A regenerable carbon dioxide removal and oxygen recovery system for the Japanese experiment module

Acta Astronautica Vol. 15, No. I, pp. 45 54, 1987 Printed in Great Britain. All rights reserved

0094-5767/87 $3.00+ 0.00 © 1987 Pergamon Journals Ltd

A REGENERABLE CARBON DIOXIDE REMOVAL A N D OXYGEN RECOVERY SYSTEM FOR THE JAPANESE EXPERIMENT M O D U L E t K. OTSUJI, I M. HIRAO2 and S. SATOH 3 Mitsubishi Heavy Industries, Ltd. ~Nagoya Aircraft Works, 10, Oye-cho, Minato-ku, Nagoya, 455, Japan 2Kobe Shipyard and Engine Works, 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe, 652, Japan 3Takasago Technical Institute, 2-1-1, Niihama, Arai-cho, Takasago, 676, Japan (Received 11 February 1986; revised version received 24 June 1986)

Abstract--The Japanese Space Station Program is now under Phase B study by the National Space Development Agency of Japan in participation with the U.S. Space Station Program. A Japanese Space Station participation will be a dedicated pressurized module to be attached to the U.S. Space Station, and is called Japanese Experiment Module (JEM). Astronaut scientists will conduct various experimental operations there. Thus an environment control and life support system is required. Regenerable carbon dioxide removal and collection technique as well as oxygen recovery technique has been studied and investigated for several years. A regenerable carbon dioxide removal subsystem using steam desorbed solid amine and an oxygen recovery subsystem using Sabatier methane cracking have a good possibility for the application to the Japanese Experiment Module. Basic performance characteristics of the carbon dioxide removal and oxygen recovery subsystem are presented according to the results of a fundamental performance test program. The trace contaminant removal process is also investigated and discussed. The solvent recovery plant for the regeneration of various industrial solvents, such as hydrocarbons, alcohols and so on, utilizes the multi-bed solvent adsorption and steam desorption process, which is very similar to the carbon dioxide removal subsystem. Therefore, to develop essential components including adsorption tank (bed), condensor, process controller and energy saving system, the technology obtained from the experience to construct solvent recovery plant can be easily and effectively applicable to the carbon dioxide removal subsystem. The energy saving efficiencyis evaluated for blower power reduction, steam reduction and waste heat utilization technique. According to the above background, the entire environment control and life support system for the Japanese Experiment Module including the carbon dioxide removal and oxygen recovery subsystem is evaluated and proposed.

I. INTRODUCTION The National Space development Agency of Japan (NASDA) has been planning to develop a Japanese Experiment Module (JEM) to participate in NASA's Space Station Program. The JEM consists of a pressurized experimental laboratory module similar to the Long Module of the Spacelab, an exposed facility to install experiment equipment and observation apparatus to be directly exposed to space outside of the module and an experiment logistics module to transport and exchange various experiment samples and logistic materials between the Space Station and the Earth, as shown in Fig. 1. The laboratory module and a part of the logistics module must be provided with ( 1 ) a n atmosphere revitalization, (2) a temperature, humidity and pressure control and (3) a trace contaminant and odor control to maintain comfortable environment, so that astronaut scientists can perform experiments in a regular shirt sleeve environment. tPaper IAF85 305 presented at the 36th Congress of the International Astronautical Federation, Stockholm, Sweden, 7 12 October 1985. 45

Mitsubishi Heavy Industries, Ltd. (MHI) having a lot of experiences in space system development through development and manufacture of launch vehicle series of N-I, N-II and H-I, is assigned to develop habitable modules for the JEM Program under the guidance and advice by NASDA. MHI also has experiences and achievements in the research and development of catalyst and the adsorption/ desorption technology required to control environment pollution by chemical plants, as well as experience in design and manufacture of submarine atmosphere control systems. This report presents the first step summary of the Environment Control and Life Support System Development Program which has been conducted by MHI for the Japanese Space Station Program. 2. CARBON DIOXIDE REMOVAL

There are dioxide from Table 1. The process Station should

various processes to remove carbon air or process-gases as shown in contemplated for use at the Space satisfy following conditions:

K. OTSUJI et al.

46

i

I_' .~.. "'~".-T}.-- I EXPERIMENT ] [ ,OGISTICS .oouLEI

Ii

~

il

OPERATING/ ( P M )

(3M X 4M} Fig. 1. Example of Japanese Experiment Module concept. (a) a regenerable system with minimum maintenance procedure; (b) operable under zero-gravity condition; (c) can be integrated with oxygen recovery system; (d) low energy consumption; (e) a small size and low weight; (f) a reliable system with a simple construction and operating process. Because of above reasons, a solid amine CO 2 removal process among others is currently evaluated as the candidate for an earliest possible application.

2.1 S o l i d a m i n e C O 2 r e m o v a l p r o c e s s

The solid amine adsorbent can be classified based on the regeneration processes in which they are used: steam regeneration and heat/vacuum regeneration processes[l,2]. These basic processes are shown in Figs 2 and 3. In Fig. 2, carbon dioxide gas in the air are adsorbed and removed in the first adsorbent tank, and in the second tank, desorption and regeneration are accomplished by steam. When a predetermined CO2 adsorption level is reached in the first tank, its process is switched to the regeneration process. In the

TABLE 1 Comparisonof Various COZ Removin9 Processes Process

Description

Finding

Zeolite Adsorbent

• P a r t i c l e screen e f f e c t and physical adsorption by Zeolite• • Collection by desorption of CO2 by heating and depressurization.

• Safe, have experience, easy maintenance and l i t t l e pollution• • Water need to be removed before use.

Solid Amine

. Amino group in adsorbent adsorbs CO2. • Collection by desorption of CO2 by heating or by steam•

. Effective to air containing water• . Need to remove smell of amine.

Electrodialysis

. CO2 is desorbed and collected from air through ion exchange membrane under e l e c t r i c potential gradient.

. L i f e time is short, maintenance is required and weight is heavy.

Base Solution Electrolysis

. To absorb CO2 with KOH. . To desorb and collect CO2 by e l e c t r o l y s i s and heating absorbent•

. L i f e time is short, maintenance is required and weight is heavy.

Fuel Battery

. A battery using H2 and 02 in the cabin air as f u e l . CO2 is separated from air through electrolyte•

Light weight• . L i f e time is short and maintenance is required.

Membrane Diffusion

. To collect CO2 utilizTng difference of d i f f u sign speed of particles in porous membrane•

Solution Absorption

. After reaction of amine or a l k a l i metal D i f f i c u l t i e s in application under zerosolution and CO2, CO2 is separated and c o l l e c t gravity condition. ed by heating. . Potentialsolution(safety)• hazard by leakage of corrosive

Freezing

. By cooling cabin a i r , CO2 is condensed and removed. • To collect CO2 gas by heating•

Low energy• D i f f i c u l t to develop membrane•

.i Safe and l i t t l e maintenance is required. ~ Weight is heavy, l i f e time is short and I power requirement is big.

47

A regenerable carbon dioxide removal and oxygen recovery system CABIN AIR

WITHC

O

~ NO.I ADSORBTANK

AIR COOLER

NO.2ADSORBTANK

©

It

CG

W TE PUAM PR

STEAM GENERATOR

WATER TANK

Fig. 2. Steam regeneration process diagram of solid amine adsorbent. second tank, upon completion of CO 2 desorption, the air starts flowing and after cooling by evaporation of residual steam, adsorption of CO 2 will be started. The steam used for desorption is recirculated through condensation for separation and heating. In Fig. 3, CO2 is adsorbed and removed from the air in the first adsorbent tank. In the second adsorbent tank, the solid amine desorbs CO2 and is regenerated by hot water heating and suction by vacuum. When the first tank reaches its predetermined adsorption level, it will be switched to the regeneration process. Upon completion of the regeneration process, the second tank will be switched to an adsorbing process after cooled by cold water. The desorbed CO L will be transferred to CO 2 storage tanks or to next CO 2 process such as cracking of CO2, by a vacuum pump. Typical types of solid amine are listed in Table 2. 2.2 Solid amine C02 removal test To select and determine the optimum process and optimum type of solid amine, the basic tests have

been performed using a test setup as shown in Fig. 4. In the tests, repeated adsorptions and desorptions of CO: from moisture controlled and CO2 mixed air have been recycled to measure CO2 removal efficiencies under the steady conditions. 2.3 Comparison of regeneration processes of solid amine Based on the result of adsorption/desorption cycle tests of solid amine, comparison of various CO 2 removal processes have been made and the result is shown in Fig. 5. To prove the superiority of solid amine, comparisons have been made with zeolite adsorbent which was used in Skylab[3]. As to adsorption efficiencies, Solid Amine A and B both show better performance than zeolite adsorbent, where Solid Amine A shows better adsorption capability than Solid Amine B. As to the amount to be loaded, the amount of solid amine to remove a given amount of CO 2 is less than one half of zeolite adsorbent. The amount of solid Amine A required is about 70% of

NO.1ADSORBTANK m

CABINAIR WITHCO,

AR I

PAN

NO.2ADSORBTANK

~ M C O O L E R

P U M P

CO

Fig. 3. Heat/vacuum regeneration process diagram of solid amine adsorbent.

K. OTSUJI et al.

48 TABLE 2 Type of Solid Amine

T]lpe of Solid Amine and Characteristics

A. lon Exchange Resin

B. Amine Impregnated Adsorbent

Principle of CO2 Removal

The amino group, one of functiRnal group, ion-exchanges and adsorbs HC03C- produced by CO2 and moisture in the air.

Principle of Regeneration

Separation of CO2 by heating and exclusive Separation of CO2 by heating ( i t w i l l be e f f i c i e n t to vacuum suck CO2 from solid desorption of CO2 by condensed water amine containing layer.) (good expelling effect of C02).

Material

Name

Weak Base Anion Exchange Resin

Material

Styren-divinylbenzene copolymer with amine as exchange base

Structural Formula

-CH-CH2-CH~

-CH-

Impregnated amine d i r e c t l y reacts tQ CO2 in air or reacts as the form of H2CO3 with moisture and adsorbs CO2.

Impregnating material

Polyethlene-imine

NH2(CH2CH2-N-)x-{CH2(H2-NH-)yCH2CH2N[ Potassium-n-methylalanate

CH3~HCOOK NHCH3

t

Other amine

CH2NH(CH2CH2NH)nH

Fig. 4. Solid amine CO z removal test setup.

i00

0.4

10

o"

o~e

0.3

g 5o

~ # 0.2

~ 5

~ ~:

"z~g.~ ~ o.1

,=,z .~ o

w

on

c~ 0

0 M

A

g

M

A

B

M

Fig. 5. Comparison of carbon dioxide removal characteristics. A: Solid Amine A by steam regeneration (CO2 loading: 3%). B: Solid Amine B by heat/vacuum regeneration (CO 2 loading: 3%). M: Zeolite Adsorbent by heat/vacuum regeneration (CO2 loading: 2%).

A regenerable carbon dioxide removal and oxygen recovery system Solid Amine B. As to the required energy for regeneration, demands of solid amine are about one quarter of zeolite adsorbent. The demand of Solid Amine A is observed about 65% of Solid Amine B. Consequently, the total performance of Solid Amine A is better than Solid Amine B. Also, as to the adsorption/desorption subsystem and its operation, the steam regeneration process is much simpler than the heat/vacuum regeneration process as shown in Figs 2 and 3. Based on above comparison, it is evaluated that the steam regeneration process using Solid Amine A is the best for our application of CO2 adsorption and removal process. 3. C A R B O N

DIOXIDE

101 O >t.o

I0 ° w

c~

CRACKING

10 - I

In a closed environment as in the space station, it will be indispensable to provide a process to recover oxygen from carbon dioxide collected from air. The most advantageous process to recover oxygen is to produce water by cracking CO: with addition of H2 gas, then to obtain oxygen by electrolyzing water. 3.1 Carbon dioxide cracking reaction There are two carbon dioxide cracking reactions as follows: (a) Bosch Reaction[4,5]: CO2 + 2H2 ~ C + 2H20 (b) Sabatier Reaction[6,7]: • First Reaction CO2 + 4H2--* CH4 + 2H20 • Second Reaction CH 4 ~ C + 2H 2 3.2 Carbon dioxide cracking tests Basic tests have been performed to establish reaction conditions and basic characteristics of Bosch and Sabatier reactions for their comparison. Tested catalysts are listed in Table 3. The relation of temperature and conversion efficiencies from CO2 to H20 in the Bosch reaction is shown in Fig. 6. It shows a trend that a better conversion efficiency can be obtained by a higher temperature. Also, it shows that a better conversion efficiency can be obtained by a gamma-alumina catalyst than by a steel wire catalyst. However, the catalytic activities will be remarkably reduced soon because of inhibition of reaction by a large amount of separated carbon deposit inside of catalyst particles as well as on their surfaces, as seen in Fig. 7. Besides, the carbon deposit inside of catalyst particles cannot be removed by a mechanical process, thus recovery of catalytic activity cannot be expected. The smaller conversion efficiency of steel wire catalyst can Table 3. Tested catalyst for carbon dioxide cracking Reaction Bosch reaction Sabatier first reaction Sabatier second reaction

Catalyst QGamma-alumina QSteel wire QRuthenium on alumina QNickel wire

49

700°C 600°C I J i , .I 1.0 i.I 1.2 TEMPERATURE,

500°C ,d 1.3

IO00/K

Fig. 6. Conversion efficiencyvs temperature characteristics of Bosch process. be improved by a greater specific surface area by densely loading the wires. In this case, like in the nickel-wire catalyst case to be discussed later, the separated carbon is considered to deposit on the wire surface which is easier to remove, thus the catalytic activity of the steel wire catalyst can be maintained longer than the gamma-alumina ones. In a Bosch reaction, a CO by-product is seen which may cause a problem to the Bosch reaction itself when a recycling system is constructed. The relation of carbon dioxide reaction rate and required H 2 mixing ratio (H:/CO2 mol ratio) in the Sabatier First Reaction is shown in Fig. 8. From this graph, if H / C O 2 equals or exceeds 5/1, 100% of oxygen in CO2 can be converted to H20. The relation of conversion efficiency from CH4 to H 2 and space velocity is shown in Fig. 9. From this curve, at space velocity of 1000-2000 I/h, approximately 15% conversion capability can be obtained. Separated carbon deposit on nickel wire catalyst can be seen on surface only and no inside deposit is observed as shown in Fig. 10. Therefore, by removing carbon deposit on the surface by a proper method, catalytic activity would be maintained. 3.3 Carbon dioxide cracking system From the tests described above, a carbon dioxide cracking system shown in Fig. I I can be proposed. A Sabatier First Reaction is used as carbon dioxide cracking reaction in which 100% oxygen can be recovered as water from carbon dioxide. At the same time, produced methane will be converted to hydrogen gas through a Sabatier Second Reaction for cyclic use of hydrogen in the First Reaction. However, further study will be necessary to solve following problems: • Effect of recycled un-reacted methane to Sabatier First Reaction.

50

K. OTSUJ] et

15

102

al.

204

0010

~OU

(a) before use

(b) after use Fig. 7. Analysis photo of carbon deposit over gamma-alumina catalyst section by XMA.

• Effect of excessive hydrogen gas to Sabatier Second Reaction. • Accumulation of small amount of by-product gases generated through recycling. • Inhibition of reaction by separated carbon deposit in Sabatier Second Reaction and preventive action against it (related to frequency of catalyst exchange). • Research for an improved catalyst, 4. HARMFUL GASES REMOVAL

AS the result of human activities in a habitable area, various harmful gases are discharged from the human body as well as discharged by various materi1.o

0

als used at various areas of the module. In a permanent Space Station, to prevent accumulation of such harmful gases, it is necessary to remove even small amounts of products. Thus, a harmful-gas removing subsystem should be applicable to all kinds of the generated products. Considering zero-gravity condition in the Space Station, one of possible removing process is to collect such gaseous products by adsorbent which will be carried back to the Earth periodically for disposition, or as another method, these gases will be converted to harmless materials or to materials easier to handle by oxidizing. Therefore, an excellent effect can be expected combining these methods. A sample of such a combined process is shown in Fig. 12. o

1.0

Z w

8 0

i

2/1

~

4/I

0

L

5/I

8/i

STOICHIOMETRIC RATIO, MOL RATIO

Fig. 8. Reaction rate vs H{CO 2 mol ratio of Sabatier First Reaction.

~

'

i000 2000

5000

SPACE VELOCITY, I/HR

Fig. 9. Conversion rate vs space velocity of Sabatier Second Reaction.

A regenerable carbon dioxide removal and oxygen recovery system

OD

!~

~OU

20

102

5

10

(a) before use: surface/inside

20

102

20

(b) after use: surface/inside Fig. 10. Analysis photo of carbon deposit over Nickel catalyst by XMA.

CO,

Ha

SABATIER FIRSTSTEP REACTOR

CH,

SABATIER SECOND STEP

CH,

REACTOR H~O

SEPARATOR H,

WA~TER H~O I ELECT~ LYTIC

I (C)

02

Fig. 11. Carbon dioxide cracking subsystem using Sabatier reaction.

TO CABIN COOLER

ADSORBER GAS FILTER

CABIN AIR

GAS FILTER ADSORBER (PRE+HEPA)

HEAT EXCHANGER

COMBUSTOR

Fig. 12. Harmful gases removal subsystem.

52

K. OTSUJI et al. _O.__..(i)_- "O AMMONIA

I0 -~

TRIETHYLAMINE

o

g I

ACID IMPREGNATED ACTIVATED CARBON

o_

~ ~ 10-z S

UNIMPREGNATED ACTIVATEDCARBON

ca

10-3

GAS TEMP : 25°C 1

L

i0'

10 2

CONCENTRATION, PPM

Fig. 13. Adsorption isotherms for basic gases. Activated carbon may be one of the best adsorbent. The activated carbon adsorbent with fully developed micro pores can adsorb various products of organic compounds, sulfide and nitrofide compounds such as hydrocarbon, hydrocarbon halide, alcohol, ketone, ester, etc. However some of polar compounds among them are less effectively adsorbed. For these items, an improved activated carbon can be used. For instance, materials which chemically react with polar compounds are impregnated in the activated carbon. Having them chemically adsorb these polar compounds on the huge surface of activated carbon, the adsorbing capability of the activated carbon will be improved. As an example, adsorbing capabilities of activated carbon impregnated with acidic materials for ammonia and tri-methyl-amine and those of activated carbon impregnated with alkali materials for hydrogen sulfide and methylmercaptan are shown in Figs 13 and 14. The catalytic activity of the activated carbon which is an excellent oxidization catalyst by itself, can be improved by impregnation of effective catalytic materials. With this, it may be possible to improve adsorption of hydrosulfide or to oxidize carbon monoxide. Even with this combination of adsorbent, such low boiling HYDROGENSULFATE .

o<

i0 o

~

10-~

.

.

.

point materials as CH4, H:, etc. will come out through these adsorbent. They can be processed by converting to CO2 and H20 through high temperature oxidizing reaction. In high temperature oxidization, catalytic oxidization process performed at a temperature as low as possible is considered appropriate for energy saving purpose. However, it should be noted that harmful byproducts will be generated in the high temperature oxidization process. For example, harmful gases are generated from hydrochloric acid, sulfer oxides, nitrogen oxides, etc. when hydrocarbon halide, hydrosulfide, nitride, etc. come through the adsorbent. Therefore, a back up device should be provided downstream of catalytic oxidization tower, as well as some consideration to minimize flow amount in a calalytic oxidization process. 5. E N E R G Y

SAVING

CONSIDERATION

In the Space Station, the volume of generated CO2 in each module is varied according to the movement of occupants. The CO2 removing subsystem must have a capability to process for maximum requirement. However, excessive energy must also be saved depending on the volume of CO2 generated. Based on this consideration, examples of energy saving devices for CO2 removing subsystem is presented in Fig. 15. Energy Saving I: Utilizing required minimum regenerating energy in accordance with volume of generated CO:. Detecting CO2 partial pressure (PCO2) in excess of a preset value at the outlet port of the CO2 removing equipment, it will generate a regenerating signal. The regenerating process would start operating only after CO2 partial pressure in the cabin is increased over the preset value and the adsorbent is saturated with CO2. In other words, the regenerating process would not operate if CO2 partial pressure is not high enough and the adsorbent has not adsorbed enough CO2. Energy Saving II: To save electric power requirement by adjusting adsorption air flow to the minimum requirement depending on the volume of generated CO2.

METHYLMERCAPTAN

0

BASEIMPREGNATED ACTIVATED CARBON

•

UNIMPREGNATED ACTIVATED CARBON

i

< ) . - " .E)" ~ ' " ~ .

g L I0 ~

GAS TEMP : 25% I i0 z

CONCENTRATION, PPM

Fig. 14. Adsorption isotherms for acid gases.

Fig. 15. Energy saving concept in CO 2 removing subsystem.

A regenerable carbon dioxide removal and oxygen recovery system

53

\

"iU F ~

1

FT- -~,

'-~II ~ ER

i

;

[ r. . . . . . . . . ~," ~vr,

I HEX

CIRCULATING FAN

ODOR CNTRL

ADSB/HEPA WATER SEP

•.•__[•WATER PUMP

WATER TANK ITEMP/HUMD CONTROLSUBSYSTEM~

LiOH CANISTER CIRCULATING FAN HEATER

LEGEND

[ t ~ I _ ABS()RBENT~,.

Shutoff Valve CO, PUMP

STEAM GENERATOR

Selector Valve

I C02 REMOVING SUBSYSTEMj

-

Check Valve ~

: Control Valve

D<

:

Hand Valve

FIA : Flow Indicator Alarm ....... ~,o~o9, ~ CATA COMBUSTOR II HEX m

FICA : Flow Indicator Controller Alarm

ADSORBER

LHARMFUL GASES REMOVINGSUBSYSTEM

COOLER

~--~ooo~

HEX '--f-'

~ , . HEATER . . . . ~)Doo~

WATER

ELECTRO- I LYZER

HEATER

]_

H:

RECOVERY

\

:

HIA

: Humidity Indicator Alarm

CO~

Heat Exchanger

PdIA : Pressure Difference Indicator Alarm TIA

HEATER

102 RECOVERINGSUBSYSTEMI __.j

HEX

: Temperature Indicator Alarm

TICA : Temperature Indicator Controller Alarm

Fig. 16. Advanced ECLS system for the Japanese Experiment Module.

Detecting PCO2 in cabin below a preset value, a signal is generated to reduce RPM or to stop the fan with inverter. Energy Saving III: To collect rejected heat for energy regeneration. Steam supplied to adsorbent for regeneration will be condensed in adsorbent while expelling CO2. The additional air when supplied will be heated and have water in the adsorbent evaporated and exhausted from outlet of adsorber as high temperature air. The exhausted air temperature will be lowered depending on the lowering temperature of the adsorber. During high temperature period, the rejected heat can be utilized to heat water supplied to generate steam for the regeneration process.

6. ECLS SYSTEM

The block diagram of the ECLS system for the JEM as described above is shown in Fig. 16. The primary circuit of cabin air consists of a circulating fan, a temperature and humidity controller, an odor controller, a dust and micro-organism remover. Operation of the circulating fan will be determined depending on dispersion and heat distribution of cabin air, and the temperature and humidity control system is adjusted by a heat-exchanger bypass line valve. The dust remover is installed at the inlet port of cabin air and a high performance micro-organism filter and an odor filter are also inserted in the primary air circuit. For odor control, removal of very

54

K. OTSUJIet

low level substances is required which can not be expected with a by-pass installation. The odor control is also able to remove smell of amine generated from CO2 removing subsystem. To remove CO2, a certain volume of air is bled and conducted to CO2 removing subsystem and air without CO2 is supplied to the rotary fan separator of humidity control system, where periodically discharged water as well as water contents in cabin air will be removed. Some of the removed water are returned to CO2 removing subsystem as water supply to generate steam for the regenerating process. Also some removed water is returned to the 02 recovering subsystem. The collected CO2 is cracked into CH 4 and H20 in the CO2 cracking equipment. 0 2 is generated electrolytically from H20 in the O: recovering equipment and returned to cabin. CH 4 is conducted to CH 4 cracking equipment where it is cracked to C and H2. The generated H 2 is returned to the CO2 deoxidizer. The accumulated carbon over the adsorbent layer will be collected as solid carbon and returned to the Earth periodically. To remove harmful gases, a selected amount of air from the outlet line of the circulating fan will be bled and processed and returned to the inlet of the fan. A single fan is used as suction fan as well as circulating fan by which the number of rotating equipment is reduced to improve the system reliability. The required process air flow depends on volume of harmful gases to be removed and the allowable density level of gases in the cabin air. A LiOH canister is also installed in the circulating line for emergency CO: removing operation for a short duration safe-heaven. Filter elements of dust and micro-organism remover and adsorbent for harmful gas remover are periodically exchanged and returned to the Earth. The exchange interval and system control is accomplished in conjunction with an adequate environment measurement subsystem, thus the environment in the JEM can be maintained comfortable at all time.

al.

7. CONCLUSION As described above, basic evaluation of the solid amine CO2 removal process with steam regeneration and the CO2 cracking have been accomplished stating the possibility for application in environment control system in the Space Station. However, there are many problems to be solved to bring it up to reality and such efforts to approach these problems should be done further. On the Earth, the circulation of oxygen and water is maintained by natural ecosystem without any human efforts. It may be said as the required energy is solely supplied from the sun. Therefore in the future Space Station, it is considered necessary to look forward to establish an environment control system not only depending on physical and chemical technologies requiring complicated operating procedures, but also including reuse of recycled water and incorporating bio-technology, as may be referred to as "MINI-EARTH". REFERENCES

I. A. M. Boehm and R. J. Cuslok, A regenerable solid amine CO2 concentrator for space station. SAE Technical Paper, 820847 (1982). 2. C. K. Boynton and A. K. Coiling Jr, Solid amine CO: removal system for submarine application. SAE Technical Paper, 831131 (1983). 3. G. D. Hopson, J. W. Littles and W. C. Patterson, Skylab environmental control and life support systems. ASME Publication, 71-Av-14 (1971). 4. D. B. Heppner, T. M. Hallick, D. C. Clark and P. D. Quattrone, Bosch: An alternate CO2 reduction technology. ASME Publication, 79-ENAs-32 (1979). 5. R. B. Jagow and R. A. Lamparter, Investigation of low temperature carbon monoxide oxidation catalysts. ASME Publication, 77-ENAs-28 (1977). 6. P. J. Birbara and 17. Sribnik, Development of an improved Sabatier reactor. A S M E Publication, 79-ENAs-36 (1979). 7. G. N. Kleiner and R. J. Cusick, Development of an advanced Sabatier CO2 reduction subsystem. ASME Publication, 81-ENAs-ll (1981).