1 Hydrogen treatment process and operation
The 200,000 t/a caustic soda project of Henan Shenma Chlor-Alkali Development Company was established in December 2008, and was put into trial operation in January 2010. The chlorine and hydrogen treatment process uses a large number of new processes and new equipment, and the degree of self-control is high, and the safety production guarantee capability is greatly improved.
The high temperature wet hydrogen (7085 ° C) from the electrolysis first enters the lower part of the hydrogen scrubber and is in countercurrent contact with the hydrogen scrubbing liquid from bottom to top. On the one hand, the hydrogen is cooled to about 45 ° C, and on the other hand, most of the moisture in the hydrogen and the entrained alkali mist are removed. The hydrogen from the top of the scrubber is pressurized into a hydrogen compressor to about 0.1 MPa and the temperature is raised to about 60 °C. The pressurized hydrogen is cooled to 1215 °C by I and II hydrogen coolers (cooled with circulating water and chilled water, respectively), and then the water mist entrained by the water mist trap is removed to prevent the conveying pipeline from being cold. Icing in the environment. The hydrogen after the water is removed from the distribution station to each user.
The company's hydrogen treatment system uses mature technology, advanced equipment and advanced DCS operation control system to provide multiple guarantees for safe production. However, there have been two accidents in the hydrogen treatment system since the start of the car. On the day of December 2009, when the system was driving the hydrogen compressor, when the 01ZV229 valve was opened, the system pressure suddenly increased rapidly, and the hydrogen positive water seal was instantaneously broken. The electrolyzed hydrogen-hydrogen pressure difference was reported to be chained and the whole line was stopped. At 5 o'clock in the morning of February 2010, the operator found that the liquid level of the vapor-liquid separator of the hydrogen compressor was low. When the hydrogen compressor unit was replenished, the liquid level of the gas-liquid separator quickly dropped from about 48% to about 6%. This causes the hydrogen compressor to lose pumping force, causing large fluctuations in system pressure.
The above two accidents caused the system to stop once, causing the system to fluctuate greatly, which seriously affected the safe and stable operation of the company.
2 problem analysis
2.1 Analysis of the whole line of parking accidents
2.1.1 Accident process
In the first accident, the operator replaced the hydrogen system with nitrogen as required during the pre-drive period. However, when the nitrogen charging operation is performed after the 01ZV229 valve to the hydrogen distribution station, the inlet and outlet of the hydrogen compressor are mistakenly closed, and the nitrogen gas enters the hydrogen treatment system from the hydrogen water washing tower, and then forms a closed state in the inlet section of the water washing tower to the hydrogen compressor. Environment, the ambient pressure rose to 400 kPa. When the 01ZV229 valve is opened again, the residual high-pressure nitrogen gas is flushed out from the positive pressure water seal; the other passes through the hydrogen manifold to the electrolysis process hydrogen self-control valve 01PCV226, causing the electrolysis hydrogen-hydrogen pressure difference to be reported as high.
2.1.2 Analysis of the cause of the accident
There are two main reasons for the accident:
(1) The operator does not fully understand the hydrogen treatment chain setting.
The rectification stops, the turbine stops completely, and the hydrogen compressor full stop chain is a first-class chain. They are mutually conditional. As long as one chain reaches the parking condition, the other two parking chains will automatically start. After the three chains are activated, it will cause the action of the self-control valve related to the chlorination treatment. First-level chain start. Among them, 01PDV218 is the accident chlorine valve, and 01ZV219 is the chlorine gas main pipe shut-off valve.
(2) The operator's sense of responsibility is not strong, and the pressure rise before the hydrogen washing tower is not found in time. The pressure before the hydrogen scrubbing tower shows two types of on-site and remote transmission. The operator did not check whether the system was unblocked during nitrogen replacement, and did not check whether the hydrogen system pressure was normal when driving again.
2.2
Hydrogen compressor loss pumping accident analysis The second accident is that when the liquid level of hydrogen compressor B drops from 50% to 48%, the operator opens the water valve to add water to the site, but the liquid level of the gas-liquid separator quickly drops to 6%. As a result, the hydrogen compressor loses its pumping force, and the hydrogen treatment pressure fluctuates greatly. After the operator closes the working fluid circulation pump, the water is normally added. After adding water to the normal level, the hydrogen compressor pumping force returns to normal.
The outlet pressure of the circulating fluid working pump was 0.4 MPa, and the pure water pressure was only 0.35 MPa. After the operator opens the water adding valve, the working fluid in the gas-liquid separator is pressed back into the pure water adding water pipe, causing the hydrogen pump liquid level to drop rapidly. The design defect of the water valve position is the main cause of the accident. The operator did not check the pure water pressure, which is also one of the important reasons for the accident. The gas-liquid separator liquid level gauge floats and the false liquid level appears, which is the accident. Incentives.
3 Improvement measures
3.1 Strengthen employee training
(1) Strengthen the responsibility education of employees, improve the reward and punishment system, and enable the employees to operate in a serious and responsible manner.
(2) Strengthen employee technical training. Improve the theory of operation and technical level through measures such as weekly questions, monthly exams, and accident case analysis to avoid mistakes. Improve the actual operation level of employees through on-site questions and technical competitions.
3.2 Process improvement
Due to the design defect of the water valve position. When the high-purity water pressure is slightly lower than the pump outlet pressure, high-purity water backflow occurs, jeopardizing safe production. Therefore, the water supply valve is changed to the circulation liquid pump inlet optimization. After optimization, even if the high purity water pressure is lower than 0.4 MPa (not lower than the gas-liquid separator pressure), there is no backflow of the working fluid. In addition, when adding water to the hydrogen pump, the pure water pressure process index is strictly controlled ≥0.5 MPa. After strengthening staff training and technological transformation, similar accidents did not occur again, and the system was safe and stable.
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