Increase In Carbon Conversion Research Articles

Influence mechanism of K on cellulose pyrolysis by stepwise isothermal method in-situ DRIFTS method

The influence mechanism of alkali metal potassium (K) on cellulose pyrolysis is a vague and fundamental key topic in the field of biomass thermal conversion. In this study, the pyrolysis of cellulose and K-impregnated cellulose was compared by in-situ DRIFTS (Diffused Reflectance Infrared Fourier Transform Spectroscopy) and TG (Thermal Gravimetric)–MS (Mass Spectrum) experiment, and quantum chemical calculations were used to verify the peak position and pyrolysis mechanism of infrared (IR) spectroscopy. Stepwise isothermal in-situ DRIFTS was designed to study the reaction path at high temperatures. It was found that in the early stage of pyrolysis, K accelerated the activation of cellulose by attacking the hydrogen bond (H-bond) in the crystal structure of cellulose, increased the dehydration rate between molecules, and promoted the decomposition of cellulose. Simultaneously, it weakened the epoxy–ether bond, inhibited the formation of dehydrated sugar, and promoted the formation of furan. Subsequently, K combined with carbonyl groups to form C–O–K structures, which improved the thermal stability of certain oxygen-containing functional groups such as carbonyls/aldehydes, so that these structures were retained until higher temperature. K promoted the conversion of dehydrated sugars to straight-chain ketones/aldehydes, which led to an increase in carbon conversion. During the coke generation stage, K promoted the formation of disordered carbon and residues, thereby inhibiting coke aromatization. The isothermal in-situ DRIFTS method proposed in this study was demonstrated to better inhibit the high temperature drift of IR spectrum during pyrolysis. It clarified the conversion between functional groups at high temperatures, which is expected to promote the development of other high-temperature pyrolysis mechanism.

Enhancing inter-particle microwave discharge for efficient coke-CO2 gasification

To mitigate the adverse effects of catalyst volatilization and deactivation on CO2 gasification, we present a simple and feasible method for enhancing CO2 gasification by enhancing the inter-particle microwave discharge without adding a catalyst. This results in an 18.0%–30.6% increase in carbon conversion with similar energy consumption, demonstrating that the enhanced reactivity provided by the microwave discharge is comparable to conventional catalysts (Na, Fe, and K) for CO2 gasification. Experimental and simulation results reveal that enhancing the inter-particle microwave discharge raises the content of excited CO2 states, particularly high-level states. This is beneficial in reducing the activation barrier for the dissociative adsorption of CO2, which has the highest activation barrier of 406 kJ·mol−1. In conclusion, this study enhances the understanding of the mechanism for CO2 gasification without a catalyst and provides new insight into reactions prone to catalyst deactivation.

Study on Cogasification of Food Waste Char with Biomass/Coal Char and Their Interaction Mechanisms

In this paper, the effects of gasification temperature and blending ratios on cogasification reactivity of food waste char with sawdust/Shenfu coal char were studied via a thermogravimetric analyzer. Moreover, the relationship between synergy and char physical–chemical structure evolution was further studied using scanning electron microscopy equipped with energy-dispersive X-ray analysis (SEM–EDS), N2 absorption, and Fourier transform (FT) Raman techniques. The results revealed a significant synergetic effect between food waste and Shenfu coal. The synergetic effect always occurred at the mid-later reaction stage and was enhanced with the increase in carbon conversion. However, no synergy was found between food waste and sawdust. In the food waste–Shenfu cogasification process, ash present in food waste (rich in Ca) transferred to the surface of Shenfu char without blocking the pore structure of Shenfu char. Moreover, the FT-Raman analysis revealed that the food waste ash reacted with Shenfu char to form...

Study on effects of ash on the evolution of physical and chemical structures of char during CO2 gasification

In this paper, the gasification reactivities of four types of Chinese coal were studied, each with different ash content and coal rank. Of the 4 coal types, 2 were HCl-washed and demineralized to investigate the effects of ash removal (for both dealkalization and demineralization) on coal gasification. The effects of ash on the evolution of physical and chemical structure were further studied using scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), N2 absorption and FT-Raman techniques. The results show that the initial gasification rate of raw chars is twice as high as the HCl-washed and ash-free chars. The gasification rate of ash-free char significantly increases with the increase in carbon conversion and surpasses the gasification rate of raw char when carbon conversion is higher than 50%. Moreover, the specific surface area of ash-free char significantly increases with carbon conversion, resulting in the significant increase in the gasification rate. Whereas the specific surface areas of raw char and HCl-washed char both decrease during high-conversion stages. The FT-Raman analysis shows that the ash-free char band area ratios AD3/AG and AD4/AG are lower than those of raw char at the initial gasification stage; this results in the initial gasification rate decrease of ash-free chars. In addition, the ash-free char band area ratio AG/Aall is smaller than that of raw char in the high conversion stages.

Retraction of “Coal and Biomass Partial Gasification and Soot Properties in an Atmospheric Fluidized Bed”

Using air as the gasification medium, one kind of coal and one kind of biomass partial gasification studies were carried out in a laboratory-scale atmospheric fluidized bed with the various operating parameters. The effects of the O/C ratio, biomass/(coal + biomass) (Fb/Fm) ratio, and bed temperature on the fuel gas compositions and the high heating value (HHV) were reported in this paper. The results show that the concentrations of carbon monoxide, hydrogen, and methane and the HHV decrease with the rise of the O/C ratio and the decline of the Fb/Fm ratio for coal and biomass partial gasification. A rise of the bed temperature favors the semi-gasification reaction of coal, but the concentrations of carbon monoxide and methane and the HHV decrease with the rise of the bed temperature, except hydrogen. In addition, the gas HHVs are between 1.0 and 3.3 MJ N–1 m–3. The gas yield and carbon conversion increase with the O/C ratio, Fb/Fm ratio, and bed temperature. The atomic percentage of carbon increases and ...

Experimental investigation of the effect of physical pre-treatment on air-blown fluidized bed biomass gasification

The effect of comminution, drying, and densification on bubbling fluidized bed gasification was investigated by fractionating a forestry residue into a feedstock consisting of different particle sizes, moisture levels, and by densifying to pellets. The gasification performance was evaluated at nominal average bed temperatures of 725°, 800° and 875 °C at a constant fluidizing velocity (0.91 m s−1) with feed input rates between 9 and 24 kg h−1.The gas composition was observed to be influenced by both the particle size and form. Smaller particles led to a gas richer in carbon monoxide and depleted in hydrogen. The gasification of pellets led to a gas with the greatest hydrogen to carbon monoxide ratio. The smallest particles tested resulted in the worst gasification performance, as defined by cold gas efficiency, carbon conversion, and tar production. Despite differences in the gas composition among the larger particles and the pellets, similar carbon conversion and cold gas efficiency was observed.Relative to comparable test conditions with dry feed fractions (having a moisture mass fraction of 7–12%), an average 11% increase in carbon conversion was observed for the wetter feed fractions containing a moisture mass fraction of 24–31%. This increase in carbon conversion offset much of the expected decrease in cold gas efficiency by using a wetter feed material. A slight increase in hydrogen production and negligible change in tar production was observed for the wetter feed fractions relative to the dry feed fraction.

Thermodynamic analysis of synergistic coal gasification using blast furnace slag as heat carrier

In this paper, a thermodynamic analysis of the synergistic coal/CO2/H2O gasification process with BFS (blast furnace slag) as heat carrier was performed using the Gibbs free energy minimization approach through Lagrange multiplier method. The effect of temperature, pressure and C/CO2/H2O were investigated. Carbon, CO2 and H2O conversion, H2 and CO yield, and H2/CO ratio were used to characterize the synergistic gasification performance. The results showed that the atmospheric pressure was preferable for coal gasification and the increasing of temperature caused the increase in carbon conversion and syngas production. The optimal temperature of the synergistic gasification was 800–900 °C. Not only did it ensure the coal gasification reaction completely, but also it recovered the BFS waste heat effectively. The results clearly showed that the addition of H2O and CO2 could lead to the reduction of the carbon residue and increase of the production of H2 and CO, respectively. Meanwhile, it was beneficial to reduce the waste heat using to heating extra steam and enhance the coal/CO2 gasification reaction rate by controlling the addition of CO2 and H2O reasonably. Moreover, the production syngas application was also investigated by changing the relative CO2/C ratio and H2O/C ratio in the feed to modify the H2/CO ratio.

Catalytic steam gasification of lignite with olivine as solid heat carrier

Catalytic coal gasification was carried on a lab-scale external circulating co-current moving-bed (ECCMB) gasification system with steam as gasification agent and olivine as catalytic solid heat carrier. The system is composed of a moving-bed gasifier and a riser combustor. The effects of gasifier temperature, steam/coal mass ratio (S/C), bed materials and bed height on the product gas compositions, carbon conversion, and chemical efficiency were investigated. The result show that the gas yield and carbon conversion increase with the increase of the gasifier temperature. The highest H2 concentration of 60.4vol.% is produced from Dayan lignite at the gasifier temperature of 800°C and S/C ratio of 1.0. The carbon conversion increases remarkably at the S/C range from 0 to 0.4. Olivine as the bed material has a satisfying catalytic tar cracking efficiency. Appropriate bed height favors tar destruction because of the increase in the contact time of the tar and steam with the catalytic bed material.

Entrained flow gasification of biocoal from hydrothermal carbonization

Hydrothermal carbonization (HTC) converts biomass into a coal-like substance, here referred to as biocoal. Beech wood chips are treated hydrothermally at 210°C for 3h in a 250L pilot scale reactor. The carbon content (daf) thereby increases from 48wt.% to 57wt.% and the volatile matter (wf) decreases from 79wt.% to 69wt.%. The carbon and energy yields are both 80% on a mass and HHV basis, respectively, with the major loss being solubilized substances. Pulverization of biocoal is found to be much less energy intensive compared to wood. Moreover, pulverized particles show a spherical shape which may facilitate fluidization.Gasification experiments are carried out at temperatures of 1000°C, 1200°C and 1400°C at atmospheric pressure in a laboratory scale entrained flow reactor. The standard particle diameter used in the experiments is 80–160μm. During each experiment char samples are collected and the synthesis gas concentration is measured. Carbon conversion at a residence time of 1.0s is 84%, at both 1000°C and 1200°C. A significant increase in carbon conversion to 88% at 1400°C is observed. Comparable gasification experiments are carried out with lignite as the fuel. Rhenish lignite is gasified using the same stoichiometry and particle size. The conversion of lignite is slightly lower indicating the high reactivity of biocoal.An increase of particle size would be beneficial due to the lower power consumption for pulverization. In experiments with biocoal at a particle size of 160–250μm, a slightly lower conversion is measured due to internal and external mass transfer limitations at the particles. The high conversion at short reaction times indicates a high reactivity of biocoal under entrained flow gasification conditions.

Coal and Biomass Partial Gasification and Soot Properties in an Atmospheric Fluidized Bed

Using air as the gasification medium, one kind of coal and one kind of biomass partial gasification studies were carried out in a laboratory-scale atmospheric fluidized bed with the various operating parameters. The effects of the O/C ratio, biomass/(coal + biomass) (Fb/Fm) ratio, and bed temperature on the fuel gas compositions and the high heating value (HHV) were reported in this paper. The results show that the concentrations of carbon monoxide, hydrogen, and methane and the HHV decrease with the rise of the O/C ratio and the decline of the Fb/Fm ratio for coal and biomass partial gasification. A rise of the bed temperature favors the semi-gasification reaction of coal, but the concentrations of carbon monoxide and methane and the HHV decrease with the rise of the bed temperature, except hydrogen. In addition, the gas HHVs are between 1.0 and 3.3 MJ N–1 m–3. The gas yield and carbon conversion increase with the O/C ratio, Fb/Fm ratio, and bed temperature. The atomic percentage of carbon increases and the atomic percentage of oxygen decreases with the rise of the O/C ratio in fly ash. The concentration of soot decreases along with the O/C ratio in fly ash.

Investigation of the Oxy-fuel Gasification of Coal in a Laboratory-Scale Spouted-Bed Reactor: Reactor Modifications and Initial Results

Fluidized-bed gasifiers in combination with integrated gasification combined cycle (IGCC) technology are an efficient way to make use of low-value coal, waste, and biomass for power generation. However, air/steam blown gasifiers produce a fuel gas diluted with N2, making expensive CO2−N2 separation processes necessary for integration with carbon capture and storage technology. To overcome this limitation, a novel process is proposed in this work where the bed is fluidized with an O2/CO2 mixture, with CO2 being recycled from the combusted fuel gas stream. A laboratory-scale spouted-bed gasifier was developed to investigate the potential of this concept. This work focuses on the overall operability of the gasifier as well as the effect of operating parameters on the gasification performance of two different coals when high partial pressures of CO2 are employed. The temperature increase in the range of 850−950 °C produced a significant increase in carbon conversion, while the effect of the O/C ratio was more...

Biomass Steam Gasification with In-Situ CO2 Capture for Enriched Hydrogen Gas Production: A Reaction Kinetics Modelling Approach

Due to energy and environmental issues, hydrogen has become a more attractive clean fuel. Furthermore, there is high interest in producing hydrogen from biomass with a view to sustainability. The thermochemical process for hydrogen production, i.e. gasification, is the focus of this work. This paper discusses the mathematical modeling of hydrogen production process via biomass steam gasification with calcium oxide as sorbent in a gasifier. A modelling framework consisting of kinetics models for char gasification, methanation, Boudouard, methane reforming, water gas shift and carbonation reactions to represent the gasification and CO2 adsorption in the gasifier, is developed and implemented in MATLAB. The scope of the work includes an investigation of the influence of the temperature, steam/biomass ratio and sorbent/biomass ratio on the amount of hydrogen produced, product gas compositions and carbon conversion. The importance of different reactions involved in the process is also discussed. It is observed that hydrogen production and carbon conversion increase with increasing temperature and steam/biomass ratio. The model predicts a maximum hydrogen mole fraction in the product gas of 0.81 occurring at 950 K, steam/biomass ratio of 3.0 and sorbent/biomass ratio of 1.0. In addition, at sorbent/biomass ratio of 1.52, purity of H2 can be increased to 0.98 mole fraction with all CO2 present in the system adsorbed.

Air and Steam Coal Partial Gasification in an Atmospheric Fluidized Bed

Using the mixture of air and steam as gasification medium, three different rank coal partial gasification studies were carried out in a bench-scale atmospheric fluidized bed with the various operating parameters. The effects of air/coal (Fa/Fc) ratio, steam/coal (Fs/Fc) ratio, bed temperature, and coal rank on the fuel gas compositions and the high heating value (HHV) were reported in this paper. The results show that there is an optimal Fa/Fc ratio and Fs/Fc ratio for coal partial gasification. A rise of bed temperature favors the semigasification reaction of coal, but the concentrations of carbon monoxide and methane and the HHV decrease with the rise of bed temperature, except hydrogen. In addition, the gas HHVs are between 2.2 and 3.4 MJ/Nm3. The gas yield and carbon conversion increase with Fa/Fc ratio, Fs/Fc ratio, and bed temperature, while they decrease with the rise of the rank of coal.

Modelling of a laboratory-scale bubbling fluidised-bed gasifier with feeds of both char and propane

A previous mathematical model developed for a bubbling fluidised-bed coal gasifier was modified for simulating the performance of a laboratory-scale gasifier with feeds of both Yallourn char and propane by incorporating propane decomposition and combustion reactions and reaction kinetics. Model predictions of the in-bed axial gas concentration profiles for O 2, CO, CO 2, CH 4, and C 3H 8 compared well, except for the minor gas species of both C 2H 4 and C 3H 6, to the experimental data at operating bed temperatures of 850 and 950 °C, respectively. In contrast, the predicted gas species show a poor agreement with the experimental data, particularly for the carbon oxide species at 750 °C. Most importantly, the addition of propane to simulate the volatile matter released from coal devolatilisation process results in an increase in the proportion of oxygen consumed by homogeneous combustion. This leads to an increase in an availability of char for char gasification reactions, subsequently showing an increase in carbon conversion due to gasification over the sole gasification of char. The specific energy of the syngas gas has been shown to increase due to the enhancement of the char gasification reactions in the presence of volatiles. This further demonstrates the importance of incorporating homogenous combustion into the model for correctly predicting the gasifier performance, particularly for the in-bed feeding of coal with high volatile content.

Steam gasification of an australian bituminous coal in a fluidized bed

To produce low calorific value gas, Australian coal has been gasified with air and steam in a fluidized bed reactor (0.1 m-I.D◊1.6 m-high) at atmospheric pressure. The effects of fluidizing gas velocity (2-5 U f/Umf), reaction temperature (750-900 o C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63-1.26) on gas composition, gas yield, gas calorific value of the product gas and carbon conversion have been determined. The calorific value and yield of the product gas, cold gas efficiency, and carbon conversion increase with increasing fluidization gas velocity and reaction temperature. With increasing air/coal ratio, carbon conversion, cold gas efficiency and yield of the product gas increase, but the calorific value of the product gas decreases. When steam/coal ratio is increased, cold gas efficiency, yield and calorific value of the product gas increase, but carbon conversion is little changed. Unburned carbon fraction of cyclone fine decreases with increasing fluidization gas velocity, reaction temperature and air/coal ratio, but is nearly constant with increasing steam/coal ratio. Overall carbon conversion decreases with increasing fluidization velocity and air/ coal ratio, but increases with increasing reaction temperature. The particle entrainment rate increases with increasing fluidization velocity, but decreases with increasing reaction temperature.

Coal gasification characteristics in a downer reactor

Subbituminous coal (Shenwha) was gasified at atmospheric pressure in a downer reactor (0.1 m I.D.×5.0 m high). The effects of reaction temperature (750–850°C), steam/coal mass ratio (0.23–0.86), O 2/H 2O mole ratio (0–1.81) and coal feeding rate (5.3–9.0 kg h −1) on the composition of product gas, carbon conversion, cold gas efficiency, gas yield and calorific value have been determined. In the case of steam injection into the loop-seal, compositions of the product gas (vol. %; N 2 free basis) in the gasification region are H 2 (35.8–39.4%), CH 4 (6.8–15.5%), CO (14.9–15.9%), CO 2 (20.7–29.5%), C 2H 4 (2.8–4.9%), C 2H 6 (2.5–3.5%), C 3H 6 (1.6–3.3%) and C 3H 8 (1.7–2.5%) with a calorific value of 13.0–15.2 MJ/m 3. By changing the reactant gas supplied into the loop-seal for solid circulation from steam to air, product gas yield and carbon conversion increase, whereas calorific value of the product gas decreases from 13.0–15.2 to 6.3–10.6 with reaction temperature.

Experiment and mathematical modeling of a bench-scale circulating fluidized bed gasifier

The gasification of two different coals and chars with CO 2 and CO 2/O 2 mixture in a 48-mm-i.d. circulating fluidized bed (CFB) gasifier is investigated. The effects of operation condition on gas composition, carbon conversion and gasification efficiency were studied. A simple CFB coal gasification district mathematical model has been set up. The effects of coal type and CFB operating conditions on CFB coal gasification are discussed based on the CFB gasification test and model simulation. The main operation parameters in CFB gasification system are coal type, gas superficial velocity, circulating rate of solids and reaction temperature. It is found that CO concentration and carbon conversion increase with increasing solids circulating rate and decreasing gas velocity due to the increase in gas residence time and solids holdup in the CFB. The carbon conversion increases with increasing temperature and O 2 concentration in the inlet gas. The experimental results prove that the CFB gasifier works well for high volatile, high reactivity coal.

Carbon conversion in an atmospheric-pressure entrained coal gasifier

Entrained gasification tests with a Utah high-volatile bituminous coal were performed at atmospheric pressure to assess the influence of particle size, coal feed rate, steam-coal ratio and oxygen-coal ratio. Independent argon-carbon balance and ash balance methods were used to evaluate carbon conversion, with good agreement observed between the methods. A higher O 2-coal ratio and finer particles increased the carbon conversion. Carbon conversion and hydrogen formation showed little dependence on the amount of steam injected in the secondary stream, indicating minimal steam-coal reaction. When the coal feed rate was varied from 23 to 27 kg h −1, a small increase in carbon conversion was observed with no significant change in the gas composition.

STEAM GASIFICATION OF BALMER COAL IN THE PRESENCE OF LIGNITE ASH

ABSTRACT Steam gasification of blends prepared from Balraer coal and the ash from combustion of Onakawana lignite was performed in a fixed bed reactor. The blends were prepared by co-slurrying followed by drying. In the presence of 20 wt % ash the gasification rate doubled at 830° and 930°C. Direct blending of coal and lignite resulted In an overall increase in carbon conversion at 830°C but had no effect at 930°C.