Boiler Economizers: Function, Types, Design And Operation

In this article, I will share the function, types, design and operation of economizers.

A boiler economizer is a boiler accessory that is used to heat the feed water before it’s taken to the boiler.

You also have the right to say it’s a heat exchanger that is used to heat feed water using waste heat energy from the flue gasses.

A boiler economizer is an important boiler accessory just like air preheaters and feed water heaters.

You might like this: Air Preheaters in Steam Boilers: Function, Types and Working Principles and Feed Water Heaters: Functions, Types, Advantages And Operation

The main function of the boiler economizer is to heat the feed water before it’s conveyed to the boiler.

In the process of heating this water, other advantages come along.

These are some of the advantages of using a boiler economizer;

Using a boiler economizer increases the efficiency of the boiler by 2% or 4%.

You get to save fuel since the consumption of it will be lower.
Using a boiler economizer reduces the thermal stresses in the boiler.

Types of boiler economizers

Boiler economizers can be categorized in various ways depending on how they operate and their functions.

These are the four times of boiler economizers I will discuss in this section;

Pressurized boiler economizer.
Non-pressurized boiler economizer.
Condensing boiler economizer.

Non-condensing boiler economizer (dry economizer).

1. Pressurized boiler economizer.

This type of boiler economizer is used in cases where the feed water heated is above the normal boiling point at atmospheric pressure.

If the boiling point of feed water is above the normal boiling point at atmospheric pressure, it’s going to be hard to get to increase the temperature of this water with normal heating.

A pressurized boiler economizer should be employed to handle such kind of feed water.

2. Non-pressurized boiler economizer.

Non-pressurized boiler economizer is used in cases where the feed water to be heated is below the boiling point at atmospheric pressure.

No pressure is needed to heat water that has a low boiling point since it’s going to be easier to increase its temperature.

3. Condensing boiler economizer.

Condensing boiler economizers are the types of heat exchangers that condense the flue gasses as they pass along the tubes and use the same condensate to absorb more heat from the gasses.

This type of economizer recovers more energy from the flue gasses due to the added advantage of the condensate absorbing heat together with the tubes also absorbing heat energy from the flue gasses.

There is something very important you should note here, you know that flue gasses contain carbon monoxide and also carbon dioxide.

If these gasses pass across the condensate, they will end up turning the condensate to be acidic.

And this will end up corroding the tubes of the economizer.

So, to prevent this problem, the economizer tubes and parts that come in contact with the acidic condensate are made of stainless steel to prevent this from happening.

4. Non-condensing boiler economizer (dry economizer)

When it comes to non-condensing boiler economizer there is no formation of condensate.

It’s the flue gasses that heat up the economizer tubes and the heat is transferred to the feed water without the flue gasses condensing.

And that is why it’s also called dry economizer since it doesn’t condense the flue gasses.

The exhaust gasses from this kind of economizer are of very low temperatures.

The general design of boiler economizers

Boiler economizers are built with corrosion-resistant materials such as stainless steel.

The boiler economizer tubes can be made of carbon steel, copper, alloy steel and aluminium.
They are also designed to provide easy access when repair and maintenance have to be done.
The boiler economizers are designed to be compact to be easier to install and also to prevent clutter above the boiler.

Safety valves are installed on the boiler economizer to regulate the pressure in the tubes and ensure the economizer doesn’t rupture from high temperatures.

You might like this: Requirements Of Steam Plant Economizer

Operation of boiler economizer

The principle of operation of a boiler economizer is that it transfers heat from one place to another through conduction.

The flue gasses from the boiler pass across the tubes of the economizer which are placed perpendicularly to the current of the flow of the gasses.

This is to ensure that enough heat is absorbed by the tubes of the economizer.

They are also coiled to increase the surface area of contact as the flue gasses pass along the tubes.

The economizer tubes absorb the heat and transfer it to feed water through conduction.

If you have an idea of how the fire tube boiler operates then you pretty much have it all covered.

You might like this: Boilers: Components, Types & Working Principle

That is the simple working principle of a boiler economizer.

Final thoughts.

A boiler economizer is a boiler accessory that is essential in the steam boiler since it increases the efficiency of the boiler, saves fuel and reduces thermal stresses in the boiler.

Steam boilers should be installed with economizer because they provide economic usage of fuel.

The exhaust gasses from the boiler are stripped of the waste of heat energy that tends to increase emissions to the atmosphere.

So, it’s necessary to install an economizer if you want to protect the environment.

Thanks for reading, if you have any questions about the economizers don’t be afraid to leave your comment. See you in my next article.