Welltech Air Cooled Heat Exchangers is designed and constructed so that 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. These Heat Exchangers can be Cover Plate / Plug Box and pipe bend models. Tube materials can be carbon or low alloy steel, stainless steel, copper, copper alloys and nickel alloys. Fin materials which are attached to the outer surface of tubes in order to create large surface area, can be of Carbon steel, Aluminum, Marine grade Aluminum and Copper Materials. Fin Type can be Plain or Crimped with ‘L’ or ‘G’ Type, Extruded or Embedded. Special imported heavy duty fans & motors are fitted for outdoor applications. Designing is done considering fouling, condensation, velocity of the air flow and enhanced tube surface area being provided by fins. The mechanical design of the exchanger takes utmost care of the process conditions including pressure, temperature, corrosivity and ease of maintenance.
Welltech Air Cooled Heat Exchangers are commonly used in industrial applications where a reliable source of water is not available as a cooling medium. These heat exchangers find favour with industry for economic and operational reasons since they eliminate need of any kind water cooling systems as well as water conditioning systems thereby reducing capital requirements, as well as operating and maintenance costs.
Welltech Air Cooled Heat Exchangers are made to be used throughout the oil and gas industry including refineries and petrochemical plants, under severe conditions including high pressure and temperature, as well as corrosive fluids and environments. 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.
Typically, an air-cooled exchanger for process use consists of a finned-tube bundle with rectangular box headers on both ends of the tubes. Cooling air is provided by one or more fans. Usually, the air blows upwards through a horizontal tube bundle. The fans can be either forced or induced draft, depending on whether the air is pushed or pulled through the tube bundle. The space between the fan(s) and the tube bundle is enclosed by a plenum chamber which directs the air. The whole assembly is usually mounted on legs or a piperack.
The fans are usually driven be electric motors through some type of speed reducer. The speed reducers are usually either V-belts, HTD drives, or right angle gears. The fan drive assembly is supported by a steel mechanical drive support system. They usually include a vibration switch on each fan to automatically shut down a fan which has become imbalanced for some reason.
What are headers and how are headers constructed?
Headers are the boxes at the ends of the tubes which distribute the fluid from the piping to the tubes.
Almost all headers on air-cooled exchangers are welded rectangular boxes. A vast majority of the headers are of the plug type. This means that there is a shoulder plug opposite each tube which allows access for inspection and cleaning of individual tubes. They can also be used to plug a leaking tube. The plug holes are used in the manufacturing process for access to roller expand the tubes into the headers.
The other common type of header is the cover plate or bonnet type. These are usually used in low pressure applications (say below 150 PSIG) where complete tube access is desired. This usually means applications where fouling is a potential problem and the tube bundle may require occasional internal cleaning.
As the name implies, these have a removable plate on the back side of the header opposite the tubes. The cover plate is attached to the header by a set of studs or through-bolts to a flange around the perimeter of the header. A bonnet header is similar, but opposite in construction. The whole header or bonnet bolts to the tubesheet and comes off. Bonnet headers are sometimes used where the corrosion potential of the process fluid is very high and the tubesheet material is some kind of expensive exotic alloy, such as titanium.
Headers are usually constructed of carbon steel or stainless steel, but sometimes more exotic alloys are used for corrosion resistance. The selection of materials is usually made by the customer.