Atmospheric refrigerants.

A steam power plant (SPP) is an external combustion heat engine operating according to the Rankine thermodynamic cycle. This cycle comprises at least the following stages:

• liquid water is pressurized by a pump and sent to a boiler;

• water is heated, vaporized and superheated;

• the steam expands and cools in the turbine, providing mechanical energy;

• the expanded steam is condensed on contact with the cold well, usually under partial vacuum.

In this dossier, we focus on this last stage, and more specifically on the device used to condense steam into liquid, known as the condenser. It's important to remember that a condenser can perform up to three successive operations: steam desuperheating, condensation and liquid subcooling. This applies to both refrigeration machine condensers and VMI condensers.

There are two main types of condenser:

• fluid-separated condensers, with no contact between the steam and the refrigerant ;

• direct contact condensers, where the steam to be condensed and the refrigerant are mixed.

In the following, we will only deal with air-cooled condensers, which are part of the split-fluid condensers and whose cold sink is atmospheric air.

The air-cooled condenser is sized according to the following main characteristics:

• steam flow to be condensed ;

• pressure at condenser inlet or turbine exhaust flange;

• enthalpy of the steam entering the condenser or steam titre ;

• design ambient temperature ;

• site elevation;

• site constraints.

The installation of an air-cooled condenser is inseparable from a set of auxiliary equipment generally supplied by the manufacturer, such as the vacuum unit, the condensate recovery circuit, and the sheath and manifold (large-diameter sheath located at the top of the bundles) for steam distribution in the bundles.

In order to guide the engineer's choice among atmospheric cooling systems, we present for the air-cooled condenser :

• operating principle ;

• the state of the art ;

• sizing principles ;

• advice on installation, commissioning and operation.