Final Report - Ntrs.nasa.gov
Final ReportNASA X-HAB Space Habitat Research GroupIowa State University14 May 20191
1 Document Scope2 Executive Summary3 Introduction3.2.1 Overview3.2.2 System Scope4 Description of Final System4.1 Requirements4.2 Workflow Breakdown5 Theory5.1 Bed Depth Service Time5.2 Gas Processors Suppliers Association (GPSA)6 Baseline Design Solution6.1 MOF Packed Bed6.2 TRL – 46.3 TRL – 66.2.1 Adsorption6.2.2 Desorption7 Performed Design Analyses7.1 MOF Chemisorption7.1.1 Testing Procedure8 Results Report8.1 MOF Testing8.2 4A Zeolite Testing8.3 MOF PXRD Analysis8.3.1 Thermogravimetric Analysis8.3.2 ASC Report9 Internal and External Interfaces9.1 Internal Interfaces9.2 External Interfaces10 Physical Environment11 Support Environment11.1 Assembly and Cleaning12 Operational Scenarios and Use Cases12.1 Nominal Conditions12.2 Off-Nominal Conditions13 Impact Considerations13.1 Organizational Impacts13.2 Scientific/Technical Impacts14 Risk MitigationTRL-4TRL-615 Costs15.1 31313233333434343434343636373838
15.1.1 Synthesis15.1.2 Process15.1.3 Design15.1.4 Controls16 Educational Outreach17 Documents17.1 Applicable Documents17.2 Reference Documents18 AppendicesA Acronyms383839394041414142423
1 Document ScopeThis document serves as the Final Report for Iowa State University's Space Habitat groupto fulfill the specifications of NASA's eXploration Systems and Habitation (X-Hab) 2019Academic Innovation Challenge for the 'Implementation of Advanced Sorbents in aCarbon Dioxide Management Unit' portion of the challenge. The scope of this documentincludes a description of the current Carbon Dioxide management systems implementedon ISS, a description of the group’s design, a description of the operational environmentand scenarios, risks and mitigations, performance and testing results of the system,outreach, and future work.2 Executive SummaryThe NASA X-Hab team at Iowa State received a 30,000 Grant from NASA to design andfabricate a prototypical pressure swing CO2 Scrubber using new MOF’s that have notbeen used at low CO2 concentrations of 2650 ppm. This project was led by Nevin Smallsand consisted of five different teams to achieve design goals. These teams werecontrols, design, chemical, process, and systems engineering. The team had two fullacademic semesters to complete the project with a delivered system due at the end ofMay. The project would be split into scheduled phases, with funds being proportionedaccordingly.3 Introduction3.1 Project Description3.1.1 BackgroundAs the scope of NASA and other space agencies begins to shift focus to manned deepspace missions, many environmental control systems will need retrofitted andredesigned for this more intensive application. NASA’s X-Hab competition awardscollegiate groups of students grants to research any of the various fields that arenecessary for deep space travel. As Carbon Dioxide management remains one of themajor components of a robust life support system, Iowa State University’s Space Habitatgroup was awarded one such grant to research the usage of advanced sorbents in a CO 2management system. The primary method of CO2 management aboard the InternationalSpace Station (ISS) is the Carbon Dioxide Removal Assembly (CDRA). While this systemhas successfully kept crews alive since 2001, a number of issues have been identifiedthat would need resolved before sending humans into deep space for longer missions.One major concern is downtime due to maintenance. CDRA has had downtime severaltimes since its installation due to repairs needed, usually involving valve replacement.Zeolite, the sorbent used to isolate CO2, releases dust particles as it decomposes. Theseparticles travel downstream and conglomerate at critical points, slowing airflow andeventually completely clogging valves. Because the zeolite decomposes as it is used,downtime is also required whenever new zeolite beds are needed to be installed.4
Downtime is expensive, wastes valuable crew time, and puts the crew in danger.Another concern is energy consumption. The method of desorption used by CDRA is amixture of temperature and pressure cycles. When the zeolite is saturated, it is heatedup to facilitate desorption and unbind the CO2, then vacuum pressure is applied to pull itaway. After desorption, the Thermal Control System (TCS) actively dissipates heat fromthe zeolite so that adsorption can again take place. This process of continual heatingthen cooling puts a burden on the energy supply of ISS, and on TCS, which is responsiblefor heat dissipation of various systems in ISS. It also accelerates the decomposition ofthe zeolite, further increasing the prevalence of maintenance issues.The final issue the group looks to resolve is that of reusability. CO2 isolated by CDRA isdumped overboard into space, as there are no storage or repurposing methods. In orderfor deep space missions to be feasible, minimal amounts of resources should be lost.Therefore, an updated system should be closed loop, and have some method of storingor repurposing captured CO2.The X-Hab group looks to research methods of resolving these identified problems bydesigning a system based around the use of advanced sorbents. In particular, the groupwill synthesize and test several types of Metal Organic Frameworks (MOFs) that haveshown promise in the field of CO2 management, but have not been extensively studied.This provides the rationale and goal for the group’s research and design.3.2 Overview of Final System3.2.1 OverviewThe group produced two baseline solutions at readiness levels of TRL-4 and TRL-6. TheTRL-4 (test bench setup), which was used to test systems integration, verify correct MOFsynthesis, and for other verification and validation purposes, was constructed andutilized by the team. Results from testing and verification are described in detail inSections 7 and 8. The TRL-6 solution remains to be constructed in the future whenresults from rigorous testing from the TRL-4 setup are obtained and the design isoptimized, and additional funding is applied to the project. Both designs are detailed indepth in Section 6.3.2.2 System ScopeThe scope of the system encompasses the synthesis, modification, and testing of MgMOF-74 produced, the design, construction and packing of packed beds, the design,testing and integration of a controls system used to control and automate allcomponents, and the determination of all piping, valves, flow meters, actuators, pumps,and sensors to control the air flow.5
The group will also determine external interfaces required for integration onto a vesselsuch as ISS, including electrical and mechanical attachment hookups, and human factorssuch as system operation, maintenance, and troubleshooting instructions.4 Description of Final System4.1 RequirementsAll requirements for the system were outlined in the X-Hab Challenge Solicitation, andare summarized here:NumberRequirementL1:01The system shall scrub Carbon Dioxide at 2650 ppmL1:02The system shall be closed loop to reduce the loss of resourcesL1:03The system shall incorporate the use of advanced sorbents for Carbon adsorptionL1:04The system shall be scalable or use modularity to accompany crews of larger or smaller sizeL1:05The system shall remove a minimum of 4.16 kg/day of Carbon Dioxide at an ambientatmosphere maintained partial pressureCO2 of 2.0 mmHg based on a 760 mmHg total pressure. The ability to operate at lower than2.0 mmHg is preferred.4.2 Workflow BreakdownThe system has been broken down into five tractable subsystems, described below: Synthesis - Responsible for the synthesis and structural modifications of MOF material. As this MOF is advanced and little is known about its specific properties, this team willalso conduct necessary tests on the MOF to determine its physical and mechanicalproperties.Process - This team will be responsible for the design and construction of the packedbed containing the MOF, air flow calculations through and around the packed bed(s),and piping required.Design - Responsible for the determination of components such as pumps anddehumidifiers to use, visualization of the process flow and CAD modeling of the systemand components.Controls - Tasked with the writing and integration of automation software forcontrolling the system, wiring and hookup of all electrical components in the system,and creation of the GUI interface display.Systems Engineering - This team is responsible for the documentation of deliverablesdescribing the system, such as the Concept of Operations, Verification and ValidationPlans, and safety analysis.6
5 Theory5.1 Bed Depth Service TimeBed depth and time for carbon dioxide adsorption have a positive linear relationship, asseen in the modified Bohart-Adams equation.𝑡 𝑁01𝐶0𝑥 𝑙𝑛 ( 1)# (1)𝐶0 𝑉𝐶0 𝐾𝐶𝐵Where:𝐶0 Initial concentration of solute (mg/L)𝐶𝐵 Concentration of solute at breakthrough (mg/L)𝐾 Adsorption rate constant (L/mg*h)𝑁0 Adsorption capacity (mg/L)𝑥 Bed depth of column (cm)𝑉 Linear flow velocity (cm/h)𝑡 Time (h)Trials can be conducted at various bed depths, with the corresponding service timesrecorded. Plotting bed depth (x) vs time (t) provides saturation lines, as seen in Figure 1.Figure: A positive linear relationship between bed depth and service timenecessary to meet the saturation requirement [1].The slopes (equation 2) and y-intercepts (equation 3) of these lines can now be used tocalculate other model parameters.7
𝑎 𝑠𝑙𝑜𝑝𝑒 𝑏 𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 𝑁0𝑥# (2)𝐶0 𝑉1𝐶0𝑙𝑛 ( 1)# (3)𝐶0 𝐾𝐶𝐵The initial concentration of solute (𝐶0) will be known. In our case, it is 2,650 mg/L. Linearflow velocity (V) can be calculated based on our readings of the mass flow controller.Bed depth (x) and slope (a) will be known from the specific trial. Knowing all thesevariables, the adsorption capacity (𝑁0 ) can be determined from equation 2.As stated previously, initial and final concentrations of solute (𝐶0 & 𝐶𝐵 ) will be known. Inour case, we are trying to achieve 95% saturation, so the final concentration (after thebed) is 132.5 mg/L. The intercept will be known from the specific trial so the adsorptionrate constant (K) can be determined from equation 3.Finally, we can use these parameters with equation 4 to determine the minimum beddepth.𝑉𝐶0𝑥0 𝑙𝑛 ( 1)# (4)𝐾𝑁0𝐶𝐵5.2 Gas Processors Suppliers Association (GPSA)The GPSA Engineering Data Book also provides models for calculating the minimum beddepth. This method is cruder, as it does not directly use any data received from trialingthe bed. However, it can be used to reconfirm the values obtained from the BDSTmethod.Mass transfer is assumed to be bulk diffusion limited. First, the superficial velocity canbe estimated using equation 5.𝑉𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑉𝑚𝑎𝑥 (𝐷𝑚𝑖𝑛𝑖𝑚𝑢𝑚 24𝑞) # ��𝑢𝑠𝑡𝑒𝑑 superficial velocity (cm/h)𝑉𝑚𝑎𝑥 max superficial velocity (cm/h)𝐷𝑚𝑖𝑛𝑖𝑚𝑢𝑚 minimum bed diameter (cm)𝐷𝑠𝑒𝑙𝑒𝑐𝑡𝑒𝑑 selected bed diameter (cm)q volumetric flowrate (cm 3/h)Now, the length of mass transfer zone can be calculated using equation 6, where themass transfer coefficient is taken from GPSA Engineering Data Book [2].𝐿𝑀𝑇𝑍 (𝑉𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 0.3) 𝐿𝑀𝑇𝑍𝑐𝑜𝑒𝑓𝑓 # (6)358
The MOF stoichiometric bed length can be calculated using equation 7.𝑀𝑂𝐹 𝑆𝑡𝑜𝑖𝑐ℎ 𝐵𝑒𝑑 𝐿𝑒𝑛𝑔𝑡ℎ 𝑚𝑀𝑂𝐹 𝐴# (7)𝜌𝑀𝑂𝐹Where:𝑚𝑀𝑂𝐹 mass of MOF (g)𝜌𝑀𝑂𝐹 density of MOF (g/cm3)𝐴 cross-sectional area of bed (cm 2)Finally, the total bed length can be estimated with equation 8𝑇𝑜𝑡𝑎𝑙 𝐵𝑒𝑑 𝐿𝑒𝑛𝑔𝑡ℎ 𝑆𝑡𝑜𝑖𝑐ℎ 𝐵𝑒𝑑 𝐿𝑒𝑛𝑔𝑡ℎ 𝐿𝑀𝑇𝑍 𝑃𝑒𝑙𝑙𝑒𝑡 𝐿𝑒𝑛𝑔𝑡ℎ 𝑈𝑛𝑢𝑠𝑒𝑑 𝐵𝑒𝑑 # (8)5.3 Normalization of graphsThe CO2 sensor that was used to read the concentration of CO2 in the air stream leavingthe packed bed was tremendously inaccurate. However the concentration readingswere very precise. For this reason, the data collected by the sensor was normalized tothe known inlet concentration of 2650 ppm. For instance, if after breakthrough theconcentration was reading 2000 ppm, it would be assumed that the reading shouldactually be 2650 ppm. For this case, all concentrations collected by the sensor would bemultiplied by 2650/2000. Before each test, the sensor was calibrated with a nitrogenstream to 0. This allowed us to normalize using only the maximum reading at the end ofthe test and not needing to account for inaccuracy with a zero-concentration reading.For this normalization it was assumed that the inaccuracies of the sensor were constantand a constant multiplier could be used for each data point. Further testing needs to bedone to determine if this assumption was correct by using multiple gas sources withvarying CO2 concentrations.5.4 Calculating CO2 Capacity of AdsorbentData was output from the CO2 sensor every three seconds. Once each data point wasnormalized due to inaccuracy from the sensor, the data points would be integrated todetermine the total mmol of CO2 absorbed. The steps below detail how this done.9
𝑚𝑔 𝐶𝑂2First, the normalized concentration was converted from ppm to a mass density (This is seen in the equation below.𝑚𝑔 𝑂2 𝑝𝑝𝑚𝐶𝑜𝑛𝑐𝐶𝑂2 1.8𝑝𝑝𝑚𝑚𝑔 𝐶𝑂2Then, the mass density concentration, 𝑚𝑎𝑠𝑠𝐶𝑜𝑛𝑐𝐶𝑂2 ( 𝑚3 ), would be used to𝑚3).𝑚𝑔 𝐶𝑂2determine the amount of CO2 absorbed, 𝐶𝑂2 𝑎𝑏𝑠𝑜𝑟𝑏 ( 𝑚3 ), at each data point. Thissubtracts the inlet concentration from the outlet to determine the amount of CO2𝑚𝑔 𝐶𝑂2absorbed, 𝐶𝑂2 𝑎𝑏𝑠𝑜𝑟𝑏 ( 𝑚3 ), from the inlet air at each data point. This is seen in theequation below.𝑚𝑔 𝐶𝑂2𝑚3 𝑚𝑎𝑠𝑠𝐶𝑜𝑛𝑐𝐶𝑂2 𝑎𝑑𝑠𝑜𝑟𝑏 2650 𝑝𝑝𝑚 1.8𝐶𝑂2𝑝𝑝𝑚𝑚𝑔 𝐶𝑂2Next, the amount of CO2 absorbed, 𝐶𝑂2 𝑎𝑏𝑠𝑜𝑟𝑏 ( 𝑚3 ), per data point was convertedto total mmol of CO2 absorbed (𝐶𝑂2 𝑠𝑝𝑎𝑛 (𝑚𝑚𝑜𝑙)). This was found using the flow rateand time between data points (3 second span for our testing). The equation used is seenbelow.𝑚3 1 𝑚𝑖𝑛1 𝑚𝑚𝑜𝑙 6̇𝐶𝑂2 𝑠𝑝𝑎𝑛 𝐶𝑂2 𝑎𝑏𝑠𝑜𝑟𝑏 𝑉 10 𝑡𝐷𝑃 𝑚𝐿 60 𝑠𝑒𝑐44.01 𝑚𝑔Where:𝑚𝐿𝑉̇ Volumetric flow rate of air (𝑚𝑖𝑛)𝑡𝐷𝑃 Time between data points (𝑠)Then, all the data points total CO2 absorbed were summed to find the total amount ofCO2 absorbed, 𝐶𝑂2 𝑡𝑜𝑡𝑎𝑙 (mmol), over the whole test run. This equation is seen below.𝐶𝑂2 𝑡𝑜𝑡𝑎𝑙 𝐶𝑂2 𝑠𝑝𝑎𝑛Lastly, the capacity of the absorbent was found by dividing the total amount of CO2absorbed (𝐶𝑂2 𝑡𝑜𝑡𝑎𝑙 (mmol)) by mass the adsorbent. This allows for a comparison ofdifferent absorbents when different masses for used for each tests. The equation forthis is seen below.𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝐶𝑂2 𝑡𝑜𝑡𝑎𝑙 (𝑚𝑚𝑜𝑙)𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑛𝑡 (𝑔)The capacity should be in the units of mmol/g.6 Baseline Design Solution6.1 MOF Packed BedAs the objective of this group revolves around the use of advanced sorbents, an indepth look at the Metal Organics Frameworks (MOF) packed bed will be given.10
The Synthesis team produced two MOF materials to be tested: Mg MOF-74 and MgMOG-BDC. The overall synthesis of MOF-74 is shown below. The structure of Mg-MOF74 consists of magnesium ions connected with two molecules of 2,5 dihydroxyterephthalic acid. DMF, which is bound to the magnesium center is to be removed byheating the material to 250 C in vacuum. This will allow for an increased uptake of CO 2from the sample. The procedure followed can be found in reference [8]. According tothis report, the MOF was touted to have a CO2 uptake up to 8.61 mmol/g obtained at298 K and 1 bar.Figure SEQ Figure \* ARABIC 3: MgMOF-74 synthesis schemeThe second MOF produced is known as [Mg4(bdc)4(DEF)4]n, or Mg-MOF-BDC. The teamfollowed the procedure described in reference [9]. This article reported CO 2 uptake at 1bar is 0.9957 mmol/g.The team used several techniques to characterize the MOFs produced. Techniques usedto characterize MOFs were Powder X-Ray Diffraction (PXRD), BET and Chemisorption. ABET instrument was used for analyzing the material’s surface area and pore sizes. CO 2Chemisorption was used to test adsorption of the MOF. PXRD was used to analyze thecrystallinity of the material. The goal in the synthesis, and possible modifications, is to11
increase adsorption capacity, reduce regeneration conditions and maximizerecyclability. The results of the PXRD and Chemisorption tests can be found in section 5.The process team decided that the optimal design for the packed beds would be to userandomly packed pelletized MOF. The MOF will be in pelletized form. The packed bedwill be made of a light, inert metal. Using GPSA method, the size of the packed bed forthe TRL-4 and TRL-6 designs can be estimated.Figure SEQ Figure \* ARABIC 5: Packed Bed layupAt the inlet and outlet of the MOF will be an area of inert ceramic balls, which will beused to keep the pelletized MOF in place and to create a more turbulent flow enteringthe MOF. Without an induced turbulent flow, the airflow remains laminar and passesthrough the MOF without achieving ideal levels of adsorption. Turbulent flow will allowthe system to achieve maximum surface area contact between the flow and the MOF.Mesh support screens will be positioned at the start and end of the inert balls on bothsides. Situated at the exit of the packed bed will be frits with a membrane size of around0.2 μm to mitigate the release of MOF into the system.12
6.2 TRL – 4The system was built around a cylindrical packed bed. All gas was piped throughout thesystem using stainless steel piping. Two gas cylinders were present for the feed. Onewas a nitrogen cylinder used for purging the system. The other was an air cylinder withan elevated CO2 concentration of 2650 ppm. This was the NASA provided CO 2concentration that would be tested. These streams were then run through a desiccant,which would ensure the streams were free of water before entering the packed bed.Then the streams passed through a mass flow controller, purchased from Aalborg withflow rate capabilities of 0-100 mL/min. Then the stream would head towards the packedbed. Before the packed bed was an actuated two-way valve and a pressure gaugecapable of reading -1 barg. The packed bed consisted of glass wool, used for holdingthings in place, glass beads, used as a filler, and MOF, which absorbed the CO 2. Thepacked bed would have an aluminum block placed around it, which would have heattape, insulation tape, and a thermocouple with the aluminum block. This was used toheat the block during a desorption cycle. After the packed bed was another -1 bargpressure gauge and then a three-way actuated valve. This valve either went towards avacuum pump or CO2 sensor and vent. The piping towards the vacuum pump had a lowflow valve in it. This was used to ensure the pull of the vacuum pump was not too muchto pop the MOF or pull the materials of the packed bed out. The CO 2 sensor would allowfor reading the CO2 concentration of the outlet flow, allowing for an estimation of theamount of CO2 absorbed on the MOF. A back-pressure regulator was placed after thesensor to allow for control over the internal pressure of the system, and then thestream was vented. As part of the plan for verification and validation of the system’sfunctionality and ability to integrate, the group will build a test-bench setup that will beknown as the TRL – 4 design. This setup will be the group’s first opportunity to verify thevalidity of theoretical CFD models and lab tests of individual components and willidentify bugs in the software system before constructing the final prototype.For this setup, the concentration of CO2 will be controlled through the use of highlypressurized CO2 tanks with pre-determined concentrations. A mass flow controller willbe used to control the mass flow into the packed beds. This setup will not require asecondary pump at the inlet of the system, as the pressurized gasses will do the workthemselves. The N2 tank will be used as a purge stream to completely clean off the MOFpacked bed. The CO2 sensor after the packed bed will be used to monitor theconcentration of CO2 and determine when the packed bed is saturated. This process willbe relatively the same as the process used in the TRL-6 design, described in section 4.3.Figure 1 in section 2.2.1 shows a diagram of this setup. Below is
The X-Hab group looks to research methods of resolving these identified problems by designing a system based around the use of advanced sorbents. In particular, the group will synthesize and test several types of Metal Organic Frameworks (MOFs) that have . 5 Theory 5.1 Bed Depth Service Time
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to the NASA Technical Report Server—Registered (NTRS Reg) and NASA Technical Report Server— Public (NTRS) thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, wh
The NASA STI program provides access to the NTRS Registered and its public interface, the NASA Technical Reports Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, which includes the following report
The NASA STI Program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI Program provides access to the NASA Technical Report Server—Registered (NTRS Reg) and NASA Technical Report Server
NASA’s STI. The NASA STI program provides access to the NTRS Registered and its public interface, the NASA Technical Reports Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA
The NASA STI program provides access to the NTRS Registered and its public interface, the NASA Technical Reports Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Ser
Page 3; RBSP CDF Training SPDF Names and Roles Bob McGuire (Project scientist) robert.e.mcguire@nasa.gov John Cooper (Chief scientist) john.f.cooper@nasa.gov Bobby Candey (Lead system architect) robert.m.candey@nasa.gov Tami Kovalick (Lead system s/w developer) tamara.j.kovalick@nasa.gov Science - Dieter Bilitza (ITM discipline scientist), dieter.bilitza@nasa.gov
2016 nasa 0 29 nasa-std-8739.4 rev a cha workmanship standard for crimping, interconnecting cables, harnesses, and wiring 2016 nasa 0 30 nasa-hdbk-4008 w/chg 1 programmable logic devices (pld) handbook 2016 nasa 0 31 nasa-std-6016 rev a standard materials and processes requirements for spacecraft 2016 nasa 0 32
