Wood Workshop on Modelling and Simulation of Coal-fired Power Generation and CCS Process


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Wood Workshop on Modelling and Simulation of Coal-fired Power Generation and CCS Process

  1. 1. The Next Generation of Activated Carbon Adsorbents for the Pre- Combustion Capture of Carbon Dioxide. Power Plant Modelling Workshop at University of WarwickDr. Joe Wood,Prof. Jihong Wang, Simon Caldwell, Yue Wang
  2. 2.  Dr Joe Wood - Introduction ◦ Project overview ◦ Modelling objectives Simon Caldwell - Modelling of carbon capture at IGCC Power Plants ◦ Dispersion Model ◦ Adsorption Model Yue Wang - Modelling of power plant performance ◦ Heat recovery steam generator ◦ Gas turbine and heat recovery module
  3. 3.  General acceptance that CO2 emissions are affecting the climate UK emissions targets for power stations is a reduction from 500 to 50 gCO2/kWhr by 2030 (1)  Up to 18 GW of investment of CCS power stations is possible in the 2020s By 2030, 26% of global emissions from China, with 98% of power generation emissions from coal (2)  $2.7 trillion investment in power by 2030 (3)  50/50 split favouring pre-combustion to post- combustion capture (3) 1. Turner, A. et al. The Fourth Carbon Budget - Reducing emissions through the 2020s. London : Committee on Climate Change, 2010. 2. Grubb, M. Generating Electricity in a Carbon Constrained World. London : Elsevier, 2010. 3. Liang, X et al. 2011, Applied Energy, Vol. 88, pp. 1873-1885
  4. 4. Diagram based on Tampa Electric IGCC ProcessFlow Diagram, National Energy Technology Laboratory, USAhttp://www.netl.doe.gov/index.html
  5. 5. • Could provide a CO2 emission free process of the future• Reaction to form Syngas• Convert CO in to CO2 in water gas shift• Separation of CO2 and hydrogen Diagram based on Scottish Carbon Capture and Storage Centre http://www.geos.ed.ac.uk/sccs/capture/precombustion.html
  6. 6.  University of Birmingham (Simon Caldwell) Simulation of pre-combustion carbon capture ◦ Developing a model of the adsorption step ◦ Producing cyclic model including all PSA steps ◦ Developing model to incorporate complete carbon capture process Incorporates adsorption isotherms, mass transfer models, fixed bed model Unsteady state heat and mass balances Parameter estimation from experimental data
  7. 7. Project Overview T, P T, PSyngas Composition Composition Fuel gas tofrom WGS gas turbineReactor Dry Molar CCS Process Molar Flowrate Flowrate Molecular Molecular Weight Weight Composition: Hydrogen, Carbon dioxide, Carbon Monoxide, Nitrogen, Methane, Hydrogen Sulphide, Water
  8. 8. Typical PSA Process Water Gas Shift High Purity Product CO2 (60% H2, 40% CO2) Adsorption Purge Blowdown Pressurisation High Purity H2
  9. 9.  University of Warwick ◦ Modelling and simulation study of IGCC power generation process Integration of power plant and CCS models ◦ Investigations of  Dynamic response  Impact on power transmission and distribution network  Effect of CCS upon plant efficiency  Effect of different fuel types  Quantified analysis of the process with plant optimization
  10. 10.  Dr Joe Wood - Introduction ◦ Project overview ◦ Modelling objectives Simon Caldwell - Modelling of carbon capture at IGCC Power Plants ◦ Dispersion Model ◦ Adsorption Model Yue Wang - Modelling of an IGCC power plant ◦ Heat recovery steam generator ◦ Gas turbine and heat recovery module
  11. 11.  Model being developed for the removal of CO2 from a H2/CO2 gas mixture by adsorption  High CO2 content compared to post-combustion processes  High pressure – favours physisorption Hierarchical model developed in gPROMS Based on Axial Dispersed Plug Flow Model Current model looks at an Adsorption system for the separation of Carbon Dioxide and Nitrogen Literature review of CO2/N2 Adsorption Models on Zeolite 13X
  12. 12.  Equations  Component Mass Balance  Use of overall Mass balance:  Adsorption rate equation (Linear Driving Force):  Equilibrium Isotherm (Langmuir):
  13. 13.  Temperature, Pressure and Transport Properties ◦ Thermal Operating Modes  Isothermal  Adiabatic  Non-isothermal ◦ Momentum Balance  No pressure drop  Ergun’s Equation  Darcy’s Equation ◦ Mass Balance Coefficients:  Mass transfer coefficient  Dispersion coefficient  Diffusivity ◦ Heat Balance Coefficients:  Heat transfer coefficient
  14. 14.  Fixed bed for removal of CO2 from a N2 flow Capable of controlling pressure, input flowrates and temperature Limited to 200° and 25 barg C Maximum CO2 content of 25% restricted by the CO2 analyser Main output is CO2 mole fraction
  15. 15.  A simplified model was established where no adsorption takes place  Allows ability to validate model to be tested  Tests the response of the entire experimental system  Assumes system to be isothermal with no pressure drop Empirical models looking at response of the system without the bed were established Experiments run with bed filled with glass beads  Model Parameters identical to experiment (i.e. bed size, flowrates etc.)
  16. 16. 0.1 0.08CO2 Mole Fraction 0.06 Flowrate (ml/min) 8.5 Pressure (barg) 25 Experimental Output CO2 Mole Fraction 0.1 Model Output 0.04 Estimated Dispersion 2.75 x 10-6 Coefficient (m2s-1) Literature Dispersion ≃10-6 0.02 Coefficient (m2s-1) 0 0 200 400 600 800 1000 1200 Time (s)
  17. 17.  More complex model developed for simulation of the adsorption step Model Assumptions 1. Fluid flow is governed by axially dispersed plug flow model 2. Equilibrium relations are given by the Langmuir Isotherm 3. MT rates are represented by LDF equations 4. Thermal effects are negligible 5. Pressure drop represented by Ergun Equation Parameters Estimated  Dispersion coefficient, Langmuir Isotherm parameters  All other parameters match experiment conditions
  18. 18. 0.12 0.1CO2 Mole Fraction 0.08 Experimental Output Model Output 0.06 Flowrate (ml/min) 8.5 0.04 Pressure (barg) 25 CO2 Mole Fraction 0.1 0.02 Bed length (cm) 7.7 Experimental Adsorption 3.3 Capacity (mmol/g) 0 0 1000 2000 3000 4000 5000 6000 7000 8000 Time (s)
  19. 19.  Parameters Estimated: ◦ Langmuir Isotherm Parameters: ◦ Dispersion Coefficient Literature results vary widely for Isotherm parameters and often do not give Dispersion Coefficient values Start point for parameter estimation severely affects estimated value Parameter Range Closest Fit Dispersion Coefficient (m2s-1) 8.2x10-7  1.1x10-4 8.2x10-7 A (N2) (mol kg-1 Pa-1) 4.4x10-7  3.1x10-5 4.4x10-7 B (N2) Pa-1) 5.5x10-7  1.4x10-5 5.5x10-7 A (CO2) (mol kg-1 Pa-1) 1.9x10-5  6.5x10-4 1.9x10-5 B (CO2) (Pa-1) 5.4x10-6  5.0x10-4 5.4x10-6 CO2 Adsorption Capacity (mol kg-1) 1.29  3.61 3.61
  20. 20.  Validation of estimated parameters by testing them against a shorter bed Glass Experiment repeated with 5g Beads adsorbent instead of 18g, the remainder filled with glass beads  All other conditions kept the same Zeolite 13X Dispersion model used for glass bead part and adsorption model CO2/N2 Mixture for 5g adsorbent part
  21. 21. 0.12 0.1 0.08CO2 Mole Fraction 0.06 Flowrate (ml/min) 8.5 Experimental Output Pressure (barg) 25 0.04 Model Output CO2 Mole Fraction 0.1 Bed Length (cm) 2.4 0.02 Experimental Adsorption 2.8 Capacity (mmol/g) 0 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s)
  22. 22. Parameter Full Bed Best Estimate Short Bed Best EstimateDispersion Coefficient 8.2x10-7 8.2x10-7(m2s-1)A (N2) (mol kg-1 Pa-1) 4.4x10-7 4.4x10-7B (N2) Pa-1) 5.5x10-7 5.5x10-7A (CO2) (mol kg-1 Pa-1) 1.9x10-5 4.5x10-5B (CO2) (Pa-1) 5.4x10-6 2.5x10-5CO2 Adsorption 3.61 1.81Capacity (mol kg-1)  Dispersion coefficients and Nitrogen Langmuir constants kept constant as they approached their bounds  Other models fit adsorption capacity closer but with significantly different parameters
  23. 23.  Hierarchy model developed based on axial dispersed plug flow model Simplistic dispersion only model validated More complex adsorption model able to mimic experimental work ◦ 5 parameters estimated to give very close approximations to experiments
  24. 24.  Adsorption Model  Improve parameter estimation  Implement energy balance Pre-Combustion Model  Switch system to using Activated Carbon adsorbent  Move towards conditions found in pre-combustion capture (i.e. Hydrogen)  Produce cyclic PSA model Power Plant Model  Complete carbon capture unit model  Combine model together with power plant model
  25. 25.  Dr Joe Wood - Introduction ◦ Project overview ◦ Modelling objectives Simon Caldwell - Modelling of carbon capture at IGCC Power Plants ◦ Dispersion Model ◦ Adsorption Model Yue Wang - Modelling of an IGCC power plant ◦ Heat recovery steam generator ◦ Gas turbine and heat recovery module
  26. 26. Figure1. Simplified IGCC power plant procedureKey modules for IGCC process:a.GEM with auxiliary systems:Coal feed, ASU, Gasifier, WGS;b.Combined cycle system: Gas turbine, Heat recovery boiler, steamturbine.
  27. 27. Coal slurry feed systemPulverize coal to 5mm particles and mixed with water to feed coalslurry to the gasifier.Coal mill model has been developed from our previous work.
  28. 28. ASU unit in IGCC power plant• Supplies oxygen to gasification island/ sulphur removal processes• Optimal integration with gas turbine –efficiency
  29. 29. ASU unit in IGCC power plant Figure3 simplified ASU unit
  30. 30. The GEM (Gasification Enabled Module )unit• Use coal slurry oxygen and air to produce syngas;• CO shift promotes the CO2 content in syngas and prepare for the PSA removal;• Supply HP &LP steam to HRSG.
  31. 31. CO+H O  CO +H -41MJ/kmol 2 2 2 •Water gas shift reaction provide high partial pressure of CO2 preferred in PSA system • Improved hydrogen extraction; • Direct contact gas / liquid exchange • Increased power output through improved where water flows against a gas gasification waste heat recovery. stream passing upwards; • Considerably aid waste heat recover• Main model based on gas and solid and lower costs, and is especially phase mass balance and energy advantageous in a shifted scheme conservation; • All of the cooling train heat exchang are liquid – liquid making them much• Chemical reaction submodel smaller and cheaper inculdes devolatilization anddrying, homogeneous reactions and heterogeneous reactions; Figure 4 the GEM unit• Heat transfer submodel;• Slag layer submodel.
  32. 32. Brayton cycleGas turbine components:
  33. 33. Gas turbine mathematical model:The Compressor (Isentropic) block increases the pressure ofan incoming flow to a given outlet pressure. It determinesthe thermodynamic state of the outgoing flow along with thecompressors required mechanical power consumption at agiven isentropic efficiency.The realized output mass flow rate A characteristic time is used to delay the mass flow.
  34. 34. Gas turbine mathematical model:Mixes two fluids with or without phase change. TheMixer block calculates temperature, composition andpressure after an adiabatic mixing of two fluids. Theoutput enthalpy is the sum of the input enthalpies.The pressure of the resulting flow Pressure loss K is the pressure loss factor
  35. 35. Gas turbine mathematical model:The Reactor block computes the outgoing flow bus (FB)after one reaction, a heat exchange with the environmentand a pressure loss. Heat exchange with the surroundingenvironment is taken into account. In general, theoutgoing flow is not in chemical equilibrium as the Reactorperforms a chemical reaction depending on a rate ofreaction.
  36. 36. Gas turbine mathematical model:The Turbine (Isentropic) block decreases the pressureof an incoming flow to a given outlet pressure. Itdetermines the thermodynamic state of the outgoingflow along with the produced mechanical power at agiven isentropic efficiency. Subscripts, ‘s’ and ‘ac’ states for isentropic and actual change of state. h3  h4 oi  Turbine is adiabatic and used with gaseous flows h3  h4
  37. 37. This heat exchanger support counter flowThe Heat Exchanger block calculates the changeof state of two media caused by indirect heatexchange. It is assumed, that this heat transfer rate is constant over the area of the heat exchanger or it represents a mean of the heat exchange rate. To approximate the dynamic thermal behavior of the block, the heat exchanger is assumed to have a thermal mass The heat exchange with environment is divided in four parts:  both thermal masses (for flow 1 and flow 2) exchange heat with environment,Each of the two flows entering the heat exchanger exchange heat with environment.  both output flows exchanges heat with its ownthermal mass, The two thermal masses are not interacting, but they have a termrepresenting the heat exchange with environment.
  38. 38. • to complete the whole system modelling• implementation of the model to software environment;• integrate the model with CCS process model.