Definition and Classification of ACC Cooling Systems

What is an ACC Cooling System

An ACC Cooling System, also known as an air-cooled system, is a large power plant cooling technology aimed at water conservation. It is a cooling method that substitutes air for water as the cooling medium, where the exhaust steam from a turbine directly enters an air-cooled condenser to be condensed using air. The heat exchange between air and steam occurs at the surface level, and the required cooling air is usually supplied by mechanical or natural ventilation. The condensate is pumped into the turbine unit's feedwater system by a condensate pump. The ACC Cooling System is an essential component for the safe and economical operation of turbine generator units in power plants. It can operate automatically, quickly, and efficiently, without causing environmental pollution during the operation process.

Turbine generator units utilizing ACC Cooling Systems are referred to as air-cooled units. According to theoretical calculations and measured results, compared to wet-cooled units of the same capacity, air-cooled units can save more than 97% of the cooling system's water. The overall water conservation for the entire plant is about 65%, meaning that the same amount of water can allow air-cooled units to be built at a scale three times larger than wet-cooled units. Therefore, air-cooled units are the best choice for constructing thermal power plants in areas that are "rich in coal but lack water" or in arid regions.

Classification of ACC Cooling Systems

Direct ACC Cooling System

In a direct ACC Cooling System, the exhaust steam from the turbine is directed into a large exhaust duct and delivered to the outdoor air-cooled condenser. Axial-flow cooling fans force air over the surface of the radiators, cooling the exhaust steam inside the radiators into water. This system is generally matched with high back-pressure turbines.

Indirect ACC Cooling System with a Jet Condenser

Also known as a Heller indirect ACC Cooling System. Cooling water enters the condenser and directly mixes with the turbine's exhaust steam, condensing it. Most of the condensing mixture water is then pumped by the cooling water circulation pump to the air-cooling tower’s radiator for surface heat exchange and cooling with air. Afterward, it’s returned to the jet condenser through a pressure regulating water turbine. A small portion of the water undergoes refined treatment by a condensate water treatment device to be used as boiler feed water. This system can be paired with medium back-pressure turbines.

Indirect ACC Cooling System with a Surface Condenser

Also known as a Harmond indirect ACC Cooling System. It is developed based on the Heller indirect ACC Cooling System, with the key difference being that the cooling water and the turbine exhaust steam do not mix, performing surface heat exchange instead. This meets the high water quality requirements for boiler feed water in large capacity units.

Both indirect and direct ACC Cooling Systems are technically mature and widely used in domestic and international power stations. Large direct air-cooled units are rapidly developing and gradually taking the lead due to their advantages of low investment, small footprint, water savings, frost prevention, and flexible and reliable summer operation methods.