The document discusses the different types of centrifugal fans used in power plant boilers. It describes the purpose of boilers in converting water to steam using heat from fuel combustion. It outlines the major types of draft fans - forced draft fans which force air into the system and induced draft fans which draw exhaust gases out. These include backward curved and airfoil centrifugal fans. It also discusses primary air fans which supply air for fuel conveying and flue gas recirculation fans which reduce nitrogen oxide emissions by recirculating exhaust gases back into the combustion chamber. Centrifugal fans of various types are used depending on system requirements.

1. Types Of Centrifugal Fans Used
In Power Plant Boilers
Neel RaoNeel Rao
Writes on Centrifugal Fan & Centrifugal blowerWrites on Centrifugal Fan & Centrifugal blower
technologies for Reitz Indiatechnologies for Reitz India

2. The purpose of boiler in thermal power plants is to covert water into steam
with the help of heat energy generated by the combustion of fuels like coal,
wood, oil or natural gas. Boiler systems use several types of fans to maintain
air flow, recirculate air and remove exhaust gases. Based on the boiler size
and air flow requirement different fans are used with varied capabilities.
Predominantly, draft fans play an important role in thermal power plants
because they regulate the air pressure inside boiler system. Draft fans are
broadly divided into two types – Forced Draft (FD Fan) and Induced Draft (ID
Fan). Apart from the draft fans, there are also other basic types of process
fans used in power plants. They are primary air fans and flue gas recirculation
fans.

3. Draft Fans
The primary difference between a forced draft and induced draft is, FD fan
forces outside air into the heating system whereas ID fan draws flue gases
from the system out into the atmosphere. Both FD fan & ID fan operate in
such a way that it balances the air system in the boiler to make the
combustion process efficient.
Forced Draft Fan

FD fan or forced draft fan, draws air from the atmosphere and forces it into
the furnace through a preheater. These fans are located at the inlet of the
boiler to push high pressure fresh air into combustion chamber, where it
mixes with the fuel to produce positive pressure.The most common
centrifugal fans used as FD fans are backward curved and airfoil centrifugal
fans.

4. Draft Fans - Continued
Forced Draft Fan

In power plants, where coal is used as fuel for combustion, FD fans are used
as secondary air fans to regulate proper combustion and maximize
efficiency of the fuel.

A typical FD fan arrangement uses inlet and outlet dampers to control and
maintain the required air pressure inside the system. These fans have a
wheel at the center that is hung on the shaft along with inlet boxes,
silencer, filter and rain hood.

When compared to ID fans, FD fans are easier to maintain and have cleaner
operating conditions.

5. Draft Fans - Continued
Induced Draft Fan

Induced draft fan is normally located at the outlet between dust collector
and chimney.

The fan takes hot flue gases from the boiler through dust collector and
delivers it to the chimney into the open atmosphere. ID fan creates negative
pressure or suction to discharge the gases out after combustion from the
furnace.

Since ID fans can handle hot flue gases, they have more corrosion and
erosion problems even when used with Electrostatic precipitators.

The most common type of fans that can be used as ID fans are radial fans
and backward inclined blade centrifugal fans.

6. Other process fans
PA fans

The main function of the Primary air fan or PA fan is to carry fuel to the
furnace for combustion.

In power plants PA fans supply air for conveying of the pulverized coal from
coal mills to the furnace area. These fans produce a pressure upstream the
pulverizer, to push the coal and air mixture through pulverizer into the
furnace.

The most common centrifugal fan used as PA fan is backward curved
centrifugal fan.

7. Other process fans - Continued
Flue gas recirculation fans

Gas recirculation fans (FGR) are typically used in power plant boilers to
reduce the flue gas pollution content in the gases exhausted from thermal
combustion processes.

Flue gas re-circulation is a highly effective technique that significantly
reduces the Nitrogen oxide (NOx) emissions from burners. Controlling NOx
is critical as it the largest contributor to other types of harmful pollutants.
NOx emissions are mostly derived from the nitrogen in the combustion air
(thermal NOx). These pollutants are produced during combustion process
when nitrogen and oxygen react at elevated temperatures.

8. Other process fans - Continued
Flue gas recirculation fans

NOx emission levels can be greatly reduced in industrial boilers by
recirculating the flue gases from the boiler exhaust duct into the main
combustion chamber.

Most common types of gas re-circulation fans are backward curved
centrifugal fans.
In power plants, industrial fans play an important role in supplying air
necessary for fuel combustion and in the maintenance of furnace
temperature. Centrifugal fans of various types and capacities are used as
process fans in power plants depending on the system requirement and
industrial process.

9. About REITZINDIA
Reitz India has set a benchmark to deliver high quality fans for heavy duty
industries which can work at precise operating conditions like high
temperatures and pressures. Reitz offer idealistic Centrifugal Fan and
Centrifugal blower design that can be used in all large scale process
industries like cement, iron & steel, power plants, fertilizers/ chemicals and
more.
Thank you for spending your precious time in reading this article!

10. About REITZINDIA
Reitz India has set a benchmark to deliver high quality fans for heavy duty
industries which can work at precise operating conditions like high
temperatures and pressures. Reitz offer idealistic Centrifugal Fan and
Centrifugal blower design that can be used in all large scale process
industries like cement, iron & steel, power plants, fertilizers/ chemicals and
more.
Thank you for spending your precious time in reading this article!