EnergyLines April 2016
Cooling system water mixture upgrade at Worthington Station saves thousands
There’s got to be a better way…
That’s what the plant workers at Worthington Generating Station kept thinking each spring and fall when they changed out the cooling system’s water mixture.
The cumbersome process to flush the system is necessary for winter operations, something the plant wasn’t originally designed for. As a peaking plant, the 174-megawatt natural gas combustion turbine plant in Greene County was initially designed to help meet member energy needs when consumer demand for electricity is especially high, such as during a hot summer afternoon or during a prolonged cold spell like the polar vortex of 2014.
In 2003, Hoosier Energy modified Worthington to provide year-round peaking power, a strategic move that has helped the G&T take advantage of lower gas prices and better meet member needs all year long.
Gas combustion turbine plants depend on water to cool the outside air, which mixes with the gas to drive the turbine, which then produces energy onto the grid. Glycol, a chemical compound that acts much like the antifreeze/coolant in your car radiator, is added to the chiller system to keep the system from freezing.
In the summer, the plant’s chiller system cools warm air to maintain the appropriate water temperature and less glycol is needed in the water to act as a refrigerant.
During the winter, however, it is impacted by frigid temperatures. An auxiliary boiler heats the air coming in and a higher percentage of glycol in the water is necessary to prevent the system from freezing.
Each spring and fall, plant workers switch out the glycol solution for the next season’s operations. Storing the seasonal glycol/water mixture saves hundreds of thousands of dollars a year. But getting it into storage tanks is tricky.
The time-consuming, multi-step process involved using an industrial vacuum to drain 30,000 gallons of chiller water into a storage tank. But the vacuum couldn’t remove all of the chiller water and typically 12,000 gallons remained behind in an area known as the vault. Workers removed the rest by manually connecting a two-inch hose to a slow-release pump similar to a basement sump pump while carefully monitoring the water as it oozed into 1,000-gallon totes.
Next, three operators loaded the full totes onto a trailer and towed them to the main storage tank. Out came the hose and pump system again to release the glycol/water mixture into the storage tank.
The entire process took three operators up to four days to complete and often required overtime.
“The Worthington staff knew something needed to change,” said Greg Vonfeldt, Manager of Gas Production facilities for Hoosier Energy. “Each transfer point posed potential risks to worker safety, hindered plant operations, and raised environmental concerns if the glycol/water solution should spill.”
The team wanted to streamline the process, he said, to eliminate the safety and environmental concerns, reduce overtime and restore the plant to maximum operating capability more quickly. They figured out a new procedure that eliminated the low-flow pump procedure. Installing an isolation valve in the vacuum pump, they theorized, would allow them to add a tee to connect a transfer pump for the remaining chill water, thus allowing them to empty the system fully without using the cumbersome offloading method.
The new procedure eliminates the safety and environmental hazards associated with the old procedure and the plant can be back to full operations in a single shift instead of four days, saving nearly $20,000 annually in overtime costs alone.