This document discusses equipment used in liquefied natural gas (LNG) processing plants, including compressors, gas turbines, and cryogenic equipment. It describes various types of compressors like reciprocating and screw compressors, and gas turbines like aeroderivative and industrial turbines. It explains their operating principles, advantages, disadvantages and applications in LNG plants. Gas turbines can drive centrifugal compressors and are used in simple or combined cycle configurations for power generation. Cryogenic pumps and heat exchangers are also discussed.

1. LNG Plant Equipemnt
Senior Project 2013
Liquefied Natural Gas

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This Chapter Discusses Different Equipments Used
in Gas Processing Plants with different
Technologies and it's Theories, Applications,
advantages and disadvantages.
Also discusses the special cryogenic equipments
such as Cryogenic Pumps, Cryogenic Heat
Exchangers and it's Characteristics, Applications,
Conditions and benefits. And finally discusses the
main points which compares between different
cryogenic technologies .

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1- Compressors
1.1 Introduction
Mechanical device that increases the pressure of a gas by reducing its
volume. Compression of a gas naturally increases its temperature.
The refrigeration compressor is the heart of the refrigeration system. It
removes the vapor from the evaporator and introduces vapor to the high-
pressure side of the systems. It maintains the low-side pressure at which
the refrigerant evaporates, and the high-side pressure at which it
condenses. In brief, it supplies the pressure differences necessary to keep
the system refrigerant flowing through the system. Many different types of
compressors have been used to do this, and many different details tried
with individual types of compressors.
FIGURE 1 REFRIGERATION COMPRESSOR
3.1 Types of gas compressors
For comparison, the different types of compressors can be subdivided into
two broad groups based on compression mode.
There are two basic modes:
 Intermittent .
 Continuous.

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FIGURE 2 COMPRESSOR CLASSIFICATION
FIGURE 3 P-Q COMPRESSOR SELECTION DIAGARM
a- Reciprocating Compressors
For large volumes of compressed gas, they are usually the most
expensive to buy and install, and require greater maintenance,
however, they may be lower cost at small capacities. Due to their
size and the vibrations caused, they require large foundations and
may not be suitable where noise emissions are an issue.
Nevertheless, they are the most energy efficient, both at full and part
loads.

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It is generally in the lower flow end of the compressor spectrum. Inlet flows
range from less than 100 to approximately 10,000 cfm / cylinder. It is
particularly well suited for high-pressure service. The reciprocating
compressor is one of the most efficient of all the compressors.
b- Positive displacement compressors
b -1 - Reciprocating Compressors
Almost every onshore gas plant and field operation uses reciprocating
compressors
b-2 - Oil-Free Rotary Screw Compressors
Rotary screw compressors use two screws, or lobes to compress the gas.
Gas enters as the threads at the suction side are separating, and it move
down the threads as the screws rotate. Clearances between the threads
decrease an compress the gas. The gas exits in an axial port at the end of the
screws. A timin drive keeps the two lobes synchronized. The screws run at
3,000 to 8,000 rpm, an the speed is easily varied to provide an efficient
means to handle lower flow rates.
Unlike reciprocating compressors, essentially all gas is displaced (i.e., the
volumetric efficiency is near 100%).
FIGURE 4 GENERAL PERFORMANCE CURVE

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FIGURE 5 CUTAWAY VIEW OF AN OIL-INJECTED ROTARY SCREW COMPRESSOR.
c- DYNAMIC COMPRESSORS
The two dynamic compressor types are centrifugal and axial. Axial
compressors handle large gas volumes (50 to 300 Macfm [80 to 500
Mam3/h]) and have higher efficiencies than do centrifugals. However, they
generally have discharge pressures below 200 psig (14 barg) and are
restricted to clean gases. Although not used for processing the natural gas,
axial compressors will be discussed briefly in the context of their use in the
gas turbines that drive centrifugal compressors.
FIGURE 6 GAS TURBINE-DRIVEN CENTRIFUGAL COMPRESSOR

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C. 1 Axial Flow Compressors
Axial compressors routinely compress large volumes of gas (50 to 500 Macfm
[80 to 800 Mam3/h]) at pressures up to about 200 psig (14 barg), although in
special applications, they may go to higher pressures. They are smaller and
more efficient than centrifugals. As the name implies, axial compressors use
stationary and rotating vanes to push the gas down the axis instead of in a
radial direction like centrifugal compressors.
FIGURE 7 A GAS-FIRED TURBINE
2. Gas Turbines
2.1 Introduction
A gas turbine, also called a combustion turbine, is a type of internal
combustion engine. It has an upstream rotating compressor coupled to a
downstream turbine, and a combustion chamber in-between. Energy is
added to the gas stream in the combustor, where fuel is mixed with air and
ignited. In the high pressure environment of the combustor, combustion of
the fuel increases the temperature.

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The products of the combustion are forced into the turbine section. There,
the high velocity and volume of the gas flow is directed through a nozzle over
the turbine's blades, spinning the turbine which powers the compressor and,
for some turbines, drives their mechanical output.
The energy given up to the turbine comes from the reduction in the
temperature and pressure of the exhaust gas. Energy can be extracted in
the form of shaft power, compressed air or thrust or any combination of
these and used to power aircraft, trains, ships, generators, or even tanks.
2.2 Types of gas turbines
 Jet engines
Airbreathing jet engines are
gas turbines optimized to
produce thrust from the
exhaust gases, or from ducted
fans connected to the gas
turbines. Jet engines that
produce thrust from the direct
impulse of exhaust gases are
often called turbojets, whereas
those that generate thrust with
the addition of a ducted fan are
often called turbofans or
(rarely) fan-jets.
FIGURE 8 : JET ENGINES

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 Turboprop engines
A turboprop engine is a type of turbine engine which drives an external
aircraft propeller using a reduction gear. Turboprop engines are generally
used on small subsonic aircraft, but some large military and civil aircraft
also used turboprop power.
 Aeroderivative gas turbines
Aeroderivatives are also used in electrical power generation due to their
ability to be shut down, and handle load changes more quickly than
industrial machines. They are also used in the marine industry to reduce
weight.
 Higher thermal efficiency than Industrial GT; 38-42% compared to 28-
32% for similar size Industrial GTs in simple cycle
 Smaller footprint area than Industrial GT because of aero design
 Shorter maintenance period; modular design allows gas engine and
power turbine sections to be swapped out
 Off-site maintenance (in factory). Thus, higher plant availability
 Most engines have free power turbines for variable speed operation
(within a range)
 Large helper motors or steam turbines may not be needed for start-up
 Range of sizes available:
o RB211 ~ 30 MW
o LM6000 ~ 40 MW
o Trent ~ 55 MW
 Higher NOX than Industrial GTs Engines need more care and
maintenance due to higher operating pressures and temperatures
and design complexity
 Fixed sizes and fixed optimal speeds
 Process and compressors must be designed around the GT (unlike
steam turbines)
FIGURE 9 TURBOPROP ENGINES

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 Power output highly sensitive to ambient conditions
 Fuel quality is critical –even more than in Industrials!
 Limited operating experience for LNG, although extensive for offshore
mechanical drive and power generation
 Powers greater than 60 MW not available in simple cycle
 Dry Low Emissions (NOX) technology adds complexity
 Higher risk technology than Industrial GTs
 Industrial Gas Turbines –Pros
 Simple cycle GT is uncomplicated in its design
 Low CAPEX
 Economies of scale when using large frame GTs
 Extensive operational experience with mechanical drive applications
 Large population; perceived as low risk technology
 Skid mounted; easier to install than a steam system
 Smaller plant footprint; less extensive civil works
 Lower NOX than Aero-derivative GT
 Range of sizes available:
o Frame 5 ~ 30 MW
o Frame 6 ~ 40 MW
o Frame 7 ~ 75 MW
o Frame 9 ~ 110 MW
 Low thermal efficiency, high CO2 emissions
Advantages and disadvantages of gas turbine engines
 Advantages of gas turbine engines
 Very high power-to-weight ratio, compared to reciprocating engines;
 Smaller than most reciprocating engines of the same power rating.
 Moves in one direction only, with far less vibration than a reciprocating
engine.
 Fewer moving parts than reciprocating engines.
 Greater reliability.
 Low operating pressures.
 High operation speeds.
 Low lubricating oil cost and consumption.
 Can run on a wide variety of fuels.

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 Disadvantages of gas turbine engines
 Cost is very high
 Less efficient than reciprocating engines at idle speed
 Longer startup than reciprocating engines
FIGURE 10 GAS TURBINE
2.3. Gas Turbine Usages in Segas Plant
Industrial gas turbines differ from aeroderivative in that the frames, bearings,
and blading are of heavier construction. Industrial gas turbines range in
size from truck-mounted mobile plants to enormous, complex
systems.[clarification needed] They can be particularly efficient up to 60%
when waste heat from the gas turbine is recovered by a heat recovery
steam generator to power a conventional steam turbine in a combined
cycle configuration. They can also be run in a cogeneration configuration:
the exhaust is used for space or water heating, or drives an absorption
chiller for cooling or refrigeration. Such engines require a dedicated
enclosure, both to protect the engine from the elements and the operators
from the noise.

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The construction process for gas turbines can take as little as several
weeks to a few months, compared to years for base load power
plants.[citation needed] Their other main advantage is the ability to be
turned on and off within minutes, supplying power during peak demand.
Since single cycle (gas turbine only) power plants are less efficient than
combined cycle plants, they are usually used as peaking power plants,
which operate anywhere from several hours per day to a few dozen hours
per year, depending on the electricity demand and the generating capacity
of the region. In areas with a shortage of base load and load following
power plant capacity or low fuel costs, a gas turbine power plant may
regularly operate during most hours of the day. A large single cycle gas
turbine typically produces 100 to 400 megawatts of power and have 35–
40% thermal efficiency.
Turbine Efficiency affects by
FIGURE 11 LOAD EFFECT FIGURE 12 INLET AIR TEMPERATURE

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2.4 Gas Turbine Starting System
The purpose of a gas turbine engine starting system is to provide power to:
 Rotate the turbine shaft to starting speed,
 Assist the turbine to self-sustaining speed after combustion occurs.
FIGURE 13 GAS TURBINE COMPONENT
2.5 Turbine Problems
 loss of lubrication
results from oil pump failure or more likely oil filter plugging. Turbine
bearing failure is generally traced to dirt in the oil or a block in the oil
supply. Therefore, filtration must be adequate to retain particles whose
size may exceed the oil film thickness. Bearing damage results from
excessive temperatures and pounding from vibration caused by shaft
bowing or other shaft misalignment problems
 Impingement
occurs when the steam quality decreases to the point that steam
condensate exists in the turbine. Water droplets impinging on turbine
blades contribute to wear by causing erosion of the blades. The steam
entering the turbine must be adequately superheated to avoid
condensation and impingement.

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3. Pumps
3.1 Introduction
A Mechanical device used to add kinetic and potential energy to a Liquid
for the purpose of moving it from one point to another. This energy will
cause the liquid to do work such as flow through a pipe or rise to a higher
level and Pump gives pressure to fluid passing through it and discharges
the fluid to the Outside
Objective of pumping system:
 Transfer liquid from source to destination.
 Circulate liquid around a system.
Main Pumping System Components:-
 Pumps.
 Prime movers: Electric motors, Diesel Engines, Air system, Turbine…
 Valves to control flow in system.
 Hydraulic Motors or Cylinders.
 Heat Exchangers, tanks, hydraulic machines.
 Other fittings, control, instrumentation.
Important notes
 A Pump doesn’t create pressure it only provides flow. Pressure is a just
an indication of the amount of resistance to flow.
 Pumps can Pump only liquid not vapor
 Pumps create flow by reducing atmospheric pressure on water (by
creating a vacuum)
The main reason for using head instead of pressure to measure a pump’s
energy is that the pressure from a pump will change if the specific gravity
(weight) of liquid changes but the head not change.

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3.2 Pump Classifications
The classifications of pump in two types
 Nonpostivie displacement pump
This type used for low pressure, high flow rate
 Positive displacement pump
This type used for high pressure, low flow rate
Centrifugal pumps
Centrifugal pumps consist of a set of rotating vanes, enclosed within a housing or
casing, used to impart energy to a fluid through centrifugal force. The pump has
two main parts: a rotating element which includes an impeller and a shaft, and a
stationary element made up of a casing (volute or solid), stuffing box , and
bearings

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illustrates a cross-section of a typical centrifugal pump
Fluid enters the inlet port at the center of the rotating impeller, or the
suction eye. As the impeller spins in a counter-clockwise direction,it thrusts
the fluid outward radially, Causing Centrifugal acceleration. As it does this,
it creates a vacuum in its wake, drawing even more fluid into the inlet .
Centrifugal acceleration creates energy proportional to the speed of the
impeller. The faster the impeller rotates, the faster the fluid movement and
the stronger its force. This energy is harnessed by introducing
A centrifugal pump has two main components
 The Moving Component
Consist of an Impeller and and a shaft .
 The stationary component
consists of a casing, cover, and bearings.
FIGURE 14 ILLUSTRATES A CROSS-SECTION OF A TYPICAL CENTRIFUGAL PUMP

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Stages:
The number of impellers determines the number of stages of the
pump.
 Single Stage Pump
Has just one impeller and is better for low head service
 Two Stage Pump
Has Two Impellers mounted in series for medium head service.
 Multi Stage Pump
Has three or more impellers mounted in series for high head
FIGURE 17 TWO STAGE
FIGURE 18 SINGLE STAGE
FIGURE 15 TWO STAGE WITH DOUBLE SUCTION FIGURE 16 MULTISTAGE

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LNG Pumps (Cryogenic Pumps)
Pumps primarily used for transfer of liquefied natural gas (LNG) and other
liquefied gases. They’re really in a class unto themselves. Over the years,
various methods of transferring LNG from ship to tank storage for transfer
later to a send-out system, or transfer directly from ship into a regasification
or send-out system have been studied, and some are already in detailed
design or under construction.
along with the rapid growth of the global LNG market has come an escalating
demand for additional LNG receiving terminals and regasification systems
around the world. Such terminals, whether on- or offshore, contain gas send-
out systems that utilize SEMPs for LNG transfer and pressurization. These
pumps typically feature an integral shaft with the entire motor, bearings and
all other components completely flooded with LNG.
The major pump services in the liquefaction unit are:
 Amine circulation (acid gas removal process).
 Reflux for scrub column and fractionation towers (liquefaction process)
 LNG product pumps.
 Seawater pumps (if seawater cooled).
 Hot oil pumps.
The amine pumping service is often split into two parts
 A low head pump working at high temperature followed by
 A high head pump operating at near-ambient temperature.
Using the low head booster pump at the high temperature avoids problems
with cavitation within the pump that would be present if the high head
pumping were done at high temperature. The booster pump is typically a
single-stage double suction pump with low net positive suction head
(NPSH)) requirements. By using a pump with low NPSH require- ments for
the booster pump, the residual dissolved CO2remains in solution. When
CO2is allowed coming out of solution, a phenomenon similar to cavitation
occurs that is potentially very damaging to the pumps. To avoid the
potential for cavitation damage, calculated
NPSH available numbers are typically reduced by three to four times to
provide sufficient actual margin. The amine circulation rate depends on the
amount of acid gas, but a train making 5 MMTPA of LNG with a natural gas
feed containing 15 percent CO2can have a circulation rate over 2000 m3/hr.
handled with 3 3 50 percent pumps.
The high-head circulation pumps are typically multistage, between-
bearings, horizontal designs driven by electric motors.

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The reflux pumps for the scrub column operate at about 230 to 250°C, and in
the fractionation unit the de-ethanizer reflux pumps also operate at about
230°C. The flow rates of these pumps depend to a large extent on the natural
gas composition. For a 5 MMTPA train handling associated gas the scrub
column reflux flow can be in the 350 to 400 m3/hr range, though a plant
processing non associated gas usually has a smaller scrub column reflux
pump. The scrub column reflux pump size depends to a great extent on the
aromatics present, but in some cases where the natural gas contains little
ethane and propane, recovering refrigerant components can be the main
factor that determines reflux pump size. These pumps are normally single-
stage.
The LNG product pump has a special design for cryogenic service. The pump
is a submerged motor, “pot mounted” pump for these applications. Figure 7
shows an illustration of the pump that
is mounted inside a container. The container, flooded with LNG during
operation, also contains the motor. The suction of the pump is at the bottom
of the container, and the LNG discharge flows
Through the motor thus providing cooling for the motor. There are no
cryogenic rotating seals with this arrangement; the only seal needed is for the
electrical connection box, and the box is always
purged with nitrogen to prevent natural gas leakage through the conduit. This
type of pump has the following advantages over conventional sealed pumps:
Multistage single stage

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Item
Capacity
M3 hr
heads
Fluid Pump specific
Lean amine booster
bump
500-
1800
80-120 Amine Double suction
Between bearing
Radial split case
Single stage
Lean amine charge
pump
500-
1800
600-
750
Amine Multi stage
Between bearing
Radial split case
Pressure lubricated sleeve and pad bearing
Scrub column reflux
pump
150-
400
90-
100
Hydrocarbon
LNG
Cryogenic
submerged motor
type
Vertical can type
LNG product pump 1100-
2000
150-
240
Hydrocarbon
LNG
Cryogenic
submerged motor
type (no seal or
coupling)
LNG loading pumps 1350-
2000
150-
240
Hydrocarbon
LNG
Cryogenic
submerged motor
type (no seal or
coupling)
LNG cargo pumps 1350-
200
150-
240
Hydrocarbon
LNG
Cryogenic
submerged motor
type (no seal or
coupling)
Sea water pumps 15000-20000 50-60 Sea water Vertical pump AL-
BR or duplex
stainless steel
material
10-15 meter shaft
lenth
Hot oil pump 1500-2000 120-140 Hot oil Same as heated
water pump
Heated
water
pump
750-1250 220-250 Heated water Double suction
Axial split case
Between bearing

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4. Valves
4.1 Introduction
Valves are integral components in piping systems they are the primary
method of controlling the flow, pressure and direction of the fluid. Valves
may be required to operate continuously e.g. control valves, or they may
be operated intermittently e.g. isolation valves, or they may be installed to
operate rarely if ever e.g. safety valves. A valve can be an extremely
simple, low cost item or it may be and extremely complicated, expensive
item. In piping design the valves probably require more engineering effort
than any other piping component.
a- direction control valve
Directional-control valves also control flow direction. However, they vary
considerably in physical characteristics and operation.
The valves may be
Poppet type, in which a piston or ball moves on and off a seat.
Rotary-spool type, in which a spool rotates about its axis.
Sliding-spool type, in which a spool slides axially in a bore.
check valve
Check valves are the most commonly used in fluid-powered systems. They
allow flow in one direction and prevent flow in the other direction. They may
be installed independently in a line, or they may be incorporated as an
integral part of a sequence, counterbalance, or pressure-reducing valve.
The valve element may be a sleeve, cone, ball, poppet, piston, spool, or
disc. Force of the moving fluid opens a check valve; backflow, a spring, or
gravity closes the valve.

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b- Pressure control valve
Pressure control valves are used to control and regulate pressure in
fluid power systems. They are often globe-shaped and designed with
flanged ends to allow for ease of maintenance. The valve is smaller than
the line in which it is attached. This design feature prevents the valve
from throttling, which would cause the seat to wear too quickly. In
hydraulic systems pressure regulators are used to unload the system
and to maintain and regulate pressure at the desired values.
Relief valves
Most fluid power systems are designed to operate within a preset
pressure range. This range is a function of the forces the actuators in
the system must generate to do the required work. Without controlling or
limiting these forces, the fluid power components (and expensive
equipment) could be damaged.
FIGURE 19 DIRECTION CONTROL VALVES
FIGURE 20 ORESSURE CONTROL VALVE

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Types of Pressure Control Valves
Pressure Regulators- Pressure regulators keep the output pressure at a
set value. Pressure regulators control pressure in lines (usually adjustable)
to remove fluctuations and maintain consistent pressure.
Counter-Balance Valves- Counter-balance valves, also called load
holding valves or over-center valves, are normally located between a
directional control valve and the outlet of a vertically mounted actuating
cylinder that must support weight or be held in position for a period of time.
The counter-balance valve serves as hydraulic resistance to the actuating
cylinder.
Sequence Valves- Sequence valves control the sequence of operation
between two branches of a circuit. They enable one unit to automatically set
another unit into motion.
Uploading Valves- The main application of an unloading valve is to unload a
pump and save energy when the flow is not required. There are both
hydraulic and pneumatic applications. Pressure control valves can handle a
wide range of media including air and gaseous materials; fuel, gas and oil;
liquids, steam and hydraulic fluids.
c- flow control valve
There are eight types of flow-control valves for example :
Orifices - A simple orifice in the line, is the most elementary method for
controlling flow. (Note that this is also a basic pressure control device.)
When used to control flow, the orifice is placed in series with the pump. An
orifice can be a drilled hole in a fitting, in which case it is fixed; or it may be
a calibrated needle valve, in which case it functions as a variable orifice, (b).
Both types are non-compensated flow-control devices
Flow regulators - This device which is slightly more sophisticated than a
fixed orifice, consists of an orifice that senses flow rate as a pressure drop
across the orifice; a compensating piston adjusts to variations in inlet and
outlet pressures. This compensating ability provides closer control of flow
rate under varying pressure conditions. Control accuracy may be 5%,
possibly less with specially calibrated valves that operate around a given
flow-rate point.
FIGURE 21 FLOW CONTROL VAALVES

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Type Function Advantages Disadvantages
Gate
( Wedge)
On / off throttling
possible
 Widely used on water
duties but can be used
for control of process
fluids.
 Cheap in large sizes
and generally made of
cast iron
 When used for
throttling may suffer
erosion and where
solids are carried at
high velocities.
Gate
( parallel)
On / off throttling
possible
 Used mainly for
stream duties at high
pressure
 As above
Plug On / off
 Can be fully PTF-lined
 have very good
chemical resistance
 Lubricant can cause
contamination of
products
 Limit the temperature
of the operation
 Not Widely Used
Globe throttling  Wide range of sizes
 pressure/temperature
 Not available as lined
valve.
Ball On / Off  Widely used for
corrosive conditions
 range of pressure /
temperature
 Can be made fire-safe.
 Poor for throttling. Not
suitable for fluids
containing solids
which damage seats.
Check Prevention of
backflow
 Wide pressure
temperature range
 Not reliable on critical
duties.
Safety Safety and protection  Reseats  Only for gases:
prevents excess
pressure
Relief Safety and protection  Reseats.  Only for liquids:
prevents excess
pressure
Bursting
disc
Safety and protection  Instantaneous
unrestricted relief.
 Wide range of
materials available.
 Not-reclosing and
expandable. Subject
to corrosion and
creep if hot causing
premature failure.
TABLE 1 VALVES GUIDE AND TYPES

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5. Turbo Expander
Most plants must compress the gas before it goes to the pipeline. The
majority of plants that have cryogenic hydrocarbon recovery use
turboexpanders to provide refrigeration in the cryogenic section. Work
generated in expansion is used to recompress the outlet gas. However,
additional compression is usually required.
5.1. Introduction
Turboexpander is a machine, which continuously converts kinetic energy
into mechanical energy. This is done by expanding the high pressure gas
from upstream to a lower pressure downstream through the expander. The
high pressure gas causes the radial expander to rotate. Rotation is
transmitted to the shaft, which is supported by a set of bearings. The power
transmitted to the shaft can be used to drive a compressor, drive an
electrical generator or can be dissipated through an oil brake or air brake.
FIGURE 22 TURBOEXPANDER
Turboexpanders are, in essence, centrifugal compressors that run
backwards. Unlike J-T expanders, they perform work during the process.
Whereas J-T expansion is essentially an isenthalpic process (therefore, no
work is done on or by the gas), an ideal, thermodynamically reversible
turboexpander is isentropic. The maximum reversible work required for
compression is isentropic, and, conversely, the maximum reversible work
recovered by a turboexpander system on expansion is also isentropic.

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Turboexpansion provides the maximum amount of heat removal from a
system for a given pressure drop while generating useful work. erosion of
internal components. Most turboexpanders drive centrifugal compressors
to provide a portion of the outlet compression. In situations where inlet
pressures are very high (e.g., offshore) turboexpanders are used in
pressure letdown to provide refrigeration for dew point control and to
generate power.
About 50% of the enthalpy change occurs in the turbine .
The increase in velocity over the vanes results in the other 50% of the total
pressure and temperature drop across the expander unit. Thus, the inlet
guide vanes are a vital part of the energy conversion process in a
turboexpander. The high velocity of the gas that exits the vanes and enters
the expander wheel greatly improves overall turboexpander efficiency
The Engineering Data Book (2004c) emphasizes some points that should
be kept in mind for turboexpanders:
• Entrainment. Gas that enters the turboexpander must be free of
both solids and liquids. Fine-mesh screens are used to protect the
device, and the pressure drop across the screen should be
monitored.
• Seal gas. This gas isolates process gas from the lubricating oil, or
isolates process gas from the shaft if magnetic bearings are used,
and must be clean and constantly available at the operating
pressure. Sales gas is commonly used. Otherwise, a warmed inlet
gas stream off of the expander inlet separator is used. (The gas
must be warmed to 70°F [20°C] or more to prevent thickening of the
lube oil, if used.)
• Lubricant pumps. These pumps must maintain a constant flow to
lubricate the bearings if oil is used. A spare pump is mandatory.
The Engineering Data Book (2004c) describes the lubrication
system.
• Shut-off valves. A quick-closure shut-off valve is used to shut in the
inlet for startup and shutdown.

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As is the case for centrifugal compressors, turboexpander efficiency
diminishes when operating off of the design point. This variance can be about
5 to 7 percentage points when the flow increases or decreases by 50%.
However, the turboexpander normally is driving a compressor, which also will
suffer loss in efficiency when off of the design point. Therefore, the overall
effect on the turboexpander−compressor unit efficiency will be larger. As with
centrifugal compressors, surge control is needed.
Expansion turbines are also widely used for:
 Energy extraction applications such as refrigeration.
 Recovery of power from high-pressure wellhead natural gas.
 In power cycles using geothermal heat.
 In Organic Rankine cycle (ORC) used in cryogenic process
plants in order to achieve overall utility consumption.
 In paper and other industries for waste gas energy recovery.
 Freezing or condensing of impurities in gas streams.
FIGURE 23 EXPANSION TURBINES APPLICATION

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6. Heat Exchanger
Most heat exchangers in a gas plant operating at or above ambient
temperature are conventional shell and tube type and are ideal for steam
and hot oil systems where fouling occurs. They are relatively inexpensive
and easy to maintain because the tube bundle can be removed and tubes
cleaned or replaced as needed.
Where the fluids are clean and fouling does not occur, such as in gas−gas
exchangers, compact heat exchangers are ideal.
6.1 Introduction
A heat exchanger is a device that is used to transfer thermal energy
(enthalpy) between two or more fluids, between a solid surface and a fluid,
or between solid particulates and a fluid, at different temperatures and in
thermal contact. In heat exchangers, there are usually no external heat and
work interactions.
Typical applications involve heating or cooling of a fluid stream of concern
and evaporation or condensation of single- or multicomponent fluid streams.
In other applications, the objective may be to recover or reject heat, or
sterilize, pasteurize, fractionate, distill, concentrate, crystallize, or control a
process fluid.
FIGURE 24 HEAT EXCHANGERS
In most heat exchangers, heat transfer between fluids takes place
through a separating wall or into and out of a wall in a transient manner. In
many heat exchangers, the fluids are separated by a heat transfer surface,
and ideally they do not mix or leak.

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Transfer of heat happens by three principle means: radiation, conduction
and convection. In the use of heat exchangers radiation does take place.
However, in comparison to conduction and convection, radiation does not
play a major role. Conduction occurs as the heat from the higher
temperature fluid passes through the solid wall. To maximize the heat
transfer, the wall should be thin and made of a very conductive material.
The biggest contribution to heat transfer in a heat exchanger is made
through convection.
Industrial Heat Exchangers :
 Double-pipe heat exchanger
 Shell and tube heat exchanger
 Plate and frame heat exchanger
 Spiral heat exchanger
 Pipe coil exchanger
 Air-cooled heat exchangers
Double-pipe heat exchanger
The double-pipe heat exchanger is one of the simplest types of heat
exchangers. It is called a double-pipe exchanger because one fluid flows
inside a pipe and the other fluid flows between that pipe and another pipe
that surrounds the first. This is a concentric tube construction. Flow in a
double-pipe heat exchanger can be co-current or counter-current. There
are two flow configurations: co-current is when the flow of the two
streams is in the same direction, counter current is when the flow of the
streams is in opposite directions.
Heat Transfer
Conduction
Convection
Radiant
FIGURE 25 : DOUBLE PIPE HEAT EXCHANGER

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In this double-pipe heat exchanger a hot process fluid flowing through the
inner pipe transfers its heat to cooling water flowing in the outer pipe. The
system is in steady state until conditions change, such as flow rate or inlet
temperature. These changes in conditions cause the temperature
distribution to change with time until a new steady state is reached.
Advantages:
 Its excellent capacity for thermal expansion
 It is easy to install and clean
 Its modular design makes it easy to add new sections
 Replacement parts are inexpensive and always in supply
Disadvantages
 It is not as cost effective as most shell and tube exchangers
 it requires special gaskets
Shell and Tube Heat Exchangers
Shell and tube heat exchangers consist of a series of tubes. One set of
these tubes contains the fluid that must be either heated or cooled. The
second fluid runs over the tubes that are being heated or cooled so that it
can either provide the heat or absorb the heat required. A set of tubes is
called the tube bundle and can be made up of several types of tubes: plain,
longitudinally finned, etc. Shell and tube heat exchangers are typically used
for high-pressure applications (with pressures greater than 30 bar and
temperatures greater than 260 °C). This is because the shell and tube heat
exchangers are robust due to their shape.
FIGURE 26 MULTI TUBE

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Plate and Frame Heat Exchanger
The plate heat exchanger. One is
composed of multiple, thin, slightly
separated plates that have very large
surface areas and fluid flow passages for
heat transfer. This stacked-plate
arrangement can be more effective, in a
given space, than the shell and tube heat
exchanger. Advances in gasket and
brazing technology have made the plate-
type heat exchanger increasingly
practical. In HVAC applications, large heat
exchangers of this type are called plate-
and-frame; when used in open loops.
Spiral Heat Exchanger
A spiral heat exchanger (SHE), may refer to a helical (coiled) tube
configuration, more generally, the term refers to a pair of flat surfaces that
are coiled to form the two channels in a counter-flow arrangement. Each of
the two channels has one long curved path. A pair of fluid ports are
connected tangentially to the outer arms of the spiral, and axial ports are
common, but optional.
The main advantage of the SHE is its highly efficient use of space. This
attribute is often leveraged and partially reallocated to gain other
improvements in performance, according to well known tradeoffs in heat
exchanger design. (A notable tradeoff is capital cost vs operating cost.) A
compact SHE may be used to have a smaller footprint and thus lower all-
around capital costs, or an over-sized SHE may be used to have less
pressure drop, less pumping energy, higher thermal efficiency, and lower
energy costs.
FIGURE 27 PLATE AND FRAME HEAT EXCHANGER
FIGURE 28: SPIRAL HEAT EXCHANGER

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The Cryogenic Heat Exchanger
Brazed Aluminum Exchanger (Prico & Phillips)
The vacuum brazed ( aluminium plate-fin heat exchangers ) are key
components in many cryogenic process plants. They are the preferred heat
exchangers in small LNG plants.
Benefits
 Compactness, saving installation space and investment costs
 Many process streams can be handled in a single unit, thus avoiding
expensive interconnecting piping of different units
 Low equipment weight
FIGURE 27 PLATE-FIN HEAT EXCHANGERS

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The Coil Wound Heat Exchanger
The practically unrestricted range of usable materials allow coil-wound
heat exchangers to be used for a wide range of applications in cold as
well as warm applications. The heat exchangers are made in aluminium.
The coil-wound heat exchanger is the core equipment in large base-load
LNG plants
Benefits
 Broad temperature and pressure ranges
 Multiple fluids can be treated in one exchanger
 Compact unit with large specific heat transfer area per
volume
 Capable for high pressure service
 Robust design suitable to cope with transient off-spec
conditions
 Integrated two-phase separator and distributor, if required
 No bundle sagging due to proprietary support system
 100% self-draining
 Available in various materials
 Possibility for bundle temperature Recording
Produces by:
 Air Products and Chemicals Inc. in USA
 Linde in Germany
FIGURE 28 COIL WOUND HEAT EXCHANGER

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Dimensions of a the main LNG coil-wound heat exchanger is as follows:
 Height 10-50 m
 Diameter 3-5 m
 Core tube diameter 1 m
 Tube length 70-100 m
 Tube diameter 10-15 mm
 Typical surface density 100-150 m2/m3
 Typical heating surface 10.000-20.000 m2
The APCI LNG Main Heat Exchanger
The Main Cryogenic Heat Exchanger, or MCHE, is the heart of the LNG
process.
 Each MCHE consists of several spiral-wound tube bundles housed
within an aluminum or stainless steel pressure shell designed to retain
refrigerants in the event of a shutdown.
 For LNG service the heat exchangers may consist of one-, two-, or
three-tube bundles, each made up of several tube circuits.
 With this type of exchanger, the tube circuit areas can be matched to
the process requirements. The result is a very efficient and compact
design
Attributes of MCR Cryogenic Heat Exchangers
 APCI is the world‟s largest supplier of baseload LNG heat exchangers.
.
 The large size of the individual heat exchanger tube bundles facilitates
the design of large process trains.
 In addition to providing economies of scale, this leads to simple piping
and control systems and, consequently, to reductions in installation,
operation, and maintenance costs.
LNG Exchanger Design
The ideal LNG exchanger would be: large single unit, highest heat
exchange surface per volume, highest heat duty per surface (lowest
temperature approach), and . . . available from many manufacturer (not a
proprietary design)
Largest single unit, with highest heat exchange per volume is currently
the APCI spiral wound heat exchanger.
Largest single unit plate finned brazed aluminum exchanger is 1/10thof
APCI LNG exchanger. Multiple units in parallel add control complexity
and gas/liquid re-mixing problem.

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LNG Heat Exchangers Comparison
Plate-Fin-Heat-Exchangers Coil-Wound-Heat-Exchangers
Characteristics
Extremely compact Compact
Multiple streams Multiple streams
Single and two-phase streams Single and two-phase streams
Fluid Very clean Clean
Flow-types
Counter-flow Cross counter-flow
Cross-flow
Heating-surface 300 - 1400 m²/m³ 20 - 300 m²/m³
Materials
Aluminum Aluminum
Stainless steel (SS)
Carbon steel (CS)
Special alloys
Temperatures -269°C to +65 °C (150 °F) All
Pressures Up to 115 bar (1660 psi) Up to 250 bar (3625 psi)
Applications
Cryogenic plants Also for corrosive fluids
Non-corrosive fluids Also for thermal shocks
Very limited installation space Also for higher temperatures
TABLE 3 :LNG HEAT EXCHANGERS COMPARISON

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Howard, I., Hannibal’s Experiences, Proceedings of the Laurance Reid
Gas Conditioning Conference, 1998, 194.
Jones, S., Lee, S., Evans, M., and Chen, R., Simultaneous Removal of
Water and BTEX from Feed Gas for a Cryogenic Plant, Proceedings of
the Seventy-Eighth Annual Convention of the Gas Processors
Association, 1999, 108.
Mallett, M.W., Conoco/Tenneco Gas Plant Meeting the Challenges,
Proceedings of the Sixty-Seventh Annual Convention of the Gas
Processors Association, Tulsa, OK, 1988, 150.