The Relationship Between Boiler Feedwater and Furnace Gas Exit Temperatures
Plant: 350 MW PF-fired Power Plant with HP&LP Turbine Bypass Systems
Query: Boiler Feedwater and Furnace Gas Exit Temperatures
Explanation of Query: Over the years, the issue of minimising plant start-up times and costs has often arisen, especially in the context of large PF-fired power plants starting from cold conditions. The initial boiler warming period is usually the most contentious, when firing is limited to the least number of oil burners (and the lowest-level burners), in order to manage boiler drum and steam pipe warming and differential temperatures, usually over many hours.
While the availability of steam bypass systems has provided major benefits, the necessary focus on managing boiler drum temperature rate and differential temperatures has often become the sole focus, at the expense of furnace flue gas exit temperature. Consequently, further delays have occurred with progressing to the next stage of a start-up, where the first pulveriser and PF burners are introduced.
It is at this time that it is realised that primary air temperature is inadequate, as a consequence of low furnace gas exit temperature, and the only apparent solution is to introduce more (and higher-level), oil burners. This is clearly not the only or the best option, as temperature rates and metal differentials will certainly be exacerbated, at potential risk to plant condition and life.
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