COOLflow™ Case Study 115

The SS Universe Explorer Achieves a 6% Fuel Savings by Increasing Boiler Efficiency with COOLflow Technology

The Situation

The SS Universe Explorer is a 23,500-ton cruise ship that serves more ports of call than any other cruise line plying Alaskan waters. One of its other functions is to serve as a floating campus for the “Semester at Sea” program offered by the University of Pittsburgh. The cost of fuel is the single largest expenditure for any seafaring vessel in a hyper-competitive environment, impacting both cruise prices and profit margins. To this end, any fuel savings realized by ships like the Universe Explorer directly affect their bottom lines.

The shipping industry is not governed by emissions regulations; however, ships are restricted in regards to limiting visible emissions while in port and often times within sight of land. Along with these restrictions, the fuel oil burners on the ship must also meet several important operational requirements, which include high burner turndown and complete carbon burnout with low excess air levels at all loads. The Universe Explorer needed to increase its operating efficiency without increasing visible emissions or compromising operational capability.

The Boilers

The Universe Explorer is operated by three main, Foster Wheeler marine D-type boilers, two of which have left-hand configurations and one that has a right-hand configuration. Design operating conditions are 105,000 lbs/hr of superheated steam at 600 psig and 855°F. Each boiler uses four cast iron TODD® D-register burners that fire light oil in a pattern of two over two.

The TODD Solution

Engineers from John Zink’s TODD Combustion Group visited the Universe Explorer at its Vancouver, B.C., port to gather information and assess the conditions of the units to develop a solution that addressed the ship’s efficiencies and emissions. In order to design low-cost retrofits for the boilers, the burner engineers recommended a COOLflow physical modeling study on the combustion air supply systems of the boilers. The engineers then gathered additional information to construct a scaled physical model, (Fig. 1) which was used to determine existing airflow patterns and design the solution. The solution took the form of baffles and turning vanes to improve airflow distribution within the windbox and to the burners.

During their visit to the Universe Explorer, the engineers observed that the existing “air casing”, or windbox, was not deep enough to contain the new required baffles. To remedy this, an 8’x8′ “window” was designed to make the burner area accessible. The “window” provided an additional benefit by enhancing combustion air residence time through the windbox.

The Universe Explorer follows typical routes from year to year during its “Semester at Sea” voyages, so fuel usage data can be easily compared between voyages using fuel bunkering reports. To verify that the airflow modifications were successful, baseline data was gathered from the previous cruise fuel reports and compared to post-retrofit fuel usage data.

The TODD Result

After the model was completed, the solution was implemented along with the installation of new TODD D-register burners of the same design, which were required due to the windowing of the windbox. Since two boilers had identical configurations and the third was a mirror image, the modelers simply provided a mirror copy of the baffle arrangement for the third unit. Much of the old fuel burning equipment was modified and reused.

Before correction, the mass flow was 45% deficient for one of the bottom burners. Large areas in the bottom burners had no air (-100% airflow). In fact, the modeling indicated reverse flow through areas of the bottom, right-hand corner burner (Burner No. 1) as seen in Fig. 2. This coincided with the burner that previously experienced inexplicable premature diffuser failure. The baffle solution designed ensured that each burner was provided with adequate airflow. As Fig. 3 indicates, the mass flow of air to each burner was brought to within +/-1% of average from an uncorrected condition of +/- 55%. Figure 4 indicates the peripheral distribution was brought to within +/-9.6% for all of the burners from an uncorrected condition of +/-112%.

Improvements in airflow distribution within the windboxes enabled the boilers to operate at reduced excess air rates, which provided a gain in boiler efficiency and resulted in reduced fuel consumption. Following the retrofit, the ship’s chief engineer helming a “Semester at Sea” reported fuel savings of between 6% to 7% when compared to historical fuel usage data for the identical route. The firesides of the boiler also remained cleaner than on previous voyages, indicating an improvement in carbon burnout.