Mathematical Modeling and Experiments on Pyrolysis of Walnut Shells Using a Fixed-Bed Reactor

Abstract

Pyrolysis is a low-emission and sustainable thermochemical technique used in the production of biofuels, which can be used as an alternative to fossil fuels. Understanding the kinetic characterization of biomass pyrolysis is essential for process upscaling and optimization. There is no accepted model that can predict pyrolysis kinetics over a wide range of pyrolysis conditions and biomass types. This study investigates whether or not the classical lumped kinetic model with a three-competitive reaction scheme can accurately predict the walnut shell pyrolysis product yields. The experimental data were obtained from walnut shell pyrolysis experiments at different temperatures (300–600 °C) using a fixed-bed reactor. The chosen reaction scheme was in good agreement with our experimental data for low temperatures, where the primary degradation of biomass occurred (300 and 400 °C). However, at higher temperatures, there was less agreement with the model, indicating that some other reactions may occur at such temperatures. Hence, further studies are needed to investigate the use of detailed reaction schemes to accurately predict the char, tar, and gas yields for all types of biomass pyrolysis.

A Study of Parallel and Competitive Reaction Schemes in Kinetic Modeling of Plastic Pyrolysis

“…The experimental data show that the solid yield drops monotonically with the maximum process temperature, while the tar and gas yields increase with the maximum process temperature for any experiments in the temperature range of 300−500 °C. 23,42 The modeling results from all three models confirmed that, with an increase of the maximum pyrolysis temperature, the final product volume of tar will increase at first and then reach an approximate plateau level for processes that peat at around 400−500 °C.…”

“…The results demonstrate that including secondary char reactions does not enhance the precision of predicting plastic pyrolysis products (at least for the PMMA-like polymer examined here) to the same extent as it did for biomass. The kinetic scheme of Model III most accurately predicts the decomposition of biomass pyrolysis. , Compared to the biomass pyrolysis modeling previously investigated by the authors, , the behavior of plastic pyrolysis is different. The results here suggest that, in plastic pyrolysis, there is the presence of secondary tar reactions, whereas primary char once formed subsequently acts as an inert substance.…”

“…The kinetic scheme of Model III most accurately predicts the decomposition of biomass pyrolysis. 23 , 30 Compared to the biomass pyrolysis modeling previously investigated by the authors, 23 , 30 the behavior of plastic pyrolysis is different. The results here suggest that, in plastic pyrolysis, there is the presence of secondary tar reactions, whereas primary char once formed subsequently acts as an inert substance.…”

“…Some studies investigate the degradation behavior of plastics pyrolysis with lumped kinetic approaches. ,,,− The majority of kinetic work utilizes lumped models because the kinetics are based on the yields of lumped products (i.e., char, tar, and gas). ,,− The conventional parallel competitive reaction model with three primary pyrolysis reactions developed by Agrawal was studied by many authors to predict plastic pyrolysis products. ,, This model is only suitable where the primary degradation of solid mass occurred (300 and 400 °C), but not at higher temperatures. − The authors previously used this reaction scheme and investigated its accuracy in predicting pyrolysis products. They concluded that the competitive reaction model with three reactions needs to be expanded to include the secondary decomposition of pyrolysis products to accurately predict yields.…”

“… 1 , 21 , 22 This model is only suitable where the primary degradation of solid mass occurred (300 and 400 °C), but not at higher temperatures. 21 − 23 The authors 23 previously used this reaction scheme and investigated its accuracy in predicting pyrolysis products. They concluded that the competitive reaction model with three reactions needs to be expanded to include the secondary decomposition of pyrolysis products to accurately predict yields.…”