Boiler operation accident cases--4
Thread Content
An over-temperature and over-pressure accident occurred at the Shijingshan Thermal Power Plant. Incident details: At 00:29 on March 13, 1996, the main fuse of the DC control power supply in Unit 4 blew, resulting in the loss of DC operation power; Unit 4 tripped and the main steam valve of the turbine was closed. Due to the failure of the \"machine-to-furnace\" interlock to be activated, the fuel was not shut off automatically after the unit lost load. The maximum main steam pressure reaches 21.3 MPa, and the main steam temperature is 576°C, while the rated superheater outlet pressure is 13.7 MPa, the drum pressure is 15.88 MPa, and the main steam temperature is 540°C. Analysis of the accident cause: During the handling of the accident, the operators failed to promptly shut down the coal grinding system in accordance with the procedures, when the boiler pressure did not drop even after the pulse safety valve was manually activated (as the safety valve and PCV valve would not function). This led to severe over-temperature and over-pressure conditions in the boiler’s pressure-bearing components.
Accident summary: 1. If, during operation, the main steam outlet pressure of the boiler exceeds the pressure at which the safety valves activate (including the PCV valve), and the safety valves fail to operate while the manual PCV valve cannot be opened either, the boiler should be shut down manually immediately. 2. During unit operation, all safety valves for the main steam, reheat cold and hot sections of the boiler, as well as the Pcv valve, and all safety valves in the plant steam pipelines must be in operation. It is strictly prohibited to disengage these safety valves arbitrarily to prevent overpressure in the system. 3. Special safety technical measures should be established for the boiler’s overpressure hydrostatic testing and the calibration of the safety valves in operation, to prevent overpressure and overheating caused by too rapid pressure increase or loss of control over pressure and temperature.
Summary: 1. One must have a strong sense of responsibility； 2. The operations must be proficient ； 3. Regularly conduct drills to coordinate in case of accidents
Often, after an accident occurs, people tend to first consider whether there were any violations on the part of the individuals involved. However, from the perspective of intrinsic safety, it is hardware-based measures that should be implemented first to ensure safety, with human behavior serving only as a supplementary measure for safety protection. Additionally, when conducting risk analysis, we need to take into account errors resulting from human characteristics such as fatigue and lack of concentration.
I believe it is appropriate to think first of human violations. Of course, when thinking about human violations, it’s not just the violation or mistake of a single operator on site. It must be admitted that people will make mistakes, but there should also be a limit to it. For example, in this case, the chain protection is not activated, fails to function, or is even deactivated in violation of regulations ； The safety valve cannot function properly, etc. These are all engineering and technical measures taken to ensure the intrinsic safety of the system; failures in normal operation can also be caused by improper human behavior. Therefore, talent is the most important factor, even if we acknowledge human limitations.
Indeed, as you said, it is for this reason that we generally incorporate many safety devices in the design – such as door safety switches and interlock mechanisms – so that if these devices fail to function properly or stop working, the equipment cannot be started or will come to a halt. Of course, there are some safety devices like safety valves whose proper operation cannot be monitored; in such cases, we can get alerts when pressure levels become too high, and the system may even shut down automatically as part of the interlock design； Of course, if those two measures cannot be implemented in certain locations, we need to rely on management techniques to make up for it, such as checking the status of key valves before the equipment is put into use – which is the second level of verification that we are currently using
Our ultimate goal is to improve preventive measures through past accidents in order to prevent similar incidents from occurring again; this is also the best form of protection for people. Holding people accountable is merely a last resort.