(730e) Numerical Simulation of a Pyrolysis and Re-Burning Combinative Low-NOx Grate Boiler

With investment in the coal industry, China retains its current position as the leading global producer and consumer of coal, even as it endeavors to diversify its energy structure. The consumption of coal in china is largely in power production, aside from this, there is a lot of industrial use along with a comparatively small amount of domestic use. However, because of the limitation of present economy conditions in some underdeveloped areas, domestic coal combustion for heat supply and cooking still relies on small grate boiler, of which efficiency is comparatively low and has a high pollutant emission rate. When coal is burned, NO_x mainly includes nitrogen oxide (NO) and nitrogen dioxide (NO₂) will be produced. These pollutants initiate reactions which result in the production of photochemical smog, ozone and acid rain. That is why NO_x has drawn much attention of all over the world.

       According to these low-NO_x combustion techniques which are widely used in industry and domestic area, this paper presents an advanced grate combustion system, which combine pyrolysis and re-burning low-NO_x techniques. This technique refers to a new design of a grate boiler, which works with three different parts. Firstly, the pyrolysis chamber gives sufficient residence time for reduction gas generation and low NO_x emission, while the main combustion chamber as the second parts can acts as a well-stirred complete combustion zone. Meanwhile, introduce industrial exhaust gas as reduction gas on both side of the furnace arch, one side to the top of the main combustion chamber and the other to the flue gas, in order to reduce the NOx generated in the oxygen-enriched combustion.

      The computational fluid dynamics technique is applied to simulate and analyze the performance of this new combustion system. A tow dimensional mathematical model has been developed to simulate the furnace structure design. Commercial software FLUENT has been used for the over bed coal volatiles combustion. Results show that the numerical simulation is successful and the pyrolysis and re-burning combinative technique generates a considerable improvement in efficiency for inferior coal combustion in modified grate coal boiler, and has good potential for future application in industry and for civil use.