Comparative Study of the MILD Combustion Characteristics of Biomass and Brown Coal Manabendra Saha,* Giovanni Gitto, Alfonso Chinnici, and Bassam B. Dally Centre for Energy Technology, School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia ABSTRACT: The present paper reports a comparative study on the burning characteristics of pulverized biomass and coal under moderate or intense low-oxygen diluted (MILD) combustion conditions. Two types of biomass fuelsnamely, grape marc and almond huskand a high volatile Victorian brown coal were used as pulverized fuels to burn in a vitiated coflow inside a vertical MILD combustion furnace. The furnace walls, as well as coflow temperature, and local oxygen concentrations were controlled by a secondary swirling burner. Fuels were introduced into the furnace employing CO 2 as a carrier gas with a constant velocity (i.e., bulk jet Reynolds number, Re jet = 20 000) and a fixed range of particle sizes (250−355 μm). Detailed measurements of in-furnace and exhaust temperatures and chemical species (i.e., O 2 , CO, CO 2 , and NO) are demonstrated and discussed, together with optical images at the top, middle, and bottom sections of the furnace. It was found that MILD combustion was successfully established for all of the fuels investigated without any visible flame inside the furnace. Under similar experimental conditions, biomass volatiles are released earlier leading to a difference of the maximum temperature within the furnace of ∼150 K along the centerline. The largest NO emission was measured to be ∼185 ppmv (db at 3% excess O 2 ) for grape marc case, because of the higher value of in-fuel N of grape marc and the lowest was ∼125 ppmv (db at 3% excess O 2 ) for coal case. From the comparison of CO emission, biomass shows more eminent burning characteristics than brown coal under MILD combustion conditions. 1. INTRODUCTION The world’s energy demand is predominantly supplied by the combustion of conventional and renewable fuels in the combination of solid, liquid, and gaseous form. Among all the available fuel sources, solid fuels play an essential role in the world’s energy supply, because they are (i) the least- expensive fossil fuel source and (ii) abundant. As a conventional fossil fuel, coal is an abundant fuel resource in the world. Although conventional combustion of coal contributes to a substantial number of adverse effects on the environment and public health, global warming is the most serious impact of coal combustion, in terms of its universal and potentially irreversible consequences. In contrast, biomass is considered to have the highest potential to replace traditional fossil fuels and significantly contribute to meeting the global energy requirement 1,2 among the available renewable energy sources. A report published by the International Energy Agency (Task40) 3 estimates that 10% of the world energy is generated using biomass, with industry utilizing a third of the resource and the rest is for domestic use. The interest in biomass as a viable alternative has been increasing in the recent years, because of the need for a more-sustainable energy production. 4 Moreover, its relevance is expected to further grow as international energy policies focus more on a greater exploitation of renewable energy sources. 4 Several advantages differentiate biomass from other renewable fuel sources. 5 Biomass energy extraction does not require expensive conversion technologies, and energy can be delivered through different energy vectors such as liquid and gaseous fuels, heat, and electricity. Moreover, biomass is a carbon-neutral energy source and can even act as a greenhouse gases (GHGs) negative emitter. 6 The amount of carbon dioxide absorbed by biomass during its growth, through the photosynthesis process, can offset its emissions during combustion. 6 Hence, the use of biomass for electricity generation is a significant option to reduce the production of GHGs. Biomass resources are mainly composed of wood and wood wastes, followed by agricultural crops and domestic solid wastes. 7 Present research is focusing on implementing and optimizing environmentally friendly and sustainable technologies for biomass exploitation as an energy resource. 1 The present work focuses on the exploitation of the grape marc and almond husk as biomass fuels and Victorian brown coal as a conventional fossil fuel for energy generation. Grape marcwhich is also known as grape pomaceis a solid waste product from grape pressing during the wine-making process and is made of skins, seeds, pulp, and stalks. Almond husk, which is also called almond hull, is the outer leathery flesh of the almond kernel obtained through the mechanical removal process of almond. On the other hand, the brown coal is collected from Loy-Yang, Victoria, Australia. The Victorian brown coal deserves particular attention, because of its high reactive nature and combustion characteristics, despite its high water content in nature. The grape marc and almond husk have a substantially higher volatile matter content and less fixed carbon, in comparison with Victorian brown coal. 8,9 However, all the fuels have a high moisture content (∼65%), which reduces the thermal efficiency of the burning process. The combustion of solid Special Issue: 6th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies Received: October 15, 2017 Revised: December 8, 2017 Article pubs.acs.org/EF Cite This: Energy Fuels XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.energyfuels.7b03158 Energy Fuels XXXX, XXX, XXX−XXX