首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 109 毫秒
1.
研究和推导了城市污泥热解的活化能分布模型(DAEM).采用直接搜索法对模型进行求解,确定其热解动力学参数,并用实验数据对DAEM模型的可靠性进行验证.结果表明,DAEM模型能较好地描述污泥的热解过程,可靠性好.此外,还分析了积分上限对DAEM模型求解精度的影响以及指前因子K0、平均活化能E0和活化能分布的标准偏差δE对热解过程的影响.  相似文献   

2.
生物质热解机理研究进展   总被引:8,自引:0,他引:8  
总结了生物质热解动力学模型的研究进展,指出了全局反应动力学模型的不足之处;由此讨论了包含具体热解产物的热解机理反应模型,介绍了近年来热解机理研究的新方法,同时列举了包含新方法的实验例子;最后指出了热解机理研究中存在的关键问题。  相似文献   

3.
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。  相似文献   

4.
核桃壳热解特性及几种动力学模型结果比较   总被引:2,自引:0,他引:2  
利用热重分析在不同升温速率和氮气气氛下对核桃壳的热失重行为进行研究.根据热重实验数据,采用4种热分析动力学方法(Coats-Redfern法、Doyle法、Ozawa法和DAEM模型),计算核桃壳热解反应活化能E、反应级数n及频率因子A,并进行比较.结果表明:采用不同的动力学分析处理方法,得出的热解动力学参数不同.利用Coats-Redfem法,核桃壳在热解主要阶段(失重10% ~95%)可由一段一级反应过程描述,升温速率20K/min时活化能为55.37k J/mol.Doyle法和DAEM模型得到的结果较为接近,Ozawa法求得的活化能值最高.核桃壳热解包含分子键能断裂的一系列复杂、连续反应过程,并获得核桃壳的热解反应活化能随失重率的变化曲线.  相似文献   

5.
生物质成型燃料热解特性及动力学研究   总被引:3,自引:0,他引:3  
杨帅  杨树斌  甘云华  黄开泉  杨泽亮 《节能技术》2010,28(3):199-201,205
利用NETZSCH STA409PC型热重-差热分析仪对生物质成型燃料在以10℃/min、20℃/min及30℃/min升温速率下的热解过程进行了热重分析。对TG-T、DTG-T曲线分析,结果表明生物质成型燃料热解过程分为干燥、热解预热、热解与炭化4个阶段,热解过程随着升温速率升高出现热滞后现象。对剧烈失重区间建立了反应动力学模型,求解出此温度区间的表观活化能、频率因子等动力学参数。  相似文献   

6.
设计搭建了能实现快速升温功能的大尺寸热重分析(macro thermo-gravimetric analyzer,macro-TGA)实验台,对大尺寸松木样品的热解特性进行了研究.该实验台可以对大尺寸样品(1~40 mm)热解过程的质量、温度信号进行在线测量,有快速升温和匀速升温两种工作模式,其中快速升温模式瞬时升温速率可达2 500℃/min,匀速升温模式升温速率可设定为1~40℃/min.实验结果表明,快速升温模式下热解目标温度为700℃时,5 mm样品热解反应达到80%转化率用时小于2 min,远小于20℃/min匀速升温工况时的9 min.对于尺寸小于10 mm的样品,其热解过程由反应动力学控制,对于尺寸大于20 mm的样品,热解由样品内部的传热控制.采用单组分一步全阶段一阶反应模型对5 mm样品的热解动力学参数进行了求解,结果表明,随着目标温度的上升,样品热解活化能下降,反应活性上升.  相似文献   

7.
不同气氛下柴油热解及热动力学特性分析   总被引:2,自引:0,他引:2  
利用热重分析技术研究了不同载气流量、载气气氛和升温速率下柴油的热解过程.比较分析了单一反应模型和DAEM模型对柴油热解动力学分析的适应性.结果表明,单一反应模型不能在整个温度区间内对柴油热解特性进行预测;而DAEM模型可以由3条不同升温速率下的失重曲线直接得到不同失重率下柴油热解的活化能分布和频率因子的值,较为准确地求解动力学参数.由DAEM模型所得的不同气氛下活化能分布曲线表明,CO2气氛中柴油稳定性更好;柴油在CO2气氛中比N2气氛中热解速度大.  相似文献   

8.
采用热重分析法对玉米芯在600℃热解条件下获得的焦油进行热解特性分析,根据TG与DTG曲线图,定义焦油的活性准则并对其进行判定,建立焦油热解动力学模型,同时对动力学参数进行求解。结果表明:焦油的热解可分为3个阶段,其动力学模型均可用一级反应表示,各阶段的活化能分别为26~33 kJ/mol、13~16 kJ/mol以及10~15 kJ/mol。  相似文献   

9.
陈鸿伟  吴亮  索新良  高松  韩亮 《动力工程》2012,32(3):255-260
研究了热解温度、热解时间以及气化温度对浑源煤焦CO2气化反应的影响,并获得了气化反应的动力学模型.结果表明:浑源煤焦的气化活性随热解温度的提高而降低;每个热解温度都对应着一个最佳热解时间,且存在最佳热解时间随温度升高而缩短的趋势;提高气化温度能够显著提高煤焦的气化反应性能,气化温度对气化反应的影响大于热解温度的影响;低温度煤焦的气化活性随气化温度的提高而增加更为剧烈;900℃及以上的高温使活性点数增加,从而使煤焦间的活性差距分布均匀;浑源煤焦的气化反应适宜用体积模型来描述,所求取的动力学参数之间存在补偿效应,其等动力学温度约为1 199.6℃.  相似文献   

10.
利用热重分析法对炼化废液与褐煤混合物的共热解特性和组分间相互作用进行研究。在升温速率30℃/min条件下,利用Coats-Redfern法求解不同掺混比例的废液固形物与褐煤混合物的热解动力学参数。废液固形物及其与褐煤混合物热解过程可分为三个阶段,而褐煤为两个阶段。随着废液固形物掺混比例的增加,混合物反应活性逐渐升高,TG曲线向低温区偏移且失重程度加剧,挥发分初析温度(t_s)、热解峰温度(t_p)、热解终止温度(t_f)及残留物含量(M_r)减小,最大失重速率(-v_p)、平均失重速率(-v_v)和挥发分综合释放特性指数(D)显著增大。废液固形物与褐煤在共热解过程中存在着一定的相互抑制作用。动力学分析结果表明,热解过程的各个阶段均可用级数反应模型来描述,活化能随温度升高而增大。  相似文献   

11.
The optimal reaction model for analysis of thermal decomposition of various types of biomasses is currently under debate. Four established models for the kinetic analysis of Polygonum lapathifolium were employed in this study: double extrapolation method, Flynn–Wall–Ozawa method (FWO), distributed activation energy model (DAEM), and global kinetic model. The values of activation energy and frequency factor calculated by global kinetic model are much lower than that of the other three methods. Moreover, it has been demonstrated that the activation energy analyzed by FWO method and DAEM is widely distributed and is not directly related to the heating rates, which are more objective than double extrapolation method and global kinetic model.  相似文献   

12.
To develop a model for biomass gasification in fluidized bed gasifiers with high accuracy and generality that could be used under various operating conditions, the equilibrium model (EM) is chosen as a general and case-independent modeling method. However, EM lacks sufficient accuracy in predicting the content (volume fraction) of four major components (H2, CO, CO2 and CH4) in product gas. In this paper, three approaches—MODEL I, which restricts equilibrium to a specific temperature (QET method); MODEL II, which uses empirical correlations for carbon, CH4, C2H2, C2H4, C2H6 and NH3 conversion; and MODEL III, which includes kinetic and hydrodynamic equations—have been studied and compared to map the barriers and complexities involved in developing an accurate and generic model for the gasification of biomass.This study indicates that existing empirical correlations can be further improved by considering more experimental data. The updated model features better accuracy in the prediction of product gas composition in a larger range of operating conditions. Additionally, combining the QET method with a kinetic and hydrodynamic approach results in a model that features less overall error than the original model based on a kinetic and hydrodynamic approach.  相似文献   

13.
A new optimization-based approach to kinetic model reduction is presented. The reaction-elimination problem is formulated as a linear integer program which can be solved to guaranteed global optimality. This formulation ensures that the solution to the integer program is the smallest possible reduced model consistent with the user-set tolerances. The method is applied to generate optimally-reduced models for isobaric, adiabatic homogeneous combustion. The computational cost and accuracy of the reduced models are compared to those of the full mechanism. Results are shown for GRImech 3.0 and the Lawrence Livermore n-heptane combustion mechanism. The accuracy of the integer programming approach is compared to existing reaction elimination methods. The method is also applied to generate a library of reduced kinetic models for an adaptive chemistry simulation of a 2-D laminar, partially-premixed methane burner flame. Preliminary results are presented comparing the computational cost of the full GRImech 3.0 chemistry to that of the reduced model library.  相似文献   

14.
A comparative study of purely diffusion controlled, kinetic, and empirical models has been executed on the predictions of evaporation characteristics of water droplet in a quiescent ambience of air with varying vapor concentrations at different pressures and temperatures. A significant increase in droplet lifetime with free stream vapor concentration has been observed at lower values of the free stream temperature, as predicted by all the models. An increase in ambient pressure increases the droplet lifetime at low temperature, while it does the opposite at higher ambient temperature. The droplet lifetime predicted by the kinetic model is always greater than that predicted by the purely diffusion controlled model. For a droplet of initial radius 20 μm, the purely diffusion controlled and kinetic models underpredict the droplet lifetime as compared to that obtained from the empirical model. For a droplet of initial radius of 5 μm, the purely diffusion controlled model underpredicts the droplet lifetime while the kinetic model overpredicts the same as compared to empirical values. The predictions of lifetime by kinetic models are closer to those obtained from empirical ones in case of evaporation in vapor rich ambience.  相似文献   

15.
A comprehensive computational simulation model has been developed to describe the performance, efficiency and emission characteristics of the four-stroke multi-cylinder spark ignition engine which uses compressed natural gas as a fuel. This model performs an integrated simulation of thermodynamic, gas dynamic, and chemical kinetics of the whole engine system coupling with intake and exhaust manifolds. The thermodynamic combustion process is modelled by using the turbulent flame propagation process with a two-zone chamber (burned and unburned). Gas dynamics in the manifold system are modelled by using unsteady compressible hyperbolic partial differential equations. These equations contain heat transfer, friction, area change in pipe and empirical constants, which are used to determine boundary conditions at pipe junctions, valves and open ends. These equations are transferred into a set of ordinary differential equations by applying the method of characteristics and are solved by the finite difference method. Regarding exhaust emissions, nitric oxide concentrations have been predicted by using the rate kinetic model in the power cycle and along the exhaust pipes. Carbon monoxide is computed under the chemical equilibrium condition and then the empirical adjustment is made for kinetic behaviours based upon experimental results. Finally, predicted results of this model have been compared with experimental results and are found to be compatible. The parametric studies have been conducted with the equivalence ratio and the engine RPM, to predict engine performance. Also, the variations of pressure, temperature, and gas compositions in the exhaust system have been studied.  相似文献   

16.
This research study combustion kinetics of four biomass samples in China, red pine (Pinus tabulaeformis), corn straw (hybrid corn Zheng Dan-958), Bermuda grass and bamboo (Phyllostachys heterocycla var), using thermogravimetric analysis (TGA). Three stages of combustion process are identified as water evaporation, removal and combustion of volatile matters and combustion of char. Thermal kinetic parameters of each sample are calculated by using 1st order Coats–Redfern method based on the TGA data. It is found that the activation energy of the global process is in the range of 53.6–65.2 kJ mol−1 with a poor linear correlation. The experimental data are then used to develop a two−stage reaction kinetic scheme with low temperature region (2nd stage) and high temperature region (3rd stage). The activation energy of the second stage is in the range of 123.5–140.5 kJ mol−1, and that of the third stage was in the range of 59.4–93.4 kJ mol−1, both of which were based on the 1st order Coats–Redfern method. Because the global process of actual combustion is different from the TGA, a modified weighted average model is proposed based on the two−stage reaction kinetic scheme. According to the modified model, the kinetic parameters of the global process for actual combustion are calculated and are all found a little smaller than that of the 2nd stages. That will benefit for the combustion simulation and the design of facility of biomass fuel.  相似文献   

17.
Six global solar irradiation models were tested against data measured at three stations from Romania in the year 2000. One of the tested models, called EIM, is an empirical global solar irradiation model fitted by us, which requires as input a single meteorological parameter associated with the mean daily cloud amount. The accuracy of the EIM is acceptable and comparable to that of parametric models, which need more than one meteorological datum as input. The main conclusion is that such simple empirical “local-models” are a useful alternative for the more complicated one. In addition, the details of obtaining EIM are presented as a driven-tool, which may serve as a guide to elaborate similar simple solar irradiation models in any other location as well.  相似文献   

18.
This study explores the possibility of developing a prediction model using artificial neural networks (ANN), which could be used to estimate monthly average daily global solar irradiation on a horizontal surface for locations in Uganda based on weather station data: sunshine duration, maximum temperature, cloud cover and location parameters: latitude, longitude, altitude. Results have shown good agreement between the estimated and measured values of global solar irradiation. A correlation coefficient of 0.974 was obtained with mean bias error of 0.059 MJ/m2 and root mean square error of 0.385 MJ/m2. The comparison between the ANN and empirical method emphasized the superiority of the proposed ANN prediction model.  相似文献   

19.
This paper investigates the global macroeconomic consequences of country-specific oil-supply shocks. Our contribution is both theoretical and empirical. On the theoretical side, we develop a model for the global oil market and integrate this within a compact quarterly model of the global economy to illustrate how our multi-country approach to modeling oil markets can be used to identify country-specific oil-supply shocks. On the empirical side, estimating the GVAR-Oil model for 27 countries/regions over the period 1979Q2 to 2013Q1, we show that the global economic implications of oil-supply shocks (due to, for instance, sanctions, wars, or natural disasters) vary considerably depending on which country is subject to the shock. In particular, we find that adverse shocks to Iranian oil output are neutralized in terms of their effects on the global economy (real outputs and financial markets) mainly due to an increase in Saudi Arabian oil production. In contrast, a negative shock to oil supply in Saudi Arabia leads to an immediate and permanent increase in oil prices, given that the loss in Saudi Arabian production is not compensated for by the other oil producers. As a result, a Saudi Arabian oil supply shock has significant adverse effects for the global economy with real GDP falling in both advanced and emerging economies, and large losses in real equity prices worldwide.  相似文献   

20.
Hydrogen-air mixing in coaxial jets was investigated using a one-equation model to simulate the velocity scale of turbulence. Combining the density fluctuation with other fluctuating components to define the eddy exchange coefficients, a set of empirical constants was derived for the closure of the partial differential equations that govern the mixing process of heterogeneous fluids. Comparing the numerical results with available experimental data, good agreements were obtained for distributions in velocity, shear stress, enthalpy, and species concentration along both axial and radial directions. The density fluctuation in hydrogen-air mixing, which is very difficult to measure, can be treated by the same method for compressible flows in a homogeneous fluid, provided that the kinetic energy of turbulence is considered simultaneously with all other governing equations.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号