Modelling of Smelt Deposition in a Pressurized Entrained Flow Black Liquor Gasifier

Transcription

1 Modelling of Smelt Deposition in a Pressurized Entrained Flow Black Liquor Gasifier Christian Mueller, Rainer Backman, Maria Selenius, Mikko Hupa Åbo Akademi Process Chemistry Group Combustion and Materials Chemistry Turku, Finland Colloquium on Black Liquor Combustion and Gasification, May 2003, Park City

2 Objectives Wall Smelt Layer Prediction Smelt layer build-up Steady state smelt layer thickness Smelt layer flow Combination of Multi-Phase Thermodynamic Equilibrium calculations and CFD modelling capabilities ChemApp Fluent Based ÅA Furnace Model

3 Outline Melting behaviour of inorganic mixtures Smelt distribution in a pressurized entrained flow black liquor gasifier Modelling approach Results Conclusions

4 Melting Behavior of Pure Smelt 100 Portion molten phase [wt-%] = Na2S/Na2CO3 60/40 m/m 2 = mol-% NaCl 3 = mol-% K 4 = mol-% Na2S2 5 = mol-% K Temperature [ C] 2 1

5 ChemApp Programmer s Library of Subroutines Calculation of complex, multicomponent, multiphase chemical equilibria FactSage ChemApp ÅA Thermochemical Database Equilibrium Calculation Database Management Results Data Files

6 Liquor Specific Flow Temperature T 70 Flow temperature dependency on liquor composition at 30 bar Liquor T 70 [ C] Closed system 635 High potassium 665 High chlorine 670 High sulfidity 690 Typical inland 700 Sulfur free 765

7 Smelt Distribution in a Pressurized Entrained FLow Gasifier Black liquor-steam Air/Oxygen Strongly dependent on: - black liquor injection - air/oxygen injection - smelt bead size distribution

8 Computational Fluid Dynamics Syngas Mixture (CO, CO 2, H 2, H 2 O, CH 4 ) Oxygen CFD Code Fluent 6.1 Turbulence Chemistry-Energy Smelt-Bead Radiation Standard k-ε model Transport of hot syngas and oxygen ÅA-Deposition model Discrete Ordinates radiation model

9 ÅA Deposition Model Deposition due to mean flow effects: Inertial impaction Particle Tracking Deposition due to near-wall effects: Thermophoresis Turbulent impaction Diffusion Deposition Velocity Approach MEAN FLOW NEAR WALL

10 Combined Modelling Approach ChemApp-Fluent Gas composition, temperature and pressure (CFD) Particle trajectory (CFD) Equilibrium Reactor (ChemApp) Composition Input System Input Results

11 Steady-State Thickness of the Smelt Layer T W T 0 T 70 Steady-state smelt layer thickness [mm] tube wall T FG flue gas d = α λ ( T T ) 70 Wall ( ) ( ) T T + σ ε T T SG 70 SG 70 Q steam T steam d deposit d = steady state thickness [mm] λ = heat conductivity of deposit [W/mK] α = heat transfer coefficient [W/m 2 K] σ = Stefan-Boltzmann constant [W/m 2 K 4 ] ε = emissivity [-] T W = wall temperature [K] T SG = fluegas temperature [K] T 70 = deposit flow temperature [K]

12 Pressurized Entrained Flow Gasifier Case 1 Oxidiser: ~ 400m N3 O 2 /h swirling, S O2 = 0.8 Black Liquor: ~ 1000 kg/h 30 tilted from vertical Smelt: ~ 360 kg/h d Smelt = µm Gasifier atmosphere: x CO = 0.26 x CO2 = 0.16 x H2 = 0.27 x H2O = 0.3 x CH4 = 0.01 T SG = 1300 K p = 30 bar Cooled Screen Temperature: T W = 723 K Wall Temperature: T 70

13 u [m/s] Results Case 1 T [K] T P [K]

14 Steady-State Smelt Layer Thickness Case 1 Steady-State Smeltlayer Thickness [mm] Gasifier Height [m] Closed System (635C) Typical Inland (700C) Sulphur Free (765C)

15 Smelt Layer Smelt Transport/Smelt Rain Case 1 Smelt Transport [kg/m 2 s] Gasifier Height [m] Smelt Rain [mm/s]

16 Pressurized Entrained Flow Gasifier Case 2 Oxidiser: ~ 400m N3 O 2 /h swirling, S O2 = % tilted from vertical Black Liquor: ~ 1000 kg/h swirling, S = % tilted from vertical Smelt: ~ 360 kg/h d Smelt = µm Gasifier atmosphere: x CO = 0.26 x CO2 = 0.16 x H2 = 0.27 x H2O = 0.3 x CH4 = 0.01 T SG = 1300 K p = 30 bar Cooled Screen Temperature: T W = 723 K Wall Temperature: T 70

17 u [m/s] Results Case 2 T [K] T P [K]

18 Smelt Layer Smelt Transport/Smelt Rain Case 2 Smelt transport [kg/m 2 s] Gasifier Height [m] Smelt Rain [mm/s]

19 Steady-State Smelt Layer Thickness Case 2 Steady-State Smeltlayer Thickness [mm] Closed System (635C) Typical Inland (700C) Sulphur Free (765C) x-axis [m]

20 Conclusions Advanced modelling approach presented combining multi-phase thermodynamic equilibrium calculations and CFD (ChemApp & Fluent Based ÅA Furnace Model) Results indicate the potential of the new approach: - Influence of flow field and energy transfer on the smelt layer thickness - Smelt layer build-up rates - Local steady-state smelt layer thickness

21 Acknowledgement Akademi of Finland Tekes ChemCom Andritz Oy Foster Wheeler Energia Oy Kvaerner Power Oy Oy Metsä-Botnia Ab Vattenfall Utveckling AB