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Improved Exhaust Transition Duct, RR Avon

Transition Section
Transition Section
Transition Section
Exhaust Transition Duct
Exhaust Transition Duct

Fern Engineering offers an improved expansion joint that replaces the current OEM transition duct connecting the gas turbine to the power turbine of Rolls-Royce Avon-powered units. The new expansion joint was originally designed for a client who was experiencing severe hot gas leakage due to excessive distortion of the OEM transition pieces and the mating hardware. Fern Engineering decided to actively market the new design after discussions with other Rolls-Royce Avon owners revealed similar patterns of distortion, leakage, and power loss.

Current Design
Current Design
Fern Engineering Design
Fern Engineering Design

Every expansion joint installed to date has met all expectations. Current worldwide total: 70+

"The installation of the first RR Avon exhaust transition duct replacement on a North Sea oil platform went like clockwork. No operational problem and the cell temperature has come down by 10°C, which is exactly what was needed. Expect a further order soon. It is getting "glowing" reports throughout the company. Thanks for your assistance in the early stages with the different size and Fern Engineering's flexibility. Good product!" - Satisfied Customer

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Turbine Spare Parts

To complement our hardware upgrade kits for Curtiss-Wright MOD-POD gas turbines, Fern Engineering stocks a supply of long-lead-time hardware such as special high-alloy bolts, nuts, tablocks, and pins for immediate delivery. To extend the life of the turbines, other parts no longer available from the OEM can be reverse engineered or designed new, if necessary.

Fern Engineering has enlisted the support of select, highly-qualified vendors to produce turbine replacement parts exceeding original component design specifications. Fern Engineering's long-term commitment to total turbine quality is reflected in our rigid quality control standards to assure clients of parts integrity. Strict auditing procedures are implemented to ensure the quality of vendor-supplied parts. Our quality control resources include skilled technicians and special tooling and machinery to analyze critical form, fit, and functional characteristics. This, in turn, helps maintain high reliability of every part processed by Fern Engineering.

In addition to our extensive inventory of spare parts for MOD-POD gas turbines, most current gas turbine fuel nozzle replacement parts are kept in stock to enable rapid turnaround times for our expert gas turbine fuel nozzle refurbishment.

Upgrade For Curtiss-Wright Mod-Pod Gas Turbines

Modified Inlet Duct
Modified Inlet Duct

From the mid-1960s to the early 1980s, Curtiss-Wright, a famous name in the history of aviation, packaged and sold more than 50 MOD-POD gas turbine units. Both 25 MW single-ended and 50 MW double-ended MOD-PODs were produced which featured gas generators from either Rolls-Royce or Pratt & Whitney paired with power turbines designed and built by Curtiss-Wright. When serious problems with power turbine and expansion joint components of these units began to surface, Curtiss-Wright mandated a de-rating which resulted in a 20% reduction in maximum power output. After Curtiss-Wright dropped out of the gas turbine business, Fern Engineering purchased their entire spare parts inventory and redesigned or reverse-engineered many of the original components, identifying deficiencies and developing improved replacements in the process. Fern Engineering now offers MOD-POD owners six redesign hardware kits which are applicable to all of these units. The kits can be fabricated and installed by Fern Engineering in 300-350 days and can boost the output of OEM units by as much as 25%.

Upgrade For Curtiss-Wright Mod-Pod Gas Turbines
Fern Engineering-designed hardware kits provide power solutions in six specific areas:

Kit 1 - Power Turbine Casing
To eliminate thermal cracking, a complete redesign of the casing was required, utilizing an upgraded material, thermal shielding, and isolating segments. The modification resulted in reduced operating temperature, reduced transient differential temperature, unlimited low cycle fatigue life and unlimited creep life.

Kit 2 - 1st Stage Support Centering Device
The redesign of the centering ring eliminates loose fitting keys and the associated vibration. The assembly is effectively de-tuned by adding stiffening and damping to the inner core.

Kit 3 - 1st Stage Support Ring and Bolt
The support ring has been redesigned to accommodate a restraining pilot diameter. This restraint prevents the flange from outgrowing its mating part and eliminates bolt bending and failure.

Kit 4 - Blade Tip Seals
The blade tip seals have been strengthened by increased thickness. Additionally, improved material has been utilized for the first stage.

Kit 5 - Inlet Housing Rear Flange
The rear flange has been replaced with a short conical section and conventional bolted flange. This flange is fabricated from a much improved material which is shielded by the housing, minimizing distortion. The conventional flange attachment to the turbine case eliminates hot gas leakage.

Kit 6 - Expansion Joint
The expansion joint has been upgraded by replacing the convolutions with improved material. The inner flow liner has also been changed to minimize liquid entrapment.

The components in the Fern Engineering kits are not merely reverse-engineered replicas of the OEM parts. In many cases, they are completely new designs that feature upgraded materials and design elements that resist fatigue failures. For example, the Fern Engineering power turbine casing in Kit 1 uses Inconel 625 which provides high creep and stress rupture strength while also giving good resistance to low cycle fatigue. In addition, Fern Engineering's design includes isolating elements and radiation shields that allow the casing shell to operate at lower temperature than the original design. The combination of improved materials and lower operating temperature results in a design that has effectively unlimited creep and low cycle fatigue life.

Since 1988, a total of 6 double-ended MOD-POD gas turbines have been upgraded with power turbine casings (Kit 1) and various other Fern Engineering MOD-POD kits. The high-time unit has accumulated in excess of 6500 hours and 1000 starts. Recent inspections have revealed the units to be in excellent condition with no distress. Clients include Newfoundland & Labrador Hydro, Hydro Quebec and The Electricity Corporation of New Zealand (ECNZ).

Hydro Quebec's Cadillac Power Station, Site of 3 Fern-Upgraded MOD-POD Units
Hydro Quebec's Cadillac Power Station, Site of 3 Fern-Upgraded MOD-POD Units

At its power station in Cadillac, Quebec, Hydro Quebec implemented an upgrade of new turbine casings (Kit 1), blade tip seals (Kit 4), inlet housing rear flange (Kit 5) and transition piece expansion joint (Kit 6) on each of its three MOD-PODs. Fern Engineering fabricated the components via source-approved vendors, arranged for packaging and shipment and provided installation supervision. The upgrade, valued at approximately $3.5 million (USD), allowed Hydro Quebec to increase the rating of the station from 120 to 150 MW and recover the penalty imposed by the OEM at a cost of about $120/kW - significantly less than the cost of installing a new 30 MW simple cycle gas turbine.

GT-Facts™

Recognizing the need for simple, low-cost gas turbine performance monitoring software, Fern Engineering has developed the product called GT-FACTS™, a useful tool for off-line monitoring of power degradation due to compressor fouling and for determining the benefits of water washing and inlet cooling. The software uses tables of manufacturers' expected performance curves to predict the expected performance of a gas turbine as a function of barometric pressure, ambient relative humidity, ambient and inlet temperatures, and inlet and exhaust pressure drops.

Direct Inlet Spray Cooler

Fern Engineering first became involved with the development of direct spray coolers in 1993 and we concluded early on that cooling of gas turbine inlet air via direct water spray was one of the most cost-effective ways of augmenting power. We offer our Direct Inlet Spray Cooler (DISC) for evaporative cooling of gas turbine inlet air. Our spray coolers have several innovative features offering improved performance over conventional media type evaporative coolers and other direct spray coolers, maximizing power by achieving 100% saturation and providing additional power through overspray. The design employs state-of-the-art of water spray nozzles and judicious placement within the inlet to maximize droplet evaporation and control the size of unevaporated droplets.

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