Assets well cared for get better with age

Pacesetter Plants: Class of 2009/2010

Stony Brook Energy Center

Ludlow, Mass.
Massachusetts Municipal Wholesale Electric Co

Stony Brook Energy Center is not your typical gas-turbine-powered generating station (Fig 1). Most of the nation’s combined cycles were built dur­ing and after the bubble of the late 1990s/early 2000s basically by set­ting equipment on a slab of concrete in a vacant field and wrapping the package with architectural siding. Nothing special.

Massachusetts Municipal Whole­sale Electric Co’s (MMWEC, pro­nounced “em wek”) Stony Brook, which began commercial operation nearly 30 years ago, was built by Bechtel Power Corp and General Electric Co at a time when design­ers and owners thought GT-powered generating facilities should be engi­neered conservatively and look like traditional powerplants (Sidebar 1). Standing on the plant’s spacious steam-turbine deck, for example, you get the feeling that an entire F-class 2 × 1 combined cycle might be shoehorned into an equivalent amount of space today (Fig 2).

1. Who is MMWEC?

The Massachusetts Municipal Wholesale Electric Co is a not-for-profit public corporation and political subdivision of the Commonwealth of Massachusetts. It was created in 1976 through an Act of the Massachusetts General Court as a Joint Action Agency. MMWEC provides a broad range of power supply, financial, risk management, and other services to improve the competitiveness of the state’s municipal utilities. Using its statutory tax-exempt financing authority, MMWEC has issued more than $4.4 billion in bonds to finance and refinance its 720-MW ownership in five New England powerplants—including Stony Brook.

The quiet 350-acre site in Lud­low, Mass, is home to many species of wildlife and while accessible, can be challenging to find. It is not read­ily visible from town roads – at least when there are leaves on the trees – and many locals don’t know the plant exists.

     

The grounds themselves draw you back to a time before the plant was built, when this “reservation” was federal property and home to perhaps the largest nuclear weapons storage facility on the East Coast. Three widely separated concentric fences, one electrified with voltage in the Cold War days, wrapped the site and allowed intimidating patrols by guard dogs, vehicles, and armed personnel.

The physical security, although no longer intact, surely would have made the guards in Stalag 17 or The Great Escape envi­ous. The sections of fence that remain, the empty munitions bunkers (some now storerooms), and the abandoned pillboxes contrib­ute to the plant’s “charm.” There probably is no other powerplant site like this in the nation – perhaps the world.

Background

Plant Manager Karl Win­kler has been at the plant since it was built, as have some others. Winkler met the editors at the gate and ushered them into his office for a backgrounder before the requisite tour. Operations Super­visor Glenn Corbiere joined the dis­cussion. First item on the agenda was a review of the physical assets. Stony Brook consists of a 354-MW Inter­mediate Unit and a 172-MW Peaking Unit, Winkler said (Fig 3).

The former is a 3 × 1 com­bined cycle, which was pow­ered by three distillate-only Frame 7Es when commis­sioned in 1981. It is owned by MMWEC (90.75%), Green Mountain Power Corp (8.8%), and the Vermont Vil­lage of Lyndonville (0.44%). As a Joint Action Agency for Massachusetts munici­pal utilities, MMWEC sells the output from its share of the Intermediate Unit to 24 municipals. The peaking unit, owned entirely by MMWEC, consisted of two distillate-only sim­ple-cycle 7Es when it was completed in 1982, and still does (Fig 4). Partici­pants in this asset include 22 Massa­chusetts municipal utilities.

     

GTs were designed for liquid fuel because no gas was available at the site when the plant was built. Dif­fusion burners were installed on the combined-cycle GTs with steam injection for NOx control; permit limit was 75 ppm at COD. Diffusion burners with water injection for NOx control were specified for the peakers because there was no steam available for them. Corbiere mentioned that he prefers steam over water for NOx control because the former is condu­cive to gentle combustion and offers a better heat rate.

All engines came equipped with the Speedtronic™ Mark II control system and its associated Integrated Temperature System. ITS provided exhaust-temperature averaging and other functions, and controlled water and steam injection. One GT serving the Intermediate Plant and one of the peakers have black-start capability. All generators are hydrogen-cooled.

Natural gas. A limited supply of low-pressure natural gas became available to the plant in 1983 and MMWEC converted the three com­bined cycle GTs (known as 1A, 1B, and 1C) to dual fuel. Booster com­pressors were added at the same time. The peakers remained oil-only. A new gas line for the Intermediate Unit was commissioned in Septem­ber 2002.

An air permit change in 1995 reduced the 75-ppm NOx cap to 42 ppm on gas, 65 ppm on oil. Aware of the impending permit change a year earlier, MMWEC conducted a thor­ough review of procedures to iden­tify any adverse operational impacts associated with the new emissions requirement.

What it found was that the steam turbine could not provide sufficient extraction steam to meet the 42-ppm limit on all engines operating simul­taneously at full load. The optimal way to address this situation was to convert GT 1B’s diffusion combustion system to DLN-1, the OEM’s dry low-NOx offering (Fig 5).

The available extraction steam flow then would be sufficient to allow continued operation of GTs 1A and 1C using the original diffusion com­bustion system. Note that conversion of GT 1B to DLN-1 required that the engine’s Speedtronic Mark II be replaced with a Mark V control sys­tem to provide the additional func­tionality needed to implement the low-emissions solution.

Winkler recalled Stony Brook’s DLN-1 retrofit as the first such con­version in the industry. He proudly reflects on the plant’s role in the com­mercialization of DLN technology.

The plant manager then went backwards in time and discussed other upgrades implemented in the years between the conversion to dual fuel and the DLN retrofit, further attesting to the plant’s role as an industry leader. These included the installation of Nimonic transition pieces and inlet guide vanes (IGVs) made from Carpenter 450, transition to blunt-edge directionally solidified first-stage buckets and GTD 222 nozzles, etc.

Corbiere and Winkler said the plant’s engine parts have been reli­able and durable over the years, due primarily to a first-rate main­tenance program. GT 1B reached the OEM’s declared limit of 5000 starts (only 64,000 operating hours) in 2008 and its rotor was replaced during an outage at the end of that year. The combined cycle’s other two gas turbines are closing in on 5000 starts. MMWEC will assess having GE inspect the original 1B rotor, which may result in the OEM certify­ing the rotor for additional service if all criteria are satisfied.

This could set a precedent for own­ers of long-lived GE frames. When the OEM first issued its lifetime limits for starts- and hours-based machines, the supplier said it would only consider hours-based rotors for life extension based on inspection results. The manufacturer’s initial position was that 5000 starts consti­tutes end of life.

Important to note here is that the Stony Brook 1A-C GTs were hours-based early in life, running upwards of 4000 hours annually for a few years. Since then, maintenance has been conducted on a starts basis.

The peakers (GT 2A and 2B) have only about 2000 starts and fewer than 6000 hours on each of them. There are plenty of spares for these machines because MMWEC refur­bished original parts from the com­bined-cycle engines when they were upgraded. Stony Brook is blessed with an abundance of storage space, made possible by the generous supply of retired (and empty) munitions bunkers

Next on the schedule was a facil­ity tour. But before leaving the office, Winkler reviewed with the editors a flow diagram for the combined cycle (Fig 6). The drawing was particularly valuable for understanding how the plant’s heat-recovery steam gen­erators (HRSG) work. The vertical forced-circulation unit was designed and manufactured by GE. As the dia­gram shows, it looks nothing like the horizontal natural-circulation HRSG preferred today for US combined cycles and cogeneration plants with frame engines (Fig 7).

Discussions with users over the years suggest that GE HRSGs were a nuisance at some plants, but Win­kler said Stony Brook’s were virtu­ally problem-free. He couldn’t recall more than perhaps a total of six tube leaks in the three boilers over three decades of service. Bypass dampers allow the combined-cycle’s GTs to start and ramp quickly, Winkler con­tinued, and the HRSGs’ forced-circu­lation design allows them to rapidly attain thermal equilibrium.

Winkler talked about the plant’s maintenance practices dur­ing the walk-around, enabling the editors to gain the insights needed to conduct a meaningful interview on Stony Brook’s controls upgrade proj­ect – the focal point of the visit. Here are some bullet points from the tour:

  • Engine borescope examinations are conducted frequently by plant staff and annually by a third-party services supplier. Winkler believes borescope inspections are critical to avoiding unwanted “sur­prises.”
  • Maintenance of the inlet-air house is relatively simple because of the clean environment. Pleated fiber­glass filters still are retained by the metal frame installed when the plant was built. Plant staff conducts periodic checks for air leaking by the filters, or entering downstream of the filters, patch­ing holes and replacing defective filters as needed. All filters are replaced on a nominal six-year interval. Winkler said this inter­val was optimal based on the life of filter material and compressor cleanliness.

Winkler paused for a moment in a cool, quiet location on the deck­plates to talk about management’s philosophy and the capabilities of plant personnel. “We don’t let things go,” he said. “Anything we find in a borescope or other type of inspection is addressed promptly. Our engineers and technicians are experienced and attuned to preventive maintenance. The plant’s safety record testifies to that: More than six years without a lost-time accident. Important, too, is that our personnel have pride of own­ership in the work they do.

     

Most maintenance is handled in-house – even hot-gas-path (HGP) inspections. “We don’t have a long-term service agreement with the OEM, Winkler continued. “And when we require specialty contract work, our people typically work alongside the service provider’s employees. We don’t pass on opportunities to learn new skills and hone existing ones.”

As the tour continued, Winkler contributed these thoughts:

  • No online compressor water wash­ing is necessary. Offline wash­ing is done annually for the peak­ers, semiannually for the engines serving the combined cycle. Plant staff made a portable wash skid for the purpose (Fig 8).
  • Stony Brook has not had the var­nish issues that have plagued some other plants. Winkler attri­butes that in part to constant attention to lube-oil cleanliness. Staff built a couple of “centrifuge on wheels” skids (Fig 9) to operate on each engine’s sump one week out of six.

Winkler recalled only one var­nish incident in plant history. It occurred in 2005 on a peaker. Plant did a chemical clean using the existing oil, changed filters until they were clean, flushed with virgin oil, and then refilled the engine’s 2700-gal sump (one sump serves the gas turbine, generator, and hydrogen seal-oil system). A practical idea that the staff developed to reduce the volume of oily waste is shown in Fig 10. The compactor squeezes discarded filter elements to about a quarter of their size to save space in the dumpster.

  • The plant installed foggers in the late 1990s to squeeze more power from its engines. Systems from both Caldwell Energy Co, Louis­ville (Fig 11), and Mee Industries Inc, Irwindale, Calif (Fig 12) were purchased. Power boost can be as high as 5 MW per engine on a hot dry day.
  • Water and steam for NOx control, plus water for fogging, contribute to a significant makeup require­ment. City water is deionized onsite by two 350-gpm makeup treatment trains. Cation, anion, and mixed-bed demineralizers are incorporated in each train.

GT control system replacement

It’s a tough job managing a power­plant in these days of deregulated generation, independent grid opera­tors (ISOs), tight emissions control, etc. There’s really little margin for error the way generators are dis­patched and paid for their services. Missed opportunities can mean a serious shortfall in revenue. The job becomes significantly more difficult when equipment ages and becomes unreliable, and is no longer support­ed by the OEM.

However, the marketplace and technological expertise of MMWEC staff have enabled Stony Brook to keep pace with today’s challenges. Winkler said management under­stands that equipment must be upgraded and replaced for the facil­ity to maintain its value. Replace­ment of the GT control systems is one example.

The plant manager explained that a significant amount of revenue comes from the ancillary services Stony Brook provides – specifical­ly capacity, availability, and black start. In one of the shoulder months, Winkler continued, you may be called only a couple of times to deliver power. A failure to start would result in financial penalties.

MMWEC bids the two peak­ers into the ISO’s 10-min forward reserve market with a critical “10 minutes from dispatch signal to base load” requirement. These units are audited by the ISO for compliance at each startup. Winkler shared with the editors a couple of the “report cards” (called Resource Performance Reports) it received.

One such report for a GT 2A start one day last May showed unit status minute by minute. The target was 65 MW within 10 minutes. First eight minutes there were zeroes in the output column, by the end of the ninth minute output was 22.7 MW. At the end of the 10th minute, the number was 65.1 MW. Winkler said they actually achieved the target in about nine and a half minutes. Not much room for error.

A green box with “PASS” in it was at the top of the report. Had the unit not met the target, there would have n a red box with “FAIL.” Get two “FAILs” and your reserve revenue suffers dramatically. Also, the unit must pass an ISO-New England audit to re-establish its 10-min capa­bility and associated revenue.

Winkler said that with the Mark IIs, Stony Brook operators weren’t confident they’d make the contract output within the 10 minutes when called upon. Something always seemed to be failing. For example, the multi-voltage (15/28/5) power supplies needed for the Speedtronic II (Figs 13-15). Plant technicians couldn’t find new ones anywhere; rebuilds were available, but not reli­able. This forced re-engineering of control panels with multiple power supplies.

This scenario certainly is not unique to Stony Brook. Relentless cost-cutting industry-wide, demand­ing power contracts, suppliers with­drawing support for legacy controls platforms, and a labor pool growing less experi­enced by the day often leaves plant owners but one option: Replace.

     

RFQ. Half a dozen ven­dors responded to the public RFQ prepared by the utility with assistance from Pond and Lucier (PAL), Clifton Park, NY. MMWEC and PAL developed what essentially was a performance spec, thereby allowing respondents the flexibility to offer creative solutions. GE and Innova­tive Control Systems Inc (ICS), Clif­ton Park, NY, were among the bid­ders. Critical in the selection process was having absolute confidence that the successful vendor would provide the functionality required and execute the project on schedule. References and experience were particu­larly important.

The ICS solution had a high degree of transpar­ency because it relied on PLCs and other control system components from Rockwell Automation Inc, Milwaukee, a unit of Allen-Bradley. This equipment is used extensively in many process indus­tries, as well as power, and replace­ment components are readily avail­able. Many controls integrators have deep experience with Rockwell equip­ment and software.

2.Emerson Process Management acquires ICS

Pittsburgh-based Emerson Process Management, Power & Water Solutions acquired ICS on June 30, 2010, exactly one year after the company was awarded the Stony Brook controls retrofit project.

Emerson is well respected in the electric power industry for its Ovation™ expert control system, perhaps the most popular upgrade solution for WDPF-equipped Westinghouse gas turbines. The Westinghouse Digital Processing Family of controls was standard on the storied company’s engines installed before Siemens AG purchased the firm.

Bob Yeager, president of Emerson’s Power & Water Solutions division, said that ICS’s turnkey turbine-control retrofit solutions—including planning, engineering, configuration, installation, and commissioning—complements Emerson’s expertise in turbine condition monitoring and protection systems, instrumentation, analyzers, and valves.

President Pat Nolan, who founded ICS in 1991, said the company has completed more than 300 turbine-control retrofits worldwide on GE, Siemens, Pratt & Whitney, Alstom, Rolls Royce, and Solar engines—among others. ICS had about three dozen employees at the time of the acquisition, including several in the field.

ICS was awarded the contract based on its experience with similar upgrades for water- and steam-inject­ed dual-fuel Frame 7 engines, plus cost, schedule, etc (Sidebar 2). There was no foot-dragging on this project: The spec was developed within a month, bids were returned by the end of the next month, bids were evalu­ated within a month, and the award was made June 30, 2009. Physical work started September 19 and the project was completed on November 10. No more than two machines were out of service at any point during the project, according to ICS President Pat Nolan.

ICS’s proposal was for the replace­ment of the legacy Mark IIs on GTs 1A, 1C, 2A, and 2B with state-of-the-art ControlLogix PLC-based controls that included the following capabili­ties: (1) operation on gas and/or liquid fuel, (2) simple- and combined-cycle operation (the Intermediate Unit’s GTs are equipped with bypass damp­ers and can operate simple cycle if necessary), and (3) NOx steam (GTs 1A and 1C) and water injection (GTs 2A and 2B). New vibration and flame sensors, automatic synchronizer, and redundant electronic overspeed were included as part of the work.

Control system redundancy was another option considered, but the value proposition did not meet MMWEC’s investment criteria. How­ever, the utility decided in favor of redundant communications systems and an engineering workstation. Winkler said ICS solved several long-standing issues associated with the Mark IIs, integrating several new features that enhance the perfor­mance and value of Stony Brook.

New panels. As part of the proj­ect, ICS prefabricated completely new cabinets for the control systems serving each engine. They had the same overall dimensions as the exist­ing Mark II cabinets. This enabled a complete factory test before delivery to the plant and quick, trouble-free installation. The panels for the two peakers each have an industrial HMI touch-screen operator interface for engine control and monitoring (Figs 16, 17). Screens for the Inter­mediate Unit’s turbines were inte­grated into the existing combined-cycle board (Fig 18). The screens communicate on a redundant Eth­ernet network to the PLC controller. Other features incorporated into the oper­ator interface are listed in Sidebar 3.

3. Auxiliary screens facilitate operation

The following are some of the screens provided, in addition to the HMI unit graphic control screens, to facilitate gas-turbine operation:

Water wash. Allows initiation of an off-line water wash and provides turbine protection during the washing process.

Ignition transformer screen allows the operator to test spark plugs by selecting an on-screen pushbutton.

Online fuel transfer (oil to gas and gas to oil) shows valve positions, fuel-flow percentage, and progress of fuel transfer.

Auto/manual synchronization. A synchroscope with a manual/auto selection available.

Startup check screen shows signal name and logic signal of all that is preventing the engine from starting.

Trip screen shows signal name and logic signal for all turbine protective trips.

Overspeed test allows operator to manually select either electrical or mechanical overspeed. Buttons are provided on screen to abort test, raise and lower speed, etc.

Counter/timers include total unit operating time, distillate-/gas-fired times, emergency trips, total starts, fast starts, peak fired hours, etc.

Wheel-space, exhaust, bearing, and generator RTD temperatures.

Hydrogen purity.

Seismic vibration.

Water injection status and valve positions; plus, the ability to stop/start water injection.

Steam injection status and valve positions; plus, the ability to stop/start steam injection and to view CEMS data.

Calibration screen allows technicians to calibrate gas valves, inlet guide vanes, and fuel-oil bypass valves.

Motor status. Operational status of both ac and dc auxiliary motors is shown on one screen.

Nolan said that ICS assigned its most experi­enced Frame 7 personnel to the project, including Proj­ect Manager Parke Brown, VP Engineering Lorcan Roche, and Installation Engineer Beshoy Sawriss. It also developed a sophisticated interactive model of the Stony Brook controls for acceptance testing and training. The factory acceptance test was conducted in the ICS conference room, which is only a 90-minute drive from the plant. Training was conducted for operators and technicians at ICS, MMWEC, and Allen-Bradley facilities.

MMWEC personnel handled loop checks, functional verification of pro­tection, etc – essentially the same things that you would do in any con­trol-system commissioning. Winkler beams with pride when dis­cussing this work. “Fast track,” he said “because of our inti­mate knowledge of the plant and its equipment. Functional checks took about three days; operational checks of various operating conditions, startups, and shutdowns perhaps anoth­er three days. And we did the tuning.” Typically it took a week to certify each engine for opera­tion, a process that became easier as time went on.

Experience. When the editors visited Stony Brook, operators had accumulated about six months of experience with the new controls. Winkler said that staff embraced the new system. It provides much more information than the Mark II did for decision-making and work was ongo­ing to customize graphics and data presentation to facilitate operations, he said.

Startups are much less stressful. The peakers now are up and running at dispatch output within about eight and a half minutes, about a minute faster than was possible before the upgrade. “That’s huge,” Operations Supervisor Corbiere said. One thing that’s critical for achieving a 10-min­ute start is to purge on unit shut­down so that no purge is necessary on the next start. Control logic assures that on a failure to fire the engine can’t be restarted unless it is purged beforehand.

Two more projects completed during the control system upgrade project were (1) replacement by ICS of legacy excitation controls serving the four GTs with Basler Electric Co’s (Highland, Ill) DECS-400 static excitation system, and (2) upgrade by MMWEC staff of the H2 control cabi­net (Fig 19).

Nolan said the DECS-400 is designed for retrofit applications to supply saturable current trans­former (SCT) control winding current to the existing SCT/power potential transformer (PPT)-type exciter. The system, he continued, uses the lat­est power semiconductor components and controller to deliver accurate and highly reliable dc current to the SCT control windings. The rectifier is supplied on a prewired subpanel and the controller section mounts nearby. Both were installed in exist­ing cabinets.

One final note: Winkler says the Mark V control system for GT 1B, which was reconfigured for DLN oper­ation, will be replaced with PLC-based controls during the March 2011 outage by ICS. The new control sys­tem will maintain common hardware, functionality, and software with the other units. Of course, modifications will be required for the additional I/O associated with the DLN system – including additional pressure trans­mitters, water-injection flowmeters, and flame detectors. Software chang­es for the DLN-1 control algorithm also will be necessary. ccj