稻壳热解气化特性的试验研究

以稻壳为试验原料,DHC-32为催化剂.高纯N2为载气,在管式炉中研究了热解温度和DHC-32催化剂对稻壳热解气化特性的影响.试验结果表明:稻壳热解气中H2,CO含量随热解温度升高而增加,CH4CO2含量随热解温度升高而呈下降趋势;添加DHC-32催化剂后,未改变H2,CO,CH4,CO2含量随热解温度的变化趋势,但对4种气体的相对含量有一定的影响;在试验温度范围内,添加10%DHC-32催化剂比3%DHC-32催化剂对稻壳热解气影响更大一些.     

Production and detailed characterization of bio-oil from fast pyrolysis of palm kernel shell

Bio-oil has been produced from palm kernel shell in a fluidized bed reactor. The process conditions were optimized and the detailed characteristics of bio-oil were carried out. The higher feeding rate and higher gas flow rate attributed to higher bio-oil yield. The maximum mass fraction of biomass (57%) converted to bio-oil at 550 °C when 2 L min⁻¹ of gas and 10 g min⁻¹ of biomass were fed. The bio-oil produced up to 500 °C existed in two distinct phases, while it formed one homogeneous phase when it was produced above 500 °C. The higher heating value of bio-oil produced at 550 °C was found to be 23.48 MJ kg⁻¹. As GC–MS data shows, the area ratio of phenol is the maximum among the area ratio of identified compounds in 550 °C bio-oil. The UV–Fluorescence absorption, which is the indication of aromatic content, is also the highest in 550 °C bio-oil.     

The effect of temperature and hemicellulose-lignin,cellulose-lignin,and cellulose-hemicellulose on char yield from the slow pyrolysis of rice husk

In this work, the effect of temperature on the char yield of untreated rice husk, cellulose removed (hemicellulose + lignin), hemicellulose removed (cellulose + lignin), and lignin removed (cellulose + hemicellulose) is investigated. The work compares the performance of acid and alkaline hydrolysis in the context of lignin removal as well. The effect of hemicellulose-lignin, cellulose-lignin, and cellulose-hemicellulose on char yield during slow pyrolysis of rice husk is also studied. The study reveals that only low temperatures favor char yield. Alkaline hydrolysis effects better lignin removal than acid hydrolysis. The effect of hemicellulose-lignin on char yield is more than cellulose-lignin and cellulose-lignin.     

Fractional characterization of a bio-oil derived from rice husk

Bio-oils usually contain many types of compounds with various chemical properties. A bio-oil sample derived from rice husk through rapid pyrolysis was fractioned using solvent- or solid-extraction techniques based on their various properties. Ultraviolet-visible spectroscopy, three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform infrared spectroscopy were used to characterize their various spectral properties for further understanding the characteristics of the bio-oil. Bio-oil mostly contains many aromatic ring components, acidic polar fractions, few weak- and non-polar components. The results all show that the main compounds and functional groups in the various bio-oil fractions were different and depended on the fractionation methods. The compositions of the bio-oil fractions were also analyzed with a gas chromatography/mass spectrometry (GC/MS) method. The consistency of the results obtained from the spectrometric methods with the GC/MS method indicates that the spectrometric methods have a good potential for rapid and effective characterization of bio-oils.     

稻壳灰显色特征试验研究

在稻壳的变色特征实验台上,通过改变可控电加热炉内的温度(450~900℃),利用CCD图像采集技术,研究了稻壳及热水浸泡稻壳在不同粒径和厚度情形下的变色特征。试验结果表明:未经处理的稻壳在炉内温度高于600℃后,稻壳灰存在黑色颗粒;未经处理的厚层稻壳在750℃附近时,稻壳灰的颜色存在一个相对较浅的状态,而这个状态停止变色的时间明显高于前后两个测点,形成一个凸峰;经过热水浸泡的稻壳形成灰的颜色要浅于未经处理稻壳灰的颜色,且热水浸泡的稻壳形成灰的变色时间随温度的升高而减少;对未经处理的厚层稻壳粉和热水浸泡的厚层稻壳粉在不同炉温加热30 min后,试样的灰度值随温度变化的特征呈双峰分布,在800~850℃存在一个灰度值较高的区域。试验和分析结果为燃稻壳锅炉的设计及稻壳灰的再利用提供了依据。     

电厂废弃稻壳灰水热合成ZSM-5分子筛

以电厂废弃稻壳灰为原料,通过KOH溶液水热处理制取硅溶胶,采用水热合成法制备ZSM-5分子筛。考察了KOH溶液浓度、反应温度和反应时间对Si溶出率的影响,探索出最佳碱溶工艺条件;研究了在复杂合成体系中,模板剂用量、Si/Al等因素对ZSM-5分子筛合成过程的影响;采用XRD,SEM,ICP,TG-DSC,N2吸附脱附等手段进行表征,结果表明,以电厂废弃稻壳灰为原料,在较宽Si/Al范围内(15～2002)均可合成出ZSM-5分子筛;当Si/Al为30～2002时,分子筛产物晶形较为完备,热稳定性好,比表面积较大,微孔分布集中于0.53 nm。     

稻壳和褐煤热解特性的初步研究

利用TG-DSC联用分析稻壳与褐煤热解过程中热失重规律及吸放热情况,结果发现,稻壳的热失重率较大,共热解失重过程相当于二者单独热失重过程的叠加。通过DSC曲线分析稻壳与褐煤热解过程的吸放热量显示,与二者单独热解过程不同的是共热解在高温热分解阶段须吸收大量的热量。利用气相色谱分析不同温度下稻壳与褐煤热解气体产物各组分比例,并与热失重过程相对应分析气体产物变化规律,结果发现,H2和CH4气体组分变化规律相同;与褐煤热解相比,稻壳热解气体产物中CO气体组分较多。总体而言,共热解产物是二者单独热解产物的简单加和,但共热解过程吸放热量变化却显示二者存在热量交换和相互影响。     

Assessment of the rice husk lean-combustion in a bubbling fluidized bed for the production of amorphous silica-rich ash

Rice husk lean-combustion in a bubbling and atmospheric fluidized bed reactor (FBR) of 0.3 m diameter with expansion to 0.4 m in the freeboard zone and 3 m height was investigated. Experiment design - response surface methodology (RSM) - is used to evaluate both excess air and normal fluidizing velocity influence (independent and controllable variables), in the combustion efficiency (carbon transformation), bed and freeboard temperature and silica content in the ashes. Hot gases emissions (CO₂, CO and NO_x), crystallographic structure and morphology of the ash are also shown. A cold fluidization study is also presented. The values implemented in the equipment operation, excess air in the range of 40-125% and normal fluidization velocities (0.13-0.15 Nm/s) show that the values near the lower limit, encourage bed temperatures around 750 °C with higher carbon transformation efficiencies around 98%. However, this condition deteriorated the amorphous potential of silica present in the ash. An opposite behavior was evidenced at the upper limit of the excess air. This thermochemical process in this type of reactor shows the technical feasibility to valorize RH producing hot gases and an amorphous siliceous raw material.     

Optimization and characterization studies on bio-oil production from palm shell by pyrolysis using response surface methodology

In this work palm shell waste was pyrolyzed to produces bio-oil. The effects of several parameters on the pyrolysis efficiency were tested to identify the optimal bio-oil production conditions. The tested parameters include temperature, N₂ flow rate, feed-stock particle size, and reaction time. The experiments were conducted using a fix-bed reactor. The efficient response surface methodology (RSM), with a central composite design (CCD), were used for modeling and optimization the process parameters. The results showed that the second-order polynomial equation explains adequately the non-linear nature of the modeled response. An R² value of 0.9337 indicates a sufficient adjustment of the model with the experimental data. The optimal conditions found to be at the temperature of 500 °C, N₂ flow rate of 2 L/min, particle size of 2 mm and reaction time of 60 min and yield of bio-oil was approximately obtained 46.4 wt %. In addition, Fourier Transform infra-red (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) were used to characterize the gained bio-oil under the optimum condition.     

Gasification of rice husk in two-stage gasifier to produce syngas,silica and activated carbon

Rice husk was utilized in the production of syngas, silica and activated carbon. Experiments were performed in two-stage gasifier for the production of syngas. The syngas is generated with minimum tar yields due cracking of tar at high temperature. Rice husk char obtained from the pyrolysis stage of the reactor was used in the silica extraction process to obtain silica and activated carbon. Using nitrogen as pyrolysis agent high purity (88.46%) silica was obtained with a good quality of syngas as compared to air as pyrolysis agent. Highest surface area of 276.91 m²/gm of silica was found at 500^?C.     

A study on the consecutive preparation of silica powders and active carbon from rice husk ash

Rice husk ash (RHA) is an abundant agricultural by-product. The present research work deals with the production of silica powders and active carbon from RHA with a consecutive method. The RHA is firstly treated with acid leaching to remove mineral composition, and then is boiled with base to leach silica. The filtrate is used to synthesize silica powders with CO₂ precipitator and solid residue is used to prepare active carbon. The optimum conditions of preparing silica powders are as follows: the concentration of Na₂CO₃ is 25 wt.%, the base-leached time is 4 h, and the impregnation ratio of Na₂CO₃ solution to RHA is 6:1. The yield of silica leached from RHA is 84.57 wt.%. The synthesized silica powders are hydrated with amorphous structure, moreover, with a relative smooth surface and high purity. The residue is activated with potassium hydroxide (KOH) after base-leached. The activated carbons are found to be a mixture of micropore and mesopore pore structures. The maximum pore volume, BET surface area and iodine adsorption capacity of as-prepared active carbon can reach 1.22 cm³/g, 1936.62 m²/g and 1259.06 mg/g, respectively. Field emission scanning electron microscopy (SEM) is used to characterize the morphological features of the ash after step by step treatment.     

Rapid and slow pyrolysis of pistachio shell: effect of pyrolysis conditions on the product yields and characterization of the liquid product

This study reports the experimental results for the pyrolysis of pistachio shell under different conditions in a tubular reactor under a nitrogen flow. For the different conditions of pyrolysis temperature, nitrogen flow rate and heating rate, pyrolysis temperature of 773 K gave the highest bio-oil yield with a value of 27.7% when the heating rate and carrier gas flow rate were chosen as 300 K min⁻¹ and 100 cm³ min⁻¹, respectively. Column chromatography was applied to this bio-oil and its subfractions were characterized by elemental analysis, FT-IR and ¹H-NMR. Aliphatic subfraction was conducted to gas chromatography–mass spectroscopy for further characterization. The results for the characterization show that using pistachio shell as a renewable source to produce valuable liquid products is applicable via pyrolysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Utilization possibilities of palm shell as a source of biomass energy in Malaysia by producing bio-oil in pyrolysis process

Agriculture residues such as palm shell are one of the biomass categories that can be utilized for conversion to bio-oil by using pyrolysis process. Palm shells were pyrolyzed in a fluidized-bed reactor at 400, 500, 600, 700 and 800 °C with N₂ as carrier gas at flow rate 1, 2, 3, 4 and 5 L/min. The objective of the present work is to determine the effects of temperature, flow rate of N₂, particle size and reaction time on the optimization of production of renewable bio-oil from palm shell. According to this study the maximum yield of bio-oil (47.3 wt%) can be obtained, working at the medium level for the operation temperature (500 °C) and 2 L/min of N₂ flow rate at 60 min reaction time. Temperature is the most important factor, having a significant positive effect on yield product of bio-oil. The oil was characterized by Fourier Transform infra-red (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) techniques.     

Catalytic pyrolysis of rice husks for syngas production over Fe-based catalyst in a fixed-bed reactor

Rice husk (RH) was pyrolyzed in a fixed-bed reactor between 400 and 800°C with Fe-based catalysts and the outlet gases were analyzed online by gas chromatography. The results showed that Fe₂O₃ has a good catalytic activity in the pyrolysis. The influence of Fe₂O₃ catalyst was to convert RH to largely syngas. The concentration of H₂ increased with increasing temperature and could be released completely at 700°C with the addition of Fe₂O₃. The concentration of CH₄ was not affected, indicating that Fe₂O₃ had no effect on the methanation.     

A comparative study of kinetics for combustion versus pyrolysis of Mesua ferrea husk,soya husk,and Jatropha curcas husk using thermogravimmetry and different methods

The combustion and pyrolysis kinetics of three selected biomasses generated as co-products of the oil and biodiesel industry – namely soya husk (SH), jatropha husk (JH), and Mesua ferrea husk (MH) – using thermogravimetric and differential thermal analysis techniques have been reported. These biomasses were initially characterized for basic fuel property, proximate analysis, ultimate analysis, and fiber analysis. The activation energy calculated using three different kinetic equations, viz. Coats and Redfern, Differential, and Friedman methods for combustion, were found higher than that for pyrolysis for all biomasses at the maximum airflow rate (20ml/min). However, the kinetic parameters are not sufficient alone to explain the suitability of the biomass.     

Selective pyrolysis of paper mill sludge by using pretreatment processes to enhance the quality of bio-oil and biochar products

Paper mill sludge (PMS) is a residual biomass that is generated at paper mills in large quantities. Currently, PMS is commonly disposed in landfills, which causes environmental issues through chemical leaching and greenhouse gas production. In this research, we are exploring the potential of fast pyrolysis process for converting PMS into useful bio-oil and biochar products. We demonstrate that by subjecting PMS to a combination of acid hydrolysis and torrefaction pre-treatment processes it is possible to alter the physicochemical properties and composition of the feedstock material. Fast pyrolysis of pretreated PMS produced bio-oil with significantly higher selectivity to levoglucosenone and significantly reduced the amount of ketone, aldehyde, and organic acid components. Pretreatment of PMS with combined 4% mass fraction phosphoric acid hydrolysis and 220 °C torrefaction processed prior to fast pyrolysis resulted in a 17 times increase of relative selectivity towards levoglucosenone in bio-oil product along with a reduction of acids, ketones, and aldehydes combined from 21 % to 11 %. Biochar, produced in higher yield, has characteristics that potentially make the solid byproduct ideal for soil amendment agent or sorbent material. This work reveals a promising process system to convert PMS waste into useful bio-based products. More in-depth research is required to gather more data information for assessing the economic and sustainability aspects of the process.     

Catalytic steam reforming of bio-oil model compounds for hydrogen production over coal ash supported Ni catalyst

The development of a high performance and low cost catalyst is an important contribution to clean hydrogen production via the catalytic steam reforming of renewable bio-oil. Solid waste coal ash, which contains SiO₂, Al₂O₃, Fe₂O₃ and many alkali and alkaline earth metal oxides, was selected as a superior support for a Ni-based catalyst. The chemical composition and textural structures of the ash and the Ni/Ash catalysts were systematically characterized. Acetic acid and phenol were selected as two typical bio-oil model compounds to test the catalyst activity and stability. The conversion of acetic acid and phenol reached as much as 98.4% and 83.5%, respectively, at 700 °C. It is shown that the performance of the Ni/Ash catalyst was comparable with other commercial Ni-based steam reforming catalysts.     

稻壳变工况反应动力学研究

采用热重分析仪研究了稻壳变工况气化特性,考察了气化反应温度、气化介质流量和操作压力对稻壳气化反应特性的影响,利用反应动力学理论对压力影响反应活化能的变化进行了计算。结果表明:稻壳气化反应过程中,碳转化率随温度的升高而增加,气化剂流量在60 ml/min以上时可以消除气化剂向外扩散的影响,随着气化压力的提高,气化反应速率加快,稻壳试样的碳转化率有所增加,在同一反应时刻,该增加关系并不是线性的,当压力较高时,空气与稻壳的还原反应所受影响较弱,稻壳气化反应活化能随压力增加先降低后上升,该现象说明压力过高对气化反应有抑制作用。     

Manipulation of chemical species in bio-oil using in situ catalytic fast pyrolysis in both a bench-scale fluidized bed pyrolyzer and micropyrolyzer

In situ catalytic fast pyrolysis (CFP) of biomass was conducted with base or acid catalysts in a bench-scale fluidized bed pyrolyzer. Complete mass balances were performed, allowing for quantitatively investigating the catalytic impacts on the final bio-oil composition. Acidic catalysts exhibited relatively higher activities for decomposition of sugar and pyrolytic lignin, dehydration, decarbonylation, and coke formation, as relative to base catalysts. Carbon balances revealed that a significant amount of carbon in bio-oil was transformed to coke during CFP. Due to the decrease in the bio-oil yield during CFP, significantly less energy was recovered in CFP products than in control fast pyrolysis products. CFP was also performed in micropyrolyzer and the results were compared with those in the bench-scale reactor to determine the consistency across the experimental systems. Different from the bench-scale pyrolyzer, the basic catalyst more strongly influenced the micropyrolyzer products and the discrepancies suggest a more rapid deactivation of the basic catalyst.     

Chemical characteristics of bio-oil from beech wood pyrolysis separated by fractional condensation and water extraction

The combination of two environmentally friendly methods was successfully performed to separate target chemicals from the beech wood pyrolytic bio-oil. Firstly, the fractional condensation pyrolysis oil was carried out using a system with three condensers. The effect of the temperature of the first and second condenser was studied. Water extraction was realized to further the separation of products from different condensers. Each chemical compound of the bio-oil products was identified and quantified using GC-MS and GC-FID. Distribution ratios of the target chemicals were calculated.Water and carboxylic acids were mainly recovered in the second and third condensers, whereas phenolics and sugar were mainly found in the first condenser. An increase in the first condenser temperature promoted the selectivity for phenolic and sugar compounds. Separation by water allowed recovering sugars in the water-soluble fraction, whereas phenolics remain in the water-insoluble fraction. Polarity, boiling point and water solubility of chemicals appear as key factors for process optimization.