Optimization of Combustion Air Delivery at Mead Paper, Escanaba, Michigan, 1996 Engineering Conference Proceedings

Allan R. Walsh, Senior Engineer

John F. La Fond

Jansen Combustion and Boiler Technologies, Inc.

Michael A. Fornetti & Tim LeGault

MEAD

Mead operates a very heavily loaded recovery boiler at its mill in Escanaba, Michigan. The boiler is a 1970 vintage unit designed to burn 1.09 million kg/d (2.4 million lb/d) of virgin liquor solids, with a steaming rate of 178,000 kg/hr (392,000 lb/hr) at 101.7 bar (1475 psi) and 496°C (925°F). Many modifications were made to the unit, including the air and liquor delivery systems, that allowed the boiler to be operated at a liquor solids firing rate of 1.36 million kg/d (3.0 million lb/d). At this load, the boiler experienced accelerated fouling in the upper furnace, unstable combustion in the lower furnace, and TRS emissions that were difficult to control. This prompted the mill to consider some unconventional changes to air delivery. Jansen Combustion and Boiler Technologies, Inc. was contracted to work with the mill to determine the best means of increasing the amount of combustion air delivered at or above the liquor guns. Several configurations were evaluated via computer modeling. This led to the implementation of air nozzles on both the front and rear walls at the liquor gun level, which was termed quaternary air. The main benefits of the modifications were reduced carryover, less plugging of flue gas passages, reduced TRS emissions, and more stable combustion in the lower furnace. The factors that showed no significant changes were the temperature at the furnace outlet and the fly ash chemistry. These benefits have led to the application for a patent to cover the air delivery system. Currently, the unit is continuously operated at a solids burning rate of just over 1.41 million kg/d (3.1 million lb/d) of virgin liquor solids, with a steaming rate up to 249,000 kg/hr (550,000 lb/hr).