• Energy Research

Abstract Performance of wood gasification genset is sensitive to the moisture content in the feedstock and the electrical load (demand of users). This study investigates the influence of these process parameters on the electrical efficiency of the genset (ηglobal), the electrical engine efficiency (ηengine), the cold gas efficiency (CGE), and the syngas composition. Experimental tests were carried out by varying the moisture content from 11% to 23% and the electrical power from 4.7 kW to 12.8 kW on a commercial gasifier equipped with precise measuring tools. The increase of the performance when the electrical load is increased or when the moisture content in the wood chips is decreased is both quantified and discussed. Such behaviour was mainly explained by differences in engine filling rates and reactor temperatures.

Substitution of fossils reducers by charcoal from woody biomass is one of the most suitable option to reduce greenhouse gas emissions of metallurgical industries. The main problem involved in fossils reducers replacement is the lack of mechanical strength of charcoal. Aim of this study is to investigate the impact of pyrolysis parameters, such as temperature and solid residence time, on the mechanical properties of charcoal. Charcoal was produced from two woody biomasses, Eucalyptus globulus and Picea abies (Spruce), in a pilot scale fixed bed rector; with three temperatures (500, 650 and 800 °C) and two solid residence times (0 and 90 min). The particle sizes used were close to those in the industry. Charcoals were characterized by proximate and ultimate analysis, apparent density, friability and compressive strength. Results show an increase in charcoal mechanical strength with increasing pyrolysis temperature. On the other hand solid residence time has a little influence on the mechanical properties. Eucalyptus has a higher density than Spruce, but Eucalyptus charcoal shows a lower mechanical stability than Spruce charcoal independently of the pyrolysis conditions. Proceedings of the 26th European Biomass Conference and Exhibition, 14-17 May 2018, Copenhagen, Denmark, pp. 1240-1243

A new two-stage gasifier with fixed-bed has recently been installed on CIRAD facilities in Montpellier. The pyrolysis and the gasifier units are removable. In order to characterise the pyrolysis products before their gasification, experiments were carried out, for the first time onlywith the pyrolysis unit and this paper deals with the results obtained. The biomass used is Pinus pinaster. The parameters investigated are: temperature, residence time and biomass flow rate. It has been found that increasing temperature and residence time improve the cracking of tars, gas production and char quality (fixed carbon rate more than 90%, volatile matter rate less than 4%). The increase of biomass flow rate leads to a bad char quality. The efficiency of tar cracking, the quality and the heating value of the charcoal and the gases, indicate that: temperature between 650 °C and 750 °C, residence time of 30 min, biomass flow rate between 10 and 15 kg/h should be the most convenient experimental conditions to get better results from the experimental device and from the biomass pyrolysis process. The kinetic study of charcoal generation shows that the pyrolysis process, in experimental conditions, is a first-order reaction. The kinetic parameters calculated are comparable with those found by other researchers. (Resume d'auteur)

Ex situ hot gas filtration (HGF) has been shown to be a simple and robust technique to upgrade the quality of flash pyrolysis oils. In this study, the secondary reactions inside the HGF unit and their impact on product yields and the chemical composition of bio-oils were investigated in a total of 18 experiments conducted at both pilot and bench reactor scales (1 and 0.1 kg/h), with beech wood (BW) and sunflower stalks (SFS). The impact of HGF on yields was found to be dependent on the extent of secondary reactions which, in turn, were determined by three parameters: (a) HGF temperature, (b) HGF char cake thickness, and (c) AAEM content of the raw feedstock. Nevertheless, independently of the conditions used, the drop in the organic yield was less than 10 wt % with both BW and SFS feedstocks. Our results demonstrated that (1) cracking reactions mainly took place in the homogeneous gas phase and (2) dehydration, coking, and decarboxylation reactions took place in the HGF char cake, probably catalyzed by th...

The effects of important practical parameters, specifically feedstock heterogeneity and heat-mass transfer on steam gasification of rice husk were investigated and quantified. Through proximate and ultimate analysis of ten rice husk types, the heterogeneity was expressed not only between different types but also within the same rice husk type. TGA-DTG curves showed notable differences in the thermal behaviors of rice husk during pyrolysis. The time required to gasify the same quantity of rice husk can vary in a ratio of 1–1.5 depending on the type. The Si content in rice husk showed an inhibitory effect to the char reactivity during steam gasification. An empirical factor of 1.3 could be applied to the conversion rate of rice husk for every 1-cm increase in the bed thickness. Results of this study could contribute to the improvement of existing systems or the design of new efficient rice husk gasifiers.

Abstract The production of charcoal for metallurgical applications requires careful selection of the wood and control of the pyrolysis conditions to ensure acceptable charcoal quality. The main properties of charcoal to be considered are density, mechanical strength, and reactivity. In this study, charcoal was produced from two types of wood commonly used in the industry, Eucalyptus globulus (eucalyptus) and Picea abies (spruce), in a pilot scale pyrolysis fixed bed reactor at three temperatures (500, 650 and 800 °C) and two solid residence times (0 and 90 min). The yields, composition, apparent density, true density, porosity, carbon structural ordering, friability, compressive strength and CO2 reactivity of the resulting charcoals were analyzed. A new method to test compressive strength was applied to a charcoal bed. Our results show that the nature of the wood has a much greater impact on these values than the pyrolysis operating conditions. Wood apparent density is not a good indicator of the mechanical behavior of charcoal. Despite its higher density, eucalyptus charcoal showed lower mechanical stability than spruce charcoal independently of the pyrolysis conditions. When the final pyrolysis temperature was increased, the mechanical strength, porosity of the charcoal increased and CO2 reactivity decreased. The impact of solid residence time during pyrolysis on the charcoal properties was negligible except for CO2 reactivity, which decreased with an increase in residence time.

Abstract In air staged gasification and advanced carbonization processes, oxidative pyrolysis occurs in downdraft continuous fixed bed reactors. An oxidation zone separates the virgin fuel from the resulting char and propagates upward. Here, the oxidation zone was stabilized at a fixed elevation in a 20 cm I.D. fixed bed reactor using wood chips or wood pellets. In controlled continuous operating mode, we investigated the impact of air flux and bed bulk density on the behavior of the oxidation zone in terms of wood consumption, and yields of char, gas and tars. An air:wood mass ratio of 0.7 was measured and in our operating conditions, and was not sensitive to air mass flux and bed density. With oxidative pyrolysis, yields of organic condensates were lower than with allothermal pyrolysis, whereas the production of pyrolysis water and permanent gases increased. Finally, the oxidation zone was shown to be flat and horizontal in a wood pellet bed but inclined in a wood chip bed.

Two-stage fixed bed gasification is one of the most promising technologies for low and medium energy production from biomass. In industrial processes, control and optimisation is often based on constructor know-how rather than on an understanding of the mechanisms involved. We present a new original tool, the Continuous Fixed Bed Reactor (CFiBR), which was specifically designed and built to enable a fine understanding of the limiting stage of a gasifier: the char bed gasification zone. The reactor, the instrumentation, the operating procedure and set-up tests are described in detail. The potential of the reactor is demonstrated through the characterisation of the gasification of a continuous wood char bed. Temperature profiles and gas concentrations along the 65 cm bed were established and showed that the most reactive zone was the first 10 cm of the char bed. Accurate energy and mass balances provided relevant information regarding the contributions of the main reactions involved in the fixed char bed gasification process.