CZESTOCHOWA UNIVERSITY OF TECHNOLOGY Faculty of Environmental Engineering and Biotechnology Institute of Advanced Energy Technologies 3rd Oxyfuel Combustion Conference September 9-13 th 2013 Ponferrada, Spain The Effect of Excess Oxygen on Nitrogen Conversion in Oxy-Fuel CFB Environment Tomasz CZAKIERT, Grzegorz KRAWCZYK, Waldemar MUSKALA, Pawel BORECKI, Sylwia JANKOWSKA, Lukasz JESIONOWSKI, Wojciech NOWAK
NCR&D Project Advanced d Technologies for Energy Generation: Oxy-combustion technology for PC and FBC boilers with CO 2 capture Budget: ~25 mln USD Period: 2010-2015 Research on kinetics and mechanisms of oxy-fuel combustion Bench-scale experiments Small pilot-scale investigations (0.1MW th CFB, 0.2MW th PCFB, 0.5MW th PC) Oxygen production issues (incl. mobile ASU) CO 2 capture issues (incl. mobile CCU) General modeling work Feasibility study for a full chain demo-scale oxy-fuel plant with CCS Academies Czestochowa University of Technology Silesian University of Technology Wroclaw University of Technology R&D Centers Institute for Chemical Processing of Coal Institute of Power Engineering Industry Tauron Wytwarzanie Lagisza Power Plant PGE GiEK Turow Power Plant Foster Wheeler Energia Polska Eurol Innovative Technology Solutions
Experimental Conditions: inlet gas: O 2 + CO 2 O 2 fraction: 35%-vol. PG/SG ratio: 70/30 gas velocity: 1.81 m/s ( SG) 3.05 m/s ( SG) excess oxygen: 1.05, 1.15, 1.25, and 1.35 fuel: bituminous coal
Properties of Fuel lower heating value (LHV) ( kj / kg ) 21888 22728 Polish bituminous coal moisture (wt %) Proximate Analysis 15.0 16.0 volatile matter (wt %) fixed carbon (by difference) (wt %) 30.6 32.7 39.7 42.5 ash (wt %) 10.3 13.8 Ultimate Analysis C (wt %) S comb (wt %) H (wt %) N (wt %) O (by difference) (wt %) 55.6 58.0 1.25 1.31 3.74 3.86 0.85 0.90 8.82 10.01
Temperature and pressure Pressure loop remains in agreement with typical pressure balance around CFB loop (Basu P., Fraser S.A., 1991) Total pressure drop in combustion chamber (P2-P9) is kept at level of 2500Pa Pressure transition (+/-) is established at level of fuel feed point The oxy-fuel CFB test rig is not equipped with any internal or external heat exchangers that could be employed to control the temperature in the CFB loop. The temperature of inlet gas and the thickness of thermal insulation on the return leg remained unchanged during the experiment. An increase in excess oxygen from 1.05 to 1.35 results in a temperature drop of 100 K.
Calculations Conversion Ratio of fuel-n to NO molar ratio of N (fixed in NO)/ C (fixed in CO 2 & CO) in flue gas molar ratio of N/ C in fuel
Calculations N NO, NO 2, N 2 O, NH 3, HCN General assumptions: Main advantages: distributions of N & C within volatile matter as well as char is uniform CR of C to CO 2 + CO corresponds to burn-out ratio of combustible matter of fuel no other source of N than fuel independence from: changes in moisture and ash contents in fuel changes in volatiles-char ratio incomplete combustion losses measurements of fuel flux and O 2 & CO 2 flows CO 2 in flue gas is considered to derive from both: oxidation of C CO 2 in inlet gas fuel behavior is more transparent data can be compared directly
Results Carbon Conversion λ=1.05 C Carbon monoxide (CO) C Carbon dioxide (CO 2 ) progress in burn-out of combustible matter can be observed high value of CR C ( 65%) at level of FG1 (0.43m) further fuel burn-out; no oxidation of CO between FG1- FG2 (0.43-1.45m) carbon conversion gets slower above FG2 low value of CR C CO
Carbon Conversion Results λ=1.15 C Carbon monoxide (CO) C Carbon dioxide (CO 2 ) v results are quite similar increased value of CR C at level of FG1 (>70%) carbon conversion to CO remains low
Carbon Conversion Results C Carbon monoxide (CO) C Carbon dioxide (CO 2 ) increase of CR C at level of FG1 (>80%) higher value of CR C CO at level of FG1; drops down in upper part of combustion chamber λ=1.25
Carbon Conversion Results C Carbon monoxide (CO) C Carbon dioxide (CO 2 ) λ=1.35 results remain similar value of CR C ultimately exceeds 85% at level of FG1 oxidation of CO is almost completed at level of FG2
Nitrogen Conversion Results λ = 1.05 N Nitrous oxide (N 2 O) N Nitrogen monoxide (NO) N Nitrogen dioxide (NO 2 ) N Hydrogen cyanide (HCN) N Ammonia (NH 3 ) low value of CR N (<10%) nitrogen converts mainly to NO no CR N->NH3 observed N >NH3 slight amount of HCN (~1%) reduction of NO 2 to N 2 in the upper part of combustion chamber NO 2 appears at the bottom of combustion chamber
Nitrogen Conversion Results 25%O 2 @CO λ = 1.15 2 N Nitrous oxide (N 2 O) N Nitrogen monoxide (NO) N Nitrogen dioxide (NO 2 ) N Hydrogen cyanide (HCN) N Ammonia (NH 3 ) higher value of CR N (<20%) nitrogen converts mainly to NO no CR N->NH3 observed slight amount of HCN (~1%) higher reduction of NO & NO 2 to N 2 in the upper part of combustion chamber NO 2 appears at the bottom of combustion chamber
Nitrogen Conversion Results N Nitrous oxide (N 2 O) N Nitrogen monoxide (NO) N Nitrogen dioxide (NO 2 ) N Hydrogen cyanide (HCN) N Ammonia (NH 3 ) λ = 1.25 value of CR N >20% nitrogen converts mainly to NO no CR N->NH3 observed slight amount of HCN (~1%) higher reduction of NO & NO 2 to N 2 in the upper part of combustion chamber, however, it stats in the lower part of the furnace
Nitrogen Conversion Results N Nitrous oxide (N 2 O) N Nitrogen monoxide (NO) N Nitrogen dioxide (NO 2 ) N Hydrogen cyanide (HCN) N Ammonia (NH 3 ) value of CR N 25% nitrogen converts mainly to NO λ = 1.35 significant conversion to N 2 O no CR N->NH3 observed slight amount of HCN (~1%)
Conclusions Generally, fuel-nitrogen conversion (CR N ) does not exceed 25% and decreases with a decrease of excess oxygen. The decrease of excess oxygen is associated with an increase in temperature, and hence, the excess oxygen seems to be a crucial factor regarding the formation mainly of NO and N 2 O. The values of CR N N2O are the highest h at the lowest temperature t regardless of the highest excess oxygen. The reduction of NO was also observed, which affects the final emissions of NO X. The nitrogen conversion to NO 2 conversion to NO and N 2 O. was found to be much lower compared with the Ammonia was not detected at any level of the combustion chamber. HCN appears only locally, and it is to be considered as a residual impurity rather than a flue gas component.
THANK YOU FOR YOUR ATTENTION 3rd Oxyfuel Combustion Conference September 9-13 th 2013 Ponferrada, Spain