Exergy Analysis of the Cryogenic Helium Distribution ... · PDF fileExergy Analysis of the...

Exergy Analysis of theCryogenic Helium Distribution System for the Large Hadron Collider (LHC)for the Large Hadron Collider (LHC)
S. Claudet, Ph. Lebrun, L. Tavian & U. Wagner
(CERN)
Cryogenic Engineering Conference
(CERN)
International Cryogenic Materials ConferenceTucson, Arizona, USAJune 28 - July 2, 2009

Outline Introduction & Methodology
From LHC Architecture & Distribution Scheme to
simplified flow diagrams for exergy calculation
Exergy calculation results Exergy calculation results
Exergy Analysis
Conclusion
CEC/ICMC09 - Tucson (AZ) Exergy Analysis of the LHC Distribution System2/18

IntroductionLarge scale (capacity) superconducting applications require distributing cooling power over long distances (high flow rates) with minimised temperature gradients for high thermodynamique efficiency
A li tiR f i t Applicationwell optimised
Refrigerator(30% Carnot)
?!??!?
Exergy analysis (applied in the past for refrigeration plants) is proposed as a way to quantify distribution losses, with the potential to help technical arbitration among competing solutions
technical arbitration among competing solutions

MethodologyExergy E is a thermodynamic function of state
Useful R lT0 = 290K Useful or
ideal
Real
Losses
T0 290K(Cooling water temperature for heat rejection) Losses
E Q (1 T /T)Useful Exergy:
h TDefinition of Exergy:
E = Q (1 T0/T)
E Q [1 (T /T T ) l T /T ]Non-isothermal cooling duties:
e = h T0 s
E (h T )Process between two points:
E = Q [1 (T0/T2-T1) ln T2/T1]Ereal = m (h T0 s)
Exergetic efficiency: = Euseful/Ereal
Losses: heat inleaks, pressure drop, mixing, mismatch cooling temp. w.r.t temperature requirements

LHC Cryogenic Architecture
Pt 4
Pt 5
Pt 6
Warm CompressorStation
Upper Cold BoxCold Box
Surfa
ce
1.8 K Refrigeration Unit New 4.5 K Refrigerator Ex-LEP 4.5 K refrigerator 1.8 K Refrigeration Unit
8 x 18kW @ 4.5 K
1800 sc magnets
Upper Cold Box
Interconnection Box
Cold Box
Lower Cold Box
Cold Compressor Cold Compressor
Shaft
Cav
ern
Pt 3 Pt 7Cryoplant DistributionPresent Version24 km & 20 kW @ 1.8 K
36000 t @ 1.9K
Interconnection Box
Distribution Line Distribution Line
Magnet Cryostats Magnet Cryostats
box box
Tunn
el
LHC Sector (3.3 km) LHC Sector (3.3 km)
Pt 8Pt 2
130 t He inventory
System to be studied
Pt 1Pt 1.8Cryogenic plant
System to be studied

Distribution & Magnet Cooling
Local distributiondistribution
LHC Sector
(Distribution and machine)(Distribution and machine)

Part 1: LHC Local Distribution4.5 K Ref.
Simplified flow diagram for helium distribution between the 4.5 K
1.8 K Unit
LHC Sector
refrigerator and a LHC sector
Each point Each point defined by P,
T, m
h, s, e calculated
with HEPAK
with HEPAK

Part 2: LHC Sector
Simplified flow diagram a LHC sector
Each point Each point defined by P,
T, m
h, s, e calculated
with HEPAK
with HEPAK

Exergy Calculation Results Part 1: Local distribution
95 %
Part 2: LHC Sector
95 % 1079
Part 2: LHC Sector
Cooling circuit Process points Ereal [kW] Euseful [kW] [%]
iMain magnets 10 to 15 501 364 73Beam screens 20 to 22 271 205 76 Current leads 25 to 26 122 63.0 52 Stand-alone magnets and mixing 22 and 30 to 23 40.1 19.0 47 Thermal shields 40 to 41 145 122 8472 %
Total - 1079 774 72
72 %

LHC Distributionn Exergy Flow Diagram
Main magnetuseful (364 kW)
1.8 K refrigerator(34.1 kW)
1.8 K Units (2400 W)
1.8 K Main Magnets (Arcs)
73 %
Beam screenuseful (205 kW)
JT valves (44.7 kW)Subcooling HX (39.6 kW)
Return line (37.5 kW)HX tube (17.5 kW)
W)11
03 k
W)
( )(2400 W)
4.5 K
Beam Screen Shielding76 %
Current leaduseful (63.0 kW)
P capillaries & control valves (65.4 kW)(107
9 kW
4.5
K re
frige
rato
r (
5Refrigerator (18
kW) Current Leads Cooling
76 %
52 %
Thermal shielduseful (122 kW)
JT valves (1.5 kW)
Standalonemagnet
useful (19.0 kW)
P & T current leads (58.9 kW)
Mixing Pt 23 (19.7 kW)
Pit (8.0 kW)Subcooling (23.9 kW)
Mixing (25.8 kW)
4.5 K Magnets (Straight sections)
Thermal Shield47 %
Pressure drop (22.9 kW)LHC sector
From surface cryoplantto underground
30 % of Refrigerator
Thermal Shield84 %
95 % 72 %
Carnot 68 %

Analysis: Main Magnets Cooling47 0 % f LHC S t U f ll E 47.0 % of LHC Sector Usefull Exergy
73 %
The exergy losses are very similar among the different sources of irreversibility
irreversibility

Analysis: Beam Screen Cooling26 5 % f LHC S t U f ll E 26.5 % of LHC Sector Usefull Exergy
76 %
This is the price to pay for maintaining the thermodynamic state of the flowing helium well above the critical point in helium well above the critical point, in order to limit the risk of instability.

Analysis: Thermal Shield Cooling15 5 % f LHC S t U f ll E 15.5 % of LHC Sector Usefull Exergy
84 %
The piping diameter was defined to
84 %
The piping diameter was defined to match ex-LEP refurbished plants, thus leaving room for optimisation in case th di t ib ti t ld h b the distribution system would have been newly designed

Analysis: Current Leads Cooling8 2 % f LHC S t U f ll E 8.2 % of LHC Sector Usefull Exergy
52 %
High temperature difference between
52 %
High temperature difference between cooling fluid and maximum tolerated by HTS part of the lead and high pressure drop in heat exchanger (incl valve)
20K
supply50K
Max. for HTS drop in heat-exchanger (incl. valve)
(Conscious wish to have temperature margin for this new application)LHe
HTS
margin for this new application)LHe

Analysis: Stand-Alone Magnets2 5 % f LHC S t U f ll E 2.5 % of LHC Sector Usefull Exergy
47 %47 %
LHeL l
GHe
Considering mixing returned GHe vapors (4.5 K) with 20 K returned gas from the beam screen cooling loop
Level
from the beam screen cooling loop (20 K) penalises the exergetic efficiency

Analysis: Local Distribution7 5 % f LHC S t U f ll E 7.5 % of LHC Sector Usefull Exergy
4.5 K Ref.
95 %
1.8 K LHC 8Unit
CSector
h = Q/m +/- g dVertical lines:
If we cannot do much against gravity, subcooling and part of mixing have
g
been imposed mostly by the constraints to be able to cool sc cavities

From Simplified Schemes to Real Distribution ?
Exergy analysis: good overview of the losses due to design choices
H t t i d t il d t i lifi ti However, not exact in every detail due to simplifications (simplified model - specification data - exergy analysis)
A complete exergy analysis of a LHC sector would certainly be interesting in order to compare the real loads and losses along the sector to the design values once at nominal operating conditionssector to the design values, once at nominal operating conditions.
Seems difficult as helium properties cannot be measured with ffi i t i i i th i t ll d i d t i l sufficient precision using the installed industrial process
instrumentation (mass flow values not measured at most locations along the sector)
g )

Conclusion Thanks to the variety of its cooling duties, a 3.3km long sector of the
LHC provides an interesting field for application of the exergetic analysis method to cryogenic distributionanalysis method to cryogenic distribution
Cooling schemes and losses of very different nature can be compared in terms of their relative exergetic cost The absolute value of the in terms of their relative exergetic cost. The absolute value of the exergy gives almost directly the input power to the refrigeration system (within efficiency factor

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