Kinetic Behavior of Torrefied Biomass in an Oxidative Environment

Abstract

ABSTRACT. The combustion of four torrefied wood samples and their feedstocks (birch and spruce) was studied at slow heating programs, under well-defined conditions by thermogravimetry (TGA). Particularly low sample masses were employed to avoid the self-heating of the samples due to the huge reaction heat of the combustion. Linear, modulated and constant-reaction rate (CRR) temperature programs were employed in the TGA experiments in gas flows of 5 and 20% O2. In 2 this way the kinetics was based on a wide range of experimental conditions. The ratio of the highest and lowest peak maxima was around 50 in the experiments used for the kinetic evaluation.A recent kinetic model of Várhegyi et al. [Energy & Fuels 2012, 26, 1323-1335 was employed with modifications. This model consists of two devolatilization reactions and a successive char burn-off reaction. The cellulose decomposition in the presence of oxygen has a self-accelerating (autocatalytic) kinetics. The decomposition of the non-cellulosic parts of the biomass was described by a distributed activation model. The char burn-off was approximated by power-law (n-order) kinetics. Each of these reactions has its own dependence on the oxygen concentration that was expressed by power-law kinetics, too. The complexity of the applied model reflects the complexity of the studied materials. The model contained 15 unknown parameters for a given biomass. Part of these parameters could be assumed common for the six samples without a substantial worsening of the fit quality. This approach increased the average experimental information for an unknown parameter by a factor of 2 and revealed the similarities in the behavior of the different samples.

Process simulation of co-firing torrefied biomass in a 220MWe coal-fired power plant

“…Recently, torrefaction, one of a biomass pretreatment technologies, is widely acknowledged as a promising method on a large scale to increase biomass energy content, break fibrous structure of biomass making it's grinding easy, promote its flowability featuring a good fluidization behavior, and also uniform the product quality [9][10][11][12][13][14]. And accordingly, torrefaction based co-firing system in a pulverized coal boiler have been proved as a co-firing option with the aim of high percentage of fuel switching [15,16].…”

Combustion kinetic study of woody and herbaceous crops by thermal analysis coupled to mass spectrometry

“…Then, the oxidation of the sample occurs at temperatures higher than 400 C. Generally, each stage is attributed to the decomposition of the biomass main components (hemicellulose, cellulose and lignin) [10,16]. Hemicellulose and cellulose are assumed to decompose during the devolatilization stage [13].…”

“…Lai et al (2011) analyzed the combustion behavior of MSW (municipal solid wastes) by thermogravimetric analysis under different N 2 /O 2 and CO 2 /O 2 atmospheres [12]. Furthermore, Tapasvi et al (2013) studied the oxidation kinetics of different wood species over a wide range of experimental conditions [13].…”

Evolution of the Mass Loss Rate During Atmospheric and Pressurized Slow Pyrolysis of Wheat Straw in a Bench-Scale Reactor

“…To better understand the pyrolysis behaviour in a bench-scale fixed-bed reactor, it can be very useful to measure the real time mass loss rate. The acquisition of the real time simple weight in such systems can allow reasearchers to study termal processes involving mass and heat transfer limitations [1]. The specific aim of this study is to determine the effect of the absolute pressure (at 0.1 MPa and at 0.5 MPa), at a constant peak temperature of 500 ºC, on the pyrolysis behavior of wheat straw pellets in a fixed-bed reactor equipped with a weighing platform.…”