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Typical
steam circuit.
Steam
runs in a closed circuit. Steam starts from the boiler, is
utilised by the process and returns back via the condensate line.
Generation.
Heat is applied to water in the boiler. We convert water to gas,
steam. The resultant expansion, pressurizes the system. Steam is
forced out of the boiler by its own pressure. It moves into the
second stage ....
Distribution.
Steam
is carried by piping to various equipment that heat or process
material. Again, the steam is carried along because of pressure
changes within the system. Steam has now arrived at its point of
use.
Utilisation.
Heat
from the steam is now put to work. Special devices absorb heat
from steam to do different types of jobs. As the steam gives up
its heat through heat transfer or use, it condenses or changes its
state - this time from a gas back into a liquid. This is called
condensate. As condensate can lead to various problems in the
steam system, it is drained via steam traps almost
immediately.
Condensate
Return.
Condensate is that is already treated before entering the steam
circuit. If this is returned to the boiler, it can replace an
equal quantity of cold make-up water. This is not only energy-wise
but also helps save fuel.
Generation
- the boiler house and its controls.
The
boiler
Our
journey starts at the boiler house. Our boiler has to be safe,
efficient, its pressure and temperature must be well controlled.
Also, it has to be economical to run.
We explain boilers in
full in the "Boilogy"
section.
Boiler
Feedtanks
One
of the most important factors in keeping your boiler on-line is to
keep enough water in it. Otherwise the boiler will shutdown on a
low water condition. This is especially true with firetube boilers
that are fired automatically. That is why it is so important to
size a feedwater system so that it has the capability of
maintaining the proper water level in your boiler.
A
properly sized feedwater system will have a tank adequately sized
to feed your boiler and pumps selected to deliver that water at
the correct rate and pressure. Typical FWT size is 2.5 to 3 times
of generation.
Furnace
Space
in a boiler where a burner burns oil, gas or pulverized (finely
ground) coal.
Burners mix air with fuel to provide oxygen
in the combustion process. A burner sends heat into the boiler
tubes and it is set to maintain the correct pressure in the
boiler. If the boiler pressure falls because of growing steam
demand, the burner switches on to produce more steam from the
boiler. As long as the amount of steam being produced in the
boiler is as great as that leaving the boiler, the boiler will
remain pressurised. This maintains correct pressure. If correct
pressure is maintained, correct temperature is also maintained as
they are interlinked.
Combustion, stack losses etc are
covered in Chemistry.
Boiler
mountings -
for maximum safety
These are provided for the safe working of
boilers. A feed check valve, a main steam stop valve, a safety
valve, water level indicator, a fusible plug are some of the
mountings. They are mounted on the boiler shell and are a must for
every boiler.
• Feed
check valve
• Main steam stop valve
• Mobrey -
water level indicator
• Safety Valve
• Gauge
glass
• Feed pumps
• Fusible plug
• MSSV
Boiler
auxillaries - for high efficiency and economical running
These are used to improve the efficiency of the boiler. An
economiser, super heater and air pre-heater are the main
accessories. These are not a must for any boiler but are highly
desirable.
• Economisers
•
Super-heaters
• Air pre-heaters
Boiler
controls - for regulating boiler parameters
We must have an
excellent control on pressure and temperature as well as other
parameters in the boiler.
• Combustion
control
• Air control
• Feedwater level control
•
Blowdown control
• Furnace Pressure control
•
Steam temperature control
• Cold end temperature control
•
Soot blower control
Distribution
– piping steam to the plant.
The
boiler has one or two main steam pipes – called steam mains.
These branch outwards to smaller pipes which distribute steam to
various processes.
Boilers generate pressurised steam, as
it occupies less space. So, more steam can be produced by a
smaller high pressure boiler and transferred to the point of use
using small bore pipework. Steam pressure is then reduced at the
point of use.
The steam flows through the pipes losing heat
via radiation. As steam condenses to water, the pressure drops,
suctioning the steam forward. This pressure drop creates the flow
of steam through the pipes.
Condensate
and Air in the distribution system
Knowing
that it is virtually impossible to keep air, oxygen and carbon
dioxide from getting into a system, lets deal with getting them
out of a system. These gases become free when the steam
condenses.
We must drain condensate out of our distribution
system because it can
• reduce
heat transfer , and
• cause water hammer
We
also should evacuate air and other non-condensible gases because
they
• can
reduce heat transfer by reducing steam temperature and insulating
the system
• foster destructive corrosion
For
this, we use a device called a steam trap, which is simply an
automatic valve that opens for condensate , air and CO2 and closes
for steam. For economic reasons , the steam trap should do its
work for long periods with minimum attention.
Water hammer,
corrosion due to gases, etc. are fully explained in
Chemistry.
Piping
details and steam traps will be taken up in detail in Training
Level 2.
Once the steam has been employed in the process,
the resulting condensate needs to be drained from the plant and
returned to the boiler house. This loop is called the condensate
loop and is talked about later in this Module.
Utilisation
– steam and the process.
Steam is
generated, distributed and now it reaches the point of use. At the
point of use, steam gives up its energy to the process, ie, a heat
transfer takes place. Steam could be utilised for example, by any
of the following processes:
•
Jacketed
vessels
• Heat
exchanger
• Autoclave
•
Heater
battery
• Process
tank heating
Pressure
reduction
We control steam to the process on start-up and
also during normal working. Why?
•
On
startup, a gradually increasing flow of steam will be needed to
deliver slow heat build-up in the plant. As the process reaches
the desired temperature, the flow must be reduced.
•
More
important, steam is usually generated at high pressure, and the
pressure may have to be reduced at the point of use, either
because of the pressure limitations of the plant, or the
temperature limitations of the process.
We
therefore need a way to control the flow of steam. A PRV is a
special Pressure Reducing Valve which functions as a safety device
to keep the low pressure header from gaining more low pressure
steam than it can distribute. A variety of pressure control
options exist, from the simplest to the more complicated and
accurate pressure reducers.
1. Pilot
operated:
Ex: Spirax DP 17 / DP 143
2. Self-acting
diaphragm-type:
It is comparatively a low cost valve, and is
easy to maintain. It is a mechanical device and can be easily
looked after by the normal maintenance crew.
Ex: Steamline
Samson 41-23
3. Pneumatically
actuated valves: Compressed air is applied to a diaphragm in the
"actuator" to open or close the valve. The process has a
sensor which is relaying process conditions to the controller.
Depending on the set values, the controller compares the process
condition with the set value and sends a corrective signal to the
actuator, which adjusts the valve setting.
The
CV is an electro-mechanical device and is highly specialized. Its
accuracy is very high, but it is expensive. It needs trained
personnel for maintenance.
Ex: Samson 241-1, Arca
Distribution
end: On the steam mains and distribution lines, we
reduce pressure using a simple direct-acting pressure reducing
valve or a pilot operated valve. ( 1 or 2 above )
Utilisation
end: This is the process end, which is a more critical
area, and here control valves are used to control the flow of
steam. ( 3 or 4 above )
The
need to drain the heat transfer unit
When steam comes in
contact with condensate cooled below the temperature of steam, it
can produce another kind of water hammer known as thermal shock.
Steam occupies a much greater volume than condensate, and when it
collapses suddenly, it can send shock waves throughout the system.
This form of water hammer can damage equipment, and it signals
that condensate is not being drained from the system. Obviously,
condensate in the heat transfer unit takes up space and reduces
the physical size and capacity of the equipment. Removing it
quickly keeps the unit full of steam.
Fig.
Coil half-full of condensate can't work at full capacity.
As
steam condenses, it forms a film of water on the inside of the
heat exchanger. Non-condensable gases do not change into liquid
and flow away by gravity. Instead, they accumulate as a thin film
on the surface of the heat exchanger - along with dirt and scale.
All are potential barriers to heat transfer.
Fig.
Potential barriers to heat transfer: steam heat and
temperature
must penetrate these potential barriers to do their work.
The
need for Steam traps
All steam pipes and heat exchangers
are drained by steam traps placed at strategic locations. The job
of the steam trap is to get condensate, air and CO2 out of the
system as quickly as they accumulate.
• Condensate
does not transmit heat effectively. A film of condensate inside
plant will reduce the efficiency with which heat is
transferred.Condensate also causes water hammer.
•
Dissolved air causes corrosion.
In
addition, for overfall efficiency and economy , the trap must also
provide.
• Minimal
steam loss. Unattended steam leaks can be very costly.
•
Long life and dependable service. Rapid wear of parts quickly
brings a trap to the point of undependability. An efficient trap
saves money by minimizing trap testing, repair, cleaning, downtime
and associated losses.
• Corrosion resistance. Working
trap parts should be corrosion -resistant in order to combat the
damaging effects of acidic or oxygen -laden condensate.
•
Air venting. Air can be present in steam at any time and
especially on start -up. Air must be vented for efficient heat
transfer and to prevent system binding.
• CO2 venting.
Venting CO2 at steam temperature will prevent the formation of
carbonic acid. Therefore, the steam trap must function at or near
steam temperature since CO2 dissolves in condensate that has
cooled below steam temperature.
• Operation against
back pressure. Pressurized return lines can occur both design and
unintentionally. A steam trap should be able to operate against
the actual back pressure in its return system.
•
Freedom from dirt problems . Dirt is an ever-present concern since
traps are located at low points in the steam system. Condensate
picks up dirt and scale in the piping, and solids may carry over
from the boiler. Even particles passing through strainer screens
are corrosive and, therefore, the steam trap must be able to
operate in the presence of dirt.
A
trap delivering anything less than all these desirable operating
/design features will reduce the efficiency of the system and
increase costs. When a trap delivers all these features the system
can achieve.
• Fast
heat-up of heat transfer equipment.
• Maximum equipment
temperature for enhanced steam heat transfer.
• Maximum
equipments capacity.
• Maximum fuel economy.
•
Reduced labour per unit of output.
• Minimum maintenance
and a long trouble-free service life.
Sometimes
an applications may demand a trap without these design features,
but in the vast majority of applications the trap which meets all
the requirement will deliver the best results.
Types of
traps
There are three primary categories of steam traps:
1. Mechanical:
This trap is made up of mechanical apparatus that are driven by
the density of the condensate to operate a float or a bucket.
Float traps
In the
float steam trap a valve is connected to a float in such a way
that a valve opens when the float rises. As condensate enters the
trap, a float is raised and the float lever mechanism opens the
main valve to allow condensate to drain. When the condensate flow
reduces the float falls and closes the main valve, thus preventing
the escape of steam. The valve is positioned so that when the
float is at rest the valve is seated in the outlet of the trap,
ie, it is closed.
 2. Thermodynamic:
In addition to downstream flash steam assist, this type of trap
operates on the difference in velocity or kinetic energy between
steam and condensate passing through a fixed or modulating
orifice. These are mostly used for mainline applications. They are
comparatively cheap. This is a blast discharge trap, not a
continuous discharge type. There is a build -up of condensate
which is then discharged at one go. The float inside this trap is
mechanically coupled to a valve.
Thermodynamic traps
contain a disc which opens to condensate and closes to steam. This
trap is reliable, effective and has a long life. The float is made
of pressed SS on Titanium and the body is generally CS or cast
iron. There are 10 times as many TD traps compared to float traps.
3. Thermostatic:
This type of trap operates on the principle of expanding liquids
and metals used to drive a valve into or back it away from a seat.
There are two basic designs for the thermostatic steam trap, a
bimetallic and a balanced pressure design. Both designs use the
difference in temperature between live steam and condensate or air
to control the release of condensate and air from the steam
line.
These are mostly used for process applications. These
traps are used in 10% of total applications. They are reliable but
expensive, so only used in critical applications.
Which
trap is preferred depends on the application. A steam trap prime
missions is to remove condensate and air preventing escape of live
steam from the distribution system. The steam trap must adapt to
the application. A disc thermodynamic steam trap should never be
used together with a modulating heat exchanger - and a floating
ball steam trap is overkill for draining steam pipes.
In
most cases, when start-up occurs, we bypass the trap. The cost of
traps rise exponentially with increasing pipe size. This way ,
when the normal load comes on and condensate reduces, we can
function with a much smaller trap.
Keeping cost in mind, we
can also decide to use cheaper (and efficient ) traps for non-
critical applications like the steam lines, and more expensive
ones for critical areas like process.
Practically, we need
to install traps every 30 M in a stream line. But, if we are using
cheaper traps, we can even reduce this distance to 25 M for
increased reliability of trapping and replace as & when
required.
Good design practice
In terms of
configuration, this should include, among other things, the
following: proper slope, the elimination of pockets, proper
trapping of condensate when pockets do occur, strategic location
of steam traps and a configuration that integrates flexibility to
keep the system piping itself within allowable stress ranges
during expansion and contraction cycles.
Condensate
return.
Condensate is the by -product of heat
transfer in a steam system. It forms in the distribution system
due to unavoidable radiation. It also forms in heating and process
equipment as a result of desirable heat transfer from the steam to
the substance heated. Onces the steam has condensed and given up
its valuable latent heat, the hot condensate must be removed
immediately.
Often, the condensate which forms will drain
easily out of the plant through a steam trap. The condensate
enters the condensate drainage system. If it is contaminated, it
will probably be drained.
Although the available heat in a
kg of condensate is small as compared to a kg of steam, condensate
is still valuable hot water and should be returned to the
boiler.
If not, the valuable heat energy it contains can be
retained by returning it to the boiler feedtank. This also saves
on water and water treatment costs.
Sometimes a vacuum may
form inside the steam using plant. This hinders condensate
drainage, but proper drainage from the steam space maintains the
effectiveness of the plant. The condensate may then have to be
pumped out.
Steam powered mechanical pumps are used for
this purpose. These, or electric powered pumps, are used to lift
the condensate back to the boiler feedtank. Steam and the
condensate system represents a continuous loop.
Fig
Steamline CRPS50
Once
the condensate reaches the feedtank, it becomes available to the
boiler for recycling.
Steam consumption
Now
almost all clients are very energy conscious and it is common for
customers to monitor the steam consumption of their plant.Steam
flowmeters measure the steam consumption, and are used to allocate
costs to individual departments or items of plant.
..More
details in Level 2.
Pipeline
accessories.
The steam pipeline has many
accessories, all designed for special purposes and needs.
• Stop
Valves
• Bypass valves
• Non-return Valves (NRV)
and Disc Check Valves (DCV)
• Control Valves (CV)
•
Pressure Reducing Valves (PRV)
• Strainers
•
Moisture Separators (Msep)
• Traps
• Pressure
gauges (PG)
• Pressure sensors
• Temperature
gauges (TG)
• Temperature sensors
• Vacuum
Breakers (VB)
• Safety Valves (SV)
Stop
Valves
These are basic valves that shut off or supply
steam, water or air supply to the downstream end. These come in
three basic types:
• Ball
•
Gate
• Globe
Our
PRS for example has two stop valves one at the inlet and the other
at the outlet.
Bypass
Valve
This valve are the normal stop valves, but installed
in a bypass line, which can be used to bypass a piece of
equipment, or a section of pipe during routine maintenance, when
new fittings are to be put online, or removed.They are usually
Globe valves.
For example, if the trap needs maintenance,
the stop valve before trap is shut, the bypass opened, and the
trap taken out.
Non-return
Valves (NRV) and Disc Check Valves (DCV)
These
are used to ensure flow in a certain direction only. Take a look
at this NRV on the steamline pump inle
Control
Valves (CV)
These
are valves that provide automatic controls in a process plant,
especially in the critical process areas. Their job could be any,
or all the following:
• Safety
- The plant or process must be safe to operate.
Dangerous and
complex plants or processes need automatic controls for safety.
•
Stability - The plant or processes should work steadily,
predictably and repeatably, without fluctuations or unplanned
shutdowns.
• Accuracy - This is a primary requirement
in processes to prevent spoilage, increase quality and production
rates, and maintain comfort.
• Economy, speed, and
reliability are other desirable benefits.
There
is normally a Sensor, that senses the process Parameter
to be Controlled, sends it to a Controller, which
matches it with a predetermined Set Point, and Actuates the
Control Valve to make the required adjustments
Pressure
Reducing Valves (PRV)
These
are specialized Control valves that provide steam at the correct
pressure for the process.
Strainers
These
keep steam clean, and free of dirt, and grit by straining them out
of the system.
Ref:
Chemistry / Quality of steam/ Clean, clean steam
Moisture
Separators (Msep)
This
eliminates wet steam from the process which is the cause of
corrosion and decreased efficiencies.
Ref:
Chemistry / Quality of steam/ Dry steam
Traps
No
matter how much we try, the twin enemies of our steam system –
air and condensate – will be present in our system in some
degree. Steam traps are used to drain condensate and air from
steam lines and heat transfer units, and are a must on every
equipment to prevent air and water related problems.
Pressure
Gauges (PG)
We
use a simple Bourdon tube type pressure gauge. It is a tube, one
end sealed and the other is open from which the gas or liquid
enters. This causes a distortion in the tube proportional to the
pressure of the process.
Our dial is normally 150 mm in
diameter and, is marked to indicate the normal working pressure
and the maximum permissible working pressure / design pressure.
Fig.
Pressure gauge
Pressure
gauges are connected to the steam space in the PRS and usually
have a ring type siphon tube which fills with condensed steam and
protects the dial mechanism from high temperatures. All Steamline
PRS's, for example are fitted with two pressure gauges. The inlet
PG helps the boiler operator to visually monitor the inlet
pressure, to check if the steam is being supplied at the correct
pressure. The outlet PG is used by him for setting and monitoring
the outlet pressure by looking at the gauge, if required. We also
fit a pressure gauge to our flash vessels to see at what pressure
flash steam is being generated.
Pressure
sensors
These sense the process parameter – Pressure,
and return a signal to a Controller.
Temperature
Gauges (TG)
The TG helps the Utilities staff to visually
monitor the temperatures, either of steam or process.
Temperature
sensors
These sense the process parameter –
Temperature, and output a signal to a Controller.
Sight
glass
Through a sight glass, we can see the water levels,
water flow and also the colour of the process, if need be. Traps
sometimes have a sight glass mounted to check correct working.
Also, if a valve or strainer is blocked flow will be affected and
that too can be checked visually.
Vacuum
Breakers (VB)
Steam, when it condenses, ie, cools, becomes
water and shrinks tremendously in volume. What happens? Around it
we have suddenly an almost perfect vacuum. This cannot be allowed
to occur, otherwise, our plant and expensive machinery may get
damaged.
Steam condenses when heat is lost to the
atmosphere for example, on the distribution lines while working,
or , more regularly when a machine in the process is switched
off.
We therefore insatll a device called a vacuum breaker
on the steam inlet of expensive machinery, before it enters the
process. It is a valve, that basically allows air in as soon as a
vacuum starts to form.
Safety Valves (SV)
The
safety valve is fitted to protect the process that the PRS is
supplying steam to. The SV protects from over pressure and in the
worst case, an explosion.
A
safety valve must meet the following criteria:
• The
total discharge capacity of the safety valve must be at least
equal to the flow through the PRS at the set pressure of PRV. This
way, the safety valve capacity will always be higher than the
actual maximum flow through the PRS.
• The full rated
discharge capacity of the safety valve(s) must be achieved within
110% of the PRS set pressure.
• There must be an
adequate margin between the normal operating pressure of the PRS
and the set pressure of the safety valve, otherwise the safety
valve will keep blowing. Typically 10% above set pressure.
Typical
steam using equipment.
Space Heaters / Hot
rooms / Air Steam heater / Radiators
Steam heaters or steam
coils are heat exchangers in which one medium is steam being
condensed while the other medium is a gas (air) being heated when
forced through the heat exchanger with a fan. The inlet air may be
ducted or simply gathered from the room in which the steam heating
unit is positioned. The actual heat exchanger is constructed as a
matrix of tubes and corrugated or flat fins (aluminium, copper or
other materials) with as high thermal conductivity as feasible for
the given application.
Process
Air heaters
Process air heating with steam coils is one of
industry’s toughest jobs. Many steam coils become early
victims of mechanical failure and the internal/external corrosion
that can be the beginning of the end of efficient heat transfer.
A process air heating solution should deliver the ability
to achieve and maintain the temperatures you need to keep
production running at optimum speed and efficiency. The coils must
have extra-sturdy fins to stand up to high-pressure cleaning and
be made out of tough materials as a defense against galvanic
action to survive the rigors of high pressures, high temperatures
and corrosive conditions.
Driers
– Tray and Rotary
Used for drying out products like
tobacco and paper with heat.
Tanks
– Injection, coil, jacketed
Steam
Sparger
Steam sparging is common in open tanks or
kettles containing liquid products or water.This is simply a pipe
mounted inside the tank, generally at the bottom, with small holes
drilled at regular positions spaced along the length of the pipe
with the end blanked off. The steam exits the pipe through the
holes as small bubbles, which will either condense as intended or
reach the surface of the liquid.
 Steam
Injection Heater
Steam injection heating for
products is a direct-contact process in which steam is mixed with
a pumpable ingredient. Heating occurs when the steam transfers
some of its internal energy to the product. Steam gives up all of
its latent heat of vaporization while condensing and, depending
upon the system pressure, some of its sensible heat. Since the
steam directly contacts the product and the condensate becomes
incorporated into it, the steam source must be clean. Typical
steam injection units are compact, inexpensive and simple to
control. An example is provided in the figure.
A direct
steam injector draws in cold liquid and mixes it with steam inside
the injector, distributing heated liquid to the tank. It
discharges of a series of steam bubbles into a liquid at a lower
temperature. The steam bubbles condense and give up their heat to
the surrounding liquid. Heat is transferred by direct contact
between the steam and the liquid, consequently this method is only
used when dilution and an increase in liquid mass is acceptable.
Therefore, the liquid being heated is usually water.
Steam
Jacketed Kettles and vats
A jacket, used to distribute
steam over a wide surface area, consists of a thin space formed
between two, parallel, metallic surfaces. Steam jackets are
typically used to heat bulk products held in tanks and kettles. An
example of a steam-jacketed kettle is shown in figure. Condensing
steam, held captive within the jacket, transfers heat to the
product in the kettle. A layer of insulation over the jacket
protects operators and conserves heat.
Used in Food
processing.
Humidifier
Certain drying and curing
processes require humidification of the air surrounding the
product to control the drying rate. Culinary steam can be injected
directly into a drying chamber or into a ventilation air duct.
Steam-In- place (SIP) Culinary steam is used to
achieve high temperatures and moisture levels required to
sterilize enclosed surfaces (such as closed tanks, pipes and
valves) in food processing equipment.
PHE
The
basic plate heat exchanger consists of a series of thin,
corrugated plates that are gasketed, welded together (or any
combination of these) or brazed together depending on application.
The plates are then compressed together in a rigid frame to create
an arrangement of parallel flow channels. One fluid travels in the
odd numbered channels, the other in the even.
Fig.
Inside a Heat Exchanger
Shell
& Tube Heat Exchanger
Shell and tube heaters are
commonly used to heat a flowing liquid by condensing plant steam
or a pumped heat transfer media. A thin-tube wall separates the
heating media from the product being heated. In the case of a
pumped heat-transfer media (such as hot water), steam is often
used to heat the media in a separate heat exchanger.
 Fixed
Tube-Sheet Exchangers
These are the most
economical and are used more often than any other type. The tubes
sheets are welded to the shell. The tubes can be examined and
replaced easily. Expansion joints are used where there is a
possibility of excessive stresses due to differential expansion
during operation.
U-Tube
Heat Exchangers
The tube Bundle, in this case,
consists of a stationery tube sheets, "U" tubes (or hair
pin tubes). The tube bundle cab be removed from the shell for
inspection and cleaning from outside. The design is particularly
recommended for high pressure, high temperature applications. The
disadvantages of this design are that the tubes cannot be
mechanically cleaned from inside, and also that the tubes can not
be replaced except for a few outer bands. Variations of this
design are used as Tank Suction Heaters and also in Kettle type
re-boilers / evaporators etc.
Evaporators
In
the field of thermal separation / concentration technology,
evaporation plants are widely used for concentration of liquids in
the form of solutions, suspensions, and emulsions.
The
major requirement in the field of evaporation technology is to
maintain the quality of the liquid during evaporation and to avoid
damage to the product. This may require the liquid to be exposed
to the lowest possible boiling temperature for the shortest period
of time.
This and numerous other requirements and
limitations have resulted in a wide variation of designs available
today. In almost all evaporators the heating medium is steam,
which heats a product on the other side of a heat transfer
surface.
• Typical
evaporator applications
• Product concentration
•
Dryer feed pre-concentration
• Volume reduction
•
Water / solvent recovery
• Crystallization
 Plate
Evaporators
Compact and economically
efficient, the plate evaporator /condenser replaces conventional
large and expensive falling
film units. Its deep channels,
large ports and laser welding allow vacuum and low pressure
evaporation and condensing for both aqueous and organic systems.
Fig.
Plate Evaporators
Framed
plates are used as heating surface. These plate assemblies are
similar to plate heat exchangers, but are equipped with large
passages for the vapor flow. In these units a product plate and a
steam plate are connected alternately. The product passage is
designed for even distribution of liquid on the plate surfaces and
low pressure drop in the vapor phase. Used especially in Dairy and
Pharmaceutical industries.
Distillation
columns
Distillation is a separation process, separating
components in a mixture by making use of the fact that some
components vaporize more readily than others. When vapours are
produced from a mixture, they contain the components of the
original mixture, but in proportions which are determined by the
relative volatilities of these components. The vapour is richer in
some components, those that are more volatile, and so a separation
occurs.
 In
fractional distillation, the vapour is condensed and then
re--evaporated when a further separation occurs. It is difficult
and sometimes impossible to prepare pure components in this way,
but a degree of separation can easily be attained if the
volatilities are reasonably different. Where great purity is
required, successive distillations may be used.
In
traditional distillation, steam or another heat source is
indirectly applied through an external reboiler. In contrast, in
direct steam distillation, the steam acts as a dilutant,
preventing the buildup of undesirable by-products at the bottom of
the distillation column.
Used especially in Chemical and
Pharmaceutical industries.
Case
study: Steam distillation is also the most common
method of extracting essential oils. Many old-time distillers
favor this method for most oils, and say that none of the newer
methods produces better quality oils.
Steam distillation is
done in a still. Fresh, or sometimes dried, botanical material is
placed in the plant chamber of the still, and pressurized steam is
generated in a separate chamber and circulated through the plant
material. The heat of the steam forces the tiny intercellular
pockets that hold the essential oils to open and release them. The
temperature of the steam must be high enough to open the pouches,
yet not so high that it destroys the plants or fractures or burns
the essential oils.
As they are released, the tiny droplets
of essential oil evaporate and, together with the steam molecules,
travel through a tube into the still's condensation chamber. As
the steam cools,it condenses into water. The essential oil forms a
film on the surface of the water. To separate the essential oil
from the water, the film is then decanted or skimmed off the
top.
Autoclaves and sterilisers
An autoclave is a
pressurized device designed to heat aqueous solutions above their
boiling point.
The
heat generated under pressure is called latent heat and has more
penetrative power to squeeze through bacteria and even their
dormant, heat-resistant form—the spores. This works just
fine on solid objects when we start to talk about hollow objects (
needles, tools etc etc) you need to make sure all the air get
sucked out or otherwise it will act as an insulation for the
bacteria you want to kill.
Their chambers are usually made of
SS316 grade stainless steel chamber, and conform to pressure
vessel codes. They have to produce sterile loads repeatedly. They
must be very easy to clean and reliable.
Autoclaves are
widely used in medicine and metallurgy.
 Sterilisation
is the elimination of all transmissible agents (such as bacteria,
prions and viruses) from a surface, a piece of equipment, food or
biological culture medium. This is different from disinfection,
where only organisms that can cause disease are removed by a
disinfectant.
In
general, any instrument that enters an already sterile part of the
body (such as the blood, or beneath the skin) should be
sterilized. This includes equipment like scalpels, hypodermic
needles and artificial pacemakers. This is also essential in the
manufacture of many sterile pharmaceuticals.
CSG
Clean Steam Generators / PSG Pure steam generators
They are
basically heat exchangers in which steam is used to convert
ultra-pure water to ultra-pure steam. Used in Pharma, Food
industries.
Steam
jacketed molding presses
Used in the following industries:
Tyre, Rubber, Chocolate, Fibre glass thermocole packaging.
Vapour
absorption chillers
The absorption chiller is a machine to
produce chilled water by using heat such as steam, hot water, gas,
oil. The chilled water is then used for airconditioning
plants.
Absorption chillers use heat instead of mechanical
energy to provide cooling. A thermal compressor consists of an
absorber, a generator, a pump, and a throttling device, and
replaces the mechanical vapor compressor.
 Chilled
water is produced by the principle that liquid, which evaporates
easily, absorbs heat from surrounding when it evaporates. In the
chiller, refrigerant vapor from the evaporator is absorbed by a
solution mixture in the absorber. This solution is then pumped to
the generator. There the refrigerant re-vaporizes using a waste
steam heat source. The refrigerant-depleted solution then returns
to the absorber via a throttling device.
Pure
water is used as refrigerant and lithium bromide solution is used
as absorbent.
Ejectors
Ejector
is the generic name of a jet appliance capable of aspirating
different products: gases, liquids and solids (powders, granulates
or sludge) and takes different names according to its functions:
jet vacuum pump, thermocompressor, gas scrubber, eductor, etc. The
operating theory is the same for every type of ejector.
Jet
vacuum pump (our main application for the
ejector)
Static operating apparatus capable of obtaining
a vacuum within a capacity. The vacuum corresponds to the suction
pressure of the steam or gas needed by process requirements. The
suction pressure is obtained by means of thermodynamic and fluid
mechanics laws: A high energy potential motive fluid is relieved
through a converging and diverging nozzle and accelerated to
velocities that are often supersonic. At the outlet of the nozzle,
the potential energy of the motive fluid is transformed into
kinetic energy.
At the inlet of the diffuser, the motive
fluid gives off part of its kinetic energy to the aspirated fluid
so that the mixture of the two fluids goes through inverse
transformation in which the velocity is converted into pressure at
the diffuser discharge.
 1.
Motive fluid inlet
2.
Vacuum – suction
3.
Nozzle
4.
Diffuser
4.1. Converging
mixing cone
4.2. Diffuser
neck
5.
Discharge
Turbines
A
steam turbine is a mechanical device that extracts thermal energy
from pressurized steam, and converts it into useful mechanical
work. It is operated by highly pressurized steam directed against
vanes on a rotor.
It has completely replaced the
reciprocating piston steam engine primarily because of its greater
thermal efficiency and higher power-to-weight ratio. Also, because
the turbine generates rotary motion, it is particularly suited to
be used to drive an electrical generator - it doesn't require a
linkage mechanism to convert reciprocating to rotary motion.
Pic.
Turbine rotors on which high-pressure steam is directed
Steam
turbines are made in a variety of sizes ranging from small 1 hp
(0.75 kW) units used as mechanical drives for pumps, compressors
and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW)
turbines used to generate electricity.
There are several
classifications for modern steam turbines.
Noncondensing
or backpressure turbines are most widely used for
process steam applications. The exhaust pressure is controlled by
a regulating valve to suit the needs of the process steam
pressure. These are commonly found at refineries, pulp and paper
plants, and desalination facilities where large amounts of low
pressure process steam is available.
Condensing
turbines are most commonly found in electrical power
plants. These turbines exhaust steam in a partially saturated
state, typically of a quality greater than 90%, at a pressure well
below atmospheric to a condenser.
Extracting
type turbines are common in all applications. In an
extracting type turbine, steam is released from various stages of
the turbine, and used for industrial process needs or sent to
boiler feed water heaters to improve overall cycle efficiency.
Extraction flows may be controlled with a valve, or left
uncontrolled. Induction turbines introduce low pressure steam at
an intermediate stage to produce additional power.
  
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