Gas Syngas Research Articles

From biomass to power: High-performance reactor design for coking-resistant operation

Biomass gasification coupled with solid oxide fuel cell (SOFC) technology utilizes the gas generated from biomass gasification directly as fuel for SOFC, thereby realizing power generation from solid waste. This technology combines the carbon–neutral feature of biomass with the high efficiency and low emissions of SOFC, making it a promising route for clean energy generation. However, biomass gasification syngas possesses a complex composition, including a high concentration of inert gases, which imposes higher requirements on SOFC. This study developed a multi-channel, hierarchical structural design based on the commercial NiO-yttria-stabilized zirconia (YSZ) material system, realizing high-performance power generation using biomass gasification syngas. The results showed that the combination of a unique structural design and an enhanced interface electrochemical reaction effectively mitigates the influence from inert composition dilution. When operating in gasification syngas with nearly 60 % inert components, the power density can reach 2.07 W·cm−2 (750 °C). In addition, due to the spatial separation of the inert support region and the electrochemically active region, the effect of controlling the position of carbon deposits was achieved, demonstrating 100 h stable operation with dry biomass gasification syngas. Hence, the combination of micro-tubular SOFC with distinctive structural regulation and biomass gasification exhibits promising prospects for further development.

Dry reforming of toluene over Ni/pyrochlore catalysts with A-site Sr doping

Dry reforming with CO2 is one potential method for tar removal and further production of syngas in biomass gasification, but the crucial catalysts with good reaction characteristics are still being developed. In the work, Ni/pyrochlore was proposed to be utilized as catalysts in the dry reforming of tar, and thermodynamic calculation, reaction progress test, and materials characterization were conducted to reveal dry reforming characteristics over Ni/pyrochlore catalysts and the reaction mechanism behind. Results show that YS0.2C catalyst exhibits the best activity (toluene and CO2 conversion of 70.1% and 79.5%) and stability among all catalysts under the optimized conditions of 700 °C with a CO2/toluene molar ratio of 7. Analysis on physicochemical properties of the catalysts indicate Sr doping can effectively promote catalytic reforming by enhanced interaction between Ni and support, CO2 adsorption and oxygen mobility. The work offers a promising catalyst type in improving tar removal by dry reforming.

In-situ biomethanation of high CO content syngas in agricultural biogas digesters

To meet global energy demands, syngas with high CO content (>50 %) generated from hydrothermal gasification of agricultural residues or wood, could be utilized as a co-substrate in anaerobic digestion (AD) processes for conversion into CH4. This study investigated in-situ biomethanation using synthetic gas (55 % CO, 35 % H2, and 15 % CO2), mimicking wood gasification syngas, during AD of cow manure, the most abundant agricultural waste. A continuously stirred tank reactor (CSTR) served as a control and was fed only cow manure, while the other two reactors were fed syngas with or without gas recirculation at different gas loading rates (GLRs).In-situ syngas injection in AD of cow manure at GLRs ≤0.3 L LRV−1 d−1 improved overall CH4 productivity compared to the control (0.35 ± 0.1 vs. 0.29 ± 0.1 L LRV−1 d−1), though the CH4 content (45 ± 5 %) was lower than the control reactor (62 ± 3 %), indicating a need for biogas upgrading. Gas recirculation enabled higher CO and H2 conversion efficiencies of 99–100 % but considerably decreased CH4 productivity from cow manure. In-situ biomethanation enhanced the relative abundance of hydrogenotrophic methanogens, highlighting their role in syngas conversion to CH4.

Biosolid Gasification Performance Prediction Using a Stoichiometric Thermodynamic Model.

The gasification process can recover energy from biosolids produced in wastewater treatment. This paper developed a stoichiometric thermodynamic equilibrium model for biosolid gasification based on the biosolid properties, thermodynamic database, and equilibrium constants. If the calculation result showed that the quantity of char was negative, the quantity of char was put to zero, and the simulation was carried out again. The model was first verified by woody gasification under isothermal conditions, and the influence of a given temperature on biosolid gasification was simulated. The model further investigated the effects of different feedstock types, moisture contents, equivalence ratios, and reaction extensions on the adiabatic temperature, exergy efficiency, and syngas properties under autothermal conditions. The four factors were all the main factors for adiabatic temperature. The exergy efficiency depended more on the operation conditions than on the feedstock type. The H2 concentration of the dry syngas in biosolid gasification exhibited a curve both against the given temperature under isothermal conditions and against the moisture content under autothermal conditions.

Experimental research on condensation flow and heat transfer characteristics of immiscible binary mixed vapors on different wettability wall surfaces

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors.

Quantum chemical study on non-thermal plasma degradation tar in gasification syngas

The bond dissociation energies (BDEs) of benzene, toluene, and naphthalene which are the main components of tar in fluidized bed gasification syngas have been investigated by B3LYP method at 6-31G (d, p), 6-31G+ (d, p), 6-31G++ (d, p) and 6-311G++ (d, p) basis setsof density functional theory (DFT).The structures of benzene, toluene, naphthalene, and corresponding radicals were optimized, and their total energiesand zero-point energies (ZPE) were calculated.The frequency analysis was carried out, then, the transition state and the high order saddle were excluded, and the influence of zero point energy scaling factors was neglected.The results showed thatthe BDEs decreased with increasing computational basis sets. The calculated results obtained by B3LYP/6-31G (d, p) are much closer to the results of the documents than the other three basis sets. This indicates that the basis set of B3LYP/6-31G (d, p) is much more credible in reproducing the BDEs. The lowest electron energy values for the ring opening of benzene, toluene and naphthalene are 8.05 eV, 7.45 eV, and 7.35 eV, respectively, indicating that when the energy of high-energy electrons reaches 8.05 eV, the ring of aromatic hydrocarbon can be broken.

Thermodynamic Simulation of the Interaction Reaction between Copper-Based Oxygen Carrier and Acid Gases from Municipal Solid Waste Pyrolysis

To reveal the interaction reaction of copper-based oxygen carriers with acid gases during chemical looping with oxygen uncoupling of MSW pyrolysis and gasification syngas, the thermodynamic analysis is employed by HSC Chemistry. The thermodynamic simulation results show that the products of the copper-chloride interactions are solid CuCl, gaseous Cu3Cl3 (g), and CuCl (g), and no solid CuCl2 is formed. In addition, it’s found that CuCl (g) originates from the high-temperature decomposition of the complex Cu3Cl3 (g). At a sufficient amount of OC, the interaction products of copper-based OC with H2S are CuSO4, SO2, and Cu2SO4, while Cu2S and CuS disappear. Compared to HCl, H2S dominates during the competitive reaction or adsorption with copper-based oxygen carrier or CaO. Due to the capture of Cl and S in the gaseous state of Ca2+, the lattice oxygen of chlorinated or sulfated oxygen carriers can be restored, suggesting that CaO can be used as an in situ dechlorinator for CLOU. The results of this work will provide theoretical guidance for the inhibition of copper-based oxygen carriers chlorination loss and active design of multifunctional oxygen carriers.

Bioconversion of C1 gases and genetic engineering modification of gas-utilizing microorganisms

C1 gases including CO, CO2 and CH4, are mainly derived from terrestrial biological activities, industrial waste gas and gasification syngas. Particularly, CO2 and CH4 are two of the most important greenhouse gases contributing to climate change. Bioconversion of C1 gases is not only a promising solution to addressing the problem of waste gases emission, but also a novel route to produce fuels or chemicals. In the past few years, C1-gas-utilizing microorganisms have drawn much attention and a variety of gene-editing technologies have been applied to improve their product yields or to expand product portfolios. This article reviewed the biological characteristics, aerobic or anaerobic metabolic pathways as well as the metabolic products of methanotrophs, autotrophic acetogens, and carboxydotrophic bacteria. In addition, gene-editing technologies (e.g. gene interruption technology using homologous recombination, group Ⅱ intron ClosTron technology, CRISPR/Cas gene editing and phage recombinase-mediated efficient integration of large DNA fragments) and their application in these C1-gas-utilizing microorganisms were also summarized.

The effect of CaO on coal gasification reaction with high-temperature copper slag as catalyst

ABSTRACT In order to improve the calorific value and reducibility of the syngas produced by traditional coal gasification technology, and to solve the problem of high cost of heat source in coal gasification, this paper proposes to use high-temperature copper slag as the heat carriers and catalyst for coal gasification, and CaO as the CO2 adsorbent during the coal gasification reaction. In this way, the proportion of H2 in the syngas gas can be increased, and the coal gasification reaction can be improved. In the experiment, the samples with different ratios were fully mixed, and then thermogravimetric experiment and gasification experiment were carried out. Through research, the following rules were found. The use of high-temperature copper slag as the heat source and catalyst in coal gasification can lead to a 20% increase in the final weight loss rate. Additionally, when CaO is used as the CO2 adsorbent during the coal gasification reaction, a noticeable secondary weight loss occurs at around 600°C and can reach a maximum speed of 0.19%/min. The use of the C/S/CaO = 1/1/2 ratio can result in a maximum weight loss rate of 23%. Meanwhile, the C/S/CaO = 1/2/1 group has been shown to achieve a maximum weight loss speed of 0.5%/min, and the C/S/CaO = 1/1/1 group exhibits a maximum secondary weight loss speed of 0.32%/min. The samples after gasification experiment were analyzed by SEM, CaO produced clustered iron-based and porous structure on the surface of copper slag in gasification reaction. Based on the Coats-Redfern method, kinetics of gasification reaction is obtained, and the optimum fitting function is C2, mechanism functions didn’t change with the variation of C/S/CaO. The research results suggest that CaO and copper slag can both enhance the coal gasification reaction. In addition, CaO is proven to be a more affordable and accessible CO2 adsorbent compared to other alternatives.

Numerical Analysis of the Deposition Characteristics in the Initial Deposition Stage in RSC

The coal gasification syngas cooler is important for recovering the sensible heat generated during coal gasification. The ash layer formed on the heat transfer surface can seriously decrease the heat exchange efficiency. Establishing the initial layer is a prerequisite for massive ash deposition and will accelerate the accumulation of the ash and slag particles. In this study, numerical simulations are conducted to analyze the behavior of ash particles in large-scale industrial equipment. The deposition characteristics during the initial fouling and slagging stage in RSC are explored. The results show that in this stage, ash or slag particles mainly stick on the side wall, and only small particles deposit on the upper cone. The surface energy is the dominant factor influencing the composition of the initial layer. The adhesion ratio of FeS2 and ZnS particles is over ten times higher than that of SiO2 particles. With the decrease of the inlet flow rate and the increase of the inlet swirl velocity, the location corresponding to the maximum deposition proportion moves upward, and the local maximum deposition proportion increases.

Predicting municipal solid waste gasification using machine learning: A step toward sustainable regional planning

The gasification process can treat and valorize municipal solid waste (MSW) in an environmentally and economically friendly way. Using this process, MSW can be safely disposed of and sustainably converted into bioenergy as part of regional planning. Experimental laboratory data is a key component in designing, optimizing, controlling, and scaling up MSW gasifiers. However, most researchers lack the resources and time to conduct experiments. Machine learning (ML) technology can resolve this issue by detecting patterns and hidden information in published data. Hence, the present study aims to construct an inclusive ML model to predict and understand the MSW gasification process. The objective is to establish a consistent and homogeneous database containing MSW sources under different gasification conditions, followed by an analysis of the database using statistical methods. Three ML models are used to predict the distribution of syngas, char, and tar and the quality of syngas in MSW gasification using feedstock characteristics and gasification parameters. When a gradient boost regressor is used to model the process, the prediction accuracy is highest (R2 > 0.926, RMSE <6.318, and RRMSE <0.304). SHAP analysis is successfully used to understand the significance and contribution of descriptors on targets in the modeling process.

Effect of calcination temperature on the attrition and activity of CuO/NiO/olivine for producing syngas in biomass chemical looping gasification

An oxygen carrier (OC), with a long lifetime and better reactivity, has become the key to the biomass chemical looping gasification (BCLG) process. In this study, CuO and NiO supported on olivine (Cu/Ni/O) was prepared at different temperatures (900–1300 °C). Various characterizations including XRD, SEM, BET, H2-TPR, TG and TG-FTIR were used to investigate the effect of calcination temperature on the composition, morphology, multiple redox, oxygen carrying capacity and activity of the resultant OCs. And the BCLG experiments were conducted in a micro fluidized bed reactor (MFBR) to examine the performance of OCs. The results showed that CuFe2O4 and NiFe2O4 phases were observed after CuO and NiO were loaded onto peridot. The increase of calcination temperature results in the decrease of surface area and oxygen-carrying capacity of the OC to 1.305 m2/g and 1.93 wt% at 1300 °C from 4.760 m2/g and 3.60 wt% at 900 °C. The final weight loss of OCs with cotton stalk (CS) showed the same variation trend as that of redox process of OCs. However, the anti-resistance of the OC was greatly improved, especially the 1100-Cu/Ni/O calcinated at 1100 °C showed better anti-resistance with the attrition rate of 0.09 wt% and pulverization rate of 0.41 wt%. Under the optimal operating conditions (mass ratio of OC to biomass = 30:1, steam injection rate = 0.05 g/min and temperature = 800 °C), the highest gasification efficiency of 59.2 % and syngas yield of 0.71 Nm3/kg were obtained over 1100-Cu/Ni/O. The cyclic experiments demonstrated better anti-sintering and cyclic performances of 1100-Cu/Ni/O, which made it very attractive for the BCLG.

New insights into the mechanism of biomass char steam gasification process by oxygen-containing functional group as aromatic carbon boundaries: Experimental and DFT study

Reducing carbon-based fossil fuel dependence and increasing environmentally friendly energy resources are crucial in combating global warming. Steam gasification technology is the most suitable for hydrogen production from biomass fuels. In addition to the main element “carbon,” the oxygen in biomass char exists in the form of oxygen-containing functional groups attached to the char surface. It could also impact the reactivity of biomass char during steam gasification. In this study, the biomass char model compounds are constructed with oxygen-containing functional groups as aromatic carbon boundaries at 800-1200℃. Firstly, the steam gasification process of different oxygen-containing aromatic boundaries is investigated using a high-temperature steam gasification experimental system. Results show that the presence of oxygen-containing functional groups increases the yield of combustible gas by nearly 20% and facilitates the gasification reaction. The oxygen-containing functional groups substituted at different positions had different effects on the gasification syngas fraction. The proportion of hydrogen produced when each oxygen-containing functional group reacted alone in the composite boundary is 16% higher than their combined level. Subsequently, a theoretical analysis is performed using a density functional theory (DFT). The oxygen-containing functional groups are preferentially generated and released as CO, and the remaining oxygen is transferred to small-molecule gaseous products. The formation of an H2 molecule normally consists of one hydrogen atom each from the H2O molecule and biomass char. The biomass char is expected to preferentially provide the oxygen-containing functional group's H rather than the aromatic boundary's H. It is demonstrated that the existence of oxygen-containing functional groups promotes hydrogen production. The optimal reaction paths and the rate-determining steps for each type of boundary are also determined. It provides new insights and a theoretical basis for understanding the biomass steam gasification process in detail.

High-Temperature Syngas Desulfurization and Particulate Filtration by ZnO/Ceramic Filters.

Combustible gas (e.g., gasification syngas) cleaning at high temperatures can obtain further gains in energy efficiency for power generation and importantly leads to a simplified process and lower cost as a commercially viable source of clean energy. Thus, a feasibility study for high-temperature desulfurization (HTDS) and additional high-temperature particulate filtration (HTPF) of a raw syngas using ZnO sorbent-dispersed Raney CuO (ZnO/R-CuO) and ceramic filter (ZnO/CF) has been carried out. By synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, mainly Zn(II) and Cu(II) are found in the ZnO/R-CuO sorbents. Both ZnO and R-CuO in the sorbents are involved in HTDS (1% H2S) at 873 K to form ZnS, Cu2S, and a small amount of CuS and reach relatively high HTDS efficiencies (82-90%). In addition, regeneration of the sulfurized sorbent by oxidation with O2 at 873 K (HTRG) for 1 h can restore ZnO and CuO for continuous and repetitive HTDS-HTRG cycles. To facilitate the HTDS engineering applications by the ZnO/R-CuO sorbents, their reaction rate constant (8.35 × 104 cm3/g/min) and activation energy (114.8 kJ/mol) at 873 K have also been determined. Furthermore, the ZnO/CF sorbent/filter can perform HTDS and additional HTPF at 873 K with very high particulate removal efficiencies (>98%). This demonstrates the feasibility for hot-syngas cleaning with a much better energy efficiency and lesser cost for cleaner power generation.

Numerical investigation of biomass and liquefied natural gas driven oxy-fuel combustion power system

Biomass as carbon-neutral renewable energy is beneficial for carbon emission reduction in power sectors. A biomass gasification integrated natural gas combined cycle is proposed in this study. Oxy-fuel combustion is utilized to realize CO2 capture with cold energy of liquefied natural gas applied for power consumption reduction. CO2 and H2O in the flue gas are separated and adopted as gasifying agents. The composition of natural gas and gasification syngas injected into the combustion chamber is restricted by the heat value and H2 concentration. The biomass mixing ratio and global energy efficiency under different gasification conditions are evaluated using Aspen Plus software. Increasing CO2 and decreasing H2O flow rate in gasifying agents are positive for increasing biomass mixing ratio which can achieve a maximum of 0.33. Gasification temperature increased from 650 °C to 950 °C causes an evident enhancement in energy efficiency. On the contrary, both biomass mixing ratio and energy efficiency are less sensitive to gasification pressure, particularly at low gasification temperature. The integrated system reaches the highest energy efficiency of 0.520 with a biomass mixing ratio of 0.10. Accordingly, the electricity cost is estimated to be 0.102 $/kWh, and the net CO2 emission considering fuel production is 91.0 g/kWh.

Fluidized bed gasification of solid recovered fuels in a 500 kWth pilot plant

On the way to climate-neutrality with low resource consumption, the economics worldwide needs ways to obtain high-quality products from existing material flows. If waste is used as a feedstock for gasification, high-quality syngas is obtained from which new products for the chemical industry (e.g. methanol) or the transport sector (Fischer-Tropsch products) can be obtained. The fluidized bed-based High-Temperature-Winkler process is particularly suitable for the gasification of solid recovered fuel (SRF) and biomass that are difficult to grind since the feedstock can be processed in lump form. The gasification characteristics of SRF pellets were investigated in a 500 kWth pilot gasifier at the Technical University of Darmstadt. After a co-gasification with pre-dried lignite, a mono SRF gasification could be realized. This paper presents the effects of operating temperature and the SRF content in the feedstock on the syngas quality, which is characterized by the target components CO and H2, the undesired fraction of CH4, and some representative higher hydrocarbons. It could be shown, that the syngas gas components CO and H2 depend mainly on the gasification temperature and not on the used feedstock. On the other hand, the higher amount of volatiles in the SRF fraction rises the methane concentration and the amount of higher hydrocarbons in the syngas. It was observed that these components are decomposed at higher gasification temperatures and an almost tar-free syngas is produced.

Spatio-Temporal Characteristics of Heat Transfer of Methanation in Fluidized Bed for Pyrolysis and Gasification Syngas of Organic Solid Waste

Spatio-Temporal Characteristics of Heat Transfer of Methanation in Fluidized Bed for Pyrolysis and Gasification Syngas of Organic Solid Waste

Developing gasification process of polyethylene waste by utilization of response surface methodology as a machine learning technique and multi-objective optimizer approach

This study set out to evaluate the performance of response surface methodology as a machine learning technique on gasification process of polyethylene waste. Different models were developed for predicting gas yield, cold gas efficiency, carbon dioxide emission and lower heating value of syngas in gasification of polyethylene waste using response surface methodology. The accuracy and validity of these models were checked in comparison with the results obtained from the validated model. Most studies in the field of response surface methodology have only focused on its application for multi-objective optimization and largely have ignored its utilization as a machine learning technique. Central composite design was utilized to develop a model between the variables and the responses. Pressure and temperature of the gasifier, moisture content of polyethylene and equivalence ratio were the variables and the responses were gas yield, cold gas efficiency, carbon dioxide emission and lower heating value of syngas. The findings revealed that root mean square errors of the models developed by response surface methodology were 0.235, 0.438, 0.294 and 1.999 indicating their high validity. Finally, multi-objective optimization of polyethylene waste gasification was carried out using response surface methodology resulting in gas yield of 96.29 g/mol, cold gas efficiency of 76.22%, carbon dioxide emission of 4.66 g/mol and lower heating value of 493.44 kJ/mol. The optimum responses were predicted by response surface methodology with errors smaller than 5%.

Combustion characteristic of low calorific gas under pilot ignition condition—Exploring the influence of pilot flame products

Low calorific gas (LCG) is a huge thermal energy resource, but its utilization is poor due to the low reactivity and a tendency of high NOx emission. Present work proposed to combine the pilot ignition and air staging approach, to respectively overcome the difficulty in LCGs ignition and reduce its NOx emission. Experiment and numerical simulation were conducted to explore combustion characteristic of LCG during pilot ignition. Some previous proposed kinetics models for CH4 or CO combustion were evaluated that whether they capture the NO or H2O influence, respectively, within this complex flue gas atmosphere, and the mechanisms were further explored. Adding 0.04 vol% NO reduces the ignition temperature of CH4 based LCG from 750 to 510 °C under pilot ignition condition. This promotion is via a NO/NO2 cycle of NO + HO2→NO2+ OH andCH3+ NO2→CH3O + NO, to enhance CH3 oxidation rate by ∼ 30 times. In that cycle, the NO formation (NO2 consumption) rate is higher than the NO2 formation (NO consumption), causing only NO but no NO2 was preserved in flue gas under pilot ignition condition. The effect of adding NO to CO based LCG is dependent on H2O presence, where it makes no difference without H2O presence, but has an improvement on “moist gas” reactivity. Neither the commonly used kinetics models of CH4 combustion nor those for CO contained syngas gas can predict reactivity of “dry CO contained LCG” under pilot ignition condition.

A novel MILD gasifier for crushed low-grade solid fuels

A novel MILD gasifier for crushed low-grade solid fuels is designed and developed to overcome the limitations of conventional packed bed and fluidized bed gasifiers, and the performance parameters of the gasifier are presented in this paper. MILD conditions in the gasifier are created by the velocity differences of the fuel-carrying enriched air jet and off-centred high-speed jets issuing CO2. Crushed high-ash coals and groundnut shells are the two low-grade fuels of particular interest to this study. Gasification of these fuels is performed on the fuel rich side and close to volatiles stoichiometry to enhance the Net CO2 Conversion (NCC), as reported in the earlier studies. Gasification parameters such as the syngas gas composition, fixed carbon conversion, gas calorific value, gasification efficiency, and NCC are evaluated and are compared against the performance of the existing conventional gasifiers. The temperature profile in the gasifier is maintained in the range of 900–1200 ∘C, ensuring self sustained stable ash fusion-free operations. Although, fixed carbon conversion and NCC are observed to be similar to that of conventional gasifiers, the lower calorific value and gasification efficiencies are seen to be lower than the conventional gasifiers. This is attributed to the high heat loss encountered in this laboratory scale MILD reactor. Normalized gasification efficiencies, accounting for the heat loss, is on par with the conventional systems. The latest design has the potential to substitute conventional gasifiers for low-grade powdered solid fuels.