How to Optimize Air-Cooled Heat Exchanger Efficiency with Advanced Design and Maintenance
Air-cooled heat exchangers (ACHEs) are used in many industries, including refining, SAGD, gas processing, gas transmission, and petrochemical. They transfer heat from process fluids to the air, helping to cool fluids or condense steam and vapours in industrial operations. Optimizing the performance and efficiency of ACHEs can impact an operation’s effectiveness and overall cost-efficiency – here’s how to optimize air-cooled heat exchangers.
Optimizing Air-Cooled Heat Exchanger Performance
The basic operation of an ACHE involves a hot process fluid flowing inside externally-finned tubes, cooled by atmospheric air moving over the outside surface. While this might seem straightforward, several factors can influence the efficiency and effectiveness of these systems.
Types of Air Cooled Heat Exchangers
Forced draft, induced draft, and natural draft are three common configurations used in air-cooled heat exchangers to facilitate air flow over the finned tubes, each suitable for different operational needs:
Induced draft fans are positioned above the heat exchanger, pulling air upwards through the tube bundle. This configuration enhances the discharge of hot air and reduces the risk of recirculation. It can provide better performance in dirty environments but makes fan and bearing maintenance more challenging due to access and surrounding air temperatures.
Forced draft fans are located below (or at the side of) the air cooler bundle, pushing air upwards (or across) the tubes. This arrangement offers easier maintenance and lower air inlet temperatures, leading to efficient cooling but can be susceptible to recirculation issues.
Natural draft relies on natural convection without fans, where cool air enters at the bottom and hot air exits from the top. Natural draft air movement is much slower than forced or induced draft, so it is less efficient and requires more surface area for similar heat duty. One advantage is that it eliminates fan-related energy costs and maintenance, making it suitable for remote locations where power is unavailable and access difficult. Natural draft coolers are also appropriate for large-scale installations where noise reduction is critical.
Fin Tube Selection
In air-cooled heat exchangers, the choice of fin type is crucial for optimizing performance and ensuring durability in various operating environments. Here’s a breakdown of the differences between L-fin, embedded fin, and extruded fin types, along with their typical applications:
L-Fins are made by wrapping a strip of aluminum or other metal around the base tube and mechanically securing the ends. The fin strip forms an ‘L’ shape as it is wrapped, which is where the name comes from. These fins are typically used in moderate environments since they can be susceptible to mechanical damage and corrosion under harsh conditions. L-Fins are limited to a maximum of 275°F (135°C) as they begin to expand and lift off the tube above this temperature, which greatly limits heat transfer. L-fins are commonly used in HVAC systems and light industrial applications where cost-effectiveness is a priority.
In embedded fin designs, the fin material (usually aluminum) is wound into a helical groove cut into the outer surface of the tube. This method provides excellent heat transfer efficiency and mechanical bond to the tube and (unlike L-fins) is suitable for temperatures above 275°F (135°C). Used in petrochemical and processing industries where higher process stream temperatures are cooled.
Extruded fins are formed by forcing both the tube and the fin material (usually aluminum) through a die in a single step, creating a strong, integral bond between the fin and tube.
This method produces fins that are highly resistant to atmospheric corrosion and mechanical damage. Extruded fins are ideal for harsh operating environments, such as offshore platforms, chemical plants, and areas with high levels of airborne contaminants.
Selecting the right fin type depends largely on the specific environmental conditions, required heat transfer efficiency, cost considerations, and maintenance practices.
Maintenance and Troubleshooting
Routine maintenance is required for longevity and optimal performance in ACHEs. This includes regular checks and lubrication of mechanical components like fans, bearings, belt drive, and motors. Louvers, linkages, actuators and positioners need routine inspection and maintenance to ensure they are able to open and close properly.
Inspecting and repairing leaking header plugs in air coolers involves identifying leaks, usually during operation or pressure testing. The repair process often requires cleaning the plug and header threads, replacing seals and/or plugs, and securely torquing the plug to ensure a tight, leak-free seal. On occasion, portable machining is required to resurface the gasket sealing surface.
Fouling in heat exchangers can occur both inside and outside the tubes, impacting efficiency and operation. Inside the tubes, fouling typically results from chemical reactions, sedimentation, or biological growth, such as scaling from minerals or biofouling from microbial deposits. Outside the tubes, common fouling includes environmental debris like poplar fluff, leaves, and dust, or atmospheric corrosion. Managing fouling involves regular cleaning, using anti-fouling coatings, and ensuring proper fluid velocities to minimize deposits. Effective fouling control is essential to maintain thermal performance, reduce energy consumption, and extend equipment lifespan.
Additionally, identifying common issues such as fouling or leaks early can prevent more severe problems down the line. Employing effective cleaning methods and timely repairs is essential in maintaining an ACHE’s efficiency.
Advanced Techniques for Enhanced Efficiency and Noise Reduction
In air-cooled heat exchangers, selecting the right fan, motor, and drive system is crucial for effective noise reduction. Opting for larger diameter fans that operate at lower speeds can significantly decrease noise output without compromising performance. The use of fan rings enhances fan efficiency and reduces tip clearance noise. Moreover, choosing high-efficiency motors and incorporating variable frequency drives (VFDs) allows for precise control of fan speeds, which can be adjusted based on real-time cooling needs, further minimizing noise levels. These components must work together to maintain operational efficiency while reducing the acoustic noise footprint.
Industry Applications and Case Studies
ACHEs are utilized in various critical sectors. The carbon capture industry uses air-cooled exchangers after compression and before transmission or storage. In gas transmission, interstage coolers are used to cool natural gas at compressor stations, as compression of gases generates heat. Petrochemical uses ACHEs to condense vapours and cool process streams. SAGD and refining industries use air-coolers to maintain the temperature of processed fluids and for utility (glycol, water, or steam) cooling.
Contact Altex Industries for Air-Cooled Heat Exchangers and Heat Exchanger Services
For industrial businesses looking to optimize their ACHE systems or address specific performance issues, you need a knowledgeable and experienced manufacturer and service provider. Altex Industries specializes in the optimized design, fabrication, maintenance, and troubleshooting of air-cooled heat exchangers. With a focus on enhancing efficiency and reliability, Altex Industries offers solutions for many industrial applications. Contact us to learn more about our fabrication and field services for air-cooled heat exchangers.
