MisterDonut
Mechanical
- Dec 18, 2007
- 64
This subject was covered some time ago in this thread:
thread292-44595
However, I think it warrants additional discussion.
ASME BPVC Section 1, PG-61 FEEDWATER SUPPLY, PG61.1 (excerpt): “…each source of feeding shall be capable of supplying water to the boiler at a pressure of 3% higher than the highest setting of any pressure relief valve on the boiler proper.”
The final entry in the old thread, davefitz stated that the flow rate required at that overpressure condition need not be the full steaming rate of the boiler, but only some amount of water.
I think the language in the code is vague and could be interpreted as above. It states “…capable of supplying water to the boiler…” but not how much water.
When selecting a pump for boiler feed water service, the normal operating cases should be considered, as well as the code-required overpressure case. But what flow does the pump need to be capable of at this overpressure condition? Anything more than zero? The full steaming rate? The total capacities of the safety valves?
For boiler fueled by gas or oil, or heat recovery steam generators behind combustion turbines, the drum high pressure switch should trip the heat source and steam generation should ramp down. If this feature works, the pressure should not exceed the high pressure switch set point, so the safety valves and overpressure condition assume this switch did not function properly and the burner continues to fire while the safety valves are relieving steam. This leads to the conclusion that the feed pump should be capable of the safety valves capacity at 103% of set pressure.
If davefitz of others have some additional justification for a position on either end of this, I’m interested in seeing it. Also, please respond if you have actual experience with an interpretation of this part of the code from a code official.
thread292-44595
However, I think it warrants additional discussion.
ASME BPVC Section 1, PG-61 FEEDWATER SUPPLY, PG61.1 (excerpt): “…each source of feeding shall be capable of supplying water to the boiler at a pressure of 3% higher than the highest setting of any pressure relief valve on the boiler proper.”
The final entry in the old thread, davefitz stated that the flow rate required at that overpressure condition need not be the full steaming rate of the boiler, but only some amount of water.
I think the language in the code is vague and could be interpreted as above. It states “…capable of supplying water to the boiler…” but not how much water.
When selecting a pump for boiler feed water service, the normal operating cases should be considered, as well as the code-required overpressure case. But what flow does the pump need to be capable of at this overpressure condition? Anything more than zero? The full steaming rate? The total capacities of the safety valves?
For boiler fueled by gas or oil, or heat recovery steam generators behind combustion turbines, the drum high pressure switch should trip the heat source and steam generation should ramp down. If this feature works, the pressure should not exceed the high pressure switch set point, so the safety valves and overpressure condition assume this switch did not function properly and the burner continues to fire while the safety valves are relieving steam. This leads to the conclusion that the feed pump should be capable of the safety valves capacity at 103% of set pressure.
If davefitz of others have some additional justification for a position on either end of this, I’m interested in seeing it. Also, please respond if you have actual experience with an interpretation of this part of the code from a code official.
