Prediction accuracy in modelling beech wood pyrolysis at different temperatures using a comprehensive, CFD-based single particle pyrolysis model

CFD modelling is a novel approach to overcome problems in predicting the pyrolysis outcome in a reliable and repeatable way. It allows through real-time, model-based investigation the assessment of parameters that are impossible to be analysed experimentally. The aim of this study was to establish a comprehensive 2D single particle model of beech wood pyrolysis, which would be a reliable tool for process optimization with respect to the properties of the resulting liquid and solid pyrolysis products (biochar). The model comprised the primary biomass degradation according to the RAC kinetic scheme (48 compounds). Modelled wood cylinders were in a dry state and had a size of Ø8 mm x 10mm, with 660 kg/m3 bulk density and 1430 kg/m3 true density. The model was validated with experimental data of pyrolysis of dry beech wood cylinders, conducted in a single-particle reactor at 5 different temperatures (300, 400, 500, 700, 900 °C). The validation dataset consisted of the evolution of particle’s center and surface temperatures, mass loss, and composition of 14 evolved volatiles (CO2, CO, H2O, CH4, C2H4, formaldehyde, acetic acid and furfural, among others). Prediction of the particle’s temperature and mass loss evolution were deemed accurate. For all products, up to 500 °C, the predictions differed from the experimental data by a few %. For the temperature range between 700 °C and 900 °C, the model however, strongly over-predicted the yield in bio-oil at the expense of pyrolysis gases. The implemented primary kinetic scheme showed satisfactory results in the investigated temperature range. However, the model did not reflect very well the pyrolysis products evolution at higher temperatures (thermal tar cracking and gasification range), so implementation of accurate secondary kinetic schemes is deemed necessary

Evaluation of heat transfer models at various fluidization velocities for biomass pyrolysis conducted in a bubbling fluidized bed

Four different models for heat transfer to the particles immersed in a fluidized bed were evaluated and implemented into an existing single particle model. Pyrolysis experiments have been conducted using a fluidized bed installed on a balance at different temperatures and fluidization velocities using softwood pellets. Using a heat transfer model applicable for fluidized beds, the single particle model was able to predict the experimental results of mass loss obtained in this study as well as experimental data from literature with a reasonable accuracy. A good agreement between experimental and modeling results was found for different reactor temperatures and configurations as well as different biomass types, particle sizes ¿ in the typical range of pellets - and fluidization velocities when they were higher than U/Umf=1.5. However, significant deviations were found for fluidization velocities close to minimum fluidization. Heat transfer models which consider the influence of fluidization velocity show a better agreement in this case although differences are still present.This project has received funding from European Union's Horizon 2020 Research and Innovation Programmeunder grant agreement number 731101 (BRISK II)

Surface properties and chemical composition of corncob and miscanthus biochars: effects of production temperature and method

Biochar properties vary, and characterization of biochars is necessary for assessing their potential to sequester carbon and improve soil functions. This study aimed at assessing key surface properties of agronomic relevance for products from slow pyrolysis at 250-800 °C, hydrothermal carbonization (HTC), and flash carbonization. The study further aimed at relating surface properties to current characterization indicators. The results suggest that biochar chemical composition can be inferred from volatile matter (VM) and is consistent for corncob and miscanthus feedstocks and for the three tested production methods. High surface area was reached within a narrow temperature range around 600 °C, whereas cation exchange capacity (CEC) peaked at lower temperatures. CEC and pH values of HTC chars differed from those of slow pyrolysis biochars. Neither CEC nor surface area correlated well with VM or atomic ratios. These results suggest that VM and atomic ratios H/C and O/C are good indicators of the degree of carbonization but poor predictors of the agronomic properties of biochar

Production and characterization of bio-oil from fluidized bed pyrolysis of olive stones, pinewood, and torrefied feedstock

Advancements in fluidized bed pyrolysis mechanisms and analytical methodologies are critical for progress in the  biorefinery sector in general and the aviation fuel sector in particular. The statistical modelling of pyrolysis  product yields and composition allowed us to observe advantages of operating temperature and feedstock selections over the torrefaction process and catalyst addition in a fluidized bed reactor. Results suggest that the  chemical composition and physical properties of bio-oil from pyrolysis of olive stones at 600◦C and pinewood  pellets at 500◦C are the most suitable for use as fuels. This work suggests that only combined use of selected gas  chromatography mass spectroscopy, UV fluorescence, nuclear magnetic resonance spectroscopy, and rheology  can provide comprehensive information on pyrolysis bio-oil composition. Importantly from a technological point  of view, bio-oil was characterized i) by a viscosity similar to that of fossil-based oil; ii) by a low oxygen and water  content; and iii) by a balanced composition of aliphatic and aromatic species. These factors indicate that bio-oil  from fluidized bed pyrolysis of biomasses is a promising material for use in the aviation industry and energy  production.  </p