REPURPOSING PACKAGE POWER PLANTS

OLDER TURBINE PACKAGES SUCH AS THE GE MS5001 CAN BE UPGRADED INEXPENSIVELY TO PROVIDE UP TO 25 MW

GE invented the MS5001 Package Power Plant (PPP) in 1961 and installed the first unit in South Carolina. Its initial purpose was to provide emergency and peaking power to the region should the need arise (Figure 1).

In November 1965, the northeastern U.S. experienced a massive blackout event that lasted about 12 hours and included New York State, and much of New England and the province of Ontario, Canada. Those locations that had PPPs were able to reestablish the power grid and bring back to life a stunned system. For instance, a PPP owned by Long Island Lighting Company (LILCO) had a Frame 5D located in Southampton, NY. It is credited with helping restore the island, because of its black start capability. Similar units in two towns in Vermont with PPPs were called upon to provide emergency power that fall evening.

During the decade following the Great Northeast Blackout, GE sold hundreds of these PPPs to public and private utilities all over the U.S., Canada and islands in the Caribbean. Power companies purchased the Frame 5s in two-, four- and eight-unit power blocks, all with at least one unit that had a diesel starting engine for blackout starts. It was not until 1970 that GE offered a larger unit (Frame 7B) to the industry, but those did not have diesel starting engines.

Many of the original PPPs throughout the U.S. have outlived their initial purpose, as utility companies have found more efficient ways to meet emergency and peaking needs. Thus, these power blocks are being resold at reduced prices to locations in need of smaller units. In short, these blocks of gas turbines are being repurposed for use in other countries and industries that are in need of 15 to 25 MW of power.

Suggested upgrades

In the 1990s, GE published a document (GER-4196) with suggested upgrades to owners-operators of the Frame 5 package power plants. The purpose of these upgrades is mostly to increase power output and modernize plants that typically had low fired starts and operating hours. This extensive publication explains what could be done to upgrade a unit to its design limit for that particular model. For instance, the Frame 5L could be taken to the 5R limit, with modern components that could be purchased from the OEM if desired. More upgrades were offered to Frame 5N units that could be taken to the 5P N/T (new technology) level. Later, other parts vendors offered the same upgrades. In Figure 2, for example, the original turbine and accessory base has been eliminated. A temporary shipping skid was made to support the so-called gas turbine “cigar.” The client wanted only the “flange-to-flange” gas turbine to replace a unit badly in need of a major overhaul.

One of the MS5001N gas turbine PPPs destined for an industrial plant is being completely upgraded, including the generator, controls and auxiliaries. Its new application will be for base load operation in a paper mill. Originally installed in Tecumseh, Kansas in 1971, they were rated at approximately 20 MW at NEMA operating conditions (80°F and 1,000 feet elevation). Their initial purpose was to provide peaking and emergency power to a township west of Kansas City. The new owner intends to operate them at base rated load, burning natural gas and operating thousands of hours per year. In short, no longer will the PPPs be peaking and emergency application, as their new purposes will be base load with heat recovery steam generators (HRSG) on the back end.

Most OEM-suggested upgrades are associated with the combustion and hot gas path. They include new liners and transition pieces. Furthermore, new first-stage turbine buckets and nozzles, as well as radial shroud blocks with N/T parts are offered by the OEM and other vendors. The second-stage buckets and nozzles are of a new design as well. These parts are made of state-of-the-art metals and ceramic coatings to allow for higher turbine firing temperatures (TF).

The segmented nozzles of the second stage require drilling through the turbine shell at specific locations. Further holes are needed for wheelspace thermocouples and borescope inspection in the upper half turbine shell. Segment pin holes are drilled around the entire circumference of the shell (Figures 3 and 4).

High-flow variable inlet guide vane (VIGV) modification is generally recommended to increase airflow and power output. This can be accomplished with the rotor in place or removed. It is a two-person job to set the vanes in their proper position (86 degrees at full open) as shown in Figure 5.

As part of the needed PPP upgrades, the Frame 5N turbine rotor receives new buckets in both stages. Both sets of buckets are of a new design, with the most notable improvement being the inter-locking shroud tips of the second stage. The first-stage buckets allow for higher turbine firing temperatures and hence more power output.

The turbine rotor needs a thrust bearing modification that involves machining 0.300 inches off the inactive thrust face disk. This allows for a non-equalizing, tilting pad thrust bearing pads to be inserted into the expanded space. The OEM recommends this modification because of a known phenomenon that occurs when operating at full speed, no load (FSNL). Excessive reverse-acting thrust (inactive direction) has been known to cause the original tapered land bearing to fail (Figure 6).

With the new buckets being added to both turbine stages, rotor machining for the inactive thrust bearing and the option of compressor blade coating, high-speed rotor balancing is recommended once these upgrades have been completed.

Inspection, refurbishment, improvement and upgrade of other components of these PPPs is a wise investment. After all, many components now have over forty years of operation. Auxiliary system components, such as cooling water radiators and lube oil heat exchangers (coolers) need to be serviced by flush cleaning and pressure testing (Figures 7 & 8). Motor starters can be serviced instead of being replaced. The OEM originally provided heavy-duty AC and DC motor starters, which can be saved, serviced and improved.

Components in the generator auxiliary compartment (GAC) should also be refurbished. Potential and current transformers also need attention and servicing. The same is true for the main power circuit breaker. Additionally, the diesel engines on PPPs often require servicing and can be rebuilt.

As part of the refurbishment, the accessory gear and load (reduction gear) were inspected and rebuilt with new bearings and seals. They were then spin-tested at rated speed to assure there were no operational issues. The client wanted gearboxes to be ready for installation on the accessory and generator bases, respectively (Figures 9 and 10).

Used PPPs

Purchasing and repurposing retired PPPs with low fired operating hours can be attractive to some industrial users in North America, or internationally for those looking for smaller power plants. While the OEM no longer manufactures these smaller turbines in the U.S., new parts are readily available in North America and the technology to make the necessary improvements is available.

Such a project can be done for approximately half the cost of a new power plant from an OEM with a turnaround time of a few months. Various U.S. power companies offer retired PPPs at reasonable cost. However, it is recommended that a control system upgrade be done using modern programmable logic controllers (PLC). Rewiring should also be done along with the elimination of junction boxes on the I-beam bases.

For those willing to engage in a more extensive conversion, it is possible to harness exhaust heat recovery to generate steam for combined cycle or co-generation industrial applications. Reduction gears can be modified from 60-cycle to 50-cycle for foreign applications, and a reduction gear can be converted to accommodate a synchronous condenser for power factor correction, if desired.

There are a surprising number of PPPs available. Consolidated Edison of New York, for instance, purchased 48 units, locating them on barges in the East River on the Brooklyn side. Other power companies, such as Commonwealth Edison of Chicago and San Diego Gas & Electric purchased multi-unit blocks as well. Such lightly used PPPs are often reasonably priced for resale.

Be aware, however, that grandfather clauses no longer apply at new locations in the U.S. Any new site attempting to make use of a PPP must meet current EPA emissions standards. The use of water or steam injection into the combustors via breech fuel nozzles can bring them into compliance. Overseas standards are often less stringent.

Author

David Lucier is owner and general manager of PAL Turbine Services, LLC. Visit www. f a c e b o o k . c o m / PAL.Turbine.Services to learn more about PAL’s PPP upgrade facility n Scotia NY.