Basic information for boiler (READ)

Instruction Manual for Boiler Design

2009 .

07.

22

Doosan VINA Boiler Shop
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Index
Chapter 1. Boiler Overview
1. What is Boiler ?
2. Type of Boiler
3. The Function of Each Component of Boiler
Chapter 2. Characteristic based on Boiler Type
1.Classification of Boiler
2.Characteristic
Chapter 3. Drum
1. Type of Drum
2. Function of Drum
3. Function and Structure of parts
Chapter 4. Header
1. Overview
2. Classification
3. Composition
4. Materials
Chapter 5. Link
1. Overview

2. Class
3. Components
4. Materials
Chapter 6. Panel
1. Overview
2. Type of Furnace Wall
3. Panel Design
Chapter 7. Coil
1. Overview
2. Types and Components
3. Materials

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Chapter 8. Strength Calculation
1. Scope
2. Applicable Code for Items
3. Definition of Terms
4. Shell Calculation
5. Nozzle Calculation
6. Fitting Calculation
7. Reinforcement of the Opening
8. Reinforcement Calculation
Chapter 9. NDE
1. Overview
2. Type of NDE
3. Fundamentals and Characteristics
Chapter 10. Vent & Drain
1. Vent

2. Drain
3. Installation

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Chapter 1. Boiler Overview
1. What is Boiler ?
Boiler(or Steam Generator) ,which is used to generate steam/vapor to be required for power plant
or industrial usage, consist of body, circulation system, firing system, air/gas draft system, air preheater, ash treatment system, safety system and subsidiaries. In the present time, the high
performance EP(Electric Precipitator) and De-NOX / De-SOX system can be considered in boiler
area, since the pollution issue has been raised.

The boiler is usually operating to take charge of middle load of required power and start-up/shutdown of boiler is required frequently to take middle load. And the boiler tends to be high
pressure, high temperature and high capacity boiler in consideration of economical efficiency. To
do this Once-Thru type boiler is commonly used.

2. Type of Boiler
2.1 Drum Type Boiler
Drum is used for a container of circulation water and separation of water/steam from saturated
steam.
There are two types in accordance with circulation system.

 Natural Circulation
This boiler is mainly used for sub-critical drum boiler having low pressure at main steam outlet.
The circulation force comes from difference of fluid density between heated and unheated area
and also hydraulic static head.

 Controlled Circulation
This boiler is used for sub-critical drum boiler having high pressure at main steam outlet. As

boiler operating pressure is high, the difference of fluid density between heated and unheated area
is reduced. Consequently the circulation force is coming down. To compensate it, boiler
recirculation pump is required.

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<Arrangement and Component Names>

2.2 Once-thru Type Boiler
There is no recirculation of fluid. The feed water pump with high pressure supply water from the
boiler inlet to outlet. Boiler circulation pump (BCP) is used to re-circulate the water from
separator to prevent water wall from over-heat during low load of boiler. However circulation
pump with small capacity is used for it.

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<Arrangement and component names>

2.3 Circulating Fluidized Bed (CFB) Boiler
This is used for boiler to use low grade coal which has much ash.
and this is most eco-friendly of existing boilers because this can reduce NOX and SOX which is
generated during combustion of coal.
This boiler apply the different way of combustion against the others boiler. Large coal size and
fluidizing the coal in the furnace are applied in order to keep low gas temperature.

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<Arrangement and Component Names>

<Schematic Diagram>

nd

2
Air

Primary Air

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2.4 Heat Recovery Steam Generator (HRSG)
In the present time, according to pollution issue building site and short construction period, this
boiler using liquefied natural gas (LNG) is supplied extensively and very eco-friendly.
This has two type of circulation such as natural and controlled circulation mention the above.

<Bird’s-Eye View>

Steam Drums Steam Silencer

Outlet
Duct &
Stack

Duct
Burner
Area

Heating
Elements

Inlet
Duct

3. The function of each item
3.1 Water Wall (in other words; Furnace Wall)
The furnace is a place where supplied coal and air are burning out to change its energy from
chemical to heat. Water wall generally consist of tubes and fins which are welded each other and
allow for water to go though it.
Followings are the purpose of it;
„ Place for combustion and enclosure of fire flame
„ Heat exchange between fire and water to heat water to high temperature
„ Protection of leakage of fire flame
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3.2 Economizer
This is for preheating feed water by reusing exhaust gas at the end of boiler.
Accordingly the more heat absorption the more efficiency the boiler can get. And by reducing the
temperature difference between heated water from water wall and feed water to drum, it is
possible to reduce a thermal stress of drum shell.
3.3 Superheater
The steam from water wall is a saturated steam which means water and steam are coexisted.
The steam separated by drum or separator is superheated by superheater to increase the plant
efficiency and to protect the turbine from water inflow.
3.4 Reheater
The steam from high pressure turbine has low pressure but high temperature. The reheater is a

item to reuse the steam with high calorie for intermediate pressure turbine and low pressure
turbine.
3.5 Drum or Separator
this is required to separate saturated steam. In other words, the saturated steam is divided into
steam and water.
The Drum is for Drum type boiler and the separator is for Once through type boiler.

<Drum>

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<Separator>

3.6 Header
The main function of header is dispensation of water or steam imported from tubes or pipes to
another tubes or pipes.
This is helpful to resolve the heat unbalance of each tube like economizer, reheater and
superheater etc. The heat exchange isn’t required in header, so the header is usually located
outside of furnace.

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3.7 Internal Piping (in other words Link)
This is pipe to connect header to header or header to drum etc.
Same as header, the heat exchange isn’t required and the pipe is usually located outside of
furnace.
3.8 Sootblower
Ash or dust of combustion is attached to boiler heating surface such as water wall, economizer,

reheater and superheater. At this moment they are obstruction of heat exchange. Sootblower can
get rid of them by using steam or compressed air by periods to maintain good condition of heating
surface for heat exchange.

<Soot Blowing>

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3.9 Air Preheater
The exhaust gas still have much heat which can be used more even though economizer absorb a
lot of heat. The air preheater is used to heat air supplied by fan for combustion.

3.10 Elctrostatic Precipitator (EP)
This is environment equipment to get rid of the dust from combustion gas.

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3.11 Flue Gas Desulfurization System (FGD)
This is environment equipment to get rid of the harmful oxide of sulfur from combustion gas by
using solid of liquid absorbent. There are two types such as dry and wet type.

3.12 Water Treatment System
This is used for maintain optimum level of the feed water quality.
If the boiler use polluted usual water, some scale can be happened inside of tubes. It causes the
water plugging and corrosion as well and
Therefore, water treatment system is an equipment to prevent corrosion.
3.13 Pulverizer or Mill
The more surface area of fired coal, the more combustion efficiency we can get.

Therefore this equipment is for pulverizing and for drying the coal to burn out the coal easily. The
hot air to dry the coal comes from the air preheater.

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[Inside of
Pulverizer]

3.14 Burner
This equipment is for making fire flame by injecting fuel into furnace inside with pulverized coal
and hot air mixed.
The oil burner for boiler start-up is required to start operating the boiler. The burner also includes
the oil burner.
There are three kinds of ways for firing such as tangential, horizontal and vertical firing system.

Burners of Tangential Firing

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Chapter 2. Characteristic based on Boiler Type
1. Classification of Boiler
1.1 According to Fuel
„ Coal Fired Boiler
„ Oil Fired Boiler
„ Gas Fired Boiler
„ Multi-Fuel Fired Boiler
1.2 According to Circulation
„ Natural Circulation Boiler

„ Controlled Circulation Boiler
„ Once-Through Boiler
1.3 According to Steam Pressure
„ Sub-critical Pressure Boiler
„ Super-critical Pressure Boiler
„ Ultra Super-critical Pressure Boiler
1.4 According to Firing
„ Fluidized Bed Firing (same as Circulating Fluidized Bed, CFB)
„ Stocker Firing
„ Suspension Firing : Tangential, Horizontal, Vertical
2. Characteristic
2.1 Natural Circulation Boiler
„ Advantage
9 The particular subsidiaries are not required. And it is efficient even though the size of boiler
is small or medium.
9 The structure is comparatively simple.
„ Disadvantage
9 This can be used for boiler whose design pressure is less than 180kg/cm2 because it is
difficult to get high circulation force. So this is restricted to use for high capacity boiler.
9 This requires long time to start up boiler, and lots of heat loss is happened when shut-down.
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„ Reference : The circulation force is generated from difference of specific weight between
water and steam. The circulation force is increased in portion to different height between lower
and upper side.
2.2 Forced Circulation Boiler
„ Advantage
9 The particular subsidiaries are not required. And it is efficient even though the size of boiler
is small or medium.

9 The structure is comparatively simple.
9 The structure of pressure part is simple and erection cost can be reduced due to the easy
arrangement of heating surface.
9 The circulation force is in good condition.
9 Long term operation is possible with high safety of fixed load.
9 When acid cleaning, water circulation is fine due to circulation pump.
9 Accumulated scale inside of tube can be detected by finding out the difference of pressure
between before and after circulation pump.
„ Disadvantage
9 If a huge drum is installed, to change boiler load is a little difficult because the drum
contain a lot of water.
9 It is required to maintain the boiler circulation pump. If problems, the boiler can not keep
the rated load.
9 Consumable electric power is required due to boiler circulation pump.
9
„ Reference : an additional boiler circulation pump will be added to enhance the circulation
force for high capacity boiler.

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Natural Circulation

Controlled Circulation

2.3 Once Through Type Boiler
„ Advantage
9 Good characteristic of operating. It means that the steam can be generated in sort time.
9 To change boiler load is easy.
9 It is also possible to maintain high efficiency in low load.

9 Daily start and shut-down is easy.

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9 There is no drum. The weight of pressure part is light due to no drum and small diameter of
tube.
9 The supplementary water is not required because there is no blow-down port.
9 It is proper type for supercritical boiler.
„ Disadvantage
9 Water wall structure is a complex form.
9 The cost for manufacturing and construction is high.
9 The power loss of feed water pump power is big because lots of the pressure drop is
happened to maintain the water speed of tube inside.
9 The heat loss is big due to discharge of boiler water during start-up.
9 The minimum boiler load is 30~40% of MCR(Maximum Continuous Rate)
<Evaporator wall comparison>
Spiral wall

Vertical wall

Smooth Tube
- Even heat distribution and minimal
Advantage
thermal stress due to passing all
envelopes by every tube during load
change or for different type of coals
- Suitable for based load and cycling
load operation
- Complex support(vertical buckstay)

Disadvantage
for spiral furnace wall
- High cost for evaporator wall
erection and manufacturing
- No limit on unit capacity

Rifled or Ribbed Tube

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Rifled Tube
- Simplified structures
- Lower cost for evaporator wall erection
and manufacturing
- Less pressure drop
- Suitable for based load operation
- Flow control by orifice to compensate
for different heat absorption, not effective
for different loads and type of coal
operation
- Possibility of rapid pressure drop
evaporator wall by small size tube if water
quality is bad
- Possibility of orifice change during
commissioning
- Suitable for based load operation
- Limit on unit capacity (> 550MW)


„ Reference

9 Start-up Mode (Based on Once-thru 500MW)
Cold Start(start again in 96 hours after shut-down)
Warm Start(start again in 56 hours after shut-down)
Hot Start(start again inr 6~12 hours after shut-down)
Restart(start again in 2 hours after shut-down)

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Chapter 3. Drum
1. Types of a Drum
Various types of drums have been developed according to their purposes and, in general, a power
plant and industrial boiler have a steam drum that has a water separator and a water drum that
keeps and distributes water. Some power plant boiler has only a steam drum.
2. Functions of a Drum
A steam drum separates water input by feed water piping to send the water to a pump or to
hydrostaic pressure through a downcomer. The water returns to the drum in a mixed state of
steam and water after passing through a furnace wall and a riser tube, then, the steam drum
separates water from vapor. The separated water is collected by a water drum (or furnace lower
feeding header) located at the lower part of a furnace through a downcomer while vapor by a
turbine through a superheater. Thus, the inside of a drum is always saturated condition. And a
various types of a separator or a dryer is selected by performance calculation that removes water
from steam in a drum after taking into account calculation of steam purity and pressure loss.
3. Functions and Structure of Parts
A drum has various nozzles and components outside of a cylindrical shell and parts inside for
water separation.
3.1. Shell & Head
A thick plate is formed into a cylindrical shell and a head. Then, they are welded together to make
a body of a drum.
3.2. Nozzle

In order to facilitate the assembly of instruments connected to a drum, various nozzles
corresponding to their specifications (e.g. piping, a link, a tube, etc.) are welded to the outside of
a drum. Major nozzles are as follows.

- Safety Valve Nozzle:
A drum is a high-temperature and high-pressure instrument so the nozzle connects a safety valve
to a drum, preventing an excessive increase of pressure inside of a drum.

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- Water Level Gauge / Transmitter Nozzle
A steam drum contains vapor in its upper part while water in the lower part (a water drum has
water only) and control of the water level in the drum is extremely important when operating a
boiler. If the water level is too high, steam containing impurities will move to a turbine, eroding
its wing, if too low, the superheater will be overheated, breaking a pipe of a tube. In order to
measure the water level in a drum, therefore, a transmitter nozzle, linked to a control room, is
attached to the drum as well as a local gauge.
- Riser, Superheater Connection Tube Nozzle
A riser allows water vapor heated in a furnace to flow into a drum while S/H Conn. (a nozzle)
sends the vapor coming out of a final dryer to S/H. The number/size of its hole influences the
thickness of a shell when calculating the strength of a drum.
3.3. Manhole
A

manhole

provides

an

engineer

with

access

to

the

inside

of

a

drum

for

installation/inspection/repair. It is closed by a hinge-type manhole cover with a gasket when a
boiler is in operation.
3.4. Internals
Internals refer to various devices inside of a drum used for water separation, which is the main
function of a drum. The major components are as follows.

- Feed Water Piping
It feeds water from an economizer to the inside of a drum and has a number of small holes on
pipe that evenly distributes water in proportion to the length of a drum.

- C.B.D (Continuous Blow Down) Piping
This system discharges some boiler water containing impurities continuously in order to maintain
the allowable concentration level of impurities in the water.

- Separator
It separates steam inside of a drum into water and vapor. Separators can be divided into a turbo
separator, used for a power plant, and a centrifugal separator (unitized separator) for HRSG by
types or, they are classified into a primary separator and a secondary separator by functions. The
principle of a primary separator is that centrifugal force is applied to a fluid in a mixed state of
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vapor and water when it passes through a blade in order to separate water from vapor by means of
the difference of specific gravity. And a secondary separator can filter out vapor by having the
fluid pass through narrow openings of overlapped nets.

- Dryer
According to the boiler type and requirements of function, a dryer is divided into ‘V’ type screen
box or a corrugated type dryer mainly used for HRSG. Also, there is a basket type corrugated
dryer for short length.

- Drain Pipe
The system sends water separated in a dryer to the lower part of a drum.
- Downcomer Spider
This component is welded to a downcomer nozzle to prevent a vortex of water drained through a
downcomer in a steam drum.

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Chapter 4. Header
1. Overview
A boiler header, also called a collector, collects and distributes fluid (water or steam) through a
small-diameter tube or large diameter link.
Most boiler headers are located outside of the furnace not to be contacted with combustion gas,
for they do not exchange heat.
The size of header is decided according to the amount of flow. If the header cannot absorb
inflowing fluid because it is too small or has any other problem, the tube may be overheated and
loss of pressure may happen.
2. Classification
2.1. Classification by functions
2.1.1. Economizer header
It is located on the backpass zone where feed water flows into the boiler. The fluid is water and
materials are selected depending on the design temperatures, and mainly carbon steel is used.
2.1.2. Furnace header
Water that flows down through downcomer or econ. mixing line is heated in a furnace wall. The
header is located at the inlet/outlet of this furnace wall and, most times, an inlet header is located
at the lower part of the furnace while an outlet header at the upper part of the header. The fluid in
the inlet header is water and in the outlet header, water and steam. The materials are selected
depending on the design temperature and are mostly composed of carbon steel.
2.1.3. Superheater header
Steam separated from water in a drum or by separator is sent to S/H tube through link to be
superheated steam. This header is located at the inlet/outlet of the S/H tube and the fluid in it is
steam. The materials are selected depending on the design temperature but are mainly carbon
steel for the low-temperature part and are alloy steel for high-temperature part.
2.1.4. Reheater header
The steam that passes through a high-pressure turbine becomes reheated steam after it is collected
at the boiler and goes through R/H tube. This header is located at the inlet/outlet of the R/H tube
and the fluid in it is steam. The materials are selected depending on the design temperature but are

mainly carbon or alloy steel for an inlet header and are alloy steel for an outlet header.
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2.2. Classification by locations, functions, and types
2.2.1. Inlet & Outlet Header
2.2.2. Front, Rear & Side Header
2.2.3. Upper, Lower & Intermediate Header
2.2.4. Primary, Secondary & Final Header
2.2.5. Platen, Spaced & FBHE Header
The terms provided above may be combined as follows.
Ex.) - Furnace Upper Side Header
- Final Superheater Inlet Header
3. Composition
3.1. Shell
Shell refers to the body of a header and fabricated as seamless or with welded round pipes. Its
components are listed below.
3.2. Head (End Plate)
It is used to seal the end of a shell. A head may be fabricated by forging or with plates and take
flat-plate, ellipsoidal, or hemi-spherical shape.
3.3. Nozzle
A nozzle, connecting a header with piping, is fabricated by forging or with pipes
3.4. Nipple (Stub)
A nipple is made up of tubes and connects a header with a panel or a header with a coil.
3.5. Hand hole or inspection hole
The hole is installed for inspecting the inside of a header. It is removed when a boiler is inspected
and cleaned or for some other reasons.
3.6. Fitting
Fittings are used to connect piping, including tee, elbow, reducer, cap, weldolet, sockolet,
threadolet, etc.

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3.7. Drain & vent nozzle
It is installed for the purpose of drain or vent when a boiler is in operation or hydro test is needed.
3.8. Thermowell
It is installed to attach thermocouple that measures the temperature of a fluid in a header or metals
of shell.
3.9. Sampling nozzle
The nozzle is installed to extract an element of fluid.
3.10. RT Plug
When RT is operated to make sure the soundness of pipe weld joint, a source is put into a pipe if
necessary in order to facilitate the testing or to reduce the photographing time. This is when an
RT plug is used and it is sealed after the testing is over.
3.11. Bracing plate
Bracing plate is fabricated by making holes on a plate with the same number as nipples. It is
attached to an end of a nipple in order to fix it so that heat deflection (when the length of a nipple
is excessively long) or bending (during the transportation) can be prevented. The plate is a
temporary component so that it must be removed before installation at a construction site.
3.12. Lug & Support
This refers to all kinds of components attached for the purpose of hanging a header or a link on a
steel frame or supporting them, mainly fabricated with a plate.
4. Used Materials
ASME materials used for each component are listed in <Table 1>. JIS materials have properties
similar to those of ASME though they are called differently. Yet, DIN materials are completely
different from them and some of the commonly used materials are 15Mo3, 15NiCuMoNb5,
13CrMo44, 10CrMo9.10, X20CrMoV12.1, etc.

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