[Haichuan Instrument Control Accident Case] Irregular grounding caused huge losses in the shutdown of the coal gasification unit and downstream purified ammonia and urea
Thread Content
"In a chemical plant in Hubei, due to irregular grounding, the entire coal gasification unit was shut down for 2 days, and the downstream purification, ammonia synthesis, and urea units were shut down accordingly, resulting in huge losses. " (1) Overview of the accident device The coal gasification device of Hubei Fertilizer Branch was newly built and put into production in 2006. The device adopts Shell pulverized coal gasification technology and uses a membrane-type water-cooled wall gasifier with four coal burners and a specially designed water-tube syngas cooler. The feed can range from anthracite to lignite, which is converted into process gas containing mainly carbon monoxide and hydrogen for final urea production. The DCS control system adopts HONEYWELL's EPKS C200 system, and the SIS control system is HONEYWELL's FSC system. (2) Overview of the accident unit The process unit where the accident occurred is the gasification island unit of the gasification device. The coal burner (A1301A/B/C/D) is fed by a mixed gas of suspended coal powder (coal powder in nitrogen), oxygen and steam. The operating temperature of the pulverized coal combustion chamber and coal burner is maintained at about 200-220°C to avoid leakage points or high temperature erosion problems. This is achieved through a circulating coal burner cooling water system whose operating pressure is slightly higher than the gasifier pressure. The instrument accident occurred on the circulating cooling water vortex flowmeter 13FT0205A/B of the 2# coal burner A1301B. This point is the second-choice interlocking point. When the indications of the two transmitters are lower than the interlocking value, it will cause the entire gasification device to stop.
2. Accident and handling process (1) Operation conditions before the accident Before the accident, the process equipment was running smoothly, with no abnormal conditions or alarms. There is no abnormal fluctuation in the 13FT0205A/B indication. (2) Detailed description of the accident phenomenon: At 22:15 on July 21, 2008, 13FT0205A/B fluctuated simultaneously and exceeded the flow low interlock value, causing the ESD large interlock to operate and the gasification device to stop. (3) Scope of Impact The entire coal gasification unit will be shut down for 2 days, and the downstream purification, ammonia synthesis, and urea units will be shut down accordingly. (4) After the accident occurred in the instrument and system processing process, the instrument personnel conducted a detailed inspection of the ESD system and the on-site flow transmitter. (1) The master control ESD system did not report any error diagnosis, and it was a normal interlock triggering action. (2) The instrumentation personnel inspected the two vortex flowmeters on site and found that the protective grounding wire was not grounded according to the specifications. They followed the grounding wire of the transmitter and found that the other end of the grounding wire was only placed on the wire trough and was not connected to the dedicated grounding point of the instrument. ； It was also found that when the transmitter indication fluctuated, there was electric welding construction nearby, and the electric welding ground wire was placed on the circulating water pipe. (3) By querying the DCS trend record and comparing it with the oral construction process of the welding construction personnel, it was found that the meter fluctuated synchronously during the welding operation. From this, it can be determined that the flow indication fluctuation was caused by the welding construction. (4) After the instrument personnel asked them to change the connection point of the welding ground wire, they contacted the electrical department to provide a grounding point nearby, and rectified the instrument grounding of the eight flow transmitters with four burners to ensure true grounding. (5) After driving again, the indications of the two flow transmitters are stable. (5) The accident caused the parking due to problems left over from the construction. (6) Accident handling evaluation During the accident handling process, the instrument personnel analyzed the problem with clear and accurate ideas. After finding the cause, the rectification plan was strictly implemented in accordance with relevant specifications, which improved the stability of the transmitter and provided a strong guarantee for stable driving again.
3. Analysis of the cause of the accident (1) Brief evaluation of the reliability of the accident unit before the accident 13FT0205A/B The two meters are Rosemount’s 8800 series vortex flowmeters. They have high measurement accuracy and strong stability, and are widely used in key devices in chemical companies. (2) Analysis of direct causes. Both flow transmitters are vortex flow meters and have grounding requirements. However, the protective grounding performed by the construction unit during the initial construction was not standardized and did not really play a grounding role, which reduced the anti-interference ability of the meter. ； When the welding personnel were working nearby, they randomly connected the welding ground wire to the circulating water pipeline. The high-current interference signal caused the flow meter to fluctuate, causing the interlock action and the entire device to stop.
4. Preventive measures (1) Experience and lessons (1) When installing a flow meter, the installation is not grounded according to the instrument grounding specifications, leaving hidden dangers that are not easily discovered. No such problems were found during the three inspections and four determinations during project acceptance. (2) The instrument personnel did not discover hidden dangers in time and take care of them during inspections. (3) The personnel of the external construction unit were careless during construction and the welding ground wires were connected randomly. (2) Preventive measures (1) Instrument personnel will further strengthen inspections so that hidden dangers can be killed in the bud in a timely manner and ensure the long-term operation of the device. (2) Strengthen employees’ appearance standards * , training, improve the technical level of instrument maintenance and repair personnel, and ensure the quality of instrument maintenance and repair. (3) Inform the external construction unit through relevant departments during construction, especially during welding, and contact instrumentation and process technicians to confirm whether relevant interlocks need to be removed. (4) The enterprise management department develops corresponding systems to further clarify the specification requirements for grounding points in electric welding operations. ； When electric welding operations are required to be carried out near the gasifier, it must be approved by the instrument workshop and the process workshop.
Twenty-eight precautions for grounding installation and maintenance https://bbs.hcbbs.com/thread-3355741-1-1.html (Source: Huahaichuanliu-Haichuan Chemical Forum Network)