Individual Gas Species Research Articles

Future warming from global food consumption

Food consumption is a major source of greenhouse gas (GHG) emissions, and evaluating its future warming impact is crucial for guiding climate mitigation action. However, the lack of granularity in reporting food item emissions and the widespread use of oversimplified metrics such as CO2 equivalents have complicated interpretation. We resolve these challenges by developing a global food consumption GHG emissions inventory separated by individual gas species and employing a reduced-complexity climate model, evaluating the associated future warming contribution and potential benefits from certain mitigation measures. We find that global food consumption alone could add nearly 1 °C to warming by 2100. Seventy five percent of this warming is driven by foods that are high sources of methane (ruminant meat, dairy and rice). However, over 55% of anticipated warming can be avoided from simultaneous improvements to production practices, the universal adoption of a healthy diet and consumer- and retail-level food waste reductions.

Development of a Porous Solid Model for the Direct Reduction of Iron Ore Pellets

The direct reduction of iron ore pellets with syngas or hydrogen is a promising technology to reduce the CO2 emissions of the iron and steel industry. The conversion rate of single iron ore pellets to iron is extensively investigated. In most of these studies, a shrinking core model is employed to reproduce the experimental observations. However, this model presents an inherent bias by assuming a sharp separation between a fully converted region and a fully unreacted one. Herein the present study, an improved porous solid model is proposed. This model solves the mass balances of the individual gas species and the solid ones assuming spherical symmetry. The governing equations, the main algorithm, and validation cases are presented. The present model also offers wide flexibility to incorporate complex phenomena such as porosity changes or carbon deposition. Furthermore, the proposed model is integrated into a computational fluid dynamics (CFD) environment. It is verified that identical input parameters yield almost identical results in both frameworks, opening the gate toward reliable CFD simulations of industrial‐scale reactors.

Gas Transport in Mixed Matrix Membranes: Two Methods for Time Lag Determination

The most widely used method to measure the transport properties of dense polymeric membranes is the time lag method in a constant volume/pressure increase instrument. Although simple and quick, this method provides only relatively superficial, averaged data of the permeability, diffusivity, and solubility of gas or vapor species in the membrane. The present manuscript discusses a more sophisticated computational method to determine the transport properties on the basis of a fit of the entire permeation curve, including the transient period. The traditional tangent method and the fitting procedure were compared for the transport of six light gases (H2, He, O2, N2, CH4, and CO2) and ethane and ethylene in mixed matrix membranes (MMM) based on Pebax®1657 and the metal–organic framework (MOF) CuII2(S,S)-hismox·5H2O. Deviations of the experimental data from the theoretical curve could be attributed to the particular MOF structure, with cavities of different sizes. The fitting procedure revealed two different effective diffusion coefficients for the same gas in the case of methane and ethylene, due to the unusual void morphology in the MOFs. The method was furthermore applied to mixed gas permeation in an innovative constant-pressure/variable-volume setup with continuous analysis of the permeate composition by an on-line mass-spectrometric residual gas analyzer. This method can provide the diffusion coefficient of individual gas species in a mixture, during mixed gas permeation experiments. Such information was previously inaccessible, and it will greatly enhance insight into the mixed gas transport in polymeric or mixed matrix membranes.

A thermomechanical material point method for baking and cooking

We present a Material Point Method for visual simulation of baking breads, cookies, pancakes and similar materials that consist of dough or batter (mixtures of water, flour, eggs, fat, sugar and leavening agents). We develop a novel thermomechanical model using mixture theory to resolve interactions between individual water, gas and dough species. Heat transfer with thermal expansion is used to model thermal variations in material properties. Water-based mass transfer is resolved through the porous mixture, gas represents carbon dioxide produced by leavening agents in the baking process and dough is modeled as a viscoelastoplastic solid to represent its varied and complex rheological properties. Water content in the mixture reduces during the baking process according to Fick's Law which contributes to drying and cracking of crust at the material boundary. Carbon dioxide gas produced by leavening agents during baking creates internal pressure that causes rising. The viscoelastoplastic model for the dough is temperature dependent and is used to model melting and solidification. We discretize the governing equations using a novel Material Point Method designed to track the solid phase of the mixture.

Off-resonant photoacoustic spectroscopy for analysis of multicomponent gas mixtures at high concentrations using broadband vibrational overtones of individual gas species.

The broadband photoacoustic spectroscopy (PAS) technique is proposed and demonstrated for measurement of CH4, CO2, and H2O vapor in the 1.6 to 2.0μm wavelength region. The wide spectrum of a supercontinuum light source is used to cover broadband absorption bands of multiple gas species. This sensor works in the off-resonant frequency of the designed photoacoustic cell and exhibits a wide concentration measurement range of parts per billion by volume (ppb-v) to 100%. The PAS sensor is further tested in real time by measuring the concentration of CO2, CH4, and H2O vapor in biogas plants.

Calibration of isotopologue-specific optical trace gas analysers: a practical guide

Abstract. The isotopic composition of atmospheric trace gases such as CO2 and CH4 provides a valuable tracer for the sources and sinks that contribute to atmospheric trace gas budgets. In the past, isotopic composition has typically been measured with high precision and accuracy by isotope ratio mass spectrometry (IRMS) offline and separately from real-time or flask-based measurements of concentrations or mole fractions. In recent years, development of infrared optical spectroscopic techniques based on laser and Fourier-transform infrared spectroscopy (FTIR) has provided high-precision measurements of the concentrations of one or more individual isotopologues of atmospheric trace gas species in continuous field and laboratory measurements, thus providing both concentration and isotopic measurements simultaneously. Several approaches have been taken to the calibration of optical isotopologue-specific analysers to derive both total trace gas amounts and isotopic ratios, converging into two different approaches: calibration via the individual isotopologues as measured by the optical device and calibration via isotope ratios, analogous to IRMS. This paper sets out a practical guide to the calculations required to perform calibrations of isotopologue-specific optical analysers, applicable to both laser and broadband FTIR spectroscopy. Equations to calculate the relevant isotopic and total concentration quantities without approximation are presented, together with worked numerical examples from actual measurements. Potential systematic errors, which may occur when all required isotopic information is not available, or is approximated, are assessed. Fortunately, in most such realistic cases, these systematic errors incurred are acceptably small and within the compatibility limits specified by the World Meteorological Organisation – Global Atmosphere Watch. Isotopologue-based and ratio-based calibration schemes are compared. Calibration based on individual isotopologues is simpler because the analysers fundamentally measure amounts of individual isotopologues, not ratios. Isotopologue calibration does not require a range of isotopic ratios in the reference standards used for the calibration, only a range of concentrations or mole fractions covering the target range. Ratio-based calibration leads to concentration dependence, which must also be characterised.

Hybrid State Space Modeling of a Spark Ignition Engine for Online Fault Diagnosis

In this work, a nonlinear hybrid state space model of a complete spark ignition (SI) gasoline engine system from throttle to muffler is developed using the mass and energy balance equations. It provides within-cycle dynamics of all the engine variables such as temperature, pressure, and mass of individual gas species in the intake manifold (IM), cylinder, and exhaust manifold (EM). The inputs to the model are the same as that commonly exercised by the engine control unit (ECU), and its outputs correspond to available engine sensors. It uses generally known engine parameters, does not require extensive engine maps found in mean value models (MVMs), and requires minimal experimentation for tuning. It is demonstrated that the model is able to capture a variety of engine faults by suitable parameterization. The state space modeling is parsimonious in having the minimum number of integrators in the model by appropriate choice of state. It leads to great computational efficiency due to the possibility of deriving the Jacobian expressions analytically in applications such as on-board state estimation. The model was validated both with data from an industry standard engine simulation and those from an actual engine after relevant modifications. For the test engine, the engine speed and crank angle were extracted from the crank position sensor signal. The model was seen to match the true values of engine variables both in simulation and experiments.

Selectivity of MoS2 gas sensors based on a time constant spectrum method

In this report, MoS2 field-effect transistor gas sensors were fabricated and demonstrated to selectively sense and distinguish different gas species. The sensing behaviors of three individual gas species including O2, water vapor, and ethanol were first characterized. The transient drain current responses after the gate voltage induced gas adsorption/desorption were then recorded and decomposed into multiple exponential terms with different time constants, which are indicators of specific gas species adsorbed on MoS2 surface. Using this time constant spectrum method, selective sensing among O2, water vapor and ethanol was demonstrated. It provides a simple and practical approach for MoS2 field-effect transistor gas sensors to selectively sense various gas species.

Electrochemical, Catalytic and O2-Permeation Studies of Iron-Doped Barium Zirconates for Membrane Reactor Applications

An Fe-doped Barium Zirconate perovskite (Ba0.9Fe0.1Zr0.9O3-δ) is investigated for electrochemical and catalytic activity at 800oC via combination of gas effluent mass spectroscopy and electrochemical impedance spectroscopy (EIS). Results confirm competitive reaction rates for both CO2 reduction to CO and O2 under dry-gas conditions and CO oxidation to CO2 and H2 in the presence of steam. A combination of both p-type and n-type semiconduction behavior is suggested to explain the complex dependence of electrical conductivity upon individual gas species partial pressure. Separate gas permeation measurements confirm an O2 permeability of 9.52×10-12 mol.m-1.s-1.Pa-1, which is competitive with similarly reported zirconate-based perovskite materials.

Experimental study on fast pyrolysis of free-falling millimetric biomass particles between 800 °C and 1000 °C

Pyrolysis experiments were performed between 800°C and 950°C on wood particles with diameters from 350 to 800μm in a lab-scale drop tube reactor to reproduce surface heat flux representative of gasifiers conditions. It was shown that particle size affected the required pyrolysis time but changed neither gas/tar/char mass yields nor composition of the products at the end of pyrolysis. The initial particle size also affected the resulting char morphology: the larger the biomass particles, the more fibrous the char. Temperature had influence neither on gas/tar/char mass yields nor on gas and solid elemental composition at the end of pyrolysis, but significantly changed the yields of individual gas species. Whatever the conditions tested, a significant shrinkage could be observed on particles during pyrolysis. These experimental results confirm the strong coupling between chemical reactions, particle geometrical properties and heat transfers during pyrolysis under these conditions.

Numerical Simulation of Infrared Signature Emitted by Liquid Rocket Plume Using Wide Band K-Distribution Model

A new wide band k-distribution model has been developed and used to investigate infrared radiation signatures of liquid rocket plume in some detectors’ working spectrum regions, in which the temperature and the gas molar concentration fields are solved using engineering empirical formulations. Based on the line parameters in HITEMP database, absorption coefficient variables of water vapor and carbon dioxide corresponding to 12-point Gauss-Lobatto quadrature points are derived and expressed as a simple formulation. The absorption coefficient variables of mixture are obtained by summing the absorption coefficient variables of individual gas species under the hypothesis that the k-distributions are statistically uncorrelated. Its validity for the numerical prediction of liquid rocket plume radiation is verified by comparison with line-by-line approach (LBL). Compared with line-by-line calculations, the maximum relative errors of the new band model are less than 10 % in the detectors’ working spectrum regions, while the computational time of the new band model is less than 1/1000 of LBL. The effects of fly parameter on infrared radiation signatures of liquid rocket plume are studied using the new model. The results showed that the integral radiation intensities of liquid rocket plume increase with the nozzle exit temperature, Mach number and the ratio of nozzle exit pressure to atmospheric pressure. The radiation intensity variation trend for liquid rocket plume with altitude is different for different detectors’ working spectrum regions.

Nitrogen as an indicator of mass transfer during in-situ gas sparging

Aiming at the stimulation of intrinsic microbial activity, pulses of pure oxygen or pressurized air were recurrently injected into groundwater polluted with chlorobenzene. To achieve well-controlled conditions and intensive sampling, a large, vertical underground tank was filled with the local unconfined sandy aquifer material. In the course of two individual gas injections, one using pure oxygen and one using pressurized air, the mass transfer of individual gas species between trapped gas phase and groundwater was studied. Field data on the dissolved gas composition in the groundwater were combined with a kinetic model on gas dissolution and transport in porous media. Phase mass transfer of individual gas components caused a temporary enrichment of nitrogen, and to a lower degree of methane, in trapped gas leading to the formation of excess dissolved nitrogen levels downgradient from the dissolving gas phase. By applying a novel gas sampling method for dissolved gases in groundwater it was shown that dissolved nitrogen can be used as a partitioning tracer to indicate complete gas dissolution in porous media.

Methane-specific gas detectors: the effect of natural gas composition

Certain gas sensors, particularly those based on optical spectroscopy, have enabled the detection of individual gas species such as methane with low cross-sensitivity to other gases. For gas-specific instruments used to measure natural gas leaks, this paper considers whether it is necessary to consider the other components of natural gas in addition to methane. We have quantified the effect of gas compositional variation on methane-based measurements on the ppm, %LEL and %volume scales. %LEL measurements, important for safety applications, are the most challenging for methane-specific detection. Acceptable levels of error have been drawn from gas detector standards and by comparison with established gas detectors. The fundamental error expected from a methane-specific detector, as a result of variations in gas composition, would be larger than this benchmark on the %LEL scale. However for gas-specific detection, measurement of an additional component such as ethane is shown to reduce the error to below the benchmark level. This has been demonstrated experimentally using an instrument based on tunable diode laser spectroscopy.

Modeling the Woody Biomass Combustion in a Vortexing Fluidized-Bed Combustor

This study develops an isothermal one-dimensional model to easily predict the performance of biomass combustion in a vortexing fluidized-bed combustor (VFBC). This model comprises a series of three reactor zones: a fluidized-bed combustion chamber, a lower freeboard, and an upper freeboard. This model can calculate the composition of the flue gas exhausted from a combustor and the concentration profiles of individual gas species at various combustor heights. This study verifies the proposed model by comparing its predictions with actual experimental data obtained from a series of systematic combustion experiments burning pinewood sawdust in a pilot-scale VFBC. This comparison revealed an air-leakage problem in the pilot-scale VFBC. The simulated results of CO2 and O2 concentrations are most sensitive to EA but almost non-sensitive to λ. As for the operating temperature, the simulation results for CO, CO2, and O2 are only sensitive at temperatures lower than 750 °C. The CO concentration in the exhaust is more affected than CO2 and O2 by the secondary air added. The fresh O2 added by secondary air can enhance CO consumption, but too much secondary air shortens the residence time of CO in the upper freeboard. Although there are obvious gaps between experimental and simulation results, the predicted change tendencies of gas concentrations correspond to the actual data. This model makes it possible to obtain more information in the preliminary steps of designing a larger scale VFBC for burning highly volatile fuel, e.g., biomass.

Effects of fuel cell anode recycle on catalytic fuel reforming

The presence of steam in the reactant gas of a catalytic fuel reformer decreases the formation of carbon, minimizing catalyst deactivation. However, the operation of the reformer without supplemental water reduces the size, weight, cost, and overall complexity of the system. The work presented here examines experimentally two options for adding steam to the reformer inlet: (I) recycle of a simulated fuel cell anode exit gas (comprised of mainly CO 2, H 2O, and N 2 and some H 2 and CO) and (II) recycle of the reformate from the reformer exit back to the reformer inlet (mainly comprised of H 2, CO, and N 2 and some H 2O and CO 2). As expected, anode gas recycle reduced the carbon formation and increased the hydrogen concentration in the reformate. However, reformer recycle was not as effective due principally to the lower water content in the reformate compared to the anode gas. In fact, reformate recycle showed slightly increased carbon formation compared to no recycle. In an attempt to understand the effects of individual gases in these recycle streams (H 2, CO, CO 2, N 2, and H 2O), individual gas species were independently introduced to the reformer feed.

A non-isothermal model of a bubbling fluidised-bed coal gasifier

A previous one-dimensional numerical isothermal model of a fluidised-bed coal gasifier has been further improved to consider the non-isothermal behaviour of gases and heat transfer mechanisms in the fluidised-bed. Comparisons were made with data simulating the performance of a full-scale fluidised-bed coal gasifier, a 2 MWth pilot plant and a laboratory-scale bed. Simulation results indicate that comparisons of overall carbon conversions, operating bed temperatures and individual gas species predicted from both the non-isothermal and isothermal models with experimental data are favourable. The temperature profile of the gas phase predicted from the non-isothermal model follows the trend of the bubble temperature due to a large majority of the product gas flowing through the bed as bubbles. The temperature of cold feed gas is predicted to experience a heating up period at the lower part of the bed and homogeneous combustion in the gas phase results in a peak temperature in the gas phase. As a consequence of the higher solid temperature predicted from the non-isothermal model than from the isothermal model, the final product gas molar flow rate and fractional carbon conversion due to gasification predicted from the non-isothermal model are all higher giving better agreeing results compared with experimental data than those predicted from the isothermal model. In addition, these comparisons show that improvement in the predictive capabilities of the model depends on ability to predict the product CO/CO 2 ratio which is particularly important for low volatile coals or char.

Assembly of full-spectrum k-distributions from a narrow-band database; effects of mixing gases, gases and nongray absorbing particles, and mixtures with nongray scatterers in nongray enclosures

Full-spectrum k-distributions provide great accuracy combined with outstanding numerical efficiency for the evaluation of radiative transfer in absorbing-emitting molecular gases, but they do have several shortcomings: (1) It is difficult to assemble k-distributions for gas mixtures from precalculated full-spectrum k-distributions of individual gas species (i.e., without calculating the mixture k-distribution directly from the HITRAN/HITEMP database), (2) it is impossible to assemble k-distributions for a gas mixed with nongray absorbing particles (such as soot) from gas-only full-spectrum k-distributions, and (3) like all global models, full-spectrum k-distributions cannot accommodate nongray scattering behavior and/or nongray wall reflectances. In the present paper we show how these restrictions can be relaxed by (1) assembling full-spectrum k-distributions for a gas mixture from a narrow-band k-distribution database created for individual gas species, (2) by assembling gas and nongray absorbing particle mixture full-spectrum k-distributions from the same narrow-band database, and finally (3) by showing how a group of part-spectrum k-distributions can be generated from the same database to accommodate nongray scattering and nongray walls.

Assembly of full-spectrum k-distributions from a narrow-band database; effects of mixing gases, gases and nongray absorbing particles, and mixtures with nongray scatterers in nongray enclosures

Full-spectrum k-distributions provide great accuracy combined with outstanding numerical efficiency for the evaluation of radiative transfer in absorbing-emitting molecular gases, but they do have several shortcomings: (1) It is difficult to assemble k-distributions for gas mixtures from precalculated full-spectrum k-distributions of individual gas species (i.e., without calculating the mixture k-distribution directly from the HITRAN/HITEMP database), (2) it is impossible to assemble k-distributions for a gas mixed with nongray absorbing particles (such as soot) from gas-only full-spectrum k-distributions, and (3) like all global models, full-spectrum k-distributions cannot accommodate nongray scattering behavior and/or nongray wall reflectances. In the present paper we show how these restrictions can be relaxed by (1) assembling full-spectrum k-distributions for a gas mixture from a narrow-band k-distribution database created for individual gas species, (2) by assembling gas and nongray absorbing particle mixture full-spectrum k-distributions from the same narrow-band database, and finally (3) by showing how a group of part-spectrum k-distributions can be generated from the same database to accommodate nongray scattering and nongray walls.

Improved Limb Atmospheric Spectrometer (ILAS) data retrieval algorithm for Version 5.20 gas profile products

The Improved Limb Atmospheric Spectrometer (ILAS), a sensor for stratospheric ozone layer observation using a solar occultation technique, was mounted on the Advanced Earth Observing Satellite (ADEOS), which was put into a Sun‐synchronous polar orbit in August 1996. Operational measurements were recorded over high‐latitude regions from November 1996 to June 1997. This paper describes the data processing algorithm of Version 5.20 used to retrieve vertical profiles of gases such as ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, and water vapor from the infrared spectral measurements of ILAS. To simultaneously derive mixing ratios of individual gas species as a function of altitude, the nonlinear least squares method was utilized for spectral fitting, and the onion peeling method was applied to perform vertical profiling. This paper also discusses in detail estimation of errors (internal and external errors) associated with the derived gas profiles and compares the errors with repeatability. The internal error estimated from residuals in spectral fitting was generally larger than the repeatability, which suggests either that some unknown factors have not been incorporated into the forward model for simulating observed transmittance data or that some parameters in the model are inaccurate. The external error was almost comparable in magnitude to the repeatability. Numerical simulations were carried out to investigate performance of the nongaseous correction technique. The results showed that the background level of sulfuric acid aerosols has little effect on the retrieved profiles, while polar stratospheric clouds (PSCs) with extinction coefficients of the order of 10−3 km−1 at a wavelength of 780 nm have nonnegligible effects on the profiles of some gas species. Despite the problems that require further investigations, it is shown that the ILAS Version 5.20 algorithm generates scientifically useful products.

Modelling of bubbling fluidised bed coal gasifiers

A previous numerical model of fluidised-bed coal gasifiers has been further improved to incorporate an overall energy balance. The improved model has been used to simulate the performance of bubbling fluidised-bed coal gasifiers of different scales. Simulations show that the predicted overall carbon conversion, operating bed temperature and concentrations of individual gas species compare well with the experimental data from three pilot-scale and a full-scale fluidised bed coal gasifier. The water–gas shift reaction, either driven by kinetics or in equilibrium in the dilute phase has significant effects on the predictions for the pilot-scale air-blown gasifiers but has little effect on a commercial-scale oxygen-blown gasifier. This is attributed to the much faster oxidation rate of H2 and CO near the distributor in the oxygen-blown commercialized gasifier than in the air-blown pilot-scale gasifiers. Results also illustrate that about 26–41% of feed oxygen is consumed in the homogeneous combustion reactions in the gasifiers simulated, the percentage of which increases with a decrease in coal rank and with an increase in operating pressure and temperature. Carbon conversions due to char gasification are significant when compared to those due to char combustion in the gasifiers simulated.