Study On Combustion Characteristics Of Blended Coal In 600MW Boiler

The design coal of Chinese coal-fired power plant is generally used bituminous coal,in addition,some coal-fired power plants using lean coal as the design coal.However,in recent years,with the increasing consumption of coal,the costs of coal production transportation has been increasing,as a result,the demand for pulverized coal in coal-fired power plants is very tight.Therefore,in order to meet the fuel supply of the power plants,it has become a common way to blend one even multiple kinds of coal.First,this paper analyzes the theory and research status of burning blended coal and the application of numerical simulation technology.Taking a 600 MW coal-fired unit in China as the research object,using GAMBIT software to build a physical model and dividing the grid,then using FLUENT software to simulate the combustion of the boiler in the design conditions.The grid independence verification has been completed and the accuracy of the simulation results have been certificated by being compared with the results of the hot test.Then,the numerical simulations under the conditions that combusting blended coa l have been made,and the results of simulation which including the flow field,temperature field,composition of flue gas,carbon content of fly ash in flue gas,NO_x are analyzed.The effect on the combustion characteristics of the boiler of blending ratios of the coals with similar or large difference characteristics have been studied.For the blending combustion with the design coal and coal-type 2,the blending combustion can improve the ignition performance of the blended coal to a certain extent.However,when the blending ratio reaches 0.8,the carbon content of the fly ash in the flue gas increases slightly.It is indicated that the blended coal with small difference characteristics will also have the phenomenon of “rod wind” during the blending process;For the combustion of blending coal-type 2 and coal-type 3,the ignition performance of the blended coal continues to decline and the combustion condition of the furnace has been continuously deteriorated with the increase of the blending ratio.Especially when the blending ratio reaches 0.5,the combustion delay is particularly serious,and the temperature in the burnout wind region is so high that it is easily causes the screen superheater to slag,which affects the safety of the boiler operation.Finally,increasing the excess air coefficient of coal-type 2 and coal type-3 blended combustion,the combustion situation in the furnace is improved.It can be seen that when combusting the blended coal with similar characteristics,the combust ion condition is similar to that burning one of them,and so it is can be performed that a large proportion of the blending;When two kinds of coal with large difference characteristics are mixed,increasing the excess air coefficient is beneficial to improve the combustion situation in the furnace and improve the burnout degree of the pulverized coal.When the proportion of blending is smal,it can meet the actual operation requirements of the power plant.