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SO 3 R eduction in the H eavy-oil F ired F urnace

SO 3 R eduction in the H eavy-oil F ired F urnace. Power Engineering Dept. Faculty of Mechanical Engineering and Naval Architecture University of Zagreb, Croatia. mr.sc. Daniel R olph Schneider Prof. dr.sc. Željko Bogdan.

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SO 3 R eduction in the H eavy-oil F ired F urnace

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  1. SO3Reduction in the Heavy-oil Fired Furnace Power Engineering Dept. Faculty of Mechanical Engineering and Naval Architecture University of Zagreb, Croatia mr.sc. Daniel Rolph Schneider Prof. dr.sc. Željko Bogdan

  2. Use of heavy-oil fuel, rich in sulphur, in combustors of steam generator • furnaces causes increased SOxemission. • Introduction • Certain amount of SO2 is transformed into SO3 . • SO3 reacts, at lower temperature, with water vapour forming sulphuricacid • causes low-temperature corrosion of the steam-generator sections.

  3. Mathematical model: coupled gas flow and liquid spray physics, non-premixedturbulent flame, Fluent code • turbulent flow: realizable k- model • radiation heat transfer: discrete ordinates model • liquid fuel spray: discrete second phase, “particle in cell”model • formation of the pollutants: NOx , postprocessor • combustion model: probability density function (PDF)formulation • reaction system: equilibrium chemistry formulation* *OK for major combustion species (except NOx and soot) but not goodenoughfor SO3 formation/destruction modelling! • SO3 model: model based on finite rate chemistry, implemented as User Defined Function routine

  4. Kinetics of SO3 formation/destruction: Recommended values for the third body reactants [M]: N2 /1.3/, SO2 /10.0/ and H2O /10.0/ KC – equilibrium constant

  5. Transport equation for SO3: • Mathematical model of SO3 formation: Schmidt-Prandtl number is: =0.7 is diffusion coefficient of SO3: The source term is defined as: The rate of SO3 change for the reactions (1) and (2) is:

  6. Results: • Mathematical model was applied to simulate SO3 formation in the furnace of a real steam generator of the 210 MW oil-fired Power Plant Sisak. • PP Sisakburns heavy-oil fuel with 2-3% sulphur and exhibits flue gas temperatures of 135-140 C at the exit of the regenerative Ljungström air-heater, reported occurrence of the severe low-temperature corrosion of the generator “cold-end” surfaces.

  7. Fig. 1. Discretization of the furnace Fig. 2. Schematic of the burner • two oil burners (Fig. 1) on each side-wall of the chamber • the burner consists of the axial/radial inflow type swirl generating register and the steam atomiser (Y-nozzle) • the airflow is divided into three streams: unswirled primary stream and then secondary and tertiary streams, which are swirled

  8. Analysis: • Influences of different combustion parameters on SO3 formation (and • CO, NOx, soot) were analysed: • combustion air excess ratio, • magnitude of the swirl of combustion air, • fuel droplet size (as a function of atomising steam pressure and number of the openings of atomiser) • fuel injection spray angle • combustion air distribution (portion of primary, secondary and tertiary stream)

  9. =0.965 =1.000 =1.035 =1.070 =1.105 =1.140 =1.175 =1.210 XSO3 Fig. 3. Distribution of SO3 for different combustion air excess ratios

  10. ~50% SO3 soot [-] soot Fig. 4. Molar fractions of a) SO3 and O , b) CO and H2 , c) NO and mean flue gas temperature, d) SO2and sootvs. combustion air excess ratio

  11. S=0.44 S=0.48 S=0.55 XSO3 S=0.63 S=0.68 S=0.71 Fig. 5. Distribution of SO3 for different swirl numbers

  12. ~30% SO3 soot [-] soot Sl. 6. Molar fractions of a) SO3 and O , b) CO and H2 , c) exit flue gas temperature and heat flux, d) SO2and sootvs. swirl number

  13. d=50 m d=70 m d=100 m d=130 m d=160 m XSO3 Fig. 7. Distribution of SO3 for different fuel droplet sizes

  14. 50-75% CO ~4.5% SO3 soot [-] soot Fig. 8. Molar fractions of a) SO3 and O , b) CO and H2 , c) NO and mean flue gas temperature, d) SO2and sootvs. fuel droplet size

  15. Proposed finite rate chemistry model of SO3realistically describes SO3 formation/destruction. • Conclusion: • Such a model could be used in analysis of SO3 reduction. • Decrease of the air excess ratio reduced SO3production, but increased CO and H2 (incomplete combustion). • Increase of magnitude of the swirl of combustion air, the fuel spray angle and finer spraying (smaller fuel droplet size) lowered SO3concentration in lesser extent than the air excess ratio, but improved combustion (reduced CO and H2formation). • The right strategy would be in combination of all these measures.

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