Think of it as a marriage with a timestamp and a substantial upfront investment to ensure its “performance.” That’s how Emera Energy, which acquired Bridgeport Energy in late 2013, and Siemens Power Generation, Orlando, are walking out of the church following an extensive plant modernization program that involved major maintenance, life extension, and technology upgrades on two 84.3A gas turbine/generators (GT/G) and one steam turbine/generator (ST/G), plus replacement of the original TXP control system with Siemens Energy Inc’s (Alpharetta, Ga) T3000.

Based on interviews with Plant Manager Paul Warren and Production Manager Donald Ross, the relationship is off to a good start, though the partners have made important discoveries about each other. Most importantly, states Warren, Siemens met its technical and budgetary performance targets and got its incentive payment for doing so. Each GT/G was guaranteed to deliver an additional 13 MW but the actual is 14-16 MW at 200-Btu/kWh lower heat rate, with 10 additional megawatts available from the ST/G.

The combined cycle was commissioned in 1998-1999; plant’s original capacity of 520 MW is now 560 MW. Turndown capability has been reduced from 62% to 50% while still maintaining a 10-ppm CO emissions limit (post-catalyst).

Clearly, Emera has a different attitude than the last five owners of the plant, six if you count the one firm that owned Bridgeport Energy twice. The Canadian asset portfolio operator has committed to a $180-million, 20-year partnership with Siemens. Already, Emera is looking at additional technology upgrades (sidebar).

Emera found the asset to be reliable and safe in 2013. However, to better capture grid market opportunities, to undertake major scheduled maintenance outages on all three turbines, and to deal with a saltwater intrusion event in 2012 under previous owners, the company embarked on a broad and deep modernization program, including:

• Increasing compressor mass flow using state-of-the-art airfoils, new inlet guide vanes (IGVs), rotor replacement/refurbishment, and new blades and vanes for rows 1 and 2.

• Use of new tiles and tile holders in the combustor, requiring less cooling air, and increasing both mass flow and flame temperature.

• Improved coatings and cooling for turbine blades and vanes.

• Addition of advanced stability margin control (ASMC) to improve combustion stability and reduce errant trips.

• Inspection and full rebuild of the ST/G (removal of the HP, IP, and LP rotors), replacement of LP rotor blades, seals, and diaphragms, and steam path valves.

• Rebuild of two of the three boiler-feed pumps (non-Siemens scope).

• Tube replacements in both HRSGs (non-Siemens scope).

• DCS upgrade/replacement.

• Replacement of obsolete static frequency converter and static excitation systems.

All this was accomplished in what both parties agree were two narrow outage windows of 70 days in fall of 2014 (first GT/G, ST/G, controls, and BOP items) and 38 days in May-June 2015 (second GT/G, ASMC installation both units) on a logistically difficult site. The facility is hemmed in tightly by adjacent industrial facilities. The more acute constraint is that only one crane is available to service all three machines. Despite these challenges, safety was stellar, report Warren and Ross; only one recordable injury occurred.

The ST/G low-pressure rotor was pulled first for fear of chloride contamination from the saltwater intrusion event. It was cleaned, balanced, and transported to and from Siemens Charlotte works. Transporting rotors from Charlotte to Bridgeport also proved challenging, with the numerous permits and highway escorts required state to state.

Modernization program helps plant capture grid opportunities

Getting the full story of a partnership requires talking to both partners. A conversation with Siemen’s Arne Wohlschlegel filled in some important details from the OEM perspective. Among other points of interest, this was the first outage of such complexity Siemens had undertaken in the US on this type of equipment, especially with a DCS upgrade included in the scope.

“Emera is a new customer for Siemens and we were impressed with its willingness to apply upgrade technology new to the US market,” Wohlschlegel observed, “especially since the company wasn’t familiar with our gas turbines.” Emera conducted a broad survey of technology options and traveled far and wide to conduct due diligence. So the trust didn’t come blind. He agreed that the outage time frames were ambitious for the scope. “We learned a great deal in the first outage that we could apply in the second.”

Customers that embark on a two-decades service contract get benefits, Wohlschlegel said. “We provide greater coverage and an enhanced warranty, the customer gets priority on parts and repair, and everyone benefits from the economies of scale of having a planned maintenance program,” he added. When asked whether maintenance costs were completely predictable over the two decades, Wohlschlegel answered, “for the most part, yes, about 85%, I’d say.”

The real eye opener is that the upgrades also extend the GT/G hot-gas-path outage interval from 25,000 to 33,000 hours and a major outage (HGP + compressor) to 66,000 hours. Thus, there are significant availability gains in scheduled outage time as well as the incremental capacity gains and improved heat rate.

Siemens benefits from long-term service agreements because they aid in planning R&D programs and large-scale management of parts inventory. Of course, Wohlschlegel also acknowledged that the benefit of LTSAs to Siemens is that the company can better control the movement of the technical design and know-how around cutting-edge components to third-party service firms.

Part of the agreement is that Siemens also remotely monitors the machines to ensure high availability. The company can compare plant data with those from the larger fleet of machines and analyze operational conditions.

Wohlschlegel freely owned up to the challenges in communicating between Orlando and Alpharetta. “The fall outage timeline was ambitious, especially integrating I&C activities into the schedule. We learned some lessons but in the end it proved a great success.”

Warren stressed that Siemens is a global company. The logistical details of transporting major components, procuring parts from sites in Germany and the US, hand-offs from mechanical to commissioning, and communicating between Orlando (which owns the long-term agreement) and Alpharetta (responsible for the DCS) “caused some churn about meeting deadlines and delivery. At one point,” Warren observed, “after we began to have issues with our grid operator/regulator, Emera had to ‘come with a big paddle’ to resolve the communication issues.”

A key lesson learned, said Ross, is that you have to budget enough time during the outage for QA/QC and logic checkout during the factory acceptance tests (FAT) and for aligning loop checks with lockout/tagout procedures. “We could have used an additional week,” he added. A specific issue was that the electrical-systems logic for GT11 was “copied over” for GT12, but the systems are not identical.

The hiccups were apparently well worth it. Ross said the big benefit of the T3000 is easier troubleshooting. “We can look at the logic behind the system right on the DCS, no more separate engineering workstation; we click on a point, see the graphics, and immediately pinpoint issues on the loop diagrams.” Operators can now have up to 10 graphics on one monitor, compared to only one with TXP. “We have more info at our fingertips, more control over the equipment. The loops are the same but they are easier to tune.” Plus, the plant has half the number of cabinets to deal with.

Bridgeport’s power marketing and gas purchasing are handled by Emera out of Halifax. Lately, the market has been soft, noted Warren. “We arranged to run the plant in 1 × 1 mode during the second outage because we thought market conditions would support that.” It turned out there were many days we were so close to the margin but ultimately were not picked up in the day-ahead market. June and July were softer than expected, too, and the plant cycled much more than normal. “Our typical day is to run for 16 or 24 hours, but rarely just for an 8-hr shift. Historically the plant has had an 80% average capacity factor, which is quite high for a combined cycle today.

The ASMC systems on the GT/Gs help the plant operate at part load. New sensors on the IGVs are used to adjust the air flow to the pilot and main burners in real time, control combustion pressure and temperature, and maintain combustion stability and emissions. Warren noted that these are software upgrades, except for the IGV sensors, and involved changes to the valving logic.

Training is going to be an on-going proposition for Bridgeport. Now that the plant has an owner that looks to stick around for a while, the staff is motivated and enthusiastic but their roles are shifting. “We have 16 of 26 professionals with new positions and responsibilities, so it’s almost like starting up a new plant.” The staff changes include three new patrol operators, three new control room operators, new production supervisor. “There’s lots of training in our future,” Ross commented wryly. Much of that is being invested with Siemens, too.

The stellar safety record is credited in part by Ross and Warren to JLN Associates, Old Lyme, Conn. “We had 30-40 workers on site during the day, and while the plant management and staff are ultimately responsible, JLN people were our eyes and ears. They essentially handled confined-space permits and served as monitors, verified LOTO, performed hot-work oversight, and generally reviewed all things pertaining to safety. One key was making sure all job safety analyses (JSA) were complete and accurate.”

The Emera/Siemens partnership isn’t resting on its laurels. Upcoming modifications include wet compression to extract an additional 20 MW from the plant and upgrades for operation at even lower loads. “We keep looking for options to maximize the value of the asset,” Warren underscored.   

Other ideas are to play in the ancillary services market and supply power to Bridgeport’s heating/cooling authority. “We’ve even negotiated a power purchase agreement for solar panels on the roof of the building, it’s less than 500 kW but that’s enough to supply the building,” Warren said. That’s good community relations, too, and complements the plant’s contributions to 30 different local charities, and local business engagement.

The HRSGs still require a few million dollars of investment as that saltwater ingress incident did a number. “We have significant under-deposit corrosion from chlorides,” Warren said. In May 2012, the plant operated for eight hours with significant condenser tube leaks, root cause being poor operator response to alarms.