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Show ~ &AI .N.. ~ o z o U &.I t ca L.I .J :l o &.. • • ,o~----~--------------------------______ ~ 5B~----------------------------------~ 3B 2B 3 6 9 12 15 18 21 24 27 3S TIME (HR) Figure 16. Historical effect of fouling in the economizer. Improved Boiler Control with the Fouling ~~nitoring System It has appeared to the authors that is it timely to propose a modified boiler control strategy which would suitably take advantage of the new instrumentation. This strategy would retain the existing set points, control loops and manipulable process variables but would incorporate into the control scheme the monitoring of the furnace exit temperature (12). It is further proposed that the degree of fouling and slagging be used as another manipulable variable in the overall control strategy. In the f 0 11 ~ i n g dis cu s s ion the s t rat egy prop 0 s ed i s for abo i 1 e r 0 f the CE design that incorporates the tilting burner system as a method of furnace control. For the end-fired or opposed fired boilers, which use gas recirculation for the equivalent control, a cOrTl>arative strategy can be proposed. In the modi fi ed strategy, the nonna 1 steam temperature and pressure control loops would be in the automatic mode, as at present. The operator would continue to monitor the burner-tilt angle, but would in addition monitor the furnace exit temperature, TFE and also the furnace and convection-section cleanliness screens. The strategy would be to keep both the burner tilt and furnace-exit terTl>erature within relatively narrow limits, at different levels for different boiler loads. This would be done as foll~s by cleaning furnace surfaces; when the TFE rises (tilt' seeks |