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Modelling Water Scrubbing Biogas Based Technology

Modelling Water Scrubbing Biogas Based Technology. William Nock, Sonia Heaven, Charles Banks Faculty of Engineering and the Environment, University of Southampton w.j.nock@soton.ac.uk. Promotion of Biogas Upgrading and Bottling in India and European Union. Why do we need a model?.

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Modelling Water Scrubbing Biogas Based Technology

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  1. Modelling Water Scrubbing Biogas Based Technology William Nock, Sonia Heaven, Charles Banks Faculty of Engineering and the Environment, University of Southampton w.j.nock@soton.ac.uk Promotion of Biogas Upgrading and Bottling in India and European Union

  2. Why do we need a model? • Description of real life situations • Tool to help design and operate a system • Provide predictions on how a system will behave under different conditions • “Everything should be made as simple as possible, but not simpler”- Albert Einstein Promotion of Biogas Upgrading and Bottling in India and European Union

  3. Modelling Approach Rate Based Models Equilibrium Based Models • Empirical design • HETP and HTU/NTU • 1D, 2D or 3D • Steady state or dynamic model • CFD Promotion of Biogas Upgrading and Bottling in India and European Union

  4. Modelling Assumptions • Well mixed system with negligible directional concentration gradients • Ideal Gas Law and ideal liquid flow • Isothermal reactor • Chemical reaction • Which species should mass transfer consider • Mass transfer liquid or gas side dominant? Promotion of Biogas Upgrading and Bottling in India and European Union

  5. Model Derivation LIN cL, Z cL, Z cG, Z+ΔZ cG, Z+ΔZ GOUT QL, Z QL, Z QG, Z+ΔZ QG, Z+ΔZ Δz cG, Z cL, Z+ΔZ cL, Z+ΔZ GIN QG, Z QL, Z+ΔZ LOUT Promotion of Biogas Upgrading and Bottling in India and European Union

  6. Plug Flow Reactor • Mass Balance: • No axial mixing • Perfect radial mixing cL, Z cG, Z+ΔZ QL, Z QG, Z+ΔZ z+Δz Δz Accumulation = input – output – reaction z cL, Z+ΔZ cG, Z QL, Z+ΔZ QG, Z Promotion of Biogas Upgrading and Bottling in India and European Union

  7. Axial Dispersion Model • Mass Balance: • Considers back mixing • Peclet number cG, Z+ΔZ cL, Z QL, Z QG, Z+ΔZ Δz Accumulation = input – output – reaction cG, Z cL, Z+ΔZ QG, Z QL, Z+ΔZ Promotion of Biogas Upgrading and Bottling in India and European Union

  8. Boundary Conditions Closed - Closed Open - Open Promotion of Biogas Upgrading and Bottling in India and European Union

  9. Mass Transfer Theory Interface • Two – Film Theory • Film thickness • Proportional to diffusion coefficient cG cGi Bulk Liquid Bulk Gas cLi cL Gas Film Liquid Film Promotion of Biogas Upgrading and Bottling in India and European Union

  10. Mass Transfer Theory Interface • Surface Renewal Theory • Contact time ‘packets’ in contact with interface • Proportional to square root of diffusion coefficient cG Bulk Liquid (cL) Bulk Gas (cG) cL Gas Film Liquid Film Promotion of Biogas Upgrading and Bottling in India and European Union

  11. Empirical Correlations • Henry’s Law • Mass transfer coefficients • Interfacial area • Pressure drop • Gas/ liquid holdup Promotion of Biogas Upgrading and Bottling in India and European Union

  12. Finite Difference • Numerical solution to ode and pde’s. • Explicit or implicit schemes • Discretisation techniques • Upwind scheme: • Multiphase counter-current flow • Gauss Seidel iteration Promotion of Biogas Upgrading and Bottling in India and European Union

  13. Finite Difference Promotion of Biogas Upgrading and Bottling in India and European Union

  14. Summary • Simple models often out perform more detailed models • Assumptions need to be taken with care Promotion of Biogas Upgrading and Bottling in India and European Union

  15. Thank you for listening Promotion of Biogas Upgrading and Bottling in India and European Union

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