Simulation of Batch Slow Pyrolysis of Biomass Materials Using the Process-Flow-Diagram COCO Simulator

Abstract

The commercial COCO simulation program was used to mimic the experimental slow pyrolysis process of five different biomasses based on thermodynamic consideration. The program generated the optimum set of reaction kinetic parameters and reaction stoichiometric numbers that best described the experimental yields of solid, liquid and gas products. It was found that the simulation scheme could predict the product yields over the temperature range from 300 to 800 • C with reasonable accuracy of less than 10% average error. An attempt was made to generalize the biomass pyrolysis behavior by dividing the five biomasses into two groups based on the single-peak and two-peak characteristics of the DTG (derivative thermogravimetry) curves. It was found that this approximate approach was able to predict the product yields reasonably well. The proposed simulation method was extended to the analysis of slow pyrolysis results derived from previous investigations. The results obtained showed that the prediction errors of product yields were relatively large, being 12.3%, 10.6%, and 27.5% for the solid, liquid, and gas products, respectively, possibly caused by differing pyrolysis conditions from those used in the simulation. The prediction of gas product compositions by the simulation program was reasonably satisfactory, but was less accurate for predicting the compositions of liquid products analyzed in forms of hydrocarbons, aromatics and oxygenated fractions. In addition, information on the kinetics of thermal decomposition of biomass in terms of the variation of fractional conversion with time was also derived as a function of temperature and biomass type.Processes 2019, 7, 775 2 of 20 applications without substantial pretreatment. As an energy source, biomass can be generally converted to biofuels by two possible routes, namely, fermentation and thermal decomposition. Based on the end-products required, thermal decomposition can be classified into direct combustion, gasification and pyrolysis [1][2][3].Pyrolysis is the thermal degradation of biomass by heat in the absence of oxygen that results in the production of charcoal (solid), bio-oil (liquid) and gas products comprising mainly of CO 2 , CO, H 2 and CH 4 . Generally, pyrolysis process operates in the temperatures ranging from 280 to 850 • C with different heating rates and residence times and can be classified into three subclasses: Conventional pyrolysis, fast pyrolysis, and flash pyrolysis.Conventional pyrolysis may also be termed "slow pyrolysis". This type of pyrolysis has been mainly used for the production of charcoal. Slow pyrolysis is characterized by the slow heating rate (less than 10 • C/s) and long residence times of gas and solids with the temperature being around 450 • C [1]. The release of vapor products does not occur as rapidly as in the fast pyrolysis. Thus, components in the vapor phase continue to react with each other, resulting in the formation of char and additional liquids.Fast pyrolysis is a high-temperature process in which biomass is rapidly...

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