Abstract: In view of the special climatic environment and working conditions of Rumaila Oilfield in southern Iraq, the selection, installation and debugging methods of radar level gauge are discussed.
The radar level gauge is a level gauge based on the time domain reflection principle (TDR). Its emitting device can emit microwave pulses. When the microwave pulse encounters the surface of the measured medium, part of the pulse is reflected to form an echo and along the edge. The same path is returned to the pulse transmitting device, and the distance between the transmitting device and the surface of the measured medium is proportional to the propagation time of the reflected pulse therebetween, and the liquid level is calculated. The radar level gauge has high reliability and measurement accuracy, and its maintenance workload is small. It is suitable for use in harsh environmental conditions such as southern Iraq. We have made beneficial attempts in the power plant project in Rumaila Oilfield. Better application results.
There are many types of radar level gauges. The selection of the temperature, pressure, density, viscosity and corrosivity of the measured medium affects the performance of the medium. Therefore, the antenna and the characteristics of the medium under certain working conditions are selected. Header.
The highest temperature in southern Iraq can reach 58.8 °C, and the sand is large. The VEGAPULS62 and VEGAFLEX81 radar level gauges of our selected VEGA company have a process temperature of -40 °C ~ 200 °C, and the protection grade is IP68, which can meet the requirements;
In order to match the signal with the DCS system, the radar level gauge uses 24VDC power supply, 4m A~20m A Hart protocol.
1.1, Germany VEGAPULS62 radar level gauge:
The fire water tank of Lumaila Power Station is 15m high, the original water tank is 13m high, and the internal medium is untreated water. It is alkaline and corrosive. If a contact radar level gauge is used, the time will be long. The probe is corroded and easy to scale. In addition, if a contact radar level gauge is used, a probe of 13m length and 15m length is required, and the probe diameter is Φ8. According to experience, probes longer than 6m are susceptible. The influence of water flow fluctuations interferes with the measurement signal; the VEGAPULS62 non-contact radar level gauge transmits and receives microwave pulses through the antenna, so we use the VEGAPU LS62 radar level gauge for liquid level measurement of fire water tanks and raw water tanks.
1.2, VEGAFLEX81 radar level gauge:
The fuel gas liquid separation tank, the torch liquid separation tank and the condensate tank of the Rumaila power station are small in volume and the height is not more than 6m. The liquid medium in the equipment is hydrocarbon condensate.
Taking into account the above characteristics, the VEGAFLEX81 radar level gauge is used to measure the liquid level of fuel gas liquid separation tanks, torch liquid separation tanks, condensate tanks and other equipment. VEGAFLEX81 is a contact guided wave radar level gauge, which measures the level by sending a microwave pulse through a probe. The contact between the probe and the measured medium can improve the measurement accuracy of the radar level gauge, and the change of the density of the medium, the change of the particle size of the medium, and even the liquefaction will not affect the measurement accuracy.
In order to achieve a high-precision, trouble-free measurement of the liquid level of the medium, it is critical to properly install the radar level gauge. Whether the radar level gauge can correctly measure the liquid level depends on the reflected wave signal. If at the selected installation position, the liquid level cannot reflect the microwave back to the radar level gauge or if the interference object reflects the interference wave to the radar level gauge within the range of the signal wave, the radar level gauge cannot correctly reflect the actual liquid level. Therefore the installation position is very important for the radar level gauge.
2.1, Instrument installation:
The vertical axis of the liquid level gauge is different from the vertical line of the tank center line, and the strokes of the transmitted wave and the reflected wave are also different, and the measurement accuracy is also affected. Install the level gauge flange on the tank nozzle, and then use the level to adjust the verticality of the transmitter so that the deviation does not exceed 1.5°.
2.1.2, Free space:
The space between the top of the tank and the zero point of the measurement within the beam range of the radar level gauge is free space. If there are any obstacles in the free space, such as structural ribs and pipes with a diameter larger than 2”, it will interfere with the radar wave and affect the measurement effect. Check the free space in the tank before installation to eliminate all possible influences on the measurement. Accuracy obstacles.
Figure 1 Schematic diagram of the installation position of the radar level gauge
The VEGAFLEX81 radar level gauge is installed at least 300mm away from the metal tank wall, and the distance from the non-metallic tank wall is at least 500mm. The minimum distance from the tank wall when the VEGAPU LS62 radar level gauge is installed is 200mm. The nozzles on the top are reviewed to ensure that the spacing requirements are met. In particular, it is not possible to install the radar level gauge at the feed port (Figure 1), which will seriously affect the measurement data.
The nozzle mounting of the VEGAPU LS62 should meet the requirements of Figure 2; the nozzle mounting of the VEGAFLEX 81 should meet the requirements of Figure 3.
Figure 2 Schematic diagram of the installation dimensions of the VEGAPULS62 radar level gauge
Figure 3 Schematic diagram of the installation dimensions of the VEGAFLEX81 radar level gauge
VEGAFLEX81 is a contact radar level gauge. The measuring component is a rod probe. In order to reduce the influence of scaling on the probe, a protective cover is added to the probe during installation. After the protective cover is installed, the probe can be fixed not only to prevent the probe. The impact of the water flow on the probe produces signal fluctuations, which also reduces the influence of fouling on its measurement. It is of great help to the inspection and maintenance of the liquid level gauge after it is put into production.
In Iraq, the solar radiation is strong in summer, and the direct surface temperature is also 60°C~70°C. Long-term direct sunlight will damage the display, causing the display to be blurred and the screen to flicker. In order to prevent the sun from directly on the display, the level gauge A sun visor is mounted on the top of the LCD display for good protection (see Figure 4).
Figure 4 Liquid level gauge sun shield installation diagram
2.2, Instrument line installation:
The instrument cable is 2*1.5mm2 flame-retardant shielded armored cable. The cable entry equipment is equipped with explosion-proof armored Glan fixed and sealed. Granite is equipped with grounding ring. The protective ground passes 6mm2 yellow-green grounding wire pressure terminal and grounding ring bolt. Pick up. In the equipment, the instrument cable is connected to the positive and negative of the equipment terminal according to the principle of white positive and black negative, and the shielding is suspended.
2.3, Instrument debugging:
Although the radar level gauge is a high-precision instrument, there are certain systematic errors and malfunctions when operating under high temperature, sand and alkali conditions for a long time. In the debugging process, it mainly manifests in the following aspects:
2.3.1. The reference height causes the liquid level error as a function of temperature:
Static pressure, temperature changes and the rise and fall of the tank floor can cause changes in the reference height, resulting in unpredictable liquid level measurement errors. This error is unique to the “air measurement method” measurement method. It is also a manual gauge and based on sound measurement. The radar level gauge of the principle of law cannot be overcome. Especially in the climate with a maximum temperature of 58.8 ° C and a minimum temperature of 0 ° C, the height of the reference object changes due to the thermal expansion and contraction of the object. Therefore, whenever the season is changed, the reference level is measured according to the change in temperature, and the level gauge is recalibrated.
2.3.2, The probe caused by long-term scaling caused failure:
Due to poor water quality, high impurities and large alkalinity, the emitter electrode will foul under long-term working conditions, hindering the emission of microwaves. Based on theoretical analysis and actual on-site operation, we found that as long as the radar level gauge is inspected and cleaned every six months, the working index requirements of the level gauge can be guaranteed.
The good application of radar level gauge is very important for the accurate measurement of liquid level, especially in the southern part of Iraq where the environmental conditions are harsh. The radar level gauge has the characteristics of high temperature resistance, high pressure resistance, high corrosion resistance and high stability. The smooth transmission of the Myra Power Station provides a strong guarantee.