Upgrading the combustion system of a 1956-vintage recovery steam generator

A design approach for retrofitting the tangentially fired combustion system was identified in August 1986 by Mid America, consultant T. King, and Babcock and Wilcox. This plan had a high probability of achieving the four requisite objectives. The cost-effectiveness of upgrade vs. new was evaluated by Mid America, and the upgrade was chosen as the best option. The traditional empirical relationships that are used to judge capacity limitations were far exceeded. For example, the furnace volume per ton of processed liquor would be 30 ft/sup 3//ton at the new rating, far surpassing the conservative limits of 65 ft/sup 3//ton for new boilers. The weight of liquor solids processed per square foot of plan area for the upgraded system would be 1020 lb solids/ft/sup 2/, much higher than the index of 555 lb solids/ft/sup 2/ utilized for new units. It was apparent that the capacity of the combustion system would be a critical aspect of the upgrade project. Scale models were used to evaluate tangential firing and BandW firing systems. The authors also reviewed the performance results from air-flow upgrades that had been installed on other BandW steam generators. The results of these studies, as well as actual performance data obtainedmore » on the existing system, indicated that traditional indices were conservative. They concluded that the 1956 combustion system could be upgraded at a relatively modest cost by improving air-flow distribution and increasing the heat level of the bed.« less