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Introduction to Chemical Reactors and Chemical Reaction Engineering
- 1. Department of Chemical Engineering University of Gujrat, Pakistan
- 2. The rate equation Chemical Reactors and their Applications The most useful measure of reaction rate for reactant A for a reaction aA +bB rR + sS Rate of reaction is some times influenced by composition and energy of material
- 3. Energy of material includes temperature, light intensity, and magnetic field intensity. So we can write Chemical Reactors and their Applications
- 4. Reactor System Homogenous Reaction Heterogeneous Reaction Check the reaction possibility of each state of matter with another???
- 5. Introduction Almost all chemical engineering process contains three operations. What does chemical reactor design means ? Unit operation (cleaning, crushing ) Chemical reactor Unit operation (separation) Raw material Product
- 6. Types of reactors 1.Batch- uniform composition everywhere in reactor but changes with time 2. Semi batch- In semi batch one reactant will be added when reaction will proceed 3. Continuous reactor a. Mixed flow- this is uniformly mixed , same composition everywhere, within the reactor and at exit b. Plug flow- flow of fluid through reactor with order so that only lateral mixing is possible. Differentiateb/wsemi-batch reactorandsystem???
- 7. Ideal Reactor Types Batch Reactor Uniform composition every where in reactor but changes with time Plug Flow Reactor Fluid passes through reactor with no mixing of earlier & later entering fluid, with no over taking like the fluid moved in single file through reactor Mixed Flow reactor Uniformly mixed same composition every wherewith in reactor and at exit Chemical Reactors and their Applications
- 8. Reactor design parameter Reactor design basically means which type, size of reactor and method of operation we should employ for a given conversation Parameters Volume of reactor Flow rate Concentration of feed Reaction kinetic Temperature pressure
- 9. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 10. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 11. Fixed Bed Reactors Concept – Collection of fixed solid particles. – The particles may serve as a catalyst or an adsorbent. – Continuous gas flow – (Trickling liquid) Chemical Reactors and their Applications Applications – Synthesis gas production – Methanol synthesis – Ammonia synthesis – Fischer-Tropsch synthesis – Gas cleaning (adsorption)
- 12. Fixed Bed Reactors Challenges/Limitations – Temperature control – Pressure drop – Catalyst deactivation Chemical Reactors and their Applications
- 13. Fixed Bed Reactors Challenges/Limitations – Temperature control – Pressure drop – Catalyst deactivation Chemical Reactors and their Applications
- 14. Fixed Bed Reactors Temperature control – Endothermic reactions may die out – Exothermic reactions may damage the reactor – Selectivity control How can we control exothermic & endothermic reaction in FBR?? Chemical Reactors and their Applications
- 15. Fixed Bed Reactors Single-Bed Reactor – All the particles are located in a single vessel Chemical Reactors and their Applications Advantages/Disadvantages – Easy to construct – Inexpensive – Applicable when the reactions are not very exo-/endothermic How can we control hot spots in FB??
- 16. Fixed Bed Reactors Multi-Bed Reactor – Several serial beds with intermediate cooling/heating stages Chemical Reactors and their Applications Advantages/Disadvantages – Applicable for exo-/endothermic reactions
- 17. Fixed Bed Reactors Chemical Reactors and their Applications SO3 reactorNH3 reactor
- 18. Fixed Bed Reactors Multi-Tube Reactor – Several tubes of small diameter filled with particles. Advantages/Disadvantages – Expensive – High surface area for heat exchange ⇒ Very good very temperature control – Applicable for very exo-/endothermic reactions Recall Shell & tube heat exchanger
- 19. Fixed Bed Reactors Reactor height: 30 m Number of tubes: 40-10000 Tube length: 6-12 m Tube diameter: 70-160 mm Chemical Reactors and their Applications Steam reformer
- 20. Fixed Bed Reactors Challenges/Limitations – Temperature control – Pressure drop – Catalyst deactivation Chemical Reactors and their Applications
- 21. Fixed Bed Reactors Pressure drop – Friction between the gas and particle phase results in a pressure drop. – High pressure drop ⇒ high gas compression costs – Some systems have low tolerance for pressure drop. – The pressure drop is mainly dependent on reactor length, particle diameter, void fraction and gas velocity. Chemical Reactors and their Applications
- 22. Fixed Bed Reactors Chemical Reactors and their Applications Large particles has to be used (dp>1mm).
- 23. Fixed Bed Reactors Porous catalyst particle – The particles are porous to increase the surface area of the catalyst. – Reactants are transported inside the pores by means of molecular diffusion – Adsorbption of reactant to the active sites where the reaction occurs. – Desorption of Products – Diffusion of product back to the bulk. – Heat is transported by conduction.
- 24. Fixed Bed Reactors Challenges/Limitations – Temperature control – Pressure drop – Catalyst deactivation Chemical Reactors and their Applications
- 25. Fixed Bed Reactors Catalyst deactivation – The catalyst gets deactivated if the active sites get contaminated. – Sulfur compounds deactivate Ni-catalysts Desulfurization is often necessary prior to reforming. – Formation of carbon deposits deactivate the catalysts. Large carbon deposits may clog the tubes, causing hot-spots that damage the reactor. – Catalyst regeneration is necessary. Chemical Reactors and their Applications
- 26. Fixed Bed Reactors Summary Advantages/Disadvantages – High conversion is possible – Large temperature gradients may occur – Inefficient heat-exchange – Suitable for slow- or non-deactivating processes Chemical Reactors and their Applications
- 27. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 28. Fluidized Bed Reactors Concept – Collection of solid particles dispersed in a continuous phase. – The particles may serve as a catalyst, adsorbent or a heat carrier. – Continuous flow of gas or liquid Chemical Reactors and their Applications Applications – Catalytic cracking processes – Fischer-Tropsch synthesis – Polymerization – Waste combustion – Drying
- 29. Fluidized Bed Reactors Chemical Reactors and their Applications
- 30. Fluidized Bed Reactors Chemical Reactors and their Applications A fluidized bed exhibits liquidlike behavior
- 31. Fluidized Bed Reactors Chemical Reactors and their Applications Continuous regeneration
- 32. Fluidized Bed Reactors Summary Advantages/Disadvantages – Conversion may be poor if gas is bypassing. – Erosion of vessel and pipe lines. – Uniform temperature – Efficient heat-exchange – Can handle rapid deactivating processes. Chemical Reactors and their Applications
- 33. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 34. Stirred tank Reactors Concept – Forced mixing by use of impeller. – Applied in reactive systems when mixing is the rate determining step. – Single phase: liquid mixing. – Two phases: liquid/gas, liquid/particle – Three phases: liquid/particle/gas Chemical Reactors and their Applications Typical applications – Chemical component and phase mixing – Fermentation reactor – Food and paper industry – Natural gas conversion/polymerization
- 35. Stirred tank Reactors The mixing is influenced by: – stirring rate and pumping capacity – liquid height – baffle design (baffles reduces solid body rotation) – size and geometry of the tank – size and geometry of heat equipment – size and type of impeller How can we add heat into the FBR, fluidized BR, STR??? solid body rotation??
- 36. Stirred tank Reactors Impellers – Radial flow impellers are suitable for dispersion of gas in liquid. – Axial flow impellers are suitable to blend liquids and suspend solids in liquids. Chemical Reactors and their Applications
- 37. Stirred tank Reactors Summary Advantages/Disadvantages – Uniform temperature – Efficient heat-exchange Exception: slurries with high concentrations of large particles (difficult mixing). Chemical Reactors and their Applications
- 38. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 39. Slurry loop Reactors Concept – Collection of solid catalyst particles dispersed in a liquid phase (slurry). – The slurry is circulating at a high velocity impelled by an axial pump. – The mixing pattern is very intensive and well defined. Chemical Reactors and their Applications Typical application – Polymerization
- 40. Slurry loop Reactors Summary Advantages/Disadvantages – Uniform temperature – Very efficient heat-exchange – Can operate at high polymer concentrations Chemical Reactors and their Applications
- 41. Reactor Concepts – Fixed bed reactors – Fluidized bed reactors – Stirred tank reactors – Slurry loop reactors – Bubble columns Chemical Reactors and their Applications
- 42. Bubble Columns Concept – Gas dispersed in a continuous liquid phase. – Two phases: liquid/gas. – Three phases: slurry/gas Chemical Reactors and their Applications Typical applications – Natural gas conversion – Waste water treatment – Bio-processes What is diffuser???
- 43. Bubble Columns Chemical Reactors and their Applications
- 44. Bubble Columns Chemical Reactors and their Applications
- 45. Bubble Columns Chemical Reactors and their Applications
- 46. Bubble Columns Summary Advantages/Disadvantages – Non-uniform product if bubble size distribution is heterogeneous – Uniform temperature – Efficient heat-exchange Chemical Reactors and their Applications
- 47. Chapter 5 Ideal Reactors for a single reaction (Chemical Reaction Engineering 3rd Edition by Octave Levenspiel) Chemical Reactors and their Applications
- 48. Mole balances for multiple reactionsMole balances for multiple reactions It is better to solve problems using moles (Nj) or molar flow rates (Fj) rather than conversion V CC r dt dC FVr dt dN V C r dt dC Vr dt dN r dV dC r dV dF r CC V r FF V r dt dC Vr dt dN BB B B BB B A A A A A A A A A A AA A AA A A A A ][ 00 0 0 0 0 0 0 − +=+= −== == − − = − − = == ν ν ν ν
- 49. Ideal Batch Reactor Things to supposed The composition is uniform throughout the reactor at any instant of time We may accounting about whole reactor Noting enters nor leave the reactor So for component A (Single reaction) Input = output + disappearance + accumulation Chemical Reactors and their Applications =0 0=
- 50. Disappearance = -Accumulation Chemical Reactors and their Applications Disappearance of A by Reaction (Moles/time) Accumulation of A (Moles/time)
- 51. Results 1. Time Required for conversion This is the general equation showing time required to achieve conversion XA for isothermal and non isothermal operation 2. Volume of reacting fluid and reaction rate Both remain under the integral sign and both change as reaction proceed
- 52. Chemical Reactors and their Applications
- 53. Chemical Reactors and their Applications 3. For constant density of fluid Equation 3 can be simplified as
- 54. 4. Volume of reacting mixtures changes with conversion Such as in single gas-phase reaction with significant density changes Chemical Reactors and their Applications Recall the expression Density = mass/volume
- 55. Space Time The natural performance measure of a batch reactor is time “t” It is denoted by τ τ = 1/s Unit = time “It is time required to process one reactor volume of feed measured at specified conditions” Thus a space time of of 3 min means that every 3 minute one reactor volume of feed at specified conditions is being treated by the reactor. Chemical Reactors and their Applications
- 56. Space Velocity It is reciprocal of space time It is denoted by s s = 1/τ Unit = 1/time “It is no of reactor volumes of feed at specified conditions which can be treated in unit time” Thus a space velocity of 5 hr-1 means that 5 reactor volumes of feed at specified conditions is being fed into the reactor per hour Chemical Reactors and their Applications
- 57. We may arbitrarily select the temperature , pressure, and state (s, l, g) at which we choose to measure the volume of material being fed to the reactor Then space time and space velocity depends upon the condition selected Chemical Reactors and their Applications
- 58. THANK YOU!