To achieve permanent human presence and activity on the moon, oxygen is required for both life support and propulsion. Lunar oxygen production using resources existing on the moon will reduce or eliminate the need to transport liquid oxygen from earth. In addition, the co-products of oxygen production will provide metals, structural ceramics, and other volatile compounds. This will enable development of even greater self-sufficiency as the lunar outpost evolves. Ilmenite is the most abundant metal-oxide mineral in the lunar regolith. A process involving the reaction of ilmenite with hydrogen at 1000 C to produce water, followed by the electrolysis of this water to provide oxygen and recycle the hydrogen has been explored. The objective of this 1990 Summer Faculty Project was to design a lunar oxygen-production plant to provide 5 metric tons of liquid oxygen per year from lunar soil. The results of this study describe the size and mass of the equipment, the power needs, feedstock quantity and the engineering details of the plant

Radhakrishnan, Ramalingam

English

NASA Technical Reports Server

N 9 1 - 27 --f09--_-/
DESIGN OF A LUNAR OXYGEN PRODUCTION PLANT f / I
Final Report
NASA/ASEE Summer Faculty Fellowship Program - 1990
JOHNSON SPACE CENTER
Prepared By:
Academic Rank:
University
& Department:
Ramalingam Radhakrishnan, Ph.D., P.E.
Assistant Professor
Prairie View A&M University
Department of Civil Engineering
College of Engineering and Architecture
Prairie View, Texas 77446
NASA/JSC
Division:
Branch:
JSC Colleagues:
Date Submitted:
Contract Number:
Solar System Exploration Division
Space Resources Utilization Office
David S. McKay, Ph.D.
Thomas A. Sullivan, Ph.D.
August 17, 1990
NGT-44-005-803
20-1
https://ntrs.nasa.gov/search.jsp?R=19910017795 2020-03-19T16:53:23+00:00Z
ABSTRACT
To achieve permanent human presence and activity on the Moon, oxygen is
required for both life support and propulsion. Lunar oxygen production using resources
existing on the Moon will reduce or eliminate the need to transport liquid oxygen from
earth. In addition, the co-products of oxygen production will provide metals, structural
ceramics and other volatile compounds. This will enable development of even greater
self-sufficiency as the lunar outpost evolves.
Ilmenite is the most abundant metal-oxide mineral in the lunar regolith. A
process involving the reaction of ilmenite with hydrogen at IO00*C to produce water,
followed by the electrolysis of this water to provide oxygen and recycle the hydrogen,
has been explored.
The objective of this 1990 Summer Faculty Project was to design a lunar
oxygen-production plant to provide 5 metric tons (rot) of liquid oxygen per year from
lunar soil. The results of this study describe the size and mass of the equipment, the
power needs, feedstock quantity and the engineering details of the plant.
20-2
INTRODUCTION
The primary objective of this project was to design a plant to produce oxygen on
the Moon from lunar materials. The Lunar Oxygen Production Plant is required to
produce 5 metric tons (mt) of oxygen per year. The plant process selected for this study
is the hydrogen reduction of ilmenite with soil feedstock. The plant consists of
equipment for mining, processing, oxygen storage, and hydrogen storage. After
construction or emplacement on the Moon, the plant will be teleoperated from Earth.
The plant is assumed to have a duty cycle of 90% and a continuous power supply.
A simplified schematic of the hydrogen reduction of ilmenite process is shown in
Figure 1. In this process, the bulk raw soil is mined and fed into the plant. The plant
separates the very large and fine fractions of the soil so that an acceptable size of the
soil can be processed. A system of storage hoppers then feeds the soil containing
ilmenite into the top of a three-stage fluidized bed reactor. The reactor heats the soil to
1000*C as the soil flows down the reactor's three stages. Hydrogen gas flows up through
the solids, mixes with the particles, and reacts with the ilmenite to form water vapor.
An electrolysis cell separates the water vapor into hydrogen and oxygen. The oxygen is
liquefied and stored. The hydrogen is fed back into the top section of the reactor. A
solids settler removes the reactor residuals (spent solids) from the bottom of the reactor.
This report describes the different plant components. The results of the design
are presented. The summary included shows the mass, power, and volume of the plant
components.
Assumptions
1. The required production capacity of the plant is 5 mt liquid Oxygen (LOX) per year
using bulk lunar soil on the surface.
2. The concentration of ilmenite in lunar regolith can be as high as 10 volume percent
(15 weight percent). However, a more likely value of 5 volume percent (7.5 weight
percent) will be used in this design. An alternate design based on 10 volume percent of
ilmenite (15% wt) concentration in regolith would be similar but the plant would be
slightly smaller in size than the current design. Another advantage would be that the
plant could produce more oxygen than the required 5 mt capacity if the feedstock
contains higher percentage of ilmenite.
3. No beneficiation. This means there will be no enrichment steps included in the plant
to increase the concentration of ilmenite in the soil.
4. Mining will be done only during the lunar day. At night, metals in the mining
equipment could become brittle unless heated. The hot noon time also will be avoided.
This requires the storage of sufficient mined regolith for operation during the night.
5. The plant operation is continuous with a 90 % duty cycle, allowing 10% of the time
for trouble-shooting, maintenance and unexpected problems.
6. The process yield (chemical reaction and ilmenite conversion) factor is 0.9.
7. Lunar surface temperature varies from -100*C to +IlI*C. Assumed feedstock
temperature is -20"C.
20=3
Hydrogen Reduction
Of Itmenite
Reduction
L---_cFeFeTiO3 + H 2 + TiO2 +H20
Electrolysis
H20 + Dec. ---_ H2+ 1/20_
SIZE FEED I ILMENITE4.!.8% 1"
x 7.5%
56.2%
_" TAtLINGS
2
REACTOR
Make-Up H2
ELECTROLYSIS
t H20-_ I _.Z-25
X 10.5_
H 2
-_0 2
0.5_
of
feed,
by
weight
Figure 1
Simplified Schematic of
Hydrogen Reduction of Ilmenite Process
20-4
LOX PRODUCTION PLANT
The oxygen production process is illustrated in Figure 2. Approximately 1620
metric tons of bulk soil feedstock is required per year. After removing the oversize and
undersize rejects, a useful feed of 710 mt is available. As shown in Figure 1,
considering a 7.5% wt of ilmenite concentration in the feed and a 90% yield of oxygen
during the hydrogen reduction process, LOX production of 5 mt per year is obtained.
The important components of the LOX production plant are described in the following
sections.
Mining
The mining equipment assumed is a front end loader and hauler. The front
end loader (FEL) is a telerobotic vehicle for mining feedstock. The FEL can complete
soil mining and will have sufficient time remaining to perform additional base
operations.
One hauler is assumed. After being filled by the FEL, the hauler will travel to
the process feed bin, dump the load, collect a load of railings from the discharge bin,
dump the tailings at the discharge area, and return to the mining site to start the new
cycle over again.
The mining operation is on a 35% duty cycle, equivalent to 3066 hrs. The
operation will be discontinued during lunar noon and night. The mining equipment has
excess capacity. Since there will be a need for the installation of additional units to
increase the oxygen production in the future, the excess capacity of the FEL and hauler
is justified.
Bulk Storage Feed Bin
Since the plant is run on a 90% duty cycle and the mining equipment is operated
on a 35% duty cycle, the feed bin is sized to hold enough soil to run the plant.du_ing
(TM)the lunar night (14 days). Using high-strength polyethylene fiber Spectra 1000 . i,n
place of A1 2024 is recommended. The shell with 2 mm thick fiber Spectra 1000 _TM),
and l-cm-thick low-density insulation to provide protection from radiation and
temperature effects reduces the mass of the bin considerably. Furthermore, this fabric
might be compacted into a much smaller volume for transport to the Moon.
Coarse Screen
The coarse Screen removes the oversize size unwanted rocks (material >0.5 ram)
in the soil to discard bin (but see recommendations for an alternative).
Fine Vibrating Screen
The minimum allowable feed size to the reactor is 0.45 mm.
was selected to remove fines.
A vibratory screen
Feed Hoppers (2)
Two hoppers will be used to minimize gas losses from the reactor. The capacity
of each hopper is adequate for 3 days of feedstock. Feedstock is fed into the reactor
continuously from the bottom hopper which is maintained at 10 atm. pressure. When
inventory in the bottom hopper is at an appropriate low point, the top hopper, which is
20-5
iMINE I
-2o......__°
16201
rnt I
per 1
year I
Gas ._
Recovery
Cornpressor
'_'Houl
-- _--]i Bulk
Storage
/ Feed
Bin
_ 7Coarse
\ /Screen
_'<" 0.5 rnrn
"_ zz:zz?Fine
\ /Vibrating
x d/ Screen
f2 (2.045 mm
l_trn.
I
!
_1_i 744 °
7440 _._F -'] Cyclone\ Separator
Electrolysis
Cell
o o°-r-_2/"P_
yclone
Heat Exchanger/
o Radiator
27 °
r
_ Oxygen
1,/Liquefier
1000 ° I 1161 °
•=_ 3-Stoqe / I Heater
C :Js k_J Fluidized /
R.=servoir ReEIoedolr t_..._ 7L1
. t I'LT
R_ ect _ _f'
_'o,,',,I IBo_I"
-_,_i°"'ir )L_ __ ,o_,_oo_e
.......\'=-'--,-i"/,"\ Recyc,'-_o.er_ -_.53°
_Discord l_°trn_ cHo2rnM_rke_UPr_ '_LH 2Tonk
1
Hy
Figure 2
rogen Reduction of Ilmenite
LOX Production Plant
20-6
operating normally in vacuum, is pressurized to 10 atm. Then a valve between the two
hoppers is opened to rapidly re-inventory the bottom hopper. After the valve between
the hoppers is closed, hydrogen gas in the top hopper is recovered. The design allows
continuous feed to the reactor and minimizes gas losses from the reactor.
Reactor
Ilmenite reduction takes place in a three-stage fluidized bed reactor (shown in
greater detail in Figure 3) at 1000*C and 10 atm. pressure. The reactor in the LOX pilot
plant (Ref. 1) was designed to use beneficiated feed rate of 71.29 kg/hr to produce 24
mt of oxygen per year. The reactor required in the current design will use
unbeneficiated feed at a rate of 90 kg/hr to produce 5 mt of LOX per year. Since the
feed quantity is nearly the same, the overall reactor dimensions of the pilot plant were
maintained in the current design. However, several specific details have been modified
as required to conform to the needs of the current design goals. The interior diameter
of the reactor is 0.31 m at middle bed section. In consideration of the temperature
variation existing in the middle (i000*C), bottom (809"C), and top (744"C) beds, the
diameter of the reactor is designed to be 0.279 m and 0.267 m at the bottom and top
beds, respectively, to maintain the gas velocity at 1 ft/sec in all the three beds. Reactor
input material is restricted to sizes greater than 0.045 mm to avoid excessive carryover
of fines to avoid clogging up of the system and less than 0.5 mm to allow fluidization to
occur. Thus, the residence time of solids is 50 minutes in the top bed, 1.4 hours in the
middle bed, and 50 minutes in the bottom bed. The total residence time of the solids in
the reactor is 3.08 hrs. The central 0.31 m core of the reactor was surrounded by 7.5 cm
of high-density (S.G. 2.24) super-duty firebrick to withstand the erosional nature of the
high temperature gas/particles in the fluidized beds. Surrounding this is 23 cm of low-
density (S.G. 0.14) insulation. The height of each bed in the reactor has been
determined so that there will be enough space above the volume occupied by the solids
for disengaging entrained solids. The outside diameter and height of the reactor are 0.9
m and 6.6 m respectively.
Electric Heater
The electric heater heats the gas stream entering the reactor middle bed.
Electrolysis Cell
The solid-state electrolysis cell, operating at 1000*C, separates the hydrogen and
water vapor coming out of the reactor into hydrogen and oxygen. The hot hydrogen is
recycled to the top bed of the reactor.
Recycle Blower
The recycle blower circulates the hydrogen gas.
reactor at the bottom bed plenum chamber.
Gas from the blower enters the
Cyclone Separators
The cyclone separators separate the solids from the gases. The cyclone separators
contain no moving parts. Dust in the exit gas coming out of each of the reactor beds is
removed to prevent the clogging of the system. This dust is returned to the reactor
below the surface of each bed.
Solids Settlers
Two solids settlers have been proposed to allow continuous flow of "spent" solids
from the bottom bed. Each hopper is sized to allow 2 days residence time for the solids
20-7
EPlate
H_
f Cyclone
Separator
_ Cyclone
eparotor
Reactor i.D. at middle bed = 0..tl m
Figure 3
Reactor Details
20-8
to settle and separate trapped gases. A gas loop recovers the hydrogen gas and recycles
it through the H 2 make-up system. Solids will be allowed into one hopper while the
other would be reduced to 0.1 atm. or less to recover gases. This arrangement may also
facilitate the addition of a heat recovery system in the future. By putting compressors
in series, as shown in Figure 2, the power of each is minimized and redundancy is
provided.
Radiator/Thermal Control System (TCS) (not shown)
The radiator/thermal control system rejects the waste heat from oxygen
liquefaction equipment. The TCS uses heat exchangers and an appropriate cooling
medium. The radiator is positioned to keep the radiator permanently shaded from the
sun.
Oxygen Liquefaction and LOX Storage
The oxygen produced by the electrolysis cell is liquefied by a stirling cycle
refrigerator. The liquid oxygen is stored in two buried tanks. The re-use of tanks from
an abandoned lunar excursion vehicle (LEV) is recommended. This will reduce mass
and is a good substitute for new LOX storage tanks brought from Earth.
Hydrogen Make-up System
The hydrogen make-up system includes a tank, a heater, and a compressor. The
tank contains enough hydrogen for six months of process leaks and losses. Resupply will
be necessary at that time.
Discard Bin
This bin holds 15 days quantity of spent solids for disposal.
Support Structure (not shown)
The process support structure
gravity flow of the solids in the reactor.
is mounted in the vertical direction to allow
RESULTS
A list of mass, power and dimensions for the equipment required in a 5 mt per
year LOX production plant is given in Table 1. The process plant mass, not including
mining equipment (front-end loader and hauler) is 5600 kg. The electric power required
is 49.0 kW. Plant equipment was sized using the equations, methods and scaling
indicators described in Ref. 1.
SUMMARY AND CONCLUSIONS
1. While there are several ways to produce oxygen from lunar materials, the
process of reducing ilmenite with hydrogen was considered in this design.
2. Using bulk lunar soil as feedstock without beneficiation components reduces
total equipment mass significantly. The mass of the beneficiation components for the 24
mt pilot plant was 3879 kg (Ref. 1). The current design, without beneficiation
components, does not require a large-size reactor and the process plant is a viable
option. This trade needs to be evaluated for larger production rates.
3. Delivery of small, modular oxygen-production units is easy compared to delivery of a
large production plant. Several of the modular units can be deployed and
20-9
TABLE 1.
LUNAR OXYGENPRODUCTIONPLANT EQUIPMENT
5 mt/yr, H 2 Reduction of Ilmenite
Ilmenite in regolith = 7.5% wt. No beneficiation.
Equipment
Front-end Loader (1)
Hauler (1)
Minin_ Total
Feed Preparation
Feed Bin
Coarse Screen
Fine Screen
Process
Total Total Dimensions
Mass Power W/D L
(kg) (kW) (m) (m)
Rate 1620 mt/yr
H V
(m) (m3).
2000 0.5 2.1 3.3 2.3 16
1000 0,2 2.5 4,0 2.5 2_
Rate
Reactor Feed
4.5 -- 3.0 40
0.5 0.8 0.4 0.2
2,_ 3,0 O,_ 3.8
Pressure Hopper 1
Pressure Hopper 2
Reactor
Electric Heater
Electrolysis Cell
Recycle Blower
Cyclone Separators (3)
Solids Settlers (2)
Discard Bin
Oxygen Liquefier
Oxygen Storage Tanks (2)
Radiator/TC$
Hydrogen System
Liquid Hydrogen Tank
H 2 Heater
H 2 Blower
3000 0.6
206 kg/hr
176 0
15 0,5
t90 6
Rate 90 kg/hr
Process Plying
In reactor, 4 cm pipe
Q_hers. 0.25 cm oive
Process Total
Mor2in 30%
(includes support structure)
PLANT TOTALS
140 -- 1.5
140 -- 1.5
1960 -- 0.9
140 25 0.9
23 4 0.4
29 0.3 0.2
3 -- 0.1
288 -- 1.2
320 -- 3.0
40 1 0.3
120 -- 1.0
400 -- _,q
I 0.5 0.5
1 0.I O.l
2 0,1 0,1
210
lO0
4298
1302
-- 2.0 3.5
-- 2.0 3.5
-- 6.6 4.4
1.1 -- 0.7
0.4 0.7 0.11
0.2 0.3 0.01
-- 0.4 0.01
-- 2.0 2.26
-- 3.0 21
0.8 -- 0.06
.... 0.5
6,_ 0,01 0,2
.... 0.05
0.1 --
-- 0,1 --
5O
80
37.5
I I
11.5
49.05600
20-10
erected on the Moon to increase the total oxygen production in stages. This may not
result in economies of scale, but there are benefits in commonality, operations and
construction.
4. A single "point design" to produce 5 mt of LOX per year using
unbeneficiated lunar soil shows feasibility and indicates that the reduction of total plant
mass is not trivial comparing the 24 mt/yr pilot plant.
5. The 5 mt/yr plant was designed for the feed rate of 90 kg/hr with 7.5% wt
ilmenite concentration. If the soil contains a higher percentage of ilmenite (as much as
15% wt.), the process plant will be able to operate without any problem producing more
oxygen with the same rate of feed. However, modifications relating to quantity of soil
mining, feed rate, heat and power would make the plant operation efficient and
effective.
6. Payback of plant mass occurs in one year of operation.
RECOMMENDATIONS
1. The proposed use of a vibrating screen to remove fines of sizes less than 45
microns results in relatively large screen areas, power and mass. An alternate design
may use air classifiers which lift the fines and allow the collection of useful material as
a "heavy stock'. The air classifier with aspirator, cyclone separator, fan and motor may
replace the vibrating fine screen. This system can be introduced between top and
bottom reactor feed hoppers. A substantial reduction in mass is expected. A detailed
pressure analysis and design to incorporate air classifier to the LOX plant is needed.
This will also provide the flexibility to change the minimum size limit of the feedstock
as required, without replacing any parts. This could be useful if problems occur during
operation, or if off-nominal operation is required, as in during start-up and shut-down.
2. Hands-on research to determine the optimum reactor configuration for
maximum ilmenite conversion, especially for soil with high ilmenite concentration, is
recommended.
3. More detailed design of dust removal and hydrogen removal from the process
stream (water and hydrogen) to the electrolysis cell is required to avoid clogging and to
reduce the load.
4. At least 90% of the feed to the reactor is rejected as waste at 809°C. Using
this waste product and providing only a little more heat, the material can be sintered or
even melted and cast into bricks and other products. Radiation and micrometeoroid
shield design for the lunar outpost will be economical using cast basalt since the density
could be as high as 2900 kg/m". Casting the co-products of a lunar oxygen plant to
form useable materials would be advantageous and may allow their use as radiation
protection. This must be explored. Alternately, recovery of this heat value could lower
the power requirements of the plant.
20-11
l°
o
°
°
REFERENCES
Christiansen, Eric L°, et al. "Conceptual Design of a Lunar Oxygen Pilot Plant"
NAS9-17878. Eagle Engineering, Inc. EEI Report No. 88-182. Houston, Texas. July
l, 1988.
Christiansen, Eric L., et al. "Support to Extraterrestrial Propellant Leveraging Trade
Study" Eagle Engineering, Inc. EEI Report No. 89-251. Houston, Texas. August 15,
1989.
Gibson, M.A. and Knudsen, C.W. " Lunar Oxygen Production from Ilmenite", Lunar
Bases and Space Activities of the Twenty-First Century. W.W.Mendell, ed. Lunar
and Planetary Institute. 1985
Anderson, C., et al. "Conceptual Design of a Technology Verification Unit for
Lunar Regolith Volatiles Extraction", Senior Project Final Report, Rice University,
April 20, 1990.
20-12


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