ForumRe: high excess air
From: Jim Watts [764]
Date: Sunday, July 25, 2010
Time: 1:38:05 AM
Remote Name: 124.181.9.163
Comments
With fuel rate held constant and air flow increased the losses to stack will increase due to increased flow.This means less steam will be generated so pressure will fall.
The increased flow of combustion gas with a reduction in steam flow means convective performance will improve so steam temperature will rise.
The air heater will see increased colling from the air but also increased heating from the fuel gas flow so will not change much in temperature
Superheat temperature in radiant tubes will fall because the radiant input is basically unchanged with load so the temperature is high with low steam flow and low with high steam flow.
Designers try to balance the ratio of radiant surfaces to convective surfaces so the temperature stays about the same with load.
ie radiant loses as convective increases.
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