Clyde Bergemann Power Group (CBPG) and Covanta Niagara, a Waste-to-Energy facility (WTE) plagued by boiler cleanliness issues, have collectively worked to implement a Shower Clean System (SCS) trial in Boiler 3’s second pass. The SCS’s cleaning concept is designed to traverse down through the roof of the boiler into a narrow open pass using a custom design water spray nozzle to clean the water walls. A SCS trial assembly was operated at the facility from July 27, 2010 to September 1, 2010. A total of 16 cleaning cycles were performed. During this trial period, on average, the second pass outlet flue gas temperature saw a 62 degrees Fahrenheit (degF) reduction after a cleaning event was performed. Based on years of SCS operating experience, CBPG determined a cleaning event should not be initiated if the temperature rise in the second pass is less than 30 degF. This insures that the second pass would not be over cleaned causing material stress to the water walls. In order to estimate the proper cleaning frequency for Niagara’s permanent SCS, an average second pass fouling rate was calculated. Using the fouling rate and the minimum allowable flue gas temperature rise, a cleaning frequency was estimated. Based on the trial results, the recommended operating frequency of the permanent SCS at Covanta Niagara will employ the Umbrella nozzle in the second pass twice per day or once per shift (12 hours). This recommendation is based on observations of the six week operating trial of the SCS and is subject to change based on myriad variables such as waste characteristics and first pass outlet flue gas temperatures. Typical boiler operation at Niagara utilizes industrial cleanings once per week to extend its boiler runtime. During the six week trial the SCS helped reduce the total number of industrial cleanings necessitated to keep the boiler online. Once a permanent SCS is implemented and used daily, there could be significant benefits to boiler runtime without having a total dependence on industrial cleanings. Becoming more reliant on the SCS to maintain lower boiler flue gas temperatures will result in less costs associated with online boiler cleaning and potentially less damage to the third pass convective surface from less high pressure water washing.
Influence of Roof Opening on Gas Temperature Rise in an Enclosure