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Why is it difficult to measure the level of high-temperature maleic anhydride? Maleic anhydride, at normal temperature and pressure, exists as colorless needle-like or flaky crystals in the orthorhombic crystal system; when the temperature exceeds its melting point of 52.8°C, it melts into a liquid state, and the viscosity of this liquid decreases as the temperature rises. Toxic. Due to the large temperature variations of maleic anhydride, it tends to crystallize and adhere easily. Liquid level measurement of maleic anhydride has become a challenge in the industry. How to solve this measurement challenge? The maleic anhydride separation tower, maleic anhydride buffer tank, and maleic anhydride aging tower at a chemical plant in Shandong have a diameter of 1.6 m and a height of 2 m; they are equipped with external heating tubes that maintain a temperature of 160°C, and the medium inside them is maleic anhydride. Since the tank went into operation, liquid level measurement has been a challenge for the company. I. Main issues: The enterprise has used a variety of measuring instruments and methods over time. 1. Differential pressure level gauges: Due to large temperature variations in the liquid medium, its viscosity increases at low temperatures; as a result, the flange connection holes on the pressure gauge at the bottom become blocked, causing the gauge to display incorrect liquid levels ； The maintenance work for clogged hair capillaries and pressure-sensitive diaphragms is extensive ； 2. A flange connection hole is provided at the top for installing a horn-shaped radar level gauge; anhydride vapor evaporates and crystallizes when it cools, sticking to the radar transmitter antenna and interfering with the radar’s measurement, thus preventing accurate determination of the liquid level ； 3. Lens level gauges have poor accuracy; the lens window is prone to being covered by crystals, resulting in an unclear view of the liquid level when viewed with the naked eye. Moreover, they do not support remote transmission of the level information ； 4. With magnetic flap level gauges, it is common for the liquid level to show no change; when the medium is viscous, the float gets stuck in the connecting tube and does not move. Effective control of the liquid level cannot be achieved during production, posing a serious risk of environmental pollution and production waste due to tank overfilling. II. Solution 1: Use a gauge produced by Xi’an Dinghua Electronics Co., Ltd. – it is a sonar-type external level gauge with the model number ELL-FI-CE03L0.2HDF1. Its measurement range is 0.1–3 meters, with an accuracy of 0.2% F.S. The suitable operating temperature range is -40–160°C, and it supports Hart bus protocol output. Features of the ELL-FI-CE sonar-type external level gauge: no additional drilling is required during installation; simply install the sensing probe on the outer wall at the bottom of the tank ； No tank cleaning required, saving installation costs ； There is no need to halt production, so no unnecessary losses will occur. The instrument can achieve accurate measurements when the viscosity of the medium is kept within a certain range, and it is not affected by pressure changes, temperature changes, or the flow of liquid in and out. 2. On-site installation: stainless steel probe mounting base, high-temperature probes, instrument transmitters. 3. Performance: After 30 days of monitoring fluid inflow and outflow during production, it was found that level measurement is accurate, and the DCS trend displays in the remote control room are precise, meeting the requirements of automated production. One unit was tested first, after which ELL sonar-type external level gauges were installed in all 5 other tanks. III. Performance 1: Completely eliminates the significant risks of environmental pollution and production waste caused by overflow in tanks ； 2. Zero-cost installation ； 3. Easy implementation of remote level monitoring for automated production control ； 4. **It reduces the workload of instrument operators, with instrument maintenance needs approaching zero.