Economisers: Enhancing Efficiency, Reducing Consumption

Economisers Enhancing Efficiency, Reducing Consumption

In the vast and complex world of engineering and technology, there are countless devices and systems designed to improve efficiency and performance. One such device, often overlooked yet critical in many industries, is the economiser.

An economiser is a mechanical device that’s used to reduce energy consumption or improve the efficiency of a system. It does this by recycling the energy that’s already present in the system. For example, in a boiler system, an economiser captures the heat from the hot flue gases and uses it to preheat the feedwater. This process reduces the amount of fuel needed to heat the water to its required temperature.

Now, you might be wondering:

  • How does an economiser work?
  • What are the different types of economisers?
  • Where are economisers commonly used?
  • What are the advantages of using economisers?

As we continue with this article, we will explore these questions in detail. This will give you a thorough understanding of economisers, including how they work, their different types, where they are used, and their advantages. By the end of this article, you will understand the important role that economisers play in saving energy and improving efficiency in various systems and industries.

So What is an Economiser?

An economiser, in the context of mechanical engineering and thermodynamics, is a device designed to reduce energy consumption or increase efficiency in a system. It achieves this by capturing waste heat in the system and using it for other processes that would otherwise require new input energy.

Let’s take the example of a boiler system. In a typical boiler system without an economiser, fuel is burned to heat water and produce steam. The hot flue gases, which carry a significant amount of heat, are then expelled out of the system and into the atmosphere. This process, while effective in producing steam, is not very efficient as a lot of heat energy is wasted with the flue gases.

This is where an economiser comes in. An economiser is installed in the flue gas exhaust stream. It consists of a series of tubes through which the feedwater (the water supplied to the boiler to be converted into steam) passes. As the hot flue gases come in contact with the tubes, heat transfer takes place from the flue gases to the cooler feedwater. This preheats the feedwater before it enters the boiler.

The result? The boiler now needs less heat to convert the preheated feedwater into steam, which means less fuel is burned. This not only reduces the energy consumption of the system but also decreases the amount of greenhouse gases emitted due to fuel burning.

In essence, an economiser repurposes the waste heat in a system, turning what would be lost energy into a valuable resource. This simple yet effective process is a testament to the principles of energy conservation and efficiency. By understanding and harnessing the power of economisers, we can make our industries and systems more sustainable and cost-effective.

How Does an Economiser Work?

The working principle of an economiser revolves around the concept of heat transfer. Heat transfer is the process of heat moving from a body of higher temperature to a body of lower temperature. In the case of an economiser, the two bodies involved are the hot flue gases and the cooler feedwater.

When the hot flue gases pass over the tubes of the economiser, the heat from the gases is transferred to the cooler water inside the tubes. This process is known as convection heat transfer. The now heated water is then fed into the boiler.

This preheating process has two significant effects. First, it reduces the amount of heat the boiler needs to convert the feedwater into steam. This means the boiler needs less fuel to achieve the same output, thereby improving the efficiency of the system. Second, it reduces the temperature of the flue gases, which means less heat is wasted to the environment.

It’s important to note that the effectiveness of an economiser depends on several factors. These include the temperature of the flue gases, the temperature of the feedwater, and the heat transfer properties of the economiser’s materials. By carefully controlling these factors, it’s possible to maximise the performance of the economiser and achieve significant energy savings.

In essence, an economiser works by harnessing the waste heat in a system and using it for useful work. It’s a brilliant example of the principle of energy conservation in action – making the most out of the energy we have and reducing our need for new energy inputs.

Types of Economisers

Economisers come in various types, each designed to suit specific applications and operating conditions. The two main types of economisers are non-condensing economisers and condensing economisers.

Non-Condensing Economisers

Non-condensing economisers are the most commonly used type of economiser. They are designed to operate at temperatures above the dew point of the flue gases. This design prevents the condensation of the flue gases and the associated corrosion issues.

In a non-condensing economiser, the feedwater is heated by the flue gases but not to the point where the water vapour in the gases condenses. This is important because the condensation of flue gases can lead to the formation of acidic compounds which can corrode the economiser and other boiler components.

Condensing Economisers

Condensing economisers, on the other hand, are designed to operate below the dew point of the flue gases, allowing the gases to condense. The latent heat from the condensation process is used to further heat the feedwater.

While condensing economisers are more efficient than non-condensing ones, they require specific materials to prevent corrosion caused by the acidic condensate. They are typically used in systems where the fuel used is relatively clean, and the risk of corrosion is low.

Type of economiser used in a system depends on various factors such as the type of fuel used, the operating conditions, and the specific requirements of the system. By choosing the right type of economiser, it’s possible to significantly improve the efficiency of the system and reduce energy consumption.

Applications of Economisers

Economisers are versatile devices with a wide range of applications across various industries. Their primary function is to improve energy efficiency, making them valuable in any system where heat is generated and potentially wasted.

One of the most common applications of economisers is in power plants. In these facilities, economisers are used in boiler systems to preheat the feedwater using the heat from the flue gases. This process significantly improves the efficiency of the power plant by reducing the amount of fuel needed to generate steam.

In addition to power plants, economisers are also used in Heating, Ventilation, and Air Conditioning (HVAC) systems. In HVAC systems, economisers can be used to control the temperature and humidity of the air inside a building. They do this by using the outside air when the conditions are appropriate, reducing the need for mechanical cooling and thus saving energy.

Economisers also find application in various industrial processes. In industries where large amounts of heat are generated—such as in steel mills, chemical plants, and oil refineries—economisers can be used to recover some of this heat and use it for other processes. This not only improves the efficiency of the industrial process but also reduces the amount of heat discharged into the environment, helping these industries reduce their environmental impact.

The applications of economisers are vast and varied. From power plants to HVAC systems to industrial processes, economisers play a crucial role in improving energy efficiency and reducing environmental impact. Their ability to capture and reuse waste heat makes them an invaluable tool in our ongoing efforts towards more sustainable and efficient energy use.

Advantages of Using Economisers

The use of economisers in various systems and industries brings numerous advantages. These benefits primarily revolve around energy efficiency, cost savings, and environmental impact.

Improved Efficiency

One of the most significant advantages of using economisers is the improvement in system efficiency. By capturing and utilising waste heat, economisers reduce the amount of new energy required for the system to function. This means that for the same amount of output, the system uses less input energy, thereby increasing its efficiency.

Reduced Energy Consumption

Linked closely with improved efficiency is reduced energy consumption. As economisers allow systems to achieve the same output with less input energy, the total energy consumption of the system decreases. This reduction in energy use can be particularly significant in large-scale industrial processes and power plants, leading to substantial energy savings.

Cost Savings

Reduced energy consumption also translates into cost savings. Energy is often one of the most significant operating costs in many industries. By reducing the amount of energy required, economisers can help lower these costs. Over time, these savings can add up to a significant amount, improving the financial performance of the operation.

Environmental Impact

Finally, economisers can help reduce the environmental impact of various systems and industries. By reducing energy consumption, economisers indirectly decrease the amount of fuel burned and the associated emissions of greenhouse gases and other pollutants. This contribution to reducing emissions is crucial in the context of global efforts to mitigate climate change.

Advantages of using economisers are manifold. From improving efficiency and reducing energy consumption to saving costs and reducing environmental impact, economisers play a crucial role in promoting sustainable and efficient energy use.


In the quest for energy efficiency and conservation, economisers have emerged as a vital tool. These devices, through their simple yet effective operation, help harness waste heat, turning it into a valuable resource. By preheating the feedwater in boiler systems, economisers significantly reduce the amount of fuel needed, thereby improving system efficiency and reducing energy consumption.

The versatility of economisers is evident in their wide range of applications, from power plants to HVAC systems to various industrial processes. Regardless of the context, the goal remains the same – to save energy and improve efficiency.

Moreover, the benefits of using economisers extend beyond just energy savings. They contribute to cost savings, improved system performance, and most importantly, a reduction in environmental impact. By reducing the amount of fuel burned, economisers indirectly contribute to the reduction of greenhouse gas emissions, playing a crucial role in our global efforts to mitigate climate change.

Economisers represent a perfect blend of engineering and environmental consciousness. They embody the principle of ‘waste not, want not’, reminding us that in our fight against energy waste and climate change, every bit of energy saved counts. As we continue to strive for more sustainable and efficient energy use, the role of devices like economisers will only become more significant.

What is the difference between an economiser and a superheater?

While both economisers and superheaters are heat exchange devices used in boiler systems, they serve different purposes. An economiser preheats the boiler feedwater, improving the boiler’s efficiency. On the other hand, a superheater increases the temperature of the steam generated by the boiler to above its saturation point, increasing the overall efficiency of the power cycle.

Can economisers be used in systems other than boilers?

Yes, economisers can be used in any system where there is a waste heat stream and a process that requires heat. This includes HVAC systems, industrial processes, and even internal combustion engines.

What materials are used to make economisers?

Economisers are typically made from steel or cast iron, but the material can vary depending on the specific application and operating conditions. For instance, condensing economisers that deal with corrosive condensate might be made from stainless steel or other corrosion-resistant materials.

How is the performance of an economiser measured?

The performance of an economiser is typically measured by its efficiency, which is the ratio of the heat recovered to the heat available in the flue gases. Other important performance indicators include the reduction in fuel consumption and the decrease in CO2 emissions.

What are the maintenance requirements for an economiser?

Like any mechanical device, economisers require regular maintenance to ensure they continue to operate efficiently. This can include cleaning to remove soot and scale, inspection for signs of wear or corrosion, and testing to ensure optimal performance.

Can economisers be used with all types of fuels?

Economisers can be used with a variety of fuels, including natural gas, coal, and oil. The type of fuel used can affect the design and material of the economiser due to differences in flue gas composition and temperature.

Are there any potential drawbacks or risks associated with using economisers?

While economisers offer many benefits, they can also present certain challenges. For instance, economisers can be prone to corrosion due to the presence of flue gases. Also, if not properly maintained, they can develop soot and scale build-up, which can reduce their efficiency.

How does an economiser fit into a boiler system?

In a boiler system, the economiser is typically located in the flue gas stack, downstream of the boiler and upstream of the air preheater. This placement allows the economiser to capture waste heat from the flue gases after they have passed through the boiler but before they are expelled into the atmosphere.

What is the lifespan of an economiser?

The lifespan of an economiser can vary widely depending on factors such as its design, the materials used, the operating conditions, and how well it is maintained. With proper care and maintenance, an economiser can last for many years.

Francois Pierrel
Francois Pierrel
Hi, my name is François and I am passionate about solving process engineering problems. Over the years, I have developed a number of process equipment and control systems which have had a significant impact on reducing energy usage, waste and impact on the environment. My business ethos is to always get to the root cause of problems and data analysis and modelling are always at the forefront of any project we undertake.

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