MINIATURE ENGINEERING SYSTEMS GROUPMINIATURE ENGINEERING SYSTEMS GROUP::

COST ANALYSIS OF PRE-CHILLING AND COST ANALYSIS OF PRE-CHILLING AND HEAT LEAKAGE DURING OPERATION HEAT LEAKAGE DURING OPERATION

FORFORLH2 VJ STORAGE & TRANSFER LH2 VJ STORAGE & TRANSFER

FACILITIES AT NASA KSC FACILITIES AT NASA KSC

Presented by –Presented by –

K.V.Krishna MurtyK.V.Krishna Murty

ReferencesReferences:: A report on ‘NASA KSC Base Center Hydrogen Operations’ by Dr.Addison Bain, 2001-2002.

Communication of Mr.Thomas Tomsik (NASA GRC).

Communication of Mr.Bill Notardonato (NASA KSC).

LH2 Storage and Transfer facilities:LH2 Storage and Transfer facilities: LH2 Storage Tank: Outer Diameter of the outer shell = 70 ft, Inner Diameter of the inner shell = 62.5 ft, Material – Stainless Steel.

LH2 Transfer Line: Fill Rate to ET = 8,400 gpm to 10,000 gpm, Outer Jacket m/l – Stainless Steel, Inner Jacket m/l – Welded Invar,

Economic Analysis of Pre-Chilling of Economic Analysis of Pre-Chilling of metals:metals:

Assumptions and Values:

Latent Heat of Vaporization of LH2 (L): 56 W-hr/lb Cost of Electricity = 0.05 $/kW-hr LH2 cost = 2 $/lb Specific Heat of 304 SS at cryogenic temperature = 144 J/lb-K

• Density of 304 SS = 0.285 lb/in3 = 7,900 kg/m3

Specific Heat of Welded Invar at cryogenic temperature = 149 J/lb-K Density of Welded Invar = 0.291 lb/in3 = 8,055 kg/m3

• Thickness of storage tank = ½ in (assumed for calculations), VJ Transfer Line Length = 1500 ft Cooling Power of 1 RTBC = 1 kW @ 19K

Cost of Pre-ChillingCost of Pre-Chilling::

304 SS304 SS::

Cost of pre-chilling per lb of SS: 310K80K 80K19KLH2 Boil-off $0.328 $0.087RTBC $0.004 $0.018

Cost of pre-chilling 304 SS over the complete range (310K 19K):

cost/lb of SS SavingsBoil-off $0.414 0 %310K to 80K by RTBC, rest by boil-off $0.091 78 %310K to 19K by RTBC $0.022 95 %

Pre-chilling withtop stage to 80 K

Time Mass

(min) (lb)

7½ 208

15 417

22½ 625

30 833

Pre-chilling with bottom stage to 19K

Time Mass

(min) (lb)

37½ 208

75 417

112½ 625

150 833

Pre-Chilling of 304 SS (with 1 RTB):

Pre-chilling with 2 stages

Time Mass

(min) (lb)

45 208

90 417

135 625

180 833

Cost of Pre-ChillingCost of Pre-Chilling::

Welded InvarWelded Invar::

Cost of pre-chilling per lb of Welded Invar: 310K80K 80K19K

LH2 Boil-off $0.339 $0.090RTBC $0.004 $0.019

Cost of pre-chilling Welded Invar over the complete range

(310K 19K):cost/lb of WI Savings

Boil-off $0.429 0 %310K to 80K by RTBC, rest by boil-off $0.094 78 %310K to 19K by RTBC $0.023 95 %

Cost savings in maintaining the system Cost savings in maintaining the system at LH2 temperature by RTBCat LH2 temperature by RTBC:

Considering 1 kW of heat leakage,

If LH2 is let to boil-off:

Rate of LH2 boil-off = 430 lb/day

Cost of LH2 boil-off = 860 $/day

If RTBC is used to prevent LH2 boil-off:

Number of RTBC required = 1

Total cost of input power for 1 RTBC = 180 $/day

The savings from complete boil-off to RTBC use for Pre-

Chill = (860-180)/860 ≈ 79 %

Input power required to maintain the Input power required to maintain the Storage Tank (Pad B) at LH2 Storage Tank (Pad B) at LH2

temperaturetemperature::

LH2 Boil - Off = m = 600 gallons/day = 355 lb/day, LH2 Boil - Off = m = 600 gallons/day = 355 lb/day,

Cost of LH2 Boil-Off = $ 260,000/yr, Cost of LH2 Boil-Off = $ 260,000/yr,

Input power required = P where,

P= m*L = (355*56)/24 = 830 W.

So, a nominal cooling power of about 1 kW at 19K would be appropriate.

Time required to pre-chill the storage tank to 19 K with Time required to pre-chill the storage tank to 19 K with 1 RTB = 770 hr,1 RTB = 770 hr,Cost of LH2 Boil-Off for Pre-Chill = $ 105,000Cost of LH2 Boil-Off for Pre-Chill = $ 105,000

Pre-Chilling of Storage TankPre-Chilling of Storage Tank::

Pre-Chilling of Transfer LinePre-Chilling of Transfer Line::

LH2 Boil-Off Cost = $ 17,000,LH2 Boil-Off Cost = $ 17,000,

Number of RTBCs required to pre-chill the transfer Number of RTBCs required to pre-chill the transfer line to 19K in 9 hrs, I.e., with both stages = 15 (1 for line to 19K in 9 hrs, I.e., with both stages = 15 (1 for every 100 feet of the transfer line),every 100 feet of the transfer line),

Number of RTBCs required to pre-chill the transfer Number of RTBCs required to pre-chill the transfer line to 80K in 9 hrs, I.e., if only the top stage is used line to 80K in 9 hrs, I.e., if only the top stage is used = 3 (1 for every 500 feet of the transfer line).= 3 (1 for every 500 feet of the transfer line).

Conclusion:Conclusion:

The calculation shows that it is economically effective to use cryo-coolers for cooling the Liquid Hydrogen Vacuum Jacket storage & transfer facilities at NASA KSC.

Please NOTE: This analysis considers only the running costs associated with the cryocoolers. It does not take into account the installation and maintenance costs associated with the cryocoolers.