The aim of the present study is to examine operating parameters that would reduce the residual tar content in the fuel gas in downdraft gasifiers and eventually eliminate it altogether. A two-stage fixed-bed reactor has been employed to simulate elements of tar cracking in a downdraft gasifier. In this reactor, tar is generated by pyrolysis in the first stage and cracking and gasification take place in the second stage. Modifications to a previous configuration of this reactor are described, which have enabled the use of smaller char particle sizes in the second stage and the generation of a more complete inventory of the reaction products. In this work, the effect of the temperature and the presence of char on product distributions are reported. Increasing the temperature from 700 to 1000°C resulted in a decrease in the quantity of tar recovered and an increase in the total amount of CO released. The amount of CH 4 released increased between 700 and 800°C before remaining steady up to 1000°C. The CO 2 content of the gas was relatively constant between 700 and 800°C and increased as the temperature increased from 800 to 1000°C. The amount of water and light hydrocarbons (C 2 -C 5 alkanes and alkenes) sharply decreased at 1000°C. The presence of char in the second stage had significant effects on tar cracking and product distributions. These effects were more obvious on the concentrations of CO, CO 2 , and H 2 O, which may be a result of reduction reactions taking place with the carbon in the packed char bed. These reactions appear to be more significant at temperatures between 900 and 1000°C, where the rates of gasification are expected to increase.

A lab scale, two stage fixed bed reactor has been used to study the cracking of tars formed during the pyrolysis of biomass, under conditions that are intended to simulate those in the downdraft gasifier. Experiments were done at near atmospheric pressure, with tars being produced at 500 °C under pyrolysis conditions in the first stage and then cracked in the second stage under a range of conditions. These conditions simulated those in the gasification zone of a downdraft gasifier. Both condensable and gaseous products were collected, quantified, and characterized. Cracking in an empty second stage reduced the tar from an inlet value of 33% (of input biomass) to 0.7% under the optimum conditions (temperature 1000 °C, velocity 0.4 ms −1 ). The presence of char in the second stage decreased the tar to 0.2%. The extent of cracking was not influenced by the source of the second stage char or particle size, within the ranges studied. The addition of a low percentage of O 2 to the inlet of the second stage had variable effects depending on the conditions in that stage, particularly the presence of char which scavenged the O 2 . A selection of biomasses was also studied, and in general, less than half of the volatile matter in the parent biomass was emitted as primary tar. Cracking of this tars in the presence of char decreased the tar by over 98% for all feedstocks. The effects observed in this work can be explained in terms of changes in the extents of cracking, reforming, gasification, and water−gas shift as a function of temperature, time, and presence of char.

, +234 for propylene desorption and simultaneously increases the activation energy for propylene dehydrogenation, which has a positive effect on the selectivity of propylene production. Lauri and Karolina (2013) also made similar deductions for the use of Pt which results in low coking while weakening the binding of propylene. Timothy (2015) confirmed that PtGa alloy has superior catalytic properties than SnGa alloy, and similar properties to those deduced for Pt-Sn alloy (as reported by Lauri ABSTRACT By converting low-value commodity fuels into high chemical and other intermediates, the dehydrogenation of light paraffin (such as ethane and propane) into olefins, can add significant value to the refining processes that generate propane. In this study, the parameterised method 3 (PM3) approximation of semi theory was employed to study the acidity and reactivity of chromium (III) oxide catalyst the dehydrogenation of propane into propylene. Ammonia and pyridine were used computationally as molecular probes for the evaluation of the Lewis acidity of the catalyst sites. The propane adsorption and dissociation activation energies were also evalua study showed that the chromium sites are highly acidic and reactive compared to the oxygen sites. In particular, the study showed that the chromium site is the main active site in the promotion of propane dehydrogenation into propylene, over chrom

Bioethanol, as a renewable energy, is vital for energy security and pollution control; but its large scale uses need to be studied for different regions. In this study, a bioethanol plant with a processing capacity of 148 million liters/annum was modelled and simulated. This was done with the aid of a process simulator. The study involved process modelling and simulation, material and energy balances, energy efficiency evaluation, and total capital and manufacturing cost estimation. The study shows that the simulated plant will be 63 % energy efficient and that the plant will yield 148 million liters of bioethanol from the processing of 402 metric tonnes of crushed sugarcane with a capital of $ 51 million and manufacturing cost of $ 89 million per annum. Thus, this suggests that the modelled plant would be able to produce 368 thousand liters of bioethanol from a metric tonne of crushed sugarcane with a capital of 0.34 $/liter and manufacturing cost of 0.61 $/liter per annum, based on the conditions adopted for the study.

Converting plastic wastes into fuels through catalytic cracking is continuously gaining interest from researchers worldwide. In this study, the influence of iron on ZSM-5 (Fe-ZSM-5) catalyst on the reforming of the gaseous products of thermal decomposition of low-density polyethylene (LDPE) was investigated. The acidified ZSM-5 catalysts (0, 0.3, 0.6 and 1 wt% of Fe) were prepared and characterized by XRD, BET, FTIR and SEM techniques. In particular, the effects of temperature (400, 450 and 500 °C) and catalyst loading (0.5, 0.75, 1.0, 1.25 and 1.5 g) on a two-stage (pyrolyser and reformer) decomposition of the LDPE wastes into fuel were studied. The liquid fraction produced was characterized using FTIR and GC/MS techniques. The study showed that the increase in pyrolysis temperature (400-500 °C) increases the volume of non-condensable gas (31-58 wt%) and decreases the volume of the condensates (69-41 wt%) in both the thermal and catalytic pyrolyses. However, the trend was at higher level for the catalytic pyrolysis. The increase in temperature for the thermal pyrolysis had less significant effect on the aromatization content of the liquid condensate compared to the catalytic pyrolysis. The FTIR results show a significant increase in aromatic contents and decrease in the aliphatic of the liquid fraction for the catalytic pyrolysis reforming when compared with thermal pyrolysis. The GC/MS results confirmed the aromatic hydrocarbon compositions, predominantly p-xylene, increased relatively to about 70% in the liquid fraction for the best catalyst (1.25 g of catalyst and 1 wt% iron loading on ZSM-5 at 450 °C).Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.