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Air-Cooled Condenser Expansion Joints

Air-Cooled Condenser PDF

Fig0 plant

 

 

Modern power plants frequently use air-cooled condensers to return spent steam back into the cycle after it has been used to spin turbine to generate electricity. This is a critical part of the Rankin cycle, which improves power generation efficiency.

Of greatest concern for the piping designer is the thermal expansion that occurs in the major duct system that feeds the condenser from the turbine.

The first expansion joint is required at the turbine case at the exhaust to the condenser duct. This is frequently a rubber dogbone design. It serves to reduce loads transmitted via differential thermal growth from the expanding ducting and turbine casing. Generally, the restrictions on the turbine case which often must comply with NEMA 23A limits preclude the use of metallic bellows expansion joints.

Rubber dogbone expansion joints are quite simple, but can be very large and require some care in design and fabrication.

Special clamps are machined to properly mount the rubber belt. In turn these clamps are welded to the frame and provide the sealing point for the dogbone.

VIDEO: Fabrication Process Start to Finish

Fig.1: Typical Air-Cooled Condenser

Fig. 2: Aerial View of
Fig.1: Typical Air-Cooled Condenser Fig. 2: Aerial View of
Dogbone Expansion Joint Frame
Fig. 3: Clamp Details
Fig. 3: Clamp Details

 

Special clamps are machined to properly mount the rubber belt. In turn these clamps are welded to the frame and provide the sealing point for the dogbone.

 

 

 

 

 

Critical analyses are performed on the associated structures to ensure that there is no risk of collapse due to full vacuum conditions, which frequently occur.

Fig. 4: Turbine Exhaust Structure Fig. 5: Turbine Exhaust Structure Loading Analysis
Fig. 4: Turbine Exhaust Structure Fig. 5: Turbine Exhaust Structure
Loading Analysis

Tied Universal Expansion Joints 

The next expansion joint is required at spent steam risers to the condenser frame. This is frequently a Tied Universal metal bellows design. It serves to reduce loads transmitted via differential thermal growth from the expanding ducting. Tied Universal expansion joints are relatively simple, but can be very large and also require some care in design and fabrication.

Fig. 6: Exhaust Riser Tied Universal Expansion Joints

Fig. 6: Exhaust Riser Tied Universal Expansion Joints

Several types of structural of structural analyses are performed to ensure conformance with design parameters and special construction loading that may occur durring erection.

VIDEO: Loading of Universal
Expansion Joint onto the
Truck for Shipment
Fig. 7: Bellows Design Calculations Fig. 8: Tie Rod Calculations
Fig. 7: Bellows Design Calculations Fig. 8: Tie Rod Calculations

 

Internal pressure calculation are performed for the bellows elements, shell and the hardware attached to the expansion joint.

Fig. 9: Shell / Hardware Interaction Under Load Fig10 shell hardward buckling
Fig. 9: Shell / Hardware Interaction
Under Load
Fig. 10: Shell / Hardware Buckling
During Vacuum Loading

Special erection considerations must be studied to ensure that the structure as defined by the customer is suitable to withstand lifting loading during installation.

Fig11 sturctural loading Fig12 sturctural loading
Fig. 11: Structural Loading
During Installation
Fig. 12: Actual Structural Loading
During Installation
VIDEO: Transportation from
PT&P’s Manufacturing Facility

As power plants have grown in generating capacity, so too have
the sizes of the ducting that must service them. The units pictured
below will be welded together in the field to form a tied universal
expansion joint assembly.

Fig13 tied universal ej
Fig. 13: 178″ Dia. Tied Universal Expansion Joints On-Site
Fig14 tied universal ej
Fig. 14: On-Site Assembly

The final expansion joint is required at spent steam lines which run perpendicular to the risers. This is frequently a single hinge or Single Gimbal metal bellows design. It serves to reduce loads created when the tied universal joint causes foreshortening in the duct system. Hinge expansion joints are moderately complex, but when dealing with a very large size require some care in design and fabrication.

Fig15 solar power plant
Fig. 15: Single Hinged and Tied Universal Expansion Joints
Installed at a Solar Power Plant

The bellows element is analyzed the same way as the tied universal except that the motion is angular instead of lateral. Hardware/shell interaction under loading will be a duplication of those for the tied universal except for the hinge arms and the pins, which are subject to classical design analysis.

Fig16 single hinge ej
Fig. 16: Single Hinged Expansion Joints
Fig17 hinge hardware calc
Fig. 17: Classic Hinge Hardware Calculation

 

Fig18 single hinge structure
Fig. 18: Single Hinge Structure Detail
Fig19 single hinge ej
Fig. 19: Single Hinged Expansion Joint Assembly
Fig20 single hinge ej
Fig. 20: Single Hinged Expansion Joints
Fig21 tied universal ej
Fig. 21: Tied Universal Expansion Joint

 

 

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