Search

The fate of sulfur and conversion of metals during the co-gasification of municipal solid waste (MSW) and gypsum is examined here using aspen plus combined with Thermo-Calc for the process model development. The effect of air ratio, temperature, and MSW-to-gypsum feed mass ratio on the syngas evolution, sulfur transformation, and mineral speciation behavior is investigated. The results showed prevention of gypsum sulfur transformation to sulfur dioxide at temperatures below 1050 °C, air ratio < 0.4, and MSW-to-CaSO4 feed mass ratio < 33 wt%. Approximately 90 wt% of feed was transformed into gas products comprising 22% CO and 19% H2. At approximately 900 °C, major minerals formed were CaS (alabandite), melilite, anorthite, rankinite, nepheline, and wollastonite. Melilite, a calcium silicate of aluminum and magnesium, dominated over all other silicates. At temperatures >1000 °C, these minerals transformed into a more stable calcium orthosilicate (CaSiO4) and molten oxysulfide. At temperatures higher than 1200 °C, all metals in MSW were transformed into molten oxides. The results show that syngas and minerals can be recovered during the co-gasification of MSW and gypsum to directly reveal the synergetic benefits of co-processing MSW and gypsum low-value waste materials.

The co-thermal chemical conversion of biomass and waste tires is an important direction for the utilization of waste resources to produce renewable energy. In this study, the product distribution and synergistic effects during the co-pyrolysis of agricultural residues and waste tire were analyzed by a pyrolyzer coupled with a gas chromatograph/mass spectrometer (Py-GC/MS). Pyrolysis and co-pyrolysis products were analyzed at 550 °C and 650 °C for maize stalk (MS), wheat straw (WS), waste tire (WT) feedstocks, as well as mixtures of wheat straw-waste tire (WS:WT mass ratio of 1:1), and maize stalk-waste tire (MS:WT mass ratio of 1:1). The results showed that the co-pyrolysis of agricultural residues and waste tire promoted the release of phenols, aldehydes, and ketone derivatives, and reduced the formation of H2 and H2O. In addition, a relatively high content of aromatic hydrocarbons was obtained at 650 °C temperature, while 550 °C was optimal when considering the formation of ketones. The results showed a synergistic effect in the co-pyrolysis of biomass and waste tire.

Manure waste from dairy, livestock, and poultry industries can pose significant challenges in their disposal due to their odor, nitrogen, phosphorous, and heavy metals contents, and pathogens. Existing disposal techniques like anaerobic digestion, although can provide biogas with energy output, is a slow process with significant carbon loss to CO2 and can also result in leaching. High-temperature pyrolysis can convert these wastes into syngas along with biochar which can be used for various applications. Thermochemical conversion needs to be feed-flexible, and operating it with manures from various animal sources such as poultry and dairy sectors can provide sustained operation, intensified process, and improved conversion throughput. So, we examined high-temperature co-pyrolysis of chicken and cow manures to understand the influence of their mixture fractions on the syngas components and char yield. Lab-scale semi-batch co-pyrolysis was carried out for cow and chicken manures at 900 °C with mixture fractions varying from 0 to 100%. Syngas analysis from these tests revealed the presence of synergistic enhancement of its components and in terms of syngas energy yield and carbon conversion, a 2:3 ratio of cow to chicken manure resulted in the most enhancement compared to the expected aggregate of pyrolyzing cow and chicken manures separately. This paper provides a detailed analysis of these syngas components from co-pyrolysis in comparison with separate pyrolysis to explore the advantages of blended feedstock toward an efficient, clean, and feed-flexible pathway for manure waste disposal and utilization.

Sustainable disposal techniques of municipal solid wastes (MSW) are essential for effective materials recovery and energy management. Synergistic incorporation of gypsum waste from the construction and demolition (C&D) sector is explored here for the low techno-economic viability of MSW in waste-to-energy facilities. Co-processing of MSW with this low-value gypsum can potentially provide improved product recovery and simultaneously furnish economic viability. To understand the impact of gypsum incorporation into MSW conversion, we tested synthetic MSW and a 1:1 mixture of MSW with gypsum from drywall wastes and compared their micro-scale mass loss kinetics along with macro-scale syngas evolution and conversion at different temperatures, and in pyrolytic and oxidizing environments. Gypsum incorporation led to increased syngas production and decreased char yields as the char was oxidized by CaSO4. Thermogravimetric analysis (TGA) revealed two different temperature zones of gypsum interaction with MSW depending on the oxidation concentration in the environment. Adding 50% gypsum only changed the final ash yield by 10% in pyrolysis conditions suggesting the viability of gypsum incorporation. While the addition of gypsum led to delayed evolution of H2 and CO, the cumulative yields of H2 and CO2 increased significantly and the yield of CO changed minimally. Additionally, hydrocarbon by-products such as CH4 decreased by gypsum addition. The results showed improved syngas yield and uniformity, as well as operational conditions from the gypsum interaction with MSW which can help in the further development of gypsum waste incorporation.

Distributed combustion was investigated with hydrogen-enriched methane fuel in a swirl-stabilized burner. Distributed reaction zones were established from conventional swirl flames at two heat release intensities of 5.72 and 7.63 MW/m3-atm by diluting the main airstream with carbon dioxide. The appearance of distributed reaction zones with hydrogen addition to methane fuel was investigated here. High-speed chemiluminescence imaging was performed for different cases without any spectral filtering to visualize the shape of reaction zones. A gradual increase of % H2 in the fuel mixture increased the chemiluminescence intensity and reduced the flame standoff distance gradually in both the swirl and distributed combustion cases. The reaction zone at higher thermal intensities was found to be wider than the lower thermal intensity case. Distributed reaction zones possessed lower visible chemiluminescence signatures than that of the conventional swirl flames considered. The increased flame chemiluminescence signatures with hydrogen enrichment were related to higher flame reactivity because of hydrogen addition. This hypothesis was verified by computing the laminar flame speed at various hydrogen-enriched cases at different O2 concentrations. The results revealed that the flame speed gradually decreased when the flame transitioned from swirl combustion to distributed combustion regime. Additionally, higher flame speed was observed at different O2 levels corresponding to higher hydrogen content in the fuel mixture.

The amount of food waste due to the product expiration date is growing globally each year. Although the expired food loses its nutritional and safe edible value, it still offers great energy conversion value. In this study, expired pistachios were pyrolyzed and gasified in a semi-batch reactor at temperatures of 873–1223 K. The gases components of the produced syngas were analyzed using a micro-gas chromatograph for the syngas yield, and gases mass flowrates as well as the energy of each component in the syngas were calculated. CO2 consumption from the gasification reaction at different temperatures was also evaluated. Experimental results showed that the syngas yield and syngas energy from pyrolysis and CO2-assisted gasification increased with the in-reaction temperatures. Higher reaction temperature resulted in a shorter reaction time for the evolution of the peak value of the syngas mass flowrate. During pyrolysis, the increase in temperature from 873 to 1223 K enhanced syngas yield by 8.6 times from 1.42 kJ/g to 13.62 kJ/g. However, during the CO2-assisted gasification, syngas energy increased from 5.43 kJ/g to 17.27 kJ/g in the temperature range of 973–1173 K. The CO2 consumption in the gasification of pistachio samples enhanced with the increase in reaction temperature. The mass of CO2 consumption at 1223 K was 0.67 g/g, which was 138 times higher than that of 0.005 g/g at 973 K. Furthermore, at the same temperature (1223 K), the syngas yield from gasification was 1.3 times higher than that from pyrolysis. Thus, higher temperatures promoted the reaction rate of gasification processes as well as the consumption of greenhouse gas (CO2). The CO2-assisted gasification technology is an effective pathway to convert expired food into clean sustainable energy.

Swirl-assisted distributed combustion was investigated with hydrogen-enriched methane. Distributed reaction zones were fostered from a conventional swirl-flame at a heat release intensity of 5.72 MW/m3-atm by diluting the main airstream with either carbon dioxide or nitrogen. The effect of hydrogen addition to the fuel mixture on the performance of distributed combustion was studied for reaction zone stability, variation of blowoff equivalence ratio, and emissions of nitrogen oxide, carbon monoxide, and carbon dioxide. High-speed imaging of reaction zone chemiluminescence was performed for different cases without any spectral filtering. Gradual increase of %H2 in the fuel mixture increased the chemiluminescence intensity in both the swirl and distributed combustion cases. The standoff distance was gradually reduced with hydrogen enrichment along with the appearance of a narrow flame shape from increased reactivity in the flame brush. Fluctuation of pressure (p′) and heat release (q′) was qualitatively measured from the microphone and photomultiplier (fitted with CH* filter) signals at different %H2 enrichments. The amplitude of fluctuation of p′ and q′ showed the existence of a common peak in swirl combustion indicating the possibility of thermo-acoustic coupling. This peak diminished in distributed combustion for H2 enrichment between 0–20% providing enhanced stability compared to swirl combustion. However, a small peak common to p′ and q′ appeared at 40% H2-enrichment indicating the departure of this reaction zone from its distributed nature. Such fluctuations of reaction zones were further investigated with the proper orthogonal decomposition to verify if the vortex shedding influenced these fluctuations. The appearance of vortex shedding characteristics for the distributed combustion with 40% H2-enrichment was found to be responsible for the fluctuations of reaction zones resulting in a departure from the purely distributed behavior. Measurement of lean blowoff equivalence ratios (ϕLBO) at different combustion conditions showed extension of ϕLBO in distributed combustion indicating wider operational limits in distributed combustion. The performance of distributed reaction zones was analyzed from the exhaust emission characteristics of NO, CO, and CO2. The NO levels (ppm) gradually increased in conventional swirl combustion while it consistently decreased in distributed combustion with the increase of %H2. The increase in NO in normal swirl combustion was attributed to the increase in flame temperature. The overall exhaust CO (ppm) decreased with hydrogen enrichment. The exhaust CO2 gradually decreased with %H2-enrichment for both swirl and distributed reaction zones. The higher CO2 observed with CO2 dilution (compared to N2 dilution) is attributed to the usage of CO2 as the diluent. Emission characteristics were also investigated with preheating of inlet airstream (in the range 373–573 K) to study the performance of distributed combustion relevant to actual gas turbines. The results of reduced pollutant emission with hydrogen enrichment at any preheats temperature were consistent with the non-preheated case. However, some increase in pollutants concentration was observed with gradual preheating that was attributed to higher flame temperature and high-temperature dissociation of CO2. The decreased CO2 emission observed in this research further signifies the favorable potential of distributed combustion with hydrogen-enriched methane to support the decarbonization goal worldwide.

Addition of 10 vol% biomass-based methyl levulinate (ML), ethyl levulinate (EL), butyl levulinate (BL), gamma-valerolactone (GVL), dimethyl carbonate (DimC), and diethyl carbonate (DieC) in gasoline were selected as blended fuels. Physical-chemical properties of six different blends of biofuels and gasoline, including miscibility, octane number, distillation, vapor pressure, unwashed gum content, solvent washed gum content, copper corrosiveness, water content, mechanical admixtures, and lower heating value was evaluated according to the China National Standards. Blended fuels were then evaluated on the performance and emissions of a gasoline test engine without any modification. The results showed that all biomass-based fuels at 10 vol% have good miscibility in gasoline at temperatures of –30 to 30 °C. Experiments were performed at 4500 rpm engine speed at different engine loads (from 10% to 100% in 10% intervals). Results showed slightly lower engine power at different loads with the blended fuels than those from gasoline fuelled engine. However, the brake specific fuel consumption (BSFC) with the blended fuels was slightly higher than that from gasoline. Emission of carbon monoxide (CO), total unburned hydrocarbon (THC) and oxides of nitrogen (NOx) was reduced significantly from the blended fuels compared to gasoline while carbon dioxide (CO2) emission was slightly higher than that from gasoline. The data suggests that 10 vol% addition of biomass-based levulinates and carbonates fuels to gasoline is suitable for use in gasoline engines.

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

Swirl-assisted distributed combustion was examined using a deep-learning framework. High intensity distributed combustion was fostered from a 5.72 MW/m3 atm thermal intensity swirl combustor (with methane fuel at equivalence ratio 0.9) by diluting the flowfield with carbon dioxide. Dilution of the flowfield caused reduction of global oxygen (%) content of the inlet mixture from 21% to 16% (in distributed combustion). The adiabatic flame temperature gradually reduced, resulting in decreased flame luminosity and increased flame thermal field uniformity. Gradual reduction of flame chemiluminescence was captured using high-speed imaging without any spectral filtering at different oxygen concentration (%) levels to gather the data input. Convolutional neural network (CNN) was developed from these images (with 85% of total data used for training and 15% for testing) for flames at O2 = 16%, 18%, 19%, and 21%. Hyperparameters were varied to optimize the model. New flame images at O2 = 20% and 17% were introduced to verify the image recognition capability of the trained model in terms of training image data. The results showed good promise of developed deep-learning-based convolutional neural network or machine learning neural network for efficient and effective recognition of the distributed combustion regime.

Lean blowoff in distributed combustion was investigated at moderate heat release intensities of 5.72, 7.63, and 9.53 MW/m3-atm to characterize the blowoff phenomenon. Distributed combustion conditions were established from a conventional swirl flame at an equivalence ratio of 0.9 using carbon dioxide as the diluent to the inlet airstream. A gradual increase in the air flowrate provided a reduction of equivalence ratio that eventually resulted in the lean blowoff limit. Blowoff occurred at relatively higher equivalence ratios for higher heat release intensities, which was attributed to higher inlet turbulence leading to the early introduction of flame instabilities and blowoff. High-speed chemiluminescence imaging (at 500 frames/second) performed near blowoff moments demonstrated the transition of distributed reaction zone to a near V-shape zone due to quenching of flame surface along the sides. A closer examination of the reduction in equivalence ratio in small steps near the global blowoff showed the presence of a very thin thread-like rotating reaction zone. The observations of blowoff were further supported by the analysis of chemiluminescence signals in each case. The effect of inlet air preheats on blowoff was also investigated. Air preheats broadened the lean blowoff to a lower equivalence ratio which was attributed to enhanced flame speed, providing additional flame stability and reduction of flowfield instabilities. The laminar flame speeds obtained at each preheats case using Chemkin-Pro© simulation with GRI-Mech 3.0 reaction mechanisms supported such a hypothesis of gradually enhanced flame speed, providing additional flame stability.

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.

In this study, a fundamental generalized thermodynamic model of internal combustion engines was applied to evaluate engine compression ratio effects principally in relation to engine size. Performance and efficiency metrics were investigated systematically. Further, cylinder wall temperature was varied across a range of cold start to stabilized operating temperatures. A very broad range of engine bore sizes and bore-to-stroke ratios were evaluated, representing small to large diesel engines in service. In general, it was observed that engine efficiency increases moderately with increasing compression ratio and bore size. Additionally, surface area-to-volume ratio is a critical metric when evaluating various size engines. This leads to greater relative heat transfer in the smaller bore engines with higher compression ratios. The sensitivity to heat losses is also much greater in the smaller engines. Smaller engines with higher compression ratios are expected to be most affected by cold starting conditions. Exhaust enthalpy is highest for larger bore engines with lower compression ratios, an important consideration for engine boosting. Higher convective heat transfer coefficients are also expected in smaller bore engines with higher compression ratios due to the higher operating pressures.

Primary Reference Fuels (PRFs) and Secondary Reference Fuels (SRFs) in the range of cetane from 30 to 60 were operated in a Waukesha Diesel Cooperative Fuels Research (CFR) engine under operating conditions that emulate the cetane rating test. Due to the large number of test points in this study, the exact ASTM cetane rating protocol was not followed precisely, however these results are representative of cetane characterization testing with very similar equivalence ratio and combustion phasing across a broad range of Ignition Delays (IGDs) that varied as a result of Compression Ratio (CR) changes in the eleven to twenty-two range. Intake air temperature was operated both heated, as in the cetane rating test, as well as at ambient laboratory conditions. Additional research instrumentation was added beyond the standard CFR equipment for advanced combustion analysis. Combustion analysis shows that engine torque and efficiency increase significantly with increases in CR. At longer IGDs representative of the cetane rating test (13 deg IGD), the increase in IGD with reduced cetane number is relatively linear. For all of the fuels tested, IGD steadily monotonically decreases with increased CR significantly by more than a factor of two. Shorter IGDs lead to longer burn durations; fuel effect differences become less important at very high CRs. Associated companion analysis shows that at the time of fuel injection (Start Of Injection – SOI), cylinder pressure roughly doubles over the CRs studied, however, cylinder charge temperature only moderately increases. This effect leads to a doubling in cylinder air charge concentration at the highest CRs showing an important effect on the fast kinetics at high CRs. A common IGD correlation was evaluated showing good agreement except for the high CN fuel. New IGD correlations are also presented.

Demand for automotive tires has been increasing at a significant rate to reach production rate of 2.9 billion in 2017 that contributed to the generation of almost 1 billion waste tires. The pathways for handling of these waste tires have been limited to aggregate construction applications and direct incineration as fuel. The rate of recycling feasibility was limited by the availability of waste tires with structure intact for their upgrading and reuse in the economy. In the USA, although 40% of the waste tires are disposed by combustion for energy recovery in cement kilns, pulp and paper mills, and electricity generation, the presence of sulfur from vulcanized rubber, the production of hazardous pollutants, and low temperatures caused due to slow heterogenous combustion leads to significant energy and resource losses. Additionally, this pathway is limited to thermal energy production and thus lacks versatility. Alternative thermochemical pathways such as pyrolysis and gasification offer better pathways for the utilization of these wastes as they provide uniform products such as synthetic gas, bio-oil and char. Versatility is also achieved via syngas production as it is a precursor to liquid fuels and various other essential petrochemicals. These pathways provide improved energy efficiency, feasibility, and scalability for increased waste tire utilization and value outcome compared to the current application pathways. Results are reported from the investigations on high-temperature pyrolysis and CO2-assisted gasification of waste tires with focus on the evolutionary behavior of syngas production, its constituents, and energy yield in lab-scale fixed-bed reactor. The impact of CO2 addition, temperature, and the addition of biomass feedstock to the waste tire was investigated to understand the feasibility of waste tire disposal via this pathway while also utilizing the CO2 pollutant and maintaining high energy efficiency. Lack of inhibitive effects observed when tire was co-processed with biomass, makes the disposal of waste tires along with other wastes easier along with established feasibility regime for efficient and economical disposal of waste tires while recovering energy and utilizing CO2.

Biomass gasification in CO2 is a promising thermochemical pathway to assist with growing issues of CO2 in the environment. However, high reaction temperature requirement and the low reaction rate is limiting its development. To resolve these issues, the effect of acid and alkali pretreatment on the pyrolysis and CO2 gasification of pinewood was examined using a semi-batch reactor. The temporal behavior of syngas components, energy, and their yield, and energy efficiency was quantified. Results showed that the decreased alkali and alkaline earth metal (AAEM) content using acid pretreatment was beneficial for the CO and syngas yield, while the effect of the increased AAEM content using alkali pretreatment provided a converse trend. In contrast, CO2-assisted gasification of alkali-pretreated biomass improved the CO and syngas yield due to the catalytic influence of AAEM on the Boudouard reaction, while the acid-washed biomass yielded the lowest syngas yield. During gasification, the syngas yield, energy yield, and overall energy efficiency were enhanced by 83.4 (by wt%), 44.6 (by wt%), and 44.6%, respectively, using alkali pretreatment. The results revealed that alkali pretreatment is an effective catalytic incorporation pathway to improve the syngas, energy output, and reactivity to CO2 gasification.

High-speed local seeding particle injection for particle image velocimetry has been developed and demonstrated by measuring Mach 3 and Mach 10 turbulent boundary layers. The seeding injectors accel...

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.

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.

Simultaneous thermal analysis (TGA-DSC) of biomass pyrolysis was conducted to understand the kinetics and energy requirements of biomass pyrolysis. DSC results revealed the energy requirement to heat biomass samples to pyrolysis temperature with contributions from both sensible enthalpy changes along with reaction enthalpy change required to break their chemical bonds. The information obtained was used to determine theoretical energy efficiency of biomass pyrolysis, which was found to be in the range of 86–95%, depending on the sample analyzed, with pinewood providing efficiency of ∼95%. The TGA results were used for inverse modeling of pyrolysis kinetics of various biomass feedstocks that varied in their source of origin. Sequential multi-step pyrolysis model was explored to understand its capability in representing the global pyrolysis reaction of lignocellulosic wastes since they are carbon neutral and can produce clean and sustainable energy to potentially replace the existing fossil fuel resources with minimal change in existing energy consumption infrastructure. Inverse modeling, by fitting with respect to thermogravimetric analysis (TGA), was carried out using global minimization in an elite multi-objective genetic algorithm and with appropriate choice on the number of reaction steps. Biomass/bio-wastes investigated were cardboard, dry-paper waste, pinewood, rice husk and chicken manure. Cellulose was also investigated as a baseline standard sample. The char formation selectivity of the components involved in biomass was obtained from this model and found similar values for most of the biomasses. A set of ∼48%, 65% and ∼70% charring tendencies (based on vi values) was common among paper, pinewood, cardboard. The α-cellulose decomposition also provided the 70% charring reaction suggesting its role in these biomasses. The obtained multi-step kinetic parameters are considered essential to develop simplified reaction mechanism of biomass gasification and pyrolysis for computational fluid dynamics (CFD) models, which can help in the design of energy efficient and feedstock flexible reactors for sustainable energy production from wastes.

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.

Combined use of plastic and biomass wastes offers promising pathway for simultaneous energy production and waste disposal. In this article, the co-pyrolysis of pinewood and polycarbonate (PC) was performed in a fixed bed reactor to quantify their synergistic interaction on the product output and determine the effect of char intermediates on the synergistic effects. The extent of synergistic effects was obtained via a direct comparison of results from co-pyrolysis of pinewood–polycarbonate mixture with the weighted average values from pyrolysis of individual components. The observed synergistic effects were further examined from the influence of char intermediates using tailored feedstock configurations to gain more insights into the synergistic mechanism. The results showed co-pyrolysis resulted in enhancement by 33% in H2, 26% in CO, and 19% in total syngas yields compared to their weighted values from individual pyrolysis. Co-pyrolysis also exhibited superiority in energy recovery with the overall energy efficiency promoted from 42.9% to 48.6%. Deconvolution of synergistic effects revealed that pinewood char catalytically enhanced PC degradation, while the effect of PC char on pinewood pyrolysis was minimal. This article provides results on deconvolved understanding of synergistic effects in co-pyrolysis of lignocellulosic biomass and PC wastes, which is very helpful in designing clean and efficient energy recovery systems from these waste resources.

Landfill reclamation is a good solution to utilize the wasted land occupied by municipal solid waste dumpsites or landfill sites. This also offers a good means to recover valuable materials and form environmentally benign green refuse-derived fuel (RDF) for use in power production. However, due to the heterogenous composition of the wastes, it is crucial to homogenize and upgrade the waste hydrocarbon fuel properties. Torrefaction is a thermochemical process that utilizes low temperature and inert environment to drive off the moisture and volatile fractions present in wastes to form valuable fuel. This upgraded RDF from reclaimed landfills offer high energy density and favorable hydrophobicity for use as a fuel feedstock in gasification to produce syngas for power generation. The objectives of this study are to first upgrading the reclaimed landfill wastes to RDF using torrefaction followed by its conversion to form clean syngas in a downdraft gasifier. This study examines the effect of air ratio on syngas heating value and cold gas efficiency. A comparison is made on the syngas produced from gasification using reclaimed landfill wastes and torrefied RDF. Experiments were conducted using a 10 kg/h lab-scale downdraft gasifier. The air ratios examined were 0.22, 0.27, and 0.32. The results showed an optimum air ratio of 0.27 operated with a gasifier using torrefied RDF. The results showed improved syngas quality, in terms of syngas composition, lower heating value, and cold gas efficiency. The lower heating value of 4.22 MJ/Nm3 and the cold gas efficiency of 65.84% were achieved. The results showed that landfill mining can provide ultimate solution to get rid of dumped wastes from landfills using torrefaction for high-quality fuel followed by the recovery of green and clean syngas energy using gasification.

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.

There is a growing need for drop-in biofuels for gas turbines for enhanced energy security and sustainability. Several fuels are currently being developed and tested to reduce dependency on fossil fuels while maintaining performance, particularly in the aviation industry. The transition from traditional fossil fuels to sustainable biofuels is much desired for reducing the rapidly rising CO2 levels in the environment. This requires biofuels to be drop-in ready, where there are no adverse effects on performance and emissions upon replacement. In this study, the performance and emissions of four different aviation drop-in biofuels were evaluated. They include UOP HEFA-SPK, Gevo ATJ, Amyris Farnesane, and SB-JP-8. These aviation biofuels are currently being produced and tested to be ready for full or partial drop-in fuels as the replacement of traditional jet fuels. The characteristic performance of each fuel from the prevaporized liquid fuels was performed in a high-intensity (20 MW/m3-atm) reverse flow combustor. The NO emissions showed near unity ppm levels for each of the fuels examined with a minimum at an equivalence ratio of ∼0.6, while CO levels were in the range of 1000–1300 ppm depending on the fuel at an equivalence ratio between 0.75 and 0.8. For an equivalence ratio range between 0.4 and 0.6, NO and CO emissions remained very low (between 1–2 ppm NO and 2400–2900 ppm CO) depending on the fuel. The examined biofuels did not show any instability over a wide range of equivalence ratios from lean to near stoichiometric condition. These results provide promising results on the behavior of these drop-in aviation biofuels for use in high-intensity gas turbine combustors providing stability and cleaner performance without any modification to the combustor design.

Growing energy demands for improved lifestyle and enhanced productivity has caused greater use of energy produced from fossil fuels, which in turn is leading to unsustainability with continuously increasing CO2 into the environment that causes significant impact to climate changes. This chapter provides a review of the CO2 capture techniques, followed by thermochemical pathways for the CO2 utilization for energy, fuels and chemicals production with focus on sustainability and carbon cycle. Thermochemical redox looping techniques are also addressed due to their significantly higher potential compared to their alternatives, along with the considerations on material development for use in redox looping. Recent developments in mixed metal oxides derived from layered double hydroxides provided promising results on sustained redox capability. Furthermore, they offer minimal inhibitive impact of sintering and high CO yield per gram of the material at lower costs, and the process is scalable compared to other methods that use rare earth elements. The challenges and future research directions on the development of oxygen carrier redox materials are provided. CO2–assisted gasification of biomass and solid wastes offers good pathway for CO2 conversion to syngas based on CO2 converted to syngas per gram of feedstock used. The results demonstrated highest throughput and higher efficiency than that known presently. Furthermore, the approach offered good potential for scalability compared to other pathways of 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.

CO2-assisted co-gasification of binary mixtures of pinewood pellets (PWP) and two kinds of plastics polyethylene-terephthalate (PET) and high-density polyethylene (HDPE) were examined at 800 °C using a fixed bed reactor. Evolutionary behavior and yields of CO, H2, and CmHn were investigated for both individual feedstock and binary mixtures of biomass and plastic. Synergetic effects in co-gasification of mixtures under CO2 atmosphere were analyzed and compared between experimental and calculated results. The results showed that PET and HDPE although had similar behavior in gasification, they provided many different characteristics on blending with solid biomass in CO2-assisted co-gasification. Both PWP–PET mixture and PWP–HDPE mixture showed positive effects on hydrocarbons yield and negative effects on solid yield. For PWP–PET mixture, H2 yield showed no change compared to the calculated value; however, CO yield and CO2 consumption showed negative effects due to the blocked porosity of solid biomass from the softened PET. For PWP–HDPE mixture, H2 yield showed significant enhancement compared to the calculated value, and CO yield showed slight enhancement but a slight reduction in CO2 consumption. It was also observed that the experimental CmHn yields obtained from biomass-plastics mixtures were of higher values than the calculated values. The morphologies of solid residues for PWP, PET, PWP–PET, and PWP–HDPE were analyzed and taken as a supplement to explain the synergetic effects in the co-gasification process. These results provide an insight into energy recovery and waste treatment potential for both biomass and waste plastic using thermochemical conversion.

Colorless distributed combustion (CDC) is a novel method to enhance flame stability and thermal field uniformity, increase combustion efficiency, and reduce pollutants’ emission. CDC is achieved through the use of a carefully prepared fuel–oxidizer mixture along with reactive species. In this study, a partially premixed, swirl-assisted cylindrical combustor utilized a propane–air flame with either nitrogen or carbon dioxide gas in order to reduce the oxygen concentration of the oxidizer. OH* chemiluminescence signatures were used to determine transition to distributed combustion condition. The results showed transition to CDC at approximately 15% using N2 and 17% using CO2 dilution. Emission of NO and CO under CDC condition showed NO levels of only 2 or 1 ppm using N2 or CO2 dilution, respectively. High-frequency PIV (3 kHz) was used to determine the flow velocity structure and eddy size effects on flame stability and emissions. Increase in dilution enhanced both the radial and axial mean and fluctuating velocities under CDC that foster mixing. Additionally, the Kolmogorov length decreased with increase in dilution resulting in smaller eddy size particularly in the swirl lobe region, which enhanced turbulent dissipation that resulted in lower peak temperatures and reduced thermal NOx emission. Reduced viscosity using CO2 dilution provided a stronger effect in reducing NO as compared to N2 as the diluent.