THE EFFECT OF CONCENTRATION AND PARTICLE SIZE ON THE BURNING VELOCITY OF LAMINAR COAL DUST FLAMES

Special Research Report SR-43 The need for basic information on pulverized coal flames is established by the increasing importance of pulverized coal combus -tion. This information is required in order to build a fund of knowledge that will enable coal technologists to meet the competition from other fuels. The pre sent work is a study of the burning velocities of coal dust suspensions. This work has been carried out on small flames on burners, under conditions of laminar flow. Most of the measurements have involved two different particle size distributions of one selected bituminous coal. Flame propagation rates have been measured as a function of coal dust concentration and of oxygen concentration in the support- / ing atmosphere. The flame propagation rate exhibits a plateau on both sides of stoichiometric for the coal volatiles. A theoretical ·~ analysis indicates that conductive heat transfer is much more important than radiative heat transfer in these small laminar flames. The dependence of the burning velocity upon particle size indicates that the average reaction rate in the volatiles combustion zone is proportional to the initial geometric surface area of an average particle.