Pulverized fuel combustion is a highly efficient method for burning coal to generate heat or electricity. It involves grinding coal into a fine powder, similar to talcum powder, and then suspending it in a stream of hot air for combustion. This process offers several advantages, making it a mainstay in large-scale power plants and industrial boilers.
2. Pulverized Fuel Combustion
Pulverized fuel combustion involves the combustion of finely ground solid fuels
(typically coal) in a furnace or boiler.
Process Overview:
โข Solid fuel (coal) is pulverized into very fine particles (often less than 100 microns in
size) using grinding mills.
โข The pulverized coal is then mixed with air and blown into the combustion chamber of
the furnace.
โข In the combustion chamber, the pulverized coal particles undergo rapid combustion due
to the high surface area exposed to oxygen.
โข Heat released during combustion is transferred to water tubes, generating steam used
for power generation or heating.
โข Efficient combustion due to rapid and complete burnout of coal particles.
โข High thermal efficiency and low emissions when combined with advanced combustion
technologies like low NOx burners.
โข Widely used in large power plants for electricity generation.
3. Advantages:
โข Higher combustion efficiency compared to solid fuel combustion with larger
particles.
โข Flexibility in fuel selection and handling due to the ability to burn various
types of coal.
Challenges:
โข Requires careful control of air-fuel ratios and combustion conditions to
avoid slagging, fouling, and emissions.
โข Produces fine ash, requiring effective ash collection and disposal systems.
4. Fluidized Bed Combustion (FBC)
Fluidized bed combustion is a combustion technology where solid particles (typically
sand or limestone) are suspended and mixed with air or other gases, creating a
fluidized state.
Process Overview:
โข Solid fuel is introduced into the fluidized bed reactor along with air or a fluidizing gas (e.g.,
steam).
โข The fluidizing gas causes the bed of solid particles to behave like a fluid, enhancing heat
transfer and combustion efficiency.
โข Combustion occurs at lower temperatures compared to pulverized fuel combustion, reducing
NOx formation.
โข Ash is collected and removed continuously from the bottom of the fluidized bed.
โข Fuel flexibility, allowing combustion of a wide range of solid fuels including coal, biomass, and
waste.
โข Lower emissions of NOx and SOx compared to conventional combustion technologies.
โข Efficient heat transfer due to the fluidized state of the bed, improving combustion efficiency.
5. Advantages:
โข Reduced emissions of pollutants due to lower
combustion temperatures and efficient air-fuel mixing.
โข Ability to handle fuels with high moisture content,
reducing the need for fuel drying.
Challenges:
โข Control of bed temperature and particle size
distribution is critical for stable operation.
โข Ash management and handling can be complex due to
the continuous removal of ash from the bed.
6. Types of FBC
Bubbling Fluidized Bed (BFB):
โข In BFB, the solid particles are
fluidized and bubble like a
boiling liquid.
โข Commonly used for smaller-
scale applications such as
industrial boilers and biomass
combustion.
Circulating Fluidized Bed (CFB):
โข In CFB, solid particles are
fluidized at higher velocities,
creating a circulating flow
pattern.
โข Suitable for larger-scale power
generation and industrial
applications.
โข Allows for efficient mixing and
combustion of fuels with lower
emissions.
7.
8. BFB
โข Bubbling Fluidized Bed (BFB) combustion is a type of
fluidized bed combustion technology used for efficiently
burning solid fuels, such as biomass, coal, or waste. In BFB
systems, the solid particles (fuel and inert bed material like
sand) are fluidized by passing a gas (typically air) through
the bed from below.
โข BFB operates at relatively low fluidization velocities,
typically in the range of 1-3 m/s.
โข The bed of solid particles (fuel and inert material) behaves
like a boiling liquid, with bubbles forming and rising through
the bed.
โข The fluidizing gas (air) ensures good mixing and contact
between the solid particles, enhancing combustion
efficiency.
9. Components
โข Fluidized Bed Reactor: The main combustion chamber where fuel
particles are suspended and burned.
โข Air Distributor: Distributes the fluidizing air uniformly across the
bottom of the bed to maintain fluidization.
โข Fuel Feeding System: Supplies solid fuel (e.g., biomass, coal) into
the fluidized bed.
โข Heat Exchanger: Transfers heat from the combustion process to
produce steam or hot gases for energy generation.
10. Advantages
โข Fuel Flexibility: BFB can burn a wide range of solid fuels,
including low-grade biomass and wastes.
โข Lower Emissions: BFB combustion typically results in lower
emissions of nitrogen oxides (NOx) compared to conventional
combustion technologies.
โข Good Mixing: The fluidized state of the bed promotes excellent
mixing of fuel and air, enhancing combustion efficiency.
โข Improved Heat Transfer: Heat transfer rates are higher due to the
turbulent fluidization, leading to efficient energy conversion.
11. CFB
โข Circulating Fluidized Bed (CFB) combustion is an
advanced fluidized bed combustion technology used
for burning solid fuels with high efficiency and low
emissions. CFB systems are widely applied in power
generation, industrial boilers, and waste-to-energy
plants
โข CFB operates at higher fluidization velocities
compared to BFB, typically in the range of 4-10 m/s.
โข Solid particles (fuel and inert material like sand) are
fluidized by a fast-moving stream of gas (typically air)
injected from the bottom of the reactor.
โข Particles are circulated between the combustion zone
and external heat exchangers or cyclones for efficient
heat transfer and combustion.
12. Components
โข Fluidized Bed Reactor (Combustor): The main combustion
chamber where solid fuels are suspended and burned.
โข Cyclone Separators: Used to capture and recycle solid particles
(ash and unburned fuel) from the flue gas.
โข Heat Exchangers: Transfers heat from the combustion process to
produce steam or hot gases for energy generation.
โข Fuel and Air Feeding Systems: Supply solid fuel and combustion
air into the fluidized bed.
13. Advantages
โข Fuel Flexibility: CFB can burn a wide range of solid fuels,
including coal, biomass, and wastes, with varying moisture
content and particle size.
โข Efficient Combustion: High turbulence and intimate contact
between fuel and air result in efficient combustion and lower
emissions of pollutants (NOx, SOx).
โข Good Heat Transfer: Enhanced heat transfer due to the turbulent
fluidization and effective mixing of gases and solids.
โข Scale and Capacity: CFB technology is scalable and suitable for
large-scale power plants as well as smaller industrial applications.
14. Challenges
โข Bed Material and Particle Size: Selection of appropriate bed
material and control of particle size distribution are critical for
stable operation.
โข Ash Handling: Effective management of ash and solid residues
produced during combustion.
โข Control Systems: Advanced control systems are required to
optimize combustion efficiency and minimize emissions.
