Ignition of bio-water-coal fuels based on coal and charcoal

The results of the theoretical and experimental studies of the ignition processes of a completely new class of fuel - Bio water-coal (Bio-WCF) based on charcoal and coal. Based on the results of a high-speed video recording of the ignition process, the main stages of thermal preparation (evaporation of moisture from the surface layer of the particle, thermal decomposition of the organic part of the coal) and the ignition of Bio-WCF drops have been identified. The experiments have been carried out on the setup providing a low level of error (not more than 11.2%) of the main recorded values (ignition delay time (t(ign)), a characteristic size of the fuel particles at the initial time d, temperature of the oxidizing agent T-e). The temperature regime has varied over a wide range (873 <= Te <= 1273 K) and corresponded to the actual operating conditions of the steam and hot water boilers. It is established that the addition of charcoal to the structure of a water-coal suspension leads to a significant acceleration of the ignition process. It has been shown that at relatively low temperatures (Te = 873 K) the addition of charcoal to the WCF structure accelerates the ignition process by 40%. Under conditions of high oxidizer temperatures, the ignition delay times of Bio-WCF and WCF are identical. According to the results of the experiments, it has been found that when particles of bio-coal-carbon fuel based on high-volatile A bituminous coal are ignited, dispersion of the surface fuel layer is possible. In the case of the ignition of Bio-WCF based on semi-anthracite, such an effect has not been registered. Based on a detailed analysis of the video frames, a mathematical model of the ignition process of suspension fuel based on water, coal, and charcoal is developed. The numerical simulation of the ignition process has been carried out and the ignition delay times have been calculated. A comparative analysis of the theoretical and experimental values of t(ign)has shown their good agreement. According to the results of a mathematical modeling, the values of the concentrations of the components of the gas mixture at the moment of ignition of a particle of bio water-coal fuel have been established. It is shown that a vapor-gas mixture is formed in the particle boundary layer with a large concentration gradient and with a complex topology caused by a convective-diffusive motion in the volatile-oxidizer system.

Automated summary

The ignition processes of a new fuel called Bio water-coal (Bio-WCF) based on charcoal and coal were studied theoretically and experimentally. It was found that adding charcoal to the water-coal suspension significantly accelerates the ignition process. A mathematical model was developed and numerical simulation was carried out to analyze the ignition delay times and gas mixture compositions.