Pyrolysis Model of Single Biomass Pellet in Downdraft Gasifier

By coupling the heat transfer equation with semi-global chemical reaction kinetic equations, a onedimensional, unsteady mathematical model is developed to describe the pyrolysis of single biomass pellet in the pyrolysis zone of downdraft gasifier. The simulation results in inert atmosphere and pyrolysis zone agree well with the published experimental results. The pyrolysis of biomass pellets in pyrolysis zone is investigated, and the results show that the estimated convective heat transfer coefficient and emissivity coefficient are suitable. The mean pyrolysis time is 15.22%, shorter than that in inert atmosphere, and the pellet pyrolysis process in pyrolysis zone belongs to fast pyrolysis. Among the pyrolysis products, tar yield is the most, gas the second, and char the least. During pyrolysis, the temperature change near the center is contrary to that near the surface. Pyrolysis gradually moves inwards layer by layer. With the increase of pyrolysis temperature and pellet diameter, the total pyrolysis time, tar yield, char yield and gas yield change in different ways. The height of pyrolysis zone is calculated to be 1.51—3.51 times of the characteristic pellet diameter.

A granular-biomass high temperature pyrolysis model based on the Darcy flow

We established a model for the chemical reaction kinetics of biomass pyrolysis via the hightemperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteristics of the liquid prdoducts., tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure, and other parameters on biomass pyrolysis and high-temperature tar cracking were investigated numerically, and the results were compared with experimental data. The simulation results showed a large endothermic pyrolysis reaction effect on temperature and the reaction process. The pyrolysis reaction zone had a constant temperature period in several layers near the center of large biomass particles. A purely physical heating process was observed before and after this period, according to the temperature index curve.

An analytical model for pyrolysis of a single biomass particle

Decreasing in emissions of greenhouse gases to confront the global warming needs to replace fossil fuels as the main doer of the world climate changes by renewable and clean fuels produced from biomass like wood waste which is neutral on the amount of CO2. An analytical and engineering model for pyrolysis process of a single biomass particle has been presented. Using a two-stage semi global kinetic model which includes both primary and secondary reactions, the effects of parameters like shape and size of particle as well as porosity on the particle temperature profile and product yields have been investigated. Comparison of the obtained results with experimental data shows that our results are in a reasonable agreement with previous researchers' works. Finally, a sensitivity analysis is done to determine the importance of each parameter on pyrolysis of a single biomass particle which is affected by many constant parameters.

Free radical reaction model for n-pentane pyrolysis

A mathematical mechanism of the n-pentane pyrolysis process based on free radical reaction model was presented.The kinetic parameters of n-pentane pyrolysis are obtained by quantum chemistry and the reaction network is established. The solution of the stiff ordinary differential equations in the n-pentane pyrolysis model is completed by semi implicit Eular algorithm. Then the pyrolysis mechanism based on free radical reaction model is built,and the computational efficiency increases 10 times by algorithm optimization. The validity of this model and its solution method is confirmed by the experimental results of n-pentane pyrolysis.

Downer reactor simulation and its application on coal pyrolysis:A review

Pyrolysis technology has received increasing attention in recent years due to its great potential in the field of lowrank coal clean and efficient conversion.Since pyrolysis reaction is very fast and prone to overreaction,the downer-type reactor is considered as a pyrolyzer due to its unique plug flow reactor characteristics.However,the low solids holdup,which is not beneficial for the fast heat transfer,limits its industrial application.Thus,how to realize high-density operation is crucial to the successful application of the downer reactor.Herein,the definition and strategies of high-density operation in the downer were introduced at first.And then,considering the increasing influence of computational fluid dynamics(CFD)in the fluidization industry,the state-of-the-art progress in downer simulation was reviewed,in which the newly developed drag models for downers were carefully discussed and compared.Also,to help prediction of the pyrolysis behaviors,the widely used pyrolysis kinetic models were systematically summarized.Combined with the potential of the downer in the field of coal pyrolysis,the relevant research progress of hot-state simulation of the downer pyrolyzer were introduced and analyzed.Finally,the suggestions on how to carry out follow-up work were given.It is expected that this review could give a better understanding for designing and optimizing downer pyrolyzer.