Boiler Feed Water Pressure Safety Valve

Is this on a line fed by positive displacement pumps or is some other type in use? Please describe the type of pump.

A piping diagram might also help in showing what valves might be accidentally closed.

If the valve relieves from the economiser to the steam drum, rather than to atmosphere, be aware of the lesser pressure difference when sizing the valve.

ASME Section I contains rules about sizing and selecting safety valves based on boiler performance and heating areas.

These valves are supplied by the boiler vendor........on a new installation

Is this a used boiler that was purchased without any safety valves ?

Please understand that this response is based on very limited information and big assumptions. But it appears the whole system needs a thorough review.

I assume the system BFW flow is: pump → economizer → steam drum

Normally, the econ. design pressure (DP) would be ≥ the steam drum DP. If the steam drum PSV is set at 54 barg and the economizer is protected by a PSV set at 52 barg (its DP), then under a boiler relieving event the boiler will be starved of make-up because the BFW pressure will be limited to 52 barg by the economizer PSV. This would create a potential boiler explosion hazard.

The working pressure of the boiler is stated as 48.3barg.

Thanks for the replies

Ok here's a rough flow diagram to better explain the question.

I believe the PRV (highlighted) is not required as the system is protected by the 2 PRV's on the steam drum, unless the screwdown check valve on the steam drum is closed.

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It looks as though the PRV protects Gen1 and Gen2 in case the downstream valve is closed.

"A picture is worth a thousand words" _{- ancient proverb.}

Now that the PFD is to hand, all becomes clear.

• The PSV in the water feed line is there to protect the two economiser units from overpressure, however it would be better positioned upstream of them, so that any blockage caused by unwanted heat exchange surface fouling in these vessels' coils doesn't cause a pressure rise upstream over that which the valve is intended to protect.
• The lifting pressure should be the lower of the two vessels' coils' maximum operating pressures.
• The flowrate through the valve at the lifting pressure is equal to that shown on the pump's performance curve at that pressure.

Now, go size the valve!

Any suggestion for the potential problem brought up in #4 ↑?

If the drum PSVs are set to 48barg and the PSV for the feedwater supply is set higher, then the problem described does not arise.

The boiler can be managed so that, in the event of a low water level persisting after a relieving event, a normal shutdown can be invoked. A feedwater pump trip might also invoke normal shutdown if no standby pump is available.

If the operating pressure is 48.3, the drum PSV setting is probably at least 53 and maybe 54. I don't want to get into a back-and-forth. OP should get concurrence with his organization and code insurer.

Agreed. Discussion and review with the Engineer/Surveyor for the company responsible for burst indemnity insurance cover on the boiler is an important and very urgent step for the original poster to make. After all, if it explodes then this is the company that picks up the tab, not the anonymous CR4 reader.

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