Boilers serve as fundamental components in heating systems, supplying the thermal energy essential for a range of industrial and commercial applications. The burner, as the central unit responsible for heat generation in the boiler, creates the flame and supplies the combustion energy. Proper burner selection not only enhances efficiency and reduces fuel consumption, but also ensures system safety, extends equipment lifespan, and guarantees stable operation. The process of selecting a suitable boiler burner involves analyzing the boiler type, required heat capacity, and environmental conditions.
This article aims to examine the process of proper boiler burner selection through a technical and step-by-step approach. First, the type of boiler is identified, followed by the calculation of its heat capacity using input and output data. Then, the burner’s input power is determined, and finally, the required burner capacity is calculated by considering and correcting for environmental conditions.
Given the critical role of burner selection in optimizing overall system performance, careful consideration must be given to each influencing factor during the evaluation process. This ensures that the burner selection is carried out accurately and scientifically.
Determining the Type of Boiler
Initially, the boiler type must be determined. Boilers are typically classified into two groups: hot water boilers and steam boilers.
Boiler burner selection depends on the boiler type, as each category has its own specific technical characteristics and requires a burner suited to its particular operating conditions.
In hot water boilers, depending on the type of boiler, water is heated from a lower temperature (e.g., 60°C) to a higher temperature required by the end user. For example, in residential heating applications, the hot water boiler must raise the water temperature to around 80°C. In this type of boiler, the mass flow rate of water, operating pressure, and the inlet and outlet water temperatures must be known in order to calculate the boiler’s capacity. These parameters also play a crucial role in selecting the appropriate burner for the hot water boiler.
In steam boiler systems, the inlet water is initially passed through a deaerator, where dissolved gases like oxygen and carbon dioxide are removed, and the water is heated to around 100°C. It is then fed into the boiler, where it reaches the saturated liquid temperature under the defined working pressure and is subsequently converted to saturated steam. Therefore, to calculate the capacity of a saturated steam boiler, it is sufficient to know the boiler’s working pressure and the water mass flow rate. Here too, selecting an appropriate burner requires careful consideration of these parameters.
In superheated (overheated) boilers, saturated steam is heated to a higher temperature in the superheater, as required by the consumer. In this case, to determine the boiler capacity, in addition to the operating pressure and the water mass flow rate, the superheated steam outlet temperature must also be specified.
Calculation of Boiler Heat Capacity Qboiler
When the thermal load of a building, factory, or any other heating-required space is defined, this value is regarded as the boiler capacity, and there is no need for further calculations. However, if the boiler capacity is unknown, it can be determined using the following formulas.
To calculate the boiler capacity, the following information is required:
- Temperature of Inlet Water
- Temperature of outlet Water (for Hot Water Boilers) or Steam (for Superheated Steam Boilers)
- Working Pressure of the Boiler
- Water Mass Flow Rate
As the temperature of the water in the boiler rises, so does its enthalpy. Enthalpy is, in simple terms, a measure of the thermal energy stored within the fluid, and the higher the temperature of the fluid, the higher its enthalpy. According to the first law of thermodynamics, the amount of heat gained by the water in the boiler is equal to the difference in its enthalpy between the initial and final states. This energy, required to heat the fluid, is a key factor in selecting a boiler burner with the appropriate heat capacity.
![\[ Q = \dot{m} \cdot (h_2 - h_1) \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-d839401fb61402c606700a21323e64c0_l3.png "Rendered by QuickLaTeX.com")
Q: Heat Supplied to the Water
ṁ: Water Mass Flow Rate
h1: Initial Enthalpy of Water
h2: Final Enthalpy of Water or Steam
As the water heats up, its enthalpy increases, and this increase represents the amount of thermal energy gained from the boiler. Therefore, it is necessary to determine the inlet and outlet enthalpies of the water. The enthalpies, given in kJ/kg, are derived from thermodynamic tables, where the enthalpy is calculated based on the boiler pressure (Pboiler) and water temperature (T). If the water is in either the liquid phase or saturated steam phase, knowing the boiler pressure is enough.
h1 = h (Pboiler, T1)
h2 = h (Pboiler, T2)
The table below shows the enthalpy of liquid and steam water at various pressures and temperatures:
|
Fluid Type |
Temperature |
Pressure (bar) |
Enthalpy |
|
Liquid Water |
40 |
1 |
167.6 |
|
Liquid Water |
40 |
5 |
168 |
|
Liquid Water |
60 |
1 |
251.2 |
|
Liquid Water |
60 |
5 |
251.6 |
|
Liquid Water |
60 |
10 |
252 |
|
Liquid Water |
80 |
1 |
335.1 |
|
Liquid Water |
80 |
5 |
335.4 |
|
Liquid Water |
80 |
10 |
335.8 |
|
Liquid Water |
100 |
5 |
419.5 |
|
Liquid Water |
100 |
10 |
419.8 |
|
Liquid Water |
100 |
15 |
420.2 |
|
Liquid Water |
150 |
5 |
632.2 |
|
Liquid Water |
150 |
10 |
632.5 |
|
Liquid Water |
150 |
15 |
632.8 |
|
Saturated Steam |
99.6 |
1 |
2674.9 |
|
Saturated Steam |
151.8 |
5 |
2748.1 |
|
Saturated Steam |
180 |
10 |
2777 |
|
Saturated Steam |
198.3 |
15 |
2856 |
|
Saturated Steam |
212.4 |
20 |
2856 |
|
Saturated Steam |
234 |
30 |
2803 |
|
Superheated Steam |
150 |
1 |
2777 |
|
Superheated Steam |
200 |
5 |
2856 |
|
Superheated Steam |
230 |
10 |
2898 |
|
Superheated Steam |
250 |
15 |
2924 |
|
Superheated Steam |
270 |
20 |
2953 |
|
Superheated Steam |
280 |
25 |
2960 |
|
Superheated Steam |
300 |
30 |
2994 |
Water mass flow is commonly given in ton/hr. To convert this to kg/s, the following equation is used.
ṁ [kg/s] = 0.2778 × ṁ [ton/hr]
Hence, using thermodynamic tables to obtain the enthalpies and having the mass flow rate of water, the boiler’s heat capacity can be determined.
Qboiler [MW] = 0.001 × ṁ [kg/s] × (h2 – h1)
Determining the Input Energy of the Burner Qinput
Since boilers do not operate at 100% efficiency, the input power required by the burner is always greater than the thermal power demanded by the end user. In fact, a portion of the energy supplied to the boiler is lost due to heat losses. This can be expressed using the following equation:
![\[ Q_{input} = \frac{Q_{boiler}}{\eta_{boiler}} \times 100 \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-ea7419350debc13104e760f895208064_l3.png "Rendered by QuickLaTeX.com")
Qinput: Burner Input Energy
Qboiler: Thermal Output of the Boiler
ηboiler: Boiler Efficiency
The efficiency of non-condensing boilers is typically around 85% without an economizer and 92% with an economizer, while condensing boilers are generally considered to have an efficiency of about 95%. Therefore, when selecting a burner, these losses must be taken into account, and the burner’s input power should be calculated based on the boiler’s efficiency.
Determining Burner Capacity Based on Ambient Conditions Qburner
For proper burner operation, the required combustion air must be accurately supplied. The combustion air needed for the burner is provided by a fan. Fans typically deliver a constant volumetric airflow 
; in other words, they supply a fixed volume of air to the burner per unit of time. However, in order for the burner to maintain a consistent thermal capacity, the critical factor is the mass flow rate of air 
, not merely its volume. The burner must receive a constant air mass flow to operate at a stable output.
The mass flow rate of air refers to the amount of air mass passing through the system per unit of time, and it is calculated using the following formula. These calculations have a direct impact on the burner selection process, as the burner must be capable of operating effectively under different environmental conditions.
![\[ \dot{m}_{air} = \dot{V}_{air} \times \rho_{air} \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-0093ad41620e32f4492005089d348b1a_l3.png "Rendered by QuickLaTeX.com")
: Mass Flow Rate of Air in 
: Volumetric Flow Rate of Air in 
: Air Density in 
Thus, as the air density decreases, a greater volume of air needs to be injected into the burner to maintain its constant thermal capacity. This makes it necessary to be aware of the air density under various environmental conditions. Air is usually considered an ideal gas, and its relationship is defined by the following equation.
![\[ \rho = \frac{P}{RT} \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-5a7d345438b7783ce5a2526afe8d5e69_l3.png "Rendered by QuickLaTeX.com")
Air density, P (air pressure), T (air temperature), and R (universal gas constant) are related variables. According to this relationship, air density has a direct relationship with pressure and an inverse relationship with temperature. Therefore, as air pressure decreases and temperature increases, its density decreases. As altitude increases above sea level, atmospheric pressure decreases, which leads to a reduction in air density. The following equation is used to calculate atmospheric pressure as a function of altitude above sea level:
![\[ P_{atmosphere} \; [\text{bar}] = 1.01325 \times \left(1 - 2.25577 \times 10^{-5} \times \text{Altitude} \right)^{5.25588} \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-f3af88b00b0bffc62f86255fb553c598_l3.png "Rendered by QuickLaTeX.com")
Patmosphere: Atmospheric Pressure (bar)
Altitude: Height from the sea level (m)
The ideal gas law can be applied to calculate air density at different temperatures. To ensure that the burner maintains a consistent capacity across varying environmental conditions, its capacity must be adjusted based on reference environmental conditions. For burners, the reference conditions are a temperature of 20°C and a pressure of 1.325 bar. Consequently, a correction factor (CF) is defined to adjust the burner’s capacity, as expressed below:
![\[ CF = \frac{1.01325}{P_{atmosphere}} \times \frac{T_{atmosphere} + 273}{293} \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-46e002a3c1f505e928e7ed5bd5f202fb_l3.png "Rendered by QuickLaTeX.com")
Tatmosphere: Ambient temperature (°C)
Patmosphere: Ambient pressure (bar)
Therefore, the burner capacity is determined by the following equation:
![\[ Q_{burner} \; [\text{MW}] = Q_{input} \; [\text{MW}] \times CF \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-eaab11f75b9e8518c484993d971b1bed_l3.png "Rendered by QuickLaTeX.com")
Qinput: Nominal burner capacity under reference conditions (20°C and 1.325 bar)
Qburner: Actual Burner Capacity under Ambient Conditions
CF: Capacity Correction Factor
For example, at higher altitudes or ambient temperatures compared to the reference conditions, air density decreases. As a result, the correction factor (CF) increases to ensure that the burner can meet the required thermal capacity. This consideration becomes even more crucial when selecting a boiler burner based on the geographical location of the project.
Example: The burner capacity for a hot water boiler with a mass flow rate of 10 ton/hr at 5 bar, which increases the water temperature from 60°C to 80°C, is calculated as follows. The altitude is 1000 m, the ambient temperature is 40°C, and the boiler efficiency is 85%.
Converting the mass flow rate of water to kilograms per second:
ṁ = 0.2778 × 10 = 2.778 kg/s
Determining the input and output enthalpies of water using thermodynamic tables:
h1= h (P=10 bar, T=60 C) = 251.7 kJ/kg
h2= h (P=10 bar, T=80 C) = 335.4 kJ/kg
Determining the heating capacity of the boiler:
Qboiler =0.001 × ṁ (h2-h1) = 0.001× 2.778 ×(335.4-251.7) = 0.232 MW
Determining the burner input power considering the boiler efficiency:
Qinput = 100 × (Qboiler/ η boiler) = 100 × (0.232/ 85) = 0.274 MW
Calculating the atmospheric pressure at the specified altitude:
Patmosphere = 1.01325 × (1-2.25577×10-5×1000)5.25588 = 0.898 bar
Correction factor for burner capacity according to ambient conditions:
![\[ CF = \frac{1.01325}{P_{atmosphere}} \times \frac{T_{atmosphere} + 273}{293} = \frac{1.01325}{0.898} \times \frac{40 + 273}{293} = 1.2 \]](https://raadmanburner.com/wp-content/ql-cache/quicklatex.com-a044c358702d523496e9c8f28b164fbd_l3.png "Rendered by QuickLaTeX.com")
Calculating the burner capacity:
Qinput = Qinput × CF = 0.274 × 1.2 = 0.329 MW
Based on the calculations, the actual burner capacity for this hot water boiler under the specified environmental conditions is 0.329 MW. In fact, the burner capacity has been set approximately 20% higher than the input power to account for the effects of ambient temperature and altitude above sea level.
Burner Selection
Once the required heat capacity is determined, the next step is to evaluate the fuel type, burner performance, and burner structure. Raadman Industrial Group manufactures burners in different categories based on the fuel used, including gas burners, oil burners, dual-fuel burners, heavy fuel burners like mazut, and hybrid burners using hydrogen. For instance, the R-Hydro burner is a hydrogen burner example from raadman Group.
After specifying the burner fuel type, the next step is to examine the burner operation. Burners are generally divided into three main categories based on their operation:
- Single-stage burners: These burners have a basic design and function with two modes only: on and off
- Multi-stage burners: These burners can operate at several distinct capacity levels, allowing for better adaptation to varying thermal demands.
- Modulating burners: The burner’s output is dynamically controlled in response to system conditions using intelligent controllers, such as the AutoFlame MK8 MM, which can simultaneously manage both boiler and burner. These burners provide exceptional accuracy and efficiency across a wide range of operating conditions
From a structural perspective, burners are categorized into two types: monoblock and dual-block. Accurate knowledge of the burner configuration plays a significant role in choosing a burner that ensures proper efficiency and appropriate sizing for the boiler.
- monoblock burners: In this configuration, both the burner and its fan are integrated into a single housing, making them an optimal solution for installations with space constraints. Raadman’s monoblock burners are available in capacities up to 22 MW.
- Dual-block burners: This design features a non-integrated structure in which the combustion air supply unit (fan) is installed separately from the burner body. The fan is positioned at a certain distance and delivers air through a duct to the burner. This configuration makes dual-block burners an ideal choice for high-capacity applications. Leveraging this technology, raadman Industrial Group manufactures dual-block burners with capacities of up to 60 MW.
Burner Operating Diagram
Burners have their own specific operating diagrams, which illustrate the burner’s capability to deliver the required capacity against system pressure drop. The horizontal axis of these diagrams represents the burner capacity under reference conditions (20°C temperature and 1.325 bar pressure), while the vertical axis indicates boiler pressure.
For accurate burner selection, the boiler pressure must first be determined. Then, a horizontal line is drawn on the burner’s operating diagram at the specified pressure level. The intersection of this line with the vertical line corresponding to the desired burner capacity indicates the burner’s operating point.
If this point falls within the bounds of the operating diagram, the burner is capable of meeting the required capacity at the given boiler pressure. If the point lies outside the diagram’s range, the selected burner is inadequate, and a higher-capacity burner must be chosen.
For example, if a burner is required to produce 20 MW of thermal energy at a boiler pressure of 15 mbar, the operating point can be identified as Point A on the RLGB-M/M-2250 burner’s operating diagram. Since Point A falls within the valid operating range of the diagram, the burner can operate effectively at this point, confirming that the burner selection is appropriate.
Final Remarks: Optimal Selection of Boiler Burner
This article examined the process of boiler burner selection through a systematic, engineering-based approach. First, the boiler type was identified, and then, using thermodynamic parameters and operating conditions, the boiler’s heat capacity and the required burner power were calculated. Next, the actual burner capacity was determined by taking into account environmental factors such as temperature and installation altitude. Given the importance of precise burner selection in ensuring performance consistency and energy efficiency, each stage of the process was carefully evaluated to match real-world application needs. In the final section, based on the calculated capacity, burners manufactured by Raadman Industrial Group were introduced as an efficient and reliable solution.
A key tool in assessing the performance of these burners is their operating diagram, which clearly show the relationship between boiler pressure and the thermal output of the burner. These graphs allow for the assessment of the burner’s compatibility with the system’s needs and provide engineers with the ability to select the most suitable model based on operational conditions.
Raadman burners, with their advanced design, low-emission combustion technology, intelligent control capabilities, and wide capacity range, are well-equipped to meet the diverse needs of the industry.
