On

PERFORMANCE OPTIMIZATION OF FORCED DRAFT

FAN

Of

BUDGE BUDGE GENERATING STATION UNIT # 1

By

Saikat Halder

Of

MECHANICAL ENGINEERING DEPERTMENT

INDIAN INSTITUTE OF ENGINEERING SCIENCE AND

TECHNOLOGY, SHIBPUR

Under the guidance of

MR. SAMIR BANDYOPADHYAY

SENIOR MANAGER, MECHANICAL MAINTAINANCE

BUDGE BUDGE GENERATING STATION

CESC LIMITED

In

Page I

BUDGE BUDGE GENERATING STATION

CESC LIMITED

PUJALI, BUDGE BUDGE

SOUTH 24 PARGANAS, WEST BENGAL

CERTIFICATE OF DECLARATION

This is to certify that Mr. Saikat Halder, 3rd year undergraduate student of Mechanical

Engineering, Indian Institute of Engineering Science and Technology, Shibpur has

successfully completed the project titled “ Performance Optimization of Forced Draft

Fan “ under my supervision and guidance during the summer internship programme,

UNMESH 2015.

Dated: ……………………………...

(Mr. Samir Bandyopadhyay)

Senior Manager, Mechanical Maintenance Department

Budge Budge Generating Station

CESC Limited.

Page II

ACKNOWLEDGEMENT

At the onset I must thank all the people at BBGS without whose active support this project

would not have materialized. In view of this I would like to extend my sincere thanks and

gratitude to everyone who has supported me during the ‘UNMESH 2015’ internship

programme.

I take this opportunity to express my sincere thanks to my project guide, Mr. Samir

Bandyopadhyay, Senior Manager, Mechanical Maintenance Department for his

invaluable guidance, advice, constant encouragement and enlightening discussions during the

course of the Summer Internship Programme, Unmesh-2015 at Budge Budge Generating

Station without which it would not have been possible for me to give the progress report in this

shape.

I would also thank Mr. Debashish Chatterjee, Mr. Subir Roy, Mr. Jagannath

Chakrovorty, Mr. Debashish Mandal and Mr. Sujoy Sahu for their constant support and

guidance.

I would also thank my Institution and the HRD Department of CESC Limited without whom

this project would have been a distant reality. I also extend my heartfelt thanks to my family

and well-wishers.

Dated: ………………………………

(Saikat Halder)

B.E 3rd year Undergraduate

Mechanical Engineering Department

IIEST, Shibpur.

Page III

CONTENTS

1. An overview of fans

1.1. Fans

1.2. Fan Types

1.3. Basic Fan Theory

2. A Brief Overview of Budge Budge Generating Station

3. Air and Flue Gas Path of BBGS Unit # 1

4. Result and Discussion

4.1. Measurement of various fan parameters

4.2. Fan design efficiency

4.3. Example: Performance Test Calculation on FD Fan

4.4. Discussion and analysis

4.5. Causes of low operating efficiency and high power consumption

4.6. Remedial suggestions for improving the operational efficiency

5. Conclusion

Page IV

ILLUSTRATIONS

LIST OF DIAGRAMS

Sl. Description Page Number

1 Centrifugal Fan 2

2 Axial Fan 2

3 Forward-Curved Centrifugal Fan Blades and its Performance Curve 3

4 Radial Blade Centrifugal Fan 3

5 Radial Blade Fan curve 4

6 Radial-Tip Centrifugal Fan 4

7 Backward-Inclined Centrifugal Fans 5

8 Backward-Inclined Centrifugal Air foil Fan and Backward-Inclined Fan Curve 5

9 Propeller Fan and Propeller Fan Curve 6

10 Tube axial Fan and Tube axial Fan Curve 7

11 Vane axial Fan and Vane axial Fan Curve 8

12 Air and Flue gas path of BBGS Unit # 1 16

LIST OF GRAPHS

Sl. Description Page Number

1 Fan Characteristics Curve 10

2 H-Q Curve of FD Fan-A 31

3 H-Q Curve of FD Fan-A 31

LIST OF TABLES

Sl. Description Page Number

1 Differences between Fans, Blower and Compressor 1

2 Fan Efficiencies 2

3 FD Fan parameter and Motor parameter 17-18

4 Parameters of FD Fan-A 21-22

5 Parameters of FD Fan-B 23-24

6 Calculated Data of FD Fan-A 26-28

7 Calculated Data of FD Fan-B 28-30

Page V

LIST OF ABBREVIATIONS USED

ASME American Society of Mechanical Engineers

BBGS Budge Budge Generating Station

BMCR Boiler Maximum Continuous Rating

BHEL Bharat Heavy Electricals Limited

BHP Break Horse Power

FD Forced Draught

FDF Forced Draught Fan

HVAC Heating, Ventilation and Air Conditioning

ID Induced Draught

kW Kilowatt

kV Kilovolt

PA Primary Air

RPM Revolutions per Minute

SC System Curve

VFD Variable Frequency Drive

WC Water Column

Page VI

Executive Summary

Objective

The objective of this project is to monitor, analyse and optimise the performance of Forced

Draft Fans of Budge Budge Generating Station Unit #1.

Introduction

Energy projects are among the most capital intensive infrastructure investments. Decisions

made today will form our lives for decades, and it is important that these decisions are based

on facts and a proper economic assessment of available options. The global power sector is

facing a number of issues, but the most fundamental challenge is meeting the rapidly growing

demand for energy services in a sustainable way, at an affordable cost and in the

environmentally acceptable manner. This challenge is further compounded by the fact that the

major part of the increase in demand for power and hence in the emissions in the future, will

come from developing countries, who strive to achieve a rapid economic development.

A power plant produces electrical energy and also consumes substantial amount of this energy

in the form of auxiliary consumption. Auxiliary power comprises the power consumption by

all the unit auxiliaries as well as the common station requirement such as station lighting, air

conditioning etc. Plant ‘auxiliaries’ include all motor-driven loads, all electrical power

conversion and distribution equipment, and all instruments and controls.

This auxiliary equipment has a critical role in the safe operation of the plant and equipment

used for auxiliary power are varying for different types of power plant. Reduction of auxiliary

power consumption could thus help increase the efficiency of a power plant.

Forced Draft (FD) fans provide control for draft and forced air zoning of fuel burned furnaces

of steam generation plant of a thermal power plant. Forced Draft (FD) fans are used for

supplying the combustion air into the furnace of a boiler. A good design of fan and its control

system increases plant reliability by improving furnace pressure control and airflow control,

which is most critical control part of combustion control system. In this report, the performance

evolution, monitoring and optimization of Forced Draft fan of BBGS unit #1 has represented.

1

Chapter-1

An overview of fans

1.1 Fans:

Fans provide air for ventilation and industrial process requirements. Fans generate a

pressure to move air (or gases) against a resistance caused by ducts, dampers, or other

components in a fan system. The fan rotor receives energy from a rotating shaft and transmits

it to the air.

Difference between Fans, Blowers and Compressors

Fans, blowers and compressors are

differentiated by the method used to

move the air, and by the system pressure

they must operate against. As per

American Society of Mechanical

Engineers (ASME) the specific ratio –

the ratio of the discharge pressure over

the suction pressure – is used for

defining the fans, blowers and

compressors (see Table 1.1).

1.2 Fan Types

Fan selection depends on the volume flow

rate, pressure, type of material handled, space

limitations, and efficiency. Fan efficiencies

differ from design to design and also by types.

Typical ranges of fan efficiencies are given in

Table 1.2.

Fans fall into two general categories: centrifugal

flow and axial flow.

In centrifugal flow, airflow changes direction

twice - once when entering and second when

leaving (forward curved, backward curved or

inclined, radial) (see Figure 1.1).

In axial flow, air enters and leaves the fan with

no change in direction (propeller, tube axial,

vane axial) (see Figure 1.2).

TABLE 1.1 DIFFERENCES BETWEEN

FANS, BLOWER AND COMPRESSOR

Equipment Specific Ratio Pressure rise

(mm Wg)

Fans Up to 1.11

1136

Blowers 1.11 to 1.20 1136 – 2066

Compressors more than 1.20 –

TABLE 1.2 FAN EFFICIENCIES

2

Figure 1.1: Centrifugal Fan Figure 1.2: Axial Fan

1.2.1 Centrifugal Fans

Centrifugal fans are the most commonly used type of industrial fan. Centrifugal fans

are capable of generating high pressures with high efficiencies, and they can be constructed to

accommodate harsh operating conditions. Centrifugal fans have several types of blade shapes,

including forward curved, radial-blade, radial-tip, backward-inclined, backward-curved, and

air foil. Some centrifugal fan types are capable of serving widely varying operating conditions,

which can be a significant advantage.

I. Forward-Curved Centrifugal Fans

This fan type, shown in Figure 1.3, has blades that curve in the direction of rotation. This

fan type is typically used in applications that require low to medium air volumes at low

pressure. It is characterized by relatively low efficiency (between 60 and 65 percent). This fan

type can operate at relatively low speeds, which translates to low levels of noise. Forward

curved fans are commonly selected because of their small size relative to other fan types. Stress

levels in fans are closely related to operating speed; consequently, forward-curved fans do not

require high-strength design attributes. Their low operating speed also makes them quiet and

well suited for residential heating, ventilation, and air conditioning (HVAC) applications. A

typical performance curve is shown in Figure 1.3. The dip in the performance curve represents

a stall region that can create operating problems at low airflow rates.

Forward-curved fans are usually limited to clean service applications. These fans are typically

not constructed for high pressures or harsh service. Also, fan output is difficult to adjust

accurately (note how the fan curve is somewhat horizontal), and these fans are not used where

airflow must be closely controlled. Forward-curved fans have a power curve that increases

steadily with airflow toward free delivery; consequently, careful driver selection is required to

avoid overloading the fan motor.

3

II. Radial Blade Centrifugal Fan

Shown in Figure 1.4, this type is commonly used in applications with low to medium

airflow rates at high pressures. The flat blade shape limits material build-up; consequently,

these fans are capable of handling high-particulate airstreams, including dust, wood chips, and

metal scrap.

This fan type is characteristically rugged. The

simple design of these fans allows many small

metalworking shops to custom build units for

special applications. In many cases, the blades

can be inexpensively coated with protective

compounds to improve erosion and corrosion

resistance. The large clearances between the

blades also allow this fan to operate at low

airflows without the vibration problems that

usually accompany operating in stall. The

characteristic durability of this fan type is a

key reason why it is considered an industry

workhorse. Figure 1.4: Radial Blade Centrifugal Fan

A typical fan curve for radial fans is shown in

Figure 1.5.

Figure 1.3: Forward-Curved Centrifugal Fan Blades and its Performance Curve

4

Figure 1.5: Radial Blade Fan curve

III. Radial-Tip Centrifugal Fan

This fan type fills the gap between clean-air fans and the more rugged radial-blade fans.

Radial-tip fans are characterized by a low angle of attack between the blades and the incoming

air, which promotes low turbulence. A radial

tip fan is shown in Figure 1.6.

Radial-tip fans have many of the characteristics

of radial-blade fans and are well-suited for use

with airstreams that have small particulates at

moderate concentrations and airstreams with

high moisture contents. Radial-tip fans can

have efficiencies up to 75 percent. These fans

are commonly used in airborne-solids handling

services because they have large running

clearances.

Figure 1.6: Radial-Tip Centrifugal Fan

IV. Backward-Inclined Centrifugal Fans

This fan type is characterized by blades that tilt away from the direction of rotation.

Within backward-inclined fans are three different blade shapes: flat, curved, and air foil. Flat

blade types, shown in Figure 1.7, are more robust. Curved-blade fans tend to be more efficient.

Air foil blades, shown in Figure 1.8, are the most efficient of all, capable of achieving

efficiencies exceeding 85 percent. Because air foil blades rely on the lift created by each blade,

this fan type is highly susceptible to unstable operation because of stall.

5

A consequence of backward-incline blade orientation is a low angle of impingement with the

airstream. This promotes the accumulation of particulates on the fan blades, which can create

performance problems. Thin air foil blades are more efficient than the other blade types because

of their lower rotating mass. However, this thin walled characteristic makes this fan type highly

Susceptible to erosion problems. Loss of blade wall thickness can lead to cavity formation in

the blades, which can severely interfere with fan performance.

A common application for backward-inclined fans is forced-draft service. In these applications,

the fan is exposed to the relatively clean

airstream on the upstream side of the process.

The high operating efficiencies available

from this fan type can provide low system

life-cycle costs. A typical performance curve

is shown in Figure 1.8. The motor brake

horsepower increases with airflow for most

of the performance curve but drops off at

high airflow rates. Because of this non-

overloading motor characteristic, this fan

type is often selected when system behaviour

at high airflow rates is uncertain.

Figure 1.7: Backward-Inclined Centrifugal Fans

’

Figure 1.8: Backward-Inclined Centrifugal Air foil Fan and Backward-Inclined Fan Curve

1.2.2 Axial Fans

The key advantages of axial airflow fans are compactness, low cost, and light weight. Axial

6

fans are frequently used in exhaust applications where airborne particulate size is small, such

as dust streams, smoke, and steam. Axial fans are also useful in ventilation applications that

require the ability to generate reverse airflow. Although the fans are typically designed to

generate flow in one direction, they can operate in the reverse direction. This characteristic is

useful when a space may require contaminated air to be exhausted or fresh air to be supplied.

I. Propeller Fans

The simplest version of an axial fan is the propeller type, shown in Figure 1.9. Propeller

fans generate high airflow rates at low pressures. Because propeller fans do not generate much

pressure, they are usually not combined with extensive ductwork. Propeller fans tend to have

relatively low efficiencies, but they are inexpensive because of their simple construction.

Propeller fans tend to be comparatively noisy, reflecting their inefficient operation.

As shown in Figure 1.9, the power requirements of propeller fans decrease with increases in

airflow. They achieve maximum efficiency, near-free delivery, and are often used in rooftop

ventilation applications.

Figure 1.9: Propeller Fan and Propeller Fan Curve

II. Tube axial Fans

A more complex version of a propeller fan is the tube axial fan. This type, shown in Figure

1.10, is essentially a propeller fan placed inside a cylinder. By improving the airflow

characteristics, tube axial fans achieve higher pressures and better operating efficiencies than

propeller fans. Tube axial fans are used in medium-pressure, high airflow rate applications and

are well-suited for ducted HVAC installations. The airflow profile downstream of the fan is

uneven, with a large rotational component. This airflow characteristic is accompanied by

moderate airflow noise. Tube axial fans are frequently used in exhaust applications because

they create sufficient pressure to overcome duct losses and are relatively space efficient. Also,

7

because of their low rotating mass, they can quickly accelerate to rated speed, which is useful

in many ventilation applications. The performance curve for tube axial fans is shown in Figure

1.10. Much like propeller fans, tube axial fans have a pronounced instability region that should

be avoided. Tube axial fans can be either connected directly to a motor or driven through a belt

configuration. Because of the high operating speeds of 2-, 4-, and 6-pole motors, most tube

axial fans use belt drives to achieve fan speeds below 1,100 revolutions per minute.

Figure 1.10: Tube axial Fan and Tube axial Fan Curve

III. Vane axial Fans

A further refinement of the axial fan is the vane axial fan. As shown in Figure 1.11, a vane

axial fan is essentially a tube axial fan with outlet vanes that improve the airflow pattern,

converting the airstream’s kinetic energy to pressure. These vanes create an airflow profile that

is comparatively uniform.

Vane axial fans are typically used in medium- to high-pressure applications, such as induced

draft service for a boiler exhaust. Like tube axial fans, vane axial fans tend to have a low

rotating mass, which allows them to achieve operating speed relatively quickly. This

characteristic is useful in emergency ventilation applications where quick air removal or supply

is required. Also, like other axial fans, vane axial fans can generate flow in reverse direction,

which is also helpful in ventilation applications. Depending on the circumstances, these

applications may require the supply of fresh air or the removal of contaminated air. Vane axial

fans are often equipped with variable pitch blades, which can be adjusted to change the angle

of attack to the incoming airstream. Variable pitch blades can change the load on the fan,

providing an effective and efficient method of airflow control.

As shown in Figure 1.11, vane axial fans have performance curves that have unstable regions

to the left of the peak pressure. These fans are highly efficient. When equipped with air foil

8

blades and built with small clearances, they can achieve efficiencies up to 85 percent. Vane

axial fans are frequently connected directly to a motor shaft.

Figure 1.11: Vane axial Fan and Vane axial Fan Curve

1.3. Basic Fan Theory

1.3.1. Principle of Operation

System that require air flow are normally supplied by one or more fans of

various types, driven by a motor.

The motor rotates the fan which delivers air to the system as it develops a

pressure in the ductwork (or air pathways) that causes the air to move through

the system.

Moving air in a streamline has energy due to the fact that it is moving and it is

under pressure.

In terms of air movement, Bernoulli’s theorem states that static pressure plus velocity pressure

at a point upstream in the direction of air flow is equals to the static pressure plus velocity

pressure as measured at a point downstream in the direction of air flow plus the friction and

dynamic losses between the two measuring point.

The motor imparts energy to the fan, which in turn transfers energy to the moving air. The duct

system contains and transports the air. This process causes some losses in static pressure due

to friction with walls and changes in the direction of flow (due to elbow and other fittings), as

well as air losses through unintentional leaks.

9

1.3.2. System Characteristics

The term "system resistance" is used when referring to the static pressure. The system

resistance is the sum of static pressure losses in the system. The system resistance is a function

of the configuration of ducts, pickups, elbows and the pressure drops across equipment-for

example back filter or cyclone. The system resistance varies with the square of the volume of

air flowing through the system. For a given volume of air, the fan in a system with narrow ducts

and multiple short radius elbows is going to have to work harder to overcome a greater system

resistance than it would in a system with larger ducts and a minimum number of long radius

turns. Long narrow ducts with many bends and twists will require more energy to pull the air

through them. Consequently, for a given fan speed, the fan will be able to pull less air through

this system than through a short system with no elbows. Thus, the system resistance increases

substantially as the volume of air flowing through the system increases; square of air flow.

Conversely, resistance decreases as flow decreases. To determine what volume the fan will

produce, it is therefore necessary to know the system resistance characteristics. In existing

systems, the system resistance can be measured. In systems that have been designed, but not

built, the system resistance must be calculated.

1.3.3. Fan Characteristics

Fan characteristics can be represented in form of fan curve(s). The fan curve is a

performance curve for the particular fan under a specific set of conditions. The fan curve is a

graphical representation of a number of inter-related parameters. Typically a curve will be

developed for a given set of conditions usually including: fan volume, system static pressure,

fan speed, and brake horsepower required to drive the fan under the stated conditions. Some

fan curves will also include an efficiency curve so that a system designer will know where on

that curve the fan will be operating under the chosen conditions (see Figure 1.12). In the many

curves shown in the Figure, the curve static pressure (SP) vs. flow is especially important.

The intersection of the system curve and the static pressure curve defines the operating point.

When the system resistance changes, the operating point also changes. Once the operating point

is fixed, the power required could be found by following a vertical line that passes through the

operating point to an intersection with the power (BHP) curve. A horizontal line drawn through

the intersection with the power curve will lead to the required power on the right vertical axis.

In the depicted curves, the fan efficiency curve is also presented.

10

Figure 1.12: Fan Characteristics Curve

1.3.4. Fan Laws

Rotational speed: Fan rotational speed is measured in terms of Revolution per Minute

(RPM). Fan rotational speed affects fan performance, as shown by the following fan laws. Air

flow rates vary in direct proportion to the rotational speed of the fan:

𝐴𝑖𝑟𝑓𝑙𝑜𝑤𝑓𝑖𝑛𝑎𝑙 = 𝐴𝑖𝑟𝑓𝑙𝑜𝑤𝑖𝑛𝑖𝑡𝑖𝑎𝑙 * 𝑅𝑃𝑀𝑓𝑖𝑛𝑎𝑙

𝑅𝑃𝑀𝑖𝑛𝑖𝑡𝑖𝑎𝑙…………………………….. (1)

Pressure built up by the fan varies as the square of the rotational speed of the fan:

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑓𝑖𝑛𝑎𝑙 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑖𝑛𝑖𝑡𝑖𝑎𝑙 * (𝑅𝑃𝑀𝑓𝑖𝑛𝑎𝑙

𝑅𝑃𝑀𝑖𝑛𝑖𝑡𝑖𝑎𝑙)

2…………………… (2)

Power required by the fan varies with the cube power of the rotational speed of the fan:

𝑃𝑜𝑤𝑒𝑟𝑓𝑖𝑛𝑎𝑙 = 𝑃𝑜𝑤𝑒𝑟𝑖𝑛𝑖𝑡𝑖𝑎𝑙 * (𝑅𝑃𝑀𝑓𝑖𝑛𝑎𝑙

𝑅𝑃𝑀𝑖𝑛𝑖𝑡𝑖𝑎𝑙)

3……………………… (3)

Care needs to be taken when using the fan laws to calculate the effect of changes in fan speed,

since these laws apply to a specific density of gaseous medium. When fan speeds changes are

accompanied by significant changes in other parameters such as gas composition, moisture

11

content and temperature, the fan laws will need to be adjusted accordingly to compensate for

the resulting change in medium density.

To avoid overloading the motor, some types of fans must be sized appropriately for the air flow

rate and pressure requirement.in particular, forward-curved blade centrifugal fans, which are

capable of generating high airflow at relatively low speeds, can readily provide excessive

airflow and pressure and overload the motor if operated at too high a speed for the application.

Moreover, operating the fan bellow the required speed can cause insufficient air flow through

the system.

Air stream temperature has an important impact on fan-speed limits because of the effect of

heat on the mechanical strength of most materials.

1.3.5. Fan Efficiency

Performance Terms and Definitions

Static Pressure: The absolute pressure at a point minus the reference atmospheric pressure.

Dynamic Pressure: The rise in static pressure which occurs when air moving with specified

velocity at a point is bought to rest without loss of mechanical energy. It is also known as

velocity pressure.

Total Pressure: The sum of static pressures and dynamic pressures at a point.

Motor Input Power: The electrical power supplied to the terminals of an electric motor drive.

Fan Shaft Power: The mechanical power supplied to the fan shaft.

Fan manufacturers generally use two ways to mention fan efficiency: mechanical

efficiency (sometimes called the total efficiency) and static efficiency. Both measure how well

the fan converts horsepower into flow and pressure.

The equation for determining total efficiency is:

𝜂𝑡𝑜𝑡𝑎𝑙 % = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑚ᵌ/ sec ∗ 𝛥𝑃 ( 𝑡𝑜𝑡𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒)𝑖𝑛 𝑚𝑚𝑊𝐶

102 ∗ 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑎𝑛 𝑠ℎ𝑎𝑓𝑡 * 100…….………... (4)

The static efficiency equation is the same except that the outlet velocity pressure is not added

to the fan static pressure:

𝜂𝑠𝑡𝑎𝑡𝑖𝑐 % = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑚ᵌ/ sec ∗ 𝛥𝑃 ( 𝑠𝑡𝑎𝑡𝑖𝑐 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒)𝑖𝑛 𝑚𝑚𝑊𝐶

102 ∗ 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑎𝑛 𝑠ℎ𝑎𝑓𝑡 * 100………………… (5)

Determination of Power Input to the fan shaft

Power Measurement: The power measurements can be done using a suitable clamp- on power

meter. Alternatively by measuring the amps, voltage and assuming a power factor of the power

can be calculated as below:

12

𝑃 = √3 * V*I*cos 𝛷……………………………………………... (6)

Transmission Systems: The interposition of a transmission system may be unavoidable

introducing additional uncertainties.

𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑎𝑛 𝑠ℎ𝑎𝑓𝑡 = 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑚𝑜𝑡𝑜𝑟 ∗ 𝜂𝑚𝑜𝑡𝑜𝑟 ∗ 𝜂𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 ……... (7)

Best Efficiency Point

The best efficiency point (BEP) is a point on the operating characteristics of the fan where a

fan operates most efficiently and cost-effectively in terms of both energy use and cost of

maintenance/replacement.

Operation of a fan near its BEP results in high efficiency and reduced wear and tear on the

equipment. Operation far away from the BEP results in lower fan efficiency, increased bearing

loads and higher noise levels.

1.3.6. Fan Design and Selection Criteria

Precise determination of air-flow and required outlet pressure are most important in

proper selection of fan type and size. The air-flow required depends on the process

requirements; normally determined from heat transfer rates, or combustion air or flue gas to be

handled.

System pressure requirement is usually more difficult to compute or predict. Detailed analysis

should be carried out to determine pressure drop across the length, bends, contractions and

expansions in the ducting system, pressure drop across filters, drop in branch lines, etc. These

pressure drops should be added to any fixed pressure required by the process (in the case of

ventilation fans there is no fixed pressure requirement). Frequently, a very conservative

approach is adopted allocating large safety margins, resulting in over-sized fans which operate

at flow rates much below their design values and, consequently, at very poor efficiency.

Once the system flow and pressure requirements are determined, the fan and impeller type are

then selected. For best results, values should be obtained from the manufacturer for specific

fans and impellers.

The choice of fan type for a given application depends on the magnitudes of required flow and

static pressure. For a given fan type, the selection of the appropriate impeller depends

additionally on rotational speed. Speed of operation varies with the application. High speed

small units are generally more economical because of their higher hydraulic efficiency and

relatively low cost. However, at low pressure ratios, large, low-speed units are preferable.

13

Chapter-2

A BRIEF OVERVIEW OF BUDGE BUDGE GENERATING STATION

Capacity 750 MW (3 x 250 MW)

Location PUJALI, BUDGE BUDGE, 24 PGS(S), WEST BENGAL

COMMERCIAL GENERATION

Unit # 1 07.10.97

Unit # 2 01.07.99

Unit # 3 28.01.10

Fuel source ECL, BCCL, ICML & Imported Coals

Fuel requirement 2.45 million tons of coal per annum

Mode of transportation Rail

Water source River Hooghly

Land area 225 acres

Ash dumping area 91 acres

Type and Make of Boiler:

Type- Horizontal Single Drum, Natural Circulation, Water Wall Tube, Two Pass, Balanced Draft,

Single Reheat, Pulverized Fuel Boiler with Common Cold PA Fan.

Make- M/S ABB ABL Limited, Durgapur, W.B. (Unit#1&2) M/S BHEL (Unit#3)

Type and Make of Turbine:

Type- Tandem Compounded, Three Cylinder, Single Reheat, Double Flow LP cylinder, Condensing

Type with uncontrolled Extraction.

Make- NEI Parsons, UK.

Type and Make of Generator:

Type- 250 MW, 3Ø Alternator with Hydrogen cooled Rotor and Stator Core and DM water cooled

Stator Windings (Unit 1&2) at a speed of 3,000 rpm.

Make- NEI Parsons.

Others

ISO 9001:2008, ISO 14001:2004 & OHSAS 18001:2007 certified

14

Chapter-3

AIR AND FLUE GAS PATH OF BBGS UNIT # 1

The detailed description of air and flue gas path of BBGS Unit # 1 is described below. There

are three basic type of fans used, namely ID, FD and PA fan. Besides these three types of fans

there are two important fans are there one is seal air fan and other is scanner fan. A brief

description is given below.

2.1. Purpose of Fans

Supply air for combustion in the furnace and for evacuation of the flue gases formed

from the combustion.

Maintain Balanced Draft inside the furnace.

Supply air for cooling of equipment working in hot zones.

Supply air for sealing of gates, feeders & mills bearings etc.

Air used for combustion is divided into 2 parts:

1. Primary Air

Portion of total air sent through mills to the furnace. This air dries the pulverized coal and

transport it to the furnace for combustion.

2. Secondary Air

Large portion of total air sent to furnace to supply necessary oxygen for the combustion.

FD FAN

Supplies secondary air to the furnace through APH to assist in combustion. Supply total air

flow to the furnace except where an independent atmospheric P.A fan is used. Provides air for

sealing requirement and excess air requirement in the furnace.

PA FAN

Supply high pressure primary air through APH needed to dry & transport coal directly from

the coal mills to the furnace.

Primary air for mills is divided into cold & hot primary air.

ID FAN

Suck the gases out of the furnace and throw them into the stack by creating sufficient negative

pressure in the furnace (5-10 mm WC) in the balanced draft units.

Located in between the ESP and Chimney in the flue gas path. Radial Fans -double suction-

backward curved vane with inlet guide vane (IGV) control and VFD control is use in all boilers

15

Handles large volume hot dust/ash laden flue gas (temp up to 150° C) from furnace and all

leakages occurring in the system till the inlet of the fan.

Overcome the pressure drop inside the furnace, Super heater, Re -heater, Economiser, Gas

ducting & ESP.

Consumes max. power in all boiler auxiliaries as it handles the large volume and heavy pressure

drop of the flue gas.

SCANNER AIR FANS

Scanner Air Fan is belong to Centrifugal Fan category.

Supply cooling air to all the flame scanners at different elevations housed in the furnace for

sensing flame.

A.C scanner fan boost the pressure of cold secondary air from F.D fan discharge duct in normal

operation.

D.C scanner operates only in case of a.c power failure and sucks air directly from the

atmosphere.

SEAL AIR FANS

Seal Air Fan is also belong to Centrifugal Fan category.

Supply seal air at a pressure higher than system or equipment pressure.

Supply seal air to raw coal feeders, mills bearings, gates etc.

Seal fan either boost the pressure of cold secondary air from F.D fan discharge duct or takes

air directly from the atmosphere in normal operation.

ID is "Induced Draft" and FD is "Forced Draft." In an induced draft system, the fan is at the

exit end of the path of flow, and the system is under negative pressure - that is, the pressure in

the flow area is below atmospheric, because the air is being drawn through the fan. In a forced

draft system the fan is at the entry end of the path of flow. It operates at positive pressure

because outside air is drawn into the fan and forced into the system.

The detailed diagram of air and gas path of BBGS Unit #1 is given in the Figure 3.1.

2.2. Air and Flue gas path of BBGS Unit # 1

The detailed diagram of air and flue gas path of BBGS unit #1 is given in the figure 3.1.

The atmospheric air enters through inlet air damper, filter and silencer to FD Fan A and B at

atmospheric pressure and then it is released at some higher pressure by the FD Fans to a

common discharge bus. From this discharge bus the air is divided into four segments. Two of

which goes to the secondary air heater A and B, where the cold air is pre-heated by the flue

gases coming out from the boiler and then this air goes to the boiler for combustion. Cold air

by-pass arrangement is there.

16

Figure 3.1: Air and Flue gas path of BBGS Unit # 1

17

During starting of the boiler after shut down, there is not enough temperature of the flue gasses,

so on that time the cold air is directly by-passed to the boiler through cold air by-pass without

sending it to the secondary air heater. In normal operating condition the cold air by-pass duct

is closed and the cold air is directed to the boiler through secondary air heater.

The other two segments from the common air bus is directed to PA Fan A and B and some

pressure rise took place there. After discharge from PA Fan A and B the air from both fan

comes to a duct and from there by a cold air tapping arrangement some cold air goes to the

mill. Rest of the air goes to the primary air heater and the air is heated by the flue gasses in the

primary air heater. After coming out from the primary air heater the hot gasses also directed to

the mill. In the mill the hot air from primary air heater and cold air from cold air tapping

arrangement before primary air heater get mixed. The temperature of the mixed air is controlled

by controlling the flow of cold and hot air after the PA Fan. The mixed air is then goes to the

mill dries down and flows away the pulverised coal to the boiler.

The hot flue gasses from boiler first goes to the economiser. After coming out eco top and

bottom bank the flue gasses goes to the primary and secondary air heater. From there it comes

to a common duct and then goes to ESP A and ESP B where ash particles present in the flue

gases get separated and then it goes to the atmosphere through ID Fan A, B and C and chimney.

The primary parameters of the forced draft fan and motor are as follows:

FD Fan parameter Motor parameter Particulars Unit Design parameter Particulars Unit Design parameter

Type Double inlet box,

constant speed

Type SCIM/ 1LA7 716-

6H.70-Z1

Specification Z9 size 207000 Rated voltage kV 6.6

Control

mode

Inlet Louvre

Dampers

Rated power kW 1182

Max Air

Quantity mᵌ/sec 196.65 Rated speed RPM 995

Air pressure mm

WG

397 No load

current

Amps 41.0

Temperature °C 45 Full load

current

Amps 126.0

Absorbed

power

Kw 1035 Max.

permitted

medium

temperature

°C

70

Rotation

speed

RPM 980 No of pole 6

Size and

design of

bearing

6’’ dia Sturtevant

type H.D. Bearing

Direction of

rotation

Clockwise

Method of

lubrication

Oil Disc Bath with

Circulating System

Method of

cooling

TETV (IC 0151)

18

Manufacturer

Howden Sirocco

limited (Rotating

parts)

ACC Babcock,

Sturtevant

Bearing(Static

parts)

Manufacturer

Bharat Heavy

Electricals Limited

2.3. Principal Parts of FD Fan in BBGS Unit #1

IMPELLER

The impeller is of double inlet design, comprising a centreplate, parallel side plates,

backwardly inclined flat plate blades, hub and hub plates to provide lateral stiffness.

It is an all welded fabrication, constructed from suitable high quality materials, having all welds

inspected by an appropriate non-destructive (N.D.T.) method, before and after stress relieving.

The finished impeller is pressed on and keyed to its shaft.

The complete assembly (rotor) is dynamically balanced.

FAN CASING

The fan casing, complete with inlet boxes, forms a composite fabrication. It is of all welded,

steel plate construction, stiffened adequately where necessary.

Bolted and/or site welded joints are incorporated to suit transportation and installation.

A section is made removable to simplify replacement of the impeller/shaft assembly.

The casing is supported on landings at its base, and these are drilled for the necessary holding

down bolts.

INLET CONE

This is a steel plate, all welded fabrication fitted at the inlet to the impeller. It is shaped so as

to create a smooth passage for the gas flow into the impeller.

The cone is flanged for attachment to a convenient member and its fixing holes are large enough

to allow any necessary adjustment for alignment. After final positioning, the inlet cone is

dowelled to prevent movement.

SHAFT

The impeller shaft is designed to give a critical speed well above its running speed and is

accurately machined from a suitable grade of forged or rolled steel.

The machining surface finish on the panels which take the bearings, seals, impeller and

coupling is to the grade required for the part.

19

SHAFT SEAL

Where the fan shaft penetrates the fan casing, a seal is fitted to reduce the leakage to a

minimum.

It is of split construction, to simplify fitting, and consists of a disc of suitable flexible material,

e.g. Klingerit, supported between a steel carrier and cover plate.

When correctly fitted, the flexible disc would just touch the rotating shaft.

BEARING PEDESTALS

The pedestal is a robustly constructed, all welded, steel fabrication designed to support the

shaft bearing.

It is adequately stiffened and, where necessary, provided with hand holes to give access to

bolts.

COUPLING AND SHAFT GUARDS

Guards are fitted over all exposed running parts and are arranged for easy removal for access

purposes.

SHAFT BEARING

These are self-aligning sleeve bearings installed in robustly constructed cast iron housings.

Lubrication is provided by means of a rotating disc which lifts oil from the sump and deposits

it into the journal area at the top of the sleeve.

LOUVRE DAMPER CONTROL

The inlet Louvre Damper Assembly, which is fitted at the fan inlets, is a multi-bladed louver

damper of robust construction. The blades are of streamlined cross section and, when fully

open, create negligible resistance to gas flow.

The direction of closing of the blades is arranged so that, when partially closed, the gas is

induced to whirl in the direction of impeller rotation. This has the effect of reducing the

pressure volume characteristic of the fan with corresponding reduced power consumption

The blades are arranged in a frame. Each blade is carried by to flanged bearings. One end of

each spindle is extended and carries a lever, these levers are linked together and connected to

an operating shaft, which is connected with the power source, and is common to both fan inlets.

The blades are not individually adjustable.

20

Chapter-4

Result and Discussion

4.1. Measurement of various fan parameters

To assess the performance efficiency of FD fan A and B of unit #1, the readings of the

following parameters were taken:

1. Pressure of air at the discharge to each FD fan at different load.

2. Flow of each FD fan at different load.

3. Current requirement (Amps) of each FD fan at different load.

4. Inlet damper position of each FD fan at different load.

5. The average temperature of the air passing through the FD Fan.

The rated voltage of each fan is taken as 6.6 kV, the motor efficiency is taken as 95%, as there

is no transmission system attached with the motor to fan, the transmission efficiency is taken

as 99% with considering some slippage loss. The power factor of the motor is taken as 0.85 as

supplied by E&I department of BBGS. The suction pressure to the FD fan is considered as

atmospheric suction. The collected data of each fan are tabulated on the next page.

21

Parameters of FD Fan-A in tabulated form

Flow (tons/hr.) Head (mm WC) Current(Amps) Damper Position (%)

401.1 252 91 46.7

404.8 256 92 48.0

412.3 264 93 43.6

416.0 264 93 44.0

417.3 265 93 45.1

417.5 267 93 44.0

417.7 267 93 45.3

418.1 267 93 44.7

418.8 267 94 45.1

419.9 270 94 45.4

422.4 269 94 45.2

423.5 266 93 47.4

434.8 255 93 48.1

438.1 257 94 49.2

443.1 256 93 50.1

446.3 263 94 50.6

451.2 251 94 53.0

459.2 248 94 53.5

468.0 249 95 55.3

472.3 253 95 56.7

473.7 277 95 59.7

475.2 259 96 57.2

476.7 276 96 59.6

476.8 275 96 59.5

478.2 265 96 58.0

479.0 274 96 60.0

479.6 277 96 60.8

479.7 277 96 60.2

480.6 277 96 60.3

482.1 279 96 60.5

483.1 299 98 64.8

485.4 273 96 61.7

487.2 297 98 64.4

490.1 301 98 64.6

490.5 272 97 63.0

491.4 273 97 63.2

491.4 296 98 64.3

22

492.2 296 98 65.7

492.3 278 97 64.1

493.0 294 98 65.5

493.1 294 99 65.8

494.2 297 98 65.4

494.6 274 97 63.7

494.6 288 98 65.3

494.9 283 97 65.0

494.9 297 98 64.7

495.2 291 98 65.2

495.3 296 98 66.1

495.6 279 97 64.4

496.4 284 98 65.3

497.1 299 98 64.3

497.7 281 97 64.7

498.1 289 98 65.1

498.4 291 98 66.2

499.1 294 98 65.8

499.5 300 98 66.4

500.1 284 98 64.9

501.0 296 98 66.6

501.4 292 98 67.5

501.8 297 98 66.9

502.3 293 98 66.8

502.6 295 98 68.1

505.6 294 98 68.4

507.1 293 98 68.2

507.8 295 99 68.8

509.6 295 98 69.2

511.1 295 99 69.5

513.0 295 99 69.7

514.9 298 99 70.1

524.8 299 100 77.1

524.8 300 100 77.0

527.8 302 99 72.9

530.0 297 101 72.9

531.5 300 100 73.2

533.8 303 100 72.7

535.2 299 100 73.1

536.8 296 101 72.6

668.1 178 109 100.0

681.5 202 110 100.0

682.7 202 110 100.0

685.0 201 111 100.0

23

Parameters of FD Fan-B in tabulated form

Flow (tons/hr.) Head (mm WC) Current(Amps) Damper Position (%)

466.8 284 98 70.8

470 260 91 49

473.8 278 98 71.8

474.5 266 92 53.9

476 267 91 53.5

479.1 270 92 54.1

481 272 92 54.8

482.1 270 92 55.1

482.3 272 92 55.5

482.4 269 92 55.2

483.9 270 93 55.3

484 271 92 55.2

488.5 302 99 75.2

491.7 270 92 57.3

502.9 261 94 58.2

504.4 263 93 59.3

511 265 93 60.1

514 269 93 61.7

524 259 93 63

538 253 94 63.9

544.1 257 95 65.4

551.1 258 96 66.8

553.5 265 96 67.3

558.9 281 97 69.7

560 300 98 72

561.8 280 97 69.4

563.1 270 97 69.4

563.4 289 97 70

563.5 282 97 69.7

563.8 283 97 70.2

564.6 305 97.7 72.7

565.7 282 98 70.2

566 283 97 70.6

568 303 98 72.9

570 300 99.3 72.2

570.8 300 98.8 72.9

571.2 301 98.3 72.9

24

572 298 98.3 72.5

575.4 299 99 72.9

582.2 277 99 70.91

582.2 300 99 74.4

582.3 279 98 73.2

583.3 305 100 74.6

583.4 304 100 74.3

585 304 99 75

586 303 100 75.1

587.6 279 98 74.2

588.1 296 100 75.2

588.5 278 98 73.9

588.5 298 100 75

589.3 301 100 75.9

590 288 99 75.4

590.1 294 100 75.4

590.2 286 99 75

591.1 297 99 76.7

591.5 295 100 76.2

591.8 283 99 74.4

591.8 299 100 75.5

592.3 300 100 75.8

592.6 286 100 74.9

592.8 292 100 75.1

594.4 284 99 74.9

594.4 299 99 76.1

594.6 298 100 75.7

595.7 298 99 76.7

596.4 299 99 76.9

598.1 303 100 76.4

600.1 297 100 77.5

601.9 299 100 77.9

603.1 297 100 78.4

603.5 298 100 78.5

604.2 297 100 79

606.2 297 101 79.6

607.5 300 100 79.3

609.7 300 101 79.8

616.2 304 102 80.2

The average air temperature is measured as 34°C.

4.2. Fan design efficiency

As per the design data provided in the fan curve chart, design volume flow rate =196.65

mᵌ/sec, design head = 397 mm WC, design power = 1027 kW

25

Hence the design fan efficiency,

𝜂𝑑𝑒𝑠𝑖𝑔𝑛,𝑡𝑜𝑡𝑎𝑙% = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑚ᵌ/ sec ∗ 𝛥𝑃 ( 𝑡𝑜𝑡𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒)𝑖𝑛 𝑚𝑚𝑊𝐶

102 ∗ 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑎𝑛 𝑠ℎ𝑎𝑓𝑡 * 100 (eqn. 4)

= 196.65 ∗ 397

102 ∗ 1027 * 100 = 74.53 %

4.3. Example: Performance Test Calculation on FD Fan

The following is a typical report on calculations made for FD Fan with respect to the

measured parameters provided and the fan efficiency is calculated.

a) Measured Parameters (FD Fan)

Mass flow rate = 607.5 tons/hr.

Total pressure (Δp) = 300 mm WC

Air temperature = 34°C (at site condition)

Speed = 980 RPM

b) Measured Parameters (Fan motor)

Rated current = 100 A

Rated voltage = 6.6 kV

Power factor = 0.85

Motor efficiency = 0.95

Transmission efficiency = 0.99

c) Air density & volume flow rate in mᵌ/sec

Air density = 273 ∗ 1.293

273+34 = 1.1498 kg/mᵌ

Calculated volume flow rate = 607.5 ∗ 1000

3600 ∗ 1.1498 = 146.76 mᵌ/sec

d) Power input to the motor

𝑃 = √3 * V*I*cos 𝛷 (eqn. 6)

= √3 * 6.6 *100 *0.85 kW

= 971.68 kW

26

e) Power input to the fan shaft

p = 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑚𝑜𝑡𝑜𝑟 ∗ 𝜂𝑚𝑜𝑡𝑜𝑟 ∗ 𝜂𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 (eqn. 7)

= 971.68 * 0.95 * 0.99 kW

= 913.84 kW

f) Fan total efficiency

𝜼𝒕𝒐𝒕𝒂𝒍 % = 𝑽𝒐𝒍𝒖𝒎𝒆 𝒊𝒏 𝒎ᵌ/ 𝐬𝐞𝐜 ∗ 𝜟𝑷 ( 𝒕𝒐𝒕𝒂𝒍 𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆)𝒊𝒏 𝒎𝒎𝑾𝑪

𝟏𝟎𝟐 ∗ 𝑷𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕 𝒕𝒐 𝒕𝒉𝒆 𝒇𝒂𝒏 𝒔𝒉𝒂𝒇𝒕 * 100 (eqn. 4)

= 146.76 ∗ 300

102 ∗ 913.84 * 100 = 47.23

The calculated data for FD Fan A and B are tabulated bellow.

Calculated Data of FD Fan-A

Volume Flow Rate(mᵌ/sec) Head(mm WC) Power(kW) Efficiency (%)

96.9 252 831.6 28.8

97.8 256 840.8 29.2

99.6 264 849.9 30.3

100.5 264 849.9 30.6

100.8 265 849.9 30.8

100.9 267 849.9 31.1

100.9 267 849.9 31.1

101.0 267 849.9 31.1

101.2 267 859.0 30.8

101.4 270 859.0 31.3

102.1 269 859.0 31.3

102.3 266 849.9 31.4

105.0 255 849.9 30.9

105.8 257 859.0 31.0

107.1 256 849.9 31.6

107.8 263 859.0 32.4

109.0 251 859.0 31.2

110.9 248 859.0 31.4

113.1 249 868.2 31.8

114.1 253 868.2 32.6

114.4 277 868.2 35.8

114.8 259 877.3 33.2

115.2 276 877.3 35.5

115.2 275 877.3 35.4

27

115.5 265 877.3 34.2

115.7 274 877.3 35.4

115.9 277 877.3 35.9

115.9 277 877.3 35.9

116.1 277 877.3 35.9

116.5 279 877.3 36.3

116.7 299 895.6 38.2

117.3 273 877.3 35.8

117.7 297 895.6 38.3

118.4 301 895.6 39.0

118.5 272 886.4 35.6

118.7 273 886.4 35.8

118.7 296 895.6 38.5

118.9 296 895.6 38.5

118.9 278 886.4 36.6

119.1 294 895.6 38.3

119.1 294 904.7 38.0

119.4 297 895.6 38.8

119.5 274 886.4 36.2

119.5 288 895.6 37.7

119.6 283 886.4 37.4

119.6 297 895.6 38.9

119.6 291 895.6 38.1

119.7 296 895.6 38.8

119.7 279 886.4 36.9

119.9 284 895.6 37.3

120.1 299 895.6 39.3

120.2 281 886.4 37.4

120.3 289 895.6 38.1

120.4 291 895.6 38.4

120.6 294 895.6 38.8

120.7 300 895.6 39.6

120.8 284 895.6 37.6

121.0 296 895.6 39.2

121.1 292 895.6 38.7

121.2 297 895.6 39.4

121.3 293 895.6 38.9

121.4 295 895.6 39.2

122.1 294 895.6 39.3

122.5 293 895.6 39.3

122.7 295 904.7 39.2

123.1 295 895.6 39.8

123.5 295 904.7 39.5

123.9 295 904.7 39.6

28

124.4 298 904.7 40.2

126.8 299 913.9 40.7

126.8 300 913.9 40.8

127.5 302 904.7 41.7

128.0 297 923.0 40.4

128.4 300 913.9 41.3

129.0 303 913.9 41.9

129.3 299 913.9 41.5

129.7 296 923.0 40.8

161.4 178 996.1 28.3

164.6 202 1008.9 32.3

164.9 202 1007.0 32.5

165.5 200 1017.9 31.9

Calculated Data of FD Fan-B

Volume Flow Rate(mᵌ/sec) Head(mm WC) Power(kW) Efficiency (%)

137.7 300 907.4 44.6

136.4 305 892.8 45.7

135.3 300 895.6 44.4

138.2 298 898.3 44.9

139.0 299 904.7 45.0

137.2 303 895.6 45.5

138.0 301 898.3 45.3

137.9 300 902.9 44.9

113.5 260 831.6 34.8

115.0 267 831.6 36.2

114.6 266 840.7 35.6

115.7 270 840.7 36.4

116.2 272 840.7 36.9

116.5 269 840.7 36.6

116.9 271 840.7 37.0

116.5 270 840.7 36.7

116.9 270 849.9 36.4

116.5 272 840.7 37.0

118.8 270 840.7 37.4

121.5 261 859.0 36.2

121.9 263 849.9 37.0

123.5 265 849.9 37.7

124.2 269 849.9 38.5

126.6 259 849.9 37.8

130.0 253 859.0 37.5

29

131.4 257 868.1 38.1

133.1 258 877.3 38.4

133.7 265 877.3 39.6

136.0 270 886.4 40.6

135.7 280 886.4 42.0

136.1 282 886.4 42.5

135.0 281 886.4 42.0

136.1 289 886.4 43.5

136.2 283 886.4 42.6

136.7 282 895.6 42.2

136.7 283 886.4 42.8

112.8 284 895.6 35.1

114.5 278 895.6 34.8

140.7 277 904.7 42.2

136.4 279 895.6 41.7

142.2 278 895.6 43.3

142.0 279 895.6 43.4

143.0 283 904.7 43.8

143.6 284 904.7 44.2

142.6 286 904.7 44.2

143.2 286 913.8 43.9

142.5 288 904.7 44.5

143.2 292 913.8 44.9

142.6 294 913.8 45.0

143.6 298 913.8 45.9

143.1 300 913.8 46.1

142.4 301 913.8 46.0

118.0 302 904.7 38.6

141.6 303 913.8 46.0

141.3 304 904.7 46.6

140.9 305 913.8 46.1

140.9 304 913.8 46.0

140.7 300 904.7 45.7

142.2 298 913.8 45.5

142.1 296 913.8 45.1

143.0 299 913.8 45.9

142.9 295 913.8 45.2

143.6 299 904.7 46.5

142.8 297 904.7 46.0

144.5 303 913.8 47.0

143.9 298 904.7 46.5

144.1 299 904.7 46.7

145.0 297 913.8 46.2

145.4 299 913.8 46.6

30

145.7 297 913.8 46.4

145.8 298 913.8 46.6

146.0 297 913.8 46.5

146.8 300 913.8 47.2

146.5 297 923.0 46.2

147.3 300 923.0 46.9

148.9 304 932.1 47.6

4.4. Discussion and analysis

It is clearly observed from the data that the capacity of the FD Fan was considerably higher

than required. When the unit was operated at full load, the FD Fan-A ran at 60% to 70% of its

rated capacity and FD Fan-B ran at 70% to 80% of its rated capacity. In some cases like at low

load as the air requirement in boiler is less, on that case only FD Fan-A was operated and FD

Fan-B was closed. On such situation also the FD Fan-A ran at a maximum of 85% to its rated

capacity. The actual current to the fan motor was 80% to 85% of the full load rated current

when both the fan was operating at maximum power output.

Data showed that the type of fan was not suitable and the forced draft fan was operated within

a low power output area over a long period of time, thereby increasing power consumption and

increasing costs of operating the unit. Due to this the fan efficiency is also considerably low

with respect to its rated design efficiency in the operating zone. With FD Fan-A efficiency

ranging from 28.3% at low load to 41.9% at full load which is 32.63% lower than its design

efficiency. In case of FD Fan-B also the efficiency range is from 34.8% to 47.6% where an

amount of 26.93% efficiency declination is noted. Also during low load operation, when only

FD Fan-A was operated, the fan efficiency was in between 30% to 35%.

As per the test data, it was observed that the high capacity of the boiler FD Fan is resulting in

the poor operating efficiency of the fan and substantially higher energy consumption. A

considerable negative impact on energy conservation was noted.

Furthermore, the operational performance of the two fans (FD Fan-A & FD Fan-B) was

mismatched; the output of FD Fan-B is far higher than the output of FD Fan-A, e.g. the

maximum operating efficiency of FD Fan-B is 47.6% which is 5.9% higher than FD Fan-A and

minimum operating efficiency of FD Fan-B is 32.83% which is 4.03% more than FD Fan-A.

This poses a threat to the stable operation of the unit.

On the next page, a plot of the design H-Q curve as reproduced in the same scale as supplied

by the manufacturer are given for both the fans. From the calculated data some representative

datas at different loads (from 50% to 100%) are selected, as well as the design points are also

plotted for both the fans as supplied by the manufacturer. In case of FD Fan-A the operating

points are plotted from 50% load to 100% load with 10% load interval and in case of FD Fan-

B they are from 60% load condition to 100% load condition because at 50% or bellow that load

condition, only FD Fan-A was being operated and FD Fan-B was closed.

31

Figure 4.1: H-Q Curve of FD Fan-A

Figure 4.2: H-Q Curve of FD Fan-B

0

50

100

150

200

250

300

350

400

450

500

550

600

650

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

70%80%

90%100%

Discharge (mᵌ/sec)

0

50

100

150

200

250

300

350

400

450

500

550

600

650

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

Hea

d (

mm

of

WC

)

Discharge ( mᵌ/sec)

80%

90%

100%

Design point

60%

20% 30% 40% 50% 60% 70% 80% 90% 100%

Hea

d (

mm

WC

)

20% 30% 40% 50% 60% 70% 80% 90% 100%

Design Point

60%

70%

32

From the two curve it is clear that the design point is very far from the actual operating point.

The operating point for both the fans at full load condition are (128.95 mᵌ/sec, 303 mm WC) f

and (143.59 mᵌ/sec, 299 mm WC) for FD Fan-A and FD Fan-B respectively. That means at

this operating condition both the fans are meeting the system demand of 100% Boiler

Maximum Continuous Rating (BMCR) which is 60% to 80% of its design capacity. Besides

this, in case of loading condition of 50% or bellow this, when only FD Fan-A was operated, in

this case also the maximum capacity not meets the demand of full capacity of the fan

(maximum of 85% of its full capacity). Hence this clearly implies an overdesign of the fan due

to which the fans were operated within an area which are inefficient with respect to its design

flow and power consumption thereby deteriorating the operational efficiency. Moreover this

the different lines shown in the H-Q curve implies H-Q curve of the fan at different inlet damper

opening position (% of damper opening are given at the bottom of each curve), provided by

the manufacturer. But in actual situation the operating points are not matching to its design

curve, for an example, in case of FD Fan-A at a flow of 128.95 mᵌ/sec and a head of 303 mm

WC, the inlet damper position as noted was 72.7%, but in the design curve it fits in between

50% and 60%. This might be due to the unintentional leaks in the system and due to the

corrosion of blades as it is working for a long period. This deviation shows a loss incorporating

in the system.

Besides this, both the fan rotates at the same speed (980 RPM) irrespective of the flow

requirements at different loading condition. Hence, there are not much variation in power

consumption. The power consumption range for FD Fan-A was in between 831.6 kW and 923

kW. In case of FD Fan-B also much variation in power consumption was not seen as it also ran

at the same speed irrespective of the load requirement. As there is no measures to control the

speed of the fan, airflow to the boilers of the generating units is regulated via mechanical inlet

louvre dampers which restricts the amount of air pushed in by the fans. The intake fan motors

remain at maximum speed but the inlet damper controls the air flow to ensure an appropriate

volume of air is supplied to the generating unit. Due to this the power consumption range at

low load to full load are near to each other which results in a poor operating efficiency and

excess auxiliary power consumption that finally affects the overall efficiency of the plant and

lowers it.

4.5. Causes of low operating efficiency and high power consumption

After analysing the various data as calculated in the previous discussion, the following

causes are incorporated for low operating efficiency and high power consumption of both the

FD Fans. The causes are enlisted bellow.

1) Oversizing of the fan:

It is one of the major cause of low operating efficiency and high power consumption of both

the fans. A conservative design tendency is to source a fan/motor assembly that will be large

enough to accommodate uncertainties in system design, fouling effects, or future capacity

increases. Designers also tend to oversize fans to protect against being responsible for

inadequate system performance. However, purchasing an oversized fan/motor assembly

creates operating problems such as excess airflow noise and inefficient fan operation. The

incremental energy costs of operating oversized fans can be significant. In this case, the FD

33

Fan-A ran at 60% to 70% of its rated capacity at full load and FD Fan-B ran at 70% to 80% of

its rated capacity at full load. In some cases like at low load as the air requirement in boiler is

less, on that case only FD Fan-A was operated and FD Fan-B was closed. On such situation

also the FD Fan-A ran at about 85% to its rated capacity. The actual current of the fan was 80%

to 85% of the full load rated current when both the fan was operating at maximum power

output. At full load the maximum actual power of FDF-A was 923 kW, hence the redundant

capability of the motor was (1182-923) = 259 kW which was 21.9% of its rated power and for

FDF-B at full load the maximum actual power was 932 kW with a redundant capability of

(1182-932) = 250 kW, which was 21.2% of its rated power. This oversizing creates long term

problem with respective to both operation and cost and decreases the operating efficiency.

2) Constant speed of the fan:

This is the most important cause of low operating efficiency and high power consumption

of both the fans. Both the fan rotates at the same speed (980 RPM) irrespective of the flow

requirements at different loading conditions. As a result of this much variation in power

consumption was not seen. The power consumption range for FD Fan-A was in between 831.6

kW and 923 kW and for FD Fan-B also much variation in power consumption was not seen.

As there is no measures to control the speed of the fan, airflow to the boilers of the generating

units is regulated via mechanical inlet louvre dampers which restricts the amount of air pushed

in by the fans. The intake fan motors remain at maximum speed but the inlet damper controls

the air flow to ensure an appropriate volume of air is supplied to the generating unit. Due to

this the power consumption range at low load to full load are near to each other which results

in a poor operating efficiency and excess auxiliary power consumption that finally affects the

overall efficiency of the plant.

3) Role of dampers:

The major frictional loss takes place in the dampers where by throttling the air and restricting

the amount of air entering the fan, the flow is controlled. Throttling processes are highly

irreversible process where a huge amount of irreversibility loss takes place. Besides this

dampers control airflow by changing the amount of restriction in an airstream. Increasing the

restriction creates a larger pressure drop across the damper and dissipates some flow energy,

while decreasing the restriction reduces the pressure differential and allows more airflow. This

losses are one of the major issue in the decrement of operating efficiency of the fan.

4) Mismatching in performance of both FD Fans:

This is also a severe cause of performance declination of both the fans. As per the data, the

output of FD Fan-B is far higher than the output of FD Fan-A. As for example, the maximum

volume flow rate as noted for FD Fan-B was 148.9 mᵌ/sec and for FD Fan-A was 165.5 mᵌ/sec.

The noted head for FDF-A and B at different loading condition was also different. This can

hamper the stable operation of the unit.

5) Characteristics of the system: The system characteristics has a great role in the

performance of the fan. For optimizing the performance of the fan it is important to know the

exact characteristics of the system.

34

4.6. Remedial suggestions for improving the operational efficiency

The possible remedies for improving the operating efficiency are given bellow. The

adaptation of any of the solution requires cost-benefit and other analysis.

The oversizing of the fan problem can be removed by properly designing the fan but as it

is an installed unit so some design modifications can be made by consulting with the

manufacturer or some consulting engineering firms.

Another method of increasing the fan efficiency is to control fan rotational speed. Use of a

motor that has multiple speeds and to select a lower rotational speed during low airflow

requirements can be adopted.

Fans that operate over a wide range of their performance curves are often attractive

candidates for Variable Frequency Drives (VFD). VFDs use electronic controls to regulate

motor speed which, in turn, adjusts the fan output more effectively. The principal advantage

offered by VFDs is a closer match between the fluid energy required by the system and the

energy delivered to the system by the fan. As the system demand changes, the VFD adjusts

fan speed to meet this demand, reducing the energy lost across dampers or in excess airflow.

Also, VFDs tend to operate at unity power factors, which can reduce problems and costs

associated with reactive power loads. Because VFDs do not expose mechanical linkages to

potential fouling from contaminants in the airflow, they can also lead to reduced

maintenance costs. The energy and maintenance cost savings provide a return that often

justifies the VFD investment.

For obtaining various rotational speed of the fan a fluid coupling with scoop control method

can be adopted between the motor driving shaft and fan driven shaft.

Proper monitoring and maintenance of the fan and its paths also required.

35

Conclusion

Based on the overall report, the following conclusions can be drawn.

1. The capacity of the FD Fan was considerably higher than required. When the unit was

operated at full load, the FD Fan-A ran at 60% to 70% of its rated capacity and FD Fan-

B ran at 70% to 80% of its rated capacity. In some cases like at low load as the air

requirement in boiler is less, on that case only FD Fan-A was operated and FD Fan-B

was closed. On such situation also the FD Fan-A ran at about 80% to its rated capacity.

The actual current of the fan was 80% to 85% of the full load rated current when both

the fan was operating at maximum power output.

2. The FD fans operated within a low power output area over a long period of time, thereby

increasing power consumption and increasing costs of operating the unit. Due to this

the fan efficiency is also considerably low with respect to its rated design efficiency in

the operating zone.

3. Both the fan rotates at the same speed (980 RPM) irrespective of the flow requirements

at different loading conditions. As a result of this much variation in power consumption

was not seen. As there is no measures to control the speed of the fan, airflow to the

boilers of the generating units is regulated via mechanical inlet louvre dampers which

restricts the amount of air pushed in by the fans. The intake fan motors remain at

maximum speed but the inlet damper controls the air flow to ensure an appropriate

volume of air is supplied to the generating unit. Due to this the power consumption

range at low load to full load are near to each other which results in a poor operating

efficiency and excess auxiliary power consumption that finally affects the overall

efficiency of the plant.

4. The operating points are not matching to its design curve, this deviation shows a loss

incorporating in the system.

5. The operational performance of the two fans (FD Fan-A & FD Fan-B) was mismatched.

This poses a threat to the stable operation of the unit.

6. Modifying the design of the fan, use of multiple speed motors, use of Variable Speed

Drives (VFDs), use of fluid coupling and proper operation and maintenance of the fans

are some corrective measures for improving the operational efficiency of the FD Fan.