Heavy Duty Heat Exchanger Design and Construction

A heat exchanger is equipment that transfers heat between two or more process streams. Choosing the right type of design can minimize energy costs and downtime.

There are several different types of heat exchangers, including parallel flow, counterflow, and crossflow. The best design depends on future scalability and ease of maintenance.

Design

Choosing the appropriate heat exchanger design starts with understanding process requirements, such as amount of thermal output and temperature change needed between fluids. Other factors to consider include the viscosity of the fluids involved, particulate content, and chemical composition. Depending on the type of process, heat exchangers can be gas-to-gas, gas-to-liquid, liquid-to-liquid, or two-phase.

A shell and tube heat exchanger contains a series of tubes in a sealed, cylindrical pressure vessel. They may be constructed from carbon steel, stainless steel, titanium, Inconel, or other materials. The tubes are designed to withstand temperature, pressure, and thermal stresses. They are positioned with a spacer stud at the center to prevent fluid bypassing and intermixing. The tube sheet width and gap are optimized for maximum efficiency, easy access, and cleanliness. 

Fabrication

Several fabrication options exist for heavy duty heat exchangers. Those designed for corrosive applications can use fiber-reinforced tubes to withstand the rugged operating conditions often found in chlorinated organics. Plate heat exchangers incorporate a series of corrugated alloy plates that are gasketed and compressed together inside a carbon steel frame to create an array of flow channels. These flow passages direct fluid flows and prevent fluid intermixing.

Stainless steels and nickel alloys are used to construct tubular and shell-and-tube heat exchangers. These units are a workhorse in the food, beverage and pharmaceutical industries. They can handle the high temperatures needed to keep production running.

Installation

In green anaerobic digestion processes that produce biogas from livestock manure, food byproducts and fats, a spiral plate heat exchanger can transfer the pathogen-free methane to pipelines for transport and storage. Biogas can then be combusted to generate electricity and heat. The remaining pathogen-free biosolids can be dewatered and used for soil conditioning as fertilizer.

In homes, an air-to-air heat exchanger recycles stale indoor air, heating it to bring in fresh, warmed air and eliminate excess water vapor that would lead to window condensation. It also helps keep occupants healthy by filtering out harmful chemicals, particulates, radon and other pollutants.

Maintenance

Keeping a heat exchanger in good shape is key to keeping production running smoothly. Excessive fouling can lead to contaminated or unusable product, corrosion and leaks. According to Ethanol Producer Magazine, it can even pose a fire hazard.

Fortunately, there are many ways to help keep a heat exchanger clean. Sampling is an effective way to gauge the condition of a system, and it is recommended that multiple fluid samples be taken from throughout the entire system. This information is vital when planning a maintenance day.

For shell and tube heat exchangers, it’s important to choose a design with a bonnet type head for ease of maintenance. This type of head can be flanged or welded, and it typically has removable channel covers for easy examination. The length of the tubes must also be sufficient to allow for easy removal and replacement.