Cfbc Operation 23MW

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INDEX

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Training Material for

VC 2x23MW Thermal Power

Project

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Date: 04th April, 2007

Section General Description of Boiler

Chapter The function of boiler

The production enterprise is called power plant. The simple flowing chart of the production

procedure of fossil fired power plant can be expressed by figure 1-1. Fuel is burning in boiler

1, the released heat will heat the water in boiler, and this water will be evaporated and

overheated into superheat steam with certain temperature and pressure. This superheat steam

will go into turbine2 through pipes. The steam will work in turbine by expansion and roll up

the steam turbine to rotate the generator 3 to generate electricity. After work in turbine, the

steam will be exhausted into

condenser 4, and cooled by thecooling water supplied by circulating

water pump 11 into condensate

water. After rising pressure by

condensate water pump 5, this

condensate water will go into LP

heater 6 to be heated. After removing

oxygen in deaerator 7, the pressure

of it will be raised by feed water

pump 8, and then it will be heated by

HP heater and then go back to boiler

to go on doing the above circulatingcourse. The heating source of water

in heater and deaerator comes from

the extraction 10 of turbine.

From the above circulation, we

will know there is a energy

transformation course of three kinds

of energy in power plant: the

chemical energy in the fuel is

transferred into the heat energy of

steam in boiler; the heat energy ofsteam is transferred into mechanical

energy in steam turbine; the

mechanical energy is transferred into

electric energy in generator. The important equipment in the course of energy transformation

---- boiler, turbine and generator are called three main equipments in fossil fired power plant.

Boiler is the most basic energy transformation equipment in these three main equipments in

fossil fired power plant. Its function is burning the fuel in boiler to release heat, and heat the

medium ---- water in boiler into superheat steam with enough amounts and certain quality

(temperature and pressure) to supply to turbine.

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1boiler 2steam turbine 3generator 4condenser

5condensate water pump 6 LP heater 7 deaerator

8feed water pump 9 extraction of steam turbine 10

circulating water pumpFigure 11

Production procedure of thermal power plant

Superheat steam

Making

up water

Cooling water


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Chapter C lassification of boiler

. Classify according to the volume of boiler

Boiler is classified into small-scale, middle-scale and large-scale according to the evaporation

volume, but there is no fixed boundary between them. Along with the development of boiler

industry, the volume of boiler is increased gradually. The large-scale boiler in past is just a

middle-scale or even small-scale boiler in nowadays. According to the condition at present,

generally, D400t/h is considered as small-scale boiler, and D670t/h is considered as large-

scale boiler.

. Classify according to the parameters of steam

According to the pressure of steam, boiler can be classified into: low pressure boiler

(P2.45Mpa gauge pressure) / middle pressure boiler (P=2.94-4.92Mpa gauge pressure), high

pressure boiler (P=7.84-10.8Mpa gauge pressure), superheat pressure boiler (P=11.8-14.7Mpa

gauge pressure), critical pressure boiler (P=15.7-19.6Mpa) and supercritical pressure boiler

(P22.1Mpa) and so on.

. Classified according to the method of combustion

According to the combustion method of method in boiler is different, boiler can beclassified into: cyclone furnace boiler and fluidized bed boiler and so on.

. Classified according to the circulating method of water

According to the different source of the main power that make work medium flow on the

evaporating heat surface, boiler can be classified into natural circulating boiler, control

circulating boiler and once-through boiler generally.

. Vikram thermal power plant

The boiler used in Vikram thermal power plant is HP, natural circulating, small-scale fluidized

bed according to the above classification method of boiler.

The mode of the boiler used in Vikram thermal power plant is DGJ130/9.81- 1; it is 130t/h

single drum, HP natural circulation, insulation cyclone separator, J valve back material

device, water cooling air room, full welding steel structure boiler support, circulating

fluidized bed combustion type boiler designed and produced by Dongfang Boiler Industry

Group Co., Ltd for M/s. Vikram Cement Indian.

Chapter The composition and principle of CFB boiler

The composition of boiler

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Boiler is very complicated in modern thermal power plants, and it consists of boiler proper

and a series of auxiliary equipments.

Boiler proper is the main part of a boiler; it consists of a pot and a furnace. The pot

consists of economizer; drum, down comers, water walls, super-heaters and their accessories,

etc. its task is to make water absorb heat and evaporate it into steam, and become into certain

pressure and temperature superheat steam at last; the furnace consists of furnace chamber,

flue, firing equipments and air preheater, etc. so as to produce flame and flue gas with high

temperature. The flue gas produced in pulverized coal combustion will be discharged into

atmosphere after removing dusts.

Except boiler proper, ID fans, FD fans, exhausters, chimney, dust and slag removal

equipments, coal pulverization equipments, thermal instruments, and automation devices

belong to auxiliary equipments of boiler.

In order to pledge the safe and economic operation of boiler, some accessories as safety

valves, water level indicators, sootblowers, water level alarm, furnace protection, etc, are

equipped.

. The working principle of circulating fluidized bed boiler

The technology of circulating fluidized bed boiler (CFB) is a new technology development in

the 70th s. Its prime power is the appreciation for the environment protection of human

society. The technology of circulating fluidized bed is a kind of clean combustion technology.Its special combustion way reduced the releasing amount of SO2 and NOx in coal fired power

plant that are the main source of air pollution in world, i.e. it solve the problem of acid rain

fundamentally. At the same time, the circulating fluidized bed boiler also has wide

conformance for fuel and good accommodation for load, and the investment and operation

cost are also lower compared with other. So this technology develops fast and strongly as one

of the three directions of the development of energy technology in the world.

Fluidization refers to the air flow cross the material on air arrangement device under certain

speed to make the particle of material contact with air flow to transfer into the state that is

similar with fluid. The type of fluidized bed is depended on the flow velocity on the section of

empty bed. Along with the rising of the velocity of air flow, the drag force produced by airflow to the material particle in bed is balanced with the gravity and buoyancy worked on the

particles; the material in bed gets to rapid fluidized state from static bed condition through

boiling, and turbulent state.

The technology of circulating combustion is developed on the base of boiling fluidized bed

combustion; the fundamental distinction of circulating combustion and boiling bed

combustion is that the multiple circulating combustion of solid material in fluidized bed is

realized. Vikram thermal power plant

The boiling fluidized bed is operated under the condition that the speed of the section of air

flow empty bed is lower than 2~3m/s, and there is obvious parting surface on the layer of bed.After the speed of air flow is increased and exceed the speed of boiling, the lay of bed begin

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to expand, and a large amount of solid particle is thrown into the suspending space over the

bed layer, and the surface of bed lay tends to diffusion, and there is no obvious parting surface

at this time, but the concentration increased along the height of combustion room is lower andlower. The air flow velocity inside of circulating fluidized bed is generally at 3.5-8m/s, the

mixture of the material in bed is uniform and the fluidization is stable. The material in bed is

brought out of furnace by high speed air, and it is caught by air solid separator, and then

this part of material is sent into fluidized bed to combust again by material returning system.

After multiple circulation, the combustion efficiency of solid material is very high, and the air

flow with high concentration of dust strengthen the heat transformation; at the same time, the

temperature of bed is controlled by the pressure of bed and the arrangement of primary air and

secondary air so that the low temperature combustion at 850-950 is realized; the

productions of SO2 and NOx are also limited effectively by adding desulphurization agent and

adopting hierarchical air arrangement to make the emission of boiler meet the standard of

environment protection.

. The technological process of circulating fluidized bed boiler

The main component parts of circulating fluidized bed boiler are as follows:

The main loop of the circulation of solid particle includes furnace, cyclone separator,

and material return device.

Tail vertical shaft (include high temperature superheater, low temperature

superheater, economizer and air preheater)

In the technological process of circulating fluidized bed boiler, the combustion and

desulphurization take place at the bed lay whose temperature is lower that is composed by a

large amount of ash particle, and the improvement of combustion efficiency and the efficiency

of desulphurization should be taken into consideration in the choose of temperature. These

fine particles or solid particles is suspending in furnace supported by the ascending flue gas

stream produced by primary air through air arrangement plate, and the secondary air is

divided into two layers to send into furnace, so the hierarchicalcombustion can be realized.

After overwhelming majority of solid particles is separated from gas solid flow by cyclone

separator, it will be sent back into furnace again and attend combustion. This forms the main

loop of circulating fluidized bed boiler. The characteristics of the main loop of circulatingfluidized bed are: strong disturbance and mixture, inside circulation and outside circulation of

high concentration of solid particle, high velocity of solid/ gas and longer staying time; the

above characteristic supplied good outside condition for heat transferring and chemical

reaction.

The good performance of reducing the pollution of SO2 of circulating fluidized bed boiler can

be described as follow:

The sulfur in the coal used in circulating fluidized bed boiler reacts with the CaO in the coal

ash or the added limestone so that the desulphurization can be realized in furnace directly. The

limestone added in furnace is decomposed into CaO, and then CaO reacts with SO 2 andproduce CaSO4, shown in following:

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CaO + CO2 CaCO3

CaO + SO2 + 1/2 O2 CaSO4

The best temperature of this reaction is about 850 . The temperature of furnace should be

controlled at 850 when the changing range of load is larger. The hierarchical combustion

and lower temperature of furnace can reduce the emission of NOx farthest at the same time.

The characteristic of the technological process of circulating fluidized bed boiler are as

follow:

The particle of material mixes uniformly and the temperature of bed distributes

uniformly.

The fuel stays in furnace for longer time.

Keep the temperature of furnace at the best temperature of removing SO 2.

The above characteristic can guarantee the realization of following performances:

The combustion rate of carbon is higher and the efficiency of desulphurization is

higher;

Low emission of NOX and better conformance

. Integral arrangement of DGJ130/9.81- 1 type boiler

This boiler is single drum, natural circulation, circulating fluidized bed combustion way, and

it is out door.

The boiler is composed by one diaphragm water wall furnace, one insulation cyclone

separator and one heat recovery area (HRA) covered by steam cooling wall enclosure

There are two plates of platen superheater in furnace. There are two coal feeders and two

limestone feeding mouths in boiler and all of them are set in front of boiler and equipped at

the compressed section at the lower part of the water wall of front wall in the direction of

width. There is water cooling air room made by the pipes of water wall at the bottom of

furnace; it is connected with two sets of air duct igniters; and one oil igniter is arranged in theair duct igniter.

Between the furnace and tail vertical well, a insulation cyclone separator is arranged here, and

a J valve material returning device is equipped under it. High temperature superheater, low

temperature superheater, economizer, and horizontal air preheater are quipped in tail vertical

well from up to down. There is secondary water jet attemperator is set in superheater system.

The whole boiler is symmetrical from its left side to right side, and it is supported by boiler

steel support.

Attached drawing 3 is the side view of boiler and attached drawing 4 is the top view of boiler.

The important structure sides and components are shown in these drawings.

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Section Fuel and Combustion Equipment

Chapter Fuel

Coal

1. The composition of coal

The composition of coal can be researched by ultimate analysis method and proximateanalysis method.

The composition of ultimate analysis of coal include carbon (C), hydrogen (H), oxygen (O),

nitrogen (N), sulfur (S), ash (A), water (W). Carbon, hydrogen, and partial sulfur are

combustible, other parts are incombustible. Carbon is the main combustible component in

coal.

The proximate analysis method of coal includes water, volatile matter, fixed carbon, and ash.

The components of volatile matter have some combustible material such as CO, H2, CH4, H2S

and so on and incombustible material such as CO2, O2, N2 and so on.

The main characteristics of coal include heat value, volatile matter, coking property, grind-

ability, and ash melting point.

The coals used Vikram thermal power plant are ignite, Indian coal, imported coal, and coke.

2. The characteristic of fuel of Vikram power plant

Characteristic of fuel

Carbon Car % 29.82

Hydrogen Har % 2.41

Oxygen Oar % 10.69

Nitrogen Nar % 0.41

Sulfur Sar % 2.06

Water Mar % 50

Ash Aar % 4.61

Volatile matter Vdaf % 27.13

Low heating value LHV kJ/kg 10292

Grind-ability index HGI /

Characteristics of limestone

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CaCO3 % 75

MgCO3 % 3

H2O % 2

Other % 20

3. The combustion of fuel and limestone of two units of Vikram power plant

Item Performancelignite

Bestlignite

Worstlignite

The consumption amount of fuel per hour (t) 74 76.6 66.8

The consumption amount of fuel per day (t) 1776 1838.4 1603.2

The consumption amount of limestone per hour (t) 18.2 18.2 6.2

The consumption amount of limestone per day (t) 436.8 436.8 148.8

Note: The above data is calculated under the condition of the unit operates 24h/per day at 100%

BMCR.

. Fuel oil

The physical characteristic of fuel oil includes viscosity, solidifying point, flash point, ignition

temperature and so on.

Viscosity refers to the resistance produced by oil to the flow of itself; it can express the flow

characteristic.

The phenomenon of the liquid material is changed into solid state is called solidification, and

the temperature when begin to solidify is called solidifying point. The temperature of fuel oil

should be controlled above the solidifying point to avoid the solidification of fuel oil to block

the pipes.

When the fuel oil is heated to a certain temperature, oil vapor will appear on the surface of oil.

When the mixture of oil and air gets a certain concentration, if there is fire near them, the blue

light of fire will be produced and this blue light will disappear instantaneously. This

temperature is called the flash point of oil. The temperature of fuel oil should be controlled

under flash point to avoid explosion.

The oil vapor molecule on the surface of fuel oil trends to saturate when the temperature of oil

rises to a certain temperature. if the mixture of it and air reaches certain concentration and

there is fire nearly, it can be burned and continuous combustion can be kept. This temperature

is called ignition temperature.

The under bed ignition method is adopted by Vikram power plant. 0# light diesel is used in

ignition. The parameters of the oil used in ignition are as follows:

Serial No. Analysis item Unit Standard requirement1 Kinetic viscosity (200C) m2/s 310-6810-6

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2 Low heating value kJ/kg 41868

3 Flash point in closed up No less than 65

4 Solidifying point 0

5 Ash % No more than 0.025

6 Sulfur % No more than 0.2

Chapter Coal preparation equipment and coal feeding equipment

. Coal crusher

Two reversible hammer coal crushers are set in the coal crushing part in the coal conveyingsystem in Vikram power plant; one is operating and one is standby. After crushing, the coal

will go into the sieve equipment to sieve, and then it will be sent into the coal conveyor in

next section, and the coal left on mesh will be sent back to the inlet of crusher by bucket

elevator to crush again.

The graininess of fuel after grading should satisfy the following requirements:

Size of grading Petroleum coke Imported coal Indian coal and ignite Limestone

The percentage left on sieve (total accumulation)

+ 90 mm 0.0 0.0 0.0 -

+ 75 mm - 4.12 20.64 3.0

+ 60 mm 1.91 8.87 12.5

+ 50 mm - - 35.58 15.0

+ 40 mm 2.56 14.16 41.21 23.0

+ 32 mm 5.47 22.74 - 32.0

+ 25 mm 25.93 30.14 46.53 38.0

+ 20 mm 34.62 41.62 - -

+ 12.5 mm - - 53.56 -

+ 10 mm 51.32 58.55 - 65.0

+ 6.3 mm 60.48 68.90 68.38 80.0

+ 4.0 mm 69.37 75.89 71.08 -

+2.8mm 74.71

+ 2.0 mm 80.46 81.65 94.0

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+ 1.0 mm 85.00 85.00 84.00 95.0

. Coal feeding equipment

The coal feeding equipment has coal bunker, limestone silo, coal feeder, and pneumatic

conveying device.

1. Coal bunker

The main task of coal bunker is coal storage and guaranteeing the necessary amount of coal

needed by coal feeder. In design, the volume of coal bunker can be used by boiler for

supporting 6~8 hours continuous operation.

The coal bunker is arranged from 27.5m to 1m in front of coal feed in Vikram thermal power

plant. It is divided into two parts: the first one is used for petroleum coke/ limestone, and the

other part is used for Indian coal/ imported coal; and the effective volume of every part is

300m3. Coal bunker is reinforced concrete structure and SS304 inside lining whose min.

thickness is 3mm is set at cone.

Limestone bunker is placed in front of coal feeder from 27.5m to 15m. It is divided into two

parts, and the effective volume of every part is 171m3. It can meet the required amount of

limestone under the condition of boiler is operating for 18.8 hours under BMCR. The

limestone bunker is reinforced concrete structure and SS304 inside lining whose min.

thickness is 3mm is set at cone.

2. Coal feeder

The task of coal feeder is mixing the raw coal that has be produced and has proper grading

with limestone and sending them into boiler to burn.

Coal and limestone is mixed inside of coal feeder. Four fully-enclosed electronic weighing

belt coal feeders whose accuracy are set 15meters layer for every boiler; and the amount of

coal feeding is changed depending on the rotating speed of pole slip operating motor. The

compatibility of this kind of coal feeder is good, and the amount of conveying is large, thestructure of it is simple, the maintenance of it is easy, and the cost of it is lower; the new

closed box structure is suitable for the operation under positive and negative pressures. The

shortage of it is the wearing of it is serious, its belt is sliding and easy to deviate, and it is easy

to leaks coal and so on. Coal feeder is installed at 15.00m place of BC span in main factory

building. Two coal feeders in every lay whose length are same should be arranged

symmetrical.

3. Pneumatic conveying device

Two pneumatic coal distributed devices are arranged at the lower part of the front wall of

furnace along the direction of width. After fuel goes into conveyor belt from coal bunker, itfalls down into wind power distributed device by gravity. Three coal distributed wind streams

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arranged under coal distributed device blow the fuel into furnace to combust. This coal

distributed wind is supplied by boost air fan.

The inner wall of coal feeding chamfer is spliced by 1Cr18Ni9Ti stainless steel plate.

Chapter Combustion Equipment

. Furnace

The furnace of Vikram Thermal Power Plant is 26554 mm (height) 5791.2mm (width)

5791.2mm (depth) combustion chamber; it is composed by front wall, rear wall and two side

walls. At the bottom of furnace, the pipes of rear become sparse and from the bottom of air

room and the air arrangement plate of fluidized bed, which form the water cooling air roomwith the water walls at two sides; the elevation of air arrangement plate is 7000mm; at the top

of furnace, the front wall is bent to the back of furnace to form the top of furnace; and the

pipes is connected with the outlet header of the water wall of front wall behind the furnace;

the highest elevation of the top of furnace is 51228mm. A down header of the water wall of

front wall and a bottom header of water wall of air room at the same level are positioned at

the place of 5000mm elevation at the lower part of furnace; there is one outlet header of the

water wall of front wall, and also on outlet header of water wall of rear wall, the elevation of

them are 38860mm; one up header and one down header are set for every side wall; the

elevation of the down header of side wall is 5000mm, and the elevation of the up header of

side wall is 38460mm. The whole furnace can be divided into three parts: up, middle, down.

Take 15511.1 elevation as boundary, because the water wall of front wall and rear wallintersect the horizontal level to form 80angle and then form a trapezoid.At the horizontal air

arrangement plate whose elevation is 7000mm, the depth of furnace is 2895mm. Wearing

material is laid on the water wall at the down density phase area, rear wall near the outlet of

up flue gas, two side walls and roof to avoid wearing, and the thickness of this wearing

material is 51mm (to the central line of pipe). The boiler water is sent to every loop from

drum by two central draining water pipes.

The pitches of the pipes of front wall (including the top of boiler), rear wall and the water

walls at two sides are 76.2mm, and the sizes are51. The pipes of front wall and rear wall are

75, and the pipes of two side walls are 75. The air distribution plate is composed by 38 inner

screwed pipes whose pitches are 152.4mm and sizes are63.5; the bottom of air room iscomposed by 38 pipes membrane wall whose pitch is 152.4mm and size is 51. The sizes of

the outlet and inlet headers of all water walls are 219.

Two coal feeding openings and two limestone openings are set at the front wall of furnace

above air distributed plate. Two rows of secondary air openings are installed at the front wall

and rear wall of furnace; there are 5 up secondary air opening at single side, and 6 down

secondary air opening at single side. There are three ash extraction openings installed evenly

at the bottom of furnace, the middle one is emergency ash extraction opening; the outlet of

flue gas of furnace is at the top of rear wall.

. The flue gas duct at the inlet of cyclone separator and cyclone separator

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One inlet flue duct of cyclone separator is installed in boiler. It connects the outlet of flue gas

of back wall of furnace with cyclone separator, and form a air seal flue gas duct.

The upper half part of cyclone separator is cylinder, and the lower half part is cone. The outlet

of flue gas is cylindrical steel plate forming a cyclone whose end is opening and whose length

will reach the certain position of cyclone separator. The fine particle and flue will flow to the

bottom of cylinder, and then flow awards to leave cyclone separator. The coarse particles fall

into the vertical pipes connected with J shape material returning device directly.

The cyclone separator is adiabatic type structure, wearing layer is laid inside of it, and its

thickness is 350mm. The size of cyclone separator is2576, and it is made by high strength,

anticorrosive, wearing Durimet RA-253MA steel plate.

. Lighting-up burner

Two air duct igniters are installed under bed for every boiler in Vikram Thermal Power Plant;

the heat capacity of ignition burner is designed according to 30% BMCR output; and it is

arranged at 5785mm elevation place of two side walls. The fuel used for ignition is fuel high-

speed diesel oil, and the oil gun is mechanical central oil back type, there are two oil guns.

The rated capacity of single oil gun is 1350kg/h, and the designed air amount of single burner

is 40380Nm3/h.

. J valve material returning device

The bed material and ash separated by steel plate type cyclone separator flow downwards

through back material vertical pipes laying fire-resistive material and are discharged to J

valve. J valve material back device is installed under cyclone separator, and it is supported

on the beam of framework. The connection between separator and material returning device,

material returning device and lower part furnace are flexible expansion joint connection. It

has two key functions: make the re-circulating bed material return to furnace continuously

and stably from cyclone separator; supply seal between the negative pressure of cyclone

separator and positive pressure of lower burner. The static pressure of separator is very near to

the atmospheric pressure, the pressure of the material returning point of burner is very high

because of primary air, so the seal between them must be supplied, or the flue gas of burner

will flow back to separator. This seal is realized by building material level in vertical pipe bythe material at the outlet at the bottom of separator by J valve. The air used by material

returning device is send by individual HP J valve, the J valve air goes into J valve through the

bottom air tank and the four layers of aeration mouth, the aeration pipes on every layer have

their own air amount measuring point that can show exact flow. The air distribution is

adjusted by manual and motor-driven governing valves to realize sending certain amount of

air. Pressure measuring point is set on vertical pipes to realize the monitor for material level.

The making up inlet of startup material is also set at the top of J valve. Emergency ash

removing opening also set at the bottom of J valve material returning device used to remove

the ash and slag under the condition of repair and emergency condition; it is not included in

ash removing system.

The J valve material running device and material returning vertical pipe are made by steel

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appendix drawing 7. The inner diameter of drum is 1600mm, the length of the straight section

of drum is 5m (not include ball shape head). The main equipments inside of it have:

Horizontal steam and water separator-----totally 32, arranged in two balanced row

Dry tank -----W type vertical wave plate dry tank, totally 12..

Distributed pipe of feed water ---- single end of feed water pipe is leaded into drum,

and two multi hole water distributed pipe along the length of drum is connected out

of it using three-way valve.

Continuous blowdown pipe ---- it is multi hole pipe, and it is leaded out from one

end after merging into single pipe in the middle of drum by three-way valve.

Dosing pipe ----- It is multi hole pipe, and it is leaded out from one end after merging

into single pipe in the middle of drum by three-way valve.

Arc dampers are installed along the straight part of the whole drum and these arc dampers

form a jacket room at the lower half of drum. The mixture of steam and water coming out

from the outlet pipe of water wall goes into this jacket, and then goes into horizontal steam

and water separator to separate, the steam goes into the upper room through central guide pipe

and then goes into drying tank; water goes down to the bottom of drum through drainage

outlet and iron wire net along water wall. The iron wire net reduces the kinetic energy of

draining water and make the brought steam overwing to steam room. The second separation

of steam is finished in drying tank. Because the flow velocity of steam gone into drying tank

is lower, and the direction of steam flow changed suddenly for many times, the water droplets

brought by steam can adhere on the wave plate better and these water droplets can flow to the

bottom of drum by gravity. After second separation, the steam will go into steam collectionroom, and it will be guide out by the connection pipe at the top of drum. The separated water

goes into drum, and goes into the centralized water draining pipe through anti-eddy device to

attend the next circulation.

. The water level in drum

The water levels of drum can influent the safe operation of boiler. The water level of drum is

controlled by adjust the feed water pump or the governing valve of feed water by operator.

The normal water level of boiler in Vikram Thermal Power Plant is at 76mm below the central

line of drum. The long-time operation under the condition of higher or lower this water level

will influent the performance of separator. If the water level of drum is 125mm higher thannormal water level (the highest safe water level or high alarm water level), DCS will alarm; if

it is 200mm higher than normal water level (The Max. highest water level or high water level

trip), the boiler will be shutdown by itself. High water level will flood the horizontal separator

and the ability of separating steam and water will be reduced; the low water level also can

reduce the efficiency of separator. The wet steam will leave the drum and go into superheating

system. If the water level in drum is 200mm lower than the normal water level (the lowest

safe water level or low alarm water level), DCS will alarm; if the water level is 280mm lower

than normal water level (lowest lowest water level or low water level trip), the boiler will be

shutdown by itself. The moisture in steam will make the solid impurities deposit on the pipe

wall of superheater and the blade of steam turbine, that will influent the safe and economic

operation of power plant seriously. So the operator should monitor the water level of drumusually.

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. Water level indicator

In order to monitor and adjust the water level and guarantee the normal water level, variouskinds of water level indicators are installed on drum.

a. Local close-up water level indicator

The local visual water level indicator is equipped near the drum of boiler. The steam and

water guide pipes are equipped in the steam and water room in drum to the outside of drum,

and then these steam and water pipes are connected and form a closed connecting device.

Transparent material such as mica is set in connection pipes, which can reflect the real water

level of drum visually. It is real and reliable.

No bland zone double color water level indicator is equipped on the drum in Vikram Thermal

Power Plant. They are installed at two sides of boiler, there is one at every left end plate and

right end plate as lock water level indicator to monitor and check the water level of drum.

b. Differential pressure type water level indicator

The differential pressure water level indicator transfers the water level signal into differential

pressure signal by a balanced container, and then it will be reflected by differential pressure

meter, thus we can know the water level and the varying condition.

Two double room balanced containers are equipped on the drum of boiler in Vikram ThermalPower Plant, and there are one on every left end plate and right end plate. It is used with

differential pressure transmitter together to monitor the water level of drum and output the

differential pressure signal when the water level is changed.

c. Remote level indicator

The remote level indicator measures the water level based on the difference of the

conductivity of steam and water. After the electrode of water level container is powering, it

will transfer the water level signal into electric signal. Electrode will become water level on

water level container. The insulation between the core of electrode and cover of water level

container should be good. Because the conductivity of steam is very small, and the resistanceis big, the electric circuit of the electrode in steam is blocked. The conductivity of water is

big, and its resistance is smaller, the electrode immersed in water connects with the shell, the

AC current will bright the indicating light by water. So the water level decides the amount of

electrodes immersed in water. If the water level is high, the electrode immersed in water will

be more, and the bright indicating lights will be more. We can know the water level from the

amount of bright indicating lights.

Remote level indicator is equipped on the drum of boiler in Vikram Thermal Power Plant, and

it is equipped at two sides of the drum of boiler. One is equipped on left end plate and one is

equipped on right end plate. There are 19 electric junctions, and there also have the functions

such as visual and audible alarm, output of lock out signal and so on as the alarm, indication,and protection of water level.

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Chapter Water wall and down comer

Water wall is the important steam heating surface that is arranged around the furnace, top of

furnace and air arrangement plate. Water wall can absorb the radiating heat released in the

combustion of fuel in furnace, and then transfer this heat to the water or mixture of steam and

water in pipes to evaporate a part of water. The pitch between the pipes of the water wall of

front wall (including the top of furnace), rear wall and side wall of boiler is 76.2mm and the

size of it is 51mm. The pipes of front wall and rear wall are 75 respectively; the air

arrangement plate is composed by 38 inside screw pipes whose size is 63.5mm pitch is

152.4mm. The bottom of air room is composed by 38 51mm whose pitch is 152.4mm. the

sizes of the outlet and inlet header of all water wall are 219mm.

Down comer is an equipment that can send the water in drum into the down header of waterwall and then into water wall continuously without interruption. Two pipes that can lead water

into every down header of water wall respectively are adopted by the boiler in Vikram thermal

power plant. The arrangement of the centralized down comer and draining water connected

pipe are shown in attached drawing 8.

Chapter Economizer

. The function of economizer

Economizer is a kind of equipment that uses the heat energy of fuel gas at the end of boiler to

heat the feed water. After adopting economizer, the Gas temperature leaving AH is reduced;and the temperature of feed water is increased; the material is saved, and the differential

temperature between feed water and the wall of drum is reduced.

. The arrangement of economizer

The economizer in Vikram thermal power plant is arranged inside of the vertical well of

boiler, and it is composed by three horizontal pipes; the pipe is 32 SA-210M A1 bare pipe;

there are 76 sheets along the direction of width, and the horizontal pitch is 74, and it is

arranged in the type of two cycle in-line position.

The routine wearing protection measures adopted by the pipes of economizer: currentdistribution plate is equipped between the inlet of pipe team of economizer and the walls

around to prevent flue gas from deviating; the pipes in the front row of every pipe team adopt

wearing cover plate.

The feed water is led from the left side of inlet header and flows through the pipe team of

economizer, and it is led into drum through connecting pipe at the right side of outlet header

at last.

. Recirculation of economizer

Because economizer is heated equipment, after shutdown or when the water is not supplied in

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the beginning time of starting up boiler, in order to avoid static vaporization of the water

inside of the pipes of economizer, the re-circulating valve of economizer should be open using

the water in drum to cool the economizer. One end of the re-circulating pipe of economizer inVikram Thermal Power Plant is connected with down comer and the other end is connected

with the distributed header of the inlet header of economizer. A motor-driven valve is installed

on this pipe. It is closed when the operation of boiler is normal to prevent the feed water from

going into drum directly and avoid threatening the safety of economizer and drum.

Chapter Feed water system

Feed water system is the important compositing part of drum. It is composed of feed water

pipe, economizer, drum, re-circulating pipe and relevant parts. Its task is supplying water to

boiler and absorbing the heat of flue gas to improve the temperature of feed water.

The feed water of the boiler in Vikram Thermal Power Plant is guided to the inlet header of

the economizer in tail flue duct firstly, and then the feed water refluxes upwards into the outlet

header through the pipe teams of economizer that are horizontally arranged, and then the feed

water goes into drum from the right end plate of drum through the guide out pipe of

economizer

The feed water coming from machine side should be inducted into control desk of feed water.

The adjustment and control of boiler feed water are realized by the control desk of feed water.

There are three feed water pipes on the control desk of feed water in Vikram Thermal Power

Plant; and motor-driven stop valves, motor-drive drop gates and governing valves areequipped on every feed water pipe to control the feed water of boiler.

Before the feed water pipes are put into operation, the air valve and the air vent valve to

atmosphere on steam header must be open, and other valves on pipes must be closed. Then

start up the feed water pump and open its outlet valve to feed water; this valve cannot be

closed until water overflows the dewatering outlet. In addition, when switch over the feed

water pipes, the motor-driven valve of the feed water pipe that is prepared to put into

operation must be open first and then the motor-driven valve of the feed water pipe that is

prepared to stop using can be closed.

The switchover procedures of feed water pipe are:

A. Open the motor-driven valve of feed water pipe that is prepared to put into operation.

B. Turn down the governing valve of feed water pipe that is prepared to stop using, and turn

up the governing valve of feed water pipe that is going to be put into operation till the

governing valve of the feed water pipe that is going to stop using is closed completely. The

flow of feed water should be not changed.

C. Close the motor-driven valve of feed water pipe that is prepared to stop using.

Chapter Blowdown of Boiler

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The feed water gone into boiler has salt content, and the boiler water will corrode the boiler to

produce corrosion product. So, the boiler water will contain various dissolved and un-

dissolved impurities more or less. Although the impurity content and corrosion produce in thefeed water of boiler is very small, but the salt content brought away by every kilogram of

steam is smaller than the salt content brought in by every kilogram of water. So the amount of

salt and water dross will be increased gradually along with the evaporation of boiler water.

The too big salt content in boiler water not only pollutes the steam but also scales on the

heating surface of water wall or even corrodes the heating surface.

In order to maintain the salt content in boiler water in allowable range, a part of boiler water

should be discharged in operation, and some clear feed water should be supplied into boiler to

instead of this part of boiler water in order to remove a part of salt and water dross. This kind

of method is called blowdown.

Blowdown of boiler is one of the most important methods to improve the quality of steam. In

power plant, there are two blowdown methods: periodic blowdown and continuous

blowdown.

Periodic blowdown is done at the down header under the water wall of boiler. Its task is

removing the water dross accumulated at the lower part of boiler and the soft deposition

produced after phosphate treatment. The time of periodic blowdown is very short, but the

ability of removing the deposition in boiler is very strong.

The continuous blowdown can blowdown the boiler water whose thickness is biggest fromthe surface of boiler water continuously. Its aim is reducing the salt content in boiler water

and preventing the too high thickness of boiler water from affecting the quality of steam.

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SectionSuperheated and Steam Temperature Adjustable Equipment

Chapter Superheater

. Classification of superheater

Superheater is the important compositing part of boiler. Its function is heating the saturated

steam coming from drum to superheated steam with certain temperature and pressure. The

superheater can be divided into three kinds: radiation, half radiation, and convection

according to the different heat exchanging methods. The arrangement of superheater can be

divided into three ways: co-current, countercurrent, and mixed-flow according to the relative

direction of steam and flue gas.

. The working characteristics of superheater

The working characteristic of superheater is called steam temperature characteristic; it refers

to the variation relationship between the load of boiler and the temperature of steam.

Generally, the temperature of the steam of convection superheater will be increased along

with the increasing of load. When the load is increasing, the consuming speed of fuel is

accelerated, and the heating transferring ratio increase; the temperature of flue gas of the

outlet of furnace increases too, so the differential temperature of heat transformation is

increased. The heat absorbing amount of unit steam increases, so the temperature of

superheater steam rises.

The steam temperature characteristic of radiation superheater is that the temperature of steam

will be reduced if the load is increased. When the load is increased, the amount of steam will

be increased; the radiation heat obtained by radiation superheater is not increased along with

the increase of steam amount in direct proportion; the amount absorbed by unit steam reduces

so the temperature of steam is reduced.

. The flow of superheater system

In Vikram Power Plant, after leading out from drum, the saturated steam is leaded into the

upper header at the inlet flue duct of insulation cyclone separator by saturated steam

connected pipes; it goes into the down header of the inlet duct after going downwards into

cooling flue duct; and then it is guided into the bottom ring header of cyclone separator by

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connected pipes; and then it is leaded into the upper header at the front enclosure of tail

vertical well from the upper ring header of cyclone separator through connected pipe after

going upwards into cooling separator. It passes through front enclosure superheater, two sidesenclosure superheater, rear enclosure superheater and collects in the inlet header of low

temperature superheater, after flowing downwards into the tube bunch of low temperature

superheater that is horizontal arranged, it is guided into the platen superheater from the left

side of boiler by connected pipe; and then it returns the high temperature superheater in the

tail vertical well from the right side of boiler by connected pipe; at last the qualified superheat

steam is leaded from the outlet header of high temperature superheater. Water spraying

temperature reduction whose adjustment is flexible is adopted for superheater system to adjust

the temperature of steam and protection the pipes of heating surface of every stages. There are

two stages of water spraying in the whole superheater system. The primary attemperator is

installed on the pipe from the outlet of low temperature superheater to the inlet of platen

superheater for coarse adjustment; the secondary attemperator is fixed on the connected pipes

between the platen superheater to high temperature superheater for fine adjustment. The

above two stages of water jet attemperator can reaches the aim of eliminate the deviation of

the temperature of steam by the method of adjusting the amount of spraying water.

1. Enclosure superheater

The walls of enclosure superheater are connected by the inlet and outlet headers; at the inlet

of flue gas at the upper part of front wall of enclosure superheater, the pipes are sparse to

make the pitch increase to 360 from 120 and form the inlet flue gas access; the upper part of

the pipes of rear wall bend to the direction of front wall and form the roof of tail vertical well;the front wall and rear wall are composed by 46 pipes respectively, the size of pipe is42, and

the size of suspending pipes at the inlet flue window of front wall is60; The walls at two

sides are composed by 3142 pipes respectively. Except the size of the upper heater and

down header of front enclosure and the inlet header of superheater is273, the size of other

headers of enclosure superheater is 219.

The characteristic of enclosure superheater is convection heat exchange.

2. Low temperature superheater

The low temperature superheater is fixed in the flue duct of tail convection vertical well. Thelow temperature superheater is composed by 46 pieces of double winding horizontal pipe

rings arranged along the width direction of boiler which is sequential and downstream

arrangement and whose size is 38. Routine wearing protection measures is adopted by low

temperature superheater. Flow blocking board is fixed between the inlet of the pipe team of

low temperature superheater and the around wall to prevent deflection of flue gas. The

wearing cover plate is adopted at the windward surface for the pipe of front row of low

temperature superheater. The 273 outlet header of low temperature superheater is arranged

at the vertical rigid beam at the rear wall of vertical flue duct.

The characteristic of low temperature superheater is convection heat exchanging.

3. Platen superheater

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The platen superheater has two pieces arranged at the upper part of furnace and near to the

front wall of furnace. The superheater is membrane structure; the pitch of pipes is 63.5mm.

There are 2442 pipes for every piece. Wearing material is laid at the lower part of platensuperheater. The whole platen superheater expands from the lower part to upper part. The

outlet header of platen superheater is installed at the upper part of furnace.

The characteristic of platen superheater is radiation heat exchanging.

4. High temperature superheater

The steam comes out from secondary water spraying attemperator and then flow into the high

temperature superheater installed at the upper part of tail flue duct through connected pipes.

The steam is leaded from the right side of the inlet header of high temperature superheater

outside the boiler, and after flowing through the high temperature superheater in the reverse

direction of flue gas, it goes into the outlet header of high temperature superheater. The high

temperature superheater is double winding four circles worm tube bunch whose outer

diameter is38; and there are 46 pieces of tube bunch along the direction of width.

The characteristic of high temperature superheater is convection heat exchange.

ChapterAttemperating water system

The temperature of steam is one of the most important parameters that have to be monitored

and controlled in the operation of boiler as water level. If the temperature of steam is too high,it will accelerate the creep deformation of metal and affect the security of boiler and steam

turbine directly; if the temperature is too low, the thermal efficiency of steam turbine will be

reduced, the humidity of the steam at the last stages of steam turbine will be increased to

corrode the blade of steam turbine even produce water impact when serious; so the

temperature of steam has to be controlled in regulated range. The adjustment of steam has two

aspects: adjustment at steam side and adjustment at flue gas side. Attemperator is the common

equipment used to adjust the temperature at steam side.

There are two kinds of attemperator: mixed attemperator and surface attemperator. The mixed

attemperator is water and steam mixture device; and surface attemperator is heat exchanger.

The attemperator used in Vikram Thermal Power Plant is mixed attemperator.

. Primary attemperator

Primary spraying water attemperator is installed in the steam connected pipe from the outlet

header of low temperature superheater to the inlet header of plant superheater at the front wall

of furnace. Spraying pipe and mixed sleeve are installed inside of it. The mixed sleeve is

installed at the downstream of spraying pipe used to prevent the attemperator from heat

impact. Temperature and flow measuring device is installed on attemperating water pipes to

measure the amount of water spraying entering into attemperator and the temperature behind

attemperator.

. Secondary attemperator

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The secondary spraying water attemperator is installed in the steam connected pipe from the

outlet header of platen superheater to the inlet header of high temperature superheater of tail

convection flue duct. The temperature of superheat steam can be adjusted further in thesecondary spraying water attemperator. The structure of secondary attemperator is same with

the primary attemperator basically.

. The application of attemperator

When the temperature is variable, the primary attemperator is used for coarse adjustment and

the protection of platen superheater to prevent the pipe wall from exceeding temperature. The

secondary attemperator is nearest with the outlet of superheater. When the temperature of

superheat steam is changed, it is used for fine adjustment and it can adjust the temperature of

steam in regulated range soon; in addition, it also can protection the convection superheater in

thermal section to prevent this superheater from exceeding temperature.

The temperature of the steam whose temperature is reduced by water spraying entering into

the inlet header of platen superheater and the inlet header of high temperature superheater

should be 11 higher than the saturated temperature under the pressure of the inlet of pipe.

In the initial stages of the startup of boiler, the temperature of steam is low, and the superheat

degree is also very small, the thermal load of furnace is not big, the flow of steam is small, the

flow velocity is low, and the speed of temperature rising is controlled within 1~1.5 usually.

This temperature rising speed should be controlled by combustion instead of controlled by

spraying water, and attemperator should not be used at this time. In the startup of boiler, whenthe pressure of steam raises to 1.0~1.2MPa, the attemperator should be back washed .The aim of this is prevent attemperator from blocking. The washing should be done in single

loop way that is benefit for the effect of washing. When the fire in boiler is flame out, the

attemperator should be paralleled off immediately to prevent the temperature of steam from

going down rapidly. After discharging water of boiler, the water deposited in the water pipes

of attemperator should be discharged that is benefit for the anticorrosion of pipes.

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Section Air and Gas System

Chapter Ventilating device

. The method of ventilation

In the combustion course of boiler, the air needed by combustion has to be sent into furnace

unceasingly, and the product of combustion should be removed continuously. This kind of

procedure is called ventilation of boiler.

The ventilation methods of boiler are four: natural ventilation, negative ventilation, boost

ventilation, and balanced ventilation. The one adopted by Vikram Power Plant is balanced

ventilation. In air and gas system, there are IDF and FDF. The resistance in airway is gotten

over by FDF, and the resistance of flue duct is gotten over by IDF.

The working condition of air fan will affect the operation of boiler greatly. The load of boiler

is usually limited by the insufficient output or insufficient pressure so that the reliability of the

operation of boiler unit becomes bad.

One primary air fan, one FDF, and one IDF will be supplied for every boiler in Vikram Power

plant. Every one of them can operate independently under 100% BMCR. Two j valve air

fan and one pressure air fan are supplied for every boiler.

. The classification and function of the air system of circulating fluidized bed boiler

1. Primary air

Function: Fluidize the bed material in furnace, and send a certain amount of oxygen to the

dense phase area at the bottom of furnace to support the combustion at the same time.

The head pressure of primary air is decided by the content and density of material, the size of

solid particles, the thickness of bed material, the temperature of bed layer, and so on. The

amount of primary air is decided by the speed of fluidization, the characteristic of fuel, the

combustion in furnace, the heat transformation, and so on. The amount of primary air is

40~70% of total air amount.

One single induction centrifugal primary air fan will be supplied for every boiler in VikramPower Plant. The model of this air fan is G9-19-11 N0 20.6D.

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2. Secondary air

Function: make up the oxygen combusted in boiler and strengthen the mixture of material; inaddition, it also can adjust the distribution of the temperature field in boiler properly. It can

prevent from too high temperature of flue gas in partial area and reducing the discharging

amount of NOx. The layered secondary air entered also can reduce the temperature of bed.

One single induction centrifugal secondary air fan (FDF) will be supplied for every boiler in

Vikram Power Plant. Its model is G6-25-14 N0 20D.

3. Sowing coal air

Function: The coal feeding can go into furnace uniformly; the combustion efficiency can be

improved to make the temperature in furnace become uniform. And it also can seal the coal

chute.

The secondary air was used as sowing coal air in past commonly, but primary air is used as

sowing coal air now. Because the air pressure of primary air is not enough, one boosting

pressure air fan should be supplied to boost the pressure.

One single induction centrifugal boosting pressure air fan is set for every boiler in Vikram

Power Plant, and its model is G9-12-11NO11.2D.

4. Returning material air

Blow the material in material returning device become loose to make the material in material

returning air room fluidize slightly and make the returning material can drop into furnace

smoothly.

Two Roots material returning air fan (J valve air fan) are set of every boiler in Vikram Power

Plant, and their model is 3L52WC.

. The operation of ventilation device

The air fan should be checked before startup to confirm the cooling water and lubricating oilare normal. The inlet damper should be closed when start up the centrifugal air fan; the outlet

and inlet dampers should be open when start up Roots material returning air fan, and then, the

air fan can be started up to prevent from startup with load. After the monitor is normal, the

inlet damper can be opened gradually.

The adjustment of air fan is changing the working condition of air fan manually to make the

working flow amount can meet the necessary of the working condition of air power in boiler.

The common adjusting methods have throttle adjustment, guiding adjustment and speed

variation adjustment. The IDF and FDF used in Vikram Power Plant adopt guide adjustor;

governing valve is set at the axial direction in front of the air inlet of air fan, and governing

guide blades are installed on governing valve that are fixed evenly on circle, the guide bladeis supported by juncture bearing; the steam amount can be adjusted by changing the openness

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of blade so that the working characteristic of air fan can be changed. This kind of adjusting

method is convenient and economic.

Chapter Air Preheater

Air preheater uses the residual heat of flue gas to raise the temperature of air, that improves

the thermal efficiency of boiler greatly and strengthen the combustion in boiler. The air

preheater can be divided into two kinds: regeneration and surface, and the second type also

can be divided into platen preheater and tube preheater.

The air preheater used in Vikram Thermal Power Plant is platen air preheater. The

arrangement of it is horizontal type, and it is positioned under the flue duct of tail vertical

well. The pipes of it are 452.5mm, 453.5mmnormal carbon steel pipes; these pipes aresequentially arranged; the transverse pitch of the pipe tanks of primary air and secondary

pipes is 76mm; and the longitudinal pitch is 60mm. Every two pipe tanks are connected by a

connecting tank to form two independent accesses from each other. The primary air and

secondary air go through these two accesses with different pressures in pipes and exchange

heat with the flue gas flowing outside the pipes. The arrangement of flue gas and air is

crossed. The temperature of the air at outlet is 199 .

Chapter Flow of air and gas system

The circulation of the material inside of the circulating fluidized bed boiler in Vikram

Thermal Power Plant is startup and maintained by the kinetic energy supplied by IDF andFDF. Balanced ventilation is adopted by for boiler, and the balanced point of pressure is

positioned at the outlet of furnace.

After the air coming from primary air fan is heated by air preheater, the first part of it goes

into the air room at the bottom of furnace, and fluidizes the bed by the blast cap arranged on

air distributed plate, and forms upward two phases flow of gas and solid that will go through

furnace; two high speed diesel oil igniting burners under bed are equipped on this road. After

heated by air preheater, the second road of hot air will be boosted by coal feeding booster fan

using for pneumatic coal distribution. The air coming from secondary air fan is divided into

two roads. After heating by air preheater, the first road is sent into furnace through the

secondary wind box at the upper part of furnace directly; the second road is not heated bypreheater, and this part of air is used as the seal wind of belt conveyor. The air fan should be

equipped for slag cooler respectively, and this air fan supplies fluidized air to slag cooler. The

wind gone out of slag cooler is leaded into boiler a secondary air.

The flue gas and the solid particles brought by it leave the furnace and go into cyclone

separator through the flue duct of the inlet of cyclone separator installed on the rear wall of

water wall. In separator, overwhelming majority material particles are separated from the flow

of flue gas, and the flue gas is guided out through the central barrel of cyclone separator, and

guide into the flue duct of tail vertical well from the flue duct of the outlet of separator; and it

enters from the flue window of front enclosure and flows downwards to wash the horizontal

convection heating surface pipe team arranged in it to transfer the heat to heating surface; and

then the flue gas flows through the horizontal air preheater and goes into dust remover; at last

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it extracts into chimney by IDF and vents into atmosphere.

There are three Roots fan with high pressure head installed for two J valve materialreturning devices of boiler; the output of every air fan is 100%. In normal operation, every

boiler uses one air fan, and the last one is used to standby for two boilers. The air fan is fixed

capacity type, so the adjusting principle of the air amount of returned material is sending the

residual air through bypass into the air duct of first road of primary air.

Section Dust Removing and Slag Disposal System

After burning in boiler, the coal becomes ash. The ash can be divided into two parts: one part

is exhausted out of boiler along with flue gas, and the other part is deposited in boiler. The

former is called fly ash, and the latter is called slag.

If a large amount of fly ash is exhausted into atmosphere, it will cause serious harm: first, the

thickness of dust in atmosphere will be raised, and the environmental health will be affected

that is bad for the health of human; second, the fly ash is bad for the power plant itself, it will

aggravate the wearing of FDF and reduce the insulation level of electric equipment.

In order to reduce the thickness of dust in atmosphere and prevent from sharp wearing of

FDF, the fly ash must be collected by dust remover. So dust remover is the indispensable

auxiliary equipment of coal-fired boiler.

The slag collected in boiler and the fly ash collected by dust remover must be snapped out intime and rapidly. Or the safe and economic operation and the environmental health on site

will be affected. So, a set of ash handing and removing system must be equipped for coal-

fired boiler.

. Dust remover

In order to satisfy the requirement of environment protection, bag filter is used in Vikram

Power Plant; the efficiency of dust remover is 99.9%. #1 and #2 boilers are connected with a

same chimney at the same time (the height is 110m, and the diameter of the outlet of every

flue duct is 3m).

. Bottom ash handling system

1. Fixed slag removing pipe

There are three fixed slag outlet (159) along the width direction of air distributed plate at the

bottom of furnace. The slag is removed from the slag outlet of water wall in air room at the

bottom of furnace. The evaporation of slag outlet is 4400. There is one emergency slag outlet

among them. The advantages of bottom slag removing are the operation is safe and reliable,

and the operation is simply and convenient.

2. Slag cooler

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There are two multi-pipe water cooling type drum slag cooler arranged under the normal slag

outlet at the bottom of furnace; the slag is removed from the bottom of wind water wall; bell

jar type blast cap is installed on the air distributed steel plate of slag entering pipe; the smoothtransportation of slag from furnace to slag cooler can be guaranteed by the uniform

arrangement by blast cap.

Multi-pipe water cooling drum slag cooler adopts several small barrel built-in spiral blade to

transfer cooled slag at the same time; the high temperature material rotates along with the

small barrel of several built-in spiral blade, and the material is transferred continuously; the

cooling water goes through the intermediate layer between small barrels continuously and

uniformly and exchange heat with the high temperature slag indirectly, in this way the high

temperature material is cooled; the temperature of cooling water rises and it can be used

again. The heat exchanging surface of this structure is large, the heat exchange is rapid, and

the efficiency is high. There is no fly ash and heat radiation because the material feeding and

discharging device and rotating barrel adopt seal structure.

The slag cooler is composed by material feeder, heat exchanging barrel, discharging device,

driving device, base frame, rotating joint, and control tank and so on. The variable frequency

governing speed control is adopted, the speed can be governed continuously according to the

carbon content in a large range of slag, and it is benefit for steadying the pressure of bed.

. The principle of impulse bag filter:

The flue gas goes into the ash hopper from the inlet, and then it will go into the bag filter. Thedust will adhere on the outside surface of filter and the purified gas will be discharged into

atmosphere through the air exhaustion pipe and then through the stack by air fan. The

resistance of bag filter will be increased continuously along with the increasing of the dust

adhered in bag filter. When the resistance is 1500-1800pa, the dust in bag filter should be

removed so that the bag filter can work continuously. The filtrate bag is arranged in a straight

line. One pulse valve is used to control the compressed air pulse to remove the dust. And the

pulse valve is controlled by program controller. In the process of removing dust, the dust

removing controller will send order to make the pulse valve release 0.5----0.7Mpa

compressed air in the same time of the action of pulse valve. This compressed air will go into

the filtrate bag through the small holes that face to the filtrate bag directly on the blowing

pipe; at the same time, and secondary gas flow is also produced at this time, so that a transientimpact will be produced and it will spread along the direction of the length of the whole filter;

so that the dust depositing on the outside of bag will drop. The dust will fall into the material

hopper and be sent into the ash yard by ash conveying system. The lasting time of pulse can

be adjusted to suit the characteristics of the different dust.

There are four rooms of the bag filter used in this power plant. There are 288 bags in each

room. The total numbers of bags is 1152, and the filtrate area is 4052 m 2. The specification of

bag is 140 800 mm.

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Section Hydraulic Test of Boiler

Hydraulic test is a method that can check the tightness of bearing components of boiler, and it

is also a test for the strength of bearing components. The hydraulic test must be done after

new installation or overhaul of boiler in order to check the unit thoroughly. It is a examinemethod to guarantee the safe operation of bearing components of boiler.

The classification of hydraulic test

1. The hydraulic test at working pressure

The hydraulic test at working pressure is generally done after repair and overhaul of boiler.

The test pressure is the working pressure of drum, i.e. 10.98Mpa.

2. The hydraulic test at over pressure

According to the Supervisory Regulation of The Safe Technology of Steam Boiler issued by

Labor and Personnel Ministry of PRC, the hydraulic test has to be done in the first operation

and after any repair of any bearing component. The test pressure is 1.25 times of the working

pressure of drum, i.e. 10.981.25=13.725MPa. The over pressure test of boiler is harm for the

service life of it, and this test is dangerous, so it should be done as less as possible.

The requirements for water quality in hydraulic test:

The boiler in hydraulic test has been filled treated water fully. The water used in the

hydraulic test in Vikram power plant should be condensate water or demineralisedwater.

The temperature of the test water should be in the range of 20~70 , but it should be

higher than the temperature of environment. The temperature of water should be near

to the temperature of the metal wall of drum at the beginning of filling water, and the

temperature of other bearing components should be no less than 20 . The aim of it

is to guarantee the hydraulic test can be finished at the temperature higher than the

transferring temperature of metal from brittleness to plasticity.

. The qualified standard of hydraulic test

Raise the pressure to test pressure, close the valves on feed water pipes; after stop the feedwater pump, the pressure reducing of drum is not bigger than 0.5Mpa in every 5 minutes;

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there is no leakage on the metal wall and welding place of compression components, and

there is also no obvious deformation.

. The operation procedure of hydraulic test:

1. The check before hydraulic test:

1) All impurities and tools have been left.

2) There is nobody in unit.

3) The pressure gauge has been calibrated correctly and it has been installed on the

drum correctly; its valves are in opening condition.

4) Any component that does not bear the pressure of hydraulic test in design has

been insulated or divided properly.

5) The action states of all valves are at correct position.

6) All spring hanging pins are fixed on a fixed position in steam system.

7) All safety valves have been insulated.

8) The emergency water discharging valve and exhaustion valve to atmosphere in

order to depressurize over pressure;

2. Fill water into boiler

1) After the water quality is qualified proved by analysis, close the water discharging

valve of drain water tank, re-circulating valve of drain water pump, stop valve gone

to deaerator, and open the demineralised water valve, and keep the water level ofdrain water tank above 1/2.

2) Close the drain water valve of feed water system, discharging water valve of

economizer, emergency water discharging valve, back washing valve of superheater,

valves on the pipes of attemperator, and drain water valve.

3) Open the inlet valve of drain water pump, exhaustion valve to atmosphere, stop

valve of the water feeding to cold boiler, general valve of periodic blowdown

station, and every branch valve.

4) Start up drain water pump, and control the speed of water feeding at outlet valve.

After seen water in drum, open the re-circulating valve of economizer to supply

water into economizer till the water in bearing components is full; after the air in

main steam system is discharged clearly, close air valve, exhaustion valve toatmosphere, and the valves in cold boiler water feeding system in succession; stop

the operation of drain water pump, and close the outlet valve of pump and the water

approaching valve of demineralised water. At the same time, when seen water in

drum, put steam into operation to increase the temperature till 50-70C. If cold boiler

water feeding system of drain water pump is in trouble, should use small bypass to

feed water and go another way.

5) In order to reach these temperatures of hydraulic test, the temperature of water can

be raised by the following ways:

When the oil ignition system under the bed of boiler cannot be put into

operation (such as in the beginning of operation), if the temperature of the

medium in drum is lower than 20 , saturated steam can be put into drum by blowdown of drum or through medicine dosing pipe to heat the water and barrel

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to the necessary temperature. when the operating water level in drum is normal,

the water should be heated till its temperature is 2~5 higher than the

recommended temperature to guarantee the final temperature of water is notlower than the smallest recommended value.

If the igniter under the bed of boiler can be put into operation, after the filling

water of unit reaches the normal water level, the high speed diesel oil igniter can

be fired to raise the temperature of drum till it is 2~5 higher than the

recommended value. Flame out and fill water continuously.

3. Raising pressure

1) After filling water fully, the feed water pump is used to pressuring the bearing

component. The adjustment for the speed of main raising pressure is controlled by

the governing valve of small bypass. In hydraulic test, the raising and reducing of

pressure should be slow. When the pressure is lower than working pressure, the

raising and reducing speed cannot exceed 0.196~0.29Mpa/min; and when the

pressure is near to the working pressure, the speed should be slower; and after

exceeding the working pressure, the raising and reducing speed cannot exceed

0.098Mpa/min. Because water does not have compactibility, every component will

bear equal pressure. The emergency water discharging valve can be used to control

the pressure release.

2) The pressure raising cannot be stopped till it reaches 1.0-1.5 MPa, and then a total

check should be done.

3) The pressure is raised to working pressure, close the governing valve and motor-driven valve at small bypass; and stop the raising pressure to check completely; stop

the operation of feed water pump after confirming there is no problem, and write

down the speed of pressure reducing.

4) Over pressure hydraulic test.

All water level monitoring instruments do not attend the over pressure

hydraulic test, and they should be paralleled off when reaching working

pressure.

When the pressure raises to working pressure, the raising pressure

should be stopped to check completely; after there is no problem, the pressure

should be raised till 1.25 times working pressure; after keeping for 20 minutes,

it should be reduced to working pressure, and check it completely.

4. Pressure release

After checking, the pressure can be reduced, and the speed of pressure reducing can be

controlled at no more than 0.3Mpa/minute by emergency water discharging valve. When the

pressure reduces to normal, open the air valve, drain water valve, pulse safety valve, steam

coming valve of steam system; and use emergency to discharge water till normal water level

in drum. After finish the test, the blind or block on safety valve should be demolished, and all

positioning bin of spring hanger should be removed.

After the hydraulic test is finished, the boiler water should be discharged clearly and theanticorrosion and maintenance measures should be set down in time; if the environment

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temperature is lower than 5 , the antifreeze measures also should be adopted.

Section Normal Startup, Shutdown and Operation of Boiler

Chapter Startup of CFB boiler

The startup of boiler include drying out, boiling out, first time startup, normal startup

for new installed unit. The normal startup of boiler can be divided into two kinds: cold state

startup and hot state startup. The cold startup refers to the startup after repair or long time

standby under the condition without pressure and the temperature is normal; the hot startup

refers to the startup under the condition of boiler has standby for short time, and it still keeps

certain pressure and temperature. The courses of hot startup and cold startup is same mainly,

just some working contents can be omit or simplify.

The cold startup of boiler include: the checks and preparation before startup, ignition,

boosting, warm up pipes, adding load and so on.

. The preparation before startup of circulating fluidized boiler

Before ignition of boiler, a thorough external check has to be done for boiler to guarantee the

security of equipment and person.

1. The following checks should be finished before the startup of boiler.

1) All air fans must be able to put into operation; the lubricating system must be able to

put into operation at any moment; the equipment should be operated normally under

the condition whose vibration is in the allowable deviation range.

2) All dampers, operators, and actuators have to be checked thoroughly; these auxiliary

equipments have to be able to satisfy the requirements of all operating working

condition without cementing or blocked. Conform the dampers can reach its right

position according to the requirement of control.

3) Guarantee the dust removing system has been connected with slag cooler and the

slag cooler has been prepared well to put into operation.

4) All remote operating valve and sliding drop gates can be able to operation. Check the

position limit switch to confirm whether the installation is correct or not and supplythe exact position indication.

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5) The trial runs of all transferring devices have to be done to guarantee its normal

operation.

6) All key flow devices have to be calibrated.7) The ignition device under bed and flame detector and interlock device must be under

the condition of preparing to operation.

8) All key thermocouples and pressure transducers have to be checked to confirm their

connections are correct and make sure they are able to operate.

9) All flue ducts, airways, pipes, grooves, or guide pipes of air, flue gas, water, steam,

and solid fluid have to be connected correctly and reliably.

10) All expansion joints have to be check to confirm the correct connection.

11) The dust remover has to be checked to confirm the system can operate normally.

12) All electric joints must be checked to prove that they have been installed correctly

and they have good insulation.

13) Check the remote water level indicator of drum is working; compare its reading with

the local water level indicator exactly. This procedure should be done periodically.

2. The following works have to be done well before operation.

1) Before operation, when the water level of drum is lower than the lowest sighted point

of double color water level indicator, the water inside of water level indicator should

be drained completely. Whenever the water level indicator is repaired or replaced,

whether draining water of it is normal or not should be checked.

2) The blowdown pipes of balance container and water level indicator should be

connected to safety area, and the blowdown valve has to be closed. Suitable lightshould be supplied for double color water level indicator in order to benefit the

operator on operating plate to obvious the reading of water level indicator.

3) All exhaustion pipes drain water pipes and blowdown pipes have to be benefit for

operation and should be connected to blowdown container or other safe place

correctly to prevent from threatening the security of operator at any time.

4) The valves between the drum and water level indicator have to be locked at fully

opening position.

5) The blinds of all safety valves and hydraulic test have to be demolished. The valves

must be under the good working condition; the dump steam of safety valve and the

drain water pipe must be arranged and supported according to the recommendation

Date post:	05-Apr-2018
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