Air Cooled Heat Exchangers

What is it?

Air cooled heat exchangers (ACHE) are used to reduce the process fluid temperature by transferring the heat from process fluid into the ambient air ACHE are commonly used in industrial applications where a reliable source of water is not available as a cooling medium.

Even if water is available, in some cases, air cooled exchangers are favored for economic or operational reasons – because dedicated cooling water circuits, pumps, water cooling systems and water conditioning systems add complexity and capital requirements, as well as operating and maintenance costs

ACHE are used throughout the entire oil & gas industry from upstream production to refineries and petrochemical plants, under conditions including high pressure and temperature, as well as corrosive fluids and environments.

Common applications include gas re-injection, gas lift and pipeline applications, cooling and condensing of hydrocarbon gases, and cooling of machinery oil and heavy hydrocarbons.

Air cooled steam condensers are a special type of heat exchanger employed to condense steam at the exhaust end of steam turbines for both power generation and mechanical drive applications

Air cooling also eliminates the fouling and corrosion problems associated with cooling water, and there is no possibility of leakage and mixing of water with the process fluid. Thus, maintenance costs are generally lower for air-cooled exchangers. Atmospheric air, which serves as the coolant, is caused to flow perpendicularly across the tubes in order to remove heat. In a typical air cooled heat exchanger, the ambient air is either forced or induced by a fan or fans to flow vertically across a horizontal section of tubes. For condensing applications, the bundle may be sloped or vertical. Similarly, for relatively small air cooled heat exchanger, the air flow may be horizontal across vertical tube bundles.

In order to improve the heat transfer characteristic of air cooled exchanger, the tubes are provided with external fins. These fins can result in a substantial increase in heat transfer surface. Parameters such as bundle length, width and number of tubes rows vary with the particular application as well as the particular finned tube design.

Atmospheric air (having temperature varying from 20 to 45[°C], depending on season) can be used as cooling medium if the process fluid is to be cooled up to 60[°C]. If it is to be cooled below 60C, then atmospheric air cannot be used as a cooling medium, as minimum driving force required for heat transfer in air cooled heat exchanger is 10[°C].

How it works?

The hot process fluid to be cooled flows through a tube while the cooling air flows across the outer surface to remove heat. The cooling air is propelled by fans in either a forced draft or induced draft configuration. Specially designed fins are attached to the outer surface of the tube to create a large surface area for more effective cooling. The heat transfer rate is a function of the fins’ surface area and the velocity of the air flow.

The mechanical design of the exchanger must accommodate the process conditions including pressure and temperature and, possibly, corrosivity, fouling and condensation. DYNAC produces various configurations to meet all these conditions. The key to quality and long service life is the proper selection of materials and fabrication technology, not the least of which is advanced welding capabilities. Large exchangers can include thousands of tubes so it is crucial to maintain dimensional stability and weld integrity.

Air-Cooled Heat Exchangers (ACHE)

Cools circulating fluid within finned tubes by forcing ambient air over the exterior of the tubes.