During normal operation, every super-heater and re-heater tubes must have steam flow sufficient to prevent overheating. For re-heater tube protection, tangential fire boiler has burner tilting mechanism for maintain re-heater outlet temperature not exceed to 540C beside re-heater spray. Also for front & rear fire boiler has gas biasing damper at back pass area for control distribution of back pass gas flow to Primary Super-heater or re-heater area and finally propose to control re-heater outlet temperature to no exceed 540C beside spray.
During start-up, before there is steam flow through every tube, the combustion gas temperature entering the super-heater and re-heater must be control to limit super-heater and re-heater metal temperature to 482C for carbon steel and 538C for alloy steel. That temperature can be detection by insert thermo-probe at re-heater area.
Other re-heater protection for tangential fire boiler during start-up can be found by calculation ratio R/H and S/H should be higher than 80% and over firing process from different fuel flow and steam flow more than 13%.
More information about Boiler Tangential Firing, click below this...
http://idpowerstation.blogspot.com/2009/04/tangential-firing.html
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