Experimental and modeling study on centimeter pine char combustion in fast-heating Macro TGA

Abstract

Biomass energy is an important renewable resource, and thermochemical conversion, including pyrolysis and combustion, is one of the main methods of biomass energy utilization. In industrial reactors, the biomass particles will experience a fast heating (∼1000 °C/min) process during pyrolysis. The particle size of biomass applied in industry has a wide range (from millimeter to centimeter scale). The study of the reaction characteristics of biomass pyrolysis and combustion is helpful for optimizing furnace design and working condition selection. In this research, the combustion of centimeter-scale pine char was studied with a newly built fast-heating Macro Thermal Gravimetric Analyzer (Macro TGA). This Macro TGA is able to conduct the pyrolysis and combustion of large biomass samples (up to 40 mm) with a fast heating rate (∼1000 °C/min), which is able to reflect the working conditions in industrial-scale reactors such as grate furnaces and dual fluidized beds. This Macro TGA can measure the online sample weight, temperature and sample size simultaneously during pyrolysis and combustion experiments. The combustion characteristics of different sizes of pine chars were investigated at various temperatures and oxygen concentrations. A zero-dimensional model was established to predict the sample weight loss, temperature change and sample shrinkage during the pine char combustion process. Three kinetic parameters α, A and E were applied in the model, and the values of the kinetic parameters were optimized by a genetic algorithm. The model prediction and experimental results are consistent with each other. Compared with previous studies, this study developed a new experimental method to measure the reaction characteristics (including sample weight, temperature and size) of centimeter-scale biomass under similar pyrolysis and combustion reaction conditions compared to industrial reactors, and a zero-dimensional model was established to describe the pine char combustion process.