Flexible combustion of coal under elevated pressure

Janusz Lasek, Jarosław Zuwała, Krzysztof Głód

OUTLINE

1. Introduction

2. Experimental

3. Results

3.1. Emission issues

3.2. Dynamic characteristic issues

4. Conclusions

2/14

3/14

Pressurized oxy-fuel combustion

Why pressurized OXY-FUEL?More efficient NOx removal

(Seepana, S. and S. Jayanti2009, Lasek et al. 2012)

Higher powerdensity -> Smaller

power plant (Wall et al. 2002, thermoenergy

2011)

Higher process efficiency

(Hong et al. 2010, Hong et al. 2009, Chen et al. 2012)

4/14

Examples of pressurized oxy-fuel instalations and research groups

…a few only…

5/14

EXPERIMENTAL

Reactor:diameter 0.075m, height 1m, bed height 0.25mfuel tank capacity 0.004 m3

Exhaust gas analysis:FTIR analyzer (GASMET DX4000)O2 analyzers:paramagnetic (Oxymat 61) and zirconium sensor (AMS Analysen) Experimental conditions:T=750-910°Cp= 1-3.4 barO2=15-30 vol.%CO2=70-85 vol.%Fuel input: 0.37-0.98 kg/h

6/14

Experimental setup- real view

7/14

Aim: application of Flexi-burnTM procedure as „scientific tool”

FLEXI-BURN TM: IDEA

Air-fired

Air

Fuel

N2, CO2, H2O, O2…

Oxy-fuel

CO2, H2O, O2…

Fuel

O2

TIME

8/14

Pressurized oxy-fuel combustion- gas flow rate and temperature

Flexi-burn combustion of “Ziemowit” coal under elevated pressure (3.5 bar), fuel feed 0.47 kg/h and 0.72 kg/h for air-

and oxy-combustion (30/70) respectively

Gas flow rate Temperature

Impact of higher heat capacity of CO2

9/14

Pressurized oxy-fuel combustion- flue gas issues

Flexi-burn combustion of “Ziemowit” coal under elevated pressure (3.5 bar), fuel feed 0.47 kg/h and 0.72 kg/h for air- and

oxy-combustion respectively

Flue gas composition NO and N2O

Exmplanation of emission issues: higher CO and lower NO concentration during oxy-fuel tests

CO2 + C(s) ↔ 2CO Boudouard reaction (predominantrole) (Toftegaard et al. 2010, Krzywanski et al. 2010)

CO2 impact; competition for the H radicals (Chen et al. 2012. Toftegaard et al. 2010))

CO2 + H ↔ CO + OH H + O2 ↔ O + OHThe most reasonable explanation of the low NOx emission during oxy-fuel combustion issynergetic impact of radical reactions and promoting of CO on NOx reduction on char.Thus, the presence of CO2 significantly reduces the concentrations of importantradicals, i.e. O and H, leading to a reduction of the fuel burning rate (Chen et al. 2012). Itis postulated that CO2 pompetes for the H radicals. As it was mentioned by Toftegaard etal [2010], limitation of O radicals influences significantly NO formation.

10/14

Process dynamics, change of CO2 concentration in outlet during flexible change of combustion regime, „first order + dead time” model

Description of DYNAMIC PARAMETERS

t< Θ, NCO2(t)=0t≥ Θ, NCO2(t)=K{1-exp(-(t-Θ)/τp)}

NCO2(t)=(CCO2(t)-CinitialCO2)/(CfinalCO2-CinitialCO2)

11/14

12/14

Process dynamics, change of CO2 concentration in outlet during flexible change of combustion regime, „first order + dead time” model

Unit Time constant τp, hour „Dead time” Θ, hourLab-scale, 3 kg/h, PBFB 0.036 0.023Pilot-scale, 30 MWth boiler 0.141 0.126

t< Θ, NCO2(t)=0t≥ Θ, NCO2(t)=K{1-exp(-(t-Θ)/τp)}

13/14

Pressurized oxy-fuel combustion

The presentened experimental setup let to expand knowledge of the pressurized oxy-fuel combustion process.

Flexi-burn TM method can be succesfully used as „scientific tool” for better understanding of phenomena during oxy-fuel combustion. Emission issues and dynamic parameters were shown and determined.

More than 50% decreasing in NO emission was observed during oxy-fuel combustion.

14/14

THANK YOU FOR YOUR KIND ATTENTION

Research and Development Strategic Program “Advanced Technologies for Energy Generation” project no.2 “Oxy-

combustion technology for PC and FBC boilers with CO2 capture”, supported by the National Centre for Research and

Development, agreement No. SP/E/2/66420/10. The support is gratefully

acknowledged.

Chen L., Yong S.Z., Ghoniem A.F.: Oxy-fuel combustion of pulverized coal: Characterization, fundamentals, stabilization and CFD modeling. Progress in Energy and Combustion Science Vol.

38 Issue 2, April 2012, pp. 156-214.

Croiset, E.; Heurtebise, C.; Rouan, J.P.; Richard, J.R. Influence of pressure on the heterogeneous formation and destruction of nitrogen oxides during char combustion. Combustion and

Flame 1998, 112(1-2), 33-44.

Hämäläinen, J. P., & Aho, M. J. (1996). Conversion of fuel nitrogen through HCN and NH3 to nitrogen oxides at elevated pressure. Fuel, 75(12), 1377-1386. doi:

http://dx.doi.org/10.1016/0016-2361(96)00100-7

Hong, J.; Chaudhry, G.; Brisson, J.G.; Field, R; Gazzino, M.; Ghoniem A.F. Analysis of oxy-fuel combustion power cycle utilizing a pressurized coal combustor. Energy, 2009, 34, 1332–1340.

Hong, J.; Field, R.; Gazzino, M.; Ghoniem, A.F. Operating pressure dependence of the pressurized oxy-fuel combustion power cycle. Energy, 2010, 35, 5391-5399.

http://www.thermoenergy.com/energy-technologies.aspx

Krzywanski J., Czakiert T., Muskala W., Sekret R., Nowak W. Modeling of solid fuel combustion in oxygen-enriched atmosphere in circulating fluidized bed boiler. Part 2. Numerical

simulations of heat transfer and gaseous pollutant emissions associated with coal combustion in O2/CO2 and O2/N2 atmospheres enriched with oxygen under circulating fluidized bed

conditions. Fuel Processing Technology, 2010, 91, 364–368

Lasek JA, Janusz M, Zuwała J, Głód K, Iluk A. Oxy-fuel combustion of selected solid fuels under atmospheric and elevated pressures. Energy. 2013.

Lin, S.; Suzuki, Y.; Hatano, H. Effect of Pressure on NOx Emission from Char Particle Combustion. Energy & Fuels 2002, 16, 634-639.

Normann, F., Andersson, K., Leckner, B., & Johnsson, F. (2008). High-temperature reduction of nitrogen oxides in oxy-fuel combustion. Fuel, 87(17–18), 3579-3585. doi:

10.1016/j.fuel.2008.06.013

Seepana, S.; Jayanti, S. Flame structure and NO generation in oxy-fuel combustion at high pressures. Energy Conversion and Management, 2009, 50(4), 1116-1123.

Toftegaard, M.B., Brix, J.; Jensen, P.A.; Glarborg, P.; Jensen, A.D. Oxy-fuel combustion of solid fuels. Progress in Energy and Combustion Science, 2010, 36(5),

Tomeczek, J.; Gil, S. Influence of pressure on the rate of nitric oxide reduction by char. Combustion and Flame, 2001, 126(1-2), 1602-1606.

Wall Terry F. , Liu Gui-su, Wu Hong-wei, Roberts Daniel G., Benfell Kathy E., Gupta Sushil, Lucas John A., Harris David J.. The effects of pressure on coal reactions during pulverised coal

combustion and gasification. Progress in Energy and Combustion Science 28 (2002) 405–433.

References/sources

1/12