3. Outline
1. Design
objectives
Design Brief
Your consulting company has been hired by the Mars Exploration
Consortium, represented by Drs. Sarkisov and Valluri. The objective of the
consortium is to build a space station on Mars, capable of a continuous
support of a 10 member crew.
It has been planned that a re-supply mission should return to Mars every 18
months, with the main resources re-supplied being water, oxygen and food.
With the current cost of the re-supplement estimated at £1 M/kg, there is a
clear need for intensive onsite recycling of the resources, including water, air
and waste. Your company has been hired to develop an integrated recycling
solution, with an objective to minimize the weight of the re-supplement cargo.
Other technologies that should be explored along with the recycling, include
collection and purification of water on Mars and local production of food stock
(high protein vegetables etc).
The primary source of energy for the Martial station will be provided by a
nuclear reactor with up to 50 MWe capacity.
4. Outline
1. Design
objectives
Design Outline
We have identified 3 key stages of the design:
1. Resource requirements assuming no recycling or utilisation of local
sources
2. Resource requirements with recycling introduced
3. Resource requirements with recycling introduced and utilisation of
local resources. Investigation into unconventional technologies
5. Outline
1. Design
objectives
Using previous isolated systems as examples the essential resources
that must be controlled in a life support system are:
• Water
• Air
• Food
• Waste
• Thermal energy
• Biomass
The last three require control but no resupply on the Mars space
station, therefore these are not considered at this stage of design.
2. Stages
1&2 Outline
Stage 1 – Design basis
6. Outline
1. Design
objectives
Stage 1 – Resource requirements
Total Water Requirement
Drinking Hygiene* Safety Total
[kg] [kg] [kg] [kg]
17472 92345 27454.25 137271.25
Total Air Requirement
N2 O2 CO2 Safety Total
[kg] [kg] [kg] [kg] [kg]
0 4599 0 1149.75 5748.75
Calorific requirement
Standard Safety Total
[MJ] [MJ] [MJ]
57.3 14.325 71.625
Total
Oxygen
Total
Water
Total Resupply
Weight
Total Resupply
Cost
[kg] [kg] [kg] [£Million]
5748.75 137271.25 143020 143020
2. Stages
1&2 Outline
8. Outline
1. Design
objectives
Stage 2 – Design basis
Stage2: Introducing recycling processes to the Mars space station in order to
minimise the resupply requirements
Of the three focus resources identified in stage one, only two can effectively be
recycled. These are:
• Water
• Air
2. Stages
1&2 Outline
11. ?
Outline
1. Design
objectives
Air Recycling
Assumptions:
1. The air treatment is split into three distinct processes: CO2 separation,
CO2 consumption and O2 production
2. Assuming same composition of air as on Earth
3. Assume N2 is a buffer
2. Stages
1&2 Outline
13. Outline
1. Design
objectives
Criteria & Constraints
1. Applicability
2. Reliability
3. Modularity
4. Resupply
But in general we look for the technology to be;
Lightweight and economical, able to recover a high percentage of waste water
and operate with minimal consumables
2. Stages
1&2 Outline
3. Criteria &
Constraints
16. ?
Outline
1. Design
objectives
Water treatment- Final 5
2. Criteria &
constraints
DOC EC ISS Membranes
Resupply
(kg/18 months)
50 Unknown 1032 0
No. of
independent
units
3 1* 4 3*
Feed streams 2 1 2 1
Recovery rate
(%)
92 - 99 90
Maintanence Unknown - 50 days >18 months
4. Water
treatment
3. Stages
1&2 Outline
17. ?
Outline
1. Design
objectives
Water treatment- Final 5
2. Criteria &
constraints
DOC EC ISS Membranes
Resupply
(kg/18 months)
50 Unknown 1032 0
No. of
independent
units
3 1* 4 3*
Feed streams 2 1 2 1
Recovery rate
(%)
92 - 99 90
Maintanence Unknown - 50 days >18 months
4. Water
treatment
3. Stages
1&2 Outline
18. ?
Outline
1. Design
objectives
DOC VS ISS WATER RECOVERY SYSTEM
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• DOC requires a Re-supply of 4393 kg every 18 months
• ISS Water Recovery System requires a Re-supply of 1032 kg
every 18 months
• Due to the difference in weight per Re-supply mission we
have decided to choose to design the ISS Water Recovery
System. However this is based on the 2007 paper where the
recovery rate of the DOC system was 96%. If a more recent
paper is able to determine a greater recovery rate the DOC
system should be reconsidered for design.
19. ?
Outline
1. Design
objectives
Gas/Liquid Separator
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• The PFD shows that the stream exiting the Reactor enters the
Gas/Liquid Separator before moving on to the Ion-Exchange
bed.
• The Stream Leaving the Reactor contains oxidized organics
which need to be removed from the system.
• The Separator needs to be designed to remove the excess
Oxygen before the Stream continues to the IX Bed.
• Excess Oxygen can be damaging and so its removal is also
important for protecting expensive equipment.
20. ?
Outline
1. Design
objectives
Methods of Removal
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• In order to determine the Method of Removal the phase and
composition of the stream exiting the Reactor needs to be
determined
• From the PFD it is known excess oxygen needs to be removed.
If the oxygen is dissolved in a liquid stream, membrane
degasification is an option as it is able to remove the dissolved
gas by allowing it to pass through the Gas-Liquid Separation
membrane.
23. ?
Outline
1. Design
objectives
List of Assumptions
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• The Water Safety factor of 27454.3 kg is taken up but kept
in storage rather than used and put through recycling
process.
• It is assumed that all water used is 100% conserved and
there is no loss as all vapours end up contributing to the
cabin humidity which is condensed before going through
the recycling process.
• The required amount of water per day for the crew will be
used up per day, thus the water is recycled on a daily basis.
• How is water consumed on board?
24. ?
Outline
1. Design
objectives
Multifiltration Beds
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• MF consists of a particulate filter upstream of six
unibeds in series. Each unibed is composed of an
adsorption bed (activated carbon) and ion
exchange resin bed.
– Particulates are removed by filtration
– Suspended organics are removed by adsorption beds
– Inorganic salts are removed by ion exchange resin
beds.
Source: Mark Kliss, NASA ARC
• The MF canisters are designed for a 30 day life,
and hence will be replaced on a monthly basis.
26. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Media Function Media Description
MCV-77 Disinfection iodinated strong base anion, SBA, exchange resin
IRN-150 Removal of anions and cations mixture of gel types strong acid cation, SAC, (IRN-77, H+ form)
and SBA (IRN 78,OH- form)
IRN-77 Removal of cations SAC gel exchange resin in the H+ form
IRA-68 Removal of strong and weak acids weak base anion, WBA, gel exchange resin in the free base
form
580-26 Removal of nonpolar organics coconut-shell based activated carbon
APA Removal of nonpolar organics bituminous-coal based activated carbon
XAD-4 Removal of nonpolar organics polymeric adsorbent
IRN-150 Removal of anions and cations mixture of gel types SAC (IRN-77 , H+ form) and SBA (IRN-78,
OH- form)
IRN-77 Removal of cations SAC gel exchange resin in the H+ form
Ref. David Robert Hokanson, MICHIGAN TECHNOLOGICAL UNIVERSITY
27. ?
Outline
1. Design
objectives
Water Storage
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• The water prior to Recycling must be stored. Based on daily recycling of 200.4
kg/day the tank would need to contain that volume plus a safety factor of 10%.
• Thus the Water Tank before the process must store 220.5 kg, which corresponds to
a volume of approximately 220.5 Litres. This volume includes the 20 kg/ day that
will come from the urea treatment process that will join the water recovery
process at the start.
• Post Water Treatment
• At 99 % Recovery Rate the amount of water obtained is 198.5 kg/day. Including a
safety factor of 10% the total tank should accommodate 218.3 kg/day,
corresponding to a volume of 218.3 litres.
28. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Tank Storage Volume (Litres)
Water Pre-Treatment 9.2
Water Post-Treatment 9.1
Tank Storage Volume (Litres)
Water Pre-Treatment 110.3
Water Post-Treatment 109.2
Alternative Rate of Recycling Storage
• Hourly Basis
• Twice a day
29. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Urine Processer Storage
• The Urine Tank for the Urine Processor should be collected
and recycled once daily
• Materials?
• Does this storage provide an acceptable hold up time?
• Long term storage can occur in Teflon bags
• Ultimately decided water should be recycled on a daily basis.
30. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Gas-Liquid Separator
• The PFD shows that the stream exiting the Reactor enters the
Gas/Liquid Separator before moving on to the Ion-Exchange
bed.
• The Stream Leaving the Reactor contains excess carbon
dioxide and oxygen which need to be removed from the
system.
• The Separator needs to be designed to remove the excess
Oxygen before the Stream continues to the IX Bed.
• Excess Oxygen can be damaging and so its removal is also
important for protecting expensive equipment
31. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Gas-Liquid Separator
• Methods of Removal
• In order to determine the Method of Removal the phase and composition of the
stream exiting the Reactor needs to be determined
• From the PFD it is known excess oxygen needs to be removed. If the oxygen is
dissolved in a liquid stream, membrane degasification is an option as it is able to
remove the dissolved gas by allowing it to pass through the Gas-Liquid Separation
membrane whilst containing the liquid.
• If the stream contains separated gas and liquid a vertical gas-liquid separator can
be used due to low holding time
• The reactor by products will remain in the liquid and thus require the ion exchange
bed to remove them.
• If the stream is completely in gaseous form it will require a gas separator and vice
versa is the stream is completely in the liquid form.
32. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Assumptions to be Determined?
• Batch process of water? I.e. wastewater collected in a tank
and when a level indicator determined the correct volume
of wastewater has been reached the process can begin?
• What will the level indicator be? I.e. What is the decided
flow-rate for the process?
• This flow rate will be based on the rate at which waste
water will collect? And the rate at which recovered water is
needed?
• If clean water from initial mission is in storage the latter will
not be an issue
• How will the water from the initial supply mission be
stored? Teflon bags?
33. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Schematic of Urine Processing Assembly (UPA)
Ref. Development of an Advanced Recycle Filter Tank Assembly for the ISS Urine Processor
Assembly
34. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
UPA System
• Urine is pretreated before enters the system
with sulphuric acid and Chromium Trioxide.
• The total amount of urine that will be
processed for a 10 man crew is 20 kg/day.
35. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Fluid Pump Assembly
• The pump assembly
consists of 4 Peristaltic
pumps:
– 1 supplies wastewater
– 2 remove excess
wastewater and sends it
to the recycle filter tank
– 1 removes water product
water from the product
side of the distillation
unit (DU).
Motion of the peristaltic pumps
Ref. Final Report on Life Testing of the Vapor
Compression Distillation/Urine Processing
Assembly (VCD/UPA) at the Marshall Space
Flight Center (1993 to 1997)
36. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Distillation Assembly
• Incoming wastewater is spread in a thin film on the
rotating drum centrifuge.
• From here it is evaporated at ambient temperature and
reduced pressure
• Water vapour is transferred to outside the drum
through a compressor, where it condenses as clean
water.
• Demister ensures only clean water is removed with the
compressor, leaving waste water droplets behind.
• Passes through 100 micron filter before going to WPA
37. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Distillation Assembly
Ref. Final Report on Life Testing of the Vapor Compression Distillation/Urine Processing
Assembly (VCD/UPA) at the Marshall Space Flight Center (1993 to 1997)
38. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Filters solids from the wastewater before it is
recirculated through the distillation unit.
• Consists of bellows to draw waste water into
the tank, and force it out as a concentrate.
• Then passes through a 10μ brine filter, which
has an estimated life of 60 days.
• This filter has a 100μ filter incase of failure of
the 10μ filter.
Advanced Recycle Filter Tank Assembly (ARFTA)
39. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Bellows Tank Brine Filter
ARFTA
Ref. Development of an Advanced Recycle Filter Tank Assembly for the ISS Urine Processor
Assembly
41. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Removes gas from the condenser side of DU when
the pressure gets to high.
• Similar to fluid pumps, except operate at a higher
RPM therefore require a cooling jacket
• Pump system compresses the non-condensable
gas & water vapour to condense the water
vapour.
Purge Pump Assembly
42. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Purge Stream Filtration
• Water that leaves these pumps is filtered
using 20μ filter.
• Stream then passed through water separator.
This sends product water to WPA, expelling
any non-condensable gases to the
atmosphere.
43. ?
Outline
1. Design
objectives
Aqueous Catalytic Oxidation Reactor
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Used as an effective post-treatment technology for the removal of low
molecular weight polar (but non-ionic) organics which are not removed
by sorption in the multifiltration (MF) train.
• Typical contaminants of this kind are ethanol, methanol, isopropanol,
acetone, and urea
44. ?
Outline
1. Design
objectives
Aqueous Catalytic Oxidation Reactor
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Design:
• The reactor operating pressure is determined primarily by the requirement to
maintain water in the liquid phase
• The ISS uses a VRA which is co-current bubble column which uses gas phase
oxygen as the oxidant over a catalyst
• Catalyst consists of a noble metal on an alumina substrate
• For design assume plug flow reactor
45. ?
Outline
1. Design
objectives
Ion Exchange Bed
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Removes dissolved products of oxidation exiting the reactor
• Including both organic & inorganic compounds
• Organic Anion exchanged bed contains a synthetic resin, often
styrene based with a capacity of 10-12 kg/ft3*
(*Nalco Chemical Company, 1998)
46. ?
Outline
1. Design
objectives
New Proposed System
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Aim to remove volatile organic compounds (VOC) from the
cabin air via catalytic oxidation prior to absorption in the
aqueous phase
• This reduces the load on the Ion exchange bed. Oxidation
kinetics indicate this is more efficient.
• Second, vapour compression distillation (VCD) technology
processes the condensate and hygiene waste streams in
addition to the urine waste stream
47. ?
Outline
1. Design
objectives
New Proposed System
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• Experimental evidence (Carter et al.,2008) shows this system
can effectively reduce the Total Organic Compounds (TOC) to
‘safe levels’:
TOC removal by
organic reactor
Carter, et al.,
2008)
48. ?
Outline
1. Design
objectives
Questions
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
• The composition and Phases of the Reactor Exit Steam?
• Confirmation of what needs removed from the Reactor Exit
Stream prior to it entering the Ion Exchange bed?
• If a Gas-Liquid Separation Membrane is the most appropriate
method of Removing Oxygen?
49. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Membrane Bioreactor – Forward Osmosis
• Originally eliminated due to reliability concerns over microorganisms survival.
• However after conversations with the NASA team responsible for designing waste
water treatment for Mars, decision was taken to reconsider.
• NASA cited this technology as their current focus, moving away from DOC & ISS
• Microorganisms spores were taken to low orbit earth in 1984 with 70% survival and
with developments in UV radiation protection, experts believe the technology is
plausible (Benardini et al., 2005)
• Membrane bioreactor has the potential for excellent treatment of waste water with
removal of contaminants in excess of >95 % (Atasoy et al., 2007)
• However significant challenges remain and will be investigated
50. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Membrane Bioreactor Continued
FEED
Aeration zone
Immersed membrane
Activated sludge
Material balances of substrate:
Rsu = Q(Si-Se)/Va = …?
Q
Si
Xi
Q, Se, Xe
51. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
Membrane Bioreactor Continued
• First we need a volume: 200 l/day requirement
• Process will operate in a continuous mode
• For our capacity assume preliminary volume of 50 l
• rsu= Q(Si-Se)/Va = 42 mg/l/day (substrate utilisation rate)
• Primary Flux?
• J= (1/A) x (dv/dt)
• A = Membrane surface area* = 0.83 m2
• Therefore J= 10 l/hr/m2
• Permeate flux? :
• Material balance of permeate in reactor?: rg=dXv/dt
*(Kraume, 2010)
52. ?
CO2 Separation
1. CDRA - Carbon Dioxide Removal Assembly (ISS)
2. PSA – Pressure Swing Adsorption
3. MEA CO2 Absorption
4. Activated Carbon Absorption
5. Scrubbers
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
53. ?
1. CDRA – Process Description
• Utilises regenerative molecular sieve technology to remove carbon dioxide.
• In the CDRA, there are four beds of two different zeolites.
• Zeolite 13x absorbs water, while zeolite 5A absorbs carbon dioxide.
• Each side of the CDRA contains a zeolite 13X connected to a zeolite 5A bed.
• As the air passes through the zeolite 13X bed, water gets trapped and removed
from the air.
• The dried air goes into the zeolite 5A bed where carbon dioxide gets trapped
and removed.
• The outgoing air is then dry and free from carbon dioxide.
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
55. ?
2. PSA – Process Description
• Similar process to the CDRA with the exception that pressure is used
instead of heat.
• Beds are operated at 150kPa or higher.
• Higher the pressure, the more CO2 is adsorbed.
• When bed becomes saturated it is depressurised to atmospheric levels.
• CO2 is released from the bed and the regeneration is complete.
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
56. ?
3. MEA CO2 Absorption
• This is a regenerative method of removing CO2 from air.
• Uses an aqueous solution of 25-30 wt.% (4-5 M) monoethanolamine (MEA),
NH2CH2CH2OH to absorb the CO2 from the air.
• The aqueous solution is then regenerated by passing it through a column of
packed glass rings and by heating it to drive off the CO2 under pressure. As
shown below.
• H-O-CH2-CH2-NH-CO-OH H-O-CH2-CH2–NH2 +O=C=O
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
57. ?
4. Activated Carbon Adsorption
• A form of carbon that has been processed to make it highly porous so as
to have a very large surface area available for adsorption or chemical
reactions.
• CO2 saturated air is passed over the activated carbon and the CO2 is
adsorbed onto the surface.
• Can be regenerated by blowing air with a low CO2 concentration through
the bed.
• Only useful to us if we have a waste stream of air from another process
that can be used to clean it.
• There is no way of gaining a pure CO2 stream, which may cause problems
in later processes when converting the CO2 to O2. Therefore this
technology is not applicable to the space station.
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
58. ?
5. Scrubbers
I. Soda Lime – used on submarines
• Constant air circulation through a scrubber system filled with 75% calcium
hydroxide. CO2 is removed via the following reaction.
CO2 + Ca(OH)2 → CaCO3 + H2O
• Non regenerative, Ca(OH)2 must be resupplied.
II. Lithium Hydroxide – used in spacesuits
• Used to remove CO2 from exhaled air by one of two reactions.
2 LiOH·H2O + CO2 → Li2CO3 + 3 H2O
2LiOH + CO2 → Li2CO3 + H2O
• Second is lighter and produces less water.
• Neither systems are regenerable and LiOH must be resupplied.
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
59. ?
Criteria & Constraints- CO2 Separation
Technology Applicability Reliability Modularity Resupply
CRDA
MEA Absorption
Activated Carbon - - -
PSA
Sorbents
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
60. ?
Criteria & Constraints- CO2 Separation
Technology Applicability Reliability Modularity Resupply
CRDA
MEA Absorption
Activated Carbon - - -
PSA
Sorbents
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
61. ?
CO2 Separation - Final 3
CDRA MEA
Absorption
PSA
Resupply
(kg/18 months)
0 0* 0
No. of
independent
units
2 2 2*
Feed streams 1 1 1
Recovery rate
(%)
- 70-90 95*
Maintenance
(years)
3-5 - 3-5
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
62. ?
CO2 Separation - Final 3
CDRA MEA
Absorption
PSA
Resupply
(kg/18 months)
0 0* 0
No. of
independent
units
2 2 2*
Feed streams 1 1 1
Recovery rate
(%)
- 70-90 95*
Maintenance
(years)
3-5 - 3-5
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
63. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CO2 Separation
• Temperature swing adsorption with molecular sieves.
– Temperature swing versus pressure swing.
– Zeolites preferred to activated carbon for the
adsorbent.
– How the ISS system operates
– Differences between the ISS system and that which
we will design
– Mass balance
– Design requirements
64. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
TSA
• Advantages:
– Can achieve higher product purities than PSA in low CO2
environments
– Cheaper than PSA
• Indirect heating
– Direct heating requires large volumes of adsorbent and high
heating requirements.
– Use of an indirect heat exchanger can solve this problem
• Water circulation to provide a heat sink during adsorption
• Steam condensation to provide heat for desorption
65. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Choice of Adsorbent
• Activated Carbon or Molecular Sieves?
• A comparison of activated carbon to two molecular sieves (13X and 4A)
showed preferential adsorption of CO2 over nitrogen or hydrogen at all
pressures up to 250 psia.
• 13X and 4A performed better than activated carbon at low pressures, but
activated carbon was preferential at high pressures.
• Our system will operate at a low (atmospheric) pressure – indicates
molecular sieves are a preferential choice.
• No data could be found on how activated carbon and molecular sieves
act at different temperatures but all examples of TSA systems used
molecular sieves – it is a proven and preferred technology.
67. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CDRA - ISS
There are a few main differences between that system and ours
that should be considered.
• Larger crew
– capacity of system should be higher.
• CO2 must be recycled
– On the ISS the space vacuum is utilised to remove the CO2
and vent it to space.
68. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Mass Balance
• 0.416667 kg/hr CO2 produced by crew members.
• Assuming composition of air inside the station is 20.95% O2,
0.03% CO2, and the remainder (79.02%) N2.
• Due to the 95% CO2 removal rate 161.95 kg/hr of cabin air
needs to be treated.
69. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Mass Balance
Air Intake
(kg/hr)
Air Return
(kg/hr)
Air
Removed
(kg/hr)
Oxygen 33.917 33.917 0
Nitrogen 127.594 127.594 0
Carbon Dioxide 0.439 0.022 0.4167
Total 161.95 153.436 0.4167
70. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Design Requirements
• 2 Parallel desiccant beds for water removal
• 2 Parallel adsorbent beds for CO2 adsorption
• Vacuum system to remove the desorbed CO2
• Indirect HE for regeneration of CO2 adsorbent bed.
• Humidity control system (Plate heat exchanger)
71. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Desiccant Bed
• To remove remaining water vapour from air.
• Desiccant subsystem consists of two beds, one adsorbs while
the other desorbs.
• Process gas flow drawn from cabin into adsorbing desiccant
bed.
• Gas is dried to its dew point (around -62˚C) using an in bed
heat exchanger.
• Desiccant beds desorbed by cycling CO2 free air back through
the bed to replace the water.
• At an inlet temperature of 10 ˚C (and an outlet of (-62˚C) silica
gel has a capacity for holding water of 7% by weight
(saturated).
72. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Desiccant Bed
• The desiccant bed consists
of alternating layers of
zeolite 13X and silica gel in
order to protect the silica gel
from entrained water
droplets which may cause
the silica gel to swell and
fracture.
• Perforated metal screens
and fibre filters in place at
each end to stop desiccant
particles and dust entering
the gas stream.
73. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Desiccant Bed
• Before design takes place we need:
– Water content of air on cabin.
– Dew point of air
– Cycle time of air streams
• Heat exchanger within bed occupies a relatively small volume
(compared to overall volume) .
– Packing of desiccant around tubes will be looser so calculated
dimensions need to be increased slightly.
74. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CO2 Adsorbent Bed
• Design decisions:
– Cycle time
– Flow direction (Down-flow preferable)
– Mode of re-generation (creation of a vacuum to draw the
CO2 into a holding chamber)
– Operating conditions (Temp, flow rates, etc)
– Vessel dimensions
75. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Indirect Heating of CO2 Adsorbent Bed
• Current ISS System has separate heating and cooling units on the air
streams passing through the bed.
• Proposed idea, to create one heat exchanger within the bed for both
cooling and heating.
• Bed would be cooled whilst adsorbing CO2, this increases the column
capacity.
• The bed would then be heated to desorb the bed.
• This reduces cycle time – however induces higher energy cost.
80. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Sabatier RWGS
Resupply
(kg/18 months)
2343.5 1334.2
No. of
independent
units
1 1
Feed streams 2 2
Maintanence Unknown Unknown
CO2 treatment – Final Two
81. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CO2 treatment
Feasibility studies for CO2 treatment methods indicate that the Sabatier
reaction is the best choice for “stage 2”.
Possibility of improving the process in “stage 3” by recovering hydrogen
from the methane, as opposed to venting it to Mars. This would create a
closed loop for both H2 and O2, meaning neither would need to be
resupplied.
85. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Comparison
Run 1 Run 2 Run 3 Run 4
Tin(K) 423 500 423 500
Tout (K) 423 500 500 518.6
P(atm) 0.9 0.9 0.9 0.9
Mode Isothermal Isothermal Non-isothermal Non-isothermal
Reactor volume(m3) 16.09 0.93 1.87 1.06
Residence time (days) 0.37 0.02 0.04 0.02
Residence time (hours) 8.83 0.43 1.03 0.49
Mass flows in (kg/day)
CO2 10.00 10.00 10.00 10.00
H2 1.82 1.82 1.82 1.82
H2O 0.00 0.00 0.00 0.00
CH4 0.00 0.00 0.00 0.00
Mass flows out (kg/day)
CO2 0.64 0.62 0.24 0.23
H2 0.13 0.12 0.05 0.04
H2O 7.65 7.68 7.99 7.99
CH4 3.40 3.40 3.55 3.56
Conversion of CO2 (mass basis) 93.6 93.8 97.6 97.7
86. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Key Points
• Operating temperatures above 550 K have
been disregarded due to material
properties such as susceptibility to creep
• Can we assume that the reactor is isobaric
even with temperature change? Pressure
affects rate of reaction and density of gas
stream (can make things much more
complex). ΔP for 500K would be 0.036
atm and for 423K =0.106 atm.
• Assuming that we would want to be able
to generate oxygen at a fast rate (in case
of emergencies), a non-isothermal reactor
operating at 500K inlet and 0.9 atm would
be the best choice (relatively compact and
lowest residence time (plus highest
conversion).
• Reason for pressure selection – Station
will be at 1 atm pressure, if a leak in the
reactor casing occurs then we would
prefer that air is sucked into the reactor
rather than a mixture of gases passed
straight into the habitat.
• The lower the pressure used, the greater
the reactor volume becomes and
therefore only a slight vacuum is needed
(i.e. just below station pressure) so 0.9
atm was selected.
88. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Other Units to be Designed
1. Gas Storage Vessels (for CO2, H2, O2, CH4)
2. Liquid Storage Vessel (for H2O)
3. Water separation HX (to remove water from reactor exit stream –
simple)
4. Gas separation (can separation group offer any advice?)
5. Electrolysis unit (continuous or cyclic?)
6. Pumps, valves etc (last)
89. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CO2 Storage Vessel
Information required for design:
• CO2 flowrate (including recycle if appropriate)
• Need to choose a “hold-up” time – depends on mode of operation of
Sabatier (and if cyclic operation then depends on time to heat up)
• Need to choose a safety factor (Trelfa’s lecture?)
• Need to choose T&P
90. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
H2 Storage Vessel
Information required for design:
• Full amount of hydrogen which must initially be delivered (flowrates and
hold-up are unnecessary as the H2 volume will never increase)
• As before, safety factor, T&P
91. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Information required for design:
• Inlet flowrate of O2 from electrolysis (need conversion from reactor and
electrolysis unit)
• Outlet flowrate of O2 to station atmosphere
• As before, safety factor, T&P, Hold-up
• Will electrolysis use continuous or cyclic operation?
O2 Storage Vessel
92. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CH4 Storage Vessel
Is this vessel necessary? If all the methane is going to be purged then can it
simply be purged as it is produced (simple no-return valve on CH4 stream
from gas separations)?
93. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Additional Questions on Gas Storage
• Will any CO2 or H2 be purged?
• Is it necessary to include a hydrogen recycle stream (in addition to the
hydrogen recycled from electrolysis)?
94. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Liquid Storage Vessel
Information required for design:
• Inlet flowrate of H2O (need conversion from reactor)
• Will electrolysis use continuous or cyclic operation?
• As for gases, safety factor, T&P, Hold-up
95. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Gas Separation
Is this necessary or are outlet flowrates of reactants (CO2 and H2) low
enough to allow them to be purged?
Need advice from CO2 separation group!
- Need to separate a mixture of CO2, CH4 and H2.
96. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrolysis Unit
• Need to check we’re not overlapping with the electrolysis group – who
will design the storage for water, oxygen and hydrogen?
• Any recycle streams around electrolysis unit?
98. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Alternatives to Electrolysis Cont…
1. Photocatalytic splitting
• Advantages – simplicity (use
catalyst suspended in water
to electrolyse solution in the
presence of sunlight)
• Disadvantages – Critical
system would depend on the
availability of sufficient
insolation
2. Thermolysis
• Advantages - Can use
methane as a fuel (if
Sabatier is used)
• Disadvantages – Extremely
high temperatures (2000°C)
required to split water which
means high rate of
component failure.
99. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Alternatives to Electrolysis Cont…
3. Thermochemical Cycles
• Advantages – Relatively low
temperature (530°C for Cu-Cl
cycle).
• Disadvantages – Requires
several different reactors and
chlorine gas may be
produced which is a potential
problem.
4. Catalysis (Milstein 3 stage
process).
• Advantages – Low
temperature (100°C) and
fairly simple system, can be
scaled up.
• Disadvantages – Relatively
new technology, may require
more research before it is a
viable alternative to
electrolysis.
100. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Alternatives to Electrolysis Cont…
Alternatives to Electrolysis Cont…
5. Bipolar Electrolysis
• Advantages – Developed from
monopolar electrolyzer. Low
energy consumption and high
efficiency make it suitable to scale
up.
• Disadvantages – Compact
conformation of this system lead to
difficulty of initial design.
6. Laser
• Advantages – Similar to
photocatalystic splitting, use
laser instead of sunlight,
simplicity structure, can be
used on Mars.
• Disadvantages – Sensitive
plant, low reliability and
difficult to repair by
astronauts. High Energy
consumption.
101. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Alternatives to Electrolysis Cont…
Alternatives to Electrolysis Cont…
7. PEM Electrolyzer
• Advantages – no electrolyte
required in this system, high
efficiency and reliability
• Disadvantages – The materials of
the anode and cathode are very
expensive and cannot be scaled up
8. Solid Oxide Electrolyzer
• Advantages - High efficiency,
exhaust heat can be recycled to
save energy.
• Disadvantages –High operating
temperatures (Over 1000°C) lead
to low system reliability. Strong
limitation on cell material
103. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Oxygen Generation using Electrolysis
Design Basis
Stage 1
Air
Pre-treatment
10 kg/day CO2
Stage 2
Air
Air treatment
8.4 kg/day O2
Air
Air
104. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Process Description
PRE-INVESTIGATION OF WATER ELECTROLYSIS
http://www.futureenergies.com/pictures/fuelcellpower.jpg
105. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Process Description
•OH- (aq) anions are oxidised at the anode,
producing O2(g), H2O (l) and electrons.
•The electrons flow through the diaphragm to
the cathode.
•At the cathode, water is reduced producing
H2(g) and OH- anions (aq).
•These hydroxide anions flow to the anode,
where the cycle is repeated.
Modelling of advanced alkaline electrolyzers: a system
simulation approach
107. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Overall Mass Balance
Assumptions
• All electrolyte is recycled
• All un-reacted water is separated and recycled
• No deterioration of electrodes
108. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Overall Mass Balance
Recycle
2.36 kg/day
Electrolysis Unit
H2
H20 1.05 kg/day
9.45
kg/day
O2
8.4 kg/day
109. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Key Process Parameters
• Voltage and Current Levels
• Electrode Surface Area
• System Temperature
• Diaphragm Material
• Electrolyte Choice
• Electrode Choice
110. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Voltage and Current Levels
Using an electrochemical basis the rate of oxygen production is
related to voltage and current levels by;
With F in mol/sec
111. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrode Surface Area
• Faradays Efficiency is dependant upon the electrode surface
area
• The equation for faradays efficiency is;
This model uses non-temperature dependant coefficients
112. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
System Temperature
• Typically operated at 70-90˚C
• Higher temperatures beneficial as they reduce the ohmic
resistance of the electrolyte solution and that of the
electrodes.
Hydrogen and Fuel Cells: Fundamentals, Technologies and Applications
113. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Diaphragm Choice – Inorganic and Organic Materials
Important properties for choice:
• Reliability / overall lifespan
• Efficiency
• Low electrolyte resistance
• Health hazard
114. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Inorganic - Asbestos
• Being phased out of use in industries (<20% in EU)
• Not suitable at higher temperatures
• Corrodes/deteriorates when used alone.
• Possible health problems – rule out
115. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Refractory-Type Materials
• Inorganic material combined with binder or alone.
• e.g. Ceria (CeO) or zirconia E fibre.
– Both exhibit high stability.
• Made into membranes by NASA.
• Combined and alone yielded poor results.
– Fragile, brittle, poor strength…
116. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Polyantimonic Acid (PAM)
• Extremely stable at high temp (up to 150oC)
• Stable in highly concentrated KOH
• Best option: Polyarylethersulfone-PAM
– Membrane resistance 0.2cm2 at 90oC
– Reasonably easy to reproduce
• Needs further testing
117. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Sintered Nickel
• Highly resistant to corrosion
• Tested at 30% KOH, 50 bar and temp >150
• Gives good ionic conductivity
• High electronic conductivity – problem
• High cost - $1000 per m2. Not a problem.
• Possibly coat with oxide.
118. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Comparison of Inorganic Materials
Material Reliability/
Lifespan
Health
Hazard
Efficiency Low
Electrolytic
Resistance
Asbestos - -
Refractory
Type - - -
Polyantimonic
Acid
(PAM)
-
Sintered Nickel -
119. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Polybenzimidazole
fibres
• They are not readily attacked by
oxidizing agents and have high
melting points and excellent
stabilities at high temperatures
• It lose 80% of its tensile-strength
after one month's exposure to 30
% KOH at 80 °C
Teflon
• It has excellent chemical and
heat resistance to alkaline
media.
• It is lack of wettability, bubble
will occur on the surface of
membrane, lead to the
conductivity decreasing.
Grafting techniques seem
more difficult to use and have
yet to be proven for the
electrolyser application.
120. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Polysulphones
• It was tested at 150 °C in KOH/O2
and KOH/H2 environments, no
loss of tensile strength when KOH
occupy more than 70% of the
solution
• Maximum service temperatures
in water electrolyzers are smaller
than expected. Hydrophobicity
lead to low conductivity
Ryton
• Excellent thermal and
oxidative stability, it is stable
in alkaline environments
even at high temperatures
and high concentration of
alkaline
• Ryton is not widely used
due to production problems
121. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Ion-exchange
membranes
• Only certain ions can pass the
membrane due to its high
selectivity. Simplify the
separation process
• More instable than other
materials even in low
temperature. Nafion is more
stable but limited to low alkaline
concentration
123. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Conclusion
• The choice is between Sintered Nickel and Ryton.
• Sintered Nickel (or other porous metal diaphragms) is the
preferred choice.
• This is because organic materials are generally used for
electrical insulation.
• We desire a low resistance to the electrolyte to avoid
prohibiting the ion pathway.
124. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrolyte Solution
• Products of Anode
1. If the anode is active electrode (metal which is more
active than Ag), anode will be dissolved.
2. If the anode is non-active electrode (Pt or Au)
According to priority of positive ions discharge:
S2- > I- > Br- > Cl- >OH-
• Products of Cathode
According to priority of negative ions discharge:
K+ < Ca2+ < Na+ < Mg2+ < Al3+ < H+ < Zn2+ < Fe2+
125. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrolyte Solution
Ions in the solution
Positive Ions: K+, H+
Negative Ion: OH-
Anode：
Cathode：
126. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrolyte Solution
• The number of electrons lost from anode is equal to
the number of electrons of cathode obtained
• Ideally, the concentration of KOH is a constant or
accumulated as new KOH comes in.
• In practice, a small part of KOH will be carried out of
system by oxygen and hydrogen
127. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Electrolyte Choice for Electrolysis
Considerations:
• High resistance to corrosion, erosion, wear.
• Electrical conductivity.
• Suitability to situation.
• Physical Properties (mass, strength).
• Cost- relatively low.
128. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Materials Considered
Material Resistances Electrical
Conductivity
Suitability Notables
Copper Oxides readily.
Brass <Resistant than Cu.
Graphite All round usage.
Titanium Lightweight.
Silver Soft. Need Alloy.
Platinum Doesn’t oxidse.
129. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Gas-liquid Separation
1. Gravity settling separator
• Advantages:
• *Simple structure
• *Low operating and capital cost
• *Excellent operating flexibility
•
• Disadvantages:
• *Long residence time
• *Separator is too big and heavy
• *Poor separation results, only works on gas
• with large liquid drop (over 100 )
m
Gas Exit
Gas Exit
Feed
Feed
Liquid Exit
Liquid Exit
130. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Gas-liquid Separation
2. Inertial separator
Advantages:
*Simple in structure
*Convenient in operation
*Large in capacity
Disadvantages:
*Large in residence
*Re-entrainment occurs on gas exit
*Poor separation results on those liquid
drop which size is smaller than 25
Different Configurations of Baffles
m
131. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Gas-liquid Separation
m
3. Filtration Separation
Advantages:
*Excellent separation results on liquid drops
with small size from 0.1 - 10
Disadvantages:
*System has limit on feed flowrate, fast
flowrate lead to poor separation.
*High operating cost
*Inconvenient in resupply and cleaning of
filter
Filter
132. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Gas-liquid Separation
4. Centrifugal separator
Advantages:
*Short residence time
*Small in vessel size, easy to install
*High reliability in continuous operation
Disadvantages:
*System requires extremely high flowrate, not
suitable to separate a small amount of feed
*High energy consumption
Entrance
Gas Exit
Liquid
Exit
Bubble Zone
Swirl Zone
g/l Splitting Zone
GLCC Separator
133. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
Condensing Heat Exchanger (CHX)
• H2/H2O and O2/H2O enter heat exchanger
-may be aided by fans
• Cooling water used to condense water vapour.
• Water condenses on hydrophilic fins.
• Sucked between capillary plates.
• Possible Centrifugal separation.
134. ?
Outline
1. Design
objectives
2. Criteria &
constraints
4. Water
treatment
3. Stages
1&2 Outline
5. Air
treatment
CHX Advantages/ Disadvantages
• Already used in Space.
• Easily designed.
• Lifespan of 10 years.
• LCOS downstream of CHX.
• Problems due to microgravity.
• Possibility of microbial growth.
