Coal Swelling Model for Pressurized High Particle Heating Rate Pyrolysis Applications

A model was previously developed to describe the decrease in swelling during coal pyrolysis at atmospheric pressure when maximum particle heating rates increase from 10(4) K/s to 10(5) K/s. That model included effects of coal type using chemical structure properties. This paper presents results of new experiments to study the effects of elevated pressure and high heating rates on coal pyrolysis. A pressurized flat-flame burner (PFFB) was designed and built to conduct these studies. The pyrolysis experiments reported in this paper were conducted at particle heating rates of similar to 10(5) K/s and maximum gas temperatures of 1700 to 1900 K at pressures of 1 to 15 atm. Residence times of 25-85 ms were used. A new coal swelling correlation was developed that predicts the effects of heating rate, pressure, and coal rank on the swelling ratio at heating rates above similar to 10(4) K/s. The coal rank index parameters from a previously published atmospheric swelling model were used to model the pressurized swelling data, and a new correlation was developed to describe the effects of pressure. The resulting empirical correlation fits pressurized swelling data from a wide range of coals and types of reactors that could not previously be explained by any one model.