Low Temperature Ignition of Biomass

Biomass is an especially reactive fuel. There have been large increases in the transportation and utilisation of biomass fuels over the past 10 years and this has raised concerns over its safe handling and utilisation. Fires, and sometimes explosions, are a risk during all stages of fuel production as well as during the handling and utilisation of the product. This paper presents a method for assessing ignition risk and provides a ranking of relative risk of ignition of biomass fuels. Tests involved single particle measurements, thermal analysis, dust layer and basket ignition tests. In all cases, smouldering combustion was observed, whereby the fuels pyrolyse to produce a black char, which then subsequently ignites. Low temperature pyrolysis kinetics have been utilised to predict ignition delay times at low temperatures. A method for evaluating risk was explored based on the activation energy for pyrolysis and a characteristic temperature from TGA analysis. Here, olive cake, sunflower husk and Miscanthus fall into the high risk category, while the woods, plane, pine, mesquite and red berry juniper, fall into the medium risk category. This method is able to capture the impact of low activation energy for pyrolysis on the increased risk of ignition

CFD Studies on Biomass Thermochemical Conversion

Thermochemical conversion of biomass offers an efficient and economically process to provide gaseous, liquid and solid fuels and prepare chemicals derived from biomass. Computational fluid dynamic (CFD) modeling applications on biomass thermochemical processes help to optimize the design and operation of thermochemical reactors. Recent progression in numerical techniques and computing efficacy has advanced CFD as a widely used approach to provide efficient design solutions in industry. This paper introduces the fundamentals involved in developing a CFD solution. Mathematical equations governing the fluid flow, heat and mass transfer and chemical reactions in thermochemical systems are described and sub-models for individual processes are presented. It provides a review of various applications of CFD in the biomass thermochemical process field

Effect of the addition of different waste carbonaceous materials on coal gasification in CO2 atmosphere

YesIn order to evaluate the feasibility of using CO2 as a gasifying agent in the conversion of carbonaceous materials to syngas, gasification characteristics of coal, a suite of waste carbonaceous materials, and their blends were studied by using a thermogravimetric analyser (TGA). The results showed that CO2 gasification of polystyrene completed at 470 °C, which was lower than those of other carbonaceous materials. This behaviour was attributed to the high volatile content coupled with its unique thermal degradation properties. It was found that the initial decomposition temperature of blends decreased with the increasing amount of waste carbonaceous materials in the blends. In this study, results demonstrated that CO2 co-gasification process was enhanced as a direct consequence of interactions between coal and carbonaceous materials in the blends. The intensity and temperature of occurrence of these interactions were influenced by the chemical properties and composition of the carbonaceous materials in the blends. The strongest interactions were observed in coal/polystyrene blend at the devolatilisation stage as indicated by the highest value of Root Mean Square Interaction Index (RMSII), which was due to the highly reactive nature of polystyrene. On the other hand, coal/oat straw blend showed the highest interactions at char gasification stage. The catalytic effect of alkali metals and other minerals in oat straw, such as CaO, K2O, and Fe2O3, contributed to these strong interactions. The overall CO2 gasification of coal was enhanced via the addition of polystyrene and oat straw

Miscanthus combustion properties and variations with Miscanthus agronomy

A study of the interaction of agronomy and its effects on fuel quality has been carried out for Miscanthus x giganteus grown in the UK through the UK’s SUPERGEN Bioenergy Consortium activities. Work on Miscanthus yield responses to N, K and S fertilizer will be reported elsewhere, and this study is focused on how fertilisers affected Miscanthus fuel quality. Six different fertiliser treatments were chosen to give interesting contrasts from the field experiment investigating yield responses; nitrogen (ammonium nitrate) at 0, 100, 150 and 250 kg N ha 1 in combination with potassium (K as KCl) at 50 kg K ha 1 and 150 kg N ha 1 also with zero K, and with 50 kg K ha 1 (K as K2SO4). A total of 270 samples were taken at five time points over the autumn and winter harvest window in each of the two growth years, 2005 and 2006. Results show that Miscanthus stems have better fuel quality than leaves, with much lower ash, N and S contents, and slightly higher C concentrations and hence higher estimated calorific value. The treatment without any N added into fertiliser seems to give a better fuel quality than other treatments considered in the study, resulting in a fuel with lower N, ash content, and a lower propensity to fouling (as indicated by the indices calculated from its ash analysis), and also higher C concentrations. In general, the late harvested Miscanthus samples have better fuel quality, with lower N, Cl, ash contents, alkali index and slightly higher C contents