[Weekly Accident Case Sharing] Accident Case 8: Instrument rain protection issue.

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I. Fault symptoms: On September 16, 2012, at 18:15, it started to rain heavily, and at 18:45, the natural gas flow rate in the ethanol dehydration heater B-1210 began to fluctuate. 19:02 The natural gas flow rate suddenly fluctuated from 480 Nm3 to 700 Nm3 ； The furnace pressure fluctuated between -100 Pa and around 600 Pa, while the interlock value was 800 Pa ； The furnace temperature also rose to 960°C instantly, with the interlock value set at 980°C. To ensure production safety and prevent an interlock shutdown of B-1210, the operator in control room 1200 quickly switched the waste gas from D-1210 to the vent system. The operator on site in control room 1200 promptly changed the control mode of the natural gas flow from automatic to manual and reduced the flow rate of natural gas. Due to fluctuations in natural gas flow, the temperature of process steam and the reactor temperature were affected; the ethanol feed rate for unit 1200# was slightly reduced, and the oxygen feed rate for unit 100# was decreased as well, with other units making corresponding adjustments. 22:15 Rainfall decreased, the operation of the furnace stabilized; the waste gas from D-1210 was directed to the furnace ； At 23:00, the natural gas flow was switched from manual control on-site to automatic control; once the furnace was operating stably, the feed rates of ethanol and oxygen were gradually increased to bring production close to full capacity. II. Cause analysis: 1. The surface of the furnace is not insulated. 2. Instrument components, etc., lack rain protection. 3. When it rains heavily, it may affect factors such as the temperature of the furnace, which in turn can impact the natural gas flow and cause significant fluctuations. III. Issues identified: 1. The project was not inspected and accepted in accordance with regulatory requirements. 2. The heating furnace has been in operation for over two years, and the process and instrumentation personnel have not carried out proper maintenance of the equipment. IV. Preventive measures: 1. During adverse weather conditions such as thunderstorms during the production process, it is necessary to strengthen monitoring of control parameters such as furnace temperature and natural gas flow rate ； In the event of significant fluctuations, the natural gas flow can be switched to manual control based on the actual situation, in order to prevent the furnace from shutting down due to interlocks. 2. During maintenance, install rain shelters for the furnace, and conduct inspections and repairs to ensure that all instruments in the plant are protected from rain, in order to prevent similar incidents from occurring. 3. Operators should strengthen their training in the tasks related to their positions, master the key aspects and precautions of their work, and enhance their knowledge of various emergency response plans. 4. In the event of an emergency, each shift supervisor should take decisive action, ensure smooth coordination between different work sections, and play a key role in directing production.