Calculation of the relief valve setting pressure
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As stated in the title, the specific issues are as follows: The safety valve of the boiler’s gas collection box operates at a pressure of 3.53 Mpa, with a set pressure of 3.67 Mpa. One of the bubble safety valves operates at a pressure of 4.0 Mpa, with a set pressure of 4.25 Mpa; the other one also operates at 4.0 Mpa, but its set pressure is 4.32 Mpa. The problem we’re facing is that the safety valve of the gas collection box trips prematurely, starting to activate at a pressure as low as 3.44 Mpa. Therefore, the client wants the set pressure of this safety valve to be increased to 3.92 Mpa. However, the design team is concerned that increasing this value might cause the bubble safety valves to trip first, as there is theoretically a resistance at the superheater outlet of around 0.4 Mpa that needs to be taken into account. I would like to ask the experts here: Is the reasoning provided by the technical team valid? Will increasing the set pressure indeed cause the bubble safety valves to activate first?
The drum safety valve will not activate prematurely; an outlet resistance of 0.4 is generally the discharge backpressure, and it has nothing to do with the activation of the safety valve!