“\"Redundancy technology\" ensures the reliable operation of the interlock protection system

Thread Content

“\"Redundancy technology\" ensures the reliable operation of interlock protection systems. An interlock protection system is a system that, in accordance with the process requirements and equipment specifications of a production facility, activates the corresponding actuators, either by automatically starting up a backup system or by enabling a safe shutdown. The interlock protection system must not only ensure the proper start-up, shutdown, and operation of production units and equipment, but also guarantee safe production in the event of abnormalities in the process by following established procedures, enabling emergency operations, safe shutdowns, emergency stops, or automatic activation of backup equipment. It is evident that ensuring the reliable operation of the interlock protection system is crucial for achieving normal production of the manufacturing facilities and the proper functioning of the equipment. By adopting \"redundancy technology\", that is, improving the existing control schemes in DCS or ESD systems, it is possible to significantly enhance the reliable operation of the interlock protection system without adding any additional equipment or investment. Large-scale units are critical equipment in process production facilities, serving as the heart of such facilities. The operating condition of large-scale units directly affects the normal production of process equipment as well as the entire factory. Therefore, ensuring the safe operation of large-scale units is of great significance not only for the units themselves but also for the production process of the entire industrial plant; moreover, whether such units can operate safely and stably directly affects the economic efficiency of the factory. Therefore, it is highly necessary to strengthen the safety protection measures for large-scale units and improve the reliability of their interlock protection systems. In an interlock protection system, the interlock protection devices are required to be installed separately in principle, and the sensing elements, actuators, and logic processing units should also be set up separately. Therefore, in the design of existing interlock protection systems, when monitoring a certain important process parameter, an interlock point is typically established to be part of the interlock protection circuit; in addition, another detection point is set up for indicating, controlling, and triggering alarms regarding that process parameter. The two loops monitor the same process parameter, but they are configured separately and have no connection to each other; this is mainly because the control interlock system is composed of separate individual instruments. Should the interlock protection system malfunction due to reasons such as aging of the instrument components in the interlock circuits, wiring faults, poor contacts, malfunctioning components, grounding of electrical circuits during rainy weather, human error, or other accidents, it will have a serious impact on the normal operation of production facilities and equipment, as well as causing unnecessary economic losses. Redundancy technology is a technique that has evolved alongside the development of computers. It generally involves creating two redundant circuits to perform a particular function, with the functionality remaining unchanged: while one circuit is operating normally, another identical circuit serves as a backup. Once a normal circuit fails, another circuit can take over immediately to carry out all the tasks, without causing any impact on the control system. Following this principle, the interlock circuit and the measurement and control circuit for monitoring a specific process parameter in practice are treated as two circuits that serve as backups for each other. They are no longer independent of one another as in the originally designed control interlock system; instead, the two circuits operate as backups for one another – this is known as \"redundancy technology\". In recent years, as a result of technological upgrades, DCS or ESD systems have been widely adopted to replace the control interlock systems that previously relied on individual gauge units. This has made it possible and feasible to use \"redundancy technology\" to improve existing control schemes, thereby enhancing the reliability of the interlock protection systems. In DCS or ESD systems, the changes in a specific process parameter at the two monitored points are first indicated and alarmed separately, which facilitates accurate identification of the faulty circuit in case of a problem. The measurement value from one of these circuits is then used as the control value for continuous regulation. Next, the monitoring values of the two circuits are processed for over-limit alarm detection separately; the over-limit alarm output signals from these two circuits are processed using a \"two-of-two\" logical OR gate, and then sent as interlock signals to the interlock circuit, with the signal being \"1\" under normal conditions. Only when the monitoring values of both circuits reach the pre-set interlock alarm values can the interlock circuit be activated, causing the process units and equipment to shut down as required. In the control interlock circuit of the original design, the control system architecture from the era of discrete unit instruments was retained; the measurement and control circuitry were completely separated from the interlock monitoring circuitry, failing to make full use of the powerful internal programming control capabilities available in DCS or ESD systems. In control interlock circuits that employ \"redundancy technology\", the measurement and control circuit as well as the interlock monitoring circuit are interconnected, with the signals fed into the interlock logic circuit being redundant to each other. Only when the measurement signals from both circuits meet the conditions set for interlock activation can the interlock logic circuit satisfy the conditions for interlock action. Thus, incidents in which the interlock system malfunctions due to factors such as aging of the instrument components in the interlock circuits, circuit failures, poor contacts, ineffective operation, grounding of electrical circuits during rainy weather, human error, and other accidents, leading to measurement values that meet the conditions for interlock activation and resulting in unplanned shutdowns of large-scale units and critical equipment, will no longer occur. It effectively ensures the safe, stable, and efficient operation of the production equipment. Our factory is equipped with more than a dozen various types of important large-scale units and equipment, all of which are key devices for the respective production facilities. Interlock malfunctions occur due to factors such as the aging of instrument components in the interlock circuits, wiring faults, poor contacts, malfunctioning devices, grounding of electrical circuits during rainy weather, human error, and other accidents. These malfunctions cause large-scale units and important equipment to stop operating, resulting in unplanned shutdowns of production facilities. Such incidents happen multiple times each year, posing a serious threat to safe production and significantly affecting the steady operation and economic efficiency of our plant’s various production units. With the large-scale technological upgrades in recent years, many of the original control interlock systems have been replaced by DCS or ESD control systems, and critical interlock points have been provided with redundancy in accordance with the \"redundancy technology\" control approach. After the renovation, excellent results were achieved over several years of operation. The main lessons learned are as follows: 1. Due to factors such as aging of instrument components in the interlock circuits, circuit failures, poor contacts, malfunctioning components, grounding of electrical circuits during rainy weather, human error, and other accidents, the frequency of such issues remained roughly the same as before; however, no unplanned shutdowns occurred. 2. The interlocking system can be safely maintained online. 3. In principle, bypass switches at interlocking points are no longer required. 4. The design of the interlocking circuit is simplified, facilitating fault analysis and handling. 5. It provides sufficient time to handle faults, reducing the likelihood of errors. 6. The DCS or ESD system provides clear indication of faults, facilitating rapid troubleshooting. Based on the above analysis, it can be concluded that the use of “redundancy technology” can greatly improve the reliability of interlock protection systems. The control interlock protection systems that were previously made up of separate unit instruments had high failure rates, poor reliability, and limited functions, making it difficult to apply \"redundancy technology\". With the use of DCS or ESD systems today, not only is reliability higher, but it is also easier to implement various functions, as this can be achieved through software programming alone. By employing \"redundancy techniques\" to ensure the reliability of the interlock protection system, it is theoretically possible to largely avoid unplanned shutdowns of production units and equipment caused by abnormal operation of the interlock protection system due to factors such as aging of the instrumentation components in the interlock circuits, wiring faults, poor contacts, malfunctioning components, grounding of electrical circuits during rainy weather, human error, and other accidents. Therefore, for the interlock protection systems of important production units and equipment, after using DCS or ESD systems, it is very easy to adopt \"redundancy technology\" to improve the reliability of these interlock protection systems, thereby ensuring the long-term, safe, and stable operation of the production units and equipment; this approach holds great potential for widespread adoption.