Rosebud Operating Services Inc., located in Billings, Mont., is a 60-MW petroleum coke–fired power plant that delivers electricity to the local utility and provides processed steam to a nearby petrochemical facility from its two boilers.
Constructed 16 years ago, Rosebud features an air-cooled condenser (ACC) system manufactured by Zurn Balcke-Durr. Composed of two A-frame structures, each assembled from five “cells,” the condenser has a surface area of more than 1.6 million square feet. Steam flows at the rate of 416,863 lb/hr through more than 12,000 cold-dipped galvanized carbon steel elliptical finned tubes, each 30 feet long. The highly finned tubes are cooled by six-bladed fans that are 26 feet in diameter and located beneath each A-frame structure.
Beginning each spring and continuing through the fall, backpressure readings indicated substantial drops in the condenser’s efficiency. Increased backpressure results in higher net plant heat rate and a corresponding measurable decrease in power generation.
“We’re located by a river,” said Dan Gray, director of operations for Rosebud. “Cottonwood pollen is a constant source of condenser fouling during the growing season, and that’s in addition to fly ash and other debris that accumulates and sticks to the condenser fins all year round, reducing the airflow around them.”
Rosebud’s first remedy was a high-pressure lance system. “This really did not give us very good results,” said Gray. “The high pressure bent some of the tubes to begin with, and then the area covered by the lance was too restricted, about an 8-inch circumference. Cleaning hundreds of thousands of square feet this way took forever. We would first clean from the top of the tube bundles and the dirt would be pushed half-way through. Then, we would spray from the bottom, and the dirt would be pushed back up about half-way. The water, although under pressure strong enough to bend the tubes if held too closely, just could not make it through the tube bundle. The efficiency factor was extremely poor. This system also was not easy on the man operating the lance, and safety is always an issue.”
Looking for an alternative solution, Gray did an Internet search and came across information about the FinTech ACC cleaning system developed by Conco Systems Inc. in Verona, Pa. “I went to observe them cleaning an air-cooled condenser outside Las Vegas and was extremely impressed, said Gray. “I contracted them within a month of that event.”
The Conco system also uses high-volume, high-pressure water to clean the tube bundles, but unlike the hard-to-control high-pressure lance, the FinTech ACC cleaning system features a computer-controlled 12-nozzle water jet assembly (Figure 5). The frame and tracks of the system are adjustable to take into consideration all types and sizes of air-cooled condensers, including vertical and flat coolers and “A-frame” and “V-frame” configurations. The Conco system, when it arrived at Rosebud on its own trailer, included the framework, computerized traveling nozzle assembly, pump, hoses, and all ancillary equipment (Figure 6).
|5. Deep cleaning. Rosebud Operating Services used the Conco air-cooled condenser cleaning system to restore lost performance when manual methods failed. The cleaning system uses 12 computer-controlled nozzles to thoroughly clean the entire surface area of the ACC tube bundles. Courtesy: Conco Systems Inc.|
|6. Thorough washing. Seen from beneath the ACC, high-pressure water from the spray nozzles removed the fouling from Rosebud’s elliptical air-cooled condenser tubes. Courtesy: Conco Systems Inc.|
“The system was set up by the two Conco technicians who brought it here,” said Gray, “and we provided what was really minimal help to get everything set up. The Conco crew has been a pleasure to work with. They operated the cleaning system up to 12 hours a day and had the entire condenser thoroughly cleaned for us by the end of the week.”
Because different condenser manufacturers produce their condensers with differing designs and cooling requirements, Conco’s FinTech ACC system has been engineered with the ability to adapt to those varying configurations by changing the angle at which the water hits the tube bundle. Plain water is used, eliminating any possible environmental concerns. The nozzles themselves are designed with varying degrees of approach to the bundles. This permits the Conco technicians to select the nozzles that are the most efficient for a particular condenser configuration, resulting in thorough surface cleaning without any tube damage.
“The plant began realizing performance increases after the Conco crew had cleaned just one-quarter of the condenser. Overall, we see up to a 10% increase in ACC efficiency, recovering about 3,000 MWh each year. The primary improvement is during high-ambient-temperature days, where the cleaned ACC can perform efficiently at the higher temperatures. On the bottom line, we’re saving about $180,000 a year.”
—Contributed by Eric Fayard ([email protected]), marketing manager for Conco Systems Inc.