玉米秸秆催化热解试验研究

利用自行设计的固定床快速热裂解试验系统,研究了玉米秸秆催化热解(催化剂为CaO)规律及催化剂对热裂解产物分布的影响,探讨了CaO的催化机理.结果表明,750℃时,CaO在促进焦油裂解的同时,也促进了焦炭和气体产物的生成;CaO对气体产物中的CO2具有吸附作用,降低了CO2的含量,它对大分子脱氢具有明显的催化选择性,增加了产气中H2的含量.在试验中采用了2种催化剂添加方式,添加比为1:1(质量比);分析了不同催化剂添加方式对催化热解的影响;采用悬挂方式时产气率达到57.68%;采用混合方式时,燃气中H2含量高达33.33%,燃气热值达到了12.389 MJ/m3.     

焦油模型化合物萘裂解耦合铁矿直接还原炼铁

以铁矿粉作为焦油裂解的催化剂,将焦油降解与铁矿还原相耦合,利用还原铁矿的催化作用,促进焦油降解转化,同时强化铁矿还原。选取焦油模型化合物萘,通过实验探讨不同热解温度、质量配比、铁矿粉粒径对模型化合物转化率、热解气体产量以及铁矿粉还原度的影响。结果表明:热解温度为600~1 000℃时,铁矿粉作用下萘的转化率随热解温度的升高而迅速增加;改变质量配比、铁矿粉粒径对萘的催化转化均有很大影响;在最优操作条件下(热解温度为1 000℃,热解时间为30 min,铁矿粉粒径为74~98μm,质量配比为1∶1),萘的转化率可达到84.5%,铁矿粉还原度可达到78.5%。     

提高生物质热解气化燃气热值的甲烷化技术

甲烷化技术应用于生物质气化，是改善燃气质量、提高燃气热值的有效方法。生物质气化气经过甲烷化技术处理以后，燃气的热值可增加3360kJ／m^3，焦油含量小于10mg／m^3，大大优化了气体的成分。     

木耳种植废料的低焦油气炭联产技术研究

文章利用生物质复合式固定床低焦油热解气化中试装置,对木耳种植废料进行了热解气化、产炭试验研究,探讨了以木耳种植废料为原料的复合式固定床低焦油气化炉的启动特性,二次风量对气体重整区温度和出炉燃气热值的影响,气体重整区温度对燃气成分和焦油裂解的影响,出炭量对生物质炭品质的影响以及稳定工况下的炉内温度分布等。试验结果表明:复合式固定床气化装置启动时间较长;二次风量与气体重整区的温度呈正向变化,与燃气热值呈反向变化;气体重整区的高温对燃气中焦油的裂解效果显著;气炭联产适宜的出炭率为25%~30%。文章研究结果对木耳种植废料的能源化利用具有指导意义。     

生物质与煤流化床催化气化制备燃气

基于单一流化床两步气化法,以煤作为热载体和发热体,水蒸气为气化剂,CaO为催化剂,在自行研制的流化床热态装置上对生物质（锯木）气化制备燃气进行了研究。探讨了温度和水蒸气与锯木比对燃气组分和低位热值的影响。在所研究的操作参数范围内,（H2 + CO）含量为67.58% ~ 74.9%,燃气低位热值为10719.09 kJ/Nm3 ~ 12002.44 kJ/Nm3。实验结果表明,含少量N2的中热值燃气可以被获得,H2和CO是燃气中最主要的两种气体。随着温度的升高,燃气中H2和CO含量增加,而CH4和CO2含量及燃气低位热值则呈现下降趋势。随着水蒸气与锯木比的增加,燃气中H2和CO2含量增加,而CH4和CO含量则相应的减小。     

两级下吸式生物质气化炉气化性能的研究

在自行设计的两级下吸式生物质气化炉中,研究了空气当量比(ER)对气体组成、气体热值、气化效率以及焦油含量的影响。试验结果表明,该新型两级气化炉能够产生焦油含量较低的燃气;在空气预热的条件下,焦油含量更低,可达238 mg/m3。该新型两级气化炉的最佳ER为0.33~0.35,当ER=0.34时,气化气低位热值(LHV)最高为4 409 kJ/m3,气化效率为63.7%,焦油含量低于300 mg/m3。     

在流化床气化炉中生物质与煤共气化研究(Ⅱ)——以水蒸汽为气化剂生产中热值燃气

以水蒸汽为气化剂,用玉米芯/煤以不同比例为原料,在600kW流化床气化炉上,按二步法制气工艺进行连续运行实验.实验研究了影响燃气热值、气体产率、燃气组成及气化效率的主要因素,确定出气化炉适宜的操作条件及较佳的原料配比范围.得出气化温度为950～1000℃,玉米芯/煤的比例为80/20,S/B在0.7～0.9范围内,燃气热值11～13MJ/m3,气体产率1.1～1.3m3/kg,气化效率75%～80%,燃气中焦油含量小于0.9mg/m3的结果.通过将本技术与国外现有生产中热值燃气的方法进行比较,发现本技术具有产生较高热值燃气和燃气中低焦油含量等优点.     

不同催化剂下玉米秸秆热解产物特性研究

在管式加热炉中对玉米秸秆进行了热解实验研究,分别在纯秸秆热解和添加催化剂(CaO、循环流化床锅炉炉渣、炉灰)的条件下进行了对比实验研究.实验结果表明,添加催化剂后热解气中COz体积含量都有显著下降,同时,添加催化剂后热解气中可燃气成分在增加;通过实验还发现,添加炉灰能够得到最高气体产率、最低液体产率.添加炉渣能够得到最高的气体热值,与纯秸秆热解相比,气体热值提高了75.4%.     

不同作物秸秆热解及其差异性分析

以水稻、小麦、玉米、棉花、油菜5种农作物秸秆为研究对象,采用管式炉对其进行热解实验,探讨热解产气量的差异性。实验结果表明在5种生物质秸中,油菜秸热解产气率为0.28 L/g,热解产物中的CO和H2气体含量分别为31.6%和26.3%,原料热值与热解燃气中可燃气体的低位热值分别为12345.84 kJ/kg和10.51 MJ/m3,5项值在5种秸秆中均为最高。5种秸秆样品的SEM照片显示其表质层分布和筛管结构形状、大小均不相同;样品的C元素含量、O/C原子比率及颗粒结构的差异会影响其热解产气总量与产物中CO气体含量。     

生物质二次裂解制取氢气的研究

采用生物质热解及二次裂解的方法制取富氢气体.通过对生物质热解产生的气液体成份进行二次裂解,实现热解组分中焦油等含氢化合物的深度转化,提高产品气体中氢气的含量,同时解决了热解产品气中焦油不易去除的难题,得到洁净的富氢气体.实验选用稻壳为原料,分析了热解温度和物料滞留时间等因素对热解气体成份的影响,比较了热解气体和二次裂解气体成份的变化,同时分析了水蒸汽、催化剂等因素对裂解气体成份的影响.实验结果表明,热解温度和物料滞留时间的增加提高了热解气体中氢气的含量,二次裂解、水蒸汽和催化剂的引入都能在一定程度上提高产品气中H2的含量.实验最终表明,氢气体积含量可达到60%以上.     

Study on solid waste pyrolysis coke catalyst for catalytic cracking of coal tar

Low value solid waste pyrolysis coke was used as a catalyst to catalytically crack gas-phase tar to improve tar yield and gas production. Pyrolysis coke with different pyrolysis final temperature and pyrolysis time were prepared, the effect of tar cracking products was studied, and the optimal pyrolysis coke were screened. The pyrolysis coke catalyst was characterized by BET, FTIR, SEM. The results show that the optimal preparation final temperature of pyrolysis coke is 750 °C, and the optimal preparation pyrolysis time is 2 h. Compared with the pyrolysis of raw coal, the tar cracking rate increased by 9.3%, after added the pyrolysis coke catalyst, the gas increased by 23.2%, and the light component increased to 36.6%. And the OH, C–N and C–O–C functional groups present on coke are the factors that affect the catalytic cracking.     

生物质炭催化裂解焦油的性能研究

采用管式反应器研究了生物质炭作为焦油裂解催化剂的性能,选用白云石和石英砂作对比试验。通过对焦油转换率、裂解产物、裂解气气体组分和动力学参数的分析对比可知:在所选用的3种材料中,生物质炭作为催化剂的焦油转化率最高,裂解产物中气体所占比重最大,且可燃气体的组分较高,反应动力学参数最小。生物质炭的催化性能显著高于石英砂,稍好于白云石,是一种高效的焦油裂解催化剂。     

生物质炭催化裂解焦油的实验研究

通过实验方法研究了生物质炭对生物质热解焦油的催化特性。通过分析焦油裂解率在催化剂及其重量、蒸汽加入量和加入方式、氮气流量等条件下的变化可知:在蒸汽条件下,生物质炭对焦油有显著的催化裂解效果,最高焦油转化率可达96.1%。通过对实验条件下裂解产物、裂解气体积分数的分析可知,生物质炭和蒸汽可以促进热解产物里面的可凝结相转化为不可凝结的气体,并且导致气体组分体积分数的变化。裂解气中氢气产量增加较快,最高可达裂解气体积的50.2%。     

Hydrogen-rich gas production by steam gasification of palm oil wastes over supported tri-metallic catalyst

The catalytic steam gasification of palm oil wastes for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor using the newly developed tri-metallic catalyst. The results indicated that the supported tri-metallic catalyst had greater activity for the cracking of hydrocarbons and tar in vapor phase and higher hydrogen yield than the calcined dolomite in catalytic steam gasification of palm oil wastes. A series of experiments have been performed to explore the effects of temperature, steam to biomass ratio (S/B) and biomass particle size on gas composition, gas yield, low heating value (LHV) and hydrogen yield. The experiments demonstrated that temperature was the most important factor in this process; higher temperature contributed to higher hydrogen production and gas yield, however, it lowered gas heating value. Comparing with biomass catalytic gasification, the introduction of steam improved gas quality and yield, the optimal value of S/B was found to be 1.33 under the present operating condition. It was also shown that a smaller particle size was more favorable for gas quality and yield. However, the LHV of fuel gas decreased with the increasing S/B ratio and the decreasing biomass particle size.     

Numerical simulation on biomass-pyrolysis and thermal cracking of condensable volatile component

We studied the physical and chemical properties of the condensable volatiles of biomass pyrolysis products. We redefine the liquid product and divide the condensable volatiles into two categories, biomass oil and tar, the latter of which comes from the secondary pyrolysis or cracking reaction of the former. We further establish a kinetic model of biomass pyrolysis and secondary cracking. The chemical reaction kinetics equation and heat transfer equation are coupled to simulate the biomass pyrolysis process. For biomass solid particles, the model not only considers the initial reaction of biomass and secondary cleavage reaction of condensable gas, but also introduces a reaction mode in which biomass oil is converted into tar. When the pyrolysis temperature is below 500 °C, the pyrolysis products are essentially biomass oil. However, when the pyrolysis temperature exceeds 500 °C, the biomass oil gradually converts into tar. The model also considers characteristics of the reaction medium (porosity, intrinsic permeability, thermal conductivity) and the unsteady gas phase process based on Darcy's law of velocity and pressure, heat convection, diffusion, and radiation transfer. We analyze the relationships among the internal temperature of the particles, particle size and position, mass fraction of the reactants and products, the gas mixture, the production share of tar and biomass oil, and the relationship between gas pressure and time. The results show that the effects of the secondary cracking reaction and internal convective flow in the biomass pyrolysis process are coupled because the flow field in the porous medium determines the volatile residence time and thus species that affect the secondary cracking reaction. The rate of volatile formation in the initial and secondary cracking reactions affects the pressure gradient and gas diffusion. Additionally, the endothermic effect influences the temperature field of the pyrolysis reaction but has no apparent effect on small particles whose chemical reaction is the control mechanism. For large particles, heat transfer inside the particles is the diffusion control mechanism and the chemical reaction on the particle surface is the speed control mechanism. Two peaks are observed in the pyrolysis gas mass proportion curve, which result from the consumption of biomass oil and tar as they flow toward hot surfaces. The first peak is the decomposition of biomass oil into non-condensable volatile matter and tar, and the second peak is the further cracking of tar into gas and coke at high temperature.     

Modeling of beech wood pellet pyrolysis under concentrated solar radiation

A two-dimensional, unsteady CFD (Computational Fluid Dynamics) single particle model was developed and used to simulate the solar pyrolysis process of beech wood pellets (10 mm in diameter and 5 mm in height). Pseudo-stoichiometric coefficients about the mass fraction of primary tar converted by the reaction into gas and secondary tar were determined at different temperatures and heating rates for the first time. The 2D model predictions were successfully validated with tests performed at 600 °C to 2000 °C final temperature, with 10 and 50 °C/s heating rates. The evolution of the final products and mass losses of pyrolyzed biomass are enhanced with temperature and heating rate. Moreover, the higher the temperature and heating rate, the higher the gas yield. This emphasizes the intra-particle tar secondary reaction into gas for pyrolysis of large size sample under high temperature and heating rate.     

High quality H2-rich syngas production from pyrolysis-gasification of biomass and plastic wastes by Ni–Fe@Nanofibers/Porous carbon catalyst

To produce the high quality H₂-rich syngas from biomass and plastic wastes, a two-stage pyrolysis-gasification system involving pyrolysis and catalytic gasification is considered as a suitable route. Generally, synthesis of highly active, low cost and coke-resistant catalyst for tar cracking is the key factor. A series of monometallic catalysts of Ni@CNF/PCs and Fe@CNF/PCs and the bimetallic Ni–Fe@CNF/PCs catalyst were prepared by a simple one-step pyrolysis approach for high quality syngas production from pyrolysis-gasification of biomass and plastic wastes. The results indicated that the bimetallic Ni–Fe@CNF/PCs catalyst appeared as the optimal catalyst in affording the best compromise between catalytic activity and stability with the existence of the excellent dispersibility of the Fe0.64Ni0.36 alloy nanoparticles and the carbon nanofibers/porous carbon composite structure. In addition, the optimal operation conditions of biomass/plastic ratio of 1/2 and gasification temperature of 700 °C were observed for the bimetallic Ni–Fe@CNF/PCs catalyst to play best roles in the H₂-rich syngas quality, with up to 33.66 mmol H₂/g biomass, and tar yields as low as 5.66 mg/g.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm³/g_wood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm³/g_wood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.