Hamon Group

Integrated solutions for a clean environnement


Air Cooled Condensers

 

The Research-Cottrell Dry Cooling Air Cooled Condenser (RCDC ACC) is the latest of its kind and most up to date achievement of the condensation units for the Power Generation Industry.

 

 

The RCDC ACC is designed with optimized key sections and equipment to guarantee a maximized efficiency (see the process diagram). The steam flows from the turbine into a steam duct and several manifolds to reach the fin tube bundles. The RCDC ACC is designed in streets sitting on a steel leg system (under structure) raised to allow proper air intake into the forced draft modules of A-shape steelframes supporting the fin tube bundles. Once condensed the steam is collected by gravity into a condensate tank located underneath or in the close vicinity of the ACC. The efficiency of the steam condensation process is guaranteed using appropriate and reliable vacuum units. RCDC guarantee the complete system and undertake integral studies related to the ducts and manifolds, the steel leg system and the pipe work and other special studies as appropriate.

 

 

Steam duct and manifolds

Riser to upper manifold elbow section

Steam upper manifold

The turbine exhaust duct delivering the steam to the ACC is designed to minimize pressure drop across the ductwork, facilitating operational efficiency with lower steam velocities. A hot well is located at the low point of the steam duct and collects the condensate that forms before reaching the fin tube bundles which is the pumped to the main condensate tank by means of drain pumps. The steam inlet duct is always provided with nozzles for bypass connections. The long expertise of RCDC will help in the optimization of the required nozzle size and location to guarantee a proper steam de-superheating and distribution into the steam duct.

 


Structure

400 MW CCGT plant – ACC unit site construction

 

The structural steel is delivered to jobsite with a piece marking system which has a proven track record in optimizing materials handling in the field, enhancing the assembly process and so reducing construction and project management man hours.

The steel design allows a high degree of pre-fabrication, either in the fabrication shop or at grade prior to being lifted into position, which further reduces field construction costs and schedules. 

 


A-Frames

3D view of A-frame

Fan bridge complete at grade before lifting

 

The steam flows and condenses in primary fin tube bundles for the most part; the remaining steam being condensed in the so-called secondary fin tube bundles. At the upper end of the secondary fin tube bunels aire extraction is made possible by means of vacuum units to ensure minimal air content during operation. Axial fans are fixed on support structures beneath the fin tube bundles. Fans are driven by electric motors coupled with speed reducing gearboxes. The fans are located within fan rings with bell shaped inlets rings and bells which move the cooling air through the fin tube bundles.

Cooling air absorbs the energy from the condensing steam in the fin tube bundles and leaves the installation as warm air at the exit of the fin tube bundles. Condensate from the fin tube bundles is collected in condensate headers located at the bottom end of the fin tube bundles and flows by gravity to the main condensate tank.

 

Condensate tank

The condensate tank is located below the level of the A-frame and high enough to provide sufficient NPSH to the main condensate pumps generally located at grade level. The condensate pumps return the condensate to the boiler island.

 

 

Typical vacuum system

The service of hogging is needed to evacuate the air accumulated in the ACC and steam ducts before returning to operation after an idle period of time. The evacuation has to reach a pre-set level of vacuum low enough to enable proper steam condensing and start-up of the steam turbine.

The service of holding is the regular continuous service during the operation that allows the evacuation of the air continuously leaking in the unit through the gland steam of the steam turbine. If the air wasn’t evacuated it would accumulate and eventually form spots causing loss of performance and hurting the operation.

For the hogging and the holding service there are basically two technologies commonly used: the steam ejectors or the liquid ring pumps. Selection of one or the other system mostly depends on the availability of steam during start up.

 


Integral studies

RCDC undertakes a full study of the flexibility of the steam ducts. It usually includes the expansion bellow system required at turbine flange (stainless steel expansion or dog bone type) that will keep the stresses and moments below the required level. It also includes the expansion bellows in the riser (standing) elements as well as any other needed along the line.

The steel structure is designed in accordance with the specified standards and codes, allowing for local conditions (wind loads, snow loads and seismic conditions).

The expertise of RCDC also covers the field of the noise emission and propagation, the computer fluid dynamics (CFD) and other complex studies as appropriate.