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This work studies the torrefaction of a solid recovered fuel (SRF) and its effect on the fuel properties for gasification. The SRF (namely FL) was torrefied at two temperatures (290 °C and 320 °C) in a pilot auger reactor (capacity of up to 100 kg/h) and evaluated as a gasification feedstock. This evaluation included the characterization of the obtained torrefied materials (FL290 and FL320) and several gasification tests in a bench-scale fluidized bed reactor. These tests were performed with different gasification agents (air and oxygen/steam) and bed materials (sand, dolomite and olivine) at similar experimental conditions (T = 850 °C and ER ∼ 0.3). The evaluation of the gasification performance was presented in terms of product yields and gas composition together with the release of contaminants. Tar species (polycyclic aromatic hydrocarbons) and minor contaminants (H 2 S, HCl, HCN and NH 3 ) were analysed by gas chromatography and ion-selective potentiometry, respectively. Additionally, the calculation of the process efficiency (gasification and its combination with torrefaction) based on the energy content of the producer gas and a preliminary cost analysis that evaluate the main benefits and drawbacks of the torrefaction process are included. The results indicated that the torrefaction process improved the SRF gasification parameters (lower tar, higher H 2 /CO ratio, carbon conversion, etc.) and strongly affected the presence of HCl in the producer gas. However, the preliminary cost analysis advised the combination of both technologies only under certain gasification conditions. [ABSTRACT FROM AUTHOR]

This work investigates the effect of temperature and bed material on the yields and composition of gas and tar produced from gasification of two types of biomass feedstock previously torrefied at 275 °C. Special attention was devoted to the evolution of tar composition under the different experimental conditions. Experiments were conducted in a fluidized bed reactor using two different types of bed material (sand and dolomite) under a constant pressure of 0.5 MPa and at two temperature levels (750 and 850 °C). Tar destruction reactions promoted by the catalyst (dolomite) enhanced the production of some of the gas components (H2, CO2, CO and CH4) whereas C2 hydrocarbons decreased, this effect being slightly more relevant at 850 °C. Comparable trends were observed with increasing temperature, which had a positive effect on cracking reactions and tar destruction. For both feedstocks, the increase in temperature resulted in (i) higher gas yields, and (ii) enhanced char gasification rate. On the other hand the evolution of tar yield and composition revealed a possible competition between two tar reaction pathways during gasification, (i) tar polymerization, and (ii) de-alkylation, dehydration and cracking of tars, depending on the experimental conditions and feedstock used. [ABSTRACT FROM AUTHOR]

• Very low concentrations of tar measured under conditions of oxy-fuel gasification. • Effects of oxy-fuel conditions on fuel-S released as H 2 S measured. • S retention influenced by the high partial pressure of CO 2. • Raising the T and P increased the proportion of fuel-N released as NH 3. • Up to 40% of fuel-N released as NH 3 in CO 2 /steam at 950 °C. The release of species of environmental concern during simulated oxy-fuel gasification in a laboratory scale fluidised bed have been investigated. Fluidising gases containing a high partial pressure of CO 2 and in some tests, steam, were used. The species considered are tars, H 2 S and NH 3 and the aim has been to gain an understanding of the impact of the gasifer operating conditions on their release. This is part of a programme of work on the potential of oxy-fuel gasification as a means of enabling the use of coal to continue as a source of energy, whilst capturing the CO 2 for sequestration to minimise the impact on climate change. It has been shown that the tars released during pyrolysis are efficiently destroyed during their passage through the hot, char containing bed. The measured emission of tar was very low, particularly when compared to a conventional fixed bed gasifier. The extent of S release as H 2 S depends on the fuel-S and ash-Ca contents, and on the operating conditions. Increasing the partial pressure of CO 2 , steam and raising the temperature increased the proportion of S released. Adding dolomite, to retain S, decreased the emission level at atmospheric pressure, provided the temperature was above 950 °C. The use of this method to reduce S emissions at elevated pressure would require careful consideration, as the high partial pressure of CO 2 in the fluidising gas can prevent the calcination of the dolomite and therefore reduce its effectiveness. Steam was found to increase the proportion of fuel-N converted to NH 3 and the concentration also depended on the bed temperature. A peak in the concentration was noted at 850 °C, due to the opposing impacts on increased release as the temperature was raised and increasing equilibration of NH 3 to N 2 and H 2. [ABSTRACT FROM AUTHOR]