Coal-fired power generation is supplying about 30% of the world’s primary energy. Almost all of coal-fired power plants in Japan employ the pulverized coal combustion method. In the pulverized coal combustion, coal is pulverized into a powder of several tens of microns. This method enables to burn coal effectively because of the large surface to volume ratio. Pulverized coal particles are supplied to the actual boilers with primary air whose Air/Coal ratio (mass flow rate of primary air/mass flow rate of pulverized coal) is set to 2.0. Co-combustion of coal with ammonia has been studied with the aim of reducing CO2 emissions in coal boilers and coal power plants in terms of a concept to use ammonia as a renewable fuel from solar, wind, etc.
To understand co-combustion processes of a single coal particle with ammonia it is necessary to build a fundamental numerical model for numerical simulation of combustion flow in coal boilers and coal power plants. Combustion process of the pulverized coal proceeds continuously as below: devolatilization, gas combustion of volatile matter, solid combustion of char and radiative heat transfer from char and formed soot. Investigation of the effect of co-combustion of pulverized coal with ammonia on processes of devolatilization and soot formation is the objective of the present study. In the pulverized coal-fired boiler, complex combustion field is formed because these phenomena mutually influence each other. In the present study, therefore, pulverized coal particles are burned with ammonia stabilized by hydrogen/air diffusion flame under atmospheric pressure in a laminar counter-flow burner in slow flow velocity. Coal particles are supplied with ammonia/air premixed gas. A high-speed camera and a microscope objective lens have provided high temporal/spatial resolution images of the co-combustion processes. Finding from a detailed observation of simplified combustion field of coal/ammonia co-combustion is as follows. A single pulverized coal particle presented a rotational behavior during the combustion process because of external force by gas expansion caused by combustion of volatile matter released from a pulverized coal particle itself and ammonia.