Control of high liquid level in hydrocracking unit
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How to switch to manual control when the control valve fails?
When the high-level control valve for hydrocracking fails, it is usually switched to the backup control valve. If there is a problem with the backup control valve, it may be time to shut down operations.
In an emergency, first shut off the valves upstream and downstream of the control valve, and use a bypass line to regulate and maintain the flow. If it is caused by instrument air, the air shut-off valve is controlled by upstream and downstream valves, while the air open valve is controlled by a bypass line
The liquid levels of the hot and cold fractions in the hydrocracking unit are both controlled by two control valves (one of these routes leads to the hydraulic turbine, in cases where there is one). Under normal conditions, only one control valve is used for regulation; if valve A fails, it is sufficient to switch to valve B for control.