Evaluation of Furnace Nose Arch Modifications to Reduce Slag Formation on a 695 MW Utility Boiler Firing PRB Coal

摘要

In 2007 Riley Power Inc., a Babcock Power Inc. company, retrofitted a 695 MW opposed-wall fired, dry-bottom, balanced draft boiler with new low NO_x CCV Dual Air Zone (DAZ) burners and an advanced overfire air (OFA) system. This unit is designed to burn pulverized Powder River Basin (PRB) coal to generate 4,440,000 lbs/hr of steam flow at 2640 psig and 1005°F. The unit is equipped with fifty-six (56) CCV-DAZ burners and twenty (20) advanced OFA ports. Aside from the low NO_x burner project, Riley Power has been contracted to replace the secondary superheater intermediate pendant and nose arch panel. As part of the contract, CFD modeling was used to evaluate three different furnace nose arch configurations to determine the optimum depth of the nose arch into the furnace. This paper describes Riley Power Inc.'s (RPI) approach to evaluate and optimize the flue gas flow and temperature distributions at the furnace exit plane, around the nose arch and through the intermediate superheater pendants to determine the optimum depth of the nose arch into the furnace. The proposed design has been evaluated in regard to desired thermal performance of the secondary superheater. CFD modeling was conducted for both burner and furnace. The full furnace modeling utilized results from burner modeling work completed for the low NO_x retrofit project. All burner, OFA settings and operating conditions were adjusted to match post-retrofit operating data from field tests as closely as possible. The different configurations, modeling results and their impact on flue gas temperatures, slagging and erosion are discussed in detail.