Kinetic modeling and optimization of parameters for biomass pyrolysis: A comparison of different lignocellulosic biomass

A primitive element for the development of sustainable pyrolysis processes is the study of thermal degradation kinetics of lignocellulosic waste materials for optimal energy conversion. The study presented here was conducted to predict and compare the optimal kinetic parameters for pyrolysis of various lignocellulosic biomass such as wood sawdust, bagasse, rice husk, etc., under both isothermal and non-isothermal conditions. The pyrolysis was simulated over the temperature range of 500–2400 K for isothermal process and for heating rate range of 25–165 K/s under non-isothermal conditions to assess the maximum pyrolysis rate of virgin biomass in both cases. Results revealed that by increasing the temperature, the pyrolysis rate was enhanced. However, after a certain higher temperature, the pyrolysis rate was diminished which could be due to the destruction of the active sites of char. Conversely, a decrease in the optimum pyrolysis rate was noted with increasing reaction order of the virgin biomass. Although each lignocellulosic material attained its maximum pyrolysis rate at the optimum conditions of 1071 K and 31 K/s for isothermal and non-isothermal conditions, respectively, but under these conditions, only wood sawdust exhibited complete thermal utilization and achieved final concentrations of 0.000154 and 0.001238 under non-isothermal and isothermal conditions, respectively.     

Kinetic modeling and optimization of biomass pyrolysis for bio-oil production

Thermo-kinetic models for biomass pyrolysis were simulated under both isothermal and non-isothermal conditions to predict the optimum parameters for bio-oil production. A comparative study for wood, sewage sludge, and newspaper print pyrolysis was conducted. The models were numerically solved by using the fourth order Runge–Kutta method in Matlab-7. It was also observed that newspaper print acquired least pyrolysis time to attain optimum bio-oil yield followed by wood and sewage sludge under the identical conditions of temperature and heating rate. Thus, at 10 K/min, the optimum pyrolysis time was 21.0, 23.8, and 42.6 min for newspaper print, wood, and sewage sludge, respectively, whereas the maximum bio-oil yield predicted was 68, 52, and 36%, respectively.     

Studies on pyrolysis of vegetable market wastes in presence of heat transfer resistance and deactivation

In the present investigation, the pyrolysis of predried vegetable market waste (d_p=5.03 mm) has been studied using a cylindrical pyrolyser having diameter of 250 mm under both isothermal and non‐isothermal conditions within the temperature range of 523–923 K with an intention to investigate the effective contribution of different heat transfer controlling regime namely intra‐particle, external along with kinetically control regime on the overall global rate of pyrolysis. Thermogravimetric method of analysis was utilized to obtain experimental data for both isothermal and non‐isothermal cases by coupling a digital balance with the pyrolyser. The pyrolysis of vegetable market waste has been observed to exhibit deactivated concentration independent pyrolysis kinetics, analogous to catalytic poisoning, throughout the entire range of study. The deactivation is of 1st order up to 723 K and follows the 3rd order in the temperature range of 723<T?923 K. Starting from the mechanistic approach, a set of differential heat and mass balance equations has been developed and a general equation containing a specific parameter (dimensionless temperature, θ) is presented which can conveniently be used to simulate concentration time histories of the participating components by assigning different expressions for θ developed in the present investigation. A detailed procedure of simulation work under different controlling regime has also been outlined. A comparison of experimental data with the simulated values under isothermal conditions shows that the system is kinetically controlled at lower temperature region (T?723 K). However, at higher temperature region (723<T<923 K), the pyrolysis process is controlled by intra‐particle heat transfer resistance. While studying the pyrolysis process under non‐isothermal conditions, a segregated ramp function of furnace temperature rise has been used. The transient profiles of the reactant and products have been simulated following the similar procedure followed under isothermal conditions. When experimental data and simulated values are compared, it is observed that unlike the case of isothermal condition, the global pyrolysis rate is controlled by intra‐particle heat transfer resistance. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermodynamic assessment of hydrogen production via solar thermochemical cycle based on MoO2/Mo by methane reduction

Inspired by the promising hydrogen production in the solar thermochemical (STC) cycle based on non-stoichiometric oxides and the operation temperature decreasing effect of methane reduction, a high-fuel-selectivity and CH₄-introduced solar thermochemical cycle based on MoO₂/Mo is studied. By performing HSC simulations, the energy upgradation and energy conversion potential under isothermal and non-isothermal operating conditions are compared. In the reduction step, MoO₂: CH₄ = 2 and 1020 K<T_red<1600 K are found to be most favorable for syngas selectivity and methane conversion. Compared to the STC cycle without CH₄, the introduction of methane yields a much higher hydrogen production, especially at the lower temperature range and atmospheric pressure. In the oxidation step, a moderately excessive water is beneficial for energy conversion whether in isothermal or non-isothermal operations, especially at H₂O: Mo= 4. In the whole STC cycle, the maximum non-isothermal and isothermal efficiency can reach 0.417 and 0.391 respectively. In addition, the predicted efficiency of the second cycle is also as high as 0.454 at T_red = 1200 K and T_oxi = 400 K, indicating that MoO₂ could be a new and potential candidate for obtaining solar fuel by methane reduction.     

热解条件对生物质焦气化活性的影响及等温气化动力学参数求解方法

生物质气化是生物质利用研究的一个重点。生物质气化包含生物质的热解和热解所得焦炭的气化两个过程。不同的热解条件将得到具有不同气化活性的生物质焦炭,不同热解条件制取的焦炭的动力学参数也不相同。本文主要概述了热解条件对生物质焦气化活性的影响。同时基于阿伦尼乌斯公式介绍了生物质焦等温气化动力学参数的两种获取方法,非等转化率法是通过选择动力学模型中的结构因子f(x) 来获取动力学参数,而等转化率法是通过避开选择动力学模型中的结构因子f(x) 来获取动力学参数。基于简单碰撞理论提出了获取等温气化动力学参数的新方法,对阿伦尼乌斯公式中的指数项、指前因子A提出了明确的物理意义。基于简单碰撞理论的等温求解气化动力学参数方法类似于基于阿伦尼乌斯公式的等温求解气化动力学参数方法。     

Thermogravimetric analysis of the co-combustion of coal and paper mill sludge

The thermal behavior of semi-anthracite coal, paper sludge and their blends during pyrolysis and combustion processes was investigated in this study. The experiments were conducted in a differential thermogravimetric analyzer at different heating rates (10 K/min, 20 K/min and 30 K/min) and at temperatures ranging from 310 K to 1300 K. The results revealed that de-volatilization of paper sludge occurred earlier with a higher rate, and that the process was further accelerated under oxygen-enriched conditions. The blends had integrative thermal profiles that reflected both paper sludge and coal. In addition, the blends showed different ignition and combustion behavior depending on the percentage of sludge. Two types of non-isothermal kinetic analysis methods were applied to evaluate the combustion processes. The kinetic parameters of the blends confirmed the improved ignition characteristics. In addition, both the TG profiles and activation energy indicated that the combustion of their blends with low percentages of sludge, such as 10 wt.%, were similar to that of coal. These experimental results help explain and predict the behavior of coal and paper sludge blends in practical applications.     

Pyrolysis Kinetics of Blends of Yeni Çeltek Lignite and Sugar Beet Pulp

Abstract

Pyrolysis kinetics of the Yeni Çeltek lignite/sugar beet pulp blends prepared at different ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100) were investigated by thermogravimetric analysis in the present study. All the experiments were carried out in nitrogen atmosphere under non-isothermal conditions with a heating rate range of 30 K/min in the pyrolysis temperature interval of 298–1,173 K. The Arrhenius model is applied to determine the kinetic parameters from TG/DTG curves. Apparent activation energies of the lignite and sugar beet pulp were calculated as 51.55 kJ/mol and 97.27 kJ/mol, respectively. Activation energies of the blends were also calculated and were found to vary between 54.87 and 74.83 kJ/mol. Effects of blending ratio of lignite to sugar beet pulp on kinetic parameters were investigated and the results were discussed.     

Pyrolysis of hardwoods residues: on kinetics and chars characterization

Evolution of chemical and textural–morphological features characterizing two native Argentinean hardwood species (Aspidosperma Quebracho Blanco Schlecht and Aspidosperma Australe) subjected to pyrolysis at different operating conditions is analysed by several techniques. Surface areas of raw materials and pyrolysed samples are evaluated from physical adsorption measurements employing N₂ at 77 K and CO₂ at 298 K. The samples are also examined by optical and scanning electronic microscopy. Results point to significant feature changes, which are, in general, strongly affected by pyrolysis conditions, particularly temperature. Furthermore, kinetic measurements of woods pyrolysis are performed by non-isothermal thermogravimetric analysis, from ambient temperature up to 1123 K. A deactivation model reported in the literature, which predicts an increase of activation energy with reaction extent, successfully describes kinetic data for both species over the whole range of degradation temperatures.     

Kinetic modeling and simulation: Pyrolysis of Jatropha residue de-oiled cake

An improved kinetic model based on thermal decomposition of biomass constituents, i.e. cellulose, hemicellulose and lignin, is developed in the present study. The model considers the independent parallel reactions of order n producing volatiles and charcoal from each biomass constituent. While estimating the kinetic parameters, the order of degradation of biomass constituents is also checked and found to be matching with the order of degradation reported in the literature. The results of thermo-gravimetric analysis of Jatropha de-oiled cakes are used to find the kinetic parameters. The experimental runs are carried out using a thermo-gravimetric analyzer (TGA 4000, Perkin Elmer). TGA study is performed in a nitrogen atmosphere under non-isothermal conditions at different heating rates and the thermal decomposition profiles are used. The model is simulated using finite difference method to predict the pyrolysis rate. The corresponding parameters of the model are estimated by minimizing the square of the error between the model predicted values of residual weight fraction and the experimental data of thermogravimetry. The minimization of square of the error is performed using non-traditional optimization technique logarithmic differential evolution (LDE).     

Effects of heating rate and water leaching of perennial energy crops on pyrolysis characteristics and kinetics

Aiming to investigate the suitability of perennial crops for heat and power applications, three energy crops produced under the Greek climatic conditions were pyrolyzed by non-isothermal thermogravimetry over the temperature range of 25–850 °C. The effects of heating rate and water washing of the fuels on thermal decomposition characteristics, reactivity and kinetics were examined.The thermochemical reactivity of the biomass materials was determined by their volatile and ash contents, as well as the distribution of organic and inorganic constituents among plant parts. Switchgrass leaves exhibited the highest pyrolysis rate, while cardoon leaves the lowest. An increase of the heating rate delayed thermal decomposition processes and increased degradation rates. Raw fuel washing enhanced reaction rates of switchgrass and giant reed, whereas it influenced the sensitivity of cardoon in nitrogen, by shifting the peak temperature to higher values. A first-order parallel reactions model fitted the experimental results accurately. A higher heating rate, or a lower content of K, P, S and Cl in ashes increased the kinetic parameters corresponding to hemicellulose and cellulose decomposition.     

Impact of fast and slow pyrolysis on the degradation of mixed plastic waste: Product yield analysis and their characterization

This work primarily investigated the pyrolysis of post-consumer mixed plastic wastes during slow pyrolysis (non-isothermal) in a batch reactor to assess the effect of different heating rates on the product yield and its composition. The effect of residence time during fast pyrolysis (Isothermal) in Pyro-GC was also investigated. Initially, TG analysis was performed to investigate the degradation temperature range at different heating rates of 5, 10, 20 and 40 °C/min. Two different heating rates of 10 and 20 °C/min were selected for examining the effect on products such as oil and gases (H₂, CO, CO₂ and C₁-C₆ hydrocarbons) during slow pyrolysis. The oil obtained at higher heating rate had higher density (0.743 kg/m³) while the amount of residue decreased with the increase in heating rate. Also, the effect of residence time during fast pyrolysis was investigated using Pyro-GC at 500 °C for the product formation. It was observed that an optimum residence time of 10sec was favourable for the higher production of lower hydrocarbons (C₁-C₃) and less production of heavier hydrocarbons (C₆). This work represents the combined analysis of fast and slow pyrolysis and their impact on the product yield. Also, the effect of heating rate on non-isothermal condition and the effect of the residence time of volatiles in isothermal condition was analysed and reported.     

油棕废弃物及生物质三组分的热解动力学研究

主要利用热重分析仪(TG)对油棕废弃物和生物质的三组分(半纤维素,纤维素和木质素)的热解特性进行了系统研究,对比分析了热解特性,计算了其热解动力学参数,并研究了升温速率对生物质热解特性的影响。研究发现半纤维素和纤维素易于热降解而木质素难于热解;油棕废弃物的热解可以化分为:干燥、半纤维素热解、纤维素热解和木质素热解4个阶段;生物质的热解反应主要是一级反应,油棕废弃物的活化能很低,约为60kJ/kg;升温速率对生物质影响很大,随升温速率加快,生物质热解温度升高,热解速率降低。     

A one-step non-isothermal method for the determination of effective moisture diffusivity in powdered biomass

The effective moisture diffusivity (D_eff) is an important drying parameter. D_eff is usually calculated using a traditional two-step isothermal method. The current study presents a one-step non-isothermal method as a promising alternative for determining D_eff of biomass particles. Non-isothermal drying experiments were performed at various heating rates (2, 4, 6, 8, and 10 °C min⁻¹) from room temperature to 100 °C. Isothermal drying experiments were also performed to obtain D_eff at five temperatures (50, 60, 70, 80, and 90 °C) for comparison. All experiments were conducted using a thermogravimetric analyzer (TGA) due to its precise temperature control capability and accurate recording of mass loss. Thermal lag was significantly reduced under non-isothermal conditions, and the values obtained by the one-step non-isothermal method were in agreement with those obtained by isothermal procedures.     

Characterisation of oils from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Biomass in the form of pine wood was pyrolysed in an externally heated 7.5 cm diameter, 100 cm high fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The compositions of the oils and gases were determined in relation to the primary fluidised bed and after catalysis at increasing catalyst bed temperatures from 400° to 550°C. The oils were analysed by a number of techniques to determine composition, including liquid chromatography, gas chromatography/mass spectrometry. Fourier transform infrared spectroscopy and size exclusion chromatography. The results showed that the oils before catalysis were highly oxygenated; after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic and polycyclic aromatic species.

The gases evolved from the fluidised bed pyrolysis of biomass were CO₂, CO, H₂, CH₄, C₂H₄, C₃H₆ and minor concentrations of other hydrocarbon gases. After catalysis the concentrations of CO₂ and CO were increased. The conversion of oxygenated compounds was mainly to H₂O at lower catalyst temperatures and CO₂ and CO at high catalyst temperatures. Detailed analysis of the oils showed that there were high concentrations of biologically active polycyclic aromatic species in the catalysed oil which increased with increasing catalyst temperature. The oxygenated compounds in the uncatalysed oil were mainly phenols and carboxylic acids. After catalysis these decreased in concentration with increasing catalyst temperature     

Exergy analysis of hydrogen production from biomass gasification

For a given set of operating conditions, the hydrogen production from biomass gasification can be improved through optimization of the operating parameters and efficiencies. The present approach can predict hydrogen production via biomass gasification in a range of 10–32 kg/s from biomass (sawdust wood). The biomass is introduced to a gasifier at an operating temperature range of 1000–1500 K. Also, 4.5 kg/s of steam at 500 K is used as gasification medium. Results indicate that improvement in hydrogen production from biomass steam gasification depending on the amount of steam and quantity of biomass feeding to the gasifier as well the operating temperature. Over the range of feeding biomass, the hydrogen yield reaches 80–130 g H₂/kg biomass while in the operating temperature examined, the hydrogen yield reaches 80 g H₂/kg biomass. On mole basis it is found that, in the first range of H₂ varies from 51 to 63% in the studied range of feeding biomass in existing 4.5 kg/s from steam while H₂ gets to 51–53% in existing of 6.3 kg/s from steam.     

宁东煤中低温热解特性实验研究

对宁东煤中低温热解特性进行研究,着重考察不同中低温度下宁东煤热解后固、液、气三相产物产率及组成,通过热解炉在相应气氛下进行反应,收集三相产物,分析所得数据来探究不同热解条件对反应的影响规律与反应机理。通过对宁东煤热解处理后得到的固体产物进行等温热重分析,根据热重曲线确认热解程度。采用气相色谱仪对宁东煤热解后得到的液相产物进行分析,研究溶液物质组成及浓度随温度的变化特性;采用气相质谱仪,根据特征峰得出产物类别,并对其进行定量分析。对宁东煤热解气体采用气相色谱仪,研究不同温度下各气体含量,并对宁东煤热解机理进行验证。     

Wood pellet production costs under Austrian and in comparison to Swedish framework conditions

Owing to the rapidly increasing importance of pellets as high-quality biomass fuel in Austria and Europe within the last years, many companies, mainly from the wood industry, are thinking of entering this market. The calculation of the production costs before starting a pellet plant is essential for an economic operation. Based on comprehensive investigations within the EU-ALTENER project “An Integrated European Market for Densified Biomass Fuels” calculations of the pellet production costs loco factory for different framework conditions with basic data based on already realised plants as well as a questionnaire survey of pellet producers in Austria, South Tyrol and Sweden have been performed.

The production costs for wood pellets are mainly influenced by the raw material costs and, in the case of using wet raw materials, by the drying costs. Depending on the framework conditions these two parameters can contribute up to one-third of the total pellet production costs. Other important parameters influencing the pellet production costs are the plant utilisation (number of shifts per week) as well as the availability of the plant. For an economic production of wood pellets at least three shifts per day at 5 days per week are necessary. An optimum would be an operation at 7 days per week. A low plant availability also leads to greatly increased pellet production costs. A plant availability of 85–90% should therefore be achieved.

The calculations show that a wood pellet production is possible both in small-scale (production rates of some hundred tonnes per year) as well as in large-scale plants (some ten thousand tonnes per year). However, especially for small-scale units it is very important to take care of the specific framework conditions of the producer, because the risk of a non-economic pellet production is considerably higher than for large-scale systems.

The direct comparison of typical pellet production costs in Austria and Sweden showed the Swedish pellet production costs to be considerably lower due to larger plant capacities, the combination of pellet production and biomass CHP or biomass district heating plants and the implementation of technologies which allow an efficient heat recovery from the dryers. Moreover, another difference between the Austrian and the Swedish framework conditions is the price of electricity, which is much lower in Sweden.     

Alkali retention/separation during bagasse gasification: a comparison between a fluidised bed and a cyclone gasifier

Biomass fuelled integrated gasification/gas turbines (BIG/GTs) have been found to be one of the most promising technologies to maximise electricity output in the sugar industry. However, biomass fuels contain alkali metals (Na and K) which may be released during the gasification processes and cause deleterious effects on the downstream hardware (e.g. the blades of gas turbines). Much research has therefore been focused on different kinds of gas cleaning. Most of these projects are using a fluidised bed gasifier and includes extensive gas cleaning which leads to a high capital investment.

Increasing alkali retention/separation during the gasification may lead to improved producer gas quality and reduced costs for gas cleaning. However, very little quantitative information is available about the actual potential of this effect. In the present work, comparative bench-scale tests of bagasse gasification were therefore run in an isothermal fluidised bed gasifier and in a cyclone gasifier to evaluate which gasification process is most attractive as regards alkali retention/separation, and to try to elucidate the mechanisms responsible for the retention.

The alkali retention in the fluidised bed gasifier was found to be in the range of 12–4% whereas in the cyclone gasifier the alkali separation was found to be about 70%. No significant coating of the fluidised bed's bed material particles could be observed. The SEM/EDS and the elemental maps of the bed material show that a non-sticky ash matrix consisting of mainly Si, Al and K were distributed in a solid form separated from the particles of bed material. This indicates the formation of a high temperature melting potassium containing silicate phase, which is continuously scavenged and lost from the bed through elutriation.     

Commercial-scale rapid thermal processing of biomass

Rapid Thermal Processing (RTP) utilizes proprietary reactor systems to convert both biomass and petroleum-based materials to high yields of chemical and liquid fuel products. The essential feature is the ability to transfer heat rapidly with precise control of short contact times. The process involves thermal or thermocatalytic refining of biomass, and is somewhat analogous to the refining of petroleum materials. Nevertheless, the chemical and fuel products from biomass are unique, and not similar to petroleum-derived products. Furthermore, RTP is not to be confused with conventional pyrolysis, from which it differs fundamentally with respect to product yield and quality, and process conditions and chemistry. Short-term applications include the production of specialty chemicals, fuel oil substitutes and engine fuels for both diesel and turbine applications. Research in support of these applications is in progress and is briefly reviewed. The paper focuses primarily on the status of RTP hardware, including the operation of a 2.5 tonne day⁻¹ plant and a 25 tonne day⁻¹ commercial plant.