Biomass pyrolysis experiments in an analytical entrained flow reactor between 1073 K and 1273 K
Introduction
The physical and chemical mechanisms involved in biomass steam gasification are still poorly understood, especially under high temperatures (1073 K < T < 1273 K) and high heating rate (>500 K s−1). The present work consists of analytical experiments that should help to better understand the processes occurring at the particle scale during the first seconds of the transformation. This first stage is called “pyrolysis” in our study and gathers both biomass decomposition, often called “primary pyrolysis”, and the secondary reactions of the vapours produced during primary pyrolysis. The experiments are performed in a free-fall reactor, also called entrained flow reactor (EFR). This reactor is an interesting analytical tool to study the global reaction of flash pyrolysis [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], since very high heating rates of the particles can be obtained. Moreover, the residence time can be varied over a range of a few seconds, and the particles can be assumed to be isolated from each other, which makes interpretation easier [1], [14]. Up to now, few experiments have been performed under the operating conditions of interest, the most complete set of data being given by Zanzi [5].
Section 2 is devoted to the description of the experiments. Results are shown and discussed in Section 3. Eventually, conclusions are drawn in Section 4.
Section snippets
Biomass samples
The biomass used in this study is a mixture of two softwoods (sylvester pine and spruce). Two particle sizes are considered: 355–530 μm, called 0.4 mm and 1.00–1.25 mm, called 1.1 mm. The data on biomass samples are given in Table 1.
Experimental facility
The entrained flow reactor is shown in Fig. 1. A complete description of the apparatus and its thermal and hydrodynamic characterization were given in previous works from Van de Steene [4] and Commandré [14].
The reactor is made up of an alumina tube heated by an
Results and discussion
Within the range of study, the most influential parameter on the results is the particle size. That is the reason why the results are separated into two sub-sections, each one being devoted to one particle size.
Conclusion
Flash pyrolysis experiments under N2 and a mixture of N2 and steam were conducted using a mixture of softwoods in an entrained flow reactor in the range of temperatures between 1073 K and 1273 K. The results are very dependent on the particle size in the range under study: 0.4 mm and 1.1 mm.
Under the conditions of study (1073 K < T < 1273 K), the decomposition of the 0.4 mm particles seems to be finished after a solid residence time smaller than 0.5 s, whereas the decomposition of the 1.1 mm particles does
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