Showing papers by "Dongke Zhang published in 2000"
TL;DR: In this article, the behavior of inorganic constituents during fluidised-bed combustion of several Australian low-rank coals was studied using a laboratory-scale spouted bed combustion system.
58 citations
TL;DR: In this paper, the role of inherent inorganic matter and additives in low-lemperatures oxidation and spontaneous combustion of a Victorian brown coal was investigated and the relative effectiveness of the additives was determined by comparing their critical ambient temperatures with that of the acid-washed coal.
Abstract: This paper reports a laboratory investigation into the role of inherent inorganic matter and additives in the low-lemperatures oxidation and spontaneous combustion of a Victorian brown coal. The raw coal, water-washed coal, acid-washed coal, and acid-washed coal respectively doped with fourteen additives, are prepared. Each of the samples is then tested in a wire-mesh reactor to obtain its critical ambient temperature, above which a thermal runaway occurs. The critical ambient temperatures of the acid-washed sample and water-washed coal are higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalyses the low-temperature oxidation. The relative effectiveness of the additives is determined by comparing their critical ambient temperatures with that of the acid-washed coal. Magnesium acetate (Mg(Ac)2). calcium acetate (Ca(Ac)2). magnesium carbonate (MgCO3). sodium hydroxide (NaOH). calcium chloride (CaC12), and sodium chloride (NaCI) arc found lo inhibit spontaneous co...
26 citations
TL;DR: In this article, the effect of combustion product distribution coefficient, φ, in the char partial combustion reaction on modelling of fluidised-bed coal gasifiers has been investigated for two cases with and without considering homogeneous gas phase combustion in the model, respectively.
Abstract: Effect of the combustion product distribution coefficient, φ, in the char partial combustion reaction on modelling of fluidised-bed coal gasifiers has been investigated for two cases with and without considering homogeneous gas phase combustion in the model, respectively. Simulations incorporating homogeneous combustion of gases indicate that φ value between 0.55 and 0.95 has little influence on the predicted operating temperatures, total carbon conversions, gas production rates and compositions of the gasifiers simulated. These results also compare well with experiments. However, for simulations without homogeneous combustion, φ does significantly affect the modelling predictions, and the simulation results compare poorly with experiments. The results suggest that homogeneous combustion of combustible gases should be incorporated in fluidised-bed coal gasifier models, and in the absence of any experimental data, φ can be chosen between 0.75 and 0.85 for simulations with negligible effect on model predictions.
21 citations
01 Jan 2000
TL;DR: In this article, experiments were performed to determine the gasification rate of South Australian Lochiel coal in CO 2 at temperatures between 750 and 950 °C, and five samples were prepared, namely, raw coal, acid-washed coal, and acid- washed coal doped with 5 wt % Na 2 CO 3, 5wt % CaCO 3, and 2.5 wt% Na 2 Co 3 +2.5wt Co 2 +2 wt ) and gasified in a TGA apparatus.
Abstract: Experiments were performed to determine the gasification rate of South Australian Lochiel coal in CO 2 at temperatures between 750 and 950 °C. Five samples were prepared, namely, raw coal, acid-washed coal, and acid-washed coal doped with 5 wt % Na 2 CO 3 , 5 wt % CaCO 3 , and 2.5 wt % Na 2 CO 3 +2.5 wt % CaCO 3 , and gasified in a TGA apparatus. While the acid-washed coal incurred a low but invariant reactivity, the raw and carbonate-doped samples experienced an increase in gasification rate with carbon conversion up to ca. 90% conversion, after which the gasification rate rapidly fell to zero at 100% conversion. It was speculated that transformation of the cations in samples during gasification might be responsible for the observed variation in the gasification rate. Further experiments using the 5 wt % Na 2 CO 3 —doped coal sample identified that the rising concentration of the active cations in the char was the primary reason for the increasing gasification rate before 90% conversion, but the lack of carbon availability was responsible for the rapid fall in gasification rate above 90% conversion. Before gasification, sodium in the 5 wt % Na 2 CO 3 —doped coal was about 30% water soluble and 70% water insoluble but acid soluble. Upon gasification, the water-insoluble sodium but acid-soluble sodium decreased to about 25% of the total sodium and remained invariant with time and temperature. The acid-insoluble sodium incurred an initial increase to 15% and then continuously reacted with silicates in the presence of coal. Heat treatment rapidly destroyed carboxylic functional groups and thus reduced the ion-exchange capacity of the acid-washed coal sample. The changes in sodium forms and quantity and the effect of heat treatment on the content of carboxylic functional groups and ion-exchange capacity explained the variation of gasification rate with carbon conversion. The change in the total surface area of the char during gasification was not the dominating factor influencing the char gasification rate.
10 citations
TL;DR: In this paper, a kinetic study of CH4 partial oxidation was performed using Chemkin II simulation package with the GRI, NIST, Alexander and Leeds CH4 oxidation mechanisms.
Abstract: A kinetic study of CH4 partial oxidation was performed using Chemkin II simulation package with the GRI, NIST, Alexander and Leeds CH4 oxidation mechanisms. Comparing kinetic simulation results with thermodynamic analysis indicates that GRI_1.2–3.0, NIST and Alexander_0.1–0.3 mechanisms give a reasonable performance in describing CH4 partial oxidation while Alexander_0.4 and the Leeds mechanisms fail to do so. Two distinct reaction zones are observed in the simulation results, which is different from the two-stage concept reported in the literature. Major global reactions within each reaction zone are identified.
6 citations
01 Jan 2000
TL;DR: In this article, the authors used the STANJAN thermodynamic simulation package to analyse the tendency of carbon formation during CH4 reforming, and found that solid carbon is the most likely type of formation.
Abstract: One of the major challenges for CH4 reforming processes is the problem of carbon deposition, which causes deactivation of catalysts. The mechanisms of carbon deposition are very complex, involving the formation of poly-aromatic compound or soot. Experimental determination of the quantity of carbon deposition is not an easy task due to its accumulative nature, small quantity and transformation after deposition. This paper discusses the use of the STANJAN thermodynamic simulation package to analyse the tendency of carbon formation during CH4 reforming. The effect of different operating conditions, such as temperature, pressure and feed equivalence ratio are examined. The steam reforming, CO2 reforming and partial oxidation reforming as well as combinations of the three processes are compared. The results show that solid carbon is the most likely type of carbon formation. CO2 reforming has the highest tendency. High pressure and temperature can significantly reduce solid carbon formation tendency and high temperature can also minimise carbon formation tendency differences between the three reforming processes. The findings can be very helpful in guiding further study of CH4 reforming and practical reformer design.
1 citations