Carbon Conversion Efficiency Research Articles

Efficiency Enhancement of the Single Line Multi-Stage Gasification of Hungarian Low-Rank Coal: Effects of Gasification Temperature and Steam/Carbon (S/C) Ratio

Coal gasification is considered a promising solution for the production of synthetic fuels and eventually as a fuel for combined heat and power systems and heating buildings. There are several factors that affect the gasification efficiency and syngas quality, such as gasification parameters (temperature, pressure, etc.), reactants and their ratio, utilisation of catalysts, and gasifier design. The multi-stage gasifier is known as a promising approach in the enhancement of process efficiency, as well as the syngas quality. In this study, the Hungarian brown coal was gasified in a two-stage gasifier. The pyrolysis stage was kept at 600 °C. The gasification stage was conducted at 700, 800, and 900 °C. The steam per carbon (S/C) ratio was examined at 0.75, 1.00, and 1.25. The positive effects of increasing gasification temperature on char and dry gas yield were obviously shown at all S/C ratios. The increase in the S/C ratio did not show a positive effect at all temperature conditions, especially at 700 and 900 °C. The highest dry syngas yield was 1.14 Nm3/kgcoal obtained at 900 °C and the S/C ratio of 1.25. The increase in the gasification temperature also had a significant impact on the volume fraction of CO and CO2. Meanwhile, the syngas concentration varied slightly when the S/C ratio increased from 0.75 to 1.25. From a chemical utilization point of view, the gasification temperature at 900 °C and the S/C ratio of 1.25 resulted in the most promising H2/CO ratio of 1.99. In addition, the highest carbon conversion and cold gas efficiency were achieved at 900 °C and an S/C ratio of 1.00–1.25, respectively.

Experimental study on effect of temperature and equivalence ratio on biomass syngas generation for fluidized bed gasifier techniques

ABSTRACT This paper presents a comparative study of selected woody biomass for the potential of fuel gas generation that can be used for heat and power generation using a Fluidized Bed Gasifier (FBG). The characteristics of produced energy gas using the thermochemical Bubbling Fluidized Gasification Technique for selected woody biomass feedstock materials were studied for selected temperatures. Initially, the CFD analysis has been implemented to determine the feasible equivalence ratio (ER) for the selected biomasses. Using CFD ANSYS solver studied gas-solid interaction and gasification process inside a fluidized bed biomass gasifier. Experimental investigations were conducted on the FBG reactor for a feeding rate of 10 kg/hr of biomass materials. Experimental investigations were conducted on the FBG reactor for a feeding rate of 10 kg/hr of biomass materials. The work characteristics of produced gas were investigated by the experimental process for bagasse, groundnut shell, and wooden shavings as feedstock biomass materials for the gasification bed temperature at 500ºC, 550ºC, and 600ºC and Equivalence Ratio (ER) ratio of 0.30. Air was employed as a gasifying agent, and sand with limestone was used as the fluidized bed material. The results show that the fluidized bed has higher temperatures of 600ºC and above, generating higher Calorific Value (CV) syngas. Among all three feedstocks, groundnut shells produced gas HHV of 4.21 MJ/m3. The lowest HHV for bagasse at 500ºC of 3.01 MJ/m3. The effect of bed temperature on Carbon Conversion Efficiency (CCE) shows maximum CCE for bagasse is 60.86%, noted at 550ºC, and the minimum for wooden shaving at 550ºC is 57.69%.

Gasification of a bituminous coal in 15MWth KEDA®circulating fluidized-bed gasifier with high-temperature preheating

The industrial-scale high-temperature preheating air-blown KEDA®circulating fluidized-bed (KEDA®CFB) gasification process has been developed by KEDA(ANHUI) Clean Energy Co., Ltd. to produce industrial fuel gas. This paper presents the design and the first operational results of a 15MWth industrial-scale demonstration KEDA®CFB plant where about 3.6 tons bituminous coal was gasified per hour. The influences of the steam to coal ratio (SC), the equivalence ratio (ER), and the oxygen concentration (OC) on gas composition, gas high heating value (HHV), carbon conversion efficiency (CCE), and cold gas efficiency (CGE) were investigated systematically. It is shown that increasing SC from 0.18 to 0.38 favors the water–gas reaction and CO–shift reaction that causes H2 and CO2 content in the raw gas to rise. As ER increases to 0.27, it is conducive to the partial combustion and Boudouard reactions of char, and the HHV and CGE of gas products are 6.38 MJ/Nm3 and 66.8%, respectively. As OC increased from 21 vol% to 27 vol%, the CCE increased from 71.8% to 79.8% mainly due to the increase of gasification reaction rate and residence time. The operational results in this work can significantly contribute to the design and operation of industrial-scale gasifiers, and the development of numerical models.

Prediction and optimization of syngas production from Napier grass air gasification via kinetic modelling and response surface methodology

In this research, a kinetic model was developed for Napier grass air gasification using Aspen Plus software and thereafter collated and validated with experimental results obtained from a lab-scale fluidized bed reactor. Herein, the model was further employed to investigate the effect of gasification operating parameters, including temperature (650–850) °C, equivalence ratio (0.2–0.4), and moisture content (0–18) wt.% on products’ yields and syngas quality. The model was segregated into four sections: the drying, devolatilization, combustion, and reduction sections. The outputs of tar, gas, and char from the devolatilization section were defined by external Microsoft Excel subroutine. Kinetic parameters were incorporated in the combustion and reduction sections to simulate tar cracking, oxidation, and reduction reactions. A good agreement was observed between the predicted and experimental results. Furthermore, response surface methodology (RSM) was employed to analyze the mutual effects of process variables and perform multi-objective optimization to maximize producer gas yield, higher heating value, carbon conversion efficiency, and cold gas efficiency by incorporating the predicted results from the developed kinetic model. The optimized syngas yield and HHV were 69.42 wt% and 8.14 MJ/Nm3 at 850 °C, 0.3021, and 15.69 wt% for temperature, ER, and moisture content, respectively.

Air gasification of high-ash solid waste in a pilot-scale downdraft gasifier: Experimental and numerical analysis

The present work investigates the effect of process parameters on the gasification potential of high-ash solid wastes in a downdraft gasifier using experimental and simulation studies. The air gasification of lignocellulosic garden waste was conducted in a lab-scale fixed bed reactor for the equivalence ratio range of 0.25–0.39. An exhaustive model was devised in Aspen Plus process simulator incorporating the parametric geometry of the gasifier and comprehensive gasification kinetics. Furthermore, the developed model was validated using the experimental results and a fair agreement was obtained. Both the experimental and simulation studies affirmed that the maximum gasification efficiency was obtained at an equivalence ratio of around 0.32. Sensitivity analysis was conducted to scrutinize the effect of critical process parameters on output parameters such as producer gas composition, lower heating value, carbon conversion efficiency, and system's cold gas efficiency. This modeling approach provides valuable insight for generating producer gas from low-grade biomass by optimizing the operating parameters of the downdraft gasifiers. This research can also assist as a guide for stakeholders in renewable energy, waste to energy, and environmentally friendly technologies.

Quantitative study on thermal conversion behaviours and gas emission properties of biomass in nitrogen and in CO2/N2 mixtures by TGA/DTG and a fixed-bed tube furnace

Introducing CO2 in the pyrolysis medium could not only provide a route for CO2 sequestration but also potentially increase the carbon conversion efficiency. Herein, to reveal the effects of introducing CO2 in the pyrolysis medium alongside N2 on the thermal conversion behaviours of biomass, a series of pyrolysis/gasification experiments with/without CO2 in the pyroysis medium were conducted in a thermogravimetric analyser (TGA) and a self-established fixed-bed experimental system. The effects of reaction temperature, atmosphere and residence time on syngas emissions and compositions were elucidated in details. Introducing CO2 in the pyrolysis agent resulted in an additional consumption of residuals, promoting CO release due to char-CO2 reactions. During gasification, the total weight loss increased with increasing CO2 concentration. As the pyrolysis reaction was prolonged, the release of CO, CO2, CH4, and H2 occurred in chronological order. Reaction temperatures below 600 °C had negligible effects on CO emissions. For pyrolysis under N2, the H2 concentration in syngas increased obviously with increasing temperature, while that of CO2 presented the opposite trend, indicating that high temperature favoured H2 release while CO2 emissions could be inhibited. The particle residence time had no obvious influence on either gas emissions or yields in a CO2-containing atmosphere.

Study on the mechanism and reaction characteristics of metal-supported phosphogypsum as oxygen carrier in a chemical looping gasification application

This study aimed to explore the chemical looping gasification (CLG) reaction characteristics of the metal-supported composite phosphogypsum (PG) oxygen carriers (OCs) and the thermodynamic mechanism. The FactSage 7.1 thermodynamic simulation was used to explore the oxygen release and H2S removal mechanisms. The experimental results showed that the syngas yield of CLG with PG-CuFe2O4 was more than that with PG–Fe2O320/CuO40 or PG–Fe2O330/CuO30 OC at 1023 K when the water vapor content was 0.3. Furthermore, the maximum syngas yield of the CO selectivity was 70.3% and of the CO2 selectivity was 23.8%. The H2/CO value was 0.78, and the highest carbon conversion efficiency was 91.9% in PG-CuFe2O4 at the gasification temperature of 1073 K. The metal-supported PG composite oxygen carrier was proved not only as an oxygen carrier to participate in the preparation of syngas but also as a catalyst to catalyze coal gasification reactions. Furthermore, both the experimental results and FactSage 7.1 thermodynamic analysis revealed that the trapping mechanism of H2S by composite OCs was as follows: CuO first lost lattice oxygen as an oxygen carrier to generate Cu2O, which, in turn, reacted with H2S to generate Cu2S. This study provided efficient guidance and reference for OC design in CLG.

Sewage sludge treatment via hydrothermal carbonization combined with supercritical water gasification: Fuel production and pollution degradation

Aqueous phase byproduct from hydrothermal carbonization of sludge (named AHT) has high COD and TOC, supercritical water gasification (SCWG)can efficiently convert AHT into rich-H2 syngas. This study investigated the effect of temperature on syngas production, elements distribution and pollutants decomposition during the HTC of sewage sludge and SCWG of AHT. Compared to traditional directly SCWG of sludge, the combined method could produce syngas with higher H2 proportion and lower gaseous sulfur concentration. The maximum H2 proportion and carbon conversion efficiency (CE) in syngas could reach 59% and 30.40%. Meanwhile, higher SCWG temperature can reduce the sulfur concentration of syngas. SCWG effectively reduce the COD and TOC in AHT. With HTC and SCWG temperature increased, the concentration of total nitrogen (TN) gradually decreased but NH4+ ions concentration (NH4+-N) increased in aqueous phase product.

Recycling exhaust emissions of internal combustion engines within the gasification systems: Performance and analysis

The current research presents a proposed system for the recycling of the exhaust emissions from internal combustion engines (ICE) inside the air-blown gasification system. A 2D Computational Fluid Dynamics (CFD) model is investigating the novel research idea and further study the combined effects on the gasifier performance. To this end, the numerical model will be validated against wide range of operating conditions. Additionally, the effect of exhaust emissions injection along with air (the gasifying medium) on gasification, carbon conversion, system performance, syngas composition, and yield will be investigated. A new parameter – CB ratio – is defined, which is the exhaust/emissions from ICE gases to the feedstock mass ratio. Optimum values of CB are recommended between (0.05–0.25). The research idea resulted in boosting the yield of H2, and CO by 10.3, and 3.3 mol.% respectively, and correspondingly, higher heating values by 5.8% within the optimum range of CB. For the same range, N2, and CO2 emissions are found to decrease within the gasifier. The exhaust emissions stream with high temperature and rich content of CO2, and H2O resulted in higher turbulence, velocity, and mixing inside the gasifier. Thus, enhanced the gasification reactions i.e., boudouard, and water gas reactions. Moreover, producer gas yield, carbon conversion and gasification efficiencies are found to be 28, 10, and 11% higher than air gasification under the same working conditions respectively. The proposed design (20 kW gasifier) – i.e., small scale industrial gasification unit – is found to consume around 3.5 kg/hr of the ICE emissions. Thus, preserving the environment, reducing CO2 and GHG emissions, and increasing the gasifier performance. The significant outcomes of the study are applicable for different scales of air-blown gasifiers.

Effect of Equivalence Ratio on EFB Pellet Gasification Characteristic using Thermal Arc Plasma Suction Downdraft Gasifier

The present study investigated the performance of thermal arch plasma suction downdraft gasification which utilizing pelletized empty fruit bunch as a feedstock in producing syngas with high thermochemical conversion efficiency. Gasifying medium of air was used in this system. Syngas produced was evaluated and measured in terms of gas composition, carbon conversion efficiency, cold gas efficiency, syngas yield and calorific value. The effect of different equivalence ratio ranged from 0.18 to 0.46 was also evaluated. The results reported that syngas produced contained higher CO of 14.2 vol% at higher equivalent ratio, 0.42. In contrast to H2 content, higher composition of 9.92 vol% was produced at lower equivalent ratio, 0.18. HHV and CGE value was higher at equivalent ratio of 0.36 which correspond to the balanced constituent of CO, H2 and CH4 at this condition. CCE and syngas yield was maximum at higher equivalent ratio of 0.46 due to higher production of CO from carbon elements. The results of the present study provided a useful data and guideline of equivalent ratio range for operational of plasma downdraft reactor.

Syngas production by bio-oil steam gasification in a fountain confined conical spouted bed reactor

The combination of delocalized units for the fast pyrolysis of biomass to produce bio-oil followed by centralized units for the gasification of bio-oil appears as an economically attractive option for the full-scale production of syngas because transportation of bio-oil is less costly than that of biomass. First goal of this study lies in the validation of a bio-oil feeding device made up of a line-thermostated at 60–80 °C and a non-atomizing injector cooled by water. This injector allows feeding the crude bio-oil in continuous mode into the conical spouted bed reactor without being clogged by the pyrolytic lignin in the bio-oil. The effect of gasification temperature on gas properties, tar composition, and carbon conversion efficiency were assessed in the 800–900 °C range. The results show that temperature promotes tar reduction (from 40.7 to 12.5 g/Nm3), carbon conversion efficiency (from 91.2 to 96.3 %) and gas yield (from 1.37 to 1.85 Nm3/kg on a dry basis) as temperature is increased from 800 to 900 °C. A novel aspect of this study is the detailed characterization of the tar evolution with temperature, which, to our knowledge, is an aspect that has not been approached in the literature related to raw bio-oil gasification.

Modeling of air gasification of dark fermentation digestate in a downdraft gasifier

The paper presents the results of numerical simulation of the gasification process in a downdraft gasifier to produce syngas with high hydrogen content. For the first time, the possibility of using dark fermentation digestate as a feedstock for thermochemical conversion using air as an oxidizer at equivalence ratio (ER) of 0.45, 0.55 and 0.65 was investigated. Modeling of the gasification process was carried out in the software package Comsol Multiphysics. As a result of numerical studies, the concentrations of the main components of the syngas were obtained. The syngas yield at air gasification was 1.8 m3/kg. At the same time, the combustion heat of the generated gas varied from 3.1 to 3.9 MJ/m3 with the molar ratio (MR) being in the range from 3.1 to 3.9. The maximum content of hydrogen (26.94%) in syngas was achieved at an ER of 0.45. The hydrogen production efficiency HPE ranged from 23.8 to 27.3%. The thermal power that can be obtained from the syngas ranges from 47 to 59 kW. Carbon conversion efficiency coefficient (CCE) was 23.6–28.8%. Based on the design calculation, the main geometric parameters of a downdraft gasifier for the production of syngas from anaerobic digestates were obtained.

Biomass combustion behaviors based on online monitoring system: Morphological, thermodynamic and kinetic analysis

Identifying the matching law between the morphology, thermodynamic and kinetic characteristics of single biomass can significantly achieve high-efficiency combustion. A visual combustion furnace with online monitoring system was designed and built to record in real-time the apparent volume shrinkage, particle heating process and gas releasing behaviors of single biomass briquette during the combustion process. Furthermore, this work aimed to present a new method to infer the effect of ambient temperature on the pore structure of volatile precipitation and char combustion, mainly through a comparative analysis of the changes in shrinkage ratio and activation energy with carbon conversion efficiency (CCE). The higher the ambient temperature, the faster the biomass heating rate, and the earlier it reached the peak heating rate and the ambient temperature, but the heating process of biomass in the water evaporation stage was almost the same at different ambient temperatures. Oxygen concentration had a significant effect on the volume shrinkage and gas product releasing characteristics, but less on the particle heat transfer. After deducting the experimental system errors, the biomass reaction mode, activation energy and pore structure changed significantly around 40–45% CCE. When the CCE was less than 40%, the biomass mainly underwent volatile precipitation and combustion, with smaller apparent volume shrinkage but larger pore volume at 700 °C compared to 900°C ambient temperature. With the CCE greater than 45% and less than 70%, the char combustion dominated the reaction process, the apparent volume shrinkage was smaller, but the pore structure was more developed at higher ambient temperatures compared to lower temperatures. When the CCE exceeded 70%, the apparent volume and carbon conversion remained almost constant at 700°C, but the volume shrinkage ratio continued to decrease at 900°C ambient temperature. This research and proposed method provide more accurate fundamental support for modeling particle combustion at the reactor scale and designing biomass combustion systems.

Experimental assessment of a pilot-scale gasification plant fueled with olive pomace pellets for combined power, heat and biochar production

This research work examines the performance of an experimental gasification plant fueled with exhausted olive pomace pellets for the concurrent production of electricity, heat and biochar in the olive oil industry. The gasification plant consists of an air-blown downdraft fixed-bed gasifier that generates a lean fuel gas, termed producer gas, in a self-sustaining autothermal process. After conditioning of the producer gas in a cooling and cleaning unit, a four-stroke spark-ignition engine coupled to an electric generator is eventually used as power generation unit. An extensive experimental assessment of this facility was performed under partial and nominal load operation and was supplemented by a physicochemical analysis of the carbonaceous solid material discharged from the gasifier. The mass and energy balances of the gasification plant were calculated, including the carbon conversion efficiency and diverse energy conversion efficiencies. The results revealed an overall stable operation of the gasification plant in terms of composition and heating value of the producer gas and cogenerative production of electricity and heat in the engine–generator set. Under nominal operating conditions, the net electrical efficiency of the gasification plant was 12%–13%, with an average carbon conversion efficiency of the biomass feedstock into producer gas just above 80% and an average cold gas efficiency close to 70%.

Experimental study on a small-scale oxygen-enriched entrained flow biomass gasifier assisted by non-thermal arc plasma

A small-scale oxygen-enriched entrained flow biomass gasifier consisting of a non-thermal arc plasma torch and a stainless steel bellows was developed. The characteristics of the non-thermal arc plasma were diagnosed. The effects of oxygen concentration and bellows length on the gasification process using rice husk powder as feedstock at a feed rate of 27.1 g/min were studied. The results show that increasing the oxygen concentration of gasifying agent and using longer bellows both lead to the improvement of cold gas efficiency, carbon conversion efficiency, and yields of H2 and CO. The cold gas efficiency of the gasifier at a bellows length of 500 mm and oxygen concentration of 34.7% is 65.8%. And benefiting from low auxiliary energy consumption, the gasifier’s energy efficiency reaches 60.5%. The non-thermal arc plasma assists the entrained flow gasification by converting part of the feedstock into activated reactants.

Aspen plus simulation model of municipal solid waste gasification of metropolitan city for syngas production

It is apparent that the population, in general, is increasing and this rise in population increases both the waste production and energy requirements. The main objective of this study to tackle the increasing demand for energy and recycling waste into energy. We will be using Waste to Energy (WTE) technique to convert MSW into energy such as bio-fuel, Hydrogen-rich gas or Syngas. The model of simulation of steam gasification of MSW used in this study is based on ASPEN PLUS. Temperature, the ratio of steam to MSW, and the ratio of air to MSW have all been adjusted in a wide range. For the production of syngas, the impact of carbon conversion efficiency (CCE) and cold gas efficiency (CGE) has been studied. The results showed that by increasing the temperature from 700 °C to 1300 °C the H2 concentration increased from 37 to 51 mol%, CO concentration increases from 35 to 40 mol% and CO2 concentration decreases from 5 to 0.025 mol%. CGE also decreases from 95 to 82% while CCE increases from 80 to 85%. By increasing the steam to MSW ratio from 0.05 to 0.8 mass fraction the H2 concentration increased from 34 to 44 mol% but is maximum at 0.35 at which it is 53 mol%, CO concentration decreases from 43 to 16 mol% and CO2 concentration increases from 0.025 to 8.5 mol%. CGE and CCE also decreases from 94 to 45% and 90 to 44% respectively.And lastly by increasing the air to MSW ratio from 0.01 to 0.5 mass fraction the H2 concentration decreases from 47 to 39 mol% but peaks at 0.05 at which it is 48 mol%, CO concentration decreases from 41 to 31 mol% and CO2 concentration increases from 0.085 to 3.5 mol%. CGE and CCE also decreases from 92 to 55% and 87 to 70% respectively. To compare our data with the base case we have kept temperature at 900 °C S/MSW ratio at 0.11 and air/MSW ratio at 0.05 and it is concluded that our simulation is inline with the base case as our results are off by just 1–3% in terms of yield.

The Combined Impact of Ni-Based Catalysts and a Binary Carbonate Salts Mixture on the CO2 Gasification Performance of Olive Kernel Biomass Fuel

In the present work, the individual or synergistic effect of Ni-based catalysts (Ni/CeO2, Ni/Al2O3) and an eutectic carbonate salt mixture (MS) on the CO2 gasification performance of olive kernels was investigated. It was found that the Ni/CeO2 catalyst presented a relatively superior instant gasification reaction rate (Rco) compared to Ni/Al2O3, in line with the significant redox capability of CeO2. On the other hand, the use of the binary eutectic carbonate salt mixture (MS) lowered the onset and maximum CO2 gasification temperatures, resulting in a notably higher carbon conversion efficiency (81%) compared to the individual Ni-based catalysts and non-catalytic gasification tests (60%). Interestingly, a synergetic catalyst-carbonate salt mixture effect was revealed in the low and intermediate CO2 gasification temperature regimes, boosting the instant gasification reaction rate (Rco). In fact, in the temperature range of 300 to 550 °C, the maximum Rco value for both MS-Ni/Al2O3 and MS-Ni/CeO2 systems were four times higher (4 × 10−3 min−1 at 460 °C) compared to the individual counterparts. The present results demonstrated for the first time the combined effect of two different Ni-based catalysts and an eutectic carbonate salt mixture towards enhancing the CO production rate during CO2 gasification of olive kernel biomass fuel, especially in the devolatilization and tar cracking/reforming zones. On the basis of a systematic characterization study and lab-scale gasification experiments, the beneficial role of catalysts and molten carbonate salts on the gasification process was revealed, which can be ascribed to the catalytic activity as well as the improved mass and heat transport properties offered by the molten carbonate salts.

Achieving High Single‐Pass Carbon Conversion Efficiencies in Durable CO2 Electroreduction in Strong Acids via Electrode Structure Engineering

AbstractAcidic CO2 reduction (CO2R) holds promise for the synthesis of low‐carbon‐footprint chemicals using renewable electricity. However, the corrosion of catalysts in strong acids causes severe hydrogen evolution and rapid deterioration of CO2R performance. Here, by coating catalysts with an electrically nonconductive nanoporous SiC‐NafionTM layer, a near‐neutral pH was stabilized on catalyst surfaces, thereby protecting the catalysts against corrosion for durable CO2R in strong acids. Electrode microstructures played a critical role in regulating ion diffusion and stabilizing electrohydrodynamic flows near catalyst surfaces. This surface‐coating strategy was applied to three catalysts, SnBi, Ag, and Cu, and they exhibited high activity over extended CO2R operation in strong acids. Using a stratified SiC‐NafionTM/SnBi/polytetrafluoroethylene (PTFE) electrode, constant production of formic acid was achieved with a single‐pass carbon efficiency of >75 % and Faradaic efficiency of >90 % at 100 mA cm−2 over 125 h at pH 1.

Achieving High Single-Pass Carbon Conversion Efficiencies in Durable CO2 Electroreduction in Strong Acids via Electrode Structure Engineering.

Acidic CO2 reduction (CO2 R) holds promise for the synthesis of low-carbon-footprint chemicals using renewable electricity. However, the corrosion of catalysts in strong acids causes severe hydrogen evolution and rapid deterioration of CO2 R performance. Here, by coating catalysts with an electrically nonconductive nanoporous SiC-NafionTM layer, a near-neutral pH was stabilized on catalyst surfaces, thereby protecting the catalysts against corrosion for durable CO2 R in strong acids. Electrode microstructures played a critical role in regulating ion diffusion and stabilizing electrohydrodynamic flows near catalyst surfaces. This surface-coating strategy was applied to three catalysts, SnBi, Ag, and Cu, and they exhibited high activity over extended CO2 R operation in strong acids. Using a stratified SiC-NafionTM /SnBi/polytetrafluoroethylene (PTFE) electrode, constant production of formic acid was achieved with a single-pass carbon efficiency of >75 % and Faradaic efficiency of >90 % at 100 mA cm-2 over 125 h at pH 1.

Air and Air-Steam Gasification of Coconut Shell in a Fluidized Bed

Coconut shells’ abundance in tropical countries, along with its high volatile combustible matter (83.51%) and energy content (18.68 MJ kg-1) make it a good biomass resource and a promising feedstock for gasification. In gasification, different mediums such as air, steam, oxygen, or their combinations can be used to react with the solid carbon and heavy hydrocarbons of biomass. Hence, the effects of using an air-steam mixture as a gasifying agent for the bench-scale fluidized bed gasification of coconut shells were studied. The steam-to-carbon ratio (SCR) was varied to evaluate its effect on the resulting syngas quality and gasification performance, while the equivalence ratio was maintained at 0.25 and the bed temperature was kept at 700°C. Results revealed that the optimum SCR is 0.6, where peak values of hydrogen (H2) and methane (CH4) content, hydrogen-to-carbon monoxide ratio (H2/CO), higher heating value (HHV), cold gas efficiency (CGE), and carbon conversion efficiency (CCE) were observed. Furthermore, the use of the air-steam mixture (SCR 0.6) as a gasifying agent was compared with the conventional air gasification. The study also showed a significant increase in syngas quality in terms of H2 content (4.70 - 5.82%), H2/CO (0.30 - 0.39), and CH4 content (3.53 - 4.38%). The syngas heating value and gasification performance revealed a statistically similar improvement: HHV from 4.95 to 5.41 MJ Nm-3, CCE from 77.64 to 81.75%, and CGE from 47.99 to 51.01%. Moreover, air-steam gasification produced less CO2 (13.42 CO2mol kgbiomass-1) and had higher energy recovery (49.67%).