Anthracite Oxy-Fuel Combustion in Fluidized Bed
Anthracite oxy-fuel combustion in fluidized bed
Isabel Guedea, Irene Bolea, Carlos Lupiáñez, Luis I. Díez, Luis M. Romeo CIRCE, University of Zaragoza, Spain
Pedro Otero, Jesús Ramos CIUDEN Ciudad de la Energía, Spain
Ponferrada, September 12th 2013 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel facility
3. Experimental activities
4. Modelling
5. Conclusions
2 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel facility
3. Experimental activities
4. Modelling
5. Conclusions
3 3 1. Introduction
Introduction
• Objective: Characterization of oxy-fuel combustion for a wide range of O2 in the fluidizing stream, and a combination of other operating variables • Combustion efficiency
• Control of emissions: SO2 and NOx
• Selection of fuel: Anthracite • Design fuel for oxy-firing at CIUDEN facilities
• Methodology: Experimentation in small-scale BFB and modeling to support experiments and simulate different conditions
4 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel facility
3. Experimental activities
4. Modelling
5. Conclusions
5 5 2. Oxy-fuel facility
6 2. Oxy-fuel facility
Main design features • Dual air- and oxy-fired bubbling fluidized bed reactor (850ºC, 1.0-1.2 m/s)
• 0.1 MWth thermal input • Two independent hoppers to feed coal, biomass, inert and/or sorbent
• O2/CO2 cylinders + mixer and wet flue gas recirculation • Flue gas circuit: cyclone, heat recovery, fabric filter • Water-cooling to control bed temperature • Modifications after initial design: secondary oxidant supply, fall chamber, several on-load solid sampling, fouling probes
Operation flexibility
• O2 in the mixture from 20% to 50% • Recycling ratios from 0% to 60% • Variety of fuels: anthracite, bituminous, lignite, culm waste, forest biomass
7 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel facility
3. Experimental activities
4. Modelling
5. Conclusions
8 3. Experimental activities
Research objectives
• Effect of O2/CO2 atmospheres and bed temperatures in: • Fluid-dynamics
• Combustion efficiency and CO2 production
• SO2 capture (limestone addition and sulphation mechanism)
• NOx control: oxygen staging and effect of limestone
Test campaigns • Low volatile fuels: anthracite • Spanish high-sulphur lignite • Blends and co-firing
9 3. Experimental activities
Anthracite Bituminous Lignite
Proximate analysis (% d.a.f.)
Volatile 15.07 19.89 45.81
Fixed carbon 84.93 80.11 54.19
Ultimate analysis (% d.a.f.) C 89.58 88.29 72.19
H 3.22 4.00 7.25
N 1.67 2.27 0.50
S 1.44 0.44 11.85
Mean Particle size (mm) 0.8 0.7 1.0
10 3. Experimental activities
3.1. Effect of • Bed temperature • Excess oxygen • Selection of limestone
… on NOx emissions for anthracite oxy-combustion
11 11 3. Experimental activities
Fluidizing Limestone Ca:S Bed temperature, Oxygen gas ratio Tbed (ºC) excess, Air None 0 800–875 1.6–1.7 #1 4 850 1.6 #2 4 850 1.6
40/60 O2/CO2 None 0 850, 875 1.6 #2 2.5 850 1.6
50/50 O2/CO2 #2 2.5 850–950 1.6
25/75 O2/CO2 #1 4 850, 900 1.1–1.7 #2 4 850 1.7
50/50 O2/CO2 #1 4 900 1.3–1.7
12 3. Experimental activities
• Use of limestone has been reported as a relevant factor affecting
NOx emissions in fluidized bed combustion (Miccio et al., de Diego et al., Hayhurst & Lawrence)
• Addition of limestone enhances NO formation, mainly due to the
catalytic effect of CaO, but also CaCO3 and CaSO4 can influence some formation/depletion reactions
• CaO increases NO formation rates, enhancing the presence of free
radicals (–O, –H, –OH) and favoring the NH3 conversion, rather than HCN
13 13 3. Experimental activities
No limestone
14 3. Experimental activities
25/75 O2/CO2
50/50 O2/CO2
Limestone #1, Tbed = 900ºC
15 3. Experimental activities
Tbed = 850ºC
16 3. Experimental activities
17 3. Experimental activities
Tbed = 850ºC
18 3. Experimental activities
3.2. Effect of • Oxygen-staging
… on NOx emissions for anthracite and lignite oxy-combustion
Two tangential ports for secondary supply: 40 cm and 80 cm over the perforated plate
Runs: 10%-20% secondary supply, 30/70 and 50/50 atmospheres
19 3. Experimental activities
30/70 O2/CO2
50/50 O2/CO2
Effect of O2 stagging (lignite, oxy-firing)
20 3. Experimental activities
30/70 O2/CO2
50/50 O2/CO2
Effect of O2 stagging (anthracite, oxy-firing)
21 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel rig
3. Experimental activities
4. Modelling
5. Conclusions
23 4. Modelling
Small-scale OF bubbling fluidized bed reactors: fluid-dynamics
• 1D, suitable for small-scale reactors
• Combination of empirical correlations and own experimentation
• On-line calculation of voidage, pressure distribution, gas and solid transfers in the bed and the free-board
24 4. Modelling
Small-scale OF bubbling fluidized bed reactors: solid conversion
• Specific fittings: • Devolatilization • Primary fragmentation • Char conversion
• On-line calculation of conversion rates and species released
• Separated model for SO2 capture is also available, based on limestone reactivity
25 4. Modelling
Small-scale OF bubbling fluidized bed reactors: global model
• Coupling of all considered phenomena in a global model to predict the performance of small- scale OF bubbling bed reactors
• Iterative process for a spatial discretization (grid independence)
• Local evolution of all relevant variables (pressure, temperature, solids concentration, chemical species, heat transfer rates)
• Validated with data gathered in experimentation at CIRCE OF-BFB
26 4. Modelling
ANTHRACITE LIGNITE BITUMINOUS
Test # 1 2 3 4 5 6 7 8 9 10
Fluidizing gas Air 30/70 30/70 30/70 Air 25/75 40/60 Air 35/65 40/60
uf (m/s) 0.87 0.97 0.86 0.81 1.26 0.90 0.84 1.30 0.90 0.83
Ca:S ratio 4 4 4 4 2.5 4 2.5 2.5 2.5 2.5
Secondary gas (%) 0 0 10 20 10 10 10 0 0 0
Tbed (ºC) 840 875 880 875 805 830 890 870 885 865
Tests to show model validation
27 4. Modelling
Temperature: model vs. experiment
AIR OXY Anthracite AIR 80 80 OXY OXY Lignite Exp #1 Model #1 Exp #5 Model #5 70 70 60 Exp #2 Model #2 60 Exp #6 Model #6 50 Exp #3 Model #3 50 Exp #7 Model #7 (cm) 40 (cm) 40
Exp #4 Model #4 H H 30 30 20 20 10 10 0 0 1070 1120 1170 1220 1070 1120 1170 1220 Tb(K) Tb(K)
28 4. Modelling
CO2 in flue gases: model vs. experiments
99 28 AIR OXY AF OF OXY ‐ ‐ 23 Model OXY OXY 94 OXY OXY (%) (%) 18 Exp. 2 2 AIR OXY 89 AIR CO 13 CO 84 8 12345678910 ANTHRACITE LIGNITE BITUMINOUS Test
29 4. Modelling
Small-scale OF bubbling fluidized bed reactors: global model validation
AIR 1500
1000 AIR OXY
(ppm) Model
500 Exp. CO OXY OXY AIR OXY OXY OXY OXY 0 12345678910 ANTHRACITE LIGNITE BITUMINOUS Test
30 4. Modelling
Detailed distribution in the reactor
Air 40/60 O2/CO2
Evolution of particle temperature
31 Anthracite oxy-fuel combustion in fluidized bed
1. Introduction
2. Oxy-fuel facility
3. Experimental activities
4. Modelling
5. Conclusions
32 5. Conclusions
• Selection of limestone is a relevant issue affecting NOx emissions in fluidized bed oxy-combustion
• Despite the increase of bed temperature can be suitable for a
higher SO2 capture efficiency (calcining conditions), NO formation ratios are also enhanced due to CaO availability
• Effect of oxygen staging has a different extent depending on the coal rank, not always leading to an effective reduction
• Oxy-combustion behaviour of anthracite is shown to be good,
with low CO records, and CO2 in flue gases over 93%
33 Thanks for your attention
www.fcirce.es Luis I. Díez, [email protected]
Acknowledgments: Spanish Ministry of Science and Technology, R&D National Program Fundación CIUDEN, Ciudad de la Energía