Have you ever heard of “fluidized bed boiler”? This is one of the important technologies in the thermal industry, playing a role in helping to produce electricity and heat efficiently. However, not everyone knows clearly about the differences between the current types of fluidized bed boilers. If you are learning about this topic, let’s join GDP Group to quickly answer and distinguish between the types of fluidized bed boilers and find out the advantages and disadvantages of each type, thereby choosing the right solution for your needs!
1. What is a Fluidized Bed Boiler?
1. What is a Fluidized Bed Boiler?
A Fluidized Bed Boiler (FBB) is a type of combustion system used primarily in power plants and industrial applications to generate steam or electricity. It is known for its high efficiency, fuel flexibility, and environmental friendliness.
🔧 How It Works:
A fluidized bed is created by blowing air (or gas) upward through a bed of solid particles (typically sand, ash, or limestone) at high velocity. This causes the particles to behave like a fluid.
When fuel (e.g., coal, biomass, or waste) is added to this bed:
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It becomes suspended in the turbulent flow.
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It mixes thoroughly with air, resulting in uniform temperature and efficient combustion.
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The bed material helps transfer heat and can capture pollutants like sulfur.
✅ Key Advantages:
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Efficient Combustion: Due to good mixing of air and fuel.
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Fuel Flexibility: Can burn low-grade fuels, biomass, coal, etc.
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Lower Emissions: Limestone can be added to reduce sulfur dioxide (SO₂); lower combustion temperatures reduce nitrogen oxides (NOₓ).
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Uniform Temperature: Reduces equipment stress and increases longevity.
🛠️ Types of Fluidized Bed Boilers:
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Bubbling Fluidized Bed (BFB):
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Lower air velocity.
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Bed behaves like a boiling liquid.
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Suitable for smaller to medium capacity boilers.
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Circulating Fluidized Bed (CFB):
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Higher air velocity.
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Particles are carried out of the furnace and captured by cyclones, then recirculated.
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Suitable for larger capacity and continuous operation.
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🔥 Applications:
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Power generation (thermal power plants)
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Industrial process heating
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Waste-to-energy systems
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Biomass and coal co-firing plants
2. Types of Fluidized Bed Boilers
Currently on the market there are many types of fluidized bed boilers with different structures, operating principles and applications. They are mainly classified into two main types: Circulating Fluidized Bed Boilers and Non-Circulating Fluidized Bed Boilers.
2.1. CIRCULATING FLUIDIZED BED – CFB
Working principle: CFB differs from BFB in that the fluidized bed is maintained at a very high speed, enough for the fuel particles and the substrate (catalyst) to continuously move and circulate back and forth between the combustion chamber and the separator. In CFB, the fuel is not only “suspended” but also carried away in the gas stream and recirculated many times through the system.
Application: CFB is widely used in large power plants or heavy industries where continuous and highly efficient fuel combustion is required. It is suitable for both low-quality and high-quality fuels.
Structure: Circulating fluidized bed boilers (CFB) use fluidized materials (usually sand or lime) as the heat transfer medium. One of the outstanding features of this type of boiler is that the hot gas stream is circulated through the fluidized bed many times, thereby helping to improve thermal efficiency and minimize energy waste.
Advantages:
High efficiency: CFB boilers are capable of maintaining uniform temperature and ensuring perfect combustion of fuel, which increases energy efficiency.
Fuel saving: The continuous circulation system helps burn most solid waste or renewable fuels, while saving fuel compared to other types of boilers.
Environmentally friendly: CFB boilers are capable of reducing CO2 emissions and other toxic gases into the environment.
Can burn many types of fuel: CFB boilers can use many different types of fuel such as coal, biogas, or industrial waste, helping to reduce costs for factories.
Disadvantages:
High initial investment: Circulating fluidized bed boilers require quite high initial installation costs due to complex technology and automatic control systems.
Require regular maintenance: Parts of the circulating boiler can wear out quickly, requiring regular maintenance to ensure longevity.
2.2. BUBBLING FLUIDIZED BED – BFB
How it works:
In a BFB, air or gas is blown from below to create a fluidized bed but at a rate sufficient to cause the fuel particles to “float” and form large air bubbles. This fluidized bed behaves like a bubbling liquid, with air bubbles rising and imploding on the surface. In a BFB, only a small portion of the material moves upward and the majority remains in the combustion chamber.
The AFBC follows the same “foam” principle as the BFB but the air is blown more strongly, creating a more vigorous fluidized bed, causing a larger amount of material and fuel particles to be pushed up and circulated through the material recovery system and then back into the combustion chamber.
Applications: BFB and AFBC are suitable for applications that require stable combustion and lower combustion temperatures, such as in biomass power plants or waste treatment. BFB and AFBC can burn a variety of fuels, from biomass to coal dust.
Structure: Non-circulating fluidized bed boilers work by creating a bed of fluidized material in the combustion chamber space. The hot gas flows from bottom to top, pushing the fluidized material particles (usually sand) up, helping the fuel to contact the heat source. However, unlike circulating fluidized bed boilers, the gas flow in this type of boiler is only pushed up and then stops at the fluidized bed.
Advantages:
Low investment cost: BFB boilers have lower initial investment costs than CFB boilers because the technology is simple and does not require complex circulation systems.
High reliability: BFB boilers are easy to operate and maintain, and are less prone to breakdowns than circulating fluidized bed boilers.
Suitable for small and medium-sized factories: This type of furnace is suitable for applications with not too large capacity requirements, helping to save costs for small-scale production facilities.
Disadvantages:
Efficiency is not as high as CFB: Due to the lack of air circulation system, the thermal efficiency of the BFB furnace is not uniform and less efficient than CFB.
When burning poor quality fuel: BFB furnaces may have problems when burning fuels with heterogeneous properties, which can lead to incomplete combustion.
2.3. PFBC (Pressurized Fluidized Bed Combustion)
Operating principle:
PFBC operates similarly to other fluidized bed systems, but with one major difference: the combustion chamber is placed in a high-pressure environment. Compressed air is blown into the combustion chamber, creating a fluidized bed at a higher speed and temperature than fluidized bed systems operating at atmospheric pressure.
In the PFBC system, the combustion chamber and the gas turbine are combined. The heat from the fluidized bed combustion chamber will heat the compressed air stream, which will then be led into the turbine to generate electricity. This system can combine a gas turbine and a steam turbine (combined cycle), which significantly increases the power generation efficiency.
Application:
PFBC is mainly used in large-capacity power plants where high efficiency and strict emission control are required. Thanks to the high pressure, PFBC can burn fuel more efficiently, while reducing NOx and SOx emissions.
This technology is also suitable for burning difficult fuels such as low-quality coal or biomass, and it is better able to handle ash and exhaust gas problems.
Advantages:
High efficiency: With the combined cycle, PFBC can achieve higher thermal efficiency than other fluidized bed systems.
Reduced emissions: Due to its high-pressure operation and better control of the combustion process, PFBC helps to reduce emissions of pollutants such as NOx, SOx, and CO2.
Combined with gas turbines: This makes PFBC a good choice for power plants that need to optimize performance and use energy efficiently.
Disadvantages:
Very high investment and operating costs, high technical requirements in operation
Comparison:
The biggest difference: BFB and AFBC have a fluidized bed with a “bubbling” state and lower gas velocity, suitable for small and medium scale, while CFB has a high gas velocity and continuous fuel circulation, suitable for larger systems. PFBC operates under high pressure, has the best emission reduction ability but the highest investment and operating costs.
Selection: PFBC is suitable for applications requiring high efficiency and strict emission control such as in large power plants. Meanwhile, systems such as BFB, AFBC and CFB provide more cost-effective solutions for small and medium scale applications, with performance and emission reduction ability suitable for business requirements.
