Thermochemical Conversion Of Solid Fuels Research Articles

In situ evolution of functional groups in char during cellulose pyrolysis under the catalysis of KCl and CaCl2

A combination of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) and two-dimensional correlation spectroscopy (2D-COS) was used to reveal the catalytic mechanism of KCl and CaCl2 on cellulose char evolution during slow pyrolysis. Pretreatments of the one-dimensional spectra ensure the semi-quantitative analysis of the evolution of functional groups in pyrolysis char, which invoked principal component analysis followed by a Butterworth filter for denoising and extended multiplicative scatter correction. Through the differential processing of the absolute changes, the char evolution product was divided into ‘char rearrangement’ and ‘char devolatilization’ processes containing a high contribution from chemical reactions and physical migration, respectively. The ‘char rearrangement’ of cellulose pyrolysis consists of four stages, i.e. the budding, development, climax and decline stages, which were dominated by H-bond network reconfiguration, the consumption of C–O–C and OH, homogeneous devolatilization and aromatization, respectively. The uppermost influence of the two salts on the pyrolysis is the relationship alteration of C–O–C cleavage, dehydration reactions and ‘char devolatilization’. For neat, KCl-loaded and CaCl2-loaded cellulose, the unsaturated bonds were formed in the light reaction intermediate, heavy reaction intermediates and cellulose chain, respectively. Especially, the cleavage of most C–O–C following dehydration reactions conduced a shoulder peak in the differential thermogravimetry curve before the maximum weight loss rate of CaCl2-loaded sample. Due to the alteration, the pyrolysis was advanced but slowed down by the high content of unsaturated bonds in char. This study provides a powerful tool for the in situ semi-quantitative analysis of char evolution during the non-catalytic and catalytic thermo-chemical conversion of solid fuels and waste, and the results benefit to both biomass pyrolysis mechanism revelation and industrial production of biochar.

Isothermal drying characteristics and kinetics of human faecal sludges.

Background: Drying is an important step for the thermochemical conversion of solid fuels, but it is energy-intensive for treating highly moist materials. Methods: To inform the thermal treatment of faecal sludge (FS), this study investigated the drying characteristics and kinetics of various faecal wastes using thermogravimetric analysis and isothermal heating conditions. Results: The findings show that FS from the anaerobic baffled reactor (ABR) and ventilated improved pit latrines (VIP) exhibit similar drying characteristics, with maximum drying rates at 0.04 mg/min during a constant rate period that is followed by a distinct falling rate period. On the contrary, fresh human faeces (HF) and FS from urine diversion dry toilets (UDDT) exhibited a falling rate period regime with no prior or intermittent constant rate periods. The absence of a constant rate period in these samples suggested limited amounts of unbound water that can be removed by dewatering and vice versa for VIP and ABR faecal sludges. The activation energies and effective moisture diffusivity for the sludges varied from 28 to 36 kJ/mol and 1.7·10 -7 to 10·10 -7 m 2/s at 55°C and sludge thickness of 3mm. The Page model was consistent in modelling the different sludges across all temperatures. Conclusions: These results presented in this study can inform the design and development of innovative drying methods for FS treatment.

Applying dynamic mesh to examine evolution of effective thermal conductivity in porous medium undergoing macrostructure change

Heat transfer dynamics in packed bed appears to be vital, particularly with respect to thermochemical conversion of solid fuels. However, due to complex bed structure varying under high temperatures the prediction of its thermal behavior is very demanding. Heating of coke oven charge is one example, regarded as being considerably affected by radiation through fissures and cracks that cross cut coke zone as the carbonization proceeds. The investigation and quantification of such impact encounters difficulties due to irregularity of fissure network that depends on a parent coal type and the process temperature regimes. Unfortunately, the analyses of this issue are very limited, meanwhile an uncertainty in the assessment of radiation contribution might be a source of notable discrepancy in effective thermal conductivity of coal/coke bed reported to date in the literature. In this respect, the CFD simulations of heating of a coal/coke bed while taking into account the crack propagation were performed to estimate an influence of structure alteration on heat transfer process. The computations were carried out using Ansys Fluent package and the dynamic mesh was implemented to simulate the crack development. The numerically-derived temperature profile at the coke oven center plane is in good agreement with the experimental temperature history. The predicted thermal conductivity values in the near-wall zone are significantly higher than for the case excluding fissure presence, and achieved ∼6.2 W(m K)-1 at the end of process (for 1373 K), showing additionally a clear increase from 1.4 to 2.9 W(m K)-1 within 1070–1090 K. The computation results also revealed that slower developing cracks, contrary to faster propagating ones, lead to higher thermal conductivity.

Steam gasification of biomass – Typical gas quality and operational strategies derived from industrial-scale plants

Steam gasification enables the thermochemical conversion of solid fuels into a medium calorific gas that can be utilized for the synthesis of advanced biofuels, chemicals or for heat and power production. Dual fluidized bed (DFB) gasification is at present the technology applied to realize gasification of biomass in steam environment at large scale. Few large-scale DFB gasifiers exist, and this work presents a compilation and analysis of the data and operational strategies from the six DFB gasifiers in Europe. It is shown that the technology is robust, as similar gas quality can be achieved despite the differences in reactor design and operation strategies. Reference concentrations of both gas components and tar components are provided, and correlations in the data are investigated. In all plants, adjusting the availability and accessibility to the active ash components (K and Ca) was the key to control the gas quality. The gas quality, and in particular the tar content of the gas, can conveniently be assessed by monitored the concentration of CH4 in the produced gas. The data and experience acquired from these plants provide important knowledge for the future development of the steam gasification of biomass.

Isothermal drying characteristics and kinetics of human faecal sludges

Background: Drying is an important step for the thermochemical conversion of solid fuels, but it is energy-intensive for treating highly moist materials. Methods: To inform the thermal treatment of faecal sludge (FS), this study investigated the drying characteristics and kinetics of various faecal wastes using thermogravimetric analysis and isothermal heating conditions. Results: The findings show that FS from the anaerobic baffled reactor (ABR) and ventilated improved pit latrines (VIP) exhibit similar drying characteristics, with maximum drying rates at 0.04 mg/min during a constant rate period that is followed by a distinct falling rate period. On the contrary, fresh human faeces (HF) and FS from urine diversion dry toilets (UDDT) exhibited a falling rate period regime with no prior or intermittent constant rate periods. The absence of a constant rate period in these samples suggested limited amounts of unbound water that can be removed by dewatering and vice versa for VIP and ABR faecal sludges. The activation energies and effective moisture diffusivity for the sludges varied from 28 to 36 kJ/mol and 1.7·10 -7 to 10·10 -7 m 2/s at 55°C and sludge thickness of 3mm. The Page model was consistent in modelling the different sludges across all temperatures. Conclusions: These results presented in this study can inform the design and development of innovative drying methods for FS treatment.

Isothermal drying characteristics and kinetics of human faecal sludges

Background: Drying is an important step for the thermochemical conversion of solid fuels, but it is energy-intensive for treating highly moist materials. Methods: To inform the thermal treatment of faecal sludge (FS), this study investigated the drying characteristics and kinetics of various faecal wastes using thermogravimetric analysis and isothermal heating conditions. Results: The findings show that FS from anaerobic baffled reactor (ABR) and ventilated improved pit (VIP) latrines exhibit similar drying characteristics, with maximum drying rates at 0.04 mg/min during a constant rate period that is followed by a distinct falling rate period. On the contrary, fresh human faeces (HF) and FS from urine-diverting dry toilets (UDDT) exhibited a falling rate period regime with no prior or intermittent constant rate periods. The absence of constant rate period in these samples suggested limited amounts of unbound water that can be removed by dewatering and vice versa for VIP and ABR faecal sludges. The activation energies and effective moisture diffusivity for the sludges varied from 20 to 30 kJ/mol and 3∙10-7 to 1∙10-5 m2/s at 55°C and sludge thickness of 3mm. The Page model was consistent in modelling the different sludges across all temperatures. Conclusions: These results presented in this study can inform the design and development of innovative drying methods for FS treatment.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ СОВМЕСТНОЙ КОНВЕРСИИ УГЛЯ И ШЛАМА СТОЧНЫХ ВОД В ОБРАЩЕННОМ СЛОЕВОМ ГАЗОГЕНЕРАТОРЕ

Актуальность исследования обусловлена необходимостью утилизации бытовых и промышленных отходов. Утилизация горючих отходов, таких как шламы сточных вод, может быть совмещена с производством энергии для небольших потребителей. Одним из способов такой утилизации может стать газификация, позволяющая получить горючий газ, пригодный для получения тепловой и электрической энергии. Цель: на основании результатов математического моделирования оценить эффективность совместной конверсии шлама с более качественным топливом (бурым углем) при разных условиях проведения процесса (коэффициент избытка окислителя, состав топливной смеси, начальная влажность шлама сточных вод); оценить допустимую долю шлама в смеси с углем. Объект: процесс обращенной слоевой газификации смесей бурого угля и шлама сточных вод. Метод: математическое моделирование процесса слоевой термохимической конверсии твердых топлив с помощью разработанной ранее автором стационарной одномерной модели. Результаты. Построены расчетные зависимости характеристик процесса газификации (химический КПД, состав и калорийность газа) от удельного расхода дутья, отношения уголь/шлам (0–100 %) и начальной влажности шлама (10–40 %). Определены максимальные значения доли шлама в смеси с углем при фиксированном на уровне 60–70 % химическом КПД и максимальные значения химического КПД при фиксированной на уровне 20–30 % доле шлама в смеси с углем (для того чтобы избежать спекания слоя). При влажности шлама 40 % его максимальная доля в смеси с углем может достигать 50 % (при исключении спекания). Влага, содержащаяся в шламе, испаряется и выступает в качестве дополнительного газифицирующего агента. При ограничении доли шлама в смеси с углем на уровне 20–30 % эффективность газификации падает незначительно по сравнению с углем без добавок шлама.

Kinetics of thermochemical conversion of the lignite coal in steam flow

Abstract Thermal analysis was applied to determine the kinetic coefficients of the processes that occur in the gasifier. To this end the conditions for such processes to run were simulated in the furnace of thermal analysis under strict kinetic control. The kinetic coefficients of the stages of thermochemical conversion of solid fuels using the NETZSCH Thermokinetics software package are determined. The effect of the steam content in the gas composition during the thermochemical conversion of lignite coal is established. Depending on the steam content in the composition of the gas, competition of mechanisms of interaction of carbon char with steam is shown.

Simulation of sub-bituminous coal hydrodynamics and thermochemical conversion during devolatilization process in a fluidized bed

The majority of the numerical studies conducted on the thermochemical conversion of solid fuels in a fluidized bed have ignored the bed materials inside the bed and just considered the effect of hot air passing the fuel particle. In this study, a sub-bituminous coal particle hydrodynamics during the devolatilization process is modeled inside a 2D fluidized bed in two different cases. In the first case, the energy exchange of inert phase with the fuel particle is included in the simulation and, in the second case, it is ignored. The coal particle’s motion is modeled including the drag force from the bed and the heat and the mass transfer are also simulated during the devolatilization process while the fuel particle is heated up using the chemical percolation devolatilization model. The simulation successfully predicted the motion of the particle inside the bed as well as the temperature increase and volatile release from the particle during the simulation time. The mass loss and temperature history of the fuel particle resulting from the simulation show good agreement with the experimental results. The simulation also indicates that inert particles have a great effect on the heat transfer coefficient inside the bed and ignoring them will cause a difference in the devolatilization time, and this difference will also increase significantly with the increase of the fuel particle’s diameter.

A kinetic analysis of the thermochemical conversion of solid fuels (A review)

The overview is focused on methods for the processing of kinetic curves (with and without models). The paper demonstrates that the kinetics of thermochemical conversion of solid fuels can be described by a great number of kinetic processing methods, which lead to inconsistent estimates of kinetic coefficients. They give a rather simple approximation of experimental thermogravimetric curves. However, the kinetic triplet to be determined (activation energy, order of reaction, and preexponential factor) depends on the conditions of thermoanalytical studies and (to a greater extent) on the reactivity of the test fuels.

PENGARUH LAJU ALIR UDARA DAN WAKTU PROSES GASIFIKASI TERHADAP GAS PRODUCER LIMBAH TANGKAI DAUN TEMBAKAU MENGGUNAKAN GASIFIER TIPE DOWNDRAFT

The continued development of industry and agriculture along with unutilized of industrial and agricultural wastes properly, the waste will only be garbage which can be an interference to environment. Is required to have waste treatment technologies that are effective, efficient and environmentally friendly to utilize the waste into renewable energy sources. The way of handling this waste is to use gasification technology. Gasification is a method of thermochemical conversion of solid fuels into the syngas gas fuel in the gasifier container by supplying a gasification agent such as steam, air and others. The purpose of this research is to determine the effect of air flow rate and the time of gasification process for tobacco leaf stalks waste againts to the composition and the components of syngas. This research is conducted using a gasifier with a capacity of 2.5 kg. The research procedures are drying, crushing, sizing, gasification process, and analysis of gas compositions. The result of this research has proven that tobacco leaf stalks waste has potential to be renewable energy sources which can produce syngas using gasification process. The concentration of syngas (CO, H2 and CH4) which is the highest obtained at variation of Q = 3 m3 / h in minutes 30 with syngas concentration of 2.27% vol CH4, CO gas amounted to 7.17% vol and H2 gas amounted to 5.79 % vol.

Experimental investigation of thermal decomposition of dihydroxybenzene isomers: Catechol, hydroquinone, and resorcinol

In this study, dihydroxybenzene isomers such as catechol, resorcinol, and hydroquinone were used as models of volatiles from solid fuels to better elucidate the mechanism of the thermochemical conversion of solid fuels. These isomers were pyrolyzed in a two-stage tubular reactor with a residence time up to 3.6s and temperature ranging from 650 to 950°C. In total, 51 products were identified by online gas chromatography. The product distribution from the pyrolysis of the three isomers was quite different. p-Benzoquinone was the primary product obtained from the pyrolysis of hydroquinone, while o-benzoquinone and m-benzoquinone were not detected from the pyrolysis of catechol and resorcinol, respectively. CO was the major final product formed from catechol, resorcinol, and hydroquinone, with maximum yields of 27.3wt%, 19.4wt%, and 20.0wt%, respectively, whereas CO2 (15.5wt%) generated from resorcinol was significantly higher than those generated from hydroquinone (1.0wt%) and catechol (0.8wt%) at 950°C and 0.3s. Considering the mass selectivity of C1–C5 light hydrocarbons, the possible reaction pathways leading to CO and CO2 were analyzed to describe the pyrolysis of catechol, resorcinol, and hydroquinone. Catechol mainly afforded CO and C4 hydrocarbons by H-migration and ring-opening reactions. Hydroquinone mainly generated CO, C2, and C4 hydrocarbons, with the initial step being the formation of p-benzoquinone. During the pyrolysis of resorcinol, competition reactions occurred for the formation of CO and CO2 with the production of C1–C5 hydrocarbons at a nearly equal mass selectivity. Compared with catechol and hydroquinone, resorcinol produced significantly more C5 hydrocarbons, which suggested the intramolecular combination of aldehyde radical and ketone radical for explaining the large amount of CO2 formed from the pyrolysis of resorcinol.

Модульные реакторы термохимической конверсии и новые возможности угольных энерготехнологий

The questions of usage of gas generation solid fuel technologies to produce electricity, thermal energy and energy sources (synthetic liquid fuel) based on the technology of thermochemical conversion of solid fuels is considered. The basis of the modular reactors of thermochemical conversion is the principle of conversion of organic material under the influence of temperature, pressure, and oxidizer fl ow rate controlled. The variants of the innovative process are proposed: <br> - Energy application at combined cycle power plants. <br> - Energy application at small thermal power plants with internal combustion engines.<br> - Application at the plants for the production of synthetic liquid fuel or its components.