Long-term challenges
Most of the staff members have worked at the plant long enough to have experienced the lean times, which makes today’s power demand boom all the more pleasant. In the early 1990s, then-owner Interstate Power negotiated a number of lucrative power purchase agreements (PPAs), which meant the DGS units were off-line for long periods of time and were daily-cycled when they were needed. Capacity factors in the mid-20% were common in those dark days that extended into the mid-1990s. By 1998, the three-way merger of IES Industries, Interstate Power and Light Co., and Wisconsin Power and Light Co. to form Alliant Energy—and the expiration of those PPAs—put DGS back into the power market overnight. Ownership changed, but the pride employees had in their plant didn’t change.
Today, repair of boiler tube leaks—an artifact of those lean, plant cycling years—remains the biggest challenge for plant staff. Repairs are frequently made during weekend outages, but maintenance workers still have to remove asbestos insulation to access the boiler tubes, slowing what is otherwise a time-sensitive repair. Even with tube leaks, the plant is still challenged to run 24 x 7, with Turbines 3 and 4 on-line for much of the year.
A typical capacity factor today is a demanding 70%. Nonfuel O&M expenditures have averaged approximately $4 million a year. Even more important, the plant produces electricity at an average cost just under $30/MWh (fuel + O&M), and has for a decade.
DGS has also embraced a number of software tools to improve O&M tasks. For example, Alliant uses Maximo as its fleetwide maintenance management system, EtaPRO for real-time performance monitoring, and a computerized lock out/tag out system. Predictive maintenance tasks are the usual ones: thermography, lube oil analysis, vibration monitoring, and on-line and off-line motor testing.
What lies ahead?
Alliant is making significant capital investments in a plant that has shown its worth over the years. Today, Unit 1 (Boiler 1 plus Turbine 4) is undergoing a distributed control system (DCS) upgrade project with an Emerson Ovation system plus upgrades to the Boiler 1 burner management system. Until only two years ago, the plant operated with two control rooms—one for the boilers and one for the turbines, as was common in the day when plants were manually operated and operators specialized in boilers or turbines. Even with a common control room, many of the key control functions, such as damper drives and valve operations, remained manual. Dual-fuel operation on gas has also revealed the need for a more robust, reliable, and automatic burner management system. The cutover to the DCS is planned during a January planned outage. Similar control upgrades to Boiler 5 will follow in a couple of years.
DGS will continue to battle the slow squeeze of urban development. The power plant is located in downtown Dubuque, three blocks away from a multi-million-dollar harbor restoration project featuring a new convention center, hotel, museum, and the obligatory casino.
Another unanswered question is, What happens to DGS when the next bigger, newer, or more economical power plant is built, or when more stringent environmental regulations force expensive retrofits at a plant without room to grow?
These questions aren’t theoretical, given the recent announcement that two of the three coal-burning units at the Lansing Energy Station will be retired and DGS will switch to gas if Alliant Energy is allowed to build a new $1.5 billion coal-fired 630-MW Sutherland Unit 4 in Marshalltown, Iowa (conditional approval for which was granted Aug. 25). These proposed changes would take place when the new coal plant begins service, possibly as early as 2013. Given our current regulatory environment, any new coal-fired plant will face many known and unknown challenges before the first shovel of dirt is turned, and the new Sutherland unit is no exception.
But DGS does have a unique advantage: It is situated in a region with limited transmission capacity and few electricity resources. DGS may have to make a fuel switch in the coming years, but I expect this station will be a valuable resource to Alliant Energy for many years to come.
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