Impact of woody biomass in the composition of coal-water suspensions on their transportation and combustion

Abstract

Relevance. A promising fuel from an environmental point of view is coal-water suspensions. Multiple studies have shown that when they are burned, emissions of anthropogenic gases into the Earth's atmosphere are significantly reduced compared to emissions from coal burning. But the large-scale introduction of coal-water suspensions into the overall balance of energy production is difficult due to a significant delay in their ignition, which can reach several tens of seconds at relatively low oxidizer temperatures (Tg≤1073 K). One of the possible ways to solve this problem is the use of new technologies for preparation for combustion, for example, the use of additional microwave heating of fuel and the introduction of special additives into the composition of coal-water suspensions, which accelerate their ignition. The introduction of such additives into the fuel composition can lead to a significant change in the rheological characteristics. Aim. To determine the degree of impact of the concentration and type of wood additive in the composition of the coal-water suspension on the rheological characteristics of droplets of coal-water fuel, as well as the possibility of reducing the duration of thermal preparation of the latter when exposed to microwave heating. Object. Water-coal suspension based on long-flame thermal coal and on long-flame thermal coal with the addition of sawdust and pine needles (Bio-water-coal suspension). Methods. Experimental studies to determine the time characteristics of water-coal suspension ignition were carried out using a high-speed video camera FASTCAM. Fuel combustion was carried out in a flow-through combustion chamber equipped with magnetrons for additional microwave heating of the fuel. Dynamic viscosity was determined using a Brookfield RVDV-II + Pro viscometer. Results. It has been established that the addition of microwave heating can significantly (up to 15%) reduce the ignition delay of water-coal suspension and Bio-water-coal suspension at relatively low oxidizer temperatures (673 K). Experimental studies shown that the type of biomass affects the time characteristics of fuel ignition at ambient temperatures up to 753 K; with a further increase in the temperature of the oxidizer, the type of additive does not have a significant effect. It is shown that when studying the rheological characteristics of the water-coal suspension, the dynamic viscosity of Bio-water-coal suspension does not go beyond the characteristic value of 1200 Pa s at a shear rate of 100 rpm when no more than 2% of pine sawdust and no more than 6% of pine needles are introduced into the water-coal suspension.