– Bradley Osburn
Gainesville Regional Utilities held a “Show & Tell” event on April 9 for staff, media and city officials at the John R. Kelly Generating Station in order to explain the repair process for one of its turbine systems.
Lonnie Little, a mechanical engineer with GRU, explained that this is the most significant maintenance performed on the downtown facility’s gas turbine No. 4 – the most efficient power producer in the utility’s fleet – since it was installed in 2000.
The system works much like the internal combustion in a car, but on a larger and continuous scale. Fuel – which is almost always natural gas, but can be switched to diesel – is added to extremely compressed air that is then ignited with a spark. The resulting flames force the turbine to spin, which then produces the power that feeds out into the city. GRU can get 75 megawatts out of the system.
Temperatures in the combustion chamber stay over 2,000 degrees and the machinery is cooled using air. Water is injected to reduce the nitrogen pollutants to nine parts per million, making it a very low emissions system. Steam from the operation is also fed out of the turbine to Unit 8, thereby helping produce essentially “free power,” according to Little.
Little said that the system is started up between 150 and 250 times per year, and this is the first time it has been fully disassembled – which includes removing all casings, rotors and compressor system. GRU staff will look for machinery that is off specification or needs repair, and the utility keeps a storage of spare parts on hand for such occasions to keep the downtime as low as possible.
Rotors from the system were shipped to Houston for overhaul, so GRU has to wait until they return for reassembly. Other factors that will affect that process are weather and unforeseen repair needs that the staff might come across. The maintenance began in mid-March and likely won’t be back to full operating capacity until early June, Little said, because the system will need to be run through a battery of tests to measure performance once it is reassembled.
To make up for the lack of power being produced, Little said that GRU measures buying wholesale from other utilities like Florida Power & Light against generating it itself through other plants like the Gainesville Renewable Energy Center and takes the most cost-effective option.
John Stanton, assistant general manager for energy supply, said that an overhauled system would perform at a more efficient level and should drive fuel costs down, though those lower costs won’t be factored in until next year, as this year’s cost are already fixed.
The repairs will cost about $1.7 million, along with some additional capital costs. Little said that GRU is constantly balancing the loss in efficiency with the cost of repairs, so performing repairs now is much like changing the oil in a car. “It’s cheaper than waiting for something to go wrong,” he said.