Numerical Study on the Impact of Varying Operation Conditions on NOx Emissions of Large-Scale Pulverized Coal-Fired Utility Boiler

Abstract

For complying with the increasingly strengthened regulation on NOx emission from coal fired power plant, newly built large-scale pulverized coal-fired utility boilers are all installed with low-NOx combustion systems to low NOx emissions. Understanding the characteristics of the system is essential for fully utilizing the system without affecting the combustion performance. In the present work, computational fluid dynamics (CFD) approach was applied to simulate the combustion and NOx formation processes in the furnace of 1,000 MW ultra- supercritical boiler equipped with an advanced low-NOx combustion system so as to study the impacts of varying the operation conditions on its NOx emission as well as combustion characteristics. The combustion system is the Mitsuibishi Advanced Combustion Technology system consisting of six levels corner-fired pollution minimum (PM) coal burners and additional air to achieve air staging combustion. With the help of CFD simulation, the distributions of the combustion temperature and CO, O₂ and NO concentrations were calculated and analyzed. The main influential operation parameters studied include coal type, additional air flow rate, excess air level and mill groups in service. The CFD simulations indicated that the main reasons of the low NOx emission from this boiler are on two aspects: rationally organizing the combustion process to achieve relatively uniform temperature distribution and reducing combustion environment in the main combustion zone, and combining the utilizations of the large amount of additional air to achieve deep air stage and the low excess air level as well as PM burners. It was also found that varying the operational parameters had considerable effects on the performance of the combustion system.