OCR Text |
Show 14 Ge nera 1 ly, measurement s of the vert 1 ca 1 ava i 1 ab 1 e heat fl ux profi 1 e showed expected trends with changes in furnace operating parameters. For example, Figure (11) shows the effect of tilt on the vertical profile. These profiles are obtained by plotting the data from the vertical profiles seen by the operators in Figure (6). The clean meter signal in millivolts is proportional to the incident heat f1 ux. The profile shape changes with the position of peak signal moving higher in the furnace as burner tilt increases. This occurs because the tilt moves the fireball higher in the furnace. Often burner tilt changes because of the level of foul ing in the furnace. At the furnace exit (furnace level 9), increasing tilt causes an increase in the clean meter signal indicating increased exit gas temperature. Conversely, in the lower part of the furnace (furnace level 2) increasing burner tilt lowers the clean signal (available heat flux). Previously, effects on vertical profiles have also been observed to result from changes in air flow, furnace cleanliness and coal quality (6). 9 8 LOAD lSI .... - TILT -38 -_. TILT -I TILT .12 - TILT .38 e I 234 561 MrrrR SICNRL (mV) Figure 11. Profiles of available heat flux showing effect of fouling and consequent tilt. Convection Section Radiant Superheaters and Reheaters Typical historical plots of the overall heat transfer coefficient for the radiant superheater are shONn in Figure (12). The "clean" coefficient is a measure of the possible heat transfer, i.e. l/hg + l/hs. The -actual" coefficient is that calculated from equation (2). Tne difference between the two can be attributed to foul ing. As expected, after sootblowing the two |