3 Key Factors That Reduce Boiler Fuel Consumption

Fuel cost is always one of the largest operating expenses in a boiler system. However, many companies focus only on selecting the right fuel while overlooking the key factors that determine the overall efficiency of the entire boiler system.

Reducing fuel consumption requires more than simply achieving efficient combustion. Heat generated during combustion must also be transferred efficiently to the water, and the water must be converted into high-quality steam. If any one of these three processes performs poorly, fuel consumption increases while steam generation efficiency decreases.

So, what are the key factors that determine boiler fuel consumption? What should manufacturers monitor to operate their boiler systems more efficiently?

This article analyzes the three core processes that directly affect boiler efficiency and highlights the critical operating practices that help reduce fuel consumption. 

I. How Does a Boiler Work?

To understand why one boiler system consumes more fuel than another, it is important to first understand its basic operating principle.

A boiler is a closed vessel filled with water. During operation, heat released from fuel combustion is transferred to the water inside the boiler. Once sufficient heat has been absorbed, the water boils and converts into steam, which is then supplied to industrial processes such as sterilizing, drying, and evaporation.

The steam generation process consists of three consecutive stages:

•     Fuel combustion 

•     Heat transfer from the flame to the water 

•     Water conversion into steam 

These three processes are closely interconnected. When each process is optimized, overall boiler efficiency increases and fuel consumption decreases. Conversely, if any one of them operates inefficiently, the entire system requires more fuel to produce the same amount of steam 

Why Must All Three Processes Be Optimized Together?

In practice, many facilities focus only on improving combustion efficiency while paying little attention to the remaining two processes.

However, boiler efficiency depends not only on how much heat is generated but also on how effectively that heat is transferred and how efficiently the water is converted into steam.

Even if combustion is efficient, poor heat transfer or incomplete steam generation still results in heat losses. Consequently, the boiler must burn more fuel to meet the same steam demand.

For this reason, reducing boiler fuel consumption requires optimizing all three processes—combustion, heat transfer, and steam generation—rather than concentrating on only one aspect.

Three key processes that determine boiler efficiency

II. Factor 1: Optimize the Fuel Combustion Process

The combustion process is the first stage that determines how much heat is generated inside a boiler. If the fuel does not burn efficiently, less heat is produced while fuel consumption increases.

To achieve efficient combustion, three key factors must be controlled:

•     Fuel moisture content 

•     Combustion intensity inside the furnace 

•    The ratio between fuel supply and combustion air (oxygen) 

These three factors are closely related and all have a direct impact on boiler efficiency. 

1. Control Fuel Moisture Content

The lower the moisture content of the fuel, the more efficient the combustion process becomes.

Conversely, when fuel contains excessive moisture, part of the heat generated during combustion is consumed to evaporate the water before the fuel can burn effectively. As a result, combustion efficiency decreases and fuel consumption increases.

Therefore, maintaining the lowest practical fuel moisture content is one of the most effective ways to improve fuel utilization and reduce fuel consumption.

2. Maintain Proper Combustion Intensity

Besides fuel moisture, combustion intensity inside the furnace also has a direct impact on boiler efficiency.

The combustion temperature must be high enough to ensure complete combustion without exceeding the ash melting point.

For biomass fuels, the appropriate combustion temperature typically ranges from 800–850°C and may reach 900°C under certain conditions. For coal-fired systems, the combustion temperature may reach approximately 950°C.

However, during normal operation, combustion intensity is difficult for operators to adjust because it mainly depends on the design of the furnace.

If the furnace is not properly designed, there is very little that can be done to significantly improve combustion efficiency. One possible solution is to use fuel with lower moisture content and a higher heating value, although this generally results in higher fuel costs.

3. Adjust the Fuel-to-Oxygen Ratio

Efficient combustion depends not only on the amount of fuel supplied to the furnace but also on the amount of oxygen available for combustion.

If the oxygen supply does not match the amount of fuel being burned, combustion efficiency decreases.

•     Too little oxygen results in incomplete combustion. 

•     Too much oxygen is also inefficient. 

Therefore, maintaining the proper balance between fuel and oxygen is essential for achieving high boiler efficiency. 

Why Is Manual Fuel Feeding Less Efficient?

To keep combustion stable, the fuel supply must continuously match the steam demand, while the combustion air supply must be adjusted accordingly.

However, in manually fed boiler systems, maintaining this balance continuously is almost impossible.

Since fuel feeding depends entirely on the operator, there are times when too much or too little fuel is added. These fluctuations cause unstable combustion, reducing efficiency and increasing fuel consumption. 

Factors That Can Be Controlled During the Combustion Process

Not every factor affecting combustion efficiency can be adjusted during boiler operation.

Operators can actively control:

•     Fuel moisture content 

•     The amount of fuel supplied according to steam demand 

•     The oxygen supply corresponding to the fuel input 

On the other hand, combustion intensity inside the furnace depends primarily on the boiler's design and can rarely be changed during operation.

For this reason, selecting an appropriate boiler design from the beginning is also a critical factor in achieving long-term fuel efficiency. 

Should the Boiler System Be Evaluated Before Any Retrofit?

Not every increase in fuel consumption is caused by the fuel itself.

A systematic evaluation of the combustion process, heat transfer process, and water-to-steam conversion process helps identify the actual cause of efficiency loss, allowing the most appropriate solution to be selected based on the system's operating condition.

III. Factor 2: Optimize the Heat Transfer Process

After fuel has burned and generated heat, the next factor that determines boiler efficiency is how effectively that heat is transferred to the water.

The objective is to transfer as much heat as possible from the combustion chamber into the water inside the boiler. If heat transfer is restricted, system efficiency decreases and additional fuel is required to compensate for the lost heat.

Heat transfer in a boiler mainly consists of two stages:

•     Heat transfer from the flame and flue gas to the heat transfer surfaces. 

•     Heat transfer from the heat transfer surfaces to the boiler water. 

To optimize both stages, the following practices should be implemented. 

1. Keep Heat Transfer Surfaces Clean

Heat generated by the flame and hot flue gases must pass through the heat transfer surfaces before being transferred to the boiler water.

If these surfaces become covered with dust, ash, or deposits, they create an insulating layer between the flue gas and the tube walls, reducing heat transfer efficiency.

Conversely, when the heat transfer surfaces are kept clean, heat is transferred more effectively, helping improve boiler efficiency and reduce boiler fuel consumption.

For this reason, regularly cleaning all surfaces directly exposed to the flame and flue gas is one of the most important maintenance tasks for maintaining efficient boiler operation. 

Comparison of boiler heat transfer surfaces before and after cleaning

2. Minimize Scale Formation Inside the Boiler

After heat passes through the tube walls, it continues to transfer from the metal surface to the water.

If scale forms on the inner tube surfaces, it acts as an insulating barrier that reduces heat transfer from the metal to the water.

As a result, the water absorbs less heat even though fuel consumption remains unchanged. To produce the same amount of steam, the boiler must burn more fuel.

Therefore, controlling internal boiler scale has a direct impact on heat transfer efficiency, boiler efficiency, and boiler fuel consumption.  

Scale buildup reduces heat transfer efficiency and increases boiler fuel consumption

3. Treat Boiler Feedwater Properly

One of the most effective ways to minimize scale formation is to properly treat the boiler feedwater before it enters the boiler.

Proper boiler feedwater treatment helps reduce the formation of scale on heat transfer surfaces, maintaining heat transfer efficiency and preventing fuel consumption from increasing over time.

In addition, using boiler water treatment chemicals correctly also helps minimize scale formation during boiler operation. 

Boiler water treatment chemicals help maintain water quality, reduce scale formation, and improve heat transfer efficiency

4. Control Feedwater Hardness

Feedwater hardness is one of the primary causes of scale formation inside a boiler.

For this reason, boiler feedwater should be treated to meet the required water quality standards before entering the system, minimizing scale buildup on heat transfer surfaces.

When water hardness is properly controlled, heat transfer efficiency remains stable throughout boiler operation.

5. Perform Blowdown Based on TDS

In addition to proper boiler feedwater treatment, regular boiler blowdown is essential for maintaining boiler water quality.

Blowdown should be performed according to the TDS (Total Dissolved Solids) level of the boiler water to keep dissolved solids within the recommended range.

Maintaining an appropriate TDS level helps reduce the risk of scale formation, improves heat transfer efficiency, and enhances overall boiler efficiency.

Read more: Proper boiler blowdown procedure

Three Essential Practices for Optimizing Heat Transfer

To maintain efficient boiler heat transfer, the following practices should be carried out simultaneously:

•     Regularly clean all surfaces exposed to the flame and flue gas. 

•     Properly treat boiler feedwater and use boiler water treatment chemicals to minimize scale formation. 

•     Perform regular boiler blowdown based on the boiler water TDS level. 

All three practices share the same objective: eliminating barriers to heat transfer so that more heat generated during combustion is transferred into the water, thereby improving boiler efficiency and reducing boiler fuel consumption. 

Why Does Heat Transfer Directly Affect Boiler Fuel Consumption?

Even if the combustion process is efficient, poor heat transfer will still result in higher fuel consumption.

This is because part of the heat generated during combustion is not absorbed by the water. Instead, it is lost due to deposits on heat transfer surfaces or scale buildup inside the boiler.

Therefore, optimizing heat transfer efficiency not only improves steam generation efficiency but is also one of the most effective ways to reduce boiler fuel consumption.

The decline in heat transfer efficiency usually occurs gradually, making it difficult to detect during day-to-day boiler operation.

Without regular cleaning, proper boiler feedwater treatment, and effective TDS control, fuel consumption may gradually increase over time while the root cause remains unnoticed.

Routine inspection and preventive maintenance help identify factors that reduce heat transfer efficiency at an early stage, ensuring stable boiler performance and long-term fuel savings.

IV. Factor 3: Optimize the Water-to-Steam Conversion Process

After fuel has burned efficiently and the maximum amount of heat has been transferred to the water, the final factor that determines boiler efficiency is the conversion of water into steam.

Many people assume that once the water has absorbed enough heat, steam will naturally be produced. While this is true, steam quality is another critical factor that directly affects overall system efficiency.

If the steam still carries tiny water droplets after it has been generated, it means the water has not been completely converted into steam. As a result, the amount of useful heat carried by the steam decreases, reducing the effectiveness of steam in industrial applications.

How Does Wet Steam Affect Boiler Efficiency?

Under ideal operating conditions, water that has absorbed sufficient heat is completely converted into steam.

However, if fine water droplets remain suspended in the steam flow, the steam produced will not achieve the desired quality.

According to the analysis, these water droplets transfer heat less effectively than dry steam while also absorbing part of the thermal energy carried by the steam. Consequently, the useful energy available before the steam reaches the end-use equipment is reduced.

This condition is commonly referred to as wet steam in a boiler system. 

What Causes Wet Steam?

For the water-to-steam conversion process, operators have very limited ability to modify the boiler's original design.

However, several operating conditions can still affect steam quality.

One of the causes mentioned is the excessive use of boiler water treatment chemicals.

According to the analysis, water treatment chemicals are alkaline and have a relatively viscous consistency. When overdosed, they can form a thin film on the water surface.

    → This surface film promotes foaming and causes boiler water to be carried over with the steam, reducing the steam dryness fraction.

Control Water Treatment Chemicals and Operating Parameters

To minimize wet steam caused by water carryover, the amount of boiler water treatment chemicals added to the system should be carefully controlled.

In addition, operating parameters such as pH and TDS (Total Dissolved Solids) in the boiler water should always be maintained within the recommended range.

Controlling these factors together helps reduce surface foaming and maintain more consistent steam quality throughout boiler operation. 

What Should You Do If Wet Steam Still Occurs?

If the dosage of water treatment chemicals has already been optimized but the steam still contains excessive moisture, the recommended solution is to install a steam separator in the steam pipeline.

A steam separator removes the remaining water droplets from the steam before it reaches the point of use, with a moisture separation efficiency of over 98%.

How Can Steam Quality Be Checked?

One simple method mentioned in the article is to discharge steam directly onto a sheet of paper.

If the paper remains dry after the steam is released, the steam can be considered to meet the required quality.

This provides operators with a quick visual method for evaluating steam quality during normal boiler operation. 

What Should Manufacturers Control to Reduce Boiler Fuel Consumption?

To improve boiler efficiency and reduce boiler fuel consumption, manufacturers should routinely monitor and control the following factors:

•     Fuel moisture content

•     The amount of fuel supplied and the combustion air (oxygen) entering the furnace. 

•     The cleanliness of the boiler heat transfer surfaces. 

•     Boiler feedwater quality and boiler water quality. 

•     Boiler water pH and TDS.

•     Regular boiler blowdown practices. 

•     Steam quality before it reaches the point of use. 

By controlling all of these factors simultaneously, the three key processes - fuel combustion, heat transfer, and water-to-steam conversion - can all operate more efficiently, helping reduce boiler fuel consumption while improving overall boiler efficiency.

V. FAQ - Frequently Asked Questions

1. What factors determine boiler fuel consumption?

Boiler fuel consumption is primarily determined by three key processes:

• Fuel combustion. 
• Heat transfer from the flame to the boiler water. 
• Water-to-steam conversion. 

If any one of these processes operates inefficiently, fuel consumption will increase even though the steam output may remain unchanged.

2. Why does high fuel moisture increase boiler fuel consumption?

When fuel contains excessive moisture, part of the heat generated during combustion is consumed to evaporate the water before the fuel can burn efficiently.

As a result, combustion efficiency decreases, and the boiler must consume more fuel to produce the same amount of steam.

3. How does scale affect heat transfer efficiency?

Scale deposited on boiler heat transfer surfaces creates an insulating layer between the metal surface and the water.

This barrier reduces heat transfer efficiency, causing the water to absorb less heat. Consequently, the boiler must burn more fuel to meet the same steam demand.

4. Why is it important to control the TDS level in boiler water?

When the TDS (Total Dissolved Solids) level becomes too high, dissolved solids accumulate inside the boiler.

Controlling TDS through regular boiler blowdown helps maintain boiler water quality, reduces the risk of scale formation, and preserves heat transfer efficiency.

5. How does wet steam affect steam quality?

If the steam contains excessive fine water droplets, the amount of useful heat carried by the steam decreases.

This reduces the effectiveness of steam at the point of use and lowers the overall efficiency of the boiler system.

6. When should a steam separator be installed?

If the dosage of boiler water treatment chemicals has already been properly controlled but the steam still contains excessive moisture, a steam separator can be installed in the steam pipeline.

The separator removes the remaining water droplets from the steam before it reaches the end-use equipment, improving steam quality.

7. How can steam quality be checked quickly?

One simple method described in this article is to discharge steam directly onto a sheet of paper.

If the paper remains dry after the steam is released, the steam can be considered to meet the required quality. This provides operators with a quick visual method for evaluating steam quality during normal boiler operation.

VI. Conclusion

Reducing boiler fuel consumption is not determined solely by the type of fuel used. It depends on the entire steam generation process within the boiler system.

The three key processes - fuel combustion, heat transfer, and water-to-steam conversion - are closely interconnected. When each of these processes is properly optimized, boiler efficiency improves, and fuel consumption is reduced accordingly.

During daily operation, manufacturers should regularly monitor key factors such as fuel quality, the condition of boiler heat transfer surfaces, boiler water quality, and steam quality. Evaluating these factors together makes it easier to identify the root causes of efficiency losses at an early stage, allowing appropriate corrective actions to be taken to maintain stable boiler operation while minimizing fuel consumption.

Need to Identify the Cause of Increasing Boiler Fuel Consumption?

If your boiler system is showing signs of higher fuel consumption, reduced boiler efficiency, or unstable steam quality, identifying the root cause should be the first step before considering any system modification or investment in new equipment.

The engineering team at DIVI Group can assist with on-site system assessments, analyze the causes of increased boiler fuel consumption, and recommend practical solutions tailored to the actual operating conditions of your boiler system.

Technical Consultation Hotline: +84 942 488 818