Upgrading of lignite in a tunnel-type microwave oven

Abstract

Lignite with high moisture content was upgraded in a tunnel-type microwave oven. The physicochemical characterizations of the upgraded lignite were investigated with chemical composition analysis, X-ray photoelectron spectroscopy, N2 adsorption porosimetry, and scanning electron microscopy. The calorific value of the upgraded lignite increased as the moisture content decreased. The carboxyl and hydroxyl groups with high hydrophilicity reduced on the upgraded lignite surfaces, indicating that the coal rank was upgraded after microwave irradiation. The specific surface area of upgraded lignite first decreased and then increased with enhancing microwave power. Particle surfaces of upgraded lignite become compact, indicating the improvement of grinding characteristics. Therefore, upgrading of lignite with microwave irradiation was beneficial for its long-distance transportation and combustion properties.