Set pressure of safety valve for liquid ammonia spherical tank
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A liquid ammonia sphere tank usually has two safety valves. Do these two valves need to be one in use and one as a backup? Also, if both are in use, should there be a gradient in the set pressures of the safety valves? For example, one at 1.92 MPa and the other at 2.2 MPa. If both safety valves are in use and have the same set pressure, they will theoretically open simultaneously at the time of activation; this results in a very high instantaneous discharge rate. If a water scrubber is used afterward, compared to the situation where only one safety valve opens, the diameter of the tower as well as the amount of water used for spraying will increase significantly.
According to the provisions of GB/T150.1-2011 B.3.2.2: When multiple relief devices are installed on a vessel, the operating pressure of one of these relief devices shall not exceed the design pressure; the operating pressure of the other relief devices may be increased to 1.05 times the design pressure. Moreover, such relief devices shall be capable of preventing overpressure in the vessel from exceeding the greater of 16% of the design pressure or 30 kPa.
Generally, one is in use and one is as a backup. According to regulation 5.5.2 of petrochemical standards, the pressure can be increased appropriately
However, in the design developed by our institute and SEI, both safety valves are in use. And the set pressures are all the same.
However, in the design developed by our institute and SEI, both safety valves are in use. And the set pressures are all the same.
Pay attention to this topic: actually, a single safety valve is sufficient for achieving the required discharge volume, so why are two valves used? There seems to be no clear specifications regarding how to set the pressure for the safety valves. The air release process you mentioned is also an issue. .
Sinopec has issued provisional regulations on technical management, namely the \"Provisional Regulations on Safety Technical Management for Liquefied Hydrocarbon Spheres in Sinopec Group Company\". These regulations require that spheres should be equipped with at least 2 safety valves and 1 emergency vent line (a secondary line for the safety valves), with each of these elements being capable of ensuring safe discharge during accidents； Manual full-bore isolation valves should be installed before and after the safety valve; the diameter of these isolation valves should not be smaller than that of the safety valve’s inlet and outlet ports. They should remain in an open position at all times, and lead seals or locks should be applied to them ； The diameter of the gas emergency vent pipe should not be smaller than the inlet diameter of the safety valve. I think two safety valves should still be installed, and both of them should be in working condition. After all, the tank area is very dangerous; if one safety valve fails, another can provide protection. If the plant is equipped with an ammonia flare, it doesn’t matter if the setting pressures of the safety valves are the same; however, if there is no ammonia flare and absorption is to be carried out by a water scrubber, it is best to set the setting pressures of the two safety valves at different levels.