Determination Method Of Optimal Operating Oxygen Content For Utility Boilers

With increase in installed capacity of a large number of new energy power generation and grid connection,depth of peak shaving for coal-fired power units is increasing day by day.In some regions,depth of peak shaving for coal-fired power units has decreased to below 20%.The longterm operation of coal-fired power units under ultra-low load conditions has led to a decrease in economic efficiency of boiler operation.Excess air coefficient has a significant impact on thermal efficiency and operating characteristics of boilers,and is an important technical parameter for monitoring coal-fired power units,which plays an extremely important role in combustion optimization and energy-saving analysis of power plant boilers.Firstly,based on theoretical framework of combustion in boiler furnace,a mathematical model for burnout characteristics of carbon particles in a coal-fired boiler furnace was established.On this basis,the relationship between carbon burnout coefficient of coal particles and boundary parameters such as coal fineness,uniformity,boiler load,coal type,and excess air coefficient was obtained,and an empirical correlation between heat loss of mechanical incomplete combustion in boilers and operating oxygen content of boilers was determined.The calculation shows that the carbon content of fly ash decreases rapidly and then slowly with the increase of oxygen content in the high-temperature environment of the furnace.Secondly,based on the empirical equation of heat loss in mechanical incomplete combustion,a quantitative analysis model of impact of changes in excess air coefficient on boiler operating characteristics was established,using boiler energy balance theory to simulate and determine optimal excess air coefficient and its corresponding optimal boiler thermal efficiency under any load and coal type of boilers,and accuracy of this model was verified.This model was used to conduct case calculations on a 660 MW ultra supercritical boiler,and the quantitative impact of excess air coefficient on boiler operating parameters and economic performance was analyzed in detail.Calculations have found that under different coal types and load conditions,the optimal excess air coefficient and corresponding economic operating range of coal-fired boilers exhibit certain regularity.Finally,based on energy balance model of boilers,a quantitative analysis model was established based on exergy analysis theory to determine the impact of changes in excess air coefficient on optimal exergy efficiency of boilers.The influence of changes in excess air coefficient on boiler performance was analyzed from perspective of the second law of thermodynamics.The work carried out in this article has certain theoretical guidance significance for quantitative analysis of boiler thermal economy,operation optimization,and diagnosis of boiler energy loss parts.