Chemical Reactors

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 MKII Batch 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 Disadvantages 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

Sequential Batch Reactors (SBR)

Carbon Steel or Stainless Steel Reactors

Stainless steel reactors for chemical plant

"Glass Lined Reactors"

Reaction Vessel (Reactor)

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.

Usage 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 II CSTR

Advantages Disadvantages 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

Semi-Batch reactor Batch reactor

Stirred contained solids reactors

Plug Flow Reactors (PFR)

Characteristics Kinds of Phases Present Arranged 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 Disadvantages 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

Fluidized bed reactor Fischer-Tropsch reaction convert synthesis gas into a mixture of alkanes and alkenes over Fe catalyst.

Four major chemical reactors in petroleum refining

THE HUMAN REACTOR

Process Design

Matters for Design Consideration Type of processing Batch Continuous Semibatch or semicontinuous 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. Type and size of reactor Mode of operation Batch Continuous (stirred tank , tubular, tower/column, bed ) 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.. Process conditions Optimality T profile P profile Feed (composition, rate) Product (composition, rate) Optimality of process conditions of size of product distribution of conversion of cost (local, global context)

Cont… Control and stability of operation Socioeconomic Instrumentation Control variables Sensitivity analysis Catalyst life, deactivation, poisons Socioeconomic Cost Environmental Safety Materials of constructional corrosion Startup and shutdown procedures

Data Required Specifications general data Reactants Products Throughput or capacity 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. Rate processes and rate laws Reaction kinetics Diffusion and mass transfer Heat transfer Fluid mechanics (flow patterns , mixing, pressure drop) Conservation and balance equations Mass balances (including stoichiometry) Continuity equation Energy balance (including energetics of reaction) Thermochemistry

Cont. Equilibrium Mathematics Reaction equilibrium Phase equilibrium Development of a reactor model Analytical or numerical methods for solution of equations Simulation statistical analysis of rate data

Cont.. Computers and computer software Process economics 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) 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