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Chemical Process

Industries

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Summary of the Course

Illustrate of the chemical process of various

industries such as in refinery, petrochemicals, sulfuric

acid, chlor-alkali industry, cement, glass, dairy, sugar,

water, soap etc, with particularparticular emphasis on

sultanate applications.

Provide introdution of definition for equipments of

unit operations coupled with flowsheeting of process

design such as PFD and P&ID.

Chapter One

Definition of Chemical

Engineering & Unit Operations

What is Chemical Engineering

Definition found in a standard dictionary:

“A branch of engineering which involves the design and operation of large scale chemical plants, petrochemical, refineries, and the like.”

Another definition :

“Concerned with processes that cause substances to undergo required changes in their chemical or physical composition, structure, energy content or physical state.”

Chemical Engineer Tasks

Chemical Engineers convert scientific discoveries into marketable products.

They are involved in many aspects of chemical production, research, and design, as well as in the construction and operation of industrial plants.

They design equipment for safe storage and transportation of chemical solids, liquids, and gases,

Design control systems for chemical plants based upon data from lab experiments and pilot plant operations.

Chemical Engineers also perform tests and take measurements in order to determine the most efficient production methods

General Steps of Chemical Process

SEPARATION PROCESS

REACTION PROCESS

SEPARATION PROCESS

RAW MATERIALS

INTERMEDIATE PRODUCT

INTERMEDIATE PRODUCT

FINAL PRODUCT

Chemical Process Design

There is no standard steps

There is no single correct solution

There is always a need to find a better

solution from several alternatives

Given Information for a Process Design

Products needed and production rate

Purity of the desired product

Raw material to be used

Utility available

The process route

Expected market

Site selection

Results of Process Design Project

Process flowsheet description

Mass and energy balances results

Equipment sizing and specification

Economic feasibility analysis

Environmental requirements

The final report

Plant Operation

In the design of an industrial plant, the methods which will be used for plant operation and control help to determine many of the design variables. For example, the extent of instrumentation can be a factor in choosing the type of process and setting the labor requirements.

It should be remembered that maintenance work will be necessary to keep the installed equipment and facilities in good operating condition.

Lets look at the overall process flow of a

modern oil refinery:

The overall process is broken down into

individual subsets:

Physical Chemical

Thermal Catalytic

Distillation

Solvent extraction

Propane deasphalting

Solvent dewaxing

Blending

Visbreaking

Delayed coking

Flexicoking

Hydrotreating

Catalytic reforming

Catalytic cracking

Hydrocracking

Catalytic dewaxing

Alkylation

With Their Own Flow Arrangement:

Distillation

Fluid Catalytic Cracking

We notice….. The number of individual processes is large, each one can be broken

down into a series of steps that appear in process after process

The individual “steps” have common techniques and are based upon

the same scientific principles

Fluid Dynamics

Heat Transfer

Evaporation

Humidification

Gas absorption

Solvent Extraction

Adsorption

Distillation

Drying

Mixing

Classification

Fluidization

Filtration

Screening

Crystallization

Centrifugation

Materials handling

Fluid Dynamics

A study of the behaviour of fluids

In Chemical processes fluid streams flow from one

process to another through pipes and ducts.

Process fluids are moved by pumps and compressors

Fluid flowrates must be monitored by meters and are

controlled by valves.

Heat Transfer:

Process fluids may need to

be heated up to a certain

temperature

Heat from a process

stream may be recovered

This can be done by

contacting two streams in

a heat exchanger.

evaporators.mpg

Evaporation:

A special case of heat transfer, where a phase change takes place.

Concentrate a solution consisting of a volatile solute and a nonvolatile solvent

The volatile solute evaporates leaving a more concentrated solution.

Humidification:

Transfer of material between a pure liquid phase and a fixed gas phase

that is nearly insoluble in the liquid

Example: Water vapor is added to a air, and thus, cooling tower is used

to decrease water temperature

Gas Absorption

Also known as stripping

process

It is mass transfer operation

A soluble vapor is absorbed

from its mixture with an inert

gas by means of a liquid in

which the solute gas is more

soluble.

Example: the removal of

CO2 and H2S from natural

gas or syngas by absorption

into amines or alkaline salts

Leaching or Liquid extraction1/3

Leaching is a process in which the solid extraction

involves the dissolving of soluble matter from its mixture

with an insoluble solid

Liquid extraction is the separation of two miscible liquids

by the use of a solvent that preferentially dissolves one of

them.

Liquid extraction an alternative to distillation for difficult

separations

Example: leaching oil from seeds, and penicillin is

separated from fermentation broth by extraction with butyl

acetate

Leaching or Liquid extraction2/3

Leaching or Liquid extraction3/3

Feed Raffinate

Solvent Extract

Distillation

Flash distillation: production of a vapour by boiling the liquid mixture to be separated and then condensing the vapours without returning any to the still.

Return part of the condensate to the still under conditions where it can be in contact with the vapours on their way to the condenser. (rectification)

Either operation may be done in batch or continuous mode.

How does distillation work? 1/3

Distillation is defined as:

a process in which a liquid or vapour mixture of two

or more substances is separated into its component

fractions of desired purity, by the application and

removal of heat.

How does distillation work? 2/3

Distillation is based on the fact that the vapour of a boiling mixture will be richer in the components that have lower boiling points.

Thus, when this vapour is cooled and condensed, the condensate will contain the more volatile components. At the same time, the original mixture will contain more of the less volatile components.

Distillation is the most common separation technique and it consumes enormous amounts of energy, both in terms of cooling and heating requirements.

Distillation can contribute to more than 50% of plant operating costs.

How does distillation work? 3/3

Distillation columns are classified by the manner in which they are operated:

1. Batch, in which the feed to the column is introduced batch-wise. That is, the column is charged with a 'batch' and then the distillation process is carried out. When the desired task is achieved, a next batch of feed is introduced.

2. Continuous columns process a continuous feed stream. No interruptions occur unless there is a problem with the column or surrounding process units. They are capable of handling high throughputs and are the most common of the two types.

Continuous Distillation Columns Classified according to:

1. Nature of the feed that they are processing: Binary column - feed contains only two components;

Multi-component column - feed contains more than two components.

2. Number of product streams they have: Multi-product column - column has more than two product streams.

3. Where extra feed exits when used to help with the separation: Extractive distillation - where the extra feed appears in the bottom

product stream;

Azeotropic distillation - where the extra feed appears at the top product stream.

4. Type of column internals: Tray column - trays of various designs used to hold up the liquid to

provide better contact between vapour and liquid;

Packed column - packings are used to enhance vapour-liquid contact.

Main Components of Distillation Columns

A vertical shell where separation of liquid components is done.

Column internals e.g.trays/plates and/or packings which are used to enhance component separations.

A reboiler to provide the necessary vaporization for the distillation process.

A condenser to cool and condense the vapour leaving the top of the column.

A reflux drum to hold the condensed vapour from the top of the column so that liquid (reflux) can be recycled back to the column.

Liquid And Vapour Flows in A Tray Column

Trays and Plates1/2

Bubble cap trays

A riser or chimney is fitted over each hole, and a cap covers the riser. The cap is mounted with a space to allow vapour to rise through the chimney and be directed downward by the cap, finally discharging through slots in the cap, and bubbling through the liquid on the tray.

Trays and Plates2/2

Valve trays

Perforations are covered by caps lifted by vapour, which creates a flow area and directs the vapour horizontally into the liquid.

Sieve trays

Sieve trays are simply metal plates with holes in them. Vapour passes straight upward through the liquid on the plate. The arrangement, number and size of the holes are design parameters.

Packings Packings are passive devices designed to increase the interfacial area

for vapour-liquid contact.

They do not cause excessive pressure-drop across a packed section, which is important because a high pressure drop would mean that more energy is required to drive the vapour up the distillation column.

Packed columns are called continuous-contact columns while trayed columns are called staged-contact columns because of the manner in which vapour and liquid are contacted.

Adsorption

Adsorption is a separation process where the fluid is contacted

with small particles of a porous solid which selectively adsorbs or

complexes with certain components of the feed.

The solid adsorbent is usually held in a fixed bed.

Drying

Removal of water

(usually small amounts)

or other liquid from a

solid material to reduce

the content of residual

liquid to an acceptable

low value

Water may be removed

by presses or centrifuge

(mechanical) or

thermally by

vaporization

Induced motion of a material in a container

Random distribution into and through one another, of two or more

initially separate phases.

Agitation and Mixing

Fluidization

Is a particle-fluid interaction

When a gas or liquid is

passed upward through a

bed of particles, at a certain

velocity the particles will

become suspended in the

fluid.

Types: Fixed Bed and

Fluidized Bed

Filtration1/2

The removal of solid particles from a fluid by passing

the fluid through a filtering medium on which the solids

are deposited.

Filtration2/2

Crystallization

The formation of solid

particles within a homogenous

phase

Formation of solid particles in

a vapour, solidification from a

liquid melt, or crystallization

from liquid solution

A variety of materials are

marketed in crystallized form.

Many are vacuum units where

adiabatic evaporative cooling

induced super-saturation.

Centrifugation1/2

Many given particles settle under gravitational force at a

fixed maximum rate

To increase the settling rate we replace the force of

gravity by a much stronger centrifugal force.

More effective than gravity separators because they will

separate fine drops and particles and are much smaller in

size for a given capacity.

Cyclones: used for solids removal from gas:

Centrifugation2/2

cyclone

Materials handling

Materials handling

Classification:

Characterization of solids by size and shape

Done in a series of standard screens or woven wire test sieves

arranged serially on a stack, with the smallest mesh on the

bottom and the largest on top.

Comminution

Size reduction of solid particles , for example, chunks of coke

must be reduced to workable size

Compression, impact, attrition (rubbing) or cutting, crushers

and grinders are good examples.

Reactors 1/4

While not a unit operation, reactors are essential

process operations

They are identified on flowsheets by the type of

vessel and their flow:

Batch reactor

Continuous stirred tank reactor (CSTR)

plug flow or tubular reactor

Batch reactor

A tank or vessel where reactants have been placed and

products are removed

There is no inflow or outflow of reactants or products.

Reactors 2/4

Continuous Stirred Tank Reactor (CSTR) Run at steady state (ie no accumulation)

Very well mixed

Modelled as having no spatial variations in concentration, temperature, pH or

reaction rate in the vessel

T an C are identical everywhere in the vessel, they are the same at the exit as

in the tank.

Reactors 3/4

Reactors 4/4

Plug Flow or Tubular Reactor

Consists of a cylindrical pipe

Assume the flow is highly turbulent and there is no radial

variation in concentration.