| OCR Text |
Show the bulk furnace gases exiting from the main burner/windbox zone . Reburn fuel/FGR and burnout air were introduced through nozzles located in the furnace corners . These nozzles had both velocity and yaw (horizontal angle ) adjustment capability. Comprehensive combustion evaluations have been conducted in the BSF while systematically varying a number of key reburn system design and operating parameters . Test results reported herein are organized to highlight the design and operating parameters which have the greatest influence on observed NOz emission levels . Test data obtained using overfire air staging ( i . e . , non-reburn ) techniques have been selectively included so that comparisons can be drawn between reburning and overfire air staging NOz control approaches . Reburn Zone Stoichiometry Reburn zone stoich i ome t ry was f ound t o have mor influence on fina l measured NO. level than any oth r parameter evaluated Figures 11 and 12 pres en t observed NOz leve l s as a fun c ti on of reburn zone stoichiometry wi th the BSF conf i gured to simulate two 26C ~------------------------------------------------, 2~ ~ C NO REBuR\ 2:1C ~ • S.,. A DAR::> GAS REBUR E EVA ION -------=-------i 200 · ac ~----------------------------------_Q~~------~ . ~ +---------------------------------~------------~ ' 4 : ______________________________ ~----------------~ · :; o ------------------------~~--__ ~--------------~ IOC ~------------------~~_r~~------------------~ e: ------------~~~~~~--~------------------~ 5: ------------------------------------------------~ 4: ______________________ --~------_,--------._----~ 1.1 1.: Fig 11 BSF Tests at Conditions Typical of ENEL's Santa Gllia Unl! No 2- 90 x 1~ Btu r Ox vs Reburn Zone Stoichiometry C !! 26C --------------------------------------------------, 2 ' ~ ~----------------------------------------------~ 2:1 ~ 1 200 - - 1 :> 0 REaLJ Rf" • S A DARO GAS REBURN ELEVATION • GAS C L OS : ·COuP~ ED REBUR'_ ~r-I------------i 18e +---------------------------------~------------~ ' !C ~------------------------------~--------------~ 1 40 +---------------------------~~~----------------1 ' 2C --------------------------~~~----------·-------- 1~ ~--------------------~~AM~------------------~ ao +-----------------~~~~----------------------I !o +-----------------------------------------------~ ~~------~------_r--------------~------~~ 0 6 07 11 '. Fig 12 BSF Tests at Conditions TYPical of ENEL 660 MW OM Ired U n lt ~ 72 x 1Q6 Btu/hr, NOx vs Reburn Zone Stolchlome tr T 6 different furnace thermal environments. Net fuel heat input (BTUfHr) and furnace insulation characteristics were varied to evaluate temperature and residence time influences on reburn technology; these influences will be detailed later in this paper . With respect to variations in reburn zone stoichiometry, it's clear that when the reburn zone is operated under oxidizing (~ >1 .0) conditions, NOz levels are at their highest , regardless of any specific test configuration . Similarly, as the reburn zone is operated in a reducing environment (~<1 . 0), NOz reductions of 50X or more from baseline levels were observed . Furnace stoichiometry in the "reburn zone" can be reduced below 1 .0 by operating the boiler with separated overfire air only (with no reburn fuel ), in addition to operating in a "reburn mode" . Figures 11 and 12 draw a comparison between NOz levels observed at specific reburn zon stoichiometries for reburn only/ overfire air only case s . Substantial NO. emiss ion reductions were demonstrated from the application of OFA alone . Reburning , however, offers a measurable advantage beyond the OFA cases (at the .ame stoichiometries) in terms of reducing NOz , as shown in Figures 11 and 12 . Reburn zone s to ichiome try also influenced particulate (smoke) emissions as shown in Figure 13 . Figure 13 compares Bacharach smoke number with rebur n zone stoichiometry . Bacharach smoke number is an indication of flue gas particulate loading ; with increasing values of smoke number indicating increases in flue gas particulate or smoke concentration. Smoke number increased with decreasing reburn zone stoichiometry in both reburn and non-reburn (separa t ed overfire air) cases, however, reburning offered a meas urable reduction in smoke number for the same given stoichiometry as compared with the separated overfire air technique . ': ~ D:: -1 to: o NO REBURN • STANDARD GAS REBu RN ELEVATIO It: : 1 :2 ~ z ~ 0 :z :l J Vl I :r u ~ ~ D < c:: O~~~---r--~~~~--~~----~~--~--~~----~ 0.6 0.7 0.8 0,9 1.0 1.1 1.: REBURN ZONE STOICHJO~R Y Fig 13 BSF Tests al Condill()('ls Typical of ENEL 660 MW Oil-Fired UOIIS - 72 10" Btu/hr, Bacharach Sm e Number vs Reburn Zone StolchlOmet Figur 14 plot mea sur ed s t ack CO emis s ions compared to r burn zo Itoichiome try . G n raI l', as r ebur n zon Itolchlom ry I r duc d, CO emi s sions increo e. It should b not d , h ~ we v e r, that i n ce r ta i n r burn te s t c S 5, r burn zon toich i ometries w re s toblish d b 1010 0 .9, ach if'ving substan::ia l NO. |
