Link to document:
Status
Electronic Resource
Call number
Publication
BR 1085; Report; April 1977.
Language
Library's review
ABSTRACT:
For high reliability all high pressure drum type boilers must avoid DNB under all operating conditions with a sufficient margin of reserve for upset transients. DNB is a localized phenomenon caused by a critical combination of operation parameters which include pressure, heat flux, steam
The overall circulation ratio often used in the power industry to compare and evaluate the safety of circulation systems is not a pertinent criterion, since it lumps together the flows of the most exposed circuits with those of low duty. Even with high circulation ratios, drum type boilers with smooth tubes may have circuits that operate during upsets close to the combinations of parameters that produce DNB.
The B&W design with ribbed tubes, however, provides high natural circulation flow rates (even at pressures approaching the critical pressure) that maintain significant margins of safety during adverse upsets. Thus, with the use of ribbed tubes, it is possible to meet utility requirements for natural circulation boilers of any size for 2900 psig drum operating pressure, that have high availability and no auxiliary power demand.
For high reliability all high pressure drum type boilers must avoid DNB under all operating conditions with a sufficient margin of reserve for upset transients. DNB is a localized phenomenon caused by a critical combination of operation parameters which include pressure, heat flux, steam
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quality, and mass velocity.The overall circulation ratio often used in the power industry to compare and evaluate the safety of circulation systems is not a pertinent criterion, since it lumps together the flows of the most exposed circuits with those of low duty. Even with high circulation ratios, drum type boilers with smooth tubes may have circuits that operate during upsets close to the combinations of parameters that produce DNB.
The B&W design with ribbed tubes, however, provides high natural circulation flow rates (even at pressures approaching the critical pressure) that maintain significant margins of safety during adverse upsets. Thus, with the use of ribbed tubes, it is possible to meet utility requirements for natural circulation boilers of any size for 2900 psig drum operating pressure, that have high availability and no auxiliary power demand.
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