chemical process industries - جامعة نزوى · from lab experiments and pilot plant...
TRANSCRIPT
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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.
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.
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
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
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.
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.
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:
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