Air Revitalization

Air Revitalization 

• Fundamentals of Air Revitalization 

• Gas Supplies 

• CO2 Collection 

• CO2 Reduction 

• H2O Electrolysis 

• Trace Contaminant Control 

U N I V E R S I T Y O F 

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© 2008 David L. Akin - All rights reserved 

http://spacecraft.ssl.umd.edu 

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ENAE 697 -Space Human Factors and Life Support

ISS Consumables Budget 

Consumable Design Load 

(kg/person-day) 

Oxygen 0.85 

Water (drinking) 1.6 

Water (in food) 1.15 

Water (clothes and dishes) 17.9 

Water (sanitary) 7.3 

Water (food prep) 0.75 

Food solids 0.62 


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Nitrogen Makeup 

• Nitrogen lost to airlock purges, leakage (can be 

>1%/day) 

• Need to replenish N 2 to maintain total 

atmospheric pressure 

• Choices: 

– High pressure (4500 psi) N 2 gas bottles 

– Cryogenic liquid nitrogen 

– Storable nitrogen-bearing compounds (NH 3 , N 2 O, 

N 2 H 4 ) 


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Nitrogen from Hydrazine (N2H4) 

from Wieland, “Designing for Human Presence in Space” NASA RP-1324, 1994 


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Air Component Storage 

• Cryogenic Liquids 

– O2: 1140 kg/m 3 , Tboil=-183°C=84K 

– N2: 808 kg/m 3 , Tboil=-196°C=77K 

– H2: 70 kg/m 3 , Tboil=-253°C=20K 

• Gases 

– O2: 1.43 kg/m 3 @STP 

– N2: 1.25 kg/m 3 @STP 

– H2: 0.09 kg/m 3 @STP 


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Cryogenic Tankage 

• Volume-based relation 

m < kg >= 68.38 V < m 3 > 0.75 

• Specific mass-based relations 

mtank < kg >= 0.3485 [MLOX < kg >] 0.75 

mtank < kg >= 0.4512 [MLN2 

mtank < kg >= 2.826 [MLH2 < kg >]0.75 

• Generic mass-based nondimensional relation 

mtank 

= 

68.38 

mcontents 


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< kg >]0.75 

(Mcontents ρ 3 contents) 0.25 



High Pressure Gas Tanks 

• Typical pressures 200 atm (mass optimized) to 

500-700 atm (volume optimized) 

• GN2 tanks 0.3-0.7 x mass of contained gas 

• GOx tank 0.4 x mass of contained gas 


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CO2 Removal Options 

• 4BMS (Four Bed Molecular Sieves) 

• 2BMS (Two Bed Molecular Sieves) 

• EDC (Electrochemical Depolarized 

Concentrator) 

• APC (Air Polarized Concentrator) 

• SAWD (Solid Amine Water Desorption) 

• LiOH (Lithium Hydroxide Canisters) 

• METOX (Metal Oxide Adsorption) 


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4BMS Schematic 



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2BMS Schematic 



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CO 2 Regenerable Scrubbing Systems 

• CO 2 production ~1 kg/person-day 

• 4-Bed Molecular Sieves (4BMS) 

– Dual paths (one scrubbing, one regenerating) 

– Desiccant bed for moisture removal, 5 A zeolite sieve 

for CO2 

– Heat to 350°-400°C to regenerate 

– 30 kg; 0.11 m 3 ; 170 W (all per kg-day of CO 2 removal) 

• 2-Bed Molecular Sieves (2BMS) 

– Carbon molecular sieve for CO 2 

– 16 kg; 0.09 m 3 ; 77 W (per kg/day CO 2 ) 


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EDC Schematic 

CO2 + OH → CO3 + HCO3 



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• Electrochemical Depolarization Concentration 

(EDC) 

– Uses fuel-cell type reaction to concentrate CO2 at the 

anode 

– CO2 + 1/2O2 + H2 --> CO2 + H2O + electricity + heat 

– CO2 and H2 are collected at anode and directed to 

CO2 recycling system (combustible mixture!) 

– 11 kg; 0.02 m 3 ; 60 W (all per kg-day of CO 2 removal); 

does not include reactants for power output 


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APC Schematic 



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SAWD Schematic 



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• Solid Amine Water Desorption (SAWD) 

– Amine resin absorbs H 2 O and CO 2 ; steam heat 

regenerates 

• Amine + H 2 O --> Amine-H 2 O (hydrated amine) 

• Amine-H 2 O + CO 2 --> Amine-H 2 CO 3 (bicarbonate) 

• Amine-H 2 CO 3 + steam --> Amine + H 2 O + CO 2 



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LiOH Schematic 


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NEED REAL LIOH DATA!!! 

LiOH + H2O → (LiOH − H2O) 

(LiOH − H2O)+CO2 → Li2CO3 + H2O 




LiOH Mass Estimating Factor 

• Space Shuttle LiOH system uses 7 kg cartridge, 

good for 4 crew-days = 1.75 kg/crew/day 


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METOX (Metal Oxide Adsorption) 

• Rechargeable cartridge system 

• Direct replacement for LiOH cannisters in EMU 

PLSS 

• 13 kg/8 person-hr cartridge 

• 14 hr recharge in oven 

• 55 cycles in operating lifetime 

• Regenerator module is 17.7”w x 19”h x 30”d, 105 

lbs (holds 2 canisters for recharge) - power is 

1000 W steady state 


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CO2 Membrane Removal Systems 

• Osmotic membranes 

– Poor gas selectivity 

– Returns CO2 to cabin air 

• Electroactive carriers 

– Electroactive molecules act as CO2 “pump” 

– Very early in development 

• Metal Oxides 

– AgO2 absorbs CO2 (0.12 kg O2/kg AgO2) 

– Regenerate at 140°C for 8 hrs (1 kW) - 50-60 cycles 

– Replacing LiOH in EMUs for ISS 


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CO2 Reduction Options 

• Bosch reactor 

• Sabatier reactor 

• ACRS (Advanced Carbon Reactor System) 

• CO2EL/BD (CO2 Electrolysis/Boudouard) 


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Sabatier Reactor Schematic 



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Bosch Reactor Schematic 



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CO 2 Reduction 

• Sabatier reaction 

– CO 2 + 4H 2 --> CH 4 + 2H 2 O 

– Lowest temperature (250°-300°C) with Ni catalyst 

– Electrolyze H 2 O to get H 2 , find use for CH 4 

– 91 kg; 3 m 3 ; 260 W (all per kg-day of CO 2 removal) 

• Bosch reaction 

– CO 2 + 2H 2 --> C + 2H 2 O 

– 1030°C with Fe catalyst 

– C residue hard to deal with (contaminates catalyst) 



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ACRS Schematic 



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CO 2 Reduction 

• Advance Carbon-formation Reactor System 

(ACRS) 

– CH 4 --> C + 2H 2 

– ALL THE STUFF BELOW IS COPIED FROM SABATIER REACTOR - GET REAL 

DATA FOR ACRS 

– Lowest temperature (250°-300°C) with Ni catalyst 

– Electrolyze H 2 O to get H 2 , find use for CH 4 



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CO2EL/BD Schematic 



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Oxygen Generation Options 

• SFWE (Static Feed Water Electrolysis System) 

• WVE (Water Vapor Electrolysis) 

• SPE (Solid Polymer Electrolyte) 

• Perchlorate candles 


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SFWE Schematic 



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WVE Schematic 



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SPE Schematic 



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Nonregenerable O2 Production 

Material kg(material)/kg(O2) 

H2O2 2.1 

LiO2 1.62 

K2O2 2.96 

MgO4 1.84 

CaO4 2.08 

LiClO4 2.8 

KClO4 2.16 

Mg(ClO4)2 1.74 

• Allocate an additional 10 kg/kg O2 for packaging, in addition to 

combustion receptacle (mass TBD) 


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Superoxides and Ozonides 

• O2 generation 

– KO 2 + 2H 2 O --> 4KOH + 3O 2 

– KO 3 + 2H 2 O --> 4KOH + 5O 2 

• CO2 reduction 

– 4KOH + 2CO 2 --> 2K 2 CO 3 + 2H 2 O 

– 2K 2 CO 3 + 2H 2 O + 2CO 2 --> 4KHCO 3 

• KO2 removes 0.31 kg CO2/kg and generates 

0.38 kg O2/kg 


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Trace Contaminant Control 

• Particulate Filters (dusts and aerosols) 

• Activated Charcoal (high molecular weight 

contaminants) 

• Chemisorbant Beds (nitrogen and sulpher 

compounds, halogens and metal hybrids) 

• Catalytic Burners (oxidize contaminants that 

can’t be absorbed) 

• 100 kg; 0.3 m 3 ; 150 W (all per person) 


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Trace Contaminant Control Schematic 



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CO2 Collection System Trade 

System Mass (kg) 

1600 

1400 

1200 

1000 

800 

600 

400 

200 

0 

0 50 100 150 200 


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Duration (days) 

CO2/LiOH CO2/2BMS 



O2 Recovery System Trade 

System Mass (kg) 

2000 

1800 

1600 

1400 

1200 

1000 

800 

600 

400 

200 

0 

0 50 100 150 200 


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Duration (days) 

O2/Open Loop O2/Sabatier 



ISS Air Revitalization System Rack 



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References 

• Peter Eckart, Spaceflight Life Support and Biospherics, 

Kluwer Academic, 1996 

• Wiley Larson and Linda Pranke, Human Spaceflight: 

Mission Analysis and Design, McGraw-Hill 

• A. E. Nicogossian, et. al., eds., Space Biology and 

Medicine - Volume II: Life Support and Habitability, 

American Institute of Aeronautics and Astronautics, 

1994 

• Susanne Churchill, ed., Fundamentals of Space Life 

Sciences, Krieger Publishing, 1997 


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Air Revitalization

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