Emergency response for the equipment: Judgment and practical procedures for DCS system power outages

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As the \"central nervous system\" for the operation of the plant, the DCS system will lead to a loss of monitoring capabilities and uncontrolled operation of control valves in the event of a power outage. If not handled promptly and properly, this can easily result in fluctuations in material levels, excessive temperatures and pressures in the equipment, and even unplanned shutdowns. In line with the actual operational conditions on site and the requirements for emergency management, the phenomena associated with DCS power outages, the methods for identifying their causes, and the key points for hierarchical handling are outlined below, to facilitate prompt responses and standardized operations by the personnel on duty. I. Characteristics of the accident phenomenon: When power is lost to the instruments in the device, the UPS uninterruptible power supply allows the DCS system to continue operating for about 30 minutes. Once this time limit is reached or if the UPS fails, the following typical phenomena occur: 1. The DCS system becomes completely non-functional: all process parameter readings return to zero, historical data recording stops, and all control signals are interrupted ； 2. Loss of control of on-site control valves: air-operated shut-off valves open fully while air-operated open valves close fully, resulting in sudden changes in the flow rate of the medium and thus significant fluctuations in system temperature and pressure ； 3. Local instruments are functioning properly: Local display instruments such as on-site pressure gauges, cumulative flow meters, pump current meters, glass plate level gauges, and float level gauges show no abnormalities in their readings, and can thus serve as a key reference for emergency operations. II. Causes and Confirmation of the Incident: Main causes include failures in the external power supply system, hardware defects in the DCS workstations, and abnormalities in the instrument control station system. Confirmation method: If the DCS operation station goes black, the main unit loses power, and all operation interfaces become unresponsive, it can be determined that there has been a power failure in the DCS system. III. Hierarchical Emergency Response (1) Local instrument power failure: The operator shall immediately switch the affected instrument circuits to manual mode ； By relying on the indications from the on-site instruments, and taking into account key parameters such as temperature, pressure, and liquid level in other parts of the unit, fine adjustments can be made using the on-site hand valves to ensure the unit operates at a low load in a stable manner, thereby preventing significant deviations in these parameters. (2) Sudden power outage: During the power outage, the operator should quickly switch the control circuit to manual mode to prevent automatic fluctuations in the system from causing cascading abnormalities ； After power supply is restored, conduct a thorough inspection of all DCS measurement points, control valves, and interlock circuits to check for any issues such as faulty instruments or stuck valve positions ； Contact the electrical and instrumentation personnel simultaneously to investigate the cause; once it is confirmed that the system is functioning properly, automatic control shall be gradually restored. Retreat mode: The device operates at low load to maintain production. If the parameters are controllable and the system is stable at low load, gradually increase the load to return to normal operation ； If operation cannot be maintained even at low load, follow the procedure for prolonged instrument power outage. (3) In the event of a prolonged power outage of the instruments, report to the dispatch team immediately; stop the feed of crude oil to the unit and initiate an emergency shutdown ； The team coordinates the personnel responsible for internal and external operations, and implements the emergency shutdown plan step by step to ensure that the equipment and pipelines remain safe and under control. Retreat mode: The entire facility is shut down. If the power supply and DCS system cannot be restored in the short term, carry out oil drainage and line cleaning operations in accordance with the plant shutdown procedures ； If the system meets the recovery conditions, crude oil is reintroduced to establish an open-loop circulation; steps such as constant-temperature dehydration are carried out according to the startup plan, thereby gradually restoring normal production. IV. Key points for on-site handling 1. After a power outage, prioritize using the local instruments on site as a basis for operations; blind adjustments are strictly prohibited ； 2. After the control valve loses control, closely monitor the temperature and pressure of key equipment to prevent risks such as overheating, overpressure, and material leakage ； 3. Implement hierarchical handling and gradual withdrawal; prioritize safety first and then maintain production stability, to prevent the accident from expanding due to panicked actions ； 4. Throughout the accident handling process, maintain timely communication with the dispatching and electrical and instrumentation teams to ensure information sharing and coordinated response.