liquefiers Outline Air Liquide range of cryogenic plants at 45K and below Few thermodynamical concepts Refrigerators and Liquefiers main equipments Helium refrigerators and ID: 781475
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Slide1
Helium refrigerators and liquefiers
Slide2OutlineAir Liquide range of
cryogenic plants at 4.5K and belowFew
thermodynamical conceptsRefrigerators and Liquefiers
main equipments
Slide3Helium refrigerators and Liquefiers
Why to use helium
refrigerators and liquefiers ?Supraconductivity
(magnets, fusion, light sources,…)Industrial
market
(
gas
transportation,…)
Cavities for particles linear accelerators (2K)Cold neutron sources (20K)Space activities
Why
?
Slide4Air Liquide range of cryogenic plants
Standard
Liquefiers
Standard
liquefiers
range
from
15 L/
hr to 650 L/hrFully automatic operation
Slide5Air Liquide range of cryogenic plants
Standard
Refrigerators
Standard
refrigerators
range
from
100W to 1000 W @ 4.5K
Fully automatic operation
Slide6Air Liquide range of cryogenic plants
Specific
refrigerators
and
liquefiers
Specific
customized
liquefiers and refrigerators above650 L/hr and 1000 W @ 4.5KExample: SCL2 - Korea
- 4.2 kW @
2K - ~4 MW of
installed
power
4.2 kW @2K CB
3.6m
20m
Slide7Air Liquide range of cryogenic plants
Specific
refrigerators
and
liquefiers
Specific
customized
liquefiers and refrigerators above650 L/hr and 1000 W @ 4.5KExample: ITER
-
France – 3 x 25
kW @
4.5K
with
pulses
operation
~24 MW of
installed
power
110
kWeq
. @ 4.5K
40
kWeq
. @ 4.5K
Loads
variation of 65% in 30 min.
Slide8Few thermodynamical concepts
General
principle
Power injection
which
will
be
transformed
into
cold
Recovery
of not
used
power
Transfer of power to a
colder
temperature
level
Heat
load
cooling
Insulation
against
heat
inleaks
Slide9Helium properties
Problem: during expansion in a valve, helium warms
-up above ~40KA valve can be
used to cool-down helium only below ~40K.
Above
~40K,
energy
needs
to be extracted with turbinesHelium
particular
properties
…
Slide10Few thermodynamical concepts
General
principle
Turbines are
used
to
extract
energy
Increasing
the
number
of turbines
steps
increases
the
efficiency
Slide11Few thermodynamical concepts
TS
Diagram
A simple
brayton
cycle
Slide12Cryogenic plants main components
Global
view
Slide13Cryogenic plants main components
Global
view
Slide14Cryogenic plants main components
Standard
Liquefier
process
scheme
Slide15Cryogenic plants main components
Helium
screw
compressors
Main Characteristics
:
Oil lubricated
screw
compressorHigh pressure up to 25 barSpecial oil is used to avoid contamination of cryogenic circuitsVariable Frequency Drive (VFD) can be used to reduce electric power when capacity reduction is requiredVolumetric compressors: mass flow m
a
P
in
/T
in
Power:
P
id
= m.
R.T
in
.Ln
(P
out
/P
in)
Yield ~ 50%
Slide16Cryogenic plants main components
Helium
screw
compressors
Ideal adiabatic compression of helium to 15 bar would lead to a temperature of 585°C.
Oil is used to keep compressor outlet temperature around 80°C.
To compress 1 g/s of helium to 15 bar, ~40 g/s of oil is required to limit temperature increase to 80°C
20% of
cooling
8
0% of
cooling
Slide17Cryogenic plants main components
Helium
screw
compressors
Helium "standard" Compressors
Up to 100 g/s and 300 kW
Specific compressors skids
Above 300 kW and when number of machines decreases reliability and generates too much maintenance
Slide18Cryogenic plants main components
Oil
Removal System (ORS)
Oil Removal System (ORS) is used to remove traces of oil in helium
Coalescing cartridges remove oil aerosols (liquid droplets of µm size)
Charcoal
adsorber
remove oil vapours
ORS efficiency is crucial to avoid cryogenic heat exchangers clogging and turbines damage
Slide19Cryogenic plants main components
Oil
Removal System (ORS)
Oil Removal System (ORS) is used to remove traces of oil in helium
Coalescing cartridges remove oil aerosols (liquid droplets of µm size)
Charcoal
adsorber
remove oil vapours
ORS efficiency is crucial to avoid cryogenic heat exchangers clogging and turbines damage
Slide20Cryogenic plants main components
Helium
Buffers
Characteristics
:
3
bar abs <
P
operation
< 13 barAt room temperatureVolume: from 5 m3 (for HELIAL SL) to 400 m3
(large
cryoplants
)
Gaseous helium storage is necessary to manage helium inventory during cool-down or warm-up.
Slide21Cryogenic plants main components
Plate fin
heat
exchangers
Brazed aluminium plate fin heat exchangers are used in cold boxes to transfer heat from low pressure circuits to high pressure circuits.
High
compacity
=> limit the size of vacuum vessels
Design with multi-streams
Sensibles
to thermal stresses
Helium
flow
Picture
from
Fives Cryo
Slide22Cryogenic plants main components
Turbines
Turbines are used to cool down helium (extract power from the gas)
High speed turbines (up to 4 000 Hz) based on static gas bearings
Large range of power: from 200 W to 200 kW
Efficiency between 70 and 85%
High reliability : MTBF > 100 000 hrs
Slide23Cryogenic plants main components
Turbines
Power extracted proportional to mass flow rate
High
pressure
flow
Kinetic
energy
production
on
fixed
Inlet
Guide Vanes
And flow calibration
mechanical
energy
transmission
through
the
shaft
Journal and
thrust
gas
Bearing
for
shaft
guidance
Fluid
enthalpy
extraction by
centripetal
turbine
impeller
Centrifugal
compressor
driven
by turbine
mechanical
energy
Slide24Cryogenic plants main components
Turbines
A complete management of the production chain : from design up to test
Slide25Cryogenic plants main components
Adsorbers
Adsorbers
are used at ~80K and ~20K to remove small traces of impurities
Molecular sieve or activated charcoal traps
air impurities in the ppm range
1 single
adsorber
: stop of the plant for
regeneration
or 2
adsorbers
operating in push-pull
for regeneration on-line
Slide26Cryogenic plants main components
Insulation
system
A vacuum vessel is used to install all cryogenic component
Multilayer Insulation (MLI) is used to stop radiations
Vacuum pumps are used to stop convection (vacuum < 10
-5
mbar)
Material with low conductivity and long thermal path are used to reduce conduction
Slide27Cryogenic plants main componentsHigh
efficiency cryomachines manufactured
by AL-aT since 80's with
new developments in 2009Technology
based
on
magnetic
bearings
for high
reliability (MTBF > 100 000 hrs)More than 40 cryomachines
produced
since
new
developments
with
flow rates
from
10 g/s up to 220 g/s
Cold
Compressors
Slide28Helium properties
Risk of Anoxia
A light
gas
Helium
Nitrogen
Gas
density
(1
bar, 300K)
0.16 kg/m3
1.12 kg/m3
Boiling
temperature
(1
bar)
4.2 K
77.3 K
Liquid density at saturation (1 bar)
125 kg/m3
809 kg/m3
Vapor density at saturation (1 bar)
16.6 kg/m3
4.6 kg/m3
Cp
5.2 J/(g.K)
1.0 J/(
g.K
)
Latent heat (1 bar)
20.7 J/g
199
J/g
Sensible
heat
(
liq
-> 300K)
1543 J/g
234
J/g
x 178
x 720
x 780
x 7.5
x 74
x 1.2
Slide29Few thermodynamical concepts
Refrigerator
vs.
liquefier
Power
is
necessary
at cold
temperature
Continuous
power
is
necessary
between
ambiant
temperature
and cold
temperature
Cold production
Cold production
Refrigerator
Liquefier
Slide3030
Liquefaction
:
To
liquefy
helium
, extraction of specific heat
from
ambient
temperature
to 4.4K
is
necessary
,
then
extraction
from
latent
heat
is
necessary
to
liquefy
the
gas
.
COLD
BOX
300 K
1573 J/g
GHe
L He
4.4 K
10 J/g
31 J/g
Energy to extract =
1563
J/g
Refrigeration vs. Liquefaction
Large turbines are
required
to
produce
the cold
required
in all the
temperature
range
Slide3131
Réfrigeration at 4.5K:
Extraction of latent heat
at cold temperature
COLD
BOX
LHe
4.4 K
LHe
4.4 K
Re-liquefaction
Cold
vapours
returns
Energy to extract
=
21
J/g@4.4K
Refrigeration vs. Liquefaction
Large
heat
exchangers
are
required
to
transfer
energy
from
vapour
returns
to
helium
supply
Slide32Helium properties
Particular
properties
…
Slide33Helium properties
Liquid Helium:1 g/s of Helium
~20 W @ 4.4K 1 g/s of Helium
~30 L/hr
Gaseous
Helium
:
1 g/s of
Helium ~20 Nm3/hrCp = 5.2 J/(g.K)
Keep
in
mind
!
20 W of
heat
inleak
at 4.4K vaporises 30L/
hr
of
liquid
helium
20 W of
heat
inleak
warm up 1g/s of ~4K
Slide3434
Specific power or Carnot efficiency
Ideally, 70W at 300K are
necessary to produce 1W
at 4.2K
.
In
practical
,
between 250 and 400 W are necessary to produce 1 W at 4.2K. The larger the installation, the higher the efficiency.
Slide35Summary
Standard helium liquefiers available
from 15L/hr to 650 L/hr
Standard helium refrigerators
available
from
100W to 1000 W @ 4.5K
Specific customized plants for helium liquefiers larger than 650 L/hr and refrigerators larger than 1000 W @ 4.5K
Several
references
at 1.8K or 2.0K
with
state of the art cold
compressor
technology
.
Helium
refrigerators
and
liquefiers
Slide36End of the presentation
Slide37Back-up slides
Slide38QuizzA
liquid helium dewar is
full of liquid helium. What
would be the pressure in the dewar if all the
liquid
vaporizes
up to ambiant
temperature ? A 1000L liquid helium dewar has 10W of heat inleaks. What is the autonomy of the dewar ?
A thermal
shield
requires
1g/s of
helium
at 35K. The
cryogenic
line to the thermal
shield
has 20W of
heat
inleaks
.
What
will
be the temperature at the thermal shield
inlet after the cryogenic
line ?
Questions
Slide39QuizzA
liquid helium dewar is
full of liquid helium. What
would be the pressure in the dewar if all the
liquid
vaporizes
up to ambiant
temperature ? 125/0.16 ~780 bar A 1000L liquid helium dewar has 10W of heat inleaks. What is the autonomy of the
dewar
?
10W = 0.5 g/s = 15 L/
hr
Autonomy
= 1000/15 ~ 67
hrs
A thermal
shield
requires
1g/s of
helium
at 35K. The
cryogenic
line to the thermal
shield has 20W of heat
inleaks. What will
be the temperature at the thermal shield
inlet after the cryogenic
line ?Q = m.Cp
.ΔT => Δ
T = 20/5.2 ~ 4K => Temperature
inlet = 39K
Answers
Slide40Thermodynamical concepts
The LATENT HEAT (Lv) is the quantity of
heat absorbed or released by a fluid
undergoing a change of state, such as ice
changing
to water or water to
steam, at constant
temperature
and pressure.
Also called heat of transformation.Applied to vaporisation, condensation, melting, solidification etc..For pure component, the process is isothermalExamples:Water : Liq to Gas @ 373K : 2300 kJ/kgWater : Solid to Liq
@ 273K : 330
kJ/kg
LN2
to GN2 at 77K : 200
kJ/kg
LHe
to
Ghe
at 4.2K : 20.7 kJ/kg
The SPECIFIC HEAT (Cp)
is
the
quantity
of
heat
necessary
to warm-up 1 g from
1 K.Examples:Water : 4.18 kJ/kg.K-1
Nitrogen : 1 kJ/kg.K-1Helium
: 5.2 kJ/kg.K-1
Latent
heat
Slide4141
Remark
:
Radiation
is
driven
by the warm
temperature
whatever the cold temperature.
T
c
= 80K, T
f
= 4K
80
4
= 4.09 x 10
7
4
4
= 256
(T
c
4
-T
f
4
) = 4.09 x 107
Thermal shields
can
thus allow
to decrease radiation
heat at 4K by a factor of 200. (
4W sur les Gardner !)
Thermal
Shields
utility:
limit
the radiation
heat
loads
Stefan-Boltzmann
law
:
Q
= kA x (
T
w
4
-T
c
4
)
Un simple calcul :
T
w
= 300K,
T
c
= 4K
T
w
= 300K,
T
c
= 80K
300
4
= 8.10 x 10
9
300
4
= 8.1 x 10
9
4
4
= 256 80
4
= 4.09 x 10
7
(
T
w
4
-T
c
4
) =
8.10 x 10
9
(
T
w
4
-T
c
4
) =
8.06 x 10
9
Helium properties
But not
so
particular
…
During an isenthalpic expansion in a valve, does helium cool down or warm-up ?