Selection of the superheater header vent valve for coal-fired boilers?
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1. May I ask everyone, for the pneumatic control valve used for venting the superheater header of coal-fired boilers (5.29 MPa, 495°C), should it be of the air-open type or air-close type? (It refers to whether the control valve should remain open or closed in the event of a failure in the instrument air supply.) △ In my opinion, a gas-actuated type should be used; the valve should stay open when there is a failure in the instrument air supply. This is because a failure in the instrument air supply usually means that the furnace needs to be shut down. If the vent valve of the collection tank cannot be opened at such times, and if there are problems with the safety valve of the collection tank as well, there is a risk of overpressure. 2. For the same issue, how should the vent valve for the drum be selected?
For the project I designed, which involves 4.4 MPaG superheated steam, the FC type pneumatic control valve is selected for reference.