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One of the major challenges in the development of micro-combustors is heat losses that result in flame quenching, and reduced combustion efficiency and performance. In this work, a novel thermal barrier coating (TBC) using hexagonal boron nitride (h-BN) nanosheets as building blocks was developed and applied to a Swiss roll micro-combustor for determining its heat losses with increased temperatures inside the combustor that contributes to improved performance. It was found that by using the h-BN TBC, the combustion temperature of the micro-combustor increased from 850 K to 970 K under the same thermal loading and operational conditions. This remarkable temperature increase using the BN TBC originated from its low cross-plane thermal conductivity of 0.4 W m−1 K−1to mitigate the heat loss from the micro-combustor plates. Such a low thermal conductivity in the h-BN TBC is attributed to its interfacial resistance between the nanosheets. The development of h-BN TBC provides an effective approach to improve thermal management for performance improvements of gas turbine engines, rocket engines, and all various kinds of micro-combustors.

To improve oil recovery from oilfield wells mineral scales derived by insoluble BaSO4 and SrSO4 salts during oil extraction should be diminished. In this work, adsorption selectivity of Barium (Ba2+) and Strontium (Sr2+) ions associated with saline formation waters was examined for the first time using nano-sized bi-functional polymer blend synthesized by Cobalt-60 (60Co) γ-rays, as green technology. A bifunctional polymer formed from poly(acrylonitrile)/(styrene-butadiene rubber) homogenous blend is functionalized by -SO3H and -COOH terminal groups (termed as SASB). Those functional groups were selected based on systematic calcium (Ca2+) ions adsorption studies of carboxylate containing molecules. Main and binary interactive effects of solution pH (3–9), adsorbents dose (1-3 g/L), total dissolved salts (TDS, up to 30 g/L), initial Ba2+ and Sr2+ concentrations (10-500 mg/L) and temperature (20–50 oC) on the adsorption selectivity were examined and optimized using Plackett-Burman factorial design (PBD) combined with multiple regression analysis. The regression statistics revealed the significance of quadratic polynomial model to optimize interactive sorption conditions from salty waters with high accuracy level (R2≈ 0.99) rather than linear and two-way interactive models at 95% confidence level. Interestingly finding, the regression and experimental data proved that the presence of up to 10 g/L TDS from alkali metal ions had a significant effect on the enhancement sorption capacity of Ba2+ and Sr2+ when using the prepared sorbent. The SASB adsorbent showed higher sorption selectivity with maximum equilibrium capacity (qmg/g) of 175.3 mg Ba+2 and 210.5 mg Sr+2 per each gram sorbent used in kinetic study. Adsorption kinetics of Ba2+ and Sr2+ sorption by both adsorbents obey pseudo-first and pseudo-second order kinetics, respectively. In sum, the adsorptive power of SASB sorbent is found to be in reverse order of the electronegativity and the hydration radii of the metal ions. Keywords: γ-radiation, Acrylonitrile/styrene-butadiene copolymer, Oilfield scale, Adsorption kinetics, Plackett-Burman factorial design (PBD) optimization

Co-pyrolysis and CO2 co-gasification of paper and polystyrene blends in different mixture ratios were studied at 1173 K using a laboratory scale tube reactor and thermogravimetric analysis. The chemical composition and yield of the syngas produced was analyzed by a micro gas chromatograph to understand the influence of mixture components. Co-pyrolysis positively impacted the syngas yield exhibiting a synergistic influence on cracking reactions leading to increased gaseous yield having almost double the amounts of hydrogen yield. Co-gasification using CO2 increased the total gas yield with enhanced synergistic conversion. This effect provided a non-linear impact on the combustible gases in the gaseous yields when compared to the separate gasification of these feedstocks. The synergistic enhancement of co-pyrolysis conversion in paper-polystyrene led to lower char present for CO2 to react during CO2 co-gasification that lead to lower CO during the gasification of this blended char residue. The mixtures of paper with polystyrene provided increased product gas yields and enhanced conversion with an increase in polystyrene content. The results showed the effectiveness of producing high energy density syngas from co-gasification which can alleviate material handling issues present in segregation of waste, such as plastics and biomass providing uniform valuable product from diverse waste feedstocks with minimal need for classification.

Thin flat-shaped carbon black particles of 1.5 mm thickness by 22.5 mm diameter were combusted in pure oxygen at atmospheric pressures and temperatures in the range of 500–650 °C. One-film kinetic-diffusion model was derived to characterize the kinetic and energy parameters for particles arranged in the form of a thin flat-shaped configuration. The kinetic and energy parameters, and operating regimes of thin flat-shaped char particles were characterized during the nonisothermal combustion process. The gasification regimes during preheating were also analyzed. Steady-state energy processes were considered to derive an energy conservation equation used for calculating the evolution of char surface temperatures as well as released peak energy rates and the specific energy, which are considered key engineering design parameters. The one-film kinetic-diffusion model showed that combustion of such particles was purely kinetic controlled under these conditions. The activation energy obtained varied between 50 and 74 kJ/mol using discrete time and linear fits to the Arrhenius equation. The total energies released per weight of char converted varied between 32.8 and 40.6 kJ/g. The highest peak energy rate released was 134 J/s when combusting char in O2 at a reactor temperature of 504 °C.

In this paper, carbonization of biomass in the presence of supercritical CO2 is investigated to obtain carbon solids with enhanced properties and potential to provide a sustainable pathway for high-value solid products which are currently resourced from expensive and carbon driven fossil-fuel routes. Carbonization of cellulose was carried out in supercritical CO2 at temperatures of 523 K and 623 K at ∼100 bar pressure in a stirred reactor for 1–8 h of residence times. The obtained solid residue was characterized for morphology using scanning electron microscopy (SEM), surface graphitization using Raman spectroscopy, thermal stability using thermogravimetric analysis (TGA), and crystallinity using powder X-ray diffraction (XRD). The solid chars were found to be dominated by clusters of microspheres (

Analysis of dynamic combustor stability is essential for the development of practical devices that employ distributed reaction zones. The fluctuation of reaction zone (RZ) was studied to compare normal air combustion and distributed combustion at an equivalence ratio of 0.9 in a swirl-stabilized burner using methane fuel. Distributed combustion was fostered by diluting the inlet air stream with carbon dioxide that resulted in a gradual drop in the adiabatic flame temperature (Tad). High-speed broadband chemiluminescence at 3 kHz was used to study the global combustion dynamics. Vortex shedding observed along the shear layers influenced the oscillation of flame base in normal air combustion. However, relatively stable bases were observed in distributed combustion. Fast Fourier Transformation performed on RZ base fluctuation data supported the observations from chemiluminescence signatures. Proper orthogonal decomposition (POD) analysis indicated various vortex-shedding patterns as the dominant structures in conventional swirl flames. The power spectral density (PSD) of POD modes showed the rotational effect of RZ and weak von Karman vortex shedding to influence fluctuation in distributed combustion. The self-sustained flame oscillations in normal swirl flames were investigated from the acoustic and heat release fluctuation signals. Both acoustic and heat release fluctuations gradually reduced when approaching the distributed combustion. The PSD of these signals demonstrated a common peak at ~ 174 Hz (in normal swirl flames) with possible thermo-acoustic coupling. This peak was consistent with the peaks obtained from the base fluctuation and POD spectra. The peak gradually diminished when approaching the state of distributed combustion. A similar observation of gradually decreasing acoustic and heat release fluctuation was made with a constant Tad. However, the drop in chemiluminescence signal intensity with CO2 dilution was relatively low in case of constant Tad compared to the variable Tad case. The local and global Rayleigh index obtained for the variable Tad cases at different dilution levels showed positive values at O2 = 21 and 20%, which signified self-sustained instability. However, the distributed combustion possessed a negative Rayleigh index indicating dampening of instability. These results support the gradual decline of thermo-acoustic instability when approaching the distributed combustion condition.

Syngas production from catalytic gasification of polystyrene and pinewood in CO2 atmosphere was investigated over Ni-Mg/Al2O3 catalyst in a fixed-bed reactor at 900 °C. A quasi in situ method was adopted for catalytic gasification wherein the catalyst placed downstream of the feedstock in the same reactor was used for enhanced syngas production. The effect of catalyst on evolutionary behavior, cumulative syngas yield, syngas composition, and cold gas efficiency was systematically analyzed. The results showed that addition of catalyst for polystyrene gasification resulted in enhanced yields of 63% H2, 20% CO, 119% CH4, and 85% C2-C3 yields. Enhanced H2 and light hydrocarbon yields were mainly from enhanced cracking of pyrolytic vapors from polystyrene degradation, while the CO yield was attributed to CO2-assisted reforming of benzene derivatives from primary cracking and polycyclic aromatic hydrocarbons (PAHs) from secondary gas phase condensations. The yields of H2, CO, CH4, and C2-C3 from pinewood gasification in the presence of catalyst was also enhanced by 150%, 14%, 39%, and 16%, respectively, indicating that Ni-Mg/Al2O3 catalyst can efficiently enhance syngas production in CO2-assisted gasification. A comparison of syngas composition between non-catalytic and catalytic conditions revealed improved syngas quality in catalytic gasification with increased H2 mole fraction but decreased CO mole fraction. Furthermore, cold gas efficiency enhanced from 44% to 57% in catalytic polystyrene gasification, and from 75% to 94% in catalytic pinewood gasification. The results suggest that catalytic CO2 gasification offers a promising pathway for efficient energy production from wastes plastics and biomass while simultaneously using CO2.

Discarded cigarette butts contain polymers, biomass, and a variety of toxins that cause an adverse effect to the human health and environment for years. The cigarette residuals are not recyclable and often get mixed with other kinds of wastes so that much of this waste ends up in landfills. This study investigates the safe disposal of cigarette butts by the thermochemical pathways using pyrolysis and gasification. Mass loss during its thermal decomposition was examined first using a thermogravimetric analyzer. The effect of temperature on the pyrolysis and CO2-assisted gasification was then conducted using a semi-batch reactor with a focus on the flowrate of total syngas and its gas components. Syngas yield, energy recovery, as well as energy efficiency were calculated and compared. The effect of temperature on the CO2 consumption during the gasification process was also examined. The thermal decomposition of cellulose acetate, tar, and wrapping paper were the main contributors during the pyrolysis of cigarette butt. However, the gasification process mainly consisted of the pyrolysis, cracking, and reforming reactions in the gas phase and gasification of char derived from wrapping paper. An increase in temperature enhanced the syngas flowrate, syngas yield, and gas efficiency while decreasing the char yield and reaction time for both the processes. Energy recovery from gasification was higher than pyrolysis due to added CO generation. The maximum syngas energy of 13.0 kJ/g under the gasification condition at 1223 K was 67.2% higher as compared with the pyrolysis. High temperature strongly affected the gasification reaction, while it was negligible at a temperature lower than 1023 K. Complete conversion occurred during gasification at 1223 K that provided only ash residue. The CO2 gasification of cigarette butts provided an effective pathway to utilize 0.5 g CO2/g feedstock at 1223 K to form valuable CO by the Boudouard reaction. Compared with the gasification of other solid wastes, syngas energy yield from cigarette butts was found to be higher than syngas from polystyrene and polyethylene terephthalate. These results support the effectiveness of thermochemical pathways in the rapid conversion of cigarette butts to valuable syngas along with CO2 utilization.

Rising atmospheric CO2 levels from significant imbalance between carbon emissions from fossil fuel utilization, especially for energy and chemicals, and natural carbon sequestration rates is known to drive-up the global temperatures and associated catastrophic climate changes, such as rising mean sea level, glacial melting, and extinction of ecosystems. Carbon capture and utilization techniques are necessary for transition from fossil fuel infrastructure to renewable energy resources to help delay the dangers of reaching to the point of positive feedback between carbon emissions and climate change which can drive terrestrial conditions to uninhabitable levels. CO2 captured from the atmosphere directly or from flue gases of a power plant can be recycled and transformed to CO and syngas for use as energy and value-added chemicals. Utilizing renewable energy resources to drive CO2 conversion to CO via thermochemical redox looping can provide a carbon negative renewable energy conversion pathway for sustainable energy production as well as value-added products. Substituted ferrites such as Co-ferrite, Mn-ferrite were found to be promising materials to aid the conversion of CO2 to CO at lower reduction temperatures. Furthermore, the conversion of these materials in the presence of Al2O3 provided hercynite cycling, which further lowered the reduction temperature. In this paper, Co-ferrite and Co-ferrite-alumina prepared via co-precipitation were investigated to understand their potential as oxygen carriers for CO2 conversion under isothermal redox looping. Isothermal reduction looping provided improved feasibility in redox conversion since it avoids the need for temperature swinging which improves thermal efficiency. These efforts alleviate the energy losses in heat recovery while also reducing thermal stresses on both the materials and the reactor. Lab-scale testing was carried out at 1673 K on these materials for extended periods and multiple cycles to gain insights into cyclic performance and the feasibility of sintering, which is a common issue in iron oxide-based oxygen carriers. Cobalt doping provided with lowering of reduction temperature requirement at the cost of oxidation thermodynamic spontaneity that required increased oxidation temperature. At the concentrations examined, these opposing phenomena made isothermal redox operation feasible by providing high CO yields comparable with oxygen carriers in the literature, which were operated at different temperatures for reduction and oxidation. Significantly high CO yields (∼750 µmol/g) were obtained from Co-ferrite isothermal redox looping. Co-ferrite-alumina provided lower CO yields compared with Co-ferrite. The oxygen storage was similar to those reported in the literature on isothermal H2O splitting, but with improved morphological stability at high temperature, especially compared with ferrite. This pathway of oxygen carrier development is considered suitable with further requirement in optimization for scaling of renewable CO2 conversion into valuable products.

Carbon monoxide generation from the splitting of CO2 is of greater importance now than ever before due to continuous increase in CO2 levels in the atmosphere and concerns on the sustainability of energy and environment. This paper examines the conversion of CO2 to CO via thermochemical redox looping of metal oxides. Oxides of Mg/Fe and Mg/Al/Fe prepared from layered double hydroxide (LDH) were explored to aid in the conversion of CO2 to CO. The prepared metal oxides from LDH offered superior stability of porous metal structure and sustained redox capability at moderate to high temperatures required for conversion. The formations of these metal oxides from LDH were analyzed using thermogravimetric analysis (TGA). The results showed 635 µmol CO/g of Mg/Fe oxides as compared 557 µmol CO/g from Mg/Al/Fe. Continuous operation resulted in some sintering effects with deteriorated redox performance. The redox capability of Mg/Fe oxide over multi-cycle operations was lower as compared to Mg/Al/Fe oxides, which showed significant thermal stability while maintaining high CO yield and redox capability over extended redox cycles. The specific LDH derived metal oxides produced CO three times higher than those reported previously in the literature using Zr-doped ceria and other perovskites per unit mass of the oxygen carriers. While the surface area was reduced in Mg/Al/Fe the yield after the first cycle remained unchanged; both the surface area and yield decreased in Mg/Fe oxides. Mixed-metal oxide prepared from co-precipitation provided highly porous Mg/Al/Fe oxide compared to Mg/Fe or Mg/Al. High porosity enhanced the surface oxidation of Mg/Al/Fe that contributed to more than 85% oxidation from fast surface reactions. After two cycles, the redox rates changed little with further increase in the number of cycles to reveal surface area stability of Mg/Al/Fe. Multiple cycle operation suggested superior redox kinetics of Mg/Al/Fe than Mg/Fe. These LDH derived mixed metal (Mg/Al/Fe) oxide provided high and sustained CO production rates compared to those reported in the current literature used other materials so that the examined materials have good potential to serve as oxygen carrier for CO2 splitting to CO.

Co-pyrolysis of pinewood and different kinds of plastic wastes in different mass fractions using polypropylene (PP), polyethylene terephthalate (PETE), and polycarbonate (BPC) were investigated. The results compared with the pyrolysis of individual components revealed non-additive synergistic effects from co-pyrolysis. Differential thermography (DTG) results showed enhanced decomposition peaks of biomass along with longer evolution of syngas and decreased peak of plastic polymers using BPC or PETE. Char residue was non-additively reduced by some 5% (dry wt. basis) using PP and BPC, and by 2–3% using PETE when pyrolyzed with biomass. This suggests increased carbon conversion efficiency and volatiles yield during co-pyrolysis compared to individual component pyrolysis. First order distributed activation energy modeling (DAEM) with 5 pseudo-components revealed that the synergistic effects of biomass with PP or PETE were mainly due to physical nature of the polymers as observed from increased activation energy bandwidth of biomass decomposition. BPC and pinewood mixtures showed an overlap in their activation energy distribution between 100 and 150 kJ/mol. This overlap caused the set of reaction with similar energetics to mutually interact chemically and enhance the composite mixture pyrolysis. Activation energy of BPC in the presence of pinewood was reduced by some 50 kJ/mol compared to individually examined polymer decomposition. The observed quantitative synergistic kinetics results in co-pyrolysis of biomass-plastic wastes mixtures as compared to individual component pyrolysis provide vital information towards the development of feed-flexible, clean pyrolysis and gasification system for efficient fuels production.

Naphthalene as a fuel additive to ethanol was examined in a swirl combustor with the objective to obtain efficient burning and ultra-low emissions using different heating value fuels. Naphthalene is a polyaromatic compound often regarded as a waste fuel that results in high levels of pollutants emission. The effectiveness of naphthalene as a fuel additive to ethanol on NO and CO emissions and stability was determined. The naphthalene concentration was varied from 0 to 0.4 mol/L in ethanol, corresponding to a heating value increase of 8.8% on a volumetric basis (or 5.7% on mass basis). Emissions data were reported for Colorless Distributed Combustion (CDC) using N2/CO2 dilution, at equivalence ratios (Φ) of 0.9 and 0.7. The data under normal fuel–air combustion conditions also reported, clearly showing the benefits of CDC. NO and CO emission below 1 and 6 ppm, respectively, were achieved under CDC conditions for each of the naphthalene-ethanol fuels examined. The results at both the equivalence ratios showed lower NO emission with increase in naphthalene concentration, which provided higher heating value fuel mixture. The CO emission was also low and remained negligibly unchanged with change in naphthalene concentration and equivalence ratio. The results show the use of naphthalene addition to ethanol for increased heating value fuel with ultra-low emissions and higher stability under distributed combustion conditions.

Co-processing of biomass and plastic wastes via pyrolysis and gasification for feed-flexibility revealed the presence of synergistic enhancement of H2 and syngas yield and lowering of char and tar yields. However, an understanding of the source of these interactions and their quantification is lacking. To address this, we investigated the co-pyrolysis of pinewood (PW) and polystyrene (PS) blends at 900 °C using uniquely arranged sample-loading configurations in a fixed-bed reactor with online product gas and energy consumption analysis. Quantification of interactions such as volatiles-volatiles, volatiles-feedstock, and volatiles-char interactions in comparison with weighted results from individual pyrolysis of PW and PS provided deconvoluted information on the synergistic effects. Volatiles-volatiles interaction accounted for a 33% increase in H2, while PS volatiles-PW intermediates interaction accounted for 17% increase, and inhibitive PW volatiles-PS intermediates interaction led to 8% decrease. This deconvolution also revealed another 20% increase associated with the evenly mixed co-pyrolysis of PW and PS that was not accounted for from the volatiles-feedstocks interaction. The co-pyrolysis of PS with PW char also revealed the catalytic activity of PW char on plastics decomposition which was found to be restricted by the capacity of PS melt to block the char’s active sites during their direct contact. Cracking of PS volatiles on these catalytic active sites led to the increased yields of CH4 and H2. These results provide quantified insight into the sources of interaction between biomass and plastics to enhance synergy, develop component compatibility, and gain prediction capability for sustainable and feed-flexible gasifier development.

Hydrogen sulfide is a hazardous gas from environmental, human health and equipment prospective. Hydrogen sulfide occurs naturally from crude oil and natural gas wells along with some other hydrocarbon impurities. Reformation of hydrogen sulfide without or with the presence of xylene (a common impurity present in hydrogen sulfide) has been investigated. Production of hydrogen concurrent with destruction of hydrogen sulfide provides a good alternative method to treat hydrogen sulfide. The role of xylene addition on the reformation of hydrogen sulfide was experimentally investigated. A laboratory-scale reactor was used to examine the effect of reactor temperature in the range of 1273–1573 K and various inlet stream composition on the production of hydrogen and destruction of both hydrogen sulfide and xylene. Results showed enhanced hydrogen production and higher hydrogen sulfide destruction at temperatures above 1273 K. Xylene was destructed completely at a relatively low temperature of 1373 K. Carbon disulfide formation increased with increase in temperature for all the inlet compositions of hydrogen sulfide and xylene examined. Reducing the formation of CS 2 and also mitigation of carbon deposition by reducing the amounts of carbon introduced to the reactor were investigated and quantified experimentally. The most favorable operational conditions for reaction between hydrogen sulfide and xylene were established. The results showed new potential of this binary mixture dissociation as an alluring treatment method of hydrogen sulfide.

Swirl assisted oxy-methane combustion investigated here has focused on the impact of carbon dioxide dilution. Carbon dioxide dilution is essential as it lowers the flame adiabatic temperature and flame speed of oxy-fuel combustion leading to a more stable operation. However, carbon dioxide dilution may result in flame fluctuations, under fuel lean conditions. Experiments using a swirl burner examined the flame fluctuations with different amounts of CO 2 dilution, with the goal to achieve stable oxy-CO 2 -methane combustion via colorless distributed combustion (CDC). This novel CDC technique has shown significant performance gains in gaseous fuel-air flames on emission reduction, enhanced thermal field uniformity, noise reduction, and improved flame stability. Results have shown that for oxy-CO 2 -fuel combustion, most of the heat release fluctuations had frequencies below 60 Hz. The results obtained revealed that increase in CO 2 dilution increased the magnitude of flame fluctuation till a maximum of 28% O 2 concentration in the oxidizer. Further increase in dilution gases and reduction in O 2 concentration led to a more stable flame, along with more favorable conditions for colorless distributed combustion. Data analysis of flame images revealed the source of oscillations under different conditions. At maximum fluctuations with 28% O 2 , the flame oscillated between two modes leading to unstable operation and large fluctuation in the heat release signal. Decrease in oxygen concentration to below 27%, promoted a more stable flame behavior, occupying a larger flame volume, which is characteristic of distributed combustion. Further reduction in O 2 led to flame blow off at around 21% O 2 . This work outlines the importance CO 2 dilution in oxy-fuel flames for achieving stable distributed combustion and mitigate the increased oscillations normally encountered in higher oxygen concentration flames.

Continuous increase in chicken meat consumption calls for the chicken industry for unpreceded dense chicken production and associated waste production. The chicken farms produce large amounts of chicken manure that can no longer be directly used as a fertilizer due to concerns of land pollution and water bodies eutrophication. The gasification of chicken manure can convert the negative economic value chicken manure into fuel to help foster energy security and energy sustainability. The pyrolysis and gasification of chicken manure was studied using different gasifying media and temperatures ranging between 600 and 1000 °C in 100 °C temperature steps. The evolved gases were analyzed using gas chromatography and the results are presented in this paper. Gasification with carbon dioxide and steam were found to give the highest energy yield in the form of syngas; air gasification required the least time and is thus expected to have a better financial feasibility. While air gasification provided highest carbon conversion with low syngas energy yield, at higher temperatures steam and carbon dioxide gasification yielded similar conversion to air gasification but with high syngas energy yield. At higher temperatures, gaseous yields were higher due to the tar cracking and further reformation to provide enhanced carbon conversion. The reduction in tar was more favorable at high temperatures. Tar is known to increase the maintenance time and costs, but its reduction comes at the cost of increased energy input.

The acoustic signal and heat release fluctuations are examined from a swirl combustor using methane as the fuel. The focus was on flame stability and noise emission that have direct relevance in further developing distributed combustion for gas turbine applications and oxy-fuel combustion. Three regimes are examined in this paper, the first being a swirl mode at equivalence ratios between 0.9 and 0.55. The second one being distributed combustion, achieved through N2/CO2 dilution to reach oxygen concentration below 15%, fostering distributed reaction. The third was oxy-fuel flame using increased amounts of CO2 dilution to reach distributed reaction. For the first case, lowering the equivalence ratio led to a reduction in the peak sound pressure level around 500 Hz and a decrease in heat release fluctuations. For all the equivalence ratios, close coupling between acoustic signature and heat release fluctuations existed around 200 Hz. Distributed combustion, achieved at oxygen concentration below 15%, showed a much lower peak sound pressure levels at the 500 Hz range with no coupling between heat release fluctuations and acoustic signal, outlining the flame stability at this regime. Also, the noise emission levels were significantly reduced under this mode. For the third regime, increase in CO2 dilution resulted in high heat release fluctuations and an unstable flame which oscillated between two different flame modes, a feature that did not exist in the first two regimes. Further increase in CO2 led to achieving distributed reaction and a much more stable flame as compared to its oscillatory behavior at lower CO2 amounts, along with reduced noise emission levels. This outlines the possibility of achieving distributed combustion in a stable manner via CO2 dilution in oxy-fuel flames.

Development of alternative carbonaceous sources for energy production is essential to alleviate the dependence on depleting fossil fuels which led to increasing atmospheric CO2 and thus global warming. While biomass utilization for energy and chemical production has been extensively studied in the literature, such studies on municipal solid wastes is difficult to interpret due to the heterogeneous nature of the waste. Understanding of the influence of individual components is necessary for comprehensive development of waste-to-energy pathway. One such waste that is complicated and has often been ignored in the literature is composite polymer absorbent material waste which can also be considered as a potential feedstock for thermochemical pathway of energy production. Composite polymer absorbent materials are ubiquitously used these days in the form of sanitary napkins, diapers, water blockers, fire blockers and surgical pads due to their high water-absorptive nature. Pyrolysis and CO2 gasification is ideal for such materials due to its versatile feedstock intake and uniform product output in the form of syngas with adjustable composition. CO2 gasification also provides the added benefit of CO2 utilization which provides carbon offset to this process. In the present study, a mixture of cellulose, absorbent material (sodium polyacrylate), polypropylene and polystyrene in a fixed proportion, to model approximate composition of a diaper, was examined for its pyrolysis and CO2 gasification capability for viable syngas production. The influence of individual components into the syngas yield from the composite waste gasification was also investigated. A fixed-bed, semi-batch reactor facility along with gas chromatography was employed to analyse the syngas yield and compositional evolution. Pyrolysis was done under nitrogen atmosphere and gasification was done under CO2 atmosphere. CO2 gasification provided net CO2 consumption which means a net reduction in carbon emissions per joule of energy produced. The sample was tested under four isothermal conditions of 973, 1073, and 1173 K to understand the impact of operational conditions on the syngas yield. Influence of individual component of the composite absorbent waste on the syngas yield and composition was also analyzed by comparing these syngas characteristics with that of the yield from gasification of its individual components separately at 1173 K. These investigations provided us with novel results on the behavior and capabilities of these composite polymer absorbent wastes and which opens up a new avenue towards efficient utilization of solid waste resources for sustainable energy production in the form of syngas which can also be used for various chemicals production such as methanol, gasoline and other petrochemical products.

Co-gasification of biomass and plastic blends has been extensively studied, however the effect of AAEMs (alkali and alkaline earth metals) in biomass on the co-gasification behavior still remains unknown. Acid and alkali pretreatment were used here to remove or introduce the AAEMs in biomass by ion-exchange method. SEM was used to obtain morphological characteristics of three pretreated pine wood (PW) samples; TG analysis of pure and blend feedstocks was used to examine the decomposition behavior. CO2 assisted co-gasification of high-density polyethylene (HDPE) and pretreated PW samples at different blend ratios were conducted in a fixed bed reactor, and the resulting flow rate and yields of H2, CO, light hydrocarbons (HC), total syngas, and output energy determined. Synergetic effects from these blends during co-gasification were evaluated by comparing the experimental results with the weighted results from individual components. Results showed that the presence of AAEMs in biomass resulted in increased char yield and char reactivity, that enhanced the syngas yield and energy output. However, acid pretreatment with low AAEM content showed the opposite trend. Irrespective of the biomass pretreatment, synergistic effect was found in the yield of each syngas component, total syngas, and energy yield during its co-gasification with HDPE plastic. The synergy during co-gasification of HDPE and alkali treated PW was more pronounced at high PW content, while those from acid pretreatment preferred low PW fraction. The highest energy yields of 28.1, 34.3 and 30.1 kJ/g were obtained from co-gasification of HDPE and water, acid and alkali pretreated PW samples at PW fraction of 44%, 22% and 55%, respectively. Maximum synergistic effect with energy yield of 69% was obtained from the gasification of HDPE and acid pretreated PW at 27% PW fraction. These results help to our understanding of the influence of biomass pretreatment on co-gasification of biomass-plastic mixtures. The results also help to achieve relatively stable energy output for varying mixtures of plastic and biomass.

The role of dual location fuel injection (versus single injection) is examined for improved mixture preparation with enhanced reaction distribution in the combustor that offers reduced emissions. A cylindrical combustor was used at a combustion intensity of 36 MW/m3 atm and heat load of 6.25 kW. Three different configurations were examined for the effect of dual location fuel injection using methane as the fuel. NO reduction of 48% was achieved with fuel injected at two locations versus single location at an overall equivalence ratio of 0.7. The OH∗ Chemiluminescence intensity distribution with dual location fuel injection showed the reaction zone to shift further downstream that provided longer fuel mixture preparation time prior to ignition under favorable fuel distribution conditions. The longer mixing time helped to improve mixture preparation with lower emissions. The NO∗ chemiluminescence signatures supported the results obtained on reduced NO emission. Mean to maximum OH∗ signal showed that dual location fuel injection enhanced distributed reaction at certain fuel distributions between the two locations (fuel injection ratio lower than 70%) for all the three configurations examined. Increase in air injection velocity from 46 m/s to 102 m/s showed up to 85% NO reduction utilizing dual location fuel injection without any increase in CO emission. Increase in air preheats from 300 K to 600 K reduced the extent of NO reduction. Dual location fuel injection provided improved reaction zone distribution in the combustor for all the experimental conditions reported here. Correlations are provided that describes the NOX emission as function of fuel injection ratio.

This paper provides experimental investigation on the potential of hydrogen production from hydrogen sulfide and methane mixtures in nitrogen. The reformation of H2S in natural gas represents a viable alternative option for the treatment of acid gases extracted from gas wells that contains H2S, CH4 and N2 in the gases without their separation, using for example, the amine process to remove H2S. A laboratory-scale quartz reactor was used to investigate experimentally the effect of temperature and inlet stream composition on the production of hydrogen from a mixture of hydrogen sulfide and methane diluted in nitrogen. The results reveal the important role of reactor temperature on the decomposition of both hydrogen sulfide and methane as well as the production of hydrogen. The results also showed that the production of hydrogen increased dramatically at temperatures exceeding 1473 K wherein the conversion of hydrogen sulfide is more significant. The methane was consumed at temperatures above 1373 K. The conversion of hydrogen sulfide in presence of methane was higher than that in case of hydrogen sulfide only. The carbon disulfide formed during the reformation process increased with increase in temperature. These results provide favorable reactor operational conditions for the reformation of methane with hydrogen sulfide. These results also provide a viable alternative option for the treatment of various waste streams containing hydrogen sulfide to produce clean hydrogen and sulfur.

Colorless Distributed Combustion (CDC) has been shown to provide benefits on ultra-low pollutants emission, enhanced stability and thermal field uniformity. The impact of fuel type (methane, propane, and hydrogen enriched methane) on achieving distributed combustion is investigated. A mixture of nitrogen and carbon dioxide was mixed, at different temperatures, with the normal air upstream of the combustor to simulate the hot recirculated gases. Increasing the amounts of nitrogen and carbon dioxide reduced the oxygen concentration within the combustor. Distributed combustion was identified through OH∗ chemiluminescence distribution across the combustor. For methane, this oxygen concentration varied between 13.8% and 11.2% (depending on the mixture temperature) with 85% reduction in NO emissions as compared to that without entrainment. Similar behavior was demonstrated with propane and hydrogen enriched methane, albeit at a lower oxygen concentration (13.7–11.6% and 12.2–10.5%), to result in 94% and 92% reduction in NO emission, respectively. The mixed gases temperature was varied between 300 K and 750 K. Experimental data using a variety of fuels showed NO emissions of 1 PPM or less. Analysis and extrapolation of obtained data suggest that distributed combustion can be achieved at an oxygen concentration of 9.5% for hot reactive entrained gases having a temperature of 1800 K. This value may be used as a guideline to achieve distributed combustion with ultra-low emission.

The role of catalyst (Ni/Al2O3) position on improved gasification of polypropylene (PP) in CO2 atmosphere using a fixed bed reactor at 900 °C was examined and the results compared with non-catalytic gasification. The catalytic gasification included in-situ and quasi-in-situ (with feedstock located close to but not directly in contact with the catalyst) configuration. Results are reported on the evolutionary behavior and yield of carbon monoxide (CO), hydrogen (H2), hydrocarbons (CmHn) and total syngas. Compared to non-catalytic gasification, in-situ, and quasi-in-situ catalytic gasification produced higher H2 by 120.5% and 137.1%, higher CO by 38.2% and 24.0%, higher CmHn by 57.1% and 98.2%, and higher total syngas by 44.1% and 43.8%, respectively. CO2-assisted gasification of PP with Ni/Al2O3 catalyst significantly enhanced the gases evolution rate and improved the syngas yield. Results revealed better catalytic activity with quasi-in-situ configuration in the thermal decomposition of PP into H2 and CmHn than in-situ catalytic configuration. However, in-situ catalytic configuration provided more CO under similar gasification conditions. Approximately 0.8, 1.1 and 1.0 kg of CO2 could be consumed per kg of PP feedstock to generate syngas energy yield of 27.5, 43.1 and 48.1 MJ with non-catalytic, in-situ and quasi-in-situ catalytic configuration, respectively, suggesting efficient utilization of both CO2 and PP waste for clean and efficient energy production.

The synergistic effects on syngas observed in co-pyrolysis of pinewood and polypropylene (PP) were systematically investigated on a fixed bed reactor with tailored feedstock configurations in this paper. The synergistic effects focused on evolutionary and cumulative behaviors of evolved syngas were quantified by juxtaposing the results from co-pyrolysis of pinewood-PP mixtures with weighted results from the pyrolysis of pinewood and PP as individual components. Examination of different feedstock configurations revealed quantified contributions on volatile interactions and catalytic effect of char to the overall synergy. Results showed that syngas yield, H2 yield and CO yield with co-pyrolysis were promoted by 27%, 80% and 63%, respectively, as compared to the weighted aggregates from individual pyrolysis. Reduced char residue and improved energy yield in co-pyrolysis contributed to a remarkable enhancement in apparent thermal efficiency from 69.93% to 80.67%. Interactions between volatiles evolved from pinewood and PP suppressed CnHm formation while significantly enhancing H2 and CO yields. Mutual interactions between the volatiles accelerated the evolution of each gas component during co-pyrolysis. Pinewood char showed a negligible catalytic effect in evenly mixed configuration, but this effect was pronounced in separated PP and pinewood char. The porous structure of pinewood char can be easily blocked by the fused PP during co-pyrolysis, which was responsible for the delayed CnHm and syngas evolution. This paper provides results that help assist to elucidate the detailed synergistic mechanism during co-pyrolysis of biomass and plastic wastes.

Polyethylene terephthalate (PET) contributes to majority of the global plastics wastes generated and its lack of sustainable recycling calls for the development of pathways for this waste transformation to energy and chemicals extraction that will help avoid landfilling of this waste. In this paper, CO2 assisted gasification of PET was investigated at 800 °C to 950 °C using a fixed bed reactor to understand the feasibility of this pathway for PET waste management. Evolutionary behavior of the yields of H2, CO, CH4, total C2-C3 gases and total syngas from fixed bed reactor were investigated to understand the influence of temperature on isothermal conversion. Gasification composition and total accumulative syngas rate were also calculated and compared. Solid residues from gasification were analyzed for morphological characteristics and CO2 consumption. Evolution rate and yield of H2, CO, CH4 and total syngas from fixed bed reactor changed with increase in reaction time and temperature. CO yields increased from 0.5 to 0.9 g/g (gas mass yield per unit mass of PET), which accounted for 89.9 to 95.2 wt% of the total syngas yield with increase in temperature from 800 °C to 950 °C. The CO mole fraction accounted for about 73.3 to 79.4 vol% of their total syngas at the different temperatures examined. Brunauer-Emmett-Teller (BET) surface area of solid resides from CO2 gasification increased from 434 to 936 m2/g with increase in temperature. These results showed thermal decomposition behavior under CO2 gasification influenced the char structure and the effect became more pronounced with increase in temperature. CO2 gasification of each mass unit of PET provided with the capability to convert about 0.1 to 0.7 mass unit of CO2 into valuable syngas (a precursor for various value-added products) which reveals the synergistic possibility of PET waste management along with CO2 utilization in this process of energy and value-added product recovery.

High intensity colorless distributed combustion has been a promising combustion technique as it enables much reduced pollutant emissions such as NO and CO, as well as more thermal uniformity, flame stability and combustion efficiency. The main requirement for achieving distributed conditions is to provide controlled entrainment of reactive hot product gases into the fresh mixture prior to ignition. In this way, the oxygen concentration is reduced, which results in lower reaction rates, promoting longer mixing times and volumetric distribution of the reaction zones. Though distributed combustion has been extensively studied for various heat loads and intensities, fuels, geometries, there is limited information related to fuel flexibility. Therefore, it is of interest to investigate hydrogen enriched gaseous fuels for greater understanding of low calorific high flame speed fuels in a distributed combustion system. Three various hydrogen content gaseous fuel (40–60% by volume) were investigated in a swirl-stabilized burner for this study, through the use of either N2 or CO2 as the diluent in order to achieve distributed conditions. The OH* chemiluminescence flame signatures were obtained in the flame front and emissions were measured from the combustor exit. The results showed that both the hydrogen concentration and diluent type considerably impacted the oxygen concentration at which transition to CDC occurred. Distributed conditions were achieved at oxygen concentrations of 10–12% with entrained N2 and 13–15% with entrained CO2 for various gaseous fuels consumed. It was determined that the transition to CDC occurred at a lower oxygen concentration for high hydrogen content fuels due to the higher flame speed of hydrogen. The flame images demonstrated that the flashback propensity of the gaseous fuels were eliminated and enhanced flame stability was achieved under the favorable CDC conditions. For NO pollutant emission, ultra-low NO level was achieved under CDC (less than 1 ppm) while CO pollutant emission decreased gradually with condition approaching distributed conditions, and then increased slightly due to the lower flammability limit and dissociation of CO2.

Controlled entrainment of hot reactive gases into the fresh oxidizer mixture prior to ignition is critical for achieving colorless distributed combustion (CDC) condition that results in a uniform thermal field, ultra-low emissions, enhanced flame stability, low noise and mitigation of combustion instability. This paper examines the fuel flexibility of colorless distributed combustion in a swirl-stabilized burner using hydrogen enriched methane gas. Distributed combustion condition was achieved by reducing the oxygen concentration in the oxidizer through addition of either N2 or CO2. Three different gas fuel compositions were investigated. Hydrogen enriched methane in various concentrations in the presence of CO2 and N2 represented coke oven gas. Results on the effect of fuel properties on global flame structure and emissions are reported here. The effect of equivalence ratio on flame stability and emissions was also investigated to determine the impact of air dilution with no change in oxygen concentration. The results showed that for the different gas compositions investigated, transition to distributed combustion conditions occurred at oxygen concentrations of 10–12% with N2 and 13–15% with CO2 as the diluent gas. Increase in hydrogen concentration (or decrease in methane concentration) in the gas mixture resulted in transition to distributed condition at reduced oxygen concentration. The NO emission decreased considerably (to less than 1 ppm) as compared to normal air combustion under the distributed combustion condition for all the gas compositions examined using the different diluents. The emission of CO decreased gradually when approaching distributed conditions, and then increased slightly when the condition moved toward the lower flammability limit. Single digit ppm CO levels were achieved with CDC under nitrogen dilution while carbon dioxide dilution resulted in slightly higher CO emission that was attributed to the dissociation of CO2 at high temperatures. The propensity for flashback with high hydrogen content gas was eliminated under distributed condition and provide wider flame stability limits. These results demonstrate fuel flexibility of diluted hydrogen rich methane gas (akin to coke oven gas) under distributed combustion that provided enhanced stability and ultra-low emissions.

Oxy-colorless distributed combustion is a novel combustion technique to achieve more uniform and controlled thermal field, enhance flame stability, and reduce emissions including combustion noise. Colorless distributed combustion (CDC) conditions was achieved through controlled entrainment of hot reactive gaseous species. This allowed for reduction of oxygen concentration to provide improved mixture preparation for distributed combustion with the reaction zone distributed across the entire volume of the combustor. In this study, oxy-colorless distributed combustion was examined for fuel flexibility using different mixtures of methane and hydrogen diluted with 10% each of N2 and CO2 to represent low heating value fuels. The oxidizer used was an O2-CO2 mixture that eliminated the formation of NOx from the combustor. The evolved OH* chemiluminescence signatures were recorded for various hydrogen concentrations in the fuel at equivalence ratios in the range of 0.6–0.9 under distributed combustion condition. At Φ = 0.9, transition to CDC initiated at oxygen concentrations of 17%, 19% and 21% for fuels having a hydrogen concentration of 60%, 50% and 40% (on volume basis), respectively. Differences in transition point were attributed to higher flame speed associated with more hydrogen in the fuel. Gaseous fuel having high hydrogen concentration provided more distributed OH* flame structures at lower oxygen concentration while the flame stability enhanced at higher oxygen concentration. Oxy-colorless conditions provided only 10–30 ppm CO even at high oxygen concentration and high (0.9) equivalence ratio. The results showed fuel flexibility from different heating value gaseous fuels having high hydrogen content. The results provided very low CO emission and enhanced flame stability under oxy-colorless distributed combustion for the low heating value fuels using O2-CO2 mixture as the oxidant.

Previous works have demonstrated that the distributed reaction regime improved the reformate product distribution, prevented soot formation, and favored higher hydrogen yields. The experimental data from these works and additional literature focusing on individual reactions provided an insight into how the distributed reaction regime influenced the reformate product composition. The distributed reaction regime was achieved through the controlled entrainment of hot reactive products (containing heat, carbon dioxide, steam and reactive radicals and species) into the premixed fuel air mixture, elongating the chemical time and length scales. High velocity jets enhanced mixing, while shortening the time and length scales associated with transport. As some steam and carbon dioxide will form in the reforming process, it was theorized that the mixing of the entrained flow (containing heat, carbon dioxide, and steam) into the premixed fuel air mixture promoted dry and steam reforming reactions, improving conversion. The available information on chemical kinetics of reformation is rather limited. In this work, the activity and timescales of these reactions were determined from the available experimental data. This was then used to assess which reactions were active under Distributed Reforming conditions. These data help in the design and development of advanced reformers using distributed reforming conditions.

The effects of adding N2 or CO2 as diluents to a premixed methane–air flames under strain conditions (associated with a stagnation plate) were examined for flame stand-off distance, stability, intensity, and global flame behavior at various equivalence ratios. A stagnation plate was used to simulate the flame behavior near a combustor wall that can help provide some insights into reducing thermal stresses and enhance combustor lifetime. Decrease in equivalence ratio at the same thermal intensity provided larger strain rates while maintaining a stable flame. At stoichiometric condition, a balance was provided between high strain rates and low oxygen concentration flames to mitigate the peak (maximum) flame temperatures, and the associated temperature-dependent pollutants emission, such as NOx, CO, and unburnt hydrocarbons. Higher thermal intensities provided higher strain rates; however, the addition of diluents impacted in destabilization of flame. The flame stand-off behavior occurred at lower strain rates, low thermal intensity, and increased equivalence ratios. CO2 dilution reduced flame intensity, increased flame stand-off distance and overall flame destabilization than that with N2 dilution.

Low temperature fuel reforming via partial oxidation in a distributed reactor has shown superior performances compared to other lower temperature approaches. Previous results and literature indicated higher reactor temperatures to yield superior results. The well-insulated reactor developed incorporated elements of the low temperature reactor design. The syngas obtained was of better quality in terms of gas species component present and the syngas heating value than that reported previously from a non-catalytic reformer. The syngas composition consisted of 19.2% hydrogen and 20.8% carbon monoxide and these values are higher than the previously reported data. Lower series of hydrocarbons (acetylene and propane) were only detected in trace amounts (less than 15 ppm). Elevated reactor temperatures promoted the dissociation of lower series of hydrocarbons (methane, acetylene, and ethylene), which provided additional syngas formation. The gas species concentrations obtained approached that of catalytic reforming. Flame regime was determined through numerical diagnostics. As reaction regime became less distributed with higher injection temperature, reformate quality was adversely impacted. The mitigation of thermal losses from the well-insulated reactor promoted superior reformer efficiency by allowing the reactor to achieve conditions not possible in low temperature reactors.

Objectives: Recent guidelines for estimation of glucose recommend the use of citrate buffer tubes to inhibit glycolysis if the sample cannot be cooled immediately and separated within 30 min. These tubes are currently not available in India. We prepared the citrate tubes and compared the glucose results obtained with sodium fluoride tubes. Methods: Random blood samples of 44 apparently healthy volunteers were collected in three pairs of citrate buffer and sodium fluoride tubes during September to October 2013. They were labeled as 0 h, 1 h and 2 h samples indicating a delay in centrifugation to separate plasma. Glucose was analyzed on the fully auto analyzer in duplicates using glucose oxidase-peroxidase method. Results: The mean glucose concentrations at 0 h in citrate tubes were 105.8 ± 19.5 mg/dl compared to 99.6 ± 18.3 mg/dl in sodium fluoride tube. There was statistically significant difference in the glucose levels measured in plasma separated from citrate buffer tube and sodium fluoride tube at 0 h, 1 h, and 2 h. The difference between citrate and sodium fluoride tube results ranged from 6.1 mg/dl at 0 h to 7.4 mg/dl at 2 h. Glucose levels decreased significantly at 2 h in both citrate and sodium fluoride tubes. Conclusion: There is a significant decrease in glucose levels in sodium fluoride tubes even with immediate separation of plasma. There is urgent need to standardize the preanalytical conditions for glucose estimation so that effective inhibition of glycolysis can be done.

Distributed combustion has demonstrated significant performance gains, especially on combustion efficiency and near zero pollutants emission. Controlled mixture preparation between air, fuel and internal hot reactive gases prior to mixture ignition is a critical requirement to achieve distributed combustion condition. Though distributed combustion have been extensively studied using a variety of geometries, heat loads and intensities, and fuels, limited information is available on the role of hot reactive gas entrainment and the resultant thermal field uniformity. In this paper, the impact of internal entrainment of hot reactive gases on thermal field uniformity and pollutants emission is investigated. A mixture of nitrogen and carbon dioxide was introduced to the fresh air stream prior to mixing with the fuel and its subsequent combustion to simulate the product gases from within the combustor. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment) significantly reduced pollutants emission, enhanced thermal field uniformity, and increased the reaction volume to occupy larger portion of the combustor. This was evident through spatial temperature measurements in the combustor along with the enhanced distribution of the flame visible signature and OH∗ chemiluminescence signal. The temperature data demonstrated that lowering oxygen concentration from 21% to 15%, through increased entrainment, promoted distributed combustion conditions with lower overall temperature rise throughout the combustor. In addition, the peak temperature regions associated with swirl burners disappeared, eliminating most of the hot spots in the combustor. The enhanced thermal field uniformity and reduced temperature variation provided ultra-low emissions, demonstrating the impact of enhanced thermal flowfield uniformity on emissions. Experiments performed at different equivalence ratios and entrained gas temperatures demonstrated similar behavior of thermal field uniformity and ultra-low emissions.

High intensity colorless distributed combustion (CDC) provides high efficiency combustion with stable operation and ultra-low emissions. The role of internal entrainment of hot reactive gases requires further investigation in order to obtain minimum requirements for distributed combustion. In this paper, the impact of internal entrainment of reactive gases on the flame behavior and structure is investigated with focus on fostering distributed combustion. A mixture of nitrogen and carbon dioxide was introduced to the air stream prior to mixing with the fuel to simulate the recirculated product gases from within the combustor. Increase dilution with nitrogen or carbon dioxide increased the reaction zone volume to result in uniform distribution of CH ∗ and OH ∗ chemiluminescence signal and uniform equivalence ratio (measured optically). These conditions replaced the normally present blue flame with a uniform almost invisible faint bluish flame. The increased entrainment also decreased NO chemiluminescence significantly for the same amounts of fuel burned. The chemiluminescence data suggested that lowering oxygen concentration from 21% to 15% resulted in improved distributed combustion conditions with the reaction volume occupying most of the combustor. These conditions provide the minimum entrainment requirement and reduction of oxygen concentration for achieving distributed combustion. Results obtained at different equivalence ratios and entrained gas temperatures showed similar behavior at oxygen concentration of 15%. The reaction distribution was further enhanced at lower oxygen concentration (∼11%) with further reduction in pollutants emissions.

Colorless Distributed Combustion (also referred to as CDC) has been shown to provide ultra-low emissions and enhanced performance of high intensity gas turbine combustors. To achieve distributed combustion, the flowfield needs to be tailored for adequate mixing between reactants and hot reactive species from within the combustor to result in high temperature low oxygen concentration environment prior to ignition. Such reaction distribution results in uniform thermal field and also eliminates any hot spots for mitigating NOx emission. Though CDC have been extensively studied using a variety of geometries, heat release intensities, and fuels, the role of internally recirculated hot reactive gases needs to be further investigated and quantified. In this paper, the impact of internal entrainment of reactive gases on flame structure and behavior is investigated with focus on fostering distributed combustion and providing guidelines for designing future gas turbine combustors operating in distributed combustion mode. To simulate the recirculated gases from within the combustor, a mixture of nitrogen and carbon dioxide is introduced to the air stream prior to mixing with fuel and subsequent combustion. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment), led to volume distributed reaction over a larger volume in the combustor with enhanced and uniform distribution of the OH* chemiluminescence intensity. At the same time, the bluish flame stabilized by the swirler is replaced with a more uniform almost invisible bluish flame. The increased recirculation also reflected on the pollutants emission, where NO emissions were significantly decreased for the same amount of fuel burned. Lowering oxygen concentration from 21% to 15% (due to increased recirculation) resulted in 80∼90% reduction in NO with no impact on CO emission with sub PPM NO emission achieved at an equivalence ratio of 0.7. Flame stabilization at excess recirculation can be achieved using preheated nitrogen and carbon dioxide, achieving true distributed conditions with oxygen concentration below 13%.Copyright © 2015 by ASME

Examination of the effect of toluene and carbon dioxide, accompanying acid gases (mainly H2S) in the sulfur recovery process is very critical to determining optimum operating conditions for enhanced sulfur recovery. Experimental and simulation results presented here with the addition of different amounts of toluene or carbon dioxide/toluene mixtures to the H2S gas stream provided direct quantification on the conversion efficiency. The results showed similar trends between the calculated and experimental data, which revealed a decrease in conversion efficiency with increase in toluene and carbon dioxide/toluene addition to the H2S gas stream. The role of reactor operating temperature was also examined. The toluene addition increased the optimum reactor temperature for enhanced sulfur recovery, whereas presence of CO2 reduced the optimum operating temperature. The presence of toluene and CO2 in the acid gas stream directly affects the sulfur recovery efficiency by altering the optimum temperature of the reactor. These results reveal the importance of temperature and its excursion for enhanced sulfur recovery in a Claus process. Detailed results and analysis are presented in the paper.

Experimental results are presented from the combustion of toluene with CO 2 and H 2 S gas in H 2 /O 2 –N 2 flames at an equivalence ratio of Φ = 3 (Claus condition). The results from the combustion of 100% H 2 S, H 2 S/C 7 H 8 and H 2 S/C 7 H 8 /CO 2 acid gases are also reported. The results showed a decrease in mole fraction of H 2 S and simultaneous evolution of SO 2 in H 2 S/H 2 /O 2 –N 2 flame. In contrast, combustion of H 2 S/C 7 H 8 acid gas showed faster initial SO 2 formation to a maximum mole fraction, but the formed SO 2 decomposed further downstream in the reactor. This is in further contrast to that of H 2 S/C 7 H 8 /CO 2 acid gas combustion, where CO 2 acted as an oxidizer (released atomic oxygen) that furthered SO 2 formation. The results also revealed the formation of CH 4 , C 2 H 2 and CS 2 with the addition of toluene. The presence of CO 2 enhanced the formation of mercaptans (COS and CS 2 ) and decomposition of formed hydrocarbons in the reactor. These results help to identify conditions under which hydrocarbons and mercaptans (COS and CS 2 ) are formed, and how they can be mitigated during sulfur and energy recovery from acid gases.

Volume distributed reaction technique was applied to examine the partial oxidation behavior of JP8 with the goal to improve reformate quality. The reactor design was based on previously developed volume distributed combustion, but modified to foster unique reforming conditions. The reactor demonstrated almost colorless reaction zone even at a high equivalence ratio of Φ = 3.0 (that is normally a soot formation regime), with no visible soot found on the walls of the reactor. A stable reaction zone was demonstrated at low temperatures of 764–863 °C. Reformate concentration consisted of 8.68–9.92% hydrogen and 18.12–18.58% carbon monoxide, which is significantly higher than that available in the literature on partial oxidation at temperatures of 700–800 °C (only 4.0–7.5% hydrogen and 5.7–17% carbon monoxide). Acetylene concentrations under distributed reaction regime were 20–23% lower than that in conventional flames. The results show that volume distributed reactions offer significant advantages to produce higher concentrations of hydrogen and carbon monoxide and very low amounts of acetylene that is a well-known precursor to soot formation.

� Effect of 0%, 0.5%, 1% and 5% of xylene in H2S gas combustion was evaluated. � Xylene favored formation of H2 and increased amounts of H2S at reactor exit. � Xylene also reduced SO2 amounts and resulted in the formation of CH4 and CO. � Xylene enhanced the formation of CH4, CO, COS and CS2. abstract Experimental results are presented on the combustion of H2S and mixtures of H2S and xylene at an equiv- alence ratio of three (Claus condition). The H2S mole fraction decreased along longitudinal central axis of the reactor to a minimum value. The SO2 mole fraction increased to a maximum value, which subse- quently decomposed due to the formation of elemental sulfur, which is favorable under Claus condition. In contrast, mixtures of H2S and trace amounts of xylene (0.5%, 1% and 2%) favored the formation of H2 and increased the amounts of H2S at reactor exit. Xylene addition reduced the maximum mole fraction of SO2, and resulted to the formation of CH4 and CO. The formed SO2 decomposed faster to yield COS and CS2 from its reaction with CH4 and CO. The formation of CH4, CO, COS and CS2 poses severe impact on sulfur capture efficiency from acid gases. These results reveal a direct impact on the Claus reactor performance with trace amount of xylene present in H2S thermal processing.

Colorless distributed combustion (CDC) has been shown to offer enhanced combustor performance for stationary gas turbine application with near zero emissions, high combustion intensity and efficiency, thermal field uniformity, and enhanced stability. Mixture preparation to form hot and low oxygen concentration environment paves the path to achieve CDC conditions. In this paper, a new approach of air dilution in partially premixed combustion conditions is employed and the results compared to premixed and non-premixed injection of air and fuel. Portion of the fuel is introduced in the air stream and portion of the air is introduced in the fuel stream such that the local equivalence ratios for each stream is well outside the flammability limit to eliminate flashback and instabilities. The experimental data demonstrated ultra-low emissions with this injection scheme. At equivalence ratio of 0.6, NO emission was 63% lower than non-premixed combustion mode. Also NO emission was similar to the premixed combustion with the advantage of eliminating flashback and flame instabilities that often prevail in premixed combustion conditions. Dilution provided 50% CO reduction as compared to non-premixed combustion. Numerical simulations, validated through Particle Image Velocimetry, were performed to outline the mixing process in each of the three cases. The methane mixture fraction prior to ignition, determined numerically, was found to be one half of that for the non-premixed case and close to that of the premixed case. This enhanced mixture preparation, associated with the new air and fuel dilution technique, resulted in reduced emission. Also the jet momentum ratio (between both streams) is enhanced, mainly due to the air addition to the fuel stream, to result in better mixing and a better reaction distribution for ultra-low emissions. Further reduction of NOx is expected with improved distributed combustion condition.

Experimental results are presented on the role of benzene addition to H2S combustion at an equivalence ratio of three with respect to H2S (Claus condition) and complete combustion of benzene. The results are reported with 0.3%, 0.5% and 1% benzene addition to H2S/O2 flame. Combustion of H2S and benzene mixtures is of practical value for sulfur recovery during combustion of acid gases. The results showed that H2S combustion caused H2S to decompose to a minimum mole fraction with high conversion of H2S while the SO2 mole fraction reached a maximum value. Addition of benzene decreased the conversion of H2S with reduced mole fraction of SO2 in the reactor to subsequently reduce the formation of elemental sulfur. Benzene also caused significant production of H2, CO and COS formation along with faster decomposition of the formed SO2. Presence of benzene, even in trace amounts, in acid gas hinders sulfur conversion in a Claus reactor and increases emission of unwanted sulfur bearing compounds. Increased hydrogen production with benzene offers potential value for hydrogen recovery under certain conditions.

Oxidation behavior of dodecane and two mixtures of dodecane and m-xylene (90/10 wt.% and 80/20 wt.%) over an Rh catalyst in a meso-scale heat recirculating combustor was examined to isolate the effect of aromatic content on performance. The fuel conversion, product selectivities, and reaction kinetics were calculated, and the global combustion behavior observed. The results showed that increasing the amount of m-xylene in the fuel increased the fuel conversion from 85% (pure dodecane) to 92% (90/10) and further to 98% (80/20). The presence of xylene also significantly increased CO 2 /H 2 O selectivity and decreased CO/H 2 selectivity. Global activation energy increased linearly with increase in xylene content, supporting that addition of aromatic species to fuel lowers the overall reactivity. The non-catalytic reaction was also simulated using Chemkin software to determine the effect of the Rh catalyst on the combustor performance and to analyze the difference in chemical mechanisms. The results revealed that the catalyst promotes total oxidation over partial oxidation, and lowers the global activation energy by up to 70%.

Previous works have demonstrated that the Distributed Reaction regime impact on the reformate product distribution. Using previous works, a theory of how the Distributed Reaction regime influences the reformate product composition is provided. Distributed Reaction regime is achieved by entraining exhaust products into the premixed fuel air mixture. As some steam and carbon dioxide will form in the exhaust, it is theorized that the mixing of the entrained flow (containing heat, carbon dioxide, and steam) into the premixed fuel air mixture will promote dry and steam reforming reactions, improving conversion. As kinetic information on reforming literature is limited, the activity and time scales of these reactions were determined from existing experimental data. This was then used to determine which reactions were active under Distributed Reforming conditions.

Sorption enhanced steam reforming of propane over Ni catalyst using in-situ carbonation of CaO provides both carbon capture, and enhanced H2 content in the product gas, and enhanced carbon conversion efficiency. Choosing propane over methane for sorption enhanced reforming provides easier fuel handling capability and higher throughput of H2 per unit volume of fuel. Such advantages help in building domestic scale hydrogen production source for sustainable energy production. The effect of propane addition on CaO carbonation and poisoning possibilities in reformation integrated with CO2 capture is explored in a packed-bed reactor. The motivation of propane addition is to model petroleum gas to address the feasibility of carbon capture integration with hydrocarbon reforming processes. Initially, different partial pressures of steam and propane will be used to study the kinetic parameters in a fixed bed reactor at different temperatures. The formed kinetic models will be used to compare the integrated CO2 capture results and the thermodynamic results to evaluate the efficiencies of such process. Higher temperatures provide better conversion efficiency, but the equilibrium of CaO carbonation suggests steam reforming enhancement and CO2 capture needs to be below 1073 K in order to avoid the backward reaction of CaCO3 releasing CO2. The balance between endothermic reformation reaction and exothermic water-gas shift and CaO carbonation reactions is the optimizing parameter for improved conversion to high H2 content. Temperatures higher than 873 K provided higher conversion with lower CO2 capture and H2 content while lower than 873 K provided lower methane conversion and higher CO2 capture and H2 content. Increase in steam to carbon ratio increased CH4 conversion and reduced CO content without affecting sorption with no further reduction in CO2 observed for most of the sorption cycle. These results supplement the available data in the literature to provide superior reaction conditions to improve the process efficiency in hydrogen production.Copyright © 2017 by ASME

Pyrolysis of hydrogen sulfide, as an alternative treatment method to Claus process, with simultaneous hydrogen production and sulfur recovery is an energy intensive process. The high energy demand of the process remains a hindrance to its application. Production of hydrogen via hydrogen sulfide oxidation at very high equivalence ratios, compared to the high equivalence ratio of 3 employed in Claus reactor, has been studied experimentally. The objective of this approach is to alleviate the energy load requirement of hydrogen production from hydrogen sulfide stream. Since combustion of hydrogen sulfide cannot be sustained at such high equivalence ratios, partial oxidation reaction was examined in a heated quartz tubular reactor that was placed inside an electrical furnace. Oxygen concentration of 1% or 2 % in 10% H2S (called the 10%H2S/O2 mixture) were injected into the reactor with the remaining 90% nitrogen gas. These results were compared to the case of decomposing H2S alone. Experimental data showed that destruction of hydrogen sulfide increased with oxygen injection and that it increased with increase in oxygen concentration. Injection of oxygen at increased concentration consumed hydrogen constituent in hydrogen sulfide to water to result in dramatic decrease in hydrogen production. Formation of sulfur dioxide was absent over the examined temperature range of 1273–1673 K. These results provide the potential of hydrogen production from hydrogen sulfide oxidation, define the favorable operational conditions and outline the potential future developments for treatment of hydrogen sulfide.

Colorless Distributed Combustion (CDC) has been shown to provide unique benefits on ultra-low pollutants emission, enhanced combustion stability, and thermal field uniformity. To achieve CDC conditions, fuel-air mixture must be properly prepared and mixed with hot reactive gases from within the combustor prior to the mixture ignition. The hot reactive gases reduce the oxygen concentration in the mixture while increasing its temperature, resulting in a reaction zone that is distributed across the reactor volume, with lower reaction rate to result in the same fuel consumption. The conditions to achieve distributed combustion were previously studied using methane and other fuels with focus on pollutants emission and thermal field uniformity. In this paper, the impact of distributed combustion on noise reduction and increased stability is investigated. Such reduced noise is critical in mitigating the coupling between flame and heat release perturbations and acoustic signal to enhance the overall flame stability and reduce the propensity of flame instabilities which can cause equipment failure. Nitrogen-carbon dioxide mixture is used to simulate the reactive entrained gases from with the combustor. Increasing the amounts of nitrogen and carbon dioxide reduced the oxygen concentration within the oxidizing mixture, fostering distributed combustion. Upon achieving distributed combustion, the overall flame noise signature decreased from 80 dB to only 63 dB, as the flame transitioned from traditional swirl flame to distributed combustion. The flow noise under these conditions was 54 dB, indicating that distributed combustion has only 9 dB increase over isothermal case as compared to 26 dB for standard swirl flame. In addition, the dominant flame frequency around 490Hz disappeared under distributed combustion. For the traditional swirl flame, both the acoustic signal and heat release fluctuations (detected through CH∗ chemiluminescence) had a peak around 150Hz, indicating coupling between the heat release fluctuations and pressure variation. However, upon transitioning to distributed combustion, this common peak disappeared, outlining the enhanced stability of distributed combustion as there is no feedback between the heat release fluctuations and the recorded acoustic signal.