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Show feed, 1S to maX1m1ze suspenS10n burn1ng o f the f1ne s wh11e ma1nta 1n1ng the combust10n on the bed. The h1ghly turbulent OFA system has successfully been demonst r ated on RDF p r oJects a s we i as b1oma s s . The three r ows of no z z l es p lus t he u s e o f the air in the f eed spouts has evolved over the year s as an exce llent m1x 1ng system. The OFA system requ1red a fan to prov1de h igh stat1c to obta1n he des1gn nozzle veloc1t1es to assu r e penetrat10n. The eX1st1ng fo r ced draf t had to be replaced w1th a h1gher stat1c- p r essure (now 5- 1nch H~O) fan t o take p r essur e d r ops a s soc1ated with fie new a1r heate r and the th1cker ash bed on the grate. A new OFA fan uS1ng hot FO fan d1 scharge alr was supplled to prov1de the required overfire a1r. Superhedters The eX1st1ng superhe aters ha ve been replaced with the new counterflow s 1ngle-pass design, with 1ncr eased clear s 1de spa c i ng. The coolest steam 1S in the hottest gas path a~d will act to l ower tube me t a l t emperatures. The o rig1nal design had 850°F final stearn temperatures; the redes1gn p r ov1des 700 °F f i nal steam temperature, WhlCh aids g r e atly i n reduc ing meta l temperatures, reducing both the f ouling and corrosion potent1al. Spray attemperatlon 1S used to provide a control temperature range, and alloy is utilized where tube metal calculations dictate. Generating Bank The 1nternal tile baffles installed by the o riginal designers to promote cross-flow generating-bank heat transfer have been removed. The generating bank is now a single-pass once-through design that reduces the erosion and p lugging potentials. The resulting reduct10n in heat transfer has been made up by adding three rows o f generat1ng bank tubes to use the drum holes c reated by the relocated screen. The additional generating surface will decrease gas temperatures entering the economizer. The eX1sting economizers--one, an extended surface; the other, bare tube with high gas velocities--were replaced with bare tube types llmiting gas-side velocities at MeR to 30 ft/ sec t o insure long life by minimizing erosion. Air heaters were described in the section on air system and are o f the plate-type design. Regenerative air heaters have been used in RDF previously but were located in a clean gas stream after the electro static precip1tators. Plugging of the hot, inlet side, due to oversize particulate carryover, was o f high enough potenti al so as to elim1nate a regenerat1ve application. Tube and shell design would have been acceptable but the plate type o ffered SLmplicity and equivalent performance. Cas temperature wil l be reduced to 450°F, which matches the eX1sting electrostatic precipitator operat1ng gas temperature. Gas-side erosion is of concern, a nd erosion s hields are being used on the leading edge of each air heater plate to minimize this p o ssib1lity . Exist1ng vari ab l e speed 10 fans and electrostatic ? reC1p1 t ators were r eutilized. INITIAL OPERATI NG PROBLEMS The 0 erfire A1r System The overf1re alr system, as designed, supplied both the w1ndswept spouts and the overflre no z=les . The w1ndswept spouts requlred separ ate flow control to permi t opt1mum d istrlbu t 10n, and the ne cessary dampers and damper d r ive w1ll be retr ofi tted to permit th1s t o occur . The s c rew fe e ders are seeing a larger RD F pa rtl cle Slze t han they were designed f or. In1tial RDF supply , r unnlng at 10 - inch minus , was over s1zed as t he fe eders were designed f o r a 6 - inch minimum . At h i gher loads, the screw woul d s t op fe eding and "sl ugg ing" occurred. RDF sizing i s being a d Justed at t he preparation p lan t a nd t h1s problem is expected to be r~s o lved when the f eed size meets specihc ation. Auxiliary Gas Firing All four boilers main tain fu ll steam gener at l on abil1ty on natural gas fuel. However, as a cost c o n t rol measure , the existing gas bu r ne r s we r e not relocated ( l ower ) t o take advantage o f the exter.ded furnace. The relatively high g a s bur ne r l ocation i n the furnace, coupled with the newly designed superheater, has made pr1mary superhea t e r temperature contro l difficult when f i r ing t wo of f our burners. The gas temperature distribution into the superheater is upset. The variation in gas temperature from the side t o the middle has reached 53S o F under the worst c onditions. The four-burner operation smooths out the furnace gas temperature distribution and permits high load operation. Steam temperature on RDF is as predicted and is controllable by the spray attemperator. EXPECTED PERFORMANCE vs. ACTUAL PERFORMANCE Table 2 compares the performance o f the o riginal coal design with that ot the predi cted RDF design and wi th the a c t u a l RDF perfo rmance. |