Progress on the CO2 Removal and Compression System

45th International Conference on Environmental Systems ICES-2015-064 12-16 July 2015, Bellevue, WA

Progress on the CO2 Removal and Compression System

Tra-My Justine Richardson1 Wyle/Logyx LLC, NASA Ames Research Center, Moffett Field, CA 94035-1000

Darrell Jan, 2John Hogan,3 Gary Palmer,4 Brian Koss, 5 Jason Samson5 NASA Ames Research Center, Moffett Field, CA 94035-1000

Roger Huang6

Wyle, NASA Ames Research Center, Moffett Field, CA 94035-1000

And

James Knox7 NASA Space Flight Center, Huntsville, Alabama, 35812

The Carbon Dioxide Removal and Compression System (CRCS) is designed to perform both the Carbon Dioxide (CO2) removal function of the four-bed molecular sieve (4BMS) system currently employed on the International Space Station (ISS), as well as additional integrated ability to thermally compress CO2 to supply downstream CO2 recovery units. The CRCS approach will reduce cost and improve reliability for future long-duration missions. This paper describes progress in CRCS development over the past year. Performances of the bulk air dryer (BAD) and residual air dryer (RAD) have been previously reported. A single unit of the 2-Stage compressor was assembled and tested for development performance. Data from those tests was used in the assembly of a second unit and integration into a two-unit system.

Nomenclature 4BMS = 4 Bed Molecular Sieve ARC = Ames Research Center BAD = Bulk Air Dryer CO2 = Carbon Dioxide CRCS = Carbon Dioxide Removal and Compression System ESM = Equivalent System Mass ISRU = In-Situ Resource Utilization ISS = International Space Station MSFC = Marshall Space Flight Center NASA = National Aeronautics and Space Administration OGA = Oxygen Generation Assembly PSA = Pressure Swing Adsorption RAD = Residual Air Dryer

1 Scientist/Engineer, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 2 Air Revitalization Lead, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 3 Physical Scientist, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 4 Engineering Technician, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 5 Mechanical Design Engineer, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 6 Engineer, Bioengineering Branch, and NASA Ames Research Center, Mail-Stop 239-15, Moffett Field, CA 94035. 7 Aerospace Engineer, Space Systems Dept./ES62.NASA MSFC, Huntsville, Alabama 35812.

International Conference on Environmental Systems

2

RTD = Resistance Temperature Detector SCFM = Standard Cubic Feet per Minute SS = Stainless Steel SwRI = Southwest Research Institute TSAC = Temperature Swing Adsorption Compressor UOP = Universal Oil Products, a Honeywell Company

I) Introduction

he Low-Power Carbon Dioxide Removal (LPCOR) concept was initiated in 20031 as an advanced low-power and low-mass carbon dioxide (CO2) removal system for spacecraft. The LPCOR design is well documented in

previous ICES conference papers2, 3, 4, 5, 6, 7, 8and will only be briefly summarized here.

A) Background The LPCOR (Figure 1) consists of the bulk air dryer (BAD), two residual air dryers (RADa and RADb), and two CO2

removal, compression, and storage (CRCSa and CRCSb) subsystems. Cabin air first enters the tube site of the BAD where approximately 80% of the water is removed. The RAD removes the remaining 20% before feeding the dry air to the CRCS. Each CRCS unit is separated into two stages, stage 1 and stage 2. Stage 1 adsorbs CO2 from the cabin air and desorbs it to stage 2. Stage 2 of each CRCS unit compresses and stores the CO2 for delivery to the Sabatier CO2 reduction system as needed. The LPCOR was designed to operate in 120 minute full cycles (60 minutes adsorb/60 minutes desorb) to maintain cabin air at or below 2600ppm CO2 and to synchronize with the Oxygen Generator Assembly (OGA). The two RADs and CRCSs accommodate the 60-minute half cycle operation. As RADa and CRCSa are adsorbing water and CO2, the RADb and CRCSb are desorbing water and CO2.

Figure 1: Flow Diagram of the low-power CO2 removal (LPCOR) system. Black lines = air flow; blue lines = CO2

flow; and dotted lines = no flow. 6

T


3

The LPCOR concept evolved from the temperature swing adsorption compressor (TSAC) concept previously

developed for Mars In-Situ Resource Utilization (ISRU)9,10 at NASA Ames Research Center (ARC)11. In addition, ARC developed both the air-cooled and the water-cooled TSAC 12, 13,14,15to work with the 4BMS and Sabatier. In 2006, the air-cooled TSAC underwent a successful integrated test with the 4BMS and the Sabatier system at MSFC16.

The CRCS design parameters were based on the lessons learned from the TSAC development process. Due to funding restrictions, the LPCOR development and testing were separated. In 2013, the BAD and RAD were tested as part of the dryer down-select activities at MSFC7. Nafion membranes in the BAD have shown decreased performance in the presence of increased ammonia leading to lower than expected membrane life expectancy. Therefore, at this time, only the CRCS is being developed.

The CRCS subsystem serves to remove, accumulate, and compress CO2 from the surrounding environment. In addition, the CRCS is solid-state compared to the SwRI mechanical compressor. With fewer moving parts, the CRCS offers higher reliability and lower ESM. Therefore, the CRCS is a competitive technology compared with the current ISS compressor architecture. This paper will describe the development and testing of the CRCSa unit. The lessons learned from the CRCSa unit will be applied to the continuing development of both CRCS units.

B) CRCS design specification The CRCS design concept relies on minimizing mass, volume, and power. The design specifications for the CRCS

are listed in Table 1. The CRCS was designed to maintain a cabin atmosphere CO2 concentration under 2600 ppm and to operate with 85% CO2 removal efficiency.

Each CRCS unit consists of two concentric lightweight cylinders made of stainless steel (SS) 316 material. The CRCS design model is shown in Figure 2. The first stage inner cylinder is filled with zeolite 5A which adsorbs CO2 from cabin air and desorbs CO2 to the annulus space between the cylinder walls (stage 2). The second stage sores and thermally compresses CO2 for delivery to the Sabatier reactor. For maximum heat transfer between the shared wall of stage 1 and stage 2, the stage 1 wall was fabricated with 0.03”SS316 material.

Based on the CO2 removal requirements for four crewmembers, the empty cylinder volumes are 12L and 3L for stage 1 and stage 2, respectively. In order to reduce pressure drop, the larger diameter cylindrical 1/16” zeolite 5A (UOP) was used for stage 1, while stage 2 uses the smaller spherical zeolite 5A in order to increase adsorption capability. For initial tests, these materials were used to generate validation data with the TSAC tests completed in 2006 (the TSAC used the smaller spherical UOP 5A). For future tests, other zeolite or other CO2 adsorbent may be used.

Spiral wound heaters (OMEGA Heater Company, Ronkonkoma, NY) are used to regenerate the zeolite in both stages. The heaters were designed to operate at 120Volts and produce uniform heating throughout the zeolite volume. Stage 1 heaters are comprised of sets of (6) Tubular Elements, 0.260” Diameter, Stainless Steel Type 316 sheath, passivated, stainless steel post terminals for 1.74Watts/inch. Only one tubular element at 1.74Watts/inches was needed for stage 2.

Stage 1 was designed to be cooled by incoming cabin air while stage 2 was cooled by a forced convection air cooling jacket driven by a blower. A 2” thick SOLIMIDE insulation (Boyd Corporation, Portland, OR) with a high R-value and low density was used for insulation. Calculation showed that 2” of insulation was needed to insulate the heated surfaces to a 45˚C touch temperature.17


4

Figure 2: Design illustrations of the CRCS showing the lids, heaters, and retaining screens.

Table 1: CRCS Adsorbent Compression Canister Design specifications. All data are for ONE canister only.

Stage 1 Stage 2 Number of Crew members 4

CO2 inlet concentration, ppm 2600 CO2 removal efficiency, % 85 Material of construction SS 316 Canister shape Concentric Cylinders CO2 input concentration, ppm 2600 TBD Canister total empty volume, L 12 2.77 CO2 delivery pressure, psia 3 20 Adsorbent size and shape UOP Molsiv Adsorbents

5A 1/16” MS-198 Cylindrical pellets

UOP 5A-MG-16X40

Adsorbent mass, kg 9.480 2.370 Adsorbent density, g/cc .79 Void space, L 0.67 .27 Heaters capacity, W 1249 422.94 Regeneration temperature, ˚C 250 250 Bake out temperatures, ˚C 300 300 Number of heater coils 6 1 # of 2 wire RTDs on heater coils 6 2 # of 2 wire RTDs in adsorbent material 12 2 Cooling jacket SS316 sheet : ¼” gap Blower, SCFM 68 Insulation ¼” High Performance SOLIMIDE Polyimide

Foam Insulation Screens Super-Small Particle-Filtering Stainless Steel Wire

Cloth, Woven, 316 Stainless Steel, 80 x 700 Mesh, 12" x 12" Sheet, 35 microns

Fabric Screen ¼” Low Density Techmat


5

II) Fabrication and Assembly This section describes the fabrication and assembly of the major CRCSa components. The fabrication of the

canisters was described in Hogan et. al.8 Pictures of the fabricated components and assembly are shown in Figure 3. For bake-out and regeneration, each stage contains a custom fabricated helical heater (Omega Heater Company, Ronkonkoma, NY) described in the previous section. Ceramic caps and high-temperature wire were used to connect the terminals.

To contain the sorbent, 1/4” low-density high temperature glass fiber insulation mat (BFG Industries, Inc. Greensboro, NC) was used. Super-small, particle-filtering 316 SS wire cloth, woven to 35 microns 80 x 700 mesh (McMaster Carr, Santa Fe Springs, CA, PN 9419T34) was used to produce uniform air flow and act as sorbent containment. In addition, o-rings were installed on the screen retaining rings to prevent dust from exiting the chamber (Figure 3c). An air blower (Ametek 116634-01) pushes air at 68CFM through the cooling jacket to cool stage 2 during the adsorption cycle.

To observe heating uniformity and characterize flow, RTDs were placed strategically throughout the heaters and materials. Two-wire RTDs were cemented on heaters using high temperature Durabond 954 metallic paste (Cotronics Corp, Brooklyn, NY). Material RTDs were anchored onto 1/16” non-porous high alumina ceramic rods (Mc Master Carr PN 87065k41). For easy assembly and disassembly, RTDs wires were spliced onto connector pins and assembled onto custom-machined Macor (Accuglass, Valencia, CA) pigtails.

Before installation, both sorbent volumes were baked at 300˚C for 10 hours. Multiple layers of 0.25” thick laser-cut SOLIMIDE was wrapped around the cooling jacket to a final thickness of 2.0”. A similar method was utilized on the top and bottom lids due to produce a final 1.75” thick SOLIMIDE insulation layer. This value is less than the side outer wrap, as there is limited spacing between the lids and the valve actuation assembly.

Figure 3: A series of photos were taken after fabrication and during assembly of the CRCSa. The descriptions are as follows: (a) the white 23-pin Macor connector connected to the retaining ring for RTD feedthroughs; (b) the spiral heater assembled with the 9-pin Macor RTD connection pigtails; (c) The retaining ring Kalrez O-ring for dust control; (d) the top and bottom retaining ring with the 30 micron screen brazed on; (e) the laser cut SOLIMIDE insulation (f) the top view of the inside of the canister; (g) the heater installed; (h) the sorbent filled in; (i) the white tech mat on top of the sorbent; (j) the retaining screen on top of the white tech mat : (k) the 30 micron screen; (l) the cooling jacket; (m) the CRCSa without the cooling jacket; (n) the cooling jacket installed; (o) the SOLIMIDE insulation installed.


6

III) The Duty Cycle and the Test Matrix There are two CRCS units (CRCSa and CRCSb) that operate in a 60-minute half-cycle. The CRCSa and CRCSb

unit operate in continuous opposing 60 minute half-cycles. When one unit is adsorbing the other is desorbing. The CRCSa was fabricated and assembled in 2014. After assembly, functional testing was completed to verify the proper operation of the heaters, the vacuum pump, airflow, and sensors. The duty cycle diagram (Figure 4) is a modified version from those initially cited in Mulloth et.al.1 When the CRCSa is in adsorption mode (at time = 0 minutes), CO2-laden dry air is fed to the CRCSa stage 1, while stage 2 receives concentrated CO2 from the CRCSb stage 1(which is in desorption mode). At 60 minutes, CRCSa stage 1 desorbs CO2 to CRCSb stage 2 while CRCSa stage 2 feeds concentrated CO2 to Sabatier. The objective of the CRCSa test cycles is to determine the actual duty cycle durations. For example, according to Figure 4, standby occurs in the last 5 minutes of the desorption mode, but this may become longer or shorter depending on the characteristics of the heating curves. The test matrix is listed in Table 2.

Figure 4: The designed duty cycles of the two-stage CRCS system.4

Table 2: The CRCSa test matrix Test objectives Stage 1 Stage 2 Heater test (desorption) 300˚C 250˚C Flow test 30SCFM

PSA air No

flow/heater on

Vacuum test 5 minutes Bake-out Determine the CO2 concentration output to stage 2

2600ppm na

Determine stage 2 delivery pressures

na 20psia


7

IV) Experimental Data and Discussion

A total of 16 one to four-hour tests were conducted. As of this writing, only heater and vacuum tests were completed, CO2 tests were not yet performed. Results from one set of a four-hour cyclic test are shown in Figure 5. The four-hour cyclic test consists of two full 120-minute adsorption and desorption cycles. The cycle starts by first heating both stages to the temperature set-point (300˚C for stage 1 and 250˚C for stage 2). Then at 55 minutes, stage one is at standby and the heaters are turned-off. At 60 minutes, adsorption begins – the stage 1 heater is turned off and cooled by PSA air passing through it at 30 SCFM, while stage 2 is cooled by the cooling jacket driven by the blower. At 115 minutes, the heater to stage 2 is turned on and vacuum is applied to stage 1, removing the residual CO2-free air. At 120 minutes, the cycle repeats for another 120 minutes.

During the run, the stage 1 heaters are turned off at 50 minutes instead of 55 minutes because the heater temperatures reached the 315˚C set-point. For optimal work capacity, the CRCS was designed with the target zeolite operating temperature of 300˚C. However, UOP recommends regeneration temperatures of 285˚C with 315˚C maximum temperature. Operating above this temperature for prolonged periods can damage the sieve or the binding material. Therefore, the “standby” step in stage 1 was 10 minutes instead of 5 minutes (as designed). The temperature drop of both heaters and the materials can be seen at 50 minutes for all the graphs.

Figure 5 shows the heater coil temperatures for stage 1. According to the graph, there is about a 120˚C differential between the observed heating coil temperatures. This resulted in around 87˚C (Figure 6) temperature difference in material temperatures from the center, top, and bottom of the canister. From the temperature profiles, the cylindrical stage 1 canister has the thermal behavior roughly resembling a sphere. The center is hotter than both the top and bottom. Furthermore, the top is colder than the bottom. There are several speculations as to why heating is not uniform. First, heat is being lost at the top and bottom via conduction to the 2” diameter plumbing used. Secondly, the top and bottom lids were designed to incorporate a “Hershey’s kiss” shape for uniform flow distribution, however fabrication difficulties prevented this geometry from being produced. Lastly, the helical heating coils were different lengths by design, but could not be individually temperature controlled due to feedthrough size limitation. Therefore the shorter elements in the middle likely heated up faster (little conductive heat loss) than the longer elements around the outside (increased conductive heat loss).

Figure 5: A graph of temperature [˚C] versus run time [hrs] of stage 1 heating coils.


8

Figure 6: A graph of temperature [˚C] versus run time [hrs] of stage 1 material temperatures.

Figure 7 shows the temperature profile of the stage 1 wall. Here, one can see that the RTD readings at the bottom of the wall are 70˚C lower than that of the middle RTD. The lower temperature may be inconsistent with complete desorption of CO2. Also, as desorption is completed and PSA air is passed through stage 1, a temporary increase in temperature is seen in the bottom RTD as heat is pushed from the top (where air enters) through the bottom.

Figure 7: A graph of temperature [˚C] versus run time [hrs] of stage 1 wall temperatures.

Figure 8 shows the RTD readings of both the heater coils and the material in stage 2. The graph shows that after 60 minutes, the material temperatures only reached 235˚C. This may be an issue if the sorbent does not fully desorb the CO2 to at least 20 psia during the 60-minute compression and delivery period.


9

Figure 8: A graph of temperature [˚C] versus run time [hrs] of stage 2 heating coil and material temperatures.

V) Lessons Learned The lessons learned from the development and testing of CRCSa are listed in Table 3. The lessons learned were

compiled to help indicate possible improvements prior to the operation of CRCSb. Since most components of both canisters were hand fabricated at the same time, the opportunities for design alterations within time and budget are limited. Under the present program, the feasible modifications are listed in Table 3, including the following: the grounding and insulation of the RTD wires, the re-fabrication of the 23-pin Macor connections, and the installation of the “Hershey kiss” into the lids. After longer tests, the cycle time can be varied to observe the impact on heating and cooling.

The 60-minute half-cycle was specified initially to accommodate the hydrogen production of the Oxygen Generation Assembly (OGA). This specification may be modified depending on testing results and application configurations.

Table 3: Lessons learned from the design, fabrication, and testing of the CRCSa adsorbent bed. Component Issues encountered Modification to CRCSb design,

fabrication, assembly 1 Macor 9 pin pig-tail

connectors Electrical shorts on the ground wires Insulate ground wires

2 23 pin macor connectors

Connectors cracks upon applied pressure during assembly

Re-design pin hole size and use ceramic paste

3 RTDs High readings Use more ground wires with smaller gauge 4 Top and bottom cap Temperature differential from the top

and bottom to the center of the canister can be as high as 100˚C

Design a “Hershey” kiss shape into the caps to improve temperature distribution and improve heat lost.

5 Heaters in stage 2 It takes 30 minutes for stage 2 temperatures to heat up to 250˚C.

None at this time.

6 Adsorbent used and temperature

300˚C temperature requirement for stage one delayed tasks and increase

Since UOP recommended only 315˚C for its adsorbent, the heaters maximum


10

specification cost temperatures will be set at this limit. 7 Heaters Stage 1 Large temperatures variation between

the top, middle, and bottom layer No change at this time. The heating elements were not designed at varying resistance to account for the length of the heater. A new heater design is needed.

8 Heater Stage 2 Stage 2 material temperature does not reached 285˚C within the 60 minutes cycle

Longer cycle time considered. Recycle hot air from the other unit to the cooling jacket.

9 Macor feedthrough Not enough feedthrough capacity to use a three 3 wires RTDs or install more RTDs for flow characterization.

None at this time.

10 Insulation Not enough space to wrap insulation Redesign the rack

VI) Conclusion and Recommendations The CRCSa fabrication, assembly, and initial testing were completed. Data from heating curves indicated that there is

a 120˚C temperature variation from the center to the top and bottom of the heater coils in stage 1. The temperature curves for stage 2 show that there may be issues with stage 2 not fully desorbing. Lessons learned from CRCSa will be applied to the fabrication and testing of CRCSb where feasible within cost and schedule.

Acknowledgement The authors would like to thank all the previous designers and authors who were referenced in this paper in the

development of the CRCS.

References 1 Mulloth, L., et al. Development of a low-power CO2 removal and compression system for closed-loop air revitalization in future spacecraft, SAE International. Paper 2005-01-2944, 2005. 2 Mulloth, L., Rosen, M., Varghese, M., Luna, B. et al., "Performance Characterization of a Temperature-Swing Adsorption Compressor for Closed-Loop Air Revitalization Based on Integrated Tests with Carbon Dioxide Removal and Reduction Assemblies," SAE Technical Paper 2006-01-2126, 2006, doi:10.4271/2006-01-2126. 3 Varghese, M.M., Mulloth, L.M., Luna, B., and Hogan, J.A. "Development Status of a Low-Power CO2 Removal and Compression System for Closed-Loop Air Revitalization." 40th International Conference on Environmental Systems, San Francisco, CA. 2010. 4 Mulloth, L., Varghese, M., Luna, B., Hogan, J., LeVan, D. and Moate. J.R. Development Status of a Low-Power CO2 Removal and Compression System for Closed-Loop Air Revitalization. No. 2008-01-2095. SAE Technical Paper, 2008. 5 Mulloth, L.M., Varghese, M. and Luna, B.. "Power Optimization Options for a Temperature-Swing Adsorption Compressor Design." (2010). 6 Hogan, J.A., Luna, B. Koss. B., Palmer, G.H., Linggi, P., Lu, Z., Varghese, M.M., and Mulloth, L.M. "The Low-Power CO2 Removal and Compression System: Design Advances and Development Status." AIAA Paper 2012-3587 (2012). 7 Hogan, J., Jan, D. Palmer, G.H., Richardson, T-M.J., Linggi, P., Lu, Z. and Kamiya, T. "Development and Testing of a Two-Stage Air Drying System for Spacecraft Cabin CO2 Removal Systems." 44th International Conference on Environmental Systems, 2014. 8 Hogan, J.A., Jan, D., Koss, B., Linggi, P., Lu, Z., Palmer, G., Melton, J. “ARREM FY12 Year End Report: Low Power CO2 Removal (LPCOR) System Development.” NASA Ames Research Center, Moffett Field, CA (2012) 9 Finn, John E., Lila M. Mulloth, and Bruce A. Borchers. Performance of Adsorption-Based CO 2 Acquisition Hardware for Mars ISRU. No. 2000-01-2238. SAE Technical Paper, 2000. 10 Mulloth, L.M., and J.E. Finn. A Solid-State Compressor for Integration of CO 2 Removal and Reduction Assemblies. SAE Technical Paper No. 2000-01-2352. 2000. 11 Mulloth, L.M., et al. Development of Next-Generation Membrane-Integrated Adsorption Processor for CO 2 Removal and Compression for Closed-Loop Air Revitalization and Analysis of Desiccating Membrane. No. 2003-01-2367. SAE Technical Paper, 2003.


11

12 Mulloth, L. and Affleck, D., "Development of a Temperature-Swing Adsorption Compressor for Carbon Dioxide," SAE Technical Paper 2003-01-2627, 2003, doi:10.4271/2003-01-2627. 13 Mulloth, L.M., et al. Air-cooled design of a temperature-swing adsorption compressor for closed-loop air revitalization systems. No. 2004-01-2374. SAE Technical Paper, 2004. 14 Knox, J.C., L.M. Mulloth, and D.L. Affleck. Integrated Testing of a 4-Bed Molecular Sieve and a Temperature-Swing Adsorption Compressor for Closed-Loop Air Revitalization. SAE Technical Paper No. 2004-01-2375. 2004. 15 Knox, James C., et al. Integrated Test and Evaluation of a 4-Bed Molecular Sieve, Temperature Swing Adsorption Compressor, and Sabatier Engineering Development Unit. SAE Technical Paper No. 2006-01-2271. 2006. 16 Murdock, K. "Integrated Evaluation of Closed Loop Air Revitalization System Components." NASA/CR—2010–216451, Somers, Connecticut (2010). 17 Marson, D., Richardson, T., Koss, B., Palmer, G., Hogan, J., Jan, D. Selection of External Thermal Insulation for the Carbon Dioxide Removal and Compression System,” NASA Ames Internal Report. 2014.

Documents

Progress on the CO2 Removal and Compression System