Increasing Boiler Efficiency with Economizer/Preheater Combos

economizers air preheaters

For coal and biomass plants, boiler efficiency is the name of the game. The more efficient your boiler system is, the better your bottom-line results will be. Even one point of efficiency increase can make a big difference, especially in a system that is, by nature, inefficient compared to other fuel sources.

To optimize efficiency, boiler systems today come with a proven combination: economizers and air preheaters. These two systems, when working together, can improve boiler efficiency by approximately 20 percent. It’s important that they work together, because an economizer by itself will only provide efficiency increases in the single-digit range.

In this article, we’ll discuss the two components and how they help keep the efficiency level high in a coal or biomass boiler system.


The purpose of an economizer is to recover wasted heat from a boiler system. They’re heat exchange components that are used to raise the temperature of heat fluids to where they reach the boiling point of the fluid but usually don’t exceed it. Economizers heat the fluid by taking in heat from flue gas from the stack and directing it to the water system.

A well-designed, professionally-installed economizer can potentially lower fuel costs by as much as 5-10 percent, which is significant for most operators.

Air Preheaters

An air preheater is another form of heat exchange device that preheats or heats the air used in boiler combustion through a combination of steam, water, flue gas, or thermal oil. The general idea is that a boiler’s combustion process is more efficient if the boiler has to work less to produce the same amount of energy. For every degree that the incoming air is heated, that results in less energy required from the boiler.

In other words, an air preheater saves energy by doing some of the heavy lifting done by the boiler in order to raise the incoming fluid to the appropriate temperature.

Air preheaters are broken down into two types: recuperative and regenerative. Recuperative preheaters are generally used in small to medium-size boilers. Regenerative preheaters are usually reserved for high-capacity boilers (producing 600 tons per hour of steam or higher).

Maximizing Efficiency with Both Systems

As mentioned, any one of the two systems outlined above will result in efficiency gains, but each one by itself can only do so much.

In order to continue to compete with natural gas, solar, wind, and other forms of energy production, coal and biomass boilers have to max out on efficiency. A custom-designed air preheater and economizer combo can go a long way toward accomplishing this goal for modern-day power plants.