Introduction to Catalytic Combustion

Description

In a clear and concise manner, this book explains how to apply concepts in chemical reaction engineering and transport phenomena to the design of catalytic combustion systems. Although there are many textbooks on the subject of chemical reaction engineering, catalytic combustion is mentioned either only briefly or not at all. The authors have chosen three examples where catalytic combustion is utilized as a primary combustion process and natural gas is used as a fuel - stationary gas turbines, process fluid heaters, and radiant heaters; these cover much of the area where research is currently most active. In each of these there are clear environmental benefits to be gained illustrating catalytic combustion as a "cleaner primary combustion process" . The dominant heat transfer processes in each of the applications are different, as are the support systems, flow geometrics and operating conditions. Cover Half Title Title Page Copyright Page Dedication Table of Contents Preface Acknowledgements Nomenclature Chapter 1. Introduction 1.1 The basics: Terminology and conservation equations 1.1.1 Commonly used terms 1.1.2 Classification of reactors 1.1.3 Momentum balances 1.1.4 Energy balances 1.1.5 Material balances 1.1.6 The coupling of material, energy and momentum balances 1.2 Catalytic combustion and transport processes 1.3 Catalytic combustion chemistry 1.4 Formation of NOx 1.5 Catalyst support systems 1.5.1 Pellets in a packed or fluidized bed 1.5.2 Multichannel monoliths 1.5.3 Parallel plates 1.5.4 Fibre pads and gauzes 1.5.5 Sintered metals 1.6 Palladium based catalysts for methane combustion 1.6.1 Influence of temperature on chemical composition of the catalyst 1.6.2 Catalyst dispersion 1.6.3 Catalyst poisoning and fouling 1.6.4 Catalyst/support interactions 1.6.5 Catalyst promoters 1.6.6 Additives to the catalyst support 1.6.7 Preparation of palladium catalyst 1.7 Example applications of catalytic combustion 1.7.1 Examples of primary combustion processes 1.7.1.1 Stationary gas turbines 1.7.1.2 Radiant heaters 1.7.1.3 Process heating 1.7.2 Examples of secondary combustion processes 1.7.2.1 Catalytic converters for gasoline (petrol) engines 1.7.2.2 Catalytic converters/traps for diesei engines 1.7.2.3 Catalytic incineration of organic emissions 1.8 Catalytic monoliths in NOx reduction reactors 1.9 System design 1.10 Summary Introductory Note to Chapters 2 to 6 Additional Reading on Catalytic Combustion Additional Reading on Catalytic Converters References Chapter 2. Thermodynamics, Kinetics and Transport Phenomena 2.1 Thermodynamics 2.1.1 Open and closed systems 2.1.2 The thermodynamic state 2.1.3 Equations of state 2.1.3.1 The ideal gas law 2.1.3.2 Non-ideal behaviour 2.1.4 Multicomponent mixtures 2.1.5 Energy balances in open and closed systems 2.1.6 Enthalpy changes in systems 2.1.6.1 Enthalpy change resulting from temperature change — the heat capacity 2.1.6.2 Enthalpy change with pressure 2.1.6.3 Enthalpy change due to compositionchange — the heat of reaction 2.1.6.4 The first law for an open steady state reacting system 2.1.6.5 Heat of combustion 2.1.7 Chemical reaction equilibrium — the equilibriumconstant 2.1.8 Catalyst decomposition pressure 2.2 Kinetics 2.2.1 Rate expressions and mechanisms 2.2.2 Homogeneaus combustion kinetics 2.2.2.1 Homogeneaus combustion of carbon monoxide 2.2.2.2 Homogeneaus combustion of hydrocarbons 2.2.3 Catalytic combustion kinetics 2.2.3.1 Adsorption 2.2.3.2 Langmuir Hinshelwood Hougen Watson reaction models 2.2.3.3 Rate models for catalytic oxidation reactions 2.2.3.4 Comments on the use of rate equations 2.2.3.5 Final word on catalytic rate models 2.3 Transport phenomena 2.3.1 Newton's law of viscosity 2.3.2 Flow regimes 2.3.3 Flow in ducts 2.3.3.1 The equation of continuity 2.3.3.2 The friction factor for flow in a duct 2.3.3.3 Flow in circular ducts 2.3.3.4 Flow in reetangular ducts 2.3.3.5 Flow in triangular ducts 2.3.3.6 Other shapes 2.3.4 Flow in porous media 2.3.5 Fourier's law of conduction and the energy equation 2.3.5.1 Conduction in one dimensional systems 2.3.5.2 Multidimensional systems 2.3.5.3 Conduction and convection influid systems — with and without reaction 2.3.5.4 Conduction in porous media 2.3.6 Boundary layers and the heat transfer coefficient 2.3.6.1 Boundary layer development over a heated flat plate 2.3.6.2 Boundary layer development in the entrance of a circular duct 2.3.7 Fick's law of diffusion and the species balance equation 2.3.8 Boundary layer development and the mass transfer coefficient 2.3.9 The mass and heat transfer analogy 2.3.10 External heat and mass transfer resistance in catalysis 2.3.11 Diffusion and reaction in porous catalysts 2.3.11.1 The effective diffusivity 2.3.11.2 The effectiveness factor 2.3.11.3 Non-isothermal effectiveness factors 2.3.11.4 Effectiveness factors with complex kinetics 2.3.11.5 Diffusion and reaction in complex catalyst geometries 2.3.12 Combined internal and external mass transfer resistance 2.3.13 Heat transfer by radiation Further Reading References Chapter 3. Modelling of Catalytic Combustion Reactors 3.1 Basic modeHing concepts 3.1.1 Types of equations 3.1.1.1 Constants and variables 3.1.1.2 Linear algebraic equations 3.1.1.3 Non-linear algebraic equations 3.1.1.4 Differential equations 3.1.2 Types of models 3.1.3 Choosing the model 3.1.4 Model validation 3.1.5 Overview/summary of the modelling process 3.2 Commercial software packages 3.3 Modelling of a single monolith channel 3.3.1 Basic model selection criteria 3.3.2 Model dimensionality 3.3.3 One dimensional steady state plug flow model — laminar/turbulent flow 3.3.3.1 1D pseudo-homogeneous plug flowmodel — steady state 3.3.3.2 1D heterogeneaus plug flow model — steady state 3.3.3.3 Heat and mass transfer coefficients 3.3.4 One dimensional steady state dispersion model — laminar/turbulent flow 3.3.5 Transient one dimensional models — laminar/turbulent flow 3.3.6 Two dimensional model in cylindrical coordinates — laminar flow 3.3.6.1 Momentum balance equations 3.3.6.2 Mass balance equation 3.3.6.3 The energy balance equation 3.3.7 Radiation modelling in a monolith channel 3.3.7.1 Integral approach to internal radiation transfer 3.3.7.2 Network of finite surfaces method for modelling internal radiation exchange 3.3.7.3 Estimating radiation loss from a monolith reactor 3.4 Modelling diffusion in the washcoat — steady state 3.4.1 1D approximation — steady state 3.4.2 Equations for solution in 2D — steady state 3.4.3 Evaluating the effectiveness factor in a monolith reactor simulation 3.4.4 Effectiveness factors for washcoats with multiple reactions — steady state 3.4.5 Transient diffusion reaction problems 3.5 Multiple channel honeycomb reactor models 3.5.1 Continuum model 3.5.2 Discrete method with honeycomb reconfiguration 3.6 Packed bed reactor models 3.6.1 One dimensional plug flow model of a packed bed reactor 3.6.1.1 1D pseudo-homogeneous PFR model foran adiabatic packed bed — steady state 3.6.1.2 1D heterogeneaus PFR model for anadi abatic packed bed — steady state 3.6.1.3 1D PFR models for a non-adiabatic packed bed — steady state 3.6.2 One dimensional dispersion model for a packed bed reactor 3.6.2.1 Pseudo-homogeneous 1D axial dispersion model for a packed bed — steady state 3.6.2.2 Heterogeneaus 1D axial dispersion model for a packed bed — steady state 3.6.3 Two dimensional model of a packed bed reactor 3.6.3.1 Pseudo-homogeneous 2D model for a packed bed — steady state 3.6.3.2 Heterogeneaus 2D model for a packed bed — steady state 3.6.4 Transport properties in packed beds 3.6.4.1 Fluid/solid mass and heat transfer coefficients in packed beds 3.6.4.2 Dispersion coefficients in packed beds 3.6.4.3 Thermal conductivities in packed beds 3.6.4.4 Bed to wall heat transfer coefficients in packed beds 3.6.5 Effectiveness factors in packed beds 3.7 Consolidated porous media models 3.8 Numerical methods 3.8.1 Methods for initial value problems 3.8.2 Introduction to boundary value problems 3.8.3 The basis of the finite difference method 3.8.4 Finite difference solution of a one dimensional dispersion model 3.8.5 The basis of the finite element method 3.8.5.1 Finite element discretization 3.8.5.2 2D discretization of a monolith reactor channel 3.8.5.3 2D discretization of the washcoat 3.8.5.4 Discretization error 3.8.5.5 Interpolation polynomials 3.8.5.6 The mathematical basis of the Galerkin finite element method 3.8.5.7 Integrating the weak form of the differential equation: The reference element 3.8.5.8 The matrix form of the elementary equations, assembling the global matrix 3.8.6 Finite element solution of a diffusion/reaction problern 3.9 Solution algorithms Further Reading References Chapter 4. Homogeneous Gas Phase Reactions 4.1 General combustion characteristics 4.1.1 Combustion chemistry 4.1.2 Auto-ignition 4.1.3 Burning velocity 4.2 Combustion models 4.2.1 Diffusion flame (laminar/turbulent) model 4.2.2 Premixed flame model 4.2.3 Shock tube model 4.2.4 Well stirred reactor model 4.2.5 Plug flow model 4.3 Structure of rigorous schemes 4.4 Inclusion of catalytic/surface terms 4.5 Flame stabilization 4.6 Summary References Chapter 5. Experimental Studies 5.1 Pre-ageing of combustion catalysts 5.2 Acquisition and analysis of catalytic rate data 5.2.1 Labaratory reactors 5.2.1.1 Tubular reactor 5.2.1.2 Temperature measurement 5.2.1.3 Stirred tank/spinning basket/Carberry reactor 5.2.1.4 Interna! recycle stirred tank/Berty reactor 5.2.1.5 Recycle tubular reactor 5.2.2 Error estimation 5.2.2.1 Errors evaluated using mathematical analysis 5.2.2.2 Errors evaluated using sensitivity analysis 5.2.3 Finding the kinetic expression 5.2.4 Inter- and intraphase mass and heat transfer 5.3 Performance of pilot-scale reactor experiments 5.3.1 Supply of air 5.3.2 Preheating of inlet stream 5.3.3 Fuel and air mixing 5.3.4 Temperature measurement 5.3.5 Flow measurement 5.3.6 Gas analysis 5.3.7 Data acquisition 5.3.8 Pressure drop measurement 5.3.8.1 Monoliths 5.3.8.2 Packed beds 5.4 Acquisition of transport property data 5.5 Measurements to characterize the catalyst system 5.5.1 The recipe 5.5.2 The support system 5.5.3 The catalyst coated/impregnated system 5.5.3.1 Pore size, volume and distribution 5.5.3.2 Hydraulic diameter of monolith 5.5.3.3 Transport distance in catalyst phase 5.5.3.4 Measurement of effective diffusion coefficients 5.5.3.5 Gravimetrie analysis 5.5.3.6 Catalyst distribution in the support 5.5.4 Catalyst loss from the reactor Further Reading on Catalyst Preparation References Chapter 6. Combustion Applications: Examples of Modelling Studies 6.1 Modelling a single monolith channel in 2D 6.1.1 Investigating the Nusselt and Sherwood numbers 6.1.2 Mass transfer limitation and the 'light-off' point 6.1.3 Oxidation of CO with LHHW kinetics — Multiple steady states 6.2 Radiation losses froma monolith channel 6.3 Diffusion in a monolith washcoat — use of diffusion barrier to reduce entrance temperature gradients 6.4 Understanding and interpreting literature results 6.5 Influence of intrusive measuring devices 6.6 Catalytic radiant heaters 6.7 Catalytic incineration of organic emissions 6.8 Summary References Appendix A Useful conversions Appendix B Physical properties of ceramic and metal supports Appendix C Physical properties of gases Appendix D Summary of dimensionless groups Appendix E Useful mathematical transformations Appendix F A note on symbols Index