Knowledge || Level measurement in the tank farm SIS system

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A major hazard source refers to a unit that permanently or temporarily produces, transports, uses, or stores hazardous substances in quantities equal to or exceeding the critical level. A unit refers to one set of production facilities or sites, or several sets of such facilities or sites that belong to the same production and operation entity and are within a distance of less than 500 meters from each other. According to GB 18218-2009 \"Identification of Major Hazard Sources for Hazardous Chemicals\", the basis for identifying major hazard sources is the dangeriness of the substances and their quantities. Why is it necessary to install an SIS system in tank areas? The complexity of chemical production, along with the relatively high concentration of hazardous chemicals in the storage areas of chemical plants, means that these chemicals can easily exceed the critical values specified in the \"Identification of Major Hazard Sources for Hazardous Chemicals,\" thus becoming major hazard sources that require thorough risk analysis and close safety monitoring. Most tank farms associated with current chemical plants use distributed control systems (DCS) for operation control and interlocking. The DCS system features a wide range of comprehensive control functions, ease of operation, scalability, and convenient maintenance, but it is not suitable for safety control. For chemical plant tank areas, operations must be carried out more frequently than in ordinary oil depots, resulting in a higher probability of errors. At this point, it is highly necessary to adopt a Safety Instrumented System (SIS) that offers higher safety levels, strong fault tolerance, self-diagnosis capabilities, and Sequence of Events (SOE) recording functions. On November 13, 2014, the **General Administration of Work Safety issued the document titled \"Guiding Opinions of the General Administration of Work Safety on Strengthening the Management of Chemical Process Safety Instrumentation Systems\", Document No. An Jian Zong Guan San [2014] 116. The document requires that the Chemical Process Safety Instrumented System (SIS) include safety interlock systems, emergency shutdown systems, as well as detection and protection systems for toxic and harmful gases, flammable gases, and fires; a separate safety instrumented system (SIS) must be provided for these purposes. What equipment is required for the SIS system in the tank farm? The tank farm SIS system, as part of the plant’s overall SIS system, provides essential safety interlock protections, an emergency shutdown system, and interlock protections for critical equipment within the tank farm, in accordance with the characteristics of the facilities. The selection of instruments for general storage tanks should take into account factors such as economic Rationality, technical maturity, a wide range of options available, ease of maintenance and calibration, as well as the possibility of maintenance-free operation or excellent after-sales service. It is considered comprehensively in light of the investment in medium characteristic projects, the automation level of the entire project, and other factors. Taking a SIL2-rated chemical raw material storage tank as an example, for a single tank, the following equipment is required: 2 level gauges + 1 level switch + 1 thermistor + 1 pressure transmitter + 1 pressure gauge. When either the level gauge or the level switch of the tank indicates a level that is higher than the set value, the SIS system activates interlocks to close the tank’s isolation valve, thereby preventing the tank’s liquid level from rising further and avoiding the risk of overflow. Among them, the level gauge and the level switch play a key role. What are the challenges in level measurement for the SIS system in the tank farm? 1. SIS systems are often part of technical renovation projects; storage tanks lack process connections, and the available measuring instruments have limitations ； 2. Traditional level measurement instruments require drilling and welding, resulting in high construction costs and poor cost-effectiveness ； 3. Compared to conventional control instruments, the tank farm SIS system requires higher reliability from the measuring instruments ； 4. The SIS system requires that instrumentation equipment possess a SIL certificate issued by a qualified certification body; the higher the SIL level, the greater the safety performance of the product ； What are the advantages of external level gauges in SIS applications? In 1990, Professor Wang Dinghua, the founder of Dinghua Electronics, invented the ELL sonar-based external liquid level gauge, which enables the accurate measurement of the liquid level from outside the container, achieving true isolated measurement – a first in the world. The ELL sonar-type external level gauge is a device that uses the principle of sonar ranging and \"micro-vibration analysis\" technology to measure the liquid level from outside the container. It does not require any openings in the tank wall, no flanges are needed, and it has no contact with the liquids or gases inside the tank. This allows for online installation and maintenance; it is therefore a completely non-contact instrument. The safe ELL external level gauge is extremely safe when measuring toxic, corrosive, pressurized, flammable, explosive, volatile, or leaky liquids; it does not use valves, connecting pipes, or fittings, has no leakage points, and does not come into contact with the liquids and gases inside the tank. Even when the instrument is damaged or under maintenance, there is absolutely no possibility of leakage, poisoning, or explosion. Convenient and cost-effective: The ELL external level gauge can be installed and maintained without the need for welding or tank cleaning, without disrupting production. It requires no maintenance, reducing both construction and maintenance costs, thus offering high economic efficiency. Stable and reliable: The ELL external level gauge has demonstrated high stability, thanks to its operation in hundreds of different conditions and years of field experience with tens of thousands of units. The high-precision ELL external level gauge utilizes the automatic calibration function developed by Dinghua to enable real-time, automatic calibration of the instrument, with a precision of up to ±1mm. The ELL-FI-CE type sonar-based external level gauge: Dinghua Electronics attaches great importance to changes in customer needs; in response to the requirements for level measurement in tank farm SIS systems, it has developed the ELL-FI-CE type sonar-based external level gauge. 1 Higher reliability ； Major upgrades to the motherboard hardware and algorithms; gain compensation functionality has been added, giving the instrument greater resistance to liquid intrusion impacts and enhancing its stability and reliability ； 2 has higher precision ； Measures and calibrates with hardware-software isolation for higher accuracy ； Sensor hardware upgrade ； Software filtering technology has been upgraded, reducing blind spots ； 3 Operation monitoring is simpler ； It features an automatic frequency scanning function, making debugging simpler; it has an LED display for an intuitive interface, and it shows the instrument’s operating status and health information, thereby enhancing the user-friendliness. 4SIL3 certification, the first in China ； As the first domestic manufacturer in the field of external level gauges to obtain SIL3 certification, given the extreme hazards associated with major petrochemical hazards and the potential for secondary damages, the use of Safety Instrumented Systems (SIS) is an inevitable trend. CE-rated sonar-based external level gauges with SIL3 certification will undoubtedly become the preferred choice for measuring tanks in chemical plants that store large quantities of flammable, explosive, combustible, or toxic substances, as these tanks represent major hazards