Boiler Economizer : What You Need To Know

Heatmizer condensing economizer or flue gas heat recovery unit.What Is A Boiler Economizer?

A boiler economizer or flue gas heat recovery unit is a piece of equipment that is installed on the stack of a boiler. This can be put in place when a new boiler is being installed or retrofit on existing system.

When a boiler begins the combustion process, exhaust gases are vented through the stack. These exhausted gasses can often range from 300 degrees to 650 degrees and can be a source of wasted energy if not captured. That is where boiler economizers come in.

How Do Boiler Economizers Work?

3D representation of a Heatmizer flue gas heat recovery unit.Economizers recover energy that would normally be lost in stack exhaust. Similar to the process used in condensing boilers, the idea is to capture the stack heat using the economizer. This reclaimed energy that would normally be lost in stack exhaust can now be used to preheat feedwater.

This process lowers the consumption of fuel for a given steam demand while reducing utility and operating costs. It can also reduce the risk of thermal shock and adds heat transfer surface to the boiler system.

“By recovering waste heat, an economizer can often reduce fuel requirements by 5% to 10% and pay for itself in less than 2 years.” – US Department of Energy

Real World Example

Let’s take a closer look at the numbers. Consider the following savings rate for a 1200HP firetube boiler with the following conditions:

  • Operating 8,000 hours per year
  • 100% firing rate
  • 100% makeup water.

8,000 hrs. X 16.00 dollars/hr. $128,000 in annual savings and $640,000 over a 5-year period

Real World Economizer Installation

Stack from boiler being pulled using a crane

1. The stack is lifted off the boiler

Pullies on facility ceiling for boiler economizer

2. The facility is rigged with pullies to place economizer over boiler.

Boiler Economizer being lifted above boiler

3. Economizer is lifted using the pully system.

Economizer sitting on top of boiler

4. Economizer is installed on boiler and stack is reattached.

Important Features Of A Boiler Economizer

It is important that condensate is not allowed to drip back down the stack to the boiler. Instead, condensate should be captured, separated and safely drained. This is also a reason why economizers should be built with corrosion resistant materials to prevent damage from condensate.

A compact design is also important to prevent clutter above the boiler. Easily accessible and preferably removal heat exchanger elements are essential for easy maintenance. Finally, it is good to have flue gas and water inlet/outlet temperature indicators. This allows for easy performance tracking.

When installing a boiler economizer, a flue gas inlet mounting flange adapter plate will generally need to be field welded to the existing boiler. An outlet mounting flange ring may also need to be field welded to the stack. Condensing applications (entering water temperature under 120 °F) require SS stack and condensate pipe to drain.

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Learn more about how a Heatmizer economizer transfers waste heat from boiler exhaust gases and uses that energy to preheat the boiler feedwater. The overall effect is a decrease in fuel energy consumption for a given steam demand so you see maximum annual savings.