Handling of Instrument Air Failure in Hydrogenation Unit

Stopping the instrument air can only be handled as an emergency shutdown. On one hand, it is not feasible to switch everything to bypass lines; on the other hand, the control valves in the hydrogenation section do not have bypass lines. Therefore, a shutdown is the only option. During this period, special attention must be paid to areas where high pressure might leak into low pressure areas

(1) The instrument air flow meter in the relevant area resets to zero or experiences a sudden sharp increase in flow, triggering audible and visual alarms indicating low or high flow. (2) The instrument air storage tank emits audible and visual alarms indicating low pressure； (3) If the reaction feed is suddenly interrupted, the flow rate at the outlet of the large-scale pump and the new hydrogen compressor drops to zero instantly, triggering a low-low flow alarm with audible and visual signals. (4) The gas flow rates of F-101 and F-201 suddenly dropped to zero, the furnace temperature declined rapidly, and the colors of all the quick-opening dampers turned green. (5) High score: When the outlet shut-off valve at the bottom of the high-pressure section connected to the low-pressure section is closed, the status color turns gray. (6) Operational fluctuations in parameters such as flow rate, temperature, pressure, and liquid level occur, triggering alarms. (7) The supply of fresh feed is completely interrupted; the output volume of diesel and naphtha from the unit, as well as the flow rate of tail oil to the catalytic unit, drop to zero, while the flow rate of tail oil to the storage area…

The device usually has a purification air tank, which under normal conditions can supply air for the device for about half an hour (this varies; ours can maintain supply for roughly that duration). The most important thing is to ensure that the device’s pressure is relieved as soon as air supply is interrupted. In particular, the pressure relief valve must be activated, and the safety valve must function properly – if the air pressure drops too low, the safety valve will no longer operate, even though there is still some air pressure present. The control valves in the high-pressure areas, although equipped with buffer air tanks, will not function properly when the pressure is low. Moreover, having all the air shut-off valves fully open can easily lead to pressure interference. Therefore, initiate pressure relief as soon as possible, use an electric valve to control the high liquid level in order to prevent pressure crossover; if pressure relief cannot be activated, then use the safety valve bypass, but be careful with the speed of pressure relief!

Large companies keep liquid nitrogen in stock to supply nitrogen temporarily for emergency use.

In some places, people don’t even know what nitrogen is