Jean-Philippe Laviolette

Determination of Enthalpy of Pyrolysis from DSC and Industrial Reactor Data: Case of Tires

Abstract This study was motivated by the fact that differential scanning calorimetry (DSC)/differential thermal analysis (DTA) results in literature showed significant exothermic peaks while in overall, pyrolysis is an endothermic phenomenon. The specific heat of the decomposing tires has been determined with a new methodology: instead of assuming constant char properties throughout pyrolysis, the specific heat of evolving solids (char) was evaluated with increasing temperature and conversion. Measured specific heat values were observed to increase until pyrolysis was triggered at 250°C. Then, the specific heat of the solids decreased continuously until 400°C at which point they started to increase. This unexpected trend pointed out that the exothermic peak observed with DSC is an artefact generated by the control system of the apparatus. To overcome this limitation, the energy balance was performed over industrial data and the newly found heat capacity values. The enthalpy of pyrolysis was found to have a term dependent on the weight loss derivative, with a constant value of 410 kJ/kg tires. Two other terms for the enthalpy of pyrolysis have been identified, which were independent of weight loss. The first one is believed to correspond to the sulphur cross-link breakage at low temperature (65 kJ/kg), while the second one, at the final stage of pyrolysis, should correspond to charring reactions approaching the thermodynamic equilibrium (75 kJ/kg). Ultimately, this work proposes a new methodology to determine the enthalpy of pyrolysis with larger scale experimental data.

Biomass Pretreatments for Biorefinery Applications: Gasification

Biorefinery is the object of significant research and development efforts due to the scarcity of economically viable crude oil, renewable energy source, and its environmental benefits. This has prompted chemical corporations to look for alternative sources of carbon and hydrogen to produce chemicals, biologics, and other products such as biomass and waste matter. Two main reaction pathways are currently explored for biorefinery: thermochemical and biochemical. The thermochemical pathway proposes significantly higher reaction rates compared to current biological processes that use non-genetically modified organisms. One of the thermochemical pathways for biomass conversion is gasification which is a decomposition of solid fuels at high temperatures and oxygen-lean atmosphere. The successful development of biomass gasification processes requires addressing several critical technical difficulties including biomass diversity, feedstock treatment, gasification mechanism and reactions, gasifier types, and their performances. This chapter reviews key features of biomass gasification as a pretreatment for biorefining which can be used as a practical guide for gasification process. This chapter consists of six sections that include types of biomass for gasification, their properties, and pretreatment steps; gasification mechanism and reactions; syngas cleaning and conditioning; different gasifier, their characteristics, and modeling.

Gas-Phase Combustion in the Freeboard of a Fluidized Bed-Freeboard Characterization

The prediction of propane autoignition in the freeboard of a fluidized bed is complicated by the presence of solids, intermediate products and non-homogeneities (solids, temperature and species gradients) that should be accounted for in a reaction model. However, the simultaneous characterization of these parameters during combustion is very challenging. An experimental study of propane combustion inside the freeboard (I.D.=0.2 m) of a fluidized bed of sand (Ug=290 μm) was performed at a low superficial gas velocity (Ug=0.24 m/s). Propane was injected inside the fluidized bed (TBed=650°C) through a downward-facing sparger. Also, solids flux and species volume fractions were measured using a non-isokinetic sampling probe. The results showed an exponential decrease with height of the upward solids flux (GSU)−GSU was zero at 0.17 m above the bed surface, which was taken as the inflection point of the Gsu curve. GSUo measurements were significantly higher than the values given by the correlation of (1982). The bed surface (boundary condition) and freeboard were characterized by measuring pressure, solids flux, species volume fractions and temperature at several radial and axial positions. During the experiments, the fluidized bed achieved a pseudo steady-state operation that ensured that the measured temperature profile corresponded to the solids flux and species fractions. Partial propane combustion in the fluidized bed (71%) produced CO and cracking species that were transported in the freeboard. Complete combustion occurred within 0.15 m of the bed surface and the propane induction time in the freeboard (<0.25 s) was on the same order as the values given by three induction time correlations for homogeneous systems.