Jet-NOx model Understanding nitrogen chemistry in biomassfired

Transcription

1 Jet-NOx model Understanding nitrogen chemistry in biomassfired boilers Markus Engblom a, Emil Vainio a, Anders Brink a, Mikko Hupa a, Erkki Välimäki b, Ville-Pekka Heikkilä b a) Åbo Akademi University, Turku, Finland b) Valmet Power, Tampere, Finland 70 th IEA-FBC meeting, June, Turku, Finland

2 Outline Model description Simulations Bubbling fluidized bed boiler Kraft recovery boiler Conclusions

3 Jet-NOx model Simplified fluid dynamics Furnace sections and air jets Detailed kinetics ÅA mechanism CHEMKIN reactor network Zwietering reactors

4 Zwietering reactor In Plug Flow Reactor Out Side stream

5 Zwietering reactor Air Jet jet length (l) Combustion air d 0 24 Furnace gas entrainment m = 0.25 l ρ 0 m 0 d 0 ρ furnace gas 1/2

6 Zwietering reactor Furnace section Fuel conversion - Moisture - Volatiles - Char-C - Char-N Furnace gas

7 Furnace height (m) T (C ) Temperature profiles Dp 3 mm Dp 5 mm Distance along jet axis (m) 10 5 T air in Temperature ( C) T jet_out = T furnace

8 Reactor network To next air jet / exit Fuel particle release profiles - Moisture - Volatiles - Char-C - Char-N Air jet Combustion air jet Entrainment of furnace gas into air jet Furnace section Furnace gas below first jet

9 Bubbling fluidized bed (BFB) boiler MW th, 118 bar, 535 C Valmet Power

10 Boiler parameters during the campaign Air distribution Fluidizing air: 50% Secondary air: 25% Tertiary air: 25% λ = 1.3 Bark / sludge / SRF 74 / 16 / 10 wt-% Temperatures Bed: 800ºC Peak temp. 1100ºC At bull nose level 950ºC In-furnace gas measurements

11 BFB simulations Prim 50%, sec 25%, tert 25% of total air Furnace temperature 1000 C Furnace gas below sec. air No in-flight release Gas composition NH ppm λ = 1.3 Air λ < 1 Air Fuel HCN 162 ppm NO 216 ppm H 2 O 31.4 Vol-% N Vol-% CO Vol-% CO 2.5 Vol-% CH Vol-% C 2 H Vol-% C 2 H Vol-%

12 BFB simulations Prim 50%, sec 25%, tert 25% of total air Furnace temperature 1000 C Furnace gas below sec. air No in-flight release Gas composition NH ppm λ = 1.3 Air λ < 1 Air Fuel HCN 162 ppm NO 216 ppm H 2 O 31.4 Vol-% N Vol-% CO Vol-% CO 2.5 Vol-% CH Vol-% C 2 H Vol-% C 2 H Vol-%

13 BFB simulations Secondary air jet TFN TFN = all nitrogen species except N 2 Temp. Temp. NH 3 TFN NO NO NO 2 N 2 O HCN

14 BFB simulations Secondary air jet Temp. NH 3 NO 2 NO TFN N 2 O HCN

15 BFB simulations Secondary air jet Temp. TFN NO 2 N 2 O NO NH 3 HCN

16 BFB simulations Measured gas composition NH ppm HCN 162 ppm NO 216 ppm H 2 O 31.4 Vol-% N Vol-% CO Vol-% CO 2.5 Vol-% CH Vol-% C 2 H Vol-% C 2 H Vol-%

17 BFB simulations Air Furnace section λ = 1.3 λ < 1 Air Fuel

18 BFB simulations Air Air Fuel

19 BFB simulations Tertiary air jet TFN Temp. NO NH 3 HCN N 2 O NO 2

20 BFB simulations λ = 1.3 Air λ < 1 Air Fuel

21 BFB simulations 10% 9% 27% 30% 95% 95%

22 BFB simulations Efficient NOx reduction NH 3 in furnace gas up to tertiary air Air jet NO, NH 3, O 2, T

23 Kraft recovery boiler 3000 tds/day DS 80% Air distribution Primary 32 % Lower secondary 32 % Upper secondary 22 % Tertiary 14 % λ =1.2 (Valmet)

24 Kraft recovery boiler Black liquor spraying Air Air Side view Top view (Valmet)

25 Kraft recovery boiler To next air jet / exit Fuel particle release profiles - Moisture - Volatiles - Char-C - Char-N Air jet Combustion air jet Entrainment of furnace gas into air jet Furnace section Furnace gas below first jet

26 Furnace height (m) Kraft recovery boiler CFD for profiles Temperature, moisture, volatiles, char-c, char-no T ( C) Volume-weighted average temperature Droplet NH 3 +NO release Temperature ( C) (gn/s/m)

27 Kraft recovery boiler N-release λ > 1

28 Kraft recovery boiler 26% 25% (TFN 100% NO)

29 Conclusions A model for calculations of NOx chemistry in pulp mill boilers BFB and Kraft recovery boiler BFB - NOx chemistry takes place in the air jets Recovery boiler - NOx chemistry between air levels Efficient in-furnace NOx reduction: NH 3, NO, and O 2 simultaneously present at temperatures favoring reduction

30 Acknowledgements Study financed by Valmet Power Oy Jet-NOx model development within FUSEC, Additional financial support from

31 More details... Vainio, E.; Brink, A.; Hupa, M.; Vesala, H.; Kajolinna, T., Fuel nitrogen reactions in a biomass fired FBC - measurements and kinetic simulations, proceeding of the 21 st International Conference on Fluidized Bed Combustion, Naples, Italy, June 3-6, ISBN , Vainio, E.; Brink, A.; Hupa, M.; Vesala, H.; Kajolinna, T., Fate of fuel nitrogen in the furnace of an industrial bubbling fluidized bed boiler during combustion of biomass fuel mixtures, Energy & Fuels, 26, pp , 2012, DOI: /ef201145j. Engblom, M., Vainio, E., Brink, A., Hupa, M., Välimäki, E., Heikkilä, V-P., Understanding the formation of NOx in pulp mill boilers, 2014 International Chemical Recovery Conference proceedings, pp , Tappi Press.