Philip G. Kosky

Catalysis of coal char gasification by alkali metal salts

Abstract A study has been made of the gasification behaviour, in carbon dioxide and steam, of a number of coal chars doped with small amounts of alkali metal carbonates. For a given additive, the magnitude of the catalytic effect increased with the rank of the parent coal. A progressive loss in catalytic activity on thermal cycling during steam gasification was associated with reaction of the alkali salts with mineral matter in the chars. The kinetic data were consistent with catalytic mechanisms involving oxidation/reduction cycles on the char substrates.

Eutectic salt catalysts for graphite and coal char gasification

Low melting binary and ternary eutectics of the alkali metal halides, carbonates and sulphates have been found to be more effective low temperature catalysts for the CO2 and steam gasification of graphite and coal chars than the pure salt components. The reduced melting points of the eutectic phase facilitate contact between the catalyst and the carbonaceous substrate.

Catalytic CO2-gasification of graphite versus coal char

Abstract The effects of alkali carbonate catalysts on the C0 2 -gasification of Illinois No. 6 hvB bituminous coal char, demineralized Illinois No. 6 coal char, Pittsburgh No. 8 hvA coal char, Navajo subbituminous coal char, Reading anthracite coal char, North Dakota A lignite char and spectroscopic grade highest purity graphite are reported. Alkali carbonate salts are effective Boudouard catalysts for all these substrates, but salient differences between coal char and graphite reactivity are observed. To account for these differences, a redox mechanism based on alkali hydride intermediates is proposed.

Space-filling models for coal. 2. Extension to coals of various ranks

Abstract Space-filling models of scale 10 8 :1 have been constructed for low-, intermediate-, and high-rank coal molecules. The molecules have been designed to conform to experimentally determined parameters, such as chemical composition, aromaticity and ring index. The molecules do not actually occur in nature, but are merely statistically-averaged structures. The low-rank coal species appears fluffy, porous and random, with essentially all interior atoms exposed as surface. The intermediate-rank coal model structure is more flat and oriented, with closed ended pores and only occasional non-coplanar protrusions due to aliphatic, alicyclic, and hydroaromatic moeities. The high-rank coal model is highly ordered with locally graphitic domains. Physicochemical properties and ultimate utilization of the various coals are discussed with respect to the model structures.

Significant parameters in the catalysed CO2 gasification of coal chars

Abstract Alkali and alkaline earth carbonates have been used to catalyse the C02 gasification of coal chars prepared by pyrolysis of Illinois No.6 coal. This study found that alkaline earth carbonates are fair gasification catalysts, though throughputs are insensitive to loadings in the range of 5–20 wt%. The order of efficacy is Ba > Sr > Ca. Alkali carbonates are excellent catalysts, with throughputs showing a dependence on loadings and atomic number. In particular, at high loadings (20 wt%) the order is Cs > K > Na > Li. As kinetic parameters for the alkali carbonate catalysed Boudouard reaction with coal chars differ significantly from those for graphites, an alternative redox cycle mechanism has been proposed involving an alkali hydride intermediate.

Observation of alkali catalyst particles during gasification of carbonaceous materials in CO2 and steam

Results of a microscopical examination of catalysed carbon gasification are reported. Both in CO2 and steam, alkali catalysts show evidence of mobility. In the steam gasification of coal chars, the catalysts irreversibly combine with indigenous mineral matter. This is less pronounced in C02. The catalysed CO2 gasification was observed by hot stage microscopy, where alkali carbonate catalysts achieve an apparently molten state during incipient gasification. For single crystal graphite, circular pitting, hexagonal pitting and channelling were observed. For coal chars, irregular morphologies tend to obscure direct observation of surface/catalyst interactions, though subsequent scanning electron micrographs reveal the consequences of extensive catalyst mobility.

A method of measurement of thermal conductivity : application to free-standing diamond sheet

Self‐supporting diamond sheets, made by the metastable chemical vapor deposition (CVD) technique, have been reported to have a range of properties, presumably dependent on the morphological details and the impurity burden of the particular sample. CVD diamonds are typically in the form of large area (i.e., many square cm) sheets averaging a few hundred microns in thickness. For this form of matter, a novel method of thermal conductivity measurement is reported based upon the well‐known principle of the phase lag of a traveling thermal wave. In the present variation of this technique, the traveling wave traverses the diamond sheet from its leading edge (which was pulsed with an infrared diode laser) through the point of measurement. The average thermal diffusivity of the sheet was calculated. The equipment is relatively simple and the sample preparation minimal. Both theoretical and experimental details are given. The random error in thermal diffusivity measurements is estimated to be about 7% due mainly t...

Comparison of effects of adding Boudouard catalysts before and after coal charring

Abstract The gasification behaviour of coal to which Boudouard catalysts were added before and after charring was compared. For Illinois coal and for Navajo subbituminous coal, experiments showed that it is not of significance if alkali carbonate catalyst is added before or after charring. The results suggest that Boudouard catalysts must be highly mobile under gasification conditions, and their activity dominates the gasification process at these conditions compared to mass transfer constraints.

Superconducting Nb3Sn joints by chemical vapour deposition

Abstract Nb3Sn is an A15 superconductor with high critical current density in high magnetic fields, e.g. 200 000 A cm−2 at 10 T and 4.2 K. Unfortunately, A15 intermetallics are brittle and difficult to manufacture in defect-free lengths for large superconducting coils. This paper describes a chemical vapour deposition (CVD) process which deposits Nb3Sn on to prespliced Nb3Sn substrates to form a superconducting joint between two superconductive sections. The CVD-deposited material has very fine grain structure (probably less than 0.2μm), a Tc of between 16.2 and 17.8K (in zero field) and a critical current density of greater than 500 000 A cm−2 at 5 T. In addition, the CVD layer definitively bridged the gap between two spliced superconductors, increasing the current capacity at 5 T from a baseline capacity of 66 A mm−1 on the original material to greater than 80 A mm−1 after a CVD Nb3Sn coating of 3.5μm per side had been applied.

Nuclear process heat—application to coal gasification

Abstract The high temperature gas cooled reactor has achieved peak coolant temperatures from 775 to 950°C, depending on the core design. These temperatures are sufficiently high to consider the HTR as a source of heat for several large industrial processes. In this article the application is to a coal gasification process which produces a mixture of carbon monoxide and hydrogen as the key product. The gasifier system itself is coupled to the HTR via a catalyzed fluidized bed coal gasifier operating at 700°C and producing methane. The feed to this gasifier is a mixture of carbon monoxide, hydrogen and steam with the stoichiometry chosen to effect an overall athermal reaction so that no heat is directly transferred into the gasifier. Its hydrogen supply is generated by steam reforming the methane produced using the direct HTR heat. This indirect system has advantages in terms of its final product, indirect heat transfer and ultimately in the savings of approximately 40% of the coal which would otherwise have been assumed in an all-coal process producing the same final product.