Devolatilization Zone Research Articles

Modeling and experimental studies on devolatilization yields from a bituminous coal

A laboratory-scale fixed bed reactor was set up to simulate conditions existing in the devolatilization zone of an air-blow, Lurgi-type, fixed bed coal gasifier. The effects of temperature (350-550/sup 0/C) and particle size (1-9 mm) on the devolatilization behavior of a bituminous coal in such a reactor were studied. The feed gas composition was chosen to approximate that entering the devolatilization zone from the gasification zone below in a commercial-scale fixed bed reactor. Similar studies were also carried out on a thermogravimetric analysis (TGA) reactor, for purposes of comparison. A semitheoretical model, describing the transport of the tar and gas species to the surface of the particle, and the subsequent evolution of these, is developed. The model takes into account the softening characteristics of bituminous coals upon heating. The volatiles yield predicted by the model is next compared with the experimental results, and the agreement appears quite good.

The influence of rank and maceral composition on ignition and char burnout of pulverized coal

Investigation of combustion characteristics for different ranks of coal was conducted in a one-dimensional vertical tube furnace without external heating. Though fuel ratio (fixed carbon content/volatile matter content) is generally believed a good index to determine combustibility,carbon burnout of various coals and fuel ratio didn't always show good correlation in this study. Various types of char were produced at the devolatilization zone of the tube furnace during combustion. Morphology of those chars depended on coal rank and maceral composition of individual coal particles. Relationship between combustion rate and morphology and properties of chars from different coals was discussed.

Parametric studies on devolatilization of a subbituminous coal in a reactive gas environment

A laboratory scale fixed bed coal gasifier was set up to simulate the conditions existing in the devolatilization zone of an air-blown, fixed-bed coal gasifier. Devolatilization behaviour of a subbituminous coal was evaluated in the temperature range 350 °C to 550 °C and at pressures 30, 300 and 375 psig. Three feed coal particle sizes, (−2, +1), (−4, +3) and (−9, +6)mm, were studied. The gas feed was a synthetic mixture of composition similar to that leaving the gasification zone of a fixed bed gasifier and contained 30% by volume of steam. Devolatilization runs were conducted over coal residence times of 5, 10, 20 and 30 min durations. The gas evolution rates showed a peak around 5 min from the start of a run and most of the gas evolution tapered off just under 30 min. Thirty key components in the tars were quantified and these included aliphatic and aromatic homologues, as well as sulphur and nitrogen substituted structures. The molecular weights of the tar samples showed a maximum between 300 and 500. A first order kinetic model applied to the total weight loss data yielded activation energies in the range 4 to 11 kcal mol −1. Differential equations for obtaining concentration profiles for tar and gas inside the coal particle were solved numerically. From these calculations it was concluded that the pressure buildup (due to evolution of tar and gas) inside the coal particle was higher for larger particles, at a given external pressure, but decreased with external pressure. The concentration of tar inside the particle did not appear to be sensitive to low pressures (around 1 atm), but increased in the higher range of pressure (above 20 atm) and also with particle size.

Effect of particle size on lignite devolatilization in a fixed-bed reactor

A fixed-bed coal gasification reactor was set up which specifically simulated the devolatilization zone in a gasifier. Samples (100 g) of lignite coal in three size ranges; −2+1 mm, −3+2 mm and −4+3 mm, were devolatilized in the temperature range 350–550 °C with a steam-oxygen mixture, at 1 atm. The effect of these operating variables on tar yield and composition, melting point, viscosity, specific gravity, and molecular weight distribution was determined. A first-order reaction model was fitted to the experimentally observed total loss in weight of the lignite.