What are Air-Cooled Heat Exchangers?
Air-Cooled Heat Exchangers, also often called ACHX, air coolers, aerial coolers, fin fans coolers, reject process heat to the surrounding atmosphere.
Air Cooled Heat Exchangers employ multiple rows of fin tubes as the heat transfer surface. A fan blows cooler ambient air across the rows of finned tubes in order to carry away heat from the fluid (or gas) inside the tubes that came from the process in order to transfer that heat to the air, thereby cooling the process fluid.
What is The Average Life One Can Expect From a Worldwide Air-Cooled Heat Exchanger?
Engineers and procurement people who specify or order these units sometimes ask what will be the life of an air-cooled heat exchanger running in their operating environment.
Worldwide have had units running for longer then 40 years with regular maintenance such as lubrication, monitoring and adjustment of the drive tension and keeping the unit from imbalance forces.
The tube bundle is often the key determinant. This is the eroding or corroding component that will most impact life.
When Worldwide application engineers select an air cooler for our clients we examine the specifications and work with you to achieve longevity. We do this by balancing a number of issues in order to deliver a custom tailored product. For instance a thinner tube wall will have a higher heat transfer rate but it also means there is less material available to protect against failure through corrosion. Higher alloy materials can be far more resistant against corrosion. But they will increase first cost.
Some of our customers have calculated that using carbon steel bundles in place of higher alloys delivers a better return when all things are considered – like energy use and first cost – even though the bundles may need to be replaced every 3-5 years.
Other plants that run very lean in maintenance personnel are willing to trade-off some points of efficiency and are willing to invest in higher cost alloys in order to not to lengthen the time between re-bundling.
Both approaches are valid and depend upon the operating strategy of each organization. Ask our application engineers to help you in navigating this area for optimizing life-cycle costs.
When Would One Select an Induced Draft or a Forced Draft Fan?
Typically Induced Draft fan coolers have better distribution of air across the bundle.
Because of the orientation there is less chance of recirculation of the hot outlet air back into the inlet side. Generally it has better process control characteristics because the outlet shroud covers more than 50% of the bundle face area. This also protects against UV deterioration and hail damage.
On the other hand Induced draft fans will have higher horsepower requirements if the leaving air is very hot. Life of the fan and components is lessened due to operating in higher temperatures.
Also with induced draft fans configurations the fan and drive is not as easily accessible for routine maintenance.