Extensive literature searches revealed the numerous advantages of using pyrolysis as a means of recovering usable resources from inedible plant biomass, paper, plastics, other polymers, and human waste. A possible design of a pyrolysis reactor with test plans and applications for use on a space-based habitat are proposed. The proposed system will accommodate the wastes generated by a four-person crew while requiring solar energy as the only power source. Waste materials will be collected and stored during the 15-day lunar darkness periods. Resource recovery will occur during the daylight periods. Usable gases such as methane and hydrogen and a solid char will be produced while reducing the mass and volume of the waste to almost infinitely small levels. The system will be operated economically, safely, and in a non-polluting manner

Roberson, Bobby J.

English

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N9 3- 26 07 6
DEVELOPMENT OF A PYROLYSIS WASTE RECOVERY
MODEL WITH DESIGNS, TEST PLANS, AND APPLICATIONS
FOR SPACE-BASED HABITATS
Final Report
NASA/ASEE SUMMER FACULTY FELLOWSHIP PROGRAM--1992
Johnson Space Center
Prepared By:
Academic Rank:
College and Department:
NASA/JSC
Directorate:
Division:
Branch:
JSC Colleague:
Date Submitted:
Contract Number:
Bobby J. Roberson, Ph.D.
Professor
Bevill State Community College,
Division of Natural Sciences,
Fayette, Alabama 35555
Engineering
Crew and Thermal Systems
Life Support Systems
Charles E. Verostko
August 7, 1992
NGT-44-005-803
17-1
https://ntrs.nasa.gov/search.jsp?R=19930016887 2020-03-17T05:32:11+00:00Z
ABSTRACT
Extensive literature searches revealed the numerous advantages of
using pyrolysis as a means of recovering useable resources from inedible
plant biomass, paper, plastics, other polymers, and human waste. A
possible design of a pyrolysis reactor with test plans and applications for
use on a space-based habitat are proposed. The proposed system will
accommodate the wastes generated by a four-person crew while requiring
solar energy as the only power source. Waste materials will be collected
and stored during the 15-day lunar darkness periods. Resource recovery
will occur during the daylight periods. Useable gases such as methane and
hydrogen and a solid char will be produced while reducing the mass and
volume of the waste to almost infinitely small levels. The system will be
operated economically, safely, and in a non-polluting manner.
17-2
INTRODUCTION
In a controlled ecological life support system (CELSS) such as a
space-based (lunar/Mars) habitat, water, food, and oxygen must be stored
and recycled. The problems of mass and volume limitations and infrequent
resupply dictate that artificial methods be employed to supply the needs of
the inhabitants (15). One of the most important aspects of a CELSS
involves a closed loop system (14). A CELSS must have the ability to:
a) process human waste and plant biomass and recover resources from
these materials; b) recondition and revitalize the air by using waste
materials; c) maintain a mass balance within the system; d) provide safe and
reliable life support for long-duration missions; e) attain a high level of
self-sufficiency; f) lower the expense and simplify the problems related to
resupply; and g) provide an Earth-like environment that is conducive to
productivity (6,11).
Requirements of a CELSS
The waste resource recovery portion of a CELSS will consist of a
waste and water management subsystem, an atmosphere management
subsystem, and a food management subsystem (5). The outputs of one
subsystem should match the requirements of the others while observing
quality and quantity tolerances (6). The design of such a CELSS should
also permit future expansion, and should be safe, reliable, flexible, and
easily maintained. A CELSS that incorporates biological and
physicochemical (B/PC) technologies to recycle water, air, food, and
biomass holds the ultimate promise of allowing humans to become
successfully established outside the Earth's biosphere (10).
Spaceflights through the Space Shuttle era have not been dependent
on recycling and regeneration of useful resources because of the short
duration of the flights. Instead, waste materials have been stabilized,
stored, and returned to Earth for analysis and disposal. This will not be
feasible on lunar and Mars missions. The majority of the food on future,
long-duration flights and missions must be grown in a CELSS. Most of the
plant biomass is inedible and must be processed to supply carbon dioxide,
water, and nutrients for plant growth, or fuel for other systems. It is
estimated that inedible plant biomass and paper products will constitute
approximately half of the total dry, solid waste material generated in a
CELSS (13).
The simplest, and probably the most obvious, method of recovering
some of the value from any organic material is by burning it for its energy
17-3
content (4). The two processes used for the destruction of materials by
heating are incineration and pyrolysis.
Incineration
Incineration is the complete oxidation of waste using either pure
oxygen or oxygen diluted with an inert gas. A temperature of 100OoC and
a pressure of approximately one atmosphere are required. All types of
combustible materials such as inedible plant biomass, paper, plastics, food
waste, human waste, etc. may be treated. The incineration process usually
involves two major steps: a) initial heating to sterilize and to vaporize the
volatiles; and b) combustion of the dry waste. The process is relatively fast
and results in 97 to 99% reduction of the waste. The end product is usually
a fine, dry powder (7). Most incinerators contain two chambers. In the
primary chamber auxiliary burners dry, volatize, and ignite the waste.
The amount of air present is in 75 to 100% excess. When combustion is
sustained, the burners are turned off. The gases and combustibles flow into
the secondary chamber for burn completion. The air is maintained at an
excess level of 75 to 150%. The excess air, turbulence, and retention time
provide conditions for complete combustion (12). The chemical reaction
for the incineration of cellulosic materials is:
C6H1005 + 6 02 + heat ...... > 6 CO2 + 5 H20
Pyrolysis
Pyrolysis is the chemical destruction of a carbonaceous material by
heating to 400 to 1000oc in the absence of oxygen, or in a controlled
oxygen environment. The pyrolytic process results in the formation of
four phases of products: a) a gaseous component including hydrogen,
methane, carbon monoxide, and carbon dioxide; b) an oil including
organic acids, alcohols, ketones, etc.; c) a char including carbon and inert
compounds; and d) an aqueous phase containing some water-soluble
compounds. In general, the faster the decomposition of the materials, the
higher the yield of gas, whereas a long, slow heating process results in
higher proportions of oil and char. Also, upon rapid heating in the absence
of oxygen, cellulose molecules "explode," and the fragments are free to
form simple compounds such as methane, carbon monoxide, hydrogen, and
water (1). During the pyrolytic process, cellulose increases in porosity and
swells as volatiles are evolved. Pyrolysis begins at approximately 200oc,
17--4
and tars evolve. As the temperature rises the products decompose or
crack, forming hydrogen-rich gaseous compounds and solid carbon which
approaches graphitic carbon. The pyrolysis of cellulose reaches
completion between 600 and 800oc (2). The overall reaction for the
pyrolysis of cellulose is:
C6H1005 + heat ---> CH4 + 2CO + 3H20 + 3C
The reaction appears to be endothermic at lower temperatures and
exothermic at higher temperatures. Retention time is usually between 12
and 15 minutes (8). Some of the gases produced are combustible and have
value by providing heat to the effluent gases. The carbon residue, a char,
can also be used as a fuel. No oxygen is added, and the starting material is
only cellulose. Since the original material is not necessarily pure cellulose,
the effluent gases may contain some simple and complex organic
compounds. The char may also contain some minerals, ash, and other
inorganics as well (4).
The major concerns of a pyrolysis and/or incineration system in a
space-based habitat are the use of high temperature, explosion potential,
energy requirements, fire propagation, production of toxics, required
maintenance, efficiency, mass and volume requirements, pre- and post-
treatment of waste, requirement for a continuous system, and longevity of
the system (13).
DISCUSSION
Comparison of the advantages and disadvantages of pyrolysis versus
incineration indicate that pyrolysis might possibly be the most appropriate
physicochemical combustion technology for the recovery of resources
from waste materials. The advantages of pyrolysis include the following:
a) greater stability with little response to change in feed rate and therefore
easier to control; b) 15 to 25% higher process rates (feed capacity per
square foot of bed area); c) fewer and smaller particulates; d) less or no
supplemental fuel required; e) generation of useable gases; and f) smaller
mass and volume waste requirement (3). A pyrolysis reactor on the lunar
surface will require no fuel other than that supplied by the sun through the
use of solar concentrators. Also, a purge gas may not be needed since the
vacuum of space could be used to evacuate the air from the chamber. In
some instances a combined incineration/pyrolysis system might be
employed.
17-5
The actual results of a commercial pyrolytic process are shown in
Table 1. The effluent gases of three wastes indicate high percentages of
two gases that are potential fuels (methane and hydrogen).
TABLE 1.- PYROLYSIS TEST RESULTS*
Type of Waste
Gases Produced (mol %) Liquid Organic Garbage Drugs
Hydrogen 34.60 30.29 ---
Carbon dioxide 6.22 14.19 ---
Ethylene 8.52 8.06 10.37
Ethane 2.35 0.91 4.13
Acetylene 0.15 0.43 0.01
Oxygen .........
Nitrogen 0.70 0.48 ---
Methane 25.53 10.80 78.78
Carbon monoxide 6.22 26.25 ---
Propane "plus" 15.71 8.58 6.71
Hydrogen sulfide .........
* Test results are from a pyrolysis system invented, owned, and operated by Benjamin P.
Fowler, Fowler Engineering Company, Houston, Texas. Complete descriptions are given
in U.S. Patent No. 4,934,286. The mention of a vendor does not imply endorsement by
NASA.
Proposed System
The proposed system will operate at high temperatures (up to
1000oc). The power source for the initial test model will be either an
electrical furnace supplying heat to ceramic plates, a carbon arc, a graphite
resistance furnace, or a gas burner. The actual space-based system will
use solar concentrators, or electrical power from solar panels or a nuclear
power source. The system will accommodate plant biomass, plastics, other
polymers, human wastes, etc.
17-6
Figure 1 is a schematic of the proposed pyrolytic process.
I scrubber
bion_ass _,
[ condensor]
shredder
dryer pyrolysis _ heat
.._ reactor
- - inert gas
mill J--.--J J -(_
Figure 1.- Schematic of the Pyrolysis Process
Proposed Test Plans
The pyrolysis reactor shall be tested using several waste materials,
individually and collectively. The test materials should include inedible
plant biomass, paper, plastics, other polymers, and possibly human biomass
waste. Test conditions shall be varied to attain the optimum rate and
degree of pyrolysis with the recovery of all products for analysis. Useable
products should be identified for each type of waste. The test conditions
shall initially include the items shown in Table 2.
17-7
TABLE 2.- PYROLYSIS TEST CONDITIONS
Maximum temperature
Pressure
Amount of biomass
Moisture content
lO00oc
ambient
10 kg
<3%
Steps in the Pyrolysis Process
The steps in the pyrolytic process are outlined in Table 3.
TABLE 3.- PYROLYSIS PROCEDURES
1. Biomass is collected.
2. Biomass is shredded.
3. Biomass is dryed to reduce moisture content to 3% or less.
4. Biomass is milled to reduce particle size to 30 microns or
less.
5. Biomass is fed into the pyrolysis reactor vessel.
6. Oxygen and air are expelled from the reactor by the
introduction of an inert gas or by evacuation to the
vacuum of space.
7. The reactor vessel is sealed to prevent the introduction of
additional oxygen or air.
8. The vessel is heated to 1000oc where pyrolysis is carried
to completion while gases are collected.
9. Effluent gases are scrubbed, separated, and condensed if
necessary.
10. The system is shut down for maintenance if required.
Design of the Pyrolysis Unit
The pyrolysis unit will be constructed, tested, and monitored under
experimental conditions. The prototype laboratory model should be built
to the specifications of a lunar/Mars model and should be tested under the
17-8
conditions that exist on the surfaces of those bodies. Careful monitoring of
effluent gases should be conducted to assure that no toxic gases will be
released to space or to the atmosphere of Mars. Analysis of the products of
the pyrolysis of various substances should also be conducted to determine
their uses as fuels, nutrients, etc. Numerous pyrolysis reactors in
commerical use offer suggestions for a possible space-based model. Some
of the criteria for a lunar/Mars pyrolysis reactor system are listed in Table
4.
TABLE 4.- PYROLYSIS REACTOR SPECIFICATIONS
1. The reactor vessel shall be relatively compact.
2. The reactor vessel and all hardware shall be constructed
of corrosion proof materials.
3. The system shall tolerate temperatures up to 1000oc.
4. The system shall accommodate a minimum of 10 kg of
waste per day.
5. The system shall operate in a batch mode.
6. The system shall permit the recovery of useful gases and
and solids.
7. The system shall be easily maintained.
8. The system shall be safe and reliable.
Figure 2 shows a possible design configuration for a pyrolysis
reactor.
17-9
stainless steel mesh
36"
T" 36"
14"
6" diameter
steel wall
m
,,,j "1_"-- gas inlet
feed door 1" I-beams
T
40" _ I
®
----7
gas inlet
Figure 2.- Pyrolysis Model
17-10
CONCLUSIONS
Pyrolysis appears to be a highly efficient method for the recovery of
useful resources from inedible plant biomass, paper, plastics, other
polymers, and even human waste. Solar furnaces can supply the power for
the operation of the unit while methane and hydrogen can be collected for
use as fuels. The hydrogen could also be used to produce water (assuming
that oxygen can be obtained from the minerals on the moon and Mars).
The gases can be scrubbed to remove possible toxic materials. The char
and oils resulting from the pyrolysis process can also be used as fuels. The
system will be capable of batch mode operation and can possibly be
integrated with other physicochemical and biological systems of a CELSS.
The system should be relatively inexpensive, easily maintained, and should
be extremely durable and safe. Further studies are essential including the
actual construction and testing of the pyrolysis unit.
17-11
REFERENCES
1. Barton, A. F. M. Resource Recovery and Recycling. 1979. John
Wiley and Sons. Pp. 418-425.
2. Combustion and Incineration Processes. W. R. Niessen, Ed. 1978.
Marcel Dekker. Pp. 68-75.
3. Design of Sewage Sludge Incineration Systems. C.J. Brunner, Ed.
1980. Noyes Data Corp.
4. Handbook oflncineration Sytems. C. R. Brunner, Ed. 1991.
McGraw-Hill.
. Henninger, D. L. "Life Support Systems Research of the Johnson
Space Center" in Lunar Base Agriculture: Soils for Plant
Growth. D. W. Ming and D. L. Henninger, Eds. 1989.
American Society of Agronomy. Pp. 173-192.
. Hoshizaki, T. and B. D. Hansen, m. "Generic Waste Management
Requirements for a Controlled Ecological Life Support System
(CELSS)." NASA Conference Publication 2247. May 3-6,
1981. Pp. 38-49.
.
"Housekeeping Concepts for Manned Space Flights." Final Report,
Manned Space Systems Advanced Programs, Fairchild Hiller,
Republic Aviation Division. October 30, 1979. Pp. 4/39-4/40.
8. Incineration Systems. C. R. Brunner, Ed. 1984. Van Nostrand-
Reinhold Co.
9. Pyrolysis of Polymers, Vol. 13: Fire and Flammable Series.
C. J. Hilado, Ed. 1976. Technonic Publ. Co., Inc.
10. Rummel, J. and T. Volk. "A Modular BLSS Simulation System" in
NASA Conference Publication. 2480. 1987. Pp. 57-66.
11. Schwartzkopf, S., J. Houle, and A. Guastaferro. "Lunar Base
Controlled Ecological Life Support System (LCELSS)."
Preliminary Conceptual Design Study. Final Report.
April 3-10, 1991. Lockheed Missiles and Space Company, Inc.
17-12
12.
13.
14.
15.
Small-Scale Resource Recovery Systems. A.E. Martin, Ed. 1982.
Noyes Data Corp. Pp. 235-329.
Verostko, C. E., N. J. C. Packham, and D. L. Henninger. "Final
Report on NASA Workshop on Resource Recovery from
Wastes Generated in Lunar/Mars Controlled Ecological Life
Support Systems (CELSS)." May 1992. JSC Document No.
25736, CTSD-ADV-035.
Volk, T. and J. P. Rummel. "The Case for Cellulose Production
on Mars" in The Case for Mars III: Strategies for Exploration.
C. E. Stoker, Ed. 1989. Pp. 87-93.
Wyedeven, T., J. Tremor, C. Koo, and R. Jacques. "Sources and
Processing of CELSS Wastes." Adv. Space Research 9:85-97
(1989).
17-13



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