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The tar-decomposing activities of dolomites and limestones in calcined and carbonated forms were compared. Tests were carried out in a fixed-bed tube reactor at 900°C under 2 MPa total pressure using an N 2 -H 2 O-CO 2 gas mixture. Toluene was used as a tar model compound. The calcined rocks decomposed toluene efficiently, but activity was almost totally lost in the carbonated...
A German bituminous coal (Gottelborn) was pyrolysed at high heating rate in a fluidised-bed reactor. The reactor featured a relatively long freeboard heated to similar temperatures to the sand bed, where the nascent volatiles are further thermally cracked. Tars from the pyrolysis of the bituminous coal were separated into fractions with a preparative size exclusion chromatography (SEC) system. ...
Bench-scale vacuum pyrolysis experimentation (600°C reaction temperature, 10°C min -1 heating rate, < 0.7 kPa total pressure) was carried out on a set of 20 Canadian coals to examine the role of coal rank and petrographic composition on conversion properties. Yields of solid residues (cokes) are a function of initial coal rank (increasing yields with increase of rank), whereas liptinite-rich...
This study has shown that injecting secondary air to a fluidised-bed at temperatures over 830-850 o C decreases the tar contents of the gasifier offgas. Tests carried out at a laboratory scale show that the formation of tars strongly depends on the raw material type and the operating conditions, especially the gasification temperature. It is also shown that an optimum ratio of secondary to...
Yallourn brown coal particles were heated at rates in the order of 103Ks−1 and pyrolyzed in two different reactors, a drop-tube reactor (DTR) and a Curie-point reactor (CPR). In DTR the vapor-phase secondary (extra-particle) reactions of volatiles occurred concurrently with the primary reactions within the particle, while in CPR the volatiles were swept out of the heating zone immediately after formed...
A Loy Yang lignite sample was pyrolysed in a wire-mesh reactor at pressures from 1 to 61bar. The char yield did not show considerable sensitivity to changes in pressure or heating rate and was mainly a function of temperature. However, the tar yield was sensitive to changes in pressure, holding time and heating rate. The tar yield at 1000Ks -1 showed a minimum at around 6-11bar. The tar...
Two pairs of raw and acid-washed coal samples were prepared from Yallourn and Loy Yang brown coals, and subjected to rapid pyrolysis in a drop-tube reactor at 1073-1173K in a stream of N 2 or H 2 O/N 2 mixture. Examinations were made on the roles of the inherent metallic species in the secondary reactions of nascent tar and char that were formed by the intraparticle primary...
A set of ion-exchanged samples prepared from Loy Yang lignite was pyrolyzed in a wire-mesh reactor at elevated pressures from 1 to 36bar. The tar yields from the pyrolysis of H-form (acid-washed) sample at a fast heating rate of 1000 o Cs -1 were drastically reduced by increasing pressure to 6bar and then remained unchanged with further increase in pressure to 36bar. This behavior...
A method has been developed, by which the tar producing propensity of coal (Fischer assay) can be assessed from a single trace of a thermogravimetric simulation of the proximate analysis of coal. It was found that, for a suite of 22 South African coal types under well defined experimental thermogravimetric conditions, the mass loss observed in the temperature interval of 460–510 °C is related to the...
This report outlines results of an investigation of the composition of bone pyrolysis tar produced in Mongolia. The liquid product (tar) yield was low: ~4.9%. The elemental composition of the tar was C: 73.3%, H:10.1%, N: 11.3%, O: 5.3%. Size-exclusion chromatograms signalled the presence of generally smaller mass material than coal tars and pitches, with a range from about 2000 U downwards. GC-MS...
Tar elimination and hot-gas conditioning in thermochemical conversion processes, i.e. thermal gasification, pyrolysis of heterogeneous materials involved two main classes of catalysts and/or additives: metallic and mineral oxides. This communication focused on the experimental kinetic data on catalytic steam cracking of vaporized toluene (P C7H8 =0.93-1.15kPa, H 2 O/C...
Conversion of biomass into producer gas by thermal gasification broadens the scope of biomass applications. Usually, tar has to be removed from the producer gas. Tar recycling within the gasification process may solve the associated waste problem and increase the system efficiency, provided tar is broken down under gasification conditions. We present results of tar recycling experiments at a Circulating...
A partial combustion burner is introduced as a cleaning system for the tar content of gaseous (bio) fuel. The results of experiments, using a synthetic low calorific gas mixture, demonstrate the effectivity of the proposed process. In these experiments naphthalene is added as a model tar component. The effect of partial combustion of the fuel gasmixture on the naphthalene is examined for different...
Ni-on-dolomite catalysts were found to be effective catalysts for coking resistance and promising sulfur tolerance for steam reforming of tar. Experiments were carried out in a fixed bed reactor at 730–850°C with a short contact time (W/F: 0.55gh/mol) and under atmospheric pressure. Toluene and naphthalene were selected as the model component of tar. The process variables such as calcination temperature,...
This paper presents a 2D axisymmetric CFD model of the oxidation zone in a two-stage downdraft gasifier. The purpose of this study is to investigate in detail this zone, which is crucial for tar cracking. Results fit satisfactorily to the experimental data regarding temperature pattern and tar concentration. Simulations highlighted several crucial points of the process: (a) tertiary tar are mainly...
In this paper the potential of using biomass char as a catalyst for tar reduction is discussed. Biomass char is compared with other known catalysts used for tar conversion. Model tar compounds, phenol and naphthalene, were used to test char and other catalysts. Tests were carried out in a fixed bed tubular reactor at a temperature range of 700–900°C under atmospheric pressure and a gas residence time...
To minimize tar in the producer gas from birch gasification at 700, 750 and 800°C, four Chinese dolomites (Zhenjiang, Nanjing, Shanxi, Anhui) and a Swedish dolomite (Sala) used as reference were studied in a laboratory-scale atmospheric fluidized bed gasifier. The gasifier was equipped with a downstream fixed catalyst bed. The results imply that all dolomites but Anhui dolomite effectively decompose...
Biomass gasification produces a low to medium-BTU product gas (or syngas) containing primarily CO 2 , H 2 , CO, CH 4 and (C 2 +C 3 ), as well as some contaminants such as tars, NH 3 , H 2 S and SO 2 . In order to achieve better efficiencies of the syngas applications, these contaminants must be removed before the syngas is used for internal...
Experiments were carried out with a woody waste fraction using a two-stage gasifier consisting of a fluidized bed zone and a tar cracking zone that was filled with activated carbon. In the experiments, the effects of experimental conditions such as the temperature and the equivalence ratio were investigated. In addition, the results of the experiments with virgin activated carbon, without activated...
Several precious metal catalysts were prepared on modified zirconia and tested for the selective catalytic clean-up of the gasification gas. The activity of the precious metal catalysts were compared to that of the modified zirconia supported nickel catalyst and to the support. The activities of the catalysts were tested in a monolithic form in a quartz laboratory reactor at temperatures of 600–900°C...
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