Application of external level switches in measuring the liquid level in crude oil backwash tank

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Description of the operating conditions in the case of using an external level switch for measuring the liquid level in a crude oil backwash tank: A petrochemical company in Shandong operates a crude oil backwash tank that is 4 meters high and 1.5 meters in diameter. There are 100 vertically arranged filter rods inside the tank, and the temperature ranges from 170 to 200 degrees℃； Purpose: On-site crude oil filter, mainly used to remove impurities such as sediment and small stones with larger particles contained in crude oil ； Purpose: To protect the proper operation of the pump and ensure the quality of crude oil. Not only is the structure inside the tank complex, but the discharge speed is also high; the process requires discharging the contents every 8 hours, and the discharge process itself takes less than 1 minute. The user originally used an imported radio frequency admittance level switch, which malfunctioned during operation. Both replacement and maintenance required shutting down the system, resulting in high maintenance costs and significant workload. The crude oil backwash tank was circulated every 8 hours; after the level switch failed, the liquid level in the tank had to be estimated based on time, which posed considerable safety risks. Other level measurement instruments were practically unsuitable for use under these conditions. Users have been looking for suitable products to replace them. Due to the simple installation and operation of the external level switch, as well as its immunity to the effects of medium viscosity, temperature changes, and material deposition on the walls, the user decided to try out the ELL external level switch. 1. The variable-frequency ultrasonic level switch is easy to install and operate, meeting the requirements for on-site use. It is a completely isolated level measuring instrument that requires no drilling, tank cleaning, use of fire, or suspension of production; simply attach a pair of probes to the area being measured, **which reduces installation costs and the amount of work required. 2. The level switch is not affected by the viscosity or purity of the liquid, making it suitable for measuring complex media. It utilizes the attenuation of ultrasonic waves as they propagate through the tank wall, and detects the remaining energy after propagation. Due to the different transmission rates of ultrasonic energy in gases and liquids, it is possible to easily detect when the liquid level reaches the desired height and trigger an alarm; a digital signal is generated to interlock the liquid inlet and outlet processes. Since the signal propagates inside the tank wall, the viscosity and purity of the liquid being measured do not affect the operation of the frequency-variable ultrasonic level switch. 3. It features a unique \"variable-frequency ultrasonic technology\" that is less affected by temperature changes and material accumulation on the walls of the container, enabling stable measurements. This variable-frequency ultrasonic level switch utilizes a proprietary patent technology; it is highly intelligent and can automatically compensate for changes in temperature and material accumulation, thereby **reducing the rate of false alarms and enhancing the stability of the instrument. This is also a key reason why the ELL variable-frequency ultrasonic level switch offers higher stability compared to products from other manufacturers. 4. The frequency-variable ultrasonic level switch features a unique design that meets the requirements for high-temperature measurements. For such applications, a \"super-high temperature\" probe as well as a special imported coupling agent have been developed, enabling this level switch to better adapt to temperature changes and achieve accurate measurements. Due to the complexity of this operating condition, the technical engineers assigned many relevant personnel to participate in the testing and to evaluate the measurement results. A total of 5 tests were conducted for liquid intake and discharge; by comparing with historical data, accurate measurements were achieved and the alarm outputs remained stable. On-site installation is extremely simple: a pair of Ø80 probes are installed 1 meter apart at a height level corresponding to 80% of the tank’s full capacity for crude oil backwashing. These probes are connected to an instrument transmitter; when the level of crude oil in the tank exceeds this height, the transmitter sends a digital signal to the control system, which then controls the pump. 1. Automated and digital safety production management has been implemented. Without any manual intervention, the crude oil backwash tank automatically controls the inflow and outflow of liquid; data is recorded within the system to calculate the oil output per unit of time. 2. Low cost. **It reduces the workload of operators and saves on labor costs ； Installation and debugging are simple and convenient, with no need for any modification costs. 3. Easy and simple to expand. If more accurate measurement of the liquid level inside the tank is required later, it is sufficient to add measurement points to the tank and install high-temperature external liquid level probes. Through prolonged monitoring by the process department, it has been confirmed that the instruments maintain stable performance, fully meeting the requirements for level measurement under such extreme operating conditions, and continuously providing the control room with updated data on liquid levels and equipment status. Since the PFDavg (T1=1Y) (failure rate under safe conditions) of the variable-frequency ultrasonic level switch is ≤6.04×10-⁵ ； With an SFF (Safety Failure Fraction) of ≤99.35%, the functional safety integrity level is SIL3, allowing it to be used directly in SIS systems (Safety Instrumented Systems). When the oil level in the tank is too high, an alarm is triggered and the interlock system stops the liquid feed pump from operating. With the continuous development and improvement of external level measurement technologies, external level gauges are being used in an increasing number of complex operating conditions. Their notable advantage of enabling level measurement without drilling holes, starting fires, emptying tanks, or shutting down production provides users with fast level measurement solutions while saving significant amounts of labor, resources, and time.