Kinetics of coal and catalytic coal pyrolysis reactions in a fixed bed reactor

Kinetics of coal and catalytic coal pyrolysis reactions in a fixed bed reactor

Conference Abstracts MHD systems, and direct fired gas turbines. Reduced heterogeneity should improve operations, increase process efficiencies, and...

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Conference

Abstracts

MHD systems, and direct fired gas turbines. Reduced heterogeneity should improve operations, increase process efficiencies, and expand application of more environmentally acceptable coal feedstocks. Although quite a few sulfur removal and separation processes have been developed, the cleaned product has a low value added to it because the only product considered is combustion feedstock, which makes the economics of most processes unfavourable. In 1990 researchers at SIU at Carbondale began exploring a new concept in coal processing termed ‘Coal Refining’. Coal refining is the separation of coal into macerals each of which may be used as a high quality fuel or a premium chemical feedstock. Until recently availability of pure maceral fractions were very limited. Pure macerals were available at l-10 g level and required 2 man-years of technician time to produce. Macerals have been found to inhibit desulfurization under both pyrolysis and supercritical methanol extraction. Maceral interactions influence combustion profiles, char yields and elemental analysis. This paper will discuss technique developed and results obtained from large scale maceral separation.

changes and revisions in the design. These were incorporated in a modified test facility that allowed ‘routine’ testing. Results of a small number of tests, conducted on South African coal, are reported here. Due to the preliminary nature of the results they may only be considered as an indication of what may be expected. Much work must still be done before quantitative conclusions may be drawn.

Techniques were developed to demineralize coal on a large scale using hydrochloric and hydrofluoric acids. A semi-continuous centrifuge (40OOOrevmin~‘) was employed to concentrate macerals. Cesium chloride was used to make coal slurry density. Large samples of

A reaction scheme consisting of three independent parallel reactions has been used to describe the pyrolysis reactions of volatile matter of coal in a fixed bed reactor, in the temperature range 700-900°C. A simple first-order kinetic model has been applied to the evolution of liquid and gases based on the distribution of carbon in the various products. The model predicts the experimental data within reasonable accuracy. Activation energies of 43.75, 55.55 and 25.00 kcal mol-’ for the non-catalytic coal and 33.33, 37.50 and 18.75 kcal mol-’ for the catalytic coal have been estimated for the evolution of gases, liquid and char, respectively.

demineralized coal were processed at five specific gravities (1.22, 1.25, 1.31, 1.35 and 1.65). Recoveries on the mass balances were over 90%. Based on the petrography, 100% of inertinite and 99% of vitrinite was recovered. Liptinite recovery was low and the loss appeared preferential. This may be due to liptinite maceral sticking to the walls of the filter funnel during filtration and sticking to the walls of the oven during drying. The sink at 1.65 specific gravity was nearly 100% pyrite with a small amount of unliberated organics in some particles. Although these fractions are not pure, these maceral sub-groups can be purified by DGC processing. Using this process it is possible to obtain lOtX2000 g of pure maceral with only 3 man-months of effort. This reduces time requirements by 87% and increases yield by 200 times. Thus, cost per gram of pure maceral has been reduced from -$5000 to $100.

Liquid fuels from coal in conjunction with power plant operation J. Dayan, A. Shauit and C. Gutjinger Department of Mechanical Engineering, Technion Institute of Technology, Haifa 32000, Israel

- Israel

The feasibility of incorporating liquid fuel production with a coal burning power plant is considered. Coal-fired power plants could produce liquid fuels at rates of - l&15% of their coal consumption by low temperature pre-pyrolysis of the coal, without compromising the operation of the power plant. This may become an important new source for liquid fuel and chemical feedstock. The larger consumption of coal may be offset by the higher economic and strategic value of the liquids. The amount of liquids and their quality as a source for fuels and chemical feedstock as well as the combustion properties of the char are important parameters of such a scheme. The process also affects the distribution of the sulfur compounds between the various streams, It may provide a way to reduce emission of sulfur compounds to the environment. The use of a fluidized bed combustor in a power plant reduces also the emission of NO, as compared to other types of combustion systems. The main goal of this research was to evaluate this parameter as a function of the operating conditions. The research was carried out in two stages. First, a long residence time batch partial pyrolysis was used. Two types of coals, commonly used in Israeli power plants, South African and Australian coals, were pyrolysed at temperatures ranging between 400°C and 600°C. The yield and the properties of the liquids and gases under long residence time were studied. Since long residence times may cause cracking of the liquids and reduce its yield, the results, therefore, reflect a lower limit to the liquid yield. Preliminary results of the laboratory bench scale study on partial pyrolysis of coal are presented. They show that, in general, the yield increases with pyrolysis temperature in most of the temperature range considered. The yield from the Australian coal dropped only slightly for pyrolysis temperature above 550°C indicating that secondary decomposition or cracking of the products at the relatively low pyrolysis temperatures, although present, was not very pronounced. Second, a continuous process fluidized bed pyrolysis pilot plant was designed and constructed. Monitoring and control of the system is accomplished with the aid of a commercial computer software (Paragon). Preliminary tests were carried out to determine the feasibility of partial pyrolysis of coal in a single-stage fluidized bed. Several problems were encountered in the operation of the plant that required

Kinetics of coal and catalytic coal pyrolysis reactions in a fixed bed reactor P. K. Dey

Department of Chemical Engineering, Centre of Energy Studies, Indian Institute of Technology, Haus Khas, New Delhi-l 10016. India

Kinetics of coal/catalyst-treated coal pyrolysis reactions in a fixed bed reactor under sweep gas flow conditions P. K. Dey

Department

Engineering,

Centre

Studies, Indian Institute of Technology, New Delhi-l 10016, India

of Chemical

Haus

for Energy Khas,

A kinetic reaction model based on a reaction mechanism consisting of three independent parallel reactions has been developed to describe the ovrolvsis reactions of volatile matter of coal in a fixed bed reactor in ;he temperature range 70@9OOC under sweep gas flow conditions. A zero-order kinetic model has been used for the determination of appropriate kinetic parameters based on the carbon content of the products. The mode1 was found to be sufficiently accurate in interpreting the yield data. Activation energies for the evolution of gases, liquid and char were estimated and found to be 27.77, 28.57 and 9.09 kcal mol 1 for non-catalytic coal and 27.27, 27.77 and 14.28 kcal mol-’ for calcium-catalysed coal, respectively.

Kinetics of calcium-catalysed carbon dioxide and steam

coal gasification in a mixture of

P. K. Dey

Department of Chemical Engineering, Centre for Energy Studies, Indian Institute of Technology, Haus Khas, New Delhi- I 10016, India The kinetics of reactions involved in the gasification of calciumcatalysed coal with the carbon dioxide-steam mixed gasifying agent in a small fixed bed reactor has been studied in the temperature range 75&9OO”C. A reaction scheme consisting of three-step gasification reactions has been used to describe the gasification reaction processes based on the distribution of carbon in the various products. In the first step, coal material pyrolyses to yield volatiles (liquid and gases). In the second step, the liquid products of the volatile components undergo reactions with steam and carbon dioxide simultaneously. Then the reaction of char with the mixed gasifying agent takes place in the third step. The gasification rates of coal material with the steamcarbon dioxide mixture can be predicted using the rate constants obtained from separate experiments, A first-order kinetic model for the coal-steam reaction and a zero-order kinetic mode1 for coal-carbon dioxide reactions have been applied to obtain the kinetic parameters. The mode1 has been proved to be adequate for the predictions of experimental results. The desired ratio of CO/H, ~0.66 in the product

Fuel 1993

Volume

72 Number

5

709