Ali Ahmadpour Ferdowsi University of Mashhad
Transcript of Ali Ahmadpour Ferdowsi University of Mashhad
Ali Ahmadpour
Ferdowsi University of Mashhad
Reactors
Flow Reactors Batch Reactors
Mixed Flow Reactors
(MFR)
Plug Flow Reactors
(PFR)
Continuous Stirred Tank Reactors
(CSTR)
Back Mixed Reactors
(BM)
Batch Reactors
Characteristics• Reactor is charged via two holes in the top of the tank;
• While reaction is carried out, nothing else is put in or taken
out until the reaction is done;
• Tank easily heated or cooled by jacket .
• This type are used for a variety of process operations.
• A typical batch reactor consists of a tank with an agitator
and integral heating/cooling system.
• These vessels may vary in size from less than 1 liter to more
than 15,000 liters .
• They are usually fabricated in steel, stainless steel, glass
lined steel, glass or exotic alloy .
Kinds of Phases Present
• Gas phase
• Liquid phase
• Liquid-Solid
CEB MKIIBatch Reactor
Usage• Small scale production
• Intermediate or one shot production
• Pharmaceutical
• Fermentation
• Solids dissolution
• Product mixing
• Chemical reactions
• Batch distillation
• Crystallization
• Liquid/liquid extraction
• Polymerization
Advantages• High conversion per unit volume for one pass
• Flexibility of operation - same reactor can produce one product at a time and different product the next
• Easy to clean
Disadvantages• High operating cost
• Product quality more variable than with continuous operation
Carbon Steel or
Stainless Steel
Reactors
Stainless steel reactors
for chemical plant
Glass Lined Reaction Vessel
Continuous Stirred
Tank Reactors
(CSTR)
Characteristics
•Run at steady state with continuous flow of
reactants and products;
•The feed assumes a uniform composition
throughout the reactor;
•Exit stream has the same composition as in
the tank.
Kinds of Phases Present
•Liquid phase
•Gas-liquid reactions
•Solid-liquid reactions
Usage•When agitation is required
• Series configurations for different
concentration stream.
CEM MK IICSTR
Advantages• Continuous operation
• Good temperature control
• Easily adapts to two phase runs
• Good control
• Simplicity of construction
• Low operating (labor) cost
• Easy to clean
Disadvantages
• Lowest conversion per unit volume
• By-passing and channeling possible with poor agitation
Batch reactor Semi-Batch reactor
Stirred contained solids reactors
Plug Flow Reactors
(PFR)
CharacteristicsArranged as one long reactor or many short
reactors in a tube bank ;
No radial variation in reaction rate
(concentration);
Concentration changes with length down the
reactor.
Kinds of Phases Present
Primarily Gas Phase
Usage• Large Scale
• Fast Reactions
• Homogeneous Reactions
• Heterogeneous Reactions
• Continuous Production
• High Temperature
Advantages• High conversion per unit volume
• Low operating (labor) cost
• Continuous operation
• Good heat transfer
Disadvantages• Undesired thermal gradients may exist
• Poor temperature control
• Shutdown and cleaning may be expensive
Tubular reactor
Plug-flow reactors for Biomass Conversion
Industrial scale Reactor
Homogeneous Continuous Reactions
(Plug Flow)
Reactive Distillation - Homogeneous
.
Reactive Distillation - Heterogeneous
creating plug-flow conditions in reactors
Fixed bed reactors
Fischer-Tropsch reaction convert synthesis gas into
a mixture of alkanes and alkenes over Fe catalyst.
Fluidized bed reactor
Four major chemical reactors
in petroleum refining
Ammonia converter
Methanol reactor
THE HUMAN REACTOR
Process Design
Matters for Design Consideration
(1) Type of processing Batch
Continuous
Semibatch or semicontinuous
(2) Type and nature of reacting system Simple
Complex (desirable,, undesirable products)
Stoichiometry
Phases, number of phases
Catalytic (choice of catalyst) or noncatalytic
Endothermic or exothermic
Possibility of equilibrium limitation
Cont.
(3) Type and size of reactor
Batch
Continuous (stirred tank , tubular, tower/column, bed )
(4) Mode of operation
Configurational (single-stage or multistage , axial or radial
flow, arrangement of heat transfer surface, flow pattern,
contacting pattern)
Thermal (adiabatic, isothermal , nonisothermal, nonadiabatic)
Use of recycle
Cont..
(5) Process conditions T profile
P profile
Feed (composition, rate)
Product (composition, rate)
(6) Optimality of process conditions
of size
of product distribution
of conversion
of cost (local, global context)
Cont…
(7) Control and stability of operation Instrumentation
Control variables
Sensitivity analysis
Catalyst life, deactivation, poisons
(8) Socioeconomic Cost
Environmental
Safety
(9) Materials of constructional corrosion
(10) Startup and shutdown procedures
Data Required
(1) Specifications
Reactants
Products
Throughput or capacity
(2) general data
Rate data/parameters relating to reaction (rate law/s, heat transfer, mass transfer, pressure drop, equilibrium data, other physical property data, cost data)
Tools Available The rational design of a chemical reactor is perhaps the most
difficult equipment-design task of a chemical engineer.
(1) Rate processes and rate laws Reaction kinetics
Diffusion and mass transfer
Heat transfer
Fluid mechanics (flow patterns , mixing, pressure drop)
(2) Conservation and balance equations Mass balances (including stoichiometry)
Continuity equation
Energy balance (including energetics of reaction)
Thermochemistry
Cont.(3) Equilibrium
Reaction equilibrium
Phase equilibrium
(4) Mathematics
Development of a reactor model
Analytical or numerical methods for solution of
equations
Simulation statistical analysis of rate data
Cont..(5) Computers and computer software
Use of a PC, workstations, etc., coupled with software packages to solve sets of algebraic and/or differential equations, and to perform statistical analyses necessary for implementation of a reactor model for design or for assessment of reactor performance
Software (spreadsheet packages, simulation software, numerical equation solvers, computer algebra system)
(6) Process economics
Mechanical Design
• Impeller or agitator design (as in a stirred tank)
• Power requirement (for above)
• Reactor-as-pressure-vessel design
• Wall thickness
• Over-pressure relief
• Fabrication
• Support-structure design
• Maintenance features