note ejector
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1) An injector, also known as an ejector or steam injector, is a type of pump that uses the Venturi effect to pump fluids without moving parts. 2) Originally used on steam locomotives to inject boiler feedwater, injectors work by converting the pressure energy of a high-pressure motive fluid like steam into velocity energy, creating a low pressure zone that draws in and mixes with a suction fluid. 3) Modern uses of injectors include pumping chemicals into boilers, removing ash from power plant flues, producing vacuum pressure, and enhancing oil recovery processes. They are commonly used in well pumps where the jet pump is installed below ground.
![VOLUME 1.
Injector
From Wikipedia, the free encyclopedia
"Ejector" redirects here. For other uses, see Injector (disambiguation) and Ejector (disambiguation).
Diagram of a typical modern ejector.
Exhaust Steam Injector
An injector, ejector, steam ejector, steam injector,eductor-jet pump or thermocompressor is a
type ofpump. There are two varieties of injector, non-lifting and lifting.
The non-lifting injector cold water input is fed by gravity. It uses the principle of induced current
(Impulse (physics)) to push water up to the boiler check valve. It avoids the premature boiling of feed
water at very low absolute pressure, by avoiding theVenturi effect. The steam cone minimum orifice
diameter is kept larger than the combining cone minimum diameter.[1]
The non-lifting Nathan 4000
injector used on the Southern Pacific 4294 could push 12,000 US gallons (45,000 L) per hour at 250
psi (17 bar).[2]
The lifting injector uses the Venturi effect of a converging-diverging nozzle to convert
the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that
draws in and entrains a suction fluid. After passing through the throat of the injector, the mixed fluid
expands and the velocity is reduced which results in recompressing the mixed fluids by converting
velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas.
The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream.[3][4]
The adjacent diagram depicts a typical modern injector. It consists of a motive fluid inlet nozzle and
a converging-diverging outlet nozzle. Water, air, steam, or any other fluid at high pressure provides
the motive force at the inlet.
The Venturi effect is a particular case of Bernoulli's principle. Fluid under high pressure is converted
into a high-velocity jet at the throat of the convergent-divergent nozzle which creates a low pressure](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-1-320.jpg)
![at that point. The low pressure draws the suction fluid into the convergent-divergent nozzle where it
mixes with the motive fluid.
In essence, the pressure energy of the inlet motive fluid is converted to kinetic energy in the form of
velocity head at the throat of the convergent-divergent nozzle. As the mixed fluid then expands in the
divergent diffuser, the kinetic energy is converted back to pressure energy at the diffuser outlet in
accordance with Bernoulli's principle. Steam locomotives use injectors to pump water into the steam-
producing boiler and some of the steam is used as the injector's motive fluid. Suchsteam
injectors take advantage of condensation of the motive steam resulting from the mixing with cold
feed water.
Depending on the specific application, an injector can take the form of an eductor-jet pump, a water
eductor, a vacuum ejector, a steam-jet ejector, or an aspirator.
Contents
[hide]
1Key design parameters
2History
o 2.1Feedwater injectors
2.1.1Cones
2.1.2Overflow
2.1.3Check valve
2.1.4Initial skepticism and advantages over mechanical feed pumps
2.1.5Exhaust steam injector
2.1.6Problems
o 2.2Vacuum ejectors
o 2.3Earlier application of the principle
3Modern uses
4Well pumps
5Multi-stage steam vacuum ejectors
6Construction materials
7See also
8References
9Additional reading
10External links
Key design parameters[edit]
The compression ratio of the injector, , is defined as ratio of the injector's outlet
pressure to the inlet pressure of the suction fluid .
The entrainment ratio of the injector, , is defined as the amount (in kg/h) of suction fluid
that can be entrained and compressed by a given amount (in kg/h) of motive fluid.
The compression ratio and the entrainment ratio are key parameters in designing an injector or
ejector.
History[edit]](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-2-320.jpg)
![A- Steam from boiler, B- Needle valve, C- Needle valve handle, D- Steam and water combine, E- Water feed,
F- Combining cone, G- Delivery nozzle and cone, H- delivery chamber and pipe, K- Check valve, L- Overflow
A more modern drawing of the injector used in steam locomotives.
Steam injector of a steam locomotive boiler.
The injector was invented by a Frenchman, Henri Giffard in 1858[5]
and patented in the United
Kingdomby Messrs Sharp Stewart & Co. of Glasgow. Motiveforce is provided at the inlet by a
suitable high-pressure fluid.
Feedwater injectors[edit]](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-3-320.jpg)
![The injector was originally used in the boilers ofsteam locomotives for injecting or pumping the boiler
feedwater into the boiler.
Cones[edit]
The injector consists of a body containing a series of three or more nozzles, "cones" or "tubes". The
motive steam passes through a nozzle that reduces its pressure below atmospheric and increases
the steam velocity. Fresh water is entrained by the steam jet, and both steam and water enter a
convergent "combining cone" which mixes them thoroughly so that the water condenses the steam,
releasing the latent heat of evaporation of the steam. This raises the heat of the feed water but the
mixing also imparts extra velocity to the water. The condensate mixture then enters a divergent
"delivery cone" which slows down the jet, and because of the additional energy thus imparted, builds
up the pressure to above that of the boiler.[6]
Overflow[edit]
An overflow is required for excess steam or water to discharge, especially during starting; if the
injector cannot initially overcome boiler pressure, the overflow allows the injector to continue to draw
water and steam.
Check valve[edit]
There is at least one check valve (called a "clack valve" in locomotives because of the distinctive
noise it makes [6]
) between the exit of the injector and the boiler to prevent back flow, and usually a
valve to prevent air being sucked in at the overflow.
Initial skepticism and advantages over mechanical feed pumps[edit]
After some initial skepticism resulting from the unfamiliar and superficially paradoxical mode of
operation, the injector was widely adopted as an alternative to mechanical pumps in steam-driven
locomotives. The addition of heat to the flow of water lessens the effect of the injected water in
cooling the water in the boiler compared to the case of cold water injected via a mechanical feed
pump. Most of the heat energy in the condensed steam is therefore returned to the boiler, increasing
the thermal efficiency of the process. Injectors are therefore thermally efficient; they are also simple
compared to the many moving parts in a feed pump.
Additionally, the amount of water supplied by a mechanical feed pump cannot easily be adjusted;
hence a feed pump must be able to supply the maximum demand for water, but then will overfill the
boiler at all other times, so an overflow must be installed returning the high-pressure water to the
pump's intake. If the feed pump is attached to the motion of the locomotive, it naturally provides
water at a rate proportional to the locomotive's speed, which reduces this problem but then means
the boiler cannot be refilled when stationary. Traction engines often use feed pumps and can
disconnect the motion from the road wheels, and can be seen stationary with their flywheels turning
in order to refill their boilers.[6]
Exhaust steam injector[edit]
Efficiency was further improved by the development of a multi-stage injector which is powered not by
live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the
residual energy in the exhaust steam which would otherwise have gone to waste. However, an
exhaust injector also cannot work when the locomotive is stationary; later exhaust injectors could
use a supply of live steam if no exhaust steam was available.
Problems[edit]
Injectors can be troublesome under certain running conditions, when vibration caused the combined
steam and water jet to "knock off". Originally the injector had to be restarted by careful manipulation
of the steam and water controls, and the distraction caused by a malfunctioning injector was largely
responsible for the 1913 Ais Gill rail accident. Later injectors were designed to automatically restart](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-4-320.jpg)
![on sensing the collapse in vacuum from the steam jet, for example with a spring-loaded delivery
cone.
Another common problem occurs when the incoming water is too warm and is less effective at
condensing the steam in the combining cone. This can also occur if the metal body of the injector is
too hot, e.g. from prolonged use.
Vacuum ejectors[edit]
An additional use for the injector technology is in vacuum ejectors in continuous train braking
systems, which were made compulsory in the UK by the Regulation of Railways Act 1889. A vacuum
ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train
brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its
rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors: a large
ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum
against leaks. The small ejector is sometimes replaced by a reciprocating pump driven from
the crosshead because this is more economical of steam.
Vacuum brakes have been superseded by air brakes in modern trains, which use pumps,
as diesel and electric locomotives no longer have a suitable working fluid for vacuum ejectors.
Earlier application of the principle[edit]
Sketch of the smokebox of a steam locomotive, rotated 90 degrees. The similarity to the generic injector
diagram at the top of this article is apparent.
An empirical application of the principle was in widespread use on steam locomotives before its
formal development as the injector, in the form of the arrangement of theblastpipe and chimney in
the locomotive smokebox. The sketch on the right shows a cross section through a smokebox,
rotated 90 degrees; it can be seen that the same components are present, albeit differently named,
as in the generic diagram of an injector at the top of the article. Exhaust steam from the cylinders is
directed through a nozzle on the end of the blastpipe, to create a negative pressure inside the
smokebox and entrain the flue gases from the boiler which are then ejected via the chimney. The
effect is to increase the draught on the fire to a degree proportional to the rate of steam
consumption, so that as more steam is used, more heat is generated from the fire and steam
production is also increased. The effect was first noted by Richard Trevithick and subsequently
developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and
this constitutes much of the reason for its notably improved performance in comparison with
contemporary machines.
Modern uses[edit]
The use of injectors (or ejectors) in various industrial applications has become quite common due to
their relative simplicity and adaptability. For example:](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-5-320.jpg)
![ To inject chemicals into the boiler drums of small, stationary, low pressure boilers. In large, high-
pressure modern boilers, usage of injectors for chemical dosing is not possible due to their
limited outlet pressures.
In thermal power stations, they are used for the removal of the boiler bottom ash, the removal
of fly ash from the hoppers of the electrostatic precipitators used to remove that ash from the
boiler flue gas, and for drawing a vacuum pressure in steam turbine exhaust condensers.
Jet pumps have been used in boiling water nuclear reactors to circulate the coolant fluid.[7]
For use in producing a vacuum pressure in steam jet cooling systems.
For enhanced oil recovery processes in the oil & gas Industry.
For the bulk handling of grains or other granular or powdered materials.
The construction industry uses them for pumping turbid water and slurries.
Some aircraft (mostly earlier designs) use an ejector attached to the fuselage to provide vacuum
for gyroscopic instruments such as an attitude indicator.
Eductors are used in aircraft fuel systems as transfer pumps; fluid flow from an engine-mounted
mechanical pump can be delivered to a fuel tank-mounted eductor to transfer fuel from that tank.
Aspirators are vacuum pumps based on the same operating principle and are used
in laboratories to create a partial vacuum and for medical use in suction of mucus or bodily
fluids.
Water eductors are water pumps used for dredging silt and panning for gold, they're used
because they can handle the highly abrasive mixtures quite well.
To create vacuum system in vacuum distillation unit (oil refinery)
Well pumps[edit]
Main article: Water well pump
Jet pumps are commonly used to extract water from water wells. The main pump, often a centrifugal
pump, is powered and installed at ground level. Its discharge is split, with the greater part of the flow
leaving the system, while a portion of the flow is returned to the jet pump installed below ground in
the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high-
energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass
flow which is then piped to the inlet of the main pump.
The S type pump is useful for removing water from a well or container.
Shallow well pumps are those in which the jet assembly is attached directly to the main pump and
are limited to a depth of approximately 5-8m to preventcavitation.
Deep well pumps are those in which the jet is located at the bottom of the well. The maximum
depth for deep well pumps is determined by the inside diameter of and the velocity through the jet.
The major advantage of jet pumps for deep well installations is the ability to situate all mechanical
parts (e.g., electric/petrol motor, rotating impellers) at the ground surface for easy maintenance. The
advent of the electrical submersible pump has partly replaced the need for jet type well pumps,
except for driven point wells or surface water intakes.](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-6-320.jpg)
![Multi-stage steam vacuum ejectors[edit]
In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually
with condensers between the ejector stages. Condensing of motive steam greatly improves ejector
set efficiency; both barometric and shell-and-tube surface condensers are used.
In operation a two-stage system consists of a primary high-vacuum (HV) ejector and a secondary
low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting
pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated
in conjunction with the LV ejector to finally pull vacuum to the required pressure.
In operation a three-stage system consists of a primary booster, a secondary high-vacuum (HV)
ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector
is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this
pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull
vacuum to the lower intermediate pressure. Finally the booster is operated (in conjunction with the
HV & LV ejectors) to pull vacuum to the required pressure.
Construction materials[edit]
Injectors or ejectors are made of carbon steel, stainless steel, titanium, PTFE, carbon, and other
materials.
See also[edit]
Aspirator (pump)
De Laval nozzle
Diffusion pump
Giovanni Battista Venturi
Gustaf de Laval
Nozzle
Surface condenser
Venturi effect
References[edit]
1. Jump up^ Pullen, William Wade Fitzherbert (1900). Injectors: their Theory, Construction and
Working (Second ed.). London: The Technical Publishing Company Limited. p. 51.
2. Jump up^ Anderson.- O'Day., David N. - Russell M. H. (17 July 2013). Cab-Forward Notes Southern
Pacific Railroad's Signature Locomotive (Revision 1 ed.). Sacramento, California: Gerald Rood. p. 66.
3. Jump up^ Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook (8th
ed.). McGraw Hill. ISBN 0-07-142294-3.
4. Jump up^ Power, Robert B. (1993). Steam Jet Ejectors For The Process Industries (First ed.).
McGraw-Hill. ISBN 0-07-050618-3.
5. Jump up^ Strickland L. Kneass (1894). Practice and Theory of the Injector. John Wiley & Sons
(Reprinted by Kessinger Publications, 2007 ). ISBN 0-548-47587-3.
6. ^ Jump up to:a b c Goldfinch & Semmens (2000). HowSteam Locomotives Really Work. Oxford
University Press. pp. 92–97. ISBN 978-0-19-860782-3.
7. Jump up^ "Steam-assisted jet pump". General Electric. Retrieved 17 March 2011. United States
Patent 4847043 ... recirculation of a coolant in a nuclear reactor
Additional reading[edit]](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-7-320.jpg)
![ J.B. Snell (1973). Mechanical Engineering: Railways. Arrow Books. ISBN 0-09-908170-9.
J.T. Hodgson and C.S. Lake (1954). Locomotive Management (Tenth ed.). Tothill Press.
External links[edit]
Wikimedia Commons has
media related to Feedwater
injectors.
Use of Eductor for Lifting Water
VOLUME 2.
Ejector-Thermo compressor
Ejector-Thermocompressor
An ejector is essentially a fluid-fluid pump that has no pistons, valves, rotors, or other moving parts
and works by transfer of momentum from the primary fluid (high pressure) to the secondary fluid
aspirated (low pressure).
The basic operating principle of an ejector is to convert the pressure into speed. This occurs by an
adiabatic expansion of motive steam through a convergent -divergent nozzle from the motive
pressure to suction pressure. The result is a supersonic speed out of the nozzle. Usually 3 or 4
Mach speeds are reached.
In operation, the motive steam expands up to a pressure below the suction pressure. This creates
a depression that enters the suction load into the ejector. Motive steam at high speed is mixed with](https://image.slidesharecdn.com/4f2da752-03de-45b0-89c8-5a2c32108f95-160405162519/85/note-ejector-8-320.jpg)
note ejector
- 1. VOLUME 1. Injector From Wikipedia, the free encyclopedia "Ejector" redirects here. For other uses, see Injector (disambiguation) and Ejector (disambiguation). Diagram of a typical modern ejector. Exhaust Steam Injector An injector, ejector, steam ejector, steam injector,eductor-jet pump or thermocompressor is a type ofpump. There are two varieties of injector, non-lifting and lifting. The non-lifting injector cold water input is fed by gravity. It uses the principle of induced current (Impulse (physics)) to push water up to the boiler check valve. It avoids the premature boiling of feed water at very low absolute pressure, by avoiding theVenturi effect. The steam cone minimum orifice diameter is kept larger than the combining cone minimum diameter.[1] The non-lifting Nathan 4000 injector used on the Southern Pacific 4294 could push 12,000 US gallons (45,000 L) per hour at 250 psi (17 bar).[2] The lifting injector uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and entrains a suction fluid. After passing through the throat of the injector, the mixed fluid expands and the velocity is reduced which results in recompressing the mixed fluids by converting velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream.[3][4] The adjacent diagram depicts a typical modern injector. It consists of a motive fluid inlet nozzle and a converging-diverging outlet nozzle. Water, air, steam, or any other fluid at high pressure provides the motive force at the inlet. The Venturi effect is a particular case of Bernoulli's principle. Fluid under high pressure is converted into a high-velocity jet at the throat of the convergent-divergent nozzle which creates a low pressure
- 2. at that point. The low pressure draws the suction fluid into the convergent-divergent nozzle where it mixes with the motive fluid. In essence, the pressure energy of the inlet motive fluid is converted to kinetic energy in the form of velocity head at the throat of the convergent-divergent nozzle. As the mixed fluid then expands in the divergent diffuser, the kinetic energy is converted back to pressure energy at the diffuser outlet in accordance with Bernoulli's principle. Steam locomotives use injectors to pump water into the steam- producing boiler and some of the steam is used as the injector's motive fluid. Suchsteam injectors take advantage of condensation of the motive steam resulting from the mixing with cold feed water. Depending on the specific application, an injector can take the form of an eductor-jet pump, a water eductor, a vacuum ejector, a steam-jet ejector, or an aspirator. Contents [hide] 1Key design parameters 2History o 2.1Feedwater injectors 2.1.1Cones 2.1.2Overflow 2.1.3Check valve 2.1.4Initial skepticism and advantages over mechanical feed pumps 2.1.5Exhaust steam injector 2.1.6Problems o 2.2Vacuum ejectors o 2.3Earlier application of the principle 3Modern uses 4Well pumps 5Multi-stage steam vacuum ejectors 6Construction materials 7See also 8References 9Additional reading 10External links Key design parameters[edit] The compression ratio of the injector, , is defined as ratio of the injector's outlet pressure to the inlet pressure of the suction fluid . The entrainment ratio of the injector, , is defined as the amount (in kg/h) of suction fluid that can be entrained and compressed by a given amount (in kg/h) of motive fluid. The compression ratio and the entrainment ratio are key parameters in designing an injector or ejector. History[edit]
- 3. A- Steam from boiler, B- Needle valve, C- Needle valve handle, D- Steam and water combine, E- Water feed, F- Combining cone, G- Delivery nozzle and cone, H- delivery chamber and pipe, K- Check valve, L- Overflow A more modern drawing of the injector used in steam locomotives. Steam injector of a steam locomotive boiler. The injector was invented by a Frenchman, Henri Giffard in 1858[5] and patented in the United Kingdomby Messrs Sharp Stewart & Co. of Glasgow. Motiveforce is provided at the inlet by a suitable high-pressure fluid. Feedwater injectors[edit]
- 4. The injector was originally used in the boilers ofsteam locomotives for injecting or pumping the boiler feedwater into the boiler. Cones[edit] The injector consists of a body containing a series of three or more nozzles, "cones" or "tubes". The motive steam passes through a nozzle that reduces its pressure below atmospheric and increases the steam velocity. Fresh water is entrained by the steam jet, and both steam and water enter a convergent "combining cone" which mixes them thoroughly so that the water condenses the steam, releasing the latent heat of evaporation of the steam. This raises the heat of the feed water but the mixing also imparts extra velocity to the water. The condensate mixture then enters a divergent "delivery cone" which slows down the jet, and because of the additional energy thus imparted, builds up the pressure to above that of the boiler.[6] Overflow[edit] An overflow is required for excess steam or water to discharge, especially during starting; if the injector cannot initially overcome boiler pressure, the overflow allows the injector to continue to draw water and steam. Check valve[edit] There is at least one check valve (called a "clack valve" in locomotives because of the distinctive noise it makes [6] ) between the exit of the injector and the boiler to prevent back flow, and usually a valve to prevent air being sucked in at the overflow. Initial skepticism and advantages over mechanical feed pumps[edit] After some initial skepticism resulting from the unfamiliar and superficially paradoxical mode of operation, the injector was widely adopted as an alternative to mechanical pumps in steam-driven locomotives. The addition of heat to the flow of water lessens the effect of the injected water in cooling the water in the boiler compared to the case of cold water injected via a mechanical feed pump. Most of the heat energy in the condensed steam is therefore returned to the boiler, increasing the thermal efficiency of the process. Injectors are therefore thermally efficient; they are also simple compared to the many moving parts in a feed pump. Additionally, the amount of water supplied by a mechanical feed pump cannot easily be adjusted; hence a feed pump must be able to supply the maximum demand for water, but then will overfill the boiler at all other times, so an overflow must be installed returning the high-pressure water to the pump's intake. If the feed pump is attached to the motion of the locomotive, it naturally provides water at a rate proportional to the locomotive's speed, which reduces this problem but then means the boiler cannot be refilled when stationary. Traction engines often use feed pumps and can disconnect the motion from the road wheels, and can be seen stationary with their flywheels turning in order to refill their boilers.[6] Exhaust steam injector[edit] Efficiency was further improved by the development of a multi-stage injector which is powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise have gone to waste. However, an exhaust injector also cannot work when the locomotive is stationary; later exhaust injectors could use a supply of live steam if no exhaust steam was available. Problems[edit] Injectors can be troublesome under certain running conditions, when vibration caused the combined steam and water jet to "knock off". Originally the injector had to be restarted by careful manipulation of the steam and water controls, and the distraction caused by a malfunctioning injector was largely responsible for the 1913 Ais Gill rail accident. Later injectors were designed to automatically restart
- 5. on sensing the collapse in vacuum from the steam jet, for example with a spring-loaded delivery cone. Another common problem occurs when the incoming water is too warm and is less effective at condensing the steam in the combining cone. This can also occur if the metal body of the injector is too hot, e.g. from prolonged use. Vacuum ejectors[edit] An additional use for the injector technology is in vacuum ejectors in continuous train braking systems, which were made compulsory in the UK by the Regulation of Railways Act 1889. A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors: a large ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum against leaks. The small ejector is sometimes replaced by a reciprocating pump driven from the crosshead because this is more economical of steam. Vacuum brakes have been superseded by air brakes in modern trains, which use pumps, as diesel and electric locomotives no longer have a suitable working fluid for vacuum ejectors. Earlier application of the principle[edit] Sketch of the smokebox of a steam locomotive, rotated 90 degrees. The similarity to the generic injector diagram at the top of this article is apparent. An empirical application of the principle was in widespread use on steam locomotives before its formal development as the injector, in the form of the arrangement of theblastpipe and chimney in the locomotive smokebox. The sketch on the right shows a cross section through a smokebox, rotated 90 degrees; it can be seen that the same components are present, albeit differently named, as in the generic diagram of an injector at the top of the article. Exhaust steam from the cylinders is directed through a nozzle on the end of the blastpipe, to create a negative pressure inside the smokebox and entrain the flue gases from the boiler which are then ejected via the chimney. The effect is to increase the draught on the fire to a degree proportional to the rate of steam consumption, so that as more steam is used, more heat is generated from the fire and steam production is also increased. The effect was first noted by Richard Trevithick and subsequently developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and this constitutes much of the reason for its notably improved performance in comparison with contemporary machines. Modern uses[edit] The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example:
- 6. To inject chemicals into the boiler drums of small, stationary, low pressure boilers. In large, high- pressure modern boilers, usage of injectors for chemical dosing is not possible due to their limited outlet pressures. In thermal power stations, they are used for the removal of the boiler bottom ash, the removal of fly ash from the hoppers of the electrostatic precipitators used to remove that ash from the boiler flue gas, and for drawing a vacuum pressure in steam turbine exhaust condensers. Jet pumps have been used in boiling water nuclear reactors to circulate the coolant fluid.[7] For use in producing a vacuum pressure in steam jet cooling systems. For enhanced oil recovery processes in the oil & gas Industry. For the bulk handling of grains or other granular or powdered materials. The construction industry uses them for pumping turbid water and slurries. Some aircraft (mostly earlier designs) use an ejector attached to the fuselage to provide vacuum for gyroscopic instruments such as an attitude indicator. Eductors are used in aircraft fuel systems as transfer pumps; fluid flow from an engine-mounted mechanical pump can be delivered to a fuel tank-mounted eductor to transfer fuel from that tank. Aspirators are vacuum pumps based on the same operating principle and are used in laboratories to create a partial vacuum and for medical use in suction of mucus or bodily fluids. Water eductors are water pumps used for dredging silt and panning for gold, they're used because they can handle the highly abrasive mixtures quite well. To create vacuum system in vacuum distillation unit (oil refinery) Well pumps[edit] Main article: Water well pump Jet pumps are commonly used to extract water from water wells. The main pump, often a centrifugal pump, is powered and installed at ground level. Its discharge is split, with the greater part of the flow leaving the system, while a portion of the flow is returned to the jet pump installed below ground in the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high- energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass flow which is then piped to the inlet of the main pump. The S type pump is useful for removing water from a well or container. Shallow well pumps are those in which the jet assembly is attached directly to the main pump and are limited to a depth of approximately 5-8m to preventcavitation. Deep well pumps are those in which the jet is located at the bottom of the well. The maximum depth for deep well pumps is determined by the inside diameter of and the velocity through the jet. The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g., electric/petrol motor, rotating impellers) at the ground surface for easy maintenance. The advent of the electrical submersible pump has partly replaced the need for jet type well pumps, except for driven point wells or surface water intakes.
- 7. Multi-stage steam vacuum ejectors[edit] In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency; both barometric and shell-and-tube surface condensers are used. In operation a two-stage system consists of a primary high-vacuum (HV) ejector and a secondary low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure. In operation a three-stage system consists of a primary booster, a secondary high-vacuum (HV) ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull vacuum to the lower intermediate pressure. Finally the booster is operated (in conjunction with the HV & LV ejectors) to pull vacuum to the required pressure. Construction materials[edit] Injectors or ejectors are made of carbon steel, stainless steel, titanium, PTFE, carbon, and other materials. See also[edit] Aspirator (pump) De Laval nozzle Diffusion pump Giovanni Battista Venturi Gustaf de Laval Nozzle Surface condenser Venturi effect References[edit] 1. Jump up^ Pullen, William Wade Fitzherbert (1900). Injectors: their Theory, Construction and Working (Second ed.). London: The Technical Publishing Company Limited. p. 51. 2. Jump up^ Anderson.- O'Day., David N. - Russell M. H. (17 July 2013). Cab-Forward Notes Southern Pacific Railroad's Signature Locomotive (Revision 1 ed.). Sacramento, California: Gerald Rood. p. 66. 3. Jump up^ Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook (8th ed.). McGraw Hill. ISBN 0-07-142294-3. 4. Jump up^ Power, Robert B. (1993). Steam Jet Ejectors For The Process Industries (First ed.). McGraw-Hill. ISBN 0-07-050618-3. 5. Jump up^ Strickland L. Kneass (1894). Practice and Theory of the Injector. John Wiley & Sons (Reprinted by Kessinger Publications, 2007 ). ISBN 0-548-47587-3. 6. ^ Jump up to:a b c Goldfinch & Semmens (2000). HowSteam Locomotives Really Work. Oxford University Press. pp. 92–97. ISBN 978-0-19-860782-3. 7. Jump up^ "Steam-assisted jet pump". General Electric. Retrieved 17 March 2011. United States Patent 4847043 ... recirculation of a coolant in a nuclear reactor Additional reading[edit]
- 8. J.B. Snell (1973). Mechanical Engineering: Railways. Arrow Books. ISBN 0-09-908170-9. J.T. Hodgson and C.S. Lake (1954). Locomotive Management (Tenth ed.). Tothill Press. External links[edit] Wikimedia Commons has media related to Feedwater injectors. Use of Eductor for Lifting Water VOLUME 2. Ejector-Thermo compressor Ejector-Thermocompressor An ejector is essentially a fluid-fluid pump that has no pistons, valves, rotors, or other moving parts and works by transfer of momentum from the primary fluid (high pressure) to the secondary fluid aspirated (low pressure). The basic operating principle of an ejector is to convert the pressure into speed. This occurs by an adiabatic expansion of motive steam through a convergent -divergent nozzle from the motive pressure to suction pressure. The result is a supersonic speed out of the nozzle. Usually 3 or 4 Mach speeds are reached. In operation, the motive steam expands up to a pressure below the suction pressure. This creates a depression that enters the suction load into the ejector. Motive steam at high speed is mixed with
- 9. the suction flow. According to this mix enters the convergent-divergent diffuser, the speed is transformed into pressure. The convergent section of the diffuser reduces the speed, pressure shock occurs in the throat of the diffuser and divergent diffuser section increases the cross - sectional area to the flow and speed are turning into pressure energy. Ejector systems can operate in very in a wide range of conditions, from very light loads to loads above the value of design. An ejector system must adapt steadily to all operating conditions which may anticipate. It is essential for a stable operation the determination of the design loads of non- condensable and light loads. Main characteristics: Dynamic fluid pumps producing medium and high vacuum. No moving parts. No maintenance required. Working with all type of fluids. Reliable operation for years. Installation in any position. Applications: Production of medium and high vacuum. Steam re-compression and gas extraction. Liquids, solutions, slurries, … suction. Mixing and agitation. Steam saturation.
- 10. Q & A > Question Details. 1. What is the purpose/function of Steam Ejector in Vacuum distillation column and how it works? 2. Why it is placed at the top of column and why not the bottom in refinery? please explain the barometric concept regarding this installation DelayedCoking Revamps Answers 20/07/2012 A: Sudhakara Babu Marpudi, Oman RefineriesandPetroleumIndustriesCompany, m_sudhakarababu@yahoo.com Ejectorshave chambersthat convertpressure energyintovelocityenergy.Steam(or motive fluid)thatactsas motive fluidisintroducedintothe chamberwithanreducer type arrangementandfollowedimmediatelybyreducerandexpanderarrangement (Please checkthe typical sketchof ejectors)Thisarrangementincreasesthe velocity of motive fluidasitentersthe chamber.Asthe motive fluidexitsthe ejectorthe emptyspace leftinthe chamberisfilledwiththe processfluid(liquid/vapor) andis carriedout alongwiththe motive fluid.Thisisthe basicphenomenathatisknownas the vacuum. Locationof steamejectorsatthe top of the systemsistoensure lesserenergy consumptionduringthe vacuumproduction.Anyvaporwill condenseinthe piping and will buildaliquidhead inthe upstreamof ejectorsandwillneedmore energyto create vacuum andsubsequentprocess.Unlessthere isspace createdforthe incomingmaterial inthe downstreamof the vacuumproductionequipment,energy costs of vacuum productionwill be expensive.The locationattopwill allow lotof vertical space andtime for the evacuationof material drawnoutof the columns.Also the systemundervacuumisreadyto take inair incase of any leak.Airingresscould be dangerousforsystemswithHydrocarbon. Soitis betterthatthe areasof possible leaks(undervacuum) toas minimumaspossible.The systeminthe downstreamof vacuumproductionequipmentwillbe onhigherpressure sideandwill notallowair ingressevenif itleaks.Soprobablyitisa combinationof safetyandenergy optimisationthatgovernsthe Ejectorslocation. 26/06/2012 A: Ralph Ragsdale, Ragsdale RefiningCourses,ralph.ragsdale@att.net The ejectors,sometimescalledeductors,alongwithanyvacuumpumpinthe process,create the low pressure (vacuum) atthe inletof the firstejector.A headof 34 feetof water(lessathigheraltitudes) canbe usedtoremove the condensed steamfromthe system.Normally,atthe bottomof the water column,the wateris pumpedfroma drumas the watercolumnisheldsuspendedbythe pressure from
- 11. the atmosphere.Thiswatercolumndictatesthe elevationof eachcomponentof the system.Crude vacuumunitsare designedthisway. A watercolumnof 34 feetisnot essential forall applications,however.A vacuum operatedglycol regenerator,forexample,mayhave simplyanoverheadcondensing systemwithaneducatorexhaustingtothe atmosphere orflare.