Carbon Conversion Ratio Research Articles

Evaluation of the chemical looping gasification characteristics of kitchen waste using CuFe2O4 and NiFe2O4 as oxygen carriers

Chemical looping gasification (CLG) technology is promising for renewable energy, efficiently transforming biomass into high-quality syngas with minimal tar and pollutants. In this study, we examined the CLG characteristics of soy protein (SP), a model compound present in kitchen waste (KW), using two different oxygen carriers (OCs): Cu-Fe and Ni-Fe. The study revealed that enhancing the carbon conversion ratio (ηc) could be effectively achieved by increasing the oxygen equivalent coefficient (α) and the steam content. Consequently, the optimal gasification performance was attained when the Cu-Fe and Ni-Fe OCs were operated at the α values of 0.3 and 0.4, and steam contents of 30% and 40%, respectively. After ten cycles of chemical looping, both OCs retained their robust oxidation activity, ensuring that the ηc remained consistent throughout the ten cycles. Under optimized experimental conditions, the CLG characteristics of KW were successfully determined. Notably, the ηc of KW was substantially enhanced, doubling in comparison to previous levels. The Cu-Fe OC emerged as a more suitable candidate for the CLG of KW due to its lower cost and non-toxic nature. This study provides important theoretical support and practical insights for the harmless treatment and resource utilization of KW.

An Entrained Flow Biomass Gasification Technology with the Fluidized Bed Concept for Low-carbon Fuel Production

For accomplishing the vision of building of a net-emission zero society, low-carbon fuels such as e-fuel, Sustainable Aviation Fuel (SAF), and chemical products generation, plays a significant role. Especially, among the low carbon fuels, SAF is the most crucial. Ammonia and electric aircraft are under way as alternatives to fossil-derived jet fuel (kerosene). However, none of these have yet found their way to commercialization. Among the SAF production technology, biomass gasification and Fischer-Tropsch (FT) synthesis technology are one of the lowest CO2 emission processes, according to Life Cycle Assessment (LCA) analysis. However, at present there are some issues about biomass grinding, tar, ash treatment, gas purification and wastewater. We, at Mitsubishi Heavy Industries (MHI) R&D laboratory have developed entrained bed gasification, adopting the fluidized bed concept in which biomass particles are recirculated in the gasifier without fluidizer. Principally desired outcomes of this development was to reduce the grinding power, simplify the structure by using atmospheric pressure process, and lower tar concentration while maintain suitable temperature to prevent ash from melting inside gasifier. Empirical and actual results showed that the developed gasifier can obtain high carbon conversion ratio and low tar as compared to the traditional gasification processes for low-carbon fuel production and produce reliably stable syngas for low-carbon fuel synthesis with single gasifier. Based on the pilot plant operation results, effectiveness of moderate (1223 – 1323 K) temperature gasification with this concept has been demonstrated too. As a conclusion, development needs and expectation of gasification technology for contributing to carbon neutral society are mentioned.

Enhanced production of hydrogen-rich gas from municipal sewage sludge gasification using a CaO-RM composite catalyst

Hydrogen-rich gas, characterized by high yield and purity, can be effectively generated through the steam gasification of sewage sludge (SS), offering substantial benefits for organic solid waste treatment and resource conservation. This study evaluated the gasification performance in a horizontal moving-bed reactor employing a wet-mixed CaO-red mud (CaO-RM) composite catalyst. The effects of CaO loading rate (CaO/RM), catalyst-to-SS ratio (CaO-RM/SS), and reaction temperature on the syngas yield, lower heating value (LHV), carbon conversion ratio, H2 to CO (H2/CO) ratio, and H2 yield were investigated. Results indicated that red mud loaded with a calcium-based catalyst significantly enhanced syngas production, particularly for hydrogen generation, during SS gasification. A maximum hydrogen molar fraction of 50.84% and a yield of 7.07 mol/kg were achieved with a CaO/RM of 40% and a CaO-RM/SS of 30% at 750 °C. With the reaction temperature increase from 700 to 900 °C, the catalytic performance for secondary tar cracking and steam reforming was further enhanced. The total syngas yield, H2 yield, hydrogen molar fraction, LHV of syngas, and carbon conversion rate peaked at 0.79 m³/kg, 19.30 mol/kg, 54.41%, 10,249.48 kJ/kg, and 65.67%, respectively, at 900 °C.

Design of an integrated system for electrofuels production through Fischer-tropsch process

There has been a growing recognition in recent years that Electrofuels (e-fuels), also known as renewable and sustainable fuels, which are produced from hydrogen and carbon dioxide as the primary feedstocks, have great potential to reduce carbon footprint and address climate change. In the present study, contrary to most previous studies in which the sources of feedstock's preparation were considered as block boxes, two stand-alone processes are taken into account and incorporated into the e-fuels production system. H2 is obtained by a high-temperature electrolysis system having an overall efficiency nearly twice that of a low-temperature electrolysis system. CO2 is captured from a power plant flue gas stream with a purity of 99.81%. Investigating heat integration potential in such an integrated plant is an up-to-date and interesting topic and has not yet been well explored. Therefore, a heat integration within the three individual processes is implemented to reduce energy consumption. The design of the process-to-process heat transfer section is carried out using pinch design rules. By integrating individual units, approximately 42% of the required cold utility, traditionally supplied by chilled water and refrigerants, is allocated to generate high and medium-pressure steams. Having used the high-temperature steam electrolysis for H2 production, a process that requires less external electricity compared to low-temperature water electrolysis, a power-to-liquid efficiency of 70% is achieved. Furthermore, the results reveal a carbon conversion ratio of 98.6%, indicating the effective converting the carbon from the feedstock into liquid hydrocarbons.

Efficient Mycoprotein Production with Low CO2 Emissions through Metabolic Engineering and Fermentation Optimization of Fusarium venenatum.

The global protein shortage is intensifying, and promising means to ensure daily protein supply are desperately needed. The mycoprotein produced by Fusarium venenatum is a good alternative to animal/plant-derived protein. To comprehensively improve the mycoprotein synthesis, a stepwise strategy by blocking the byproduct ethanol synthesis and the gluconeogenesis pathway and by optimizing the fermentation medium was herein employed. Ultimately, compared to the wild-type strain, the synthesis rate, carbon conversion ratio, and protein content of mycoprotein produced from the engineered strain were increased by 57% (0.212 vs 0.135 g/L·h), 62% (0.351 vs 0.217 g/g), and 57% (61.9 vs 39.4%), respectively, accompanied by significant reductions in CO2 emissions. These results provide a referential strategy that could be useful for improving mycoprotein synthesis in other fungi; more importantly, the obtained high-mycoprotein-producing strain has the potential to promote the development of the edible protein industry and compensate for the gap in protein resources.

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

Experimental study on the activation of coal gasification fly ash from industrial CFB gasifiers

Coal gasification fly ash (CGFA) is an industrial solid waste from the coal circulating fluidized bed (CFB) gasification process, and it needs to be effectively disposed to achieve sustainable development of the environment. To realize the application of CGFA as a precursor of porous carbon materials, the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed. Then, the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor. Finally, the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig, and its advantages are highlighted. The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%, an ultrafine particle size (d50: 16.3–26.1 μm), and a relatively developed pore structure (specific surface area SSA: 139.29–551.97 m2·g−1). The proportion of micropores in CGFA increases gradually with the coal rank. Steam activation experiments show that the pore development of CGFA mainly includes three stages: initial pore development, dynamic equilibrium between micropores and mesopores and pore collapse. The SSA of lignite fly ash (LFA), subbituminous fly ash (SBFA) and anthracite fly ash (AFA) is maximally increased by 105%, 13% and 72% after steam activation; the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA > LFA > AFA. As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19, the carbon conversion ratio increases from 14.4% to 26.8% and the cold gas efficiency increases from 6.8% to 10.2%. The SSA of LFA increases by up to 53.9% during the fluidization activation process, which is mainly due to the mesoporous development. Relative to steam activation in a tube furnace reactor, fluidization activation takes an extremely short time (seconds) to achieve the same activation effect. It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35% to create pores in the initial development stage.

Co-Fermentation of Chlorella vulgaris with Oleaginous Yeast in Starch Processing Effluent as a Carbon-Reducing Strategy for Wastewater Treatment and Biofuel Feedstock Production

Low biomass yield and nutrient removal efficiency are problems challenging the employment of microorganisms for wastewater remediation. Starch processing effluent (SPE) was used as a fermentation substrate to co-culture Chlorella vulgaris and Rhodotorula glutinis for biofuel feedstock production. Co-culture options were compared, and the optimal conditions were identified. The result shows that microalgae and yeast should be inoculated simultaneously at the beginning of SPE-based fermentation to achieve high biomass yield and the optimal inoculation ratio, light intensity, and temperature should be 2:1, 150 μmol/m2/s, and 25 °C, respectively. Under the optimal conditions, the lipid yield of microorganisms was 1.81 g/L and the carbon–conversion ratio reached 82.53% while lipid yield and the carbon–conversion ratio in a monoculture fell in the range of 0.79–0.81 g/L and 55.93–62.61%, respectively. Therefore, compared to the monoculture model, the co-fermentation of Chlorella vulgaris and Rhodotorula glutinis in starch processing effluent could convert nutrients to single-cell oil in a more efficient way. It should be noted that with the reduced concentration of residual organic carbon in effluent and the increased carbon–conversion ratio, co-fermentation of microalgae and yeast can be regarded as a promising and applicable strategy for starch processing effluent remediation and low-cost biofuel feedstock production.

Use of brewer's residual yeast for production of bacterial nanocellulose with Gluconacetobacter hansenii

Bacterial nanocellulose (BNC) has attained elevated interest due to its versatile structure and high resistance characteristics. Accordingly, efforts have been made in order to reduce its production costs, such as the employment of its by-products as a nutrient broth to yield the microorganism. Residual brewer's yeast is an excellent recourse, due to its high nutritional value and availability. Therefore, research which aimed to contribute to the development of a low cost, efficient and biosustainable technology for BNC production with Gluconacetobacter hansenii was carried out. BNC was obtained from residual brewer's yeast hydrolysate at pH 7.0 and five days of incubation at 30 °C in static culture. The hydrolysate was characterized by the amount of sugars, fatty acids, total proteins and ash content. Subsequently, BNC obtained was characterized in terms of yield, carbon conversion ratio, hydrodynamic size, crystallinity, morphology, Fourier-transform infrared spectroscopy, and surface analysis. Residual brewer's yeast hydrolysate proved to be efficient in BNC production via gluconeogenesis with consumption of alanine, threonine and glycerol, obtaining 1.9 times the yield of the chemically defined broth adopted as standard. Additionally, properties observed in the obtained BNC were equal to those obtained from conventional chemical medium. The research contributed to bacterial nanocellulose production using by-products from the brewing industry.

Techno-economic analysis and life cycle analysis of e-fuel production using nuclear energy

Electrofuels, or e-fuels, are synthetic liquid hydrocarbon fuels which may be produced using carbon dioxide (CO2) and low carbon hydrogen (H2) as feedstock. They are of great interest because they have much lower carbon intensity compared to the conventional petroleum fuels and can utilize the existing fuel infrastructure owing to their ability to blend with or replace existing fuels. We modeled an e-fuel production process to produce low carbon jet, diesel, and naphtha using a reverse water gas shift process to produce synthesis gas, followed by a Fischer-Tropsch (FT) synthesis process. Nuclear energy is considered for e-fuel production due to its steady energy supply, near-zero carbon emissions, capability to produce hydrogen with high efficiency via high temperature electrolysis, and proximity to biogenic CO2 sources from nearby corn-ethanol plants in the United States. The modeled FT process achieved a high carbon conversion ratio of 99% by recycling CO2 and the use of oxy-combustion, and a process energy efficiency of approximately 70%. The life cycle greenhouse gases emissions are estimated to be 7 and −25 gCO2e/MJ, without and with steam coproduct credit, respectively, by using the Greenhouse gases, Regulated Emissions, and Energy use in Technologies (GREET®) model. Additionally, the process economics were evaluated for three scales corresponding to nuclear power plant capacities of 100, 400, and 1000 MWe, estimating a minimum fuel selling price (MFSP) of $3.61/gal ($0.95/L), $2.82/gal ($0.74/L), and $2.66/gal ($0.70/L) of FT fuel mix, respectively, by considering $3/kg of H2 tax credit prescribed in the recent Inflation Reduction Act.

Steam co-gasification characteristics of black liquor char and petroleum coke coupled with TiO2 direct causticization

The isothermal steam gasification experiments of a ternary mixture (BTP) containing black liquor char (BLC), causticizing agent (TiO2) and petroleum coke (PC) were carried out at 850 °C based on a thermogravimetric analyzer (TGA) and a horizontal fixed-bed reactor. A co-gasification process of BLC and PC coupled with TiO2 direct causticization was explored from the aspect of reaction rate as well as the characteristics of gaseous products and gasification residues (GR). The results show that in comparison to the weighted average (BTPtheo) of the independent gasification of TiO2 direct causticized BLC and PC, significant synergistic effects could be aroused during the coupled co-gasification process due to promoting action of mNa2O·nTiO2 on gasification of organic carbon. Specifically, the maximum reaction rate of BTP reaches 7.0%/min, which is 2.9 times that of BTPtheo. The content and yield of effective gas components, i.e., H2+CO, in the gas products, as well as its lower heating value (LHV) of BTP are 81.1%, 2059 mL/g, and 9343 kJ/m3, respectively, which is 6.8%, 137.3%, and 5.5% higher than that of BTPtheo. The carbon conversion and energy output ratio of BTP reaches 95.0% and 1.13, respectively, which is increased by 61.6% and 135.4% relative to the theoretical superposition value. In addition, the relative loss of inorganic salts in BTP during the whole thermochemical conversion process is effectively controlled at a lower level of about 9.4%. Since the Na-containing salts in GR of BTP are mainly mNa2O·nTiO2 with higher thermal stability, and GR maintains good particle flowability, it is conducive to downstream alkali recovery.

Experimental study and theoretical analysis on fluidized activation of coal gasification fly ash from an industrial CFB gasifier

The gasification fly ash (GFA), a bulk industrial solid waste from coal gasification process, urgently needs to be effectively disposed. In order to use the GFA as porous carbon materials, fluidized activation experiments of the GFA from an industrial circulating fluidized bed (CFB) gasifier were conducted in a bench-scale CFB test rig, as well as steam activation experiments of GFA in a vertical tube furnace and theoretical analysis on the activation process. Due to the ultrafine particle size, the GFA faces a fluidization problem and auxiliary particles are needed to stabilize its fluidization. In the fluidized activation, the pore structure of GFA particles becomes developed in a seconds-level time (about 1.5 s). The specific surface area (SBET) of activated GFA increases with temperature, maximally increasing by 48.9 % and reaching 204 m2/g. Steam activation experiments show that the GFA has an activation potential of 362 m2/g (SBET) and the pore structure evolution of GFA can be quantified by carbon conversion ratio. Based on this, the fluidized activation of GFA is found in the stage of pore development. By appropriately increasing the carbon conversion ratio (below 40 %), the fluidized activation effect of GFA is expected to be improved. Theoretical analysis indicates for the GFA the features of ultra-fine particle size and well-developed pore structure greatly enhance the diffusion rate of active component into the particles. Under the strong diffusion effect, increasing temperature is a critical means to realize the rapid and effective activation of GFA in a finite time.

Sequential hydrothermal carbonization and CO2 gasification of sewage sludge for improved syngas production with mitigated emissions of NOx precursors

Due to high moisture and protein contents in sewage sludge (SS), conventional thermal treatment of SS is energy-intensive and a large amount of harmful nitrogen-containing gases are emitted. In this study, a sequential hydrothermal carbonization (HTC) and CO2 gasification system has been proposed to effectively improve the gasification efficiency and considerably reduce the emissions of NOx precursors (i.e., NH3 and HCN) in SS treatment. Yield and quality of syngas were comprehensively investigated during CO2 gasification in terms of various temperatures with different dosages of CaO additive in HTC, and varied reaction temperature and CO2 percentage in gasification process. On the whole, CO2 gasification of SS derived hydrochar (HC) demonstrated obvious reduction of tar formation from 10.9 to 6.8 % and enhancement of calorific value of formed syngas from 14.1 to 15.7 MJ/Nm3. Production of NOx precursors was greatly reduced due to formed non-active quaternary-N in HC, while HTC with CaO favored the mitigated NOx precursors in syngas owing to enriched pyrrole-N and quaternary-N therein. Catalytic tar decomposition and Boudouard reaction in CO2 gasification were responsible for the distinct reduction of tar formation, and notable increase of carbon conversion ratio and syngas yield. Although facilitated catalytic gasification in CO2 atmosphere can maximize syngas yield, lower portion of CO2 (ca. 20 %) was more beneficial to drastically mitigate emissions of NOx precursors, especially the reinforced transformation of NH3 to N2. The fundamental knowledge could ultimately help to achieve significant abatement of NOx precursors during CO2 gasification for improved syngas production.

Kinetic Studies on the Steam Gasification of Chars Derived from Coals by Different Isoconversional Methods

Previous studies have successfully assessed the extent to which a kinetic model accurately represents a specific reaction mechanism by comparing the kinetic parameters derived from the kinetic model to those obtained using isoconversional methods. However, this approach remains underdeveloped for the important steam gasification reaction of char. This study addresses this issue by conducting a series of steam-assisted char gasification tests, using thermogravimetric analysis at five different heating rates. The results indicate that the carbon conversion ratio of the char gasification reaction increases with the increasing heating rate. The activation energies of the reaction process are determined with different carbon conversion ratios using three isoconversional methods, including the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink methods. The gasification mechanism is also analyzed using model-fitting methods with a wide variety of carbon conversion models, and the accuracies of the models are evaluated, firstly, by comparing the obtained goodness of fit values of the models with the experimental results, and, secondly, by comparing the obtained activation energies with those derived using the isoconversional methods. The goodness of fit results and the results of the comparisons between the activation energies obtained using the various models with the isoconversional values demonstrate that the three-dimensional Avrami–Erofeev model best represents the steam gasification char reaction, where the difference between the two activation energy values is only 0.70 KJ.mol−1. The reliability of the proposed approach for evaluating the applicability of a given kinetic model to the steam gasification reaction of char is tested by comparing the results obtained for char samples derived from three different bituminous coal sources.

Investigation of the CN and C2 emission characteristics and microstructural evolution of coal to char using laser-induced breakdown spectroscopy and Raman spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was employed to study the spectral characteristics of the C2 and CN emissions of three types of coal and their pyrolysis char samples. By analysing the atomic and molecular emissions, the electron temperature, electron density and rotational temperature were calculated to evaluate the characteristics of the laser-induced plasma. The correlation between the molecular emissions and coal combustion characteristics was also investigated, which was explained from the aspect of microstructural evolution obtained by Raman spectroscopy. The molecular emissions were gradually inhibited with increasing pyrolysis temperatures, however the molecules tended to distribute at a higher equilibrium temperature. The rotational temperatures increase by 1000–3300 K relative to the raw coal for chars prepared at pyrolysis temperatures of 293–1173 K. The reduction of C2 and CN emissions, which are thought to be mainly caused by small aromatic rings and amorphous carbon structures, is consistent with the Raman spectroscopy results in that the microstructures evolve towards a more stable large aromatic-ring skeleton after pyrolysis. When the carbon conversion ratio is Xc = 50% for three kinds of coal, the R2 values of the exponential fitting between C2 emission and carbon conversion rate are all higher than 0.99.

Separate physicochemical effects of CO2 on the coal char combustion: An experimental and kinetic study

The overall impact of CO2 on the coal char combustion is complicated due to the interplay between the CO2 thermal effect and chemical effect (including the gasification endothermicity, and its direct additional carbon consumption). To assess the impact of these factors on the carbon consumption process, we conduct a quantitative study on the separate physicochemical effects of CO2 through experimental and kinetic research. Two oxygen concentrations (15% and 21% O2), representing industrial boiler and air combustion environments, were selected. The experiment research on its thermal effect (evaluated by carbon conversion ratios) is performed at 1773 K in a high-temperature drop tube furnace. The chemical effect of CO2 is predicted for a 100 μm coal char particle using a self-developed char burning kinetics model. Results indicate that the carbon conversion ratios show a V-type distribution with higher CO2 concentrations, as a result of its complex physicochemical effects, with minimal carbon conversion points around the CO2 concentrations of 5–10 vol.%. The thermal effect initially increases with higher CO2 concentrations from 0 to 10 vol.%, but it declines with a further increase in CO2 concentrations, while the endothermicity effect of the gasification reaction increases with higher CO2 concentrations. The relative contribution of the endothermicity effect on the char consumption is 20.4% in the 21%O2/10CO2/N2 environment, lower than the thermal effect (29.9%), but it continuously increases and becomes the most influential inhibitory factor at higher CO2 concentrations. The strongest suppression effect of CO2 corresponds to the CO2 concentrations of 10 vol.%.

Simulation studies on the co-production of syngas and activated carbon from waste tyre gasification using different reactor configurations

• Waste tyre gasification was evaluated in three different reactor configurations. • Fluidized bed, fixed bed and rotary kiln reactors were evaluated. • Fixed bed reactor was the most suitable reactor configuration for syngas production. • Fluidized bed reactor was the most suitable for activated carbon production. • Coproduction of syngas and activated carbon was most suitable in fluidized reactor. Gasification is one of the most efficient thermo-chemical conversion processes for transforming waste tyres into syngas and high-valued solid carbon products such as activated carbon (AC). This study evaluated the co-production of syngas and AC in three reactor configurations: fluidized bed, fixed bed, and rotary kiln at the systems level. A single-stage steam gasification and char activation process was simulated using Aspen Plus V10 software. The effects of gasification parameters such as equivalence ratio (ER) and steam-to-fuel ratio (SFR) were investigated and compared. The best conditions for the co-production of syngas and AC in the reactors were evaluated and compared. Brunauer-Emmett-Teller (BET) computational analysis was used to predict the surface area of the AC. The fluidized bed gasifier has the potential to produce syngas with a low heating value (LHV) of 6.67 MJ/Nm 3 , cold gas efficiency (CGE) of 82.4% LHV , AC with BET surface area of 698.63 m 2 /g and a carbon conversion ratio (CCR) of 92.5%, the fixed bed gasifier has a syngas LHV of 6.25 MJ/Nm 3 , CGE of 85.9% LHV , AC with BET surface area of 432.51 m 2 /g and CCR of 97.3% and the rotary kiln gasifier has a syngas LHV of 5.96 MJ/Nm 3 , CGE of 74% LHV , AC with BET surface area of 661.73 m 2 /g and CCR of 93%.

Study on scale-up characteristics in supercritical CO2 circulating fluidized bed boiler by 3D CFD simulation

For the wide industrial applications of supercritical CO2 (S-CO2) circulating fluidized bed (CFB) technology, the simulation on scale-up characteristics would be a crucial and reliable means to investigate specific combustion process before establishing costly and complex boilers in industry. This study conducted 3D CFD simulations in lab-scale, pilot-scale, and industry-scale S-CO2 CFB boilers (0.1 MW to 600 MW) based on the Eulerian-Lagrangian method. The scale-up characteristics were comprehensively discussed from the angles of furnace structure, gas-solid flow dynamic, combustion characteristics, heat transfer characteristics, gas emission characteristics, and boiler efficiency with the fitting formulas of the scaled-up regularities derived. Results show that with the power capacity increased, the heating surface area in the furnace and flue system enlarged, in which the furnace heating surface accounted for a larger proportion. The particle flow rates and the circulating ratio increased, and the voidage distribution was less affected by disturbance with more complicated core-annulus structures appeared. With the thermal input increased, furnace temperature decreased accompanied by better thermal inertia, and the heat transfer of cold walls enhanced although its transverse distribution became uneven. The emissions of CO, NOx, and SO2 from the industry-scale CFB were lower than the other two scales. The carbon conversion ratio and the combustion efficiency increased with the thermal input increased, and the growth slowed for industry-scale boiler.

Experimental and kinetics studies on the evolution and effects of ash film during pulverized coal char combustion

The char reactivity loss during the burnout stage is closely related to the effects of ash minerals, which show complex transformation behaviors (ash vaporization, ash film, and ash dilution). To assess the impact of ash behaviors, we computed the char consumption characteristics in a 21%O2/79%N2 environment using the Char Burning and Particulate Matter Kinetics (CBPMK) model with a user-design allocation of the ash film and dilution. Regretfully, the ash film fractions have not been experimentally studied due to the irregular ash structure and the high combustion temperatures. On basis of the research on ash formation mechanism, this paper aims to provide appropriately measured ash film fractions of chars as a function of carbon conversion ratio for further development of the kinetic model. The ash film fraction F increases exponentially with carbon conversion ratio N, and their relationship is summarized as F=aN23.66Y (0<a ≤ 1, 0<N<1), where a is the coefficient related to the combustion temperature and mineral components, and Y denotes the initial ash content in coal char. The kinetics model CBPMK is then modified by integrating this self-derived function, and complex ash evolution is predicted during dynamic combustion process. Simulated char combustion characteristics (particle temperature and carbon conversion) are discussed in detail. With higher ash film fraction and a thicker ash film, both the particle temperature and carbon conversion rate decrease. For low to intermediate levels of burnout (N<0.6), the carbon conversion characteristics in the case of full ash dilution (F = 0) are identical to those in the normal combustion (F = f(N)). At the char burnout stage (N>0.8), the relative deviations from the normal carbon conversion ratio are more than +10% when ignoring ash film and -20% when ignoring ash dilution.

Experimental and mechanistic study on chemical looping combustion of caking coal

Under high-temperature batch fluidized bed conditions and by employing Juye coal as the raw material, the present study determined the effects of the bed material, temperature, OC/C ratio, steam flow and oxygen carrier cycle on the chemical looping combustion of coal. In addition, the variations taking place in the surface functional groups of coal under different reaction times were investigated, and the variations achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed. As revealed from the results, the carbon conversion ratio and rate were elevated significantly, and the volume fraction of the outlet CO2 remained more than 92% under the oxygen carriers. The optimized reaction conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900 °C, an OC/C ratio of 2, as well as a steam flow rate of 0.5 g·min−1. When the coal was undergoing the chemical looping combustion, volatiles primarily originated from the pyrolysis of aliphatic CH3 and CH2, and CO and H2 were largely generated from the gasification of aromatic carbon. In the CLC process, H2O and CO2 began to separate out at 270 °C, CH4 and tar began to precipitate at 370 °C, and the amount of CO2 was continuously elevated with the rise of the temperature.