Herman P. Meissner

Rapid devolatilization and hydrogasification of bituminous coal

Abstract Rapid devolatilization and hydrogasification of a Pittsburgh Seam bituminous coal were studied and an appropriate coal conversion (weight loss) model was developed that accounts for thermal decomposition of the coal, secondary char-forming reactions of volatiles, and homogeneous and heterogeneous reactions involving hydrogen. Approximately monolayer samples of coal particles supported on wire mesh heating elements were electrically heated in hydrogen, helium, and mixtures thereof. Coal weight loss (volatiles yield) was measured as a function of residence time (0–20 s), heating rate (65–10000 °C/s), final temperature (400–1100 °C), total pressure (0.0001–7 MPa), hydrogen partial pressure (0–7 MPa), and particle size (70–1000 μm). Volatiles yield under these conditions increases significantly with decreasing pressure, decreasing particle size, increasing hydrogen partial pressure and increasing final temperature, but only slightly with increasing heating rate. The data support the view that coal conversion under these conditions involves numerous parallel thermal decomposition reactions forming primary volatiles and initiating a sequence of secondary reactions leading to char. Intermediates in this char-forming sequence can escape as tar if residence time in the presence of hot coal surfaces is sufficiently short (e.g. low pressures and small particles well dispersed). Hydrogen at sufficiently high partial pressure can interrupt the char-forming sequence thereby increasing volatile yield. Rate of total product generation is largely controlled by coal pyrolysis while competition between mass transfer, secondary reactions, and rapid hydrogenation affects only the relative proportions of volatile and solid products formed.

Rapid devolatilization of pulverized coal

The rapid devolatilization of a lignite and a bituminous coal was studied by electrically heating in helium approximately monolayer samples of small particles supported on wire mesh heating elements. The samples were rapidly brought to a desired temperature, held there for a desired time, and then rapidly cooled. Devolatilization rates, measured by weighing samples before and after experiments of known duration, were determined as a function of residence time (0.05–20 sec), temperature (400–1100°C), heating rate (102–104°C/sec), pressure (0.001–100 atm), and particle size (50–1000 μm). Devolatilization kinetics were determined by non-isothermal techniques since substantial reaction occurred during heating even under the most rapid heating rates. Weight loss from both coals was essentially complete within a fraction to a few seconds depending upon temperature, and increased with increasing final temperature up to 900 to 950°C. Weight loss (corrected to its value at a fixed temperature) was found to be independent of pressure, heating rate and particle size for the lignite, i.e., it depended only on temperature and time; but for the bituminous coal it increased with decreasing pressure, decreasing particle size and, to a small extent, increasing heating rate. The general reaction scheme appears to involve thermal decomposition forming volatiles and initiating a sequence of secondary polymerization and char-forming reactions. The kinetics and yields of the primary decomposition are successfully described by a set of independent first-order parallel reactions represented by a Gaussian distribution of activation energies around a mean of 56 kcal/mole for the lignite, with a standard deviation of 11, and 51 kcal/mole for the bituminous coal at 69 atm and 70 μm particle diameter, with a standard deviation of 7. For the bituminous coal it was necessary in addition to allow for pressure- and particle-size-dependent secondary reactions representing competition between char-forming reactions and diffusional escape of volatiles. Attempts to correlate the data in terms of a single first-order reaction lead to an overall activation energy (∼10 kcal/mole) that is considerably lower than the mean activation energy of the multiple-reaction system, and to a different set of kinetic parameters for each set of experimental conditions. Conditions such as lower pressure, smaller particle size, and better particle dispersion which help to diminish the effect of secondary reactions appear to be more important than rapid heating in the production of volatile yields in excess of the volatile content obtained by proximate analysis.

Apparatus for determining high pressure coal‐hydrogen reaction kinetics under rapid heating conditions

A simple and relatively inexpensive method is described for measuring the rate and extent of the reaction of coal with hydrogen under conditions of commercial interest. A thin layer of pulverized coal is supported on an electrically heated metal screen strip capable of initial heating rates of 600–12 000°C/sec followed by extended time at final temperatures of 400–200°C. The device is enclosed in a vessel designed for hydrogen pressures up to 205 atm. Typical results are illustrated and shown to compare favorably with data from previous investigations.

Calculating activity coefficients in hydrometallurgy — A review

Abstract Recent developments for estimating activity coefficients of electrolytes both in pure and multicomponent aqueous solutions are reviewed with good success generally attained up to saturation. Examples are presented to illustrate applications of these methods in calculating ion concentrations, vapor pressures, and solubility limits, for some problems encountered in hydrometallurgy.