Lesson 4 Flashcards
the synthesis of the
complete process as an assembly of units; each carrying out a
specific process operation.
process design
designed and manufactured by specialist firms
Proprietary equipment
- designed as special, one-off, items for particular processes
Non-proprietary equipment
Examples of Proprietary equipment
Pumps
Compressors
Filters
Centrifuge
Dryers
Examples of Non-Proprietary equipment
Reactors
Distillation Columns
Heat Exchangers
T/F: the
chemical engineer is not normally involved in the detailed design of
proprietary equipment.
T
- The chemical engineer’s job in design of Proprietary Equipment
- select and specify the equipment
needed for a particular duty - ; consulting with the vendors to ensure that the
equipment supplied is suitable
may be involved with the vendor’s designers in modifying
standard equipment for particular applications
Chemical engineers
T/F: The use of standard equipment, whenever possible, will reduce costs
T
are usually designed as special
items for a given project.
Reactors, columns and other vessels
In particular, reactor designs are usually unique, except where more
or less standard equipment is used; such as
agitated, jacketed,
vessel
will be designed to conform to recognized
standards and codes; this reduces the amount of design work
involved.
Distillation columns, vessels and tubular heat exchangers
The chemical engineer’s part in the design of “non-proprietary”
equipment is usually
limited to selecting and “sizing” the equipment.
In the design of a distillation column the design engineer will
typically
- determine the number of plates;
- the type and design of plate;
- diameter of the column; and the
- position of the inlet, outlet and instrument nozzles.
information on selection and sizing of equipment would then be transmitted, in the form of
sketches
and specification sheets
sketches
and specification sheets would be transmitted to ___ or ____ for detailed design
specialist mechanical design group,
or the fabricator’s design team,
is an essential
part of most production processes in the chemical and allied
industries; covering all processing stages, from the preparation of
reagents through to the final blending of products.
preparation of mixtures of solids, liquids and gases
equipment used in preparation of mixtures of solids, liquids and gases depends on:
- nature of the materials and
- degree of mixing required
Mixing is often associated with other operations
reaction and
heat transfer
T/F: * Liquid and solids mixing operations are frequently carried out as
batch processes
T
T/F: Specialized equipment is needed for mixing gases.
F (Seldom, because of their low viscosities, they’ll mix easily
T/F: The mixing given by turbulent flow in a length of pipe is usually
sufficient for most purposes.
in gas mixing
T
Turbulence promoters in gas mixing that increases the rate of mixing
orifices or baffles
Factors to take into account when choosing equipment for mixing liquids:
- Batch or continuous process
- Nature of the process (miscible liquids, preparation of solutions or dispersion of immiscible liquids)
- Degree of Mixing
- Physical properties (viscosity)
- Whether the mixing is associated with other operations (rxn and heat transfer)
can be used for the continuous mixing of low viscosity fluids.
Inline mixers
For other mixing operations, in liquid mixing, what are required?
stirred vessels or proprietary mixing
equipment
promote turbulent mixing in pipelines and provide an
inexpensive way of continuously mixing fluids
Static devices
simple mixing tee followed by a length of pipe equal to
10 to 20 pipe diameters, is suitable for mixing low viscosity fluids of?
50 milli poise
Examples of Inline mixers
Tee
Injection
Annular
are used when one fluid is
introduced into the flowing stream of the other through a concentric
pipe or an annular array of jets, mixing will take place by entrainment
and turbulent diffusion.
Injection mixers
Such devices should be used where one flow is much lower than the
other, and will give a satisfactory blend in about 80 pipe diameters.
Injection mixers
Inline mixers will give a satisfactory blend in about ___ pipe diameter
80
- The inclusion of _____ will reduce the
mixing length required.
baffles or other flow restrictions
effective in both laminar
and turbulent flow, and can be used to mix viscous mixtures
Static mixer (Kenics corporation)
are effective inline mixers for blending and
dispersing liquids
Centrifugal pumps
are the most
commonly used type of equipment for blending viscous liquids and
preparing solutions of dissolved solids.
Mixing vessels fitted with some form of agitator
The most suitable agitator for a particular application will depend
- type of mixing required
- capacity of the vessel
- fluid
properties, mainly the viscosity
Mixing occurs through the____ and on the microscopic scale,
- bulk flow of the liquid
- the motion of the turbulent eddies created by the agitator.
is the predominant mixing mechanism required for the blending of
miscible liquids and for solids suspension.
- Bulk flow
is important in operations involving mass and heat
transfer; which can be considered as shear-controlled processes.
Turbulent mixing
three basic types of impeller that are used at high Reynolds numbers
(low viscosity)
Turbine Impeller
Pitched bladed turbine
Marine Propeller
are essentially radial-flow devices,
suitable for processes controlled by turbulent mixing (shear-controlled
processes)
flat-bladed (Rushton) turbines
are essentially axial-flow devices,
suitable for bulk fluid mixing.
propeller and pitched bladed turbines
– force applied perpendicular to shaft
radial flow
– force applied in the same direction as the shaft
axial flow
are used for more viscous fluids and are called low-speed agitators
Paddle, anchor, helical ribbon
Selection chart can be used to make preliminary selsction of the agitator type based on?
Liquid viscosity and tank volume
Required to drive an agitator
Shaft power
In the laminar flow region, the index “𝑏” = ?
1
at high Reynolds
number the power number is independent of? and the indec c = ?
Froude number, 0
are used for blending low viscosity liquids in
large tanks, where it is impractical to use conventional agitators
supported from the top of the tank
Side-entering agitators
they are used with flammable liquids, particular care must be
taken in the design and maintenance of the shaft seals, as any
leakage may cause a fire.
Side-entering Agitators
For blending flammable liquids, the use of ___ should be
considered as an “intrinsically” safer option
liquid jets
Gases can be mixed into liquids using either
inline mixing
stirred vessel
vapor-liquid contacting devices
Can be used when a small amount of gas is fed or the gas dissolves completely
Inline mixing
The most common arrangement for gas-liquid mixing is ____ (Fig. 10.70b)
followed by _____
is an injection mixer
a static mixer
a long injection tube with multiple holes drilled in it
sparger
If a gas is injected into a stirred tank, the location of the gas injection
must be chosen based on
mixing pattern obtained with the
impeller that has been selected
The gas injection device is usually _____ and the openings are oriented to promote the desired
circulation of gas bubbles.
annular ring with multiple small
openings
are used to
analyze the gas bubble flow pattern and ensure that the gas hold-up
and interfacial area are adequate
computational fluid dynamics (CFD)
A small flow of liquid can be dispersed into a gas stream using
Spray nozzle
When large flow rates of vapour and liquid are to be contacted to
carry out mass transfer or direct heat transfer, what can be used ?
plate or packed
columns
Wet solids or?
pastes
are used for free-flowing solids.
Cone blenders
can be used for dry solids and for blending liquids
with solids.
Ribbon blenders
are used for kneading heavy pastes
and doughs.
Z-blade mixers and pan mixers
Most solid and paste mixers are designed for
Batch operation
type of equipment best suited for the pumping of gases in
pipelines depends on:
Flow rate
Differential pressure required
Operating pressure
Used where Gas has pressure drop is small,
Fans
for high flow-rates and moderate differential
pressures
axial flow compressors
for high flow-rates and, by staging, high differential
pressures
Centrifugal compressors
Fans are used when gas pressure drop is less than
35 cm H20 or 0.03 bar
can be used over a wide range of
pressures and capacities, but are normally only specified in
preference to centrifugal compressors where high pressures are
required at relatively low flow-rates
Reciprocating compressors
are the
principal types used in the chemical process industries
Reciprocating, centrifugal,axial flow compressors
Displacement Compressor with highest rpm
Screw compressor
Dynamic Compressor with highest rpm
Turbo Compressor
Highest Differential pressure compressor when used in multiple stage
Reciprocating
Sub-atmospheric pressure or?
vacuum
The production of vacuum (sub-atmospheric pressure) is required for
many chemical engineering processes like?
vacuum distillation, drying and filtration
The type of vacuum pump needed will depend on
- degree of
vacuum required - capacity of the system
- rate of air inleakage.
are
commonly used where moderately low vacuum is required, and moderate to high high flowrates such as in vacuum filtration
Reciprocating and rotary positive displacement pumps
Reciprocating and rotary positive displacement pumps are commonly used when the vacuum required is about?
10
mmHg (0.013 bar),
are versatile and economic vacuum pumps and
are frequently used, particularly in vacuum distillation.
Steam jet ejectors
They can handle high vapour flow rates and
Steam ejectors
using this in series can produce low pressures down to 0.1 mmHg or 0.13 bar
Steam jet ejectors
are used where very low pressures are required
diffusion pumps
very low pressure or?
Hard vacuum
Processes where very low or hard vacuum pressures are required
Molecular distillation
Used on molecular distillation
Diffusion pumps
are stored at low pressure in gas holders similar to those used for town
gas
gases
In storing gases these are most commonly used
Liquid-sealed type
These consist of a number of telescopic sections (lifts) that rise and fall as gas is
added to or withdrawn from the holder
liquid-sealed types
is used where the gas must be kept dry.
Dry-sealed type
the gas is contained by a piston moving in a large vertical cylindrical
vessel.
Dry-sealed type
are intrinsically safer for use with flammable gases than the
dry seal type; as any leakage through the piston seal may form an explosive
mixture in the closed space between the piston and the vessel roof.
Water-seal holders
Gases are stored at____where this is a process
requirement and to reduce the storage volume
High pressures
- For some gases, the volume can be further reduced by
Liquefying the gas
Refrigeration
They are used for reducing the volume of some gases by liquefying and refrigeration
Cylindrical and spherical vessels (Horton spheres) are used
will normally be the first choice for pumping
process fluids
Centrifugal pumps
Pumps used for metering
reciprocating and gear pumps
The efficiency of centrifugal pumps depends on their
size
The efficiency of reciprocating pumps is usually around
90%
are usually stored in bulk in vertical cylindrical steel tanks
Liquids
To store liqud what are used?
Fixed and floating-roof tanks
in this tank, a movable piston floats on the surface of the liquid and
is sealed to the tank walls.
floating-roof tank
are used to eliminate evaporation losses and, for
flammable liquids, to obviate the use of inert gas blanketing to prevent an
explosive mixture forming above the liquid, as would be the situation with a
fixed-roof tank.
floating-roof tank
are also used for storing
liquids, usually for relatively small quantities
Horizontal cylindrical tanks and rectangular tanks
T/F:The movement and storage of solids is usually more expensive than
the movement of liquids and gases, which can be easily pumped down
a pipeline.
T
tHE BEST EQUIPMENT FOR THE MOVEMENT AND STORAGE OF SOLIDS WILL DEPEND ON
tHROUGHPUT
Length of travel
Change of elevation
Nature of the solids
Nature of the solids
size
bulk density
angle of repose
abrasiveness
corrosiveness
wet/dry
are the most commonly used type of equipment for the
continuous transport of solids
belt conveyor
They can carry a wide range of materials economically over long and short
distances; either horizontally or at an appreciable angle, depending on the
angle of repose of the solids.
Belt conveyor
consists of an endless belt of a flexible material, supported
on rollers (idlers), and passing over larger rollers at each end, one of which is
driven.
belt conveyor
The belt material is usuall used in belt conveyor is usually
fabric reinforced rubber or plastics; segmental
metal belts
can be specified to withstand abrasive and corrosive materials.
Belt
also called worm conveyors
Screw conveyors
are used for
materials that are free flowing.
Screw conveyors
The basic principle of the screw conveyor has been known since the
time of
Archimedes
The modern conveyor consists of a
helical screw rotating in a Ushaped trough.
They can be used horizontally or, with some loss of capacity, at an
incline to lift materials.
screw conveyor
are less efficient than belt conveyors, due to the
friction between the solids but are cheaper and easier to maintain
Screw conveyor
They are used to convey solids over short distances, and when some
elevation (lift) is required.
Screw conveyor
can also be used for delivering a metered flow of solids.
screw conveyor
is used for movement of solids over relatively
short distances
Pneumatic conveying
It is generally suitable only for free-flowing particles in the range 20
μm to 50 mm, as finer dusts tend to stick to the pipes, while larger
particles are hard to entrain.
Pneumatic conveying
the solids are transported in suspension in a
gas or liquid.
Pneumatic conveying
In Pneumatic, The solids may be either dilute phase or dense, with void fraction typically
greater than
95% and 50%
In here, the The velocity of carrier fluid must be large enough to keep the
particles suspended.
Pneumatic conveyor
can be used for both horizontal and vertical
transport of solids, including making pipe turns
Pneumatic conveying
In pneumatc conveying these are avoided as these cause solids attrition and
pipe abrasion
Sharp turns
are a relatively new technology that is becoming
widely used in minerals handling
Pipe conveyors
is similar to a belt conveyor in that solids are
dropped onto a flexible belt
Pipe conveyor
The most widely used equipment where a vertical lift is required is the
Bucket elevator
consists of buckets fitted to an endless chain or belt, which
passes over a driven roller or sprocket at the top end.
Bucket elevator
can handle a wide range of solids, from heavy lumps
to fine powders, and are suitable for use with wet solids and slurries
Bucket elevators
The simplest way to store solids is to
Pile on the ground in the open air
This is satisfactory for the long-term storage of materials that do not
deteriorate on exposure to the elements;
Pile on the ground in the open air
Examples of Pile on the ground in the open air
the seasonal stock
piling of coal at collieries and power stations
For large stockpiles, ____are usually installed for distributing
and reclaiming the material; travelling gantry cranes, grabs and drag
scrapers feeding belt conveyors are used.
Permanent facilities
Where the cost of recovery from the stockpile is large compared with the
value of the stock held,____ should be considered
storage in silos or bunkers
Also called bins or hoppers
Overhead bunkers
are normally used for
the short-term storage of materials that must be readily available for
the process
Overhead bunkers
are arranged so that the material can be withdrawn at a steady
rate from the base of the bunker on to a suitable conveyor
Overhead bunkers
Bunkers must be carefully designed to ensure the free flow of
material within the bunker, to avoid
packing and bridging.
