The rate of gas formation from wood pyrolysis has been experimentally measured at temperatures from 300°C to 1000°C. The formation rate of specific product gases has been measured rather than the rate of solid weight loss. Even for very fine particles, the rate becomes heat transfer limited a: high temperatures. The product gases also approach thermodynamic equilibrium rapidly at high temperatures. The results are corrected using the experimental residence time distribution. 相似文献
The gasification reactivities of three char samples derived from coals of varying ranks (“Turów” lignite, “Piast”, and “Wieczorek” sub-bituminous coals) toward CO2 were investigated isothermally using thermogravimetric analysis. Kinetic behavior was studied at temperatures of 900, 950, and 1,000 °C under atmospheric pressure. Conditions for the chemical-controlled regime were established at these temperatures and pressure. In this paper, four kinetic models were applied to describe the varying conversion rate: volumetric model, grain model, modified volumetric model, and random pore model. From these models, only the random pore and the volumetric models positively corresponded to nearly the entire range of experimental results. Calculated values of activation energy for study samples were in the range of 180–250 kJ mol?1, which is in accordance with other reported data. Moreover, the obtained results confirmed the significant impact of parent coal rank on its char reactivity, offering possibilities in the approximation of coal char kinetic behavior after further more detailed studies with a larger number of samples. 相似文献
Differential thermal analysis (DTA) of low-rank coals of high lignite to subbituminous rank from coal mines of Pakistan is
reported. The studies carried out in dynamic oxygen atmosphere indicate that the exothermic reactions occur between 300 and
650°C and that the samples undergo stepwise oxidation of the organic matter rather than a continuous process as indicated
by the pattern of shoulders from 250 to 350°C accompanying the main peak around 450°C. The effect of heating rate, particle
size and volatile content was also studied in relation to oxidation. The results show that the increase in heating rate from
10 to 80 deg min−1 results in a marked shift in all the events in the DTA curve towards higher temperatures. As for the effect of particle size,
the DTA records of 100–75, 150–100, 250–150 μm and greater than 250 μm fractions show that the magnitude and position of shoulder
peaks are more sensitive to changes in particle sizes compared to the main peak. The curves recorded to study the effect of
changing volatile content of samples between 30–40% indicate a complex pattern of shoulders accompanying the main peak. In
general, the number of shoulder peaks increases with increasing volatile content of samples but their positions do not follow
any trend. The DTA curves recorded in nitrogen contain ill-de-fined oxothermic effects over the 300–750°C temperature range.
These curves consist of an endothermic peak around 150°C, two exothermic shoulders in the temperature region 300–400°C and
a large broad exothermic whip between 500 and 700°C. The heating rates have similar effects as in oxygen while the particle
size do not influence the results.
It has been concluded that the organic matter in the coals studied here is extremely heterogeneous with different burning
characteristics; as a result it is very difficult to quantify energy changes associated with poorly resolved exothermic events
along the DTA curve. The effects also dominate in N2 atmosphere thus making identification of mineral matter difficult. The overall pattern of DTA events in oxygen can be correlated
with the heating rate, particle size and volatile content of samples. 相似文献
Journal of Thermal Analysis and Calorimetry - The experiments of biomass char gasification in granulated blast-furnace (BF) slag using CO2 as gasification agent were carried out isothermally with a... 相似文献
The physico-chemical effects caused by supercritical CO2 (ScCO2) exposure is one of the leading problems for CO2 storage in deep coal seams as it will significantly alter the flow behaviors of gases. The main objective of this study was to investigate the effects of ScCO2 injection on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals. The powdered coal samples were immersed in ScCO2 for 30 days using a high-pressure sealed reactor. Then, the diffusion and adsorption kinetics of CH4, CO2 and water vapor in the coals both before and after exposure were examined. Results indicate that the diffusivities of CH4 and CO2 are significantly increased due to the combined matrix swelling and solvent effect caused by ScCO2 exposure, which may induce secondary faults and remove some volatile matters that block the pore throats. On the other hand, the diffusivities of water vapor are reduced due to the elimination of surface functional groups with ScCO2 exposure. It is concluded that density of the surface function groups is the controlling factor for water vapor diffusion rather than the pore properties. The unipore model and pseudo-first-order equation can simulate the diffusion and adsorption kinetics of CH4 and CO2 very well, but the unipore model is not capable of well describing water vapor diffusion. The effective diffusivity (De), diffusion coefficient (D) and adsorption rates (k1) of CH4 and CO2 are significantly increased after ScCO2 exposure, while the values of water vapor are decreased notably. Thus, the injection of ScCO2 will efficiently improve the transport properties of CH4 and CO2 but hinder the movement of water molecules in coal seams. 相似文献
The gasification with carbon dioxide of residual carbons prepared from Timahdit and Tarfaya oil shale kerogens has been studied
by thermal analysis techniques (TG and DTA) under heating rates varying from 5 to 48°C min-1. The reactions obey first order kinetics. Activation energies have been calculated by several methods, such as Kissinger,
Chen-Nuttall and Coats-Redfern methods, and are broadly comparable with literature data for similar carbons. 相似文献
Although the influence of metallic and alkaline elements on biomass char reactivity is well known, a quantitative assessment of this catalytic effect is hard to obtain because of the chemical and textural complexity of biomass. The effect of K and Si on the CO2 gasification reactivity of a biomass char was studied using thermogravimetric analysis. A beech sample was pyrolyzed at 800 °C and then impregnated with known amounts of silicon or potassium allowing to obtain a wide range of K/Si ratios. The reactivity of the impregnated samples was studied under a CO2 (20% vol.) atmosphere. The results show that at low conversion ratios, the char reactivity depends on its textural properties, with strong diffusional limitations. When conversion reaches 60%, the presence of a catalyst (K) and an inhibitor (Si) becomes the major parameter influencing reactivity. From these experiments, a general trend was obtained between K/Si ratio and reactivity as a function of conversion. 相似文献
Photocatalytic conversion of CO2 into fuels and valuable chemicals using solar energy is a promising technology to combat climate change and meet the growing energy demand. Extensive effort is going on for the development of a photocatalyst with desirable optical, surface and electronic properties. This review article discusses recent development in the field of photocatalytic CO2 conversion using defective TiO2. It specifically focuses on the different synthesis methodologies adapted to generate the defects and their impact on the chemical, optical and surface properties of TiO2 and, thus, photocatalytic CO2 conversion. It also encompasses theoretical investigations performed to understand the role of defects in adsorption and activation of CO2 and identify the mechanistic pathway which governs the formation and selectivity of different products. It is divided into three parts: (i) general mechanism and thermodynamic criteria for defective TiO2 catalyzed CO2 conversion, (ii) theoretical investigation on the role of defects in the CO2 adsorption–activation and mechanism responsible for the formation and selectivity of different products, and (iii) the effect of variation of physicochemical properties of defective TiO2 synthesized using different methods on the photocatalytic conversion of CO2. The review also discusses the limitations and the challenges of defective TiO2 photocatalysts that need to be overcome for the production of sustainable fuel utilizing solar energy.This review discusses photocatalytic CO2 conversion using defective TiO2, with emphasis on the mechanism, the role of defects on CO2 adsorption–activation and product selectivity, as well as challenges of defective TiO2 to produce solar fuels.相似文献
The combustion of coal and coal/fir (Abies bornmulleriana) wood blends at the proper ratio (20, 40, 50 wt%) was investigated with thermogravimetric analysis (TG). The influence of biomass blends on thermal and kinetic behavior of coal was studied under non-isothermal conditions. The activation energy of the samples was evaluated with the Ozawa–Flynn–Wall model which compares the combustion of these biowastes with coal under non-isothermal conditions. Our research found that blending influences activation energy of coal; moreover, activation energy related to 50 wt% blend was more similar to pure wood combustion than to coal combustion. Therefore, the activation energy profile shifted from 80.6 to 169.3 kJ/mol. The average reaction order of the samples ranged from 0.13 to 0.35. 相似文献
The chemical composition and reactivity of fir (Abies bornmulleriana) wood under non-isothermal thermogravimetric (TG) conditions were studied. Oxidation of the wood sample at temperatures near
600 °C caused the loss of aliphatics from the structure of the wood and created a char heavily containing C–O functionalities
and of highly aromatic character. On-line FTIR recordings of the combustion of wood indicated the oxidation of carbonaceous
and hydrogen content of the wood and release of some hydrocarbons due to pyrolysis reactions that occurred during combustion
of the wood. TG analysis was used to study combustion of fir wood. Non-isothermal TG data were used to evaluate the kinetics
of the combustion of this carbonaceous material. The article reports application of Ozawa–Flynn–Wall model to deal with non-isothermal
TG data for the evaluation of the activation energy corresponding to the combustion of the fir wood. The average activation
energy related to fir wood combustion was 128.9 kJ/mol, and the average reaction order for the combustion of wood was calculated
as 0.30. 相似文献
Oxyfuel combustion represents one way for cleaner energy production using coal as combustible. The comparison between the oxycombustion and the conventional air combustion process starts with the investigation of the pyrolysis step. The aim of this contribution is to evaluate the impact of N2 (for conventional air combustion) and CO2 (for oxy-fuel combustion) atmospheres during pyrolysis of three different coals. The experiments are conducted in a drop tube furnace over a wide temperature range 800–1400 °C and for residence time ranging between 0.2 and 1.2 s. Coal devolatilized in N2 and CO2 atmospheres at low temperatures (1200 °C) provides similar results regarding mass loss, char combustion in thermogravimetric analysis and CO concentration. At higher temperatures (>?1200 °C) and longer residence times (>?0.5 s), the char-CO2 reaction is clearly observed, whose intensity depends on the nature of the coal. Furthermore, the volatile yields are simulated using Kobayashi’s scheme and kinetic parameters are predicted for each coal. The char gasification under CO2 is also accounted for by the model.
Forschungszentrum Karlsruhe has developed a concept for the utilization of cereal straw and other thin-walled biomass with
high ash content. The concept consists of a regional step (drying, chopping, flash-pyrolysis, and mixing) and a central one
(pressurized entrained-flow gasification, gas cleaning, synthesis of fuel, and production of byproducts). The purpose of the
regional plant is to prepare the biomass by minimizing its volume and producing a stable and safe storage and transport form.
In the central gasifier, the pyrolysis products are converted into syngas. The syngas is tar-free and can be used for Fischer-Tropsch
synthesis after gas cleaning. 相似文献
Bench-scale research demonstrated that using an efficient esterification step to integrate an ethanol with a carboxylic acid
fermentation stream offers potential for producing valuable ester feedstocks and fuels. Polar organic acids from bacterial
fermentations are difficult to extract and purify, but formation of the ammonium salts and their conversion to esters facilitates
the purifications. An improved esterification procedure gave high yields of esters, and this method will lower the cost of
ester production. Fuel characteristics have been determined for a number of ester-gasoline blends with promising results for
lowering Reid vapor pressure and raising octane numbers. 相似文献
This paper discusses possible mechanisms for the pyrolytic reaction of biomass with steam in the presence of alkali carbonate and supported-nickel catalysts. In addition to catalyzing the carbon/steam reaction, the alkali carbonates alter the biomass pyrolysis reaction path-ways, producing gas and char at the expense of tars. Nickel catalyst, while quite effective for secondary tar and gas reactions, tend to lose activity over time; therefore, studies of these catalysts were directed toward identifying mechanisms of carbon deposition, the primary cause of catalyst deactivation. 相似文献