Reliability
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Direct Air-Cooled Condensers

In 1979 GEA became involved in feasibility studies for Eskom in respect of new generation large scale power stations using dry cooling systems. This research and development culminated in the award of a turnkey contract in 1982 for the design, manufacture, supply, delivery, erection and commissioning of six air-cooled steam condensers for Eskom's 6 x 665 MWe Matimba Power Station.

This constitutes the largest direct air-cooled steam condenser installation and, therefore, the largest direct air-cooled power station operating in the world. In 1984, Eskom also placed the order for air-cooled condensers for the 6 x 660 MWe Majuba Power Station with GEA. Of the six units at the Majuba Power Station, only three units were eventually equiped with air-cooled condensers.

Two features distinguish the GEA air-cooled condenser: highly efficient and durable finned tubes, and a single-pressure two-stage condensing process.

The GEA air-cooled condenser is comprised of finned tube bundles grouped together into modules and mounted in an A-frame configuration on a concrete or steel support structure. Vertical and horizontal configurations are also available.

Both the Matimba and Majuba air-cooled condensers use a hot-dip galvanized two tube row design with oval tubes and rectangular fins (A-tube). The tube and fin marterial is hot dip galvanized steel.

GEA also offers a single tube row air-cooled condenser design using a flat steel tube with aluminium fins, i.e. the Alex tube. Please follow the animation below to learn more about the single tube row Air Cooled Condensers.

GEA employs a two-stage, single-pressure condensing process to achieve efficient and reliable condensation. In this process, the steam is first ducted from the steam turbine to the air-cooled condenser, where it enters in parallel/concurrent flow from the top. The steam is only partly condensed in the parallel flow modules and the remaining steam is ducted to the lower headers of the counterflow finned tube bundles (dephlegmator). The steam enters from the bottom and rises in the finned tubes to a point where condensation is completed. Non-condensables are drawn off above this point by vacuum equipment. The condensate drains to a condensate tank and is then piped back to the feedwater system to complete the cycle.

GEA's two-stage, single-pressure air-cooled condenser

 

 

   Matimba Under Construction

Matimba Power Station, Ellisras, South Africa - the largest direct air-cooled power station in the world. Winner in 1988 of the South African Institute of Mechanical Engineers, Project and Systems Award.

   Matimba Power Station ACC during construction.

Parallel Condensing System (PAC) 

Exhaust steam from the steam turbine is separated into two streams. One stream flows into a water cooled surface condenser while the other is directed to an air-cooled condenser.

Condensate from the surface condenser and the air-cooled condenser can be collected in a common hotwell. Water consumption is controlled by the distribution of the heat load between the two condensers.

The PAC System TM should not be confused with a "hybrid" cooling tower, which is used primarily to reduce visible plume from a wet cooling tower. A "hybrid" cooling tower has practical limits to the amount of heat that can be rejected in the dry section, since the latter is sized for plume abatement only. With the PAC System TM there is complete flexibility in the amount of heat rejected in the dry section.

The dry section of the PAC System TM employs direct condensation in contrast to most "hybrid" systems, which are indirect condensing systems, i.e. water is cooled through both the wet and dry sections and is then pumped through a common condenser. As a result, the dry section of the PAC System TM can efficiently reject a substantial amount of heat even on hot days, thereby reducing peak water usage. During cooler periods, the amount of heat rejected in the dry section can be increased up to 100% if so designed, thus further reducing the plant's water consumption.

An additional benefit of the PAC System TM is the reduction of plume. Plume can be reduced or eliminated entirely when danger of icing exists, simply by shutting off the wet section.