REACTION ENGINEERING INTERNATIONAL. Committed Individuals Solving Challenging Problems

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1 REACTION ENGINEERING INTERNATIONAL Committed Individuals Solving Challenging Problems A MODEL FOR PREDICTION OF SELECTIVE NON-CATALYTIC REDUCTION OF NITROGEN OXIDES BY AMMONIA, UREA, AND CYANURIC ACID WITH MIXING LIMITATIONS IN THE PRESENSE OF CO by J. Brouwer, M. P. Heap Reaction Engineering International D. W. Pershing and P. J. Smith University of Utah Presented at the Twenty Sixth International Symposium on Combusion, July, 1996, Naples, Italy. 77 West 2 South, Suite 21 Salt Lake City, Utah 8493 Telephone: FAX: info@reaction-eng.com

2 Abstract A reduced chemical kinetic mechanism for the prediction of selective non-catalytic reduction (SNCR) chemistry has been developed and incorporated into a three-dimensional, CFD-based turbulent reacting flow model. The model can be used for prediction and investigation of thermal and mixing effects as well as the influence of CO on the SNCR process in practical systems. The model accurately describes the SNCR chemistry as indicated by comparisons of NO reduction efficiency, ammonia slip and N 2 O emissions with predictions using a complete chemical mechanism (7 species, 327 reactions) and experimental measurements from independent investigators. The reduced mechanism (6 species, 7 reactions) and individual rate constants are provided so that the mechanism could be incorporated into any CFD-based computer code. The effects of thermal environment (injection temperature and quench rate), reactant ratios (initial NO and NH 3 /NO) and reagent mixing on NO reduction by ammonia were investigated in the presence and absence of CO using a pilot scale facility. Comparison with the coupled CFD/chemistry model predictions indicated good agreement, and both suggest that SNCR effectiveness is critically influenced by (1) finite rate chemistry, (2) imperfect reagent dispersion, (3) mixing delay times, (4) local CO concentrations, and (5) non-isothermal temperature profile. Page 2

3 Introduction Twenty years after Lyon s patent 1 defining the conditions for selective, non-catalytic NO reduction to N 2 by ammonia (SNCR, excess air conditions, 85 to 11 o C), there is continuing industrial interest in its use as a low cost, effective and retrofittable NO x control technique. Current applications include utility boilers, waste incinerators and other stationary combustion equipment; however, the NO x removal efficiency is equipment specific and depends on the time available for contacting the selective reducing agent within the appropriate temperature range. There has been considerable other laboratory and pilot scale work to identify the controlling process parameters. Muzio et al. 2 first demonstrated the effectiveness of urea and other amines. A temperature range for selective reduction under fuel rich conditions was also identified 3,4. Perry and Siebers 5 found cyanuric acid could be an effective selective reducing agent and Heap et al. 6 noted that these reactions could be catalyzed by stainless steel at temperatures as low as 6 o C. Chen et al. 7 suggested a hybrid NO x control scheme using selective reducing agents with combustion modifications like reburning. Lyon 8 characterized the interactions with hydrogen and CO. Teixeira et al. 9 evaluated the effect of trace combustion species and others have tested proprietary compounds for NO reduction in practical applications. Under well-mixed, plug flow conditions SNCR can provide excellent reduction efficiencies 8 (> 9% at NH 3 /NO ratios < 1.2) but such performance has not been achieved in practical applications where typical reduction efficiencies are often less than fifty percent for various boiler types and fuels 11,12,13,14. SNCR is effective over a very narrow temperature range (or window ). Reduction at higher temperatures is poor because the reducing agent itself oxidizes to NO. Below the optimum temperature, the selective reduction reactions are too slow and unreacted reagent can be emitted (e.g., ammonia slip). In existing combustion systems the spatial location of the optimum temperature window may vary with operating conditions or occur in regions of large thermal gradients, e.g., convective heat exchangers. This places severe design constraints on the reagent injection system which must disperse the reagent throughout the entire combustion product Page 3

4 stream and mix the reagent with the NO while the gases are within the appropriate temperature window. Although reactant mixing and injection location optimization have been evaluated 8,1,13, few studies have quantified the impact of mixing limitations on SNCR performance. Muzio et al. 15 defined the effects of residence time and identified three characteristic times: 1) mixing of the reducing reagent with combustion products; 2) reactive nitrogen compound release from the reagent (maybe an aqueous solution), and 3) chemical reaction times. Improved computational tools are needed for SNCR design and optimization because of tightened emissions standards and the desire for lower cost control techniques in developing nations. Unfortunately, SNCR effectiveness at full scale is governed by rate-limiting processes including turbulent mixing, heat transfer, spray droplet evaporation, devolatilization and others. Since these processes are coupled, incorporation of fully detailed chemistry in a turbulent reacting flow computation is prohibitive, hence a reduced chemical kinetic mechanism is needed. The specific objectives of this study were to: Develop a reduced chemical mechanism and verify that it was capable of accurately predicting the chemical behavior of ammonia, urea or cyanuric acid in SNCR model. Incorporate the reduced mechanism into a comprehensive three-dimensional combustion Compare the resulting predictions with existing and new pilot scale data quantifying interactions of reagent composition, injection temperature, thermal quench rate, mixing rates and the impact of trace species such as CO to validate the model for practical applications. Page 4

5 Model Development Mixing/Reacting Flow Code The base computer models 16,17 (JASPER and GLACIER) are steady-state, 2 and 3- dimensional, computational-fluid-dynamics codes which fully couple reacting gases, solids and liquids with turbulent mixing and radiative heat transfer. Coupling turbulence and heat transfer with reaction chemistry requires the number of chemical kinetic steps be small. These codes use partial equilibrium to compute local instantaneous chemistry from a set of reduced kinetic steps for slow reactions and minimize Gibbs free energy for all other species. Mean values for species concentrations, temperature and density are obtained from computed probability density functions consistent with a κ ε turbulence model. The discrete ordinates method is used for radiation and is also fully coupled with the turbulent fluid mechanics and reaction chemistry. This model can be distinguished from other CFD based SNCR models 19,2 in that it fully couples and incorporates the chemistry into the CFD calculation. The resulting model is directly applicable to industrial equipment. Fully Detailed Chemical Kinetic Model The kinetic rates of Miller and Bowman 21, with recent literature modifications 22,23 were applied in SENKIN 24 to model the complete SNCR chemistry under quenched or isothermal conditions. The simplified SNCR mechanism and its rates were derived from this same database through sensitivity analyses and curve fitting as described below. The reduced SNCR chemistry was incorporated into the CFD code to model the coupled turbulent mixing, radiation and chemical kinetic problem. Reduced Chemical Mechanism Development Principle reaction pathways for NO reduction in the SNCR process have been suggested in the literature 21,25. With cyanuric acid ((HNCO) 3 ) or iso-cyanic acid (HNCO), N 2 O is a major Page 5

6 intermediate species and product 26. Ammonia injection results indicate very little N 2 O formation 1,2 ; NH 2 and HNO are the key intermediates. Sensitivity analyses applied to the complete chemical mechanism agreed with this view; the principle NO reduction pathways occur by reaction with NH 2 to form N 2 for ammonia and by reaction with NCO forming N 2 O as an intermediate for the cyanuric acid case. With urea both pathways are important. This understanding was used to develop a reduced mechanism for the homogeneous chemistry of the SNCR process with ammonia, urea and cyanuric acid reagents (Figure 1.). Ostberg and Dam-Johansen developed a similar reduced kinetic model for ammonia only 18. Vaporization and devolatilization for liquid or solid reagents is simulated by sub-models described elsewhere 16,17. The mechanism assumes instantaneous reagent break down into ammonia (NH 3 ) and iso-cyanic acid (HNCO) in the gas phase. Breakdown of urea into equal parts NH 3 and HNCO and cyanuric acid into 3 moles of HNCO has been suggested in the literature 21,26. However, to account for the HNCO that subsequently reacts along the ammonia pathway, the reduced mechanism assumes that 1% of the isocyanic acid is converted to ammonia (based on full chemistry calculations). This produces 1.1 moles of NH 3 and.9 moles of HNCO per mole of urea and.3 moles of NH 3 and 2.7 moles of HNCO per mole of cyanuric acid. The reduced SNCR mechanism consists of seven irreversible, finite rate reactions describing the ammonia and iso-cyanic acid reactions, given in Table 1. The first two reactions describe the ammonia pathway. Reaction 1 dominates NO reduction at lower temperatures; reaction 2 produces NO from NH 3 and oxygen at higher temperatures. Rate parameters for these equations were determined through detailed sensitivity analyses performed with the full chemical kinetic mechanism for conditions spanning typical SNCR operation. Parameters that were varied included initial NO, reagent nitrogen to NO ratio, injection temperature, and quench rate in the SNCR zone. The rate parameters from the sensitivity analyses were fit to a modified Arrhenius form with a pre-exponential factor, temperature exponent and activation energy. Page 6

7 Table 1: Rate Parameters for the Reduced SNCR Model. (Units are: A [=] cm-mol-sec-k, Ea [=] cal/mol) Reaction A b E a Reaction No. NH 3 +NO -> N 2 +H 2 O+H 4.24E ,6 (1) NH 3 +O 2 -> NO+H 2 O+H 3.5E ,3 (2) HNCO+M -> H+NCO+M 2.4E , (3) NCO+NO -> N 2 O+CO 1.E (4) NCO+OH -> NO+CO+H 1.E+13. (5) N 2 O+OH -> N 2 +O 2 +H 2.E+12. 1, (6) N 2 O+M -> N 2 +O+M 6.9E ,76 (7) Reactions 3 through 7 describe the iso-cyanic acid pathway. Reaction 3 describes the decomposition of HNCO to NCO, the reactant responsible for NO reduction in this pathway. This rate was determined to match the observed HNCO decomposition with the complete chemical mechanism. Reaction 4 is the desired NO reduction reaction producing N 2 O; the complete mechanism indicated this was primary NO destruction pathway, accounting for more than 9% of the NO reduction over a wide range of conditions). The rate parameters for reactions 4, 5, 6 and 7 were all obtained from the literature 21 without modification. However, when applied in the reduced mechanism without radical chemistry, the rates for reactions 5 and 6 would not match the complete mechanism due to the assumption of equilibrium OH. The mechanism presented above compares well with the fully detailed chemical kinetic mechanism as indicated in Figure 2 for isothermal, homogeneous conditions at various temperatures. The reduced mechanism accurately predicts the decay of ammonia and iso-cyanic acid as well as the NO reduction and N 2 O emissions of the fully detailed model. In general, reduced chemistry schemes do not work well over a wide range of conditions. However, since the applicable range of SNCR is limited to a temperature window, as described above, reduced chemical kinetic mechanisms for SNCR are not required for a broad range of conditions. As Page 7

8 indicated in Figure 2, the reduced mechanism accurately represents the fully detailed mechanism in the temperature range of interest. Effects of CO Several studies have shown the influence of CO on the selective reduction process 8,9,1 indicating that the presence of CO shifts the selectivity by increasing the rate of NH 2 formation and the rate of NH 3 oxidation to NO. Figure 3 shows results of detailed chemical kinetic calculations showing the effect of various CO levels on SNCR in a thermally quenched reactor. As the injected CO level increases the optimal temperature for NO reduction shifts to lower temperatures due to enhanced chemical rates in the presence of CO. The shift in selectivity is accomplished by two mechanisms: increasing local temperatures and increasing net production of OH radical. The first effect is due to the exothermicity of the main CO burnout reaction, CO + OH -> CO 2 + H, while the second effect is due to chain branching reactions that result from the H produced in this reaction. The contribution of CO oxidation to the local temperature is accounted for in the model. Without including details of radical chemistry, an empirical adjustment to the rates must be included to account for the effect of CO on radical concentrations. This empirical adjustment was determined by detailed chemical kinetic calculations over a wide range of SNCR conditions (1 < NOi < 1 ppm,.5 < N/NO i < 3., and K/sec < quench rates < 25 K/sec) at specified temperatures. The empirical adjustment is applied in the form of a shift in the effective temperature to account for the radical chemistry effects of CO as follows. For example, the rate of reaction (1) of Table 1 is calculated as: k 1 8 [ NO] [ NH 3 ]( )( T+ S( CO) ) , 6 = exp ( T+ S( CO) ) (8) Page 8

9 where k 1 is the rate of NO+NH 3 =>N 2, and S(CO) is the shift in temperature required to achieve the same NO reduction and reagent decomposition compared to the case without CO. In the current model, the empirical adjustment, S(CO), is given by SCO ( ) = 17.5ln( [ CO] ) 68. (9) where [CO] is the concentration of CO in ppm. This adjustment is applied to reactions 1, 2, 3, 5, and 6 of Table 1 since the rates of each of these reactions were developed to fit reactions or groups of reactions that involved OH radical chemistry. Reactions 4 and 7 are assumed to be unaffected by the presence of CO. Verification of Model Predictions - Alternative Reagents To verify the predictive capability of the reduced mechanism, model calculations were compared with experimental measurements from the literature for ammonia, cyanuric acid and urea. Ammonia Reagent Figure 4 compares the reduced mechanism applied in JASPER to the premixed ammonia data of Lyon 27 and to calculations with the complete mechanism. Initial conditions for the data and model are 225 ppm NO, 1.23% O 2, 45 ppm NH 3, balance helium. The reduced mechanism predicts both the absolute reduction and the temperature dependence equally as well as the complete mechanism for this premixed condition. Cyanuric Acid Reagent Figure 5 compares predictions of the reduced mechanism to the data of Caton and Siebers 26 for cyanuric acid. The data was obtained in a 1.6 cm-id quartz reactor which flowed simulated exhaust gases into which was injected vaporized cyanuric acid (at nominally 74 K) through an Page 9

10 orifice. The mixing limitations were considered small for this experiment, so the model was applied to conditions of premixed reactants. Notice that the reduced model accurately predicts the NO reduction observed by Siebers and Caton for both cases with and without CO. Urea Reagent Application of the SNCR model for urea reagent was accomplished for the conditions of Teixeira et al. 9. The data was obtained by injecting a 2.4 wt.% urea/water solution through an atomizer into the throat of a furnace with controlled injection temperature and a temperature profile which drops at a nominal rate of 25 K/s. Figure 6 presents the results obtained from modeling these experiments using the coupled turbulent flow model (JASPER) and chemical kinetic mechanism of Table 1 for conditions of liquid urea/water injection into combustion products as in the experiment. The predictions show good agreement with data except for a slight over-prediction of NH 3 slip at lower temperatures and a slight shifting of the peak NO reduction and N 2 O emission levels to higher temperatures. With mixing limitations and a quenched thermal profile one would expect the peak reduction to shift to higher temperatures than those predicted by homogeneous kinetics. The fully detailed chemistry applied to premixed, quenched (-25 K/s) conditions predicts a minimum NO level of 2 ppm at 126 K which severely over-predicts NO reduction compared to the experiment and the fully coupled model. Practical System Constraints - Impacts of CO, Mixing and Decaying Thermal Profiles To provide SNCR performance data under typical industrial conditions (discrete jet injection into an actual flue gas with decreasing temperatures), the authors performed small pilot scale experiments 28 in a 29 kw, refractory lined furnace (16 cm in diameter by 7.3 m long.) Ammonia was injected through a water-cooled stainless steel injector located on the chamber axis at the beginning of the SNCR section (centerline axial injection.) The ammonia was injected with nitrogen to allow variation of the reagent stream momentum and thus reagent/product mixing characteristics. The product stream entering the SNCR section contained 2.5% O 2, 8.4% CO 2, Page 1

11 16.7% H 2 O, and 5 ppm NO in nitrogen. The injected ammonia level corresponded to 75 ppm with various amounts of nitrogen and CO injected with the reagent. NO was measured by chemiluminescence and ammonia slip by FTIR. In practical systems imperfect mixing and inadequate residence time at temperature can lead to emissions of the reagent which is a major concern. Figure 7 presents a comparison of ammonia slip measurements and JASPER model predictions for a low quench rate (~2K/s), and 1267 K injection temperature as a function of the amount of CO that was injected with the reagent. The model predicts the data well except at low CO levels (where the measured data are believed low because the FTIR measurement system was not calibrated for such high NH 3 concentrations.) The model predictions suggest that the ammonia slip decreases at higher CO concentrations because the CO oxidation increases local radical concentrations which enhance ammonia reactions. Figure 8 summarizes comprehensive measurements and predictions of SNCR effectiveness (NO final /NO initial ) for 1267 K injection as a function of: (1) local CO concentration (none vs. 75 ppm) (2) temperature decay rate at the injection point (2 K/s vs. 12 K/s) (3) momentum ratio of ammonia jet /combustion product flow (1:1 to 8:1) The turbulent reacting flow model with the reduced chemistry mechanism correctly predicts the four complex trends: SNCR performance is much worse in rapidly quenched systems due to decreased reaction rates downstream of the injection point Without CO, increasing the momentum ratio (reagent/bulk mixing rate) decreases SNCR effectiveness because the reactants pass through the temperature window before they can react. The presence of CO is beneficial under rapid quench conditions because it enhances the radical pool at the lower temperature conditions Page 11

12 The presence of CO is detrimental under slow quench conditions, particularly with slow mixing rates because the radical pool is enhanced at higher temperatures which favors ammonia oxidation to NO (see also Figure 3). Conclusions A reduced mechanism to describe the finite rate chemistry of SNCR reactions with ammonia, urea or cyanuric acid injection has been developed and is suitable for incorporation into turbulent reacting flow models. The reduced mechanism has been validated for each of the three reagent types by comparison to a complete detailed chemical kinetic mechanism and experimental data from independent investigators. Incorporation of the reduced mechanism into existing CFD-based turbulent flow codes and subsequent application to experimental conditions proved the capabilities of the model for predicting NO reduction, ammonia slip, and N 2 O emissions during SNCR. Comparison of model predictions for conditions of practical concern (which include mixing constraints and quenched thermal profiles in the presence of CO) indicate good agreement between model and data. More importantly, both the model and the data demonstrate that SNCR effectiveness is critically influenced by practical constraints which reduce the reductions achieved in most full scale systems. Optimization of SNCR must properly account for (1) finite rate chemistry, (2) imperfect reagent dispersion, (3) mixing delay times, (4) local CO concentration, and (5) nonisothermal temperature profile. Hence, a fully coupled chemical reaction/turbulent mixing/radiant heat transfer model is needed to help achieve maximum NO reduction efficiency. Acknowledgments Financial support for this program was provided by the US EPA under Contract No. 68D2121. The authors would like to acknowledge the help of Dr. Adel Sarofim in the development of the SNCR mixing model and Messrs. Dana Overacker, Dale Inkley, Dave Wagner and Dave Warren for the construction and operation of the test facility. Page 12

13 References 1 Lyon, R.K., U.S. Patent No. 3,9,554, Muzio, L.J., Arand, J.K., and Teixeira, D.P., Sixteenth Symposium (International) on Combustion, p.199. The Combustion Institute, Arand, J.K.: U.S. Patent No. 4,325,924, Brogan, T. R.: U.S. Patent No. 4,335,84, Perry, R.A., and Siebers, D.L.: Nature vol. 324, p. 657, Heap, M.P., Chen, S.L., McCarthy, J.M., and Pershing, D.W. Nature vol p. 691, Chen, S.L., Lyon, R.K., and Seeker, W.R., AFRC Fall International Symposium on NO x Control, Waste Incineration and Oxygen Enriched Combustion, Paper #32, San Francisco, CA, Lyon, R.K. and Hardy J.E, Ind. Eng. Chem. Fundam., vol. 25 p.19, Teixeira, D.P., Muzio, L.J.,and Montgomery, T.A. AFRC/JFRC International Conference on Environmental Control of Combustion Processes, Honolulu, Hawaii, Chen, S.L., Ho, L, Maly, P.M., Payne R., and Seeker, W.R. Joint EPRI/EPA Symposium on Stationary NO x Control, Bal Harbor, Florida, Jodal, M., Nielsen, C., Hulgaard, T., and Dam-Johansen, K., Twenty-Third Symposium (International) on Combustion, pp , The Combustion Institute, Jodal, M., Lauridsen, T.L., and Dam-Johansen, K., Environmental Progress, Vol. 11, No. 4, pp , Teixeira, D.P., Lin, C.J., Muzio, L.M., Jones, D.G., and Okazki.: Joint EPRI/EPA Symposium on Stationary NO x Control, Bal Harbor, Florida, Shore, D.E., Buening, H.J., Prodan, Teetz, R.D., Muzio, L.M., Quartucy, G.C., Sun,W.H., Carmignani, P.G.,Stallings, J.W.,O Sullivan, R.C.: Joint EPRI/EPA Symposium on Stationary NO X Control, Bal Harbor, Florida, Muzio, L.J., Montgomery, T.A., Quartucy, G.C., and Texeira, D.P., Joint EPRI/EPA Symposium on Stationary Combustion NO X Control, Bal Harbor, Florida, Smith, P.J., and Eddings, E.G., User Guide for JASPER 1.3, Reaction Engineering International, Page 13

14 17 Smith, P.J., Adams, B.R., and Eddings, E.G., User Guide for GLACIER 2.5, Reaction Engineering International, Ostberg, M., and Dam-Johansen, K., Chemical Engineering Science, Vol. 49, No. 12, pp , Sun, W.H., Michels, W.F., Stamatakis, P., Comparato, J.R., and Hofmann, J.E., AFRC Fall International Symposium, Cambridge, MA, Sun, W.H., Hoffman, J.E., and Pachaly, R., Post Combustion NO x control with Urea: Theory and Practice, Seventh Annual International Pittsburgh Coal Conference, Miller, J.A., and Bowman, C.T., Mechanism and Modeling of Nitrogen Chemistry in Combustion, Progress in Energy and Combustion Science, vol. 15, pp , Miller, J.A., and Melius, C.F., Twenty-First Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, pp , Dean, A.J., Hanson, R.K., and Bowman, C.T., Journal of Physical Chemistry, vol. 95, pp , Lutz, A.E., Kee, R.J., and Miller, J.A., SENKIN: A FORTRAN Program for Predicting Homogeneous Gas Phase Chemical Kinetics With Sensitivity Analysis, Sandia National Laboratories, Albuquerque NM. Sandia Report SAND , Kramlich, J.C., Cole, J.C., McCarthy, J., Lanier, S.W., and McSorely, J.A., Combustion and Flame, Vol. 77, p. 375 ff., Caton, J.A., and Siebers, D.L., Combustion Science and Technology, Vol. 65, pp , Lyon, R.K., Kinetics and Mechanism of Thermal DeNO x : A Review, 194th Annual ACS Meeting, Div. of Fuel Chemistry, vol. 32, p. 433 ff., Heap, M.P., Brouwer, J., and Pershing, D.W., Prototype Demonstration of the Augmented Selective Reduction Process, Final Report, EPA contract No. 68D2121, July, Page 14

15 List of Figures: Figure 1. Schematic of the reduced SNCR model (numbers in parentheses correspond to reaction numbers in Table 1). Figure 2. Comparison of the reduced SNCR model to fully detailed chemical kinetic predictions for homogeneous, isothermal conditions at various temperatures. Figure 3. Effect of CO on SNCR with ammonia for homogeneous conditions with NOi = 5 ppm, NH3/NOi = 1.5, and a thermal quench rate of 26K/sec. Figure 4. Comparison of the reduced SNCR chemistry in JASPER with the full chemistry set and the data of Lyon for homogeneous conditions. Figure 5. Comparison of the reduced SNCR model to the data of Caton and Siebers (1989) for homogeneous conditions with and without CO. Figure 6. Comparison of the measurements of Teixeira et al. (1991) to predictions of the turbulent reacting flow model with the simplified SNCR chemical model for urea injection. Figure 7. Comparison of measurements and model predictions of ammonia slip for low quench rate (~4K/s), an injection temperature of 1267 K, NO i = 5 ppm and NH 3 / NO i = 1.5. Figure 8. Measurements and predictions of the effect of reagent jet/product stream momentum ratio on SNCR with and without CO at high and low quench rates. Page 15

16 Solid or Liquid Reagent Gaseous Ammonia vaporization, devolatilization cyanuric acid urea.3 HNCO NH (1) (5).9 (3) (4) NCO (2) N 2 O NO (6)(7) N 2 Figure 1. Schematic of the reduced SNCR model (numbers in parentheses correspond to reaction numbers in Table 1). 5 r r NO (full) pq o p qr p q p r r r p o o o qr o qr qp r o qop qop Temperature (K) NO (reduced) q NH3 (full) NH3 (reduced) p HNCO (full) HNCO (reduced) o N2O (full) N2O (reduced) Figure 2. Comparison of the reduced SNCR model to fully detailed chemical kinetic predictions for homogeneous, isothermal conditions at various temperatures. Page 16

17 Temperature (C) w/o CO 8 1 ppm CO 6 1 ppm CO 4 5 ppm CO Homogeneous Case Quench Rate = -26C/sec Figure 3. Effect of CO on SNCR with ammonia for homogeneous conditions with NOi = 5 ppm, NH3/NOi = 1.5, and a thermal quench rate of 26K/sec full chemistry JASPER - homog. 6 Lyon's data Temperature (K) Figure 4. Comparison of the reduced SNCR chemistry in JASPER with the full chemistry set and the data of Lyon for homogeneous conditions. Page 17

18 N/NOi data (w/ CO) 8 data (w/o CO) model (w/ CO) model (w/o CO) Figure 5. Comparison of the reduced SNCR model to the data of Caton and Siebers (1989) for homogeneous conditions with and without CO q 5 q 5 5 q 5 5 q 5 q q Temperature (K) 5 NO data q NH3 data 1 N2O data NO model NH3 model N2O model Data of Teixeira and Muzio, 1991 Figure 6. Comparison of the measurements of Teixeira et al. (1991) to predictions of the turbulent reacting flow model with the simplified SNCR chemical model for urea injection. Page 18

19 CO Injected (ppm) NH3 slip data NH3 slip model U-Furnace, FTIR measurements NO = 5 ppm i NH = 75 ppm 3i Figure 7. Comparison of measurements and model predictions of ammonia slip for low quench rate (~4K/s), an injection temperature of 1267 K, NO i = 5 ppm and NH 3 /NO i = Low Quench High Quench CO = Low Quench 8 CO = 75, Low Quench 6 CO =, High Quench 4 CO = 75, High Quench Model (CO = Low Quench) Model (CO = 75, Low Quench) Model (CO =, High Quench) Model (CO = 75, High Quench) Momentum Ratio (reagent/products) Injection Temperature = 1267 K Figure 8. Measurements and predictions of the effect of reagent jet/product stream momentum ratio on SNCR with and without CO at high and low quench rates. Page 19