B.M. Wagenaar

Flash pyrolysis kinetics of pine wood

The kinetics of sawdust pyrolysis in the temperature range from 300 to 600 °C has been measured. A thermogravimetric analyser was applied for the temperature range from 300 to 450 °C while for measurements in the temperature range from 450 to 600 °C, an entrained flow reactor has been used. The kinetic expression that describes the mass loss of sawdust due to pyrolysis is assumed to be of a single first-order in the unconverted wood. The first-order rate constant obtained from measurements in both the thermogravimetric analyser and the entrained flow reactor can be described by an Arrhenius equation with k0 = 1.4 1010 kg.kg?1.s?1 and Ea = 150 KJ.mol?1.

Pyrolysis of biomass in the rotating cone reactor: modelling and experimental justification

In the rotating cone reactor, wood particles fed to the bottom of the rotating cone, together with an excess of inert heat carrier particles, are converted while being transported spirally upwards along the cone wall. The cone geometry is specified by a top angle of π/2 radians and a maximum diameter of 650 mm. Products obtained from the flash pyrolysis of wood dust in a rotating cone reactor are non-condensable gases, bio-oil and char. This paper reports on results of computations and measurements to determine the influence of process parameters like the cone rotational speed (6–15 Hz), the reactor volume (3–200 l), the wood-dust feed rate (1–3.5 g s−1) and the reactor temperature (550−700°C) on the product composition. The experimental results are compared with predictions of an integrated reactor model which accounts for: (i) the type of particle flow in the reactor; (ii) the wood decomposition kinetics; (iii) the rate of heat transfer to the wood particles; (iv) the kinetics of gas phase reaction (tar cracking); and (v) gas exchange with the space in which ash, char and partially unconverted wood is collected. For the conditions applied, the difference between predicted and measured weight fractions of gas, tar and char produced was always less than 10%. If further appeared that the wood particles were always completely converted inside the reactor and that the product distribution is only affected by the gas-phase reaction kinetics and residence time. The gas-phase residence time is determined by the available reactor volume and the feed rate of the wood particles. At optimal reactor conditions, the tar yield is almost maximal (70% d.a.f. wood base).

The rotating cone flash pyrolysis reactor

The velocity of nearly spherical mono-sized PVC powder in a cold-flow rotating cone reactor (top angle π/3 rad, height 0.43 m) was measured under variation of the particle diameter (140 –780 μm) and the cone rotational speed (up to 1800 rpm). Derived residence times for these particles vary from 0.05 to 0.3 second. The gas velocity distribution near the cone wall appeared to have a considerable influence on the velocity of particles smaller than 200 μm. Next to the experimental work a mathematical model is presented, using a single-particle description and a gas-flow description near the wall according to the universal velocity profile [1]. The conversion of biomass can be calculated by combining the hydrodynamic model together with a proper heat transfer and pyrolysis model. Particles smaller than 200 μm may pyrolyse completely in the present rotating cone flash pyrolysis reactor.

Fluoroptic measurements of the local heat transfer coefficient inside the rotating cone reactor

The rotating cone reactor is a novel reactor type for rapid thermal processing of solids. This paper focuses on the experimental determination of the gas-to-particle heat transfer coefficient. This quantity has been measured for several particle diameters (average size of 150, 280 and 425 ?m) and cone rotational frequencies (11.3 and 28.3 Hz). The gas-to-particle heat transfer coefficient obtained from these experiments varied between 280 and 1030 W m?2 W?1. Experimental parameters which were kept constant in this study were the particle mass flow rate (5 g s?1), the cone geometry (cone top angle ?/3 radians) and the temperature of the particle feed (280°C). The experimentally determined heat transfer coefficients were represented in dimensionless form as a function of the particle Reynolds number. The particle Reynolds number has been obtained from measurements of the local gas-phase velocity and the local particle velocity. Analysis of the experimental results revealed that the gas-to-particle heat transfer coefficient could roughly be represented by the well-established Ranz?Marshall correlation (Ranz and Marshall, 1952, Chem. Engng Progress 48, 173) for isolated non-rotating particles. The difference between the experimentally observed particle Nusselt numbers and the theoretically predicted Nusselt numbers based on the Ranz-Marshall equation is probably due to the influence of particle rotation on the gas-to-particle heat transfer process. Calculations showed that the time in which the particles lose half of their rotation frequency is typically in the order of the particle residence time in the rotating cone reactor