Application of ELL external level gauge in liquid chlorine storage tanks.doc

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Application of ELL External Level Gauge in Liquid Chlorine Storage Tanks By Jiang Lianyou, Deputy Director of the Instrumentation Workshop at Hebei Cangzhou Dahuahua TDI Co., Ltd. Abstract: This paper briefly describes the application of the ELL external level gauge, which excels in terms of environmental protection and safety, in the liquid chlorine storage tanks of Cangzhou Dahuahua TDI Company. Keywords: Safety and explosion prevention, intelligence, isolated measurement, high-performance network-based external level gauge, automatic temperature compensation 1. Company Overview Our company’s full name is Hebei Cangzhou Dahuahua TDI Co., Ltd. Construction of the facility was approved by the **Planning Commission in 1996; trial production began in 2000, and the facility was officially completed and put into use in 2002. By 2006, the company’s TDI production volume had reached 30,000 tons. We have always attached great importance to environmental protection, requiring that waste emissions meet specified standards. Additionally, we install monitoring instruments with environmental protection functions in the storage tanks used for various types of media, in order to safeguard the environment and ensure stable production. The following is a detailed introduction to the ELL external level gauge, an environmentally friendly instrument of independent intellectual property rights that is world-first in its kind. It was independently developed and produced by Dinghua Electronics Co., Ltd., and is used by our company on liquid chlorine storage tanks. 2. Use of ELL-type level gauges in our company 2.1 Background of introducing the ELL-type external level gauge The original T5001A/B liquid chlorine storage tanks used double-flange differential pressure level gauges for level measurement. In 2001, the double-flange level gauge installed on the T5001A liquid chlorine storage tank malfunctioned; since there were no valves at the connection points between the level gauge and the equipment, it was not possible to remove the gauge from the equipment for on-site inspection or replacement. Under these circumstances, our company introduced external level gauges produced by Dinghua Electronics Co., Ltd. The biggest advantage of this type of gauge, as compared to any other level measuring device available domestically or internationally (except gamma-ray level gauges), is that it does not require any holes to be made in the container. The measuring head simply needs to be attached, welded, or stuck to the outer wall of the container, allowing for the measurement of the liquid level inside the container. Since its installation, this external level gauge has been in normal operation for 5 years, with very stable performance throughout that time. In 2005, due to harsh environmental conditions and corrosion by the medium being measured, liquid chlorine seeped out of the diaphragm of the level gauge in tank T5001B. If the leakage site expanded, the consequences would have been severe; the situation was extremely critical at that time. The process engineers immediately reported the issue to the control room, and with approval from the company’s management, we took action by reducing the system’s load, urgently replacing the liquid chlorine tank, replacing the gauge, and installing a ball valve in front of it. Although the system lost some efficiency due to reduced load, it prevented a safety accident caused by a chlorine liquid leak. As a result, the company urgently purchased another ELL external level gauge in the same month and installed it on this chlorine liquid storage tank. Both gauges are used together, and their readings show consistent trends; to date, the external level gauge has been functioning well (Figure 1 shows the operating curves of both gauges). Our company currently uses 7 ELL external level gauges, and the main reason for this is that using external level gauges on tanks containing hazardous substances is the most environmentally friendly and safe approach. Figure 1 shows that, as can be analyzed from the above figure, the trends of the two gauges are consistent, and the external level gauge has been functioning properly to date. 2. Principle of the external level gauge ELL: Unlike various level gauges used both domestically and internationally that detect the liquid level inside containers or their connected vessels, the ELL external level gauge utilizes harmless micro-vibration analysis to continuously determine the exact height of the liquid surface below it on the outside of the container wall, without any contact with the liquid or gas inside the container. Therefore, it is extremely safe and reliable, particularly convenient for installation and maintenance, and is an environmentally friendly instrument. It can be widely used for the continuous and accurate measurement of liquid levels in various containers. The external level gauge is an intelligent field transmitter-type instrument, with its explosion-proof main unit installed near the container being measured. The instrument’s sensing head is pressed tightly against the outer wall of the container, detecting tiny mechanical vibrations on the container wall, which are then converted into electrical signals and transmitted to the instrument’s main unit. Inside the host, the signal is converted to a digital form and sent to the CPU, where it is analyzed using Dinghua Company’s proprietary artificial intelligence algorithm to determine the liquid level height. The characteristics of the micro-mechanical vibration waveforms detected on the outside of the container wall are determined by the vibration properties of the liquid and those of the container. After being processed using Dinghua Company’s specialized algorithm, this vibration waveform allows for the determination of its liquid level characteristics. There is a relationship between the measured height of the liquid surface and the liquid temperature, as described by the following mathematical model: a – a coefficient specific to the liquid; t – the liquid temperature; – a characteristic value of the liquid level related to the vibration waveform. This instrument consists of two main parts: the measuring head and the main unit. The measuring head is attached directly to the outside of the container wall and is responsible for collecting information ； The host is installed next to the container under test and is responsible for analysis and computation. The measuring head is connected to the main unit via a cable; the main unit is equipped with a junction box (an explosion-proof junction box is used in flammable and explosive environments) that connects the signal and power cables coming from the level and temperature measuring heads, as well as those from the main unit and the control room. The host is powered by DC24V, and it provides an isolated standard output of 4–20mA. It can be used in conjunction with PLCs, regulators, recorders, and DCS systems. The instrument is configured using a dedicated magnetic pen; five magnetic buttons located on the transparent window of the instrument are used to input various parameters. 2.3 Performance Features of External Level Gauges The ELL (ELL-FI-SE and ELL-FI-AE models) series of external level gauges enable continuous and accurate measurement of the liquid level inside a tank from outside the tank, without any contact with the liquid or gas inside the tank, thus achieving true isolated measurement. 2.3.1 It features a wide measurement range of up to 30 meters, as well as high measurement accuracy of ±0.2% of the set full scale. 2.3.2 It can be used in the most demanding environments: it is capable of measuring liquids at any pressure. The liquid with the most severe measurable toxicity. It can measure the most corrosive liquids. Measurable requirements apply to liquids that must be sterile or of high purity. It can measure flammable, explosive, leaky, and polluting liquids. 2.3.3 Safety: When measuring liquids that are toxic, corrosive, under pressure, flammable, explosive, volatile, or prone to leakage, since both the measuring probe and the instrument are located outside the container, there is no contact with the liquids and gases inside the tank during installation, repair, or maintenance, making it very safe. Even when the instrument is damaged or under maintenance, there is absolutely no possibility of leakage. 2.3.4 Environmental protection: It neither leaks liquids nor gases, and does not pollute the environment at all; it is a green, environmentally friendly instrument. 2.3.5 Convenience and cost-effectiveness: No holes need to be made in the container during installation; no flanges or connecting pipes are required. There is no need for welding, and installation and adjustment can be carried out at any time without shutting down production. The measuring head simply needs to be fixed to the outer wall of the container using a magnetic holder or adhesive designed for this purpose, and after simple wiring, measurement can be performed. This makes installation and maintenance extremely convenient and cost-effective. It can also perform parameter calibration automatically and calculate the temperature compensation factor automatically; regardless of changes in the ambient temperature, the liquid temperature, or the composition of the liquid being measured, the instrument maintains high measurement accuracy at all times. The installation method is shown in the figure below: spherical tank, vertical tank. 2.3.6 Durable and reliable – The measuring head and instruments contain no mechanical moving parts, and they are tightly sealed to be isolated from the outside environment. It does not wear out or corrode, making it very durable and reliable. The maintenance workload is very small. 2.3.7 The precise ELL external level gauge is continuously automatically calibrated to ensure the highest measurement accuracy at all times. 2.4 Comparison of the performance of external-level gauges with other types of level gauges Sequence Number Gauge Type Main Features Disadvantages Installation Method Price 1 Ultrasonic Level Gauge Does not come into direct contact with the medium; only the gas phase is in contact. Relatively low accuracy; cannot be used for measuring pressure vessels or volatile media. Installed at the top of the equipment; requires a hole to be made in the equipment. Medium 2 Radio Frequency Admittance Level Gauge Can measure the interface between different fluids. Difficult to calibrate; the medium being measured cannot be viscous, as otherwise the probe may get clogged and affect measurement accuracy. Requires a hole at the top of the equipment. Medium 3 Magnetic Flip Level Gauge Intuitive operation and easy to install. Magnetic balls can get stuck, preventing remote indication. Must be connected to the equipment; requires a hole to be made. Low 4 Differential Pressure Level Gauge Widely used and easy to calibrate. Its performance is closely related to changes in the density of the medium; when measuring corrosive media, high requirements are placed on the material of the gauge’s diaphragm. Requires a hole to be made in the equipment. Medium-Low 5 Gamma Ray Level Gauge Measures non-contactly with the medium; high accuracy. Nuclear radiation can be harmful to humans; not suitable for large-diameter containers. No hole is required in the equipment. High 6 Float Level Gauge Comes into direct contact with the medium; strict sealing requirements are needed for the float. Cannot be used for measuring viscous media. Requires a hole at the top of the equipment. Low 7 External-Level Gauge Completely non-contact measurement; suitable for harsh environments. Easy to install and maintain. Depends on the viscosity of the medium