Interaction of water droplets with pyrolyzing coal particles and tablets

Abstract

The paper presents the experimental research findings for the patterns of collisions of water droplets with pressed tableted samples used as substrates and with small particles of a pyrolyzing solid fuel. Brown coal samples were used. Droplet-substrate interactions were studied when varying the droplet diameter in the range from 1 to 4 mm and velocity from 0.5 to 4 m/s. That corresponded to the Weber number range of 7–830. The coal tablet surface temperature was varied from 20 to 700 °C. In the interactions of water droplets (0.7–1.5 mm in diameter, pre-collision velocity from 1 to 3 m/s) with coal particles (with a size of 0.2–1 mm, pre-collision velocity 0.7–2 m/s), the temperature of the latter was varied in the range of 330–480 °C. The following regimes of the interaction of droplets with solid particles during chemical reactions and phase transformations were distinguished: spreading/agglomeration and break-up/separation. Differences in the characteristics of the interaction of water droplets with coal particles at varying temperatures were identified. Droplet-particle interaction regime maps for B(We), We(Oh) and We(Ca) were constructed. The collision regime boundaries were described using fitted curves that can be utilized to develop the existing mathematical models of droplet-particle collisions in gas. It was established that the gaseous volatile production in coal pyrolysis has a modest effect on the regimes and characteristics of the droplet destruction in the temperature range under consideration (20–700 °C).