图106，analysis of liquid level measurement and control measures of lng storage tank (2) - doer equipment
classification：forum publishtime：2019-11-02 14:07:58
analysis of liquid level measurement and control measures of lng storage tank
the storage tank is equipped with two servo liquid level meters and one radar liquid level meter to continuously measure the liquid level in the tank. the servo liquid level meter and radar liquid level meter (sil2 certification) output 4 ~ 20ma signals to the user sis system in the control room. at the same time, high and low switches are provided for ultra-high or ultra-low interlocking of the storage tank liquid level, and output signals to dcs for liquid level display and tank capacity management.
the design, installation and replacement of the liquid level gauge shall not affect the operation of the storage tank, and the full-diameter ball valve shall be used to connect with the storage tank body. prevent liquid overflow caused by high liquid level or empty tank caused by starting the pump or compressor when the liquid level is too low. one servo level gauge can detect the density and measure the medium density at different liquid levels in the storage tank.
temperature measurement facilities are set on the inner tank, tank wall and tank bottom of the full capacity tank.
the tank wall and bottom are equipped with multi-point armored thermal resistance (the thermal resistance and extended shielded cable are integrated and encapsulated in stainless steel protective tube（ φ within 6mm), the protective tube is filled with mgo.
a set of average thermometer with multipoint temperature transmitter is set in the liquid in the inner tank. the multi-point temperature transmitter and average thermometer output modbus-rs485 signals to the dcs system in the control room for display, which can ensure accurate temperature measurement at different positions of the storage tank during start-up precooling and normal operation, and meet the production operation needs of uniform cooling, precooling and flexible adjustment.
a temperature measuring point is set at the bottom of the insulation foundation of the inner tank to detect whether there is liquid leakage.
in addition, an armored thermal resistor is respectively set on the tank vent pipeline, and the rtd signal is output to the dcs system for display and alarm.
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