Search Results

A hydrogen economy is an increasingly popular solution to lower global carbon dioxide emissions. Previous research has been focused on the economic conditions necessary for hydrogen to be cost competitive, which tends to neglect the effectiveness of greenhouse gas mitigation for the very solutions proposed. The holistic carbon footprint assessment of hydrogen production, distribution, and utilization methods, otherwise known as “well-to-wheels” carbon intensity, is critical to ensure the new hydrogen strategies proposed are effective in reducing global carbon emissions. When looking at these total carbon intensities, however, there is no single clear consensus regarding the pathway forward. When comparing the two fundamental technologies of steam methane reforming and electrolysis, there are different scenarios where either technology has a “greener” outcome.

Bioregenerative systems for removal of gaseous contaminants are desired for long-term space missions to reduce the equivalent system mass of the air cleaning system. This paper describes an innovative design of a new biofiltration test lab for investigating the capability of biofiltration process for removal of ersatz multi-component gaseous streams representative of spacecraft contaminants released during long-term space travel. The lab setup allows a total of 24 bioreactors to receive identical inlet waste streams at stable contaminant concentrations via use of permeations ovens, needle valves, precision orifices, etc. A unique set of hardware including a Fourier Transform Infrared (FTIR) spectrometer, and a data acquisition and control system using LabVIEW™ software allows automatic, continuous, and real-time gas monitoring and data collection for the 24 bioreactors. This lab setup allows powerful factorial experimental design.

The Sabatier reactor is an exothermic, heterogeneous catalytic reactor that has the function of reducing carbon dioxide to methane and water vapor. Sabatier reactor operation is affected by gravity through the effects of buoyant forces. The buoyant forces affect the transfer of heat and can be significant in determining the temperatures of the various portions of the reactor. The temperatures then affect the fundamental processes such as the chemical reaction rate. This paper presents the results of zero “G” computer model simulations of Sabatier reactor operation. Groundbase experiments were made for various manned loadings under normal ambient and gravity (l-G) conditions and were correlated with normal gravity simulations. The zero “G” simulations show the reactor will run significantly hotter in a zero “G” environment if cooling air flow is not increased to compensate for the loss of natural convections.

The kinetics of the Sabatier methanation reaction, the reduction of carbon dioxide with hydrogen to methane and water, was investigated for 58 percent nickel on kieselguhr catalyst and 20 percent ruthenium on alumina catalyst. Differential rate data from an experimental program were correlated with a power function rate equation both for forward and reverse reactions. The kinetic parameters of activation energy, frequency rate constant and reaction order were determined for the rate equation. The values of these parameters were obtained from an Arrhenius plot of the experimental differential rate data. Also the carbon monoxide side reaction effect was measured and included in the correlation of parameters. The reaction was found to fit the rate equation experimentally within the temperature range 421°K, where the reaction effectively begins, to 800°K where the reaction rate drops and departs from the rate equation form.

The feasibility of a near-complete and biosafe conversion of human- and food waste into biogas was investigated in the context of ESA’s MELiSSA loop (Micro Ecological Life Support System Alternative). The treatment comprises of a series of processes, i.e. a mesophilic lab-scale CSTR (continuously stirred tank reactor), an upflow biofilm reactor, a fibre liquefaction reactor containing the rumen bacterium Fibrobacter succinogenes and a hydrothermolysis system in near-critical water. In the one-stage CSTR, a biogas yield of 75% with a specific biogas production of 0.37 L biogas g-1 added VS (volatile suspended solids) at a HRT (hydraulic retention time) of 15 to 25 days was obtained. When the SRT (solid retention time) was uncoupled from the HRT, and all solids were completely retained in the methane reactor, a more complete biogas conversion was observed at a SRT of above 20 days, corresponding to a 10% increase of degradation on a total COD basis.

After the launch to the ISS (International Space Station) with The Space Shuttle flight STS 118 13A.1 on August 9th 2007 and the accommodation in the US lab Destiny, the air quality monitor ANITA (Analysing Interferometer for Ambient Air) has been successfully put into operation. ANITA is a technology demonstrator flight experiment being able to continuously monitor with high time resolution the air conditions within the crewed cabins of the ISS. The system has its origin in a long term ESA technology development programme. The ANITA mission itself is an ESA-NASA cooperative project. ESA is responsible for the provision of the HW, the data acquisition and data evaluation. NASA's responsibilities are launch, accommodation in the US Lab Destiny, operation and data download. The ANITA air analyser is currently calibrated to detect and quantify online and with high time resolution 33 gases simultaneously with down to sub-ppm detection limits.

To decrease consumable usage by current physico-chemical (P/C) air Trace Contaminant Control Systems (TCCS), there is an increased focus on developing regenerative TCCS technologies for long duration missions. This potentially includes reducing the need for disposable activated charcoal canisters (which pre-treat air prior to thermal catalytic treatment) as well as decreasing catalyst regeneration/replacement from eventual (and predictable) poisoning. Biofiltration is a low-energy, bio-regenerative air treatment technology capable of removing a variety of air contaminants and may substantially reduce loading to subsequent P/C TCCS components, thereby decreasing consumable usage. The design, operation and integration of biofilters are tightly coupled with waste stream characteristics. In particular, the inlet gas carbon to nitrogen ratio (C:N) will directly affect whether the system eventually becomes limited through nitrogen depletion or excess.

The development of the air revitalisation system ( AR) for a crewed spacecraft was initiated in 1985. The selected technical approach is a three-step process consisting of (1) a solid amine water steam desorption system to concentrate (the mainly) metabolically produced carbon dioxide(CO2) from the air (2) a Sabatier reactor to reduce the CO2 to water and methane (CH4) and (3) a fixed alkaline electrolyser to reclaim from the water the oxygen O2 for the crew. During 1996 / 1997 the AR system was successfully demonstrated on a laboratory scale configuration for a crew of three persons equivalent. During 1998 / 2000 the AR system was transformed into a rack-mounted so-called Air Revitalisation System Technology Demonstrator (ARSD) for ‘closed loop’ testing in a dedicated Closed Chamber, to demonstrate the readiness of the technology for a possible incorporation in the ISS enhancement programme.

Since 1985 in a step by step approach an advanced air revitalisation system has been developed for a crewed spacecraft. The metabolically produced carbon dioxide is concentrated through a solid amine water steam desorp-tion system and reduced to water and methane in a so-called Sabatier reactor. The water is currently fed into a fixed alkaline electrolyser to reclaim the oxygen for the crew. However, also water from other sources may be used. The hydrogen is recycled into the Sabatier reactor. The present system handles methane as a waste product closing so far the oxygen loop only. The system has been already successfully demonstrated in a laboratory scale configuration for a crew of three persons in 1996/1997. This paper discusses the results of the current development phase in which the system is reconfigured to fit into an International Space Station payload rack (ISPR). For this purpose the complete system design has been reviewed and upgraded where necessary.

Reduction of metabolic carbon dioxide is one of the essential steps in physiochemical air revitalization for long-duration manned space missions. Under contract with NASA Johnson Space Center, Hamilton Standard is developing an Advanced Carbon Reactor Subsystem (ACRS) to produce water and dense solid carbon from carbon dioxide and hydrogen. The ACRS essentially consists of a Sabatier Methanation Reactor (SMR) to reduce carbon dioxide with hydrogen to methane and water, a gas-liquid separator to remove product water from the methane, and a Carbon Formation Reactor (CFR) to pyrolyze methane to carbon and hydrogen. The hydrogen is recycled to the SMR, while the produce carbon is periodically removed from the CFR. The SMR is well-developed, while the CFR is under development. In this paper, the fundamentals of the SMR and CFR processes are presented and results of Breadboard CFR testing are reported.

The photocatalytic oxidation of trace contaminants such as human metabolite gas and outgas from the component materials over a UV-illuminated film of titanium dioxide (TiO2) has been studied to apply for an environmental purification in manned spacecraft. The trace contaminants studied were as follows: methanol, ethanol, acetal-dehyde, toluene, acetone, methane, ethylene, ammonia, 1,4-pentadiene, hydrogen sulfide, carbonyl sulfide, hydrogen and carbon monoxide. Most of these compounds are the representative human metabolic gas. It was found that these compounds except for methane, ethylene, carbonyl sulfide, hydrogen and carbon monoxide are sufficiently removed in the photocatalytic reactor. This report describes the result of the removal test using the photocatalysts performed in National Space Development Agency of Japan/Tsukuba Space Center (NASDA / TKSC).

High Solids Leachbed Anaerobic Digestion (HSLAD) is a biological waste treatment system that has been successfully demonstrated for solid waste treatment in terrestrial applications. The process involves a solid phase leach bed fermentation, employing leachate recycle between new and mature reactors for inoculation, wetting, and removal of volatile organic acids during startup. HSLAD also offers a potential option for treatment of biodegradable wastes on long-duration space missions and for permanent planetary bases. This process would produce 1.5 kg of methane, 4.1 kg of carbon dioxide and 1.9 kg of compost from 7.5 kg of biodegradable solid wastes generated daily from a crew of six. HSLAD can operate at low temperature and pressure and has the potential for being a net energy producer. A detailed analysis of this process was conducted to design the system size required for a space mission with a 6-person crew.

The technical feasibility of applying anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during space missions was investigated. This process has the advantages of not requiring oxygen or high temperature and pressure while producing methane, carbon dioxide, nutrients, and compost as valuable products. High-solids leachbed anaerobic digestion employed here involves a solid-phase fermentation with leachate recycle between new and old reactors for inoculation, wetting, and removal of volatile organic acids during startup. After anaerobic conversion is complete, the compost bed may be used for biofiltration and plant growth medium. The nutrient-rich leachate may also be used as a vehicle for nutrient recycle. Physical properties of representative waste feedstocks were determined to evaluate their space requirements and hydraulic leachability in the selected digester design.

This paper describes the results of a project involving an anaerobic digestion system used in treating the human and vegetative wastes from a Controlled Ecological Life Support System (CELSS). The anaerobic digester biologically breaks down the organic matter in the wastes into a mixture of methane gas and carbon dioxide, while significantly reducing the BOD(biological oxygen demand ) of the wastewater. A standard waste was formulated consisting of a mixture of swine waste (the surrogate for human feces and urine), green wastes (primarilly lettuce), and paper wastes. The equipment used for this project was a 2.7 cubic meter digester tank filled with plastic media and heated to an average temperature of 35°C. The digester was run over period of 200 days and loaded on the average of five days per week. The results over this test period showed a 94% reduction in BOD and a 98% reduction in suspended solids in the wastewater.

The Centrifuge Facility will provide a life sciences research laboratory for rodents and plants on the space station. During a 90-day experiment increment, soiled waste trays from the rodent habitats must be safely stored. The present tests investigated what gases are generated and what bacteria survive during long-term storage of rodent waste and waste tray materials. Soiled filter material from flight and ground control Animal Enclosure Modules (AEM) flown on STS-54 in January, 1993 and from the Research Animal Holding Facility (RAHF) flown on Spacelab Life Sciences - 2 (SLS-2) in October, 1993 were placed in individual air-tight glass test vessels. Gas samples were withdrawn from each vessel and analyzed for a target list of volatile organics, odiferous compounds and methane using a GC/MS and detector tubes. No target compounds were detected in any of the AEM or RAHF samples. Ammonia, methane and some non-target compounds were detected in one AEM sample and the RAHF samples.

The concept for the “Biological Air Filter” (BAF) is based onto the property of certain selected microorganisms for the complete oxidation to water, carbon dioxide and salts, of gaseous contaminants. The EXEMSI manned space mission simulation campaign offered a good opportunity for testing the performances of an experimental BAF on a real confined atmosphere.

The longer human beings in closed habitats need to be supplied with life support functions, the more the closure of the ECLSS loops becomes a must. This is certainly valid for habitats in space, where a steady resupply of consumables from Earth is impossible due to excessive distances or prohibitive high cost, but it may apply in general to earthbound habitats as well, if for instance large submarines want to extend their diving time. In two harmonised programs for the two customers European and German Space Agency (ESA/ESTEC, DARA), Dornier is now in charge with the development of the technologies for the closure of the oxygen loop.

The current operation of the International Space Station (ISS) calls for the oxygen used by the occupants to be vented overboard in the form of CO2, after the CO2 is scrubbed from the cabin air. Likewise, H2 produced via electrolysis in the oxygen generator is also vented. NASA is investigating the use of the Sabatier process to combine these two product streams to form water and methane. The water is then used in the oxygen generator, thereby conserving this valuable resource. One of the technical challenges to developing the Sabatier reactor is transferring CO2 from the Carbon Dioxide Removal Assembly (CDRA) to the Sabatier reactor at the required rate, even though the CDRA and the Sabatier reactor operate on different schedules. One possible way to transfer and store CO2 is to use a mechanical compressor and a storage tank.