ABSTRACT
The objective of this study was to optimize sootblower performance in order to prevent slagging incidents at New England Power's Brayton Point Unit #3. Continuous monitoring of the furnace exit gas temperature (FEGT) provided a direct mesure of boiler performance. Operating the sootblowers to maintain constant FEGT reduced sootblowing rate, minimized reheat spray flows, and reduced NOx emissions.
SUMMARY New England Power's (NEP) Brayton Point Unit #3 falls into a class of boilers built in the late 1960's when furnace heat release rates were maximized. High furnace temperatures and compact furnace dimensions make Brayton Point #3 and other boilers of similar design susceptible to rapid waterwall slagging unless either coal quality or sootblower operations are carefully monitored. At Brayton Point very strict specifications for ash content and ash fusion temperature are imposed on the many coal suppliers selected by NEP. In spite of these coal specifications, slagging incidents occur. Boiler operating conditions such as excess air, mill configuration, or sootblowing cycle have been observed to affect the frequency and severity of these slagging incidents. This paper describes a test program to optimize sootblower performance and prevent slagging incidents at this unit. Continuous furnace exit gas temperature (FEGT) measurements were made as a direct measure of furnace absorption and sootblower effectiveness. Additional measurements were made with a Diamond Power Specialty Company Cleaning Advisor system. This system monitored the effectiveness of individual sootblowers. Together, these diagnostic tools were used to quantify the wall deposition rate (time from clean to dirty) for several coals and to set optimal sootblowing schedules for these coals.
42The results of these tests showed that clean and dirty furnace FEGT were characteristic of each coal and mill configuration at full boiler load. The optimal time to initiate sootblowing is when FEGT just reaches its equilibrium value. At this point, the deposit is about 3 cm thick and lightly sintered. Deposit removal can be accomplished by one sweep of the sootblower. The paper also describes the effects of mill configuration and excess air on FEGT. In turn, optimizing FEGT is shown to minimize superheater and reheater attemperator spray flows. Controlling FEGT has other qualitative benefits in that NOx emissions were reduced, and the risk for superheater fouling and tube overheating was also ameliorated.
