Comparison and Analysis of Commonly Used Horizontal Tank Level Gauges

Storage tank overview: Horizontal storage tanks are long containers used to store oil products, vegetable oils, chemical solvents, water or other petroleum products. Horizontal storage tanks are composed of end caps and horizontal circular or oval tank walls and saddles, and are usually used in production links or gas stations. The volume of the horizontal storage tank is generally less than 100 cubic meters, it is generally round, oval, and there are other irregular shapes. (Picture) Physical properties: The medium stored in the horizontal tank: liquid ammonia, liquefied gas, propylene, propane, liquid chlorine, hydrogen fluoride, bromine, ethylene oxide, monomethyl monomer, hydrogen chloride, nitric acid, gasoline, diesel oil, aviation Kerosene, tert-butylamine, sulfur dioxide. Safety requirements: first-class explosion-proof pressure: 0.1-1.3 temperature: (-20)-32 horizontal tank Material: carbon steel, aluminum tank, stainless steel, enamel-lined carbon steel tank There are four types of liquid level gauges that are widely used in horizontal storage tanks at present, radar level gauges, differential pressure level gauges, ultrasonic external level gauges, and magnetic flap liquid level gauges. Level gauges, among which the first three liquid level gauges can realize DCS and SIS remote transmission, the magnetic flap level gauge is mainly for on-site display, the radar level gauge, the differential pressure level gauge, and the magnetic flap level gauge are the same as the measured The liquid level gauge in direct contact with the medium, while the ultrasonic externally attached liquid level gauge is a non-contact liquid level gauge. The working principles of the four types of level gauges Radar level gauges are mainly divided into two types: pulse radar and guided wave radar. Pulse radar level transmitters can be simple and reliable non-contact measurement of metal tanks, pools or other containers Fluid level. A 6.3GHz pulse is generated from the microprocessor control circuit and emitted through the sensor surface. The time when the pulse signal hits the surface of the measured fluid and is reflected back to the antenna is converted into a current signal proportional to the liquid level and output by the microprocessor. Pulse radar uses high-frequency and narrow pulses to modulate the microwave source signal, and transmits pulse waves with a fixed frequency (ie, carrier frequency) in the form of beams, which are received by the receiver after being reflected on the surface of the medium. The distance to the surface of the medium, the guide radar level gauge is a radar level gauge based on the principle of time domain reflection. The electromagnetic pulse of the radar level gauge propagates along the steel cable or probe at the speed of light. When it encounters the surface of the measured medium , Part of the pulse of the radar level gauge is reflected to form an echo and returns to the pulse transmitter along the same path. The distance between the transmitter and the surface of the measured medium is proportional to the propagation time of the pulse during the period, and the liquid level height is calculated. The measurement principle of the differential pressure level gauge is to connect the positive pressure end of the differential pressure gauge to the bottom of the liquid to be measured with a steel pipe, and the negative pressure end to the gas phase, according to the principle of hydrostatics; the differential pressure level transmitter is a It works on the principle that when the liquid level in the container changes, the static pressure generated by the liquid column also changes accordingly. The ultrasonic externally attached liquid level gauge is mainly installed at the bottom of the storage tank and does not directly contact the measured medium. It emits ultrasonic waves through its own unique measuring probe, and adjusts the difference in the speed of sound of different types of media through the host, and measures the ultrasonic wave from the bottom of the tank to the liquid level. time to detect the height of the liquid level. The magnetic flap liquid level gauge mainly measures the liquid level through the characteristics of the floating ball in the bypass pipe that changes with the liquid level. When the liquid level rises, the floating ball will turn the magnetic flap at the corresponding position by magnetic force. The advantages and disadvantages of the four types of level gauges The main advantage of the pulse radar level gauge is that it can measure a range of up to 70 meters, with a small error, and is not affected by temperature, dust and steam, and has a wide range of applications, which can be used in oil storage tank areas , Asphalt storage tanks, liquefied petroleum gas, reactors, sewage tanks in the petrochemical industry and continuous level measurement of molten steel in blast furnaces in the iron and steel industry. The disadvantage of pulsed radar is that most economical pulsed microwave level meters use microwave frequencies of 5.8Hz or 6.3GHz, and the radiation angle is large (about 30 degrees), which is easy to generate interference echoes on the container wall or internal structure. The main disadvantage of the guided wave radar level gauge is that the liquid level jumps when some impurities or liquid are attached to the probe. At the same time, on a pressure vessel such as a horizontal tank, it is not easy to replace the radar level gauge after a problem occurs, and it can be replaced only after the tank is cleaned. The advantage of the differential pressure level gauge is that the measurement has no mechanical wear, the structure is simple, and it is easy to operate and maintain. The main disadvantage is that when there is steam in the container, it will condense into liquid in the negative-phase impulse pipe, resulting in serious measurement errors. It is necessary to install a liquid storage tank in the impulse pipe and perform manual drainage regularly. When the weather is cold, the liquid in the impulse pipe is easy to be collected. Solidification requires heat tracing and heat preservation, which is troublesome when put into use. It must be filled with water in the pressure-inducing pipe of the transmitter or after water vapor condenses to fill the pressure-inducing pipe before it can be accurately put in. The comprehensive error of the measurement is large, and the measurement difference of the transmitter The accuracy of the sampling is limited, coupled with the instability of the liquid column in the sampling pipeline and other factors, resulting in a large comprehensive error in the actual measurement. The advantage of the magnetic flap level gauge is mainly that the price is relatively cheap, and it is a mechanized structure.The height of the liquid level can be visually displayed, and the range of use is very wide. Almost all storage tanks that meet the installation requirements are installed. The disadvantage of the magnetic flap level gauge is that the measurement mainly passes through the bottom of the storage tank and the bypass pipe at the bottom. When the medium settles a lot, it may block the bottom pipe,
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