Why is the safety valve of a superheater set at a lower pressure than a safety valve of a boiler drum? (Central BOE-2021)

The safety valve of a superheater is set at a lower pressure than a safety valve of a boiler drum to protect the superheater tubes from overheating and damage.

When the pressure in the boiler system rises too high, the safety valve on the superheater will open first, allowing some of the steam to escape to the atmosphere. This will reduce the pressure in the superheater and prevent the tubes from overheating.

If the safety valve on the boiler drum were to open first, it would release all of the steam from the boiler, including the steam that is flowing through the superheater tubes. This could cause the tubes to dry out and overheat, which could lead to damage or rupture.

Here are some of the specific reasons why the safety valve of a superheater is set at a lower pressure than a safety valve of a boiler drum:

The superheater tubes are more susceptible to overheating than the boiler drum. The boiler drum is a large, thick-walled vessel that can withstand high pressures. The superheater tubes, on the other hand, are much thinner and are more likely to overheat if the pressure in the system gets too high.

The superheater tubes are more likely to be damaged if they dry out. The superheater tubes are cooled by the steam that flows through them. If the pressure in the system drops too low, the steam may not be able to flow through the tubes, and the tubes may dry out. This could cause the tubes to overheat and crack.

The superheater tubes are more expensive to repair or replacement. If the superheater tubes are damaged, it can be very expensive to repair or replace them. This is why it is important to protect the superheater tubes from overheating in the first place.

In addition to protecting the superheater tubes, setting the superheater safety valve at a lower pressure can also help to improve the efficiency of the boiler. By allowing some of the steam to escape to the atmosphere, the safety valve can help to reduce the back pressure on the boiler, which can allow the boiler to operate more efficiently.