Modelling fast pyrolysis of biomass in a fluidized bed reactor

Abstract

A compartmental one‐dimensional model of a fluidized bed pyrolytic converter of biomass is presented. Reference conditions are those of non‐catalytic fast pyrolysis of biomass in a shallow fluidized bed with external regeneration of the bed material. The fate of biomass and of the resulting char has been modelled by considering elutriation of biomass and char particles, char attrition as well as bed drain/regeneration. The course of primary and secondary pyrolitic reactions is modelled according to a semi‐lumped reaction network using well‐established kinetic parameters taken from the literature. A specific focus of the present study is the role of the heterogeneous volatile–char secondary reactions, whose rate has been modelled by borrowing a kinetic expression from the neighbouring area of tar adsorption/decomposition over char. The results of computations highlight the relevance of heterogeneous volatile–char secondary reactions and of the closely associated control of char loading in the bed. The sensitivity of the reactor performance to char elutriation and attrition, to proper management of bed drain/regeneration, and to control of gas phase backmixing is demonstrated. Model results provide useful guidelines for optimal design and control of fluidized bed pyrolyzers and pinpoint future research priorities.

Fluidized Bed Pyrolysis of Biomass: A Model-Based Assessment of the Relevance of Heterogeneous Secondary Reactions and Char Loading

“…In the present study, a model-based assessment of the relevance of heterogeneous secondary reactions between pyrolysis vapors and biomass char is undertaken. To this end, a one-dimensional (1D) model based on a simplified, although comprehensive, representation of the key features of the fluidized bed pyrolytic converter has been developed, moving from preliminary results obtained with a simplified compartmental model . The reactor design and operating conditions considered in the model have been selected to minimize the expected secondary interaction between primary products of biomass pyrolysis and the biochar.…”

“…To this end, a one-dimensional (1D) model based on a simplified, although comprehensive, representation of the key features of the fluidized bed pyrolytic converter has been developed, moving from preliminary results obtained with a simplified compartmental model. 45 The reactor design and operating conditions considered in the model have been selected to minimize the expected secondary interaction between primary products of biomass pyrolysis and the biochar. Accordingly, a shallow fluidized bed with overbed feeding of relatively fine biomass particles has been considered.…”

Issue Highlights

“…The model provides useful guidelines for design and control of fluidized bed pyrolyzers and pinpoints future research priorities. [ 2 ]…”

Preface to the special issue section in memory of John R. Grace

“…This special issue includes 18 papers spanning John's main interests in clean energy, [4][5][6][7][8] fluidization and fluidparticle systems, [9][10][11][12][13][14][15][16][17][18] and chemical engineering perspectives [19][20][21] but cannot fully capture his significance. Listing someone's professional work rarely reveals why they leave a unique hole or why those who had the good fortune to regard them as a colleague feel a strong sense of loss.…”