OCR Text |
Show Reburn Fuel Carrier Cas - FCR vs . Air Tests were conducted in the BSF with both FGR and air, respectively, as the carrier gases. Figure 17 shows consistently higher NOz emissions when air is used as the reburn carrier gas versus FGR at a given reburn zone stoichiometry . The lower O2 concentration which the natural gas is exposed to when FGR is in use reduces the potential for some NOz formation in the reb urn zone as compared with the air carrier gas case . These data demonstrate the potential tradeoff of installing and operating an FGR fan versus less optimum NOz reduction efficiency when using air as a carrier gas . 260 I 1 2-0 1 Clou-Coupled Rebum ElevllllOn. Nalural Gas Album FUll 22C ~ 2CC ~ N c ' ! C - ~ .. · 60 i ~ • 4C 2 · 20 ·oc e:: 6: - -: c ! : 090 0.85 1.00 R£!!1JIUI %Ollt S"!'OICHlOw:E'TRY Fig 7 BSF ests a Conditions TYPical 01 ENEL 660 MW Oil-Fired Units - 72 x 1()6 Bt I r Companson 01 FGR to Air as Close-Coupled Reburn Carner Gas Furnace Exit Gas Temperatures and Volumetric Heat Release Rates Base.ine anc optimized NOz emissions (ppm) were only moderately influenced by furnace temperatures as quantified by horizonta furnace outlet plane (HFOP ) tempe~ature or by furnace volumetric heat release ra tes . As shown in Figure 18, baseline horizontal furnace outlet plane temperatures (HFOP ) ranged from 1230·C to 1400·C (11% variance about mean) , and cubic heat release rates from 25 ,000 to 35,000 Btu/hr/ft 3 ( 33% variance about mean ) over the range of thermal conditions tested For these tests baseline NOz emissions (ppm ) varied by at most 15% between the tests , while optimized NOz emissions reduct ions va r i ed by a max imum of only 6 percent . For al l the reburn test issues, a nominal reburn configuration of 15% reburn fuel, 17% burnout air and 10% FGR resulted in lower HFOP temperatures than at baseline operation . The temperature reduction varied from 30·C to l3S·C for the tests . In field tests of OFA-only systems by ENEL and others, HFOP tem eratures have been found to increase in certain cases due to delayed combustion . For lower OFA levels field r sult~ have shown the HFOP temperatures to some tim s deer a due to thermal dilution withou t the delayed combu~tion found for higher OFA levels . For a reburn syst m, th~ quenching effect of the 10 percent reburn FGR carr! l gas likely lowers the temperature in the reburn zone contributing to the decreased FOTs observed in the BSF tes ts . Fig 18 Comparison 01 Baseline and Reburn Temperatures at DIHerent BSF Thermal Conditions #6 Oil as a Reburn Fuel For the majority of the oil reburn tests NOz emissions were similar to those found with overflre air alone, and typically higher than those found for comparable gas reburn tests (Figure 19) . However, one oil reburn test with a higher elevation of overfire air in-service produced the same NOz emiss ions (85 ppm) at the same test condition with natural gas usee as the reburn fuel, This data shows that when oil is used as the reburn fuel, reburn zone residence times are more important than for natural gas used as the reburn fuel , since the same final em is sions levels were obtained wi th oil and gas even though the oil emissions were significantly higher for other reduced residence time cases . Future testing is planned which will explore this and other areas such as improved reburn oil atornizatior. , in order to enhance oi reburning performance . 260 240 _0 ... ...,.. e_ ,.U' . , 220 - .01._ 200 ... 1&0 c ~ 160 ~ ~ 14(; , ~ 120 10C f-- t. CU:f 11K _.,o.:=: o / ~ - 001.1(-'- / ,. o.s: 10K / / --Y . 0 . ~ I I I I I I 0 1 De 11 1. Fig 19 Bsr 1 ests at CondiIlOl"l:; 1 YPlcal 01 ENEL 660 MW Oil-Fired Untts - 72)( 1()6 Btu/hr, NO vs Raburn ZOI"Ie StOichiometry |