
(1) Petrochemical Automatic Control Design Manual ISBN 7-5025-2696-X
(2) “Application of External Level Gauge on Hydrofluoric Acid Storage Tankâ€, Gao Fenglin, Automation of Petrochemical Industry, 1007-7324(2014)05 0071 03
(3) "ELL-SA outer measuring level switch Manual", OF: West Anding Hua Electronics Co., Ltd. (4) "West Anding Hua Product Sample" OF: West Anding Hua Electronics Co., Ltd. (5 ) "ELL-SA outside the test level switches enterprise standards", author: West Anding Hua Electronics Co., Ltd. (6) "ultrasonic level measurement technology research to improve the accuracy of the test," Qi Jiantang, Cong, Germany Miao Lin, Shaanxi Province nnd annual meeting -2002
(7) "Study on Ultrasonic Level Measurement Method" Mo Deju, Liu Yanyan - "Instrumentation and Analysis Monitoring" - 2007
(8) "Error Analysis and Anti-jamming Measures of Ultrasonic Level Gauge" Li Ping - 《Transportation Technology and Economy》-2006
Abstract: Liquid level monitoring and chaining is an important link in the safety production of petrochemical enterprises. Liquid level switch is the key equipment to ensure this important link. Whether the liquid level can be accurately monitored and whether the interlocking action is reliable depends directly on the performance of the liquid level switch. Good or bad. This article briefly describes the advantages and disadvantages of several common liquid level switch operating principles, and discusses in detail the measurement principle and characteristics of the ELL-SA external level switch, and describes the installation method in conjunction with the industrial scene; through several level The comparison of the switches can be used as a reference for the user to select the appropriate level switches according to their own industrial site conditions.
Figure II: Instrument Installation Diagram