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