boiler operating course

7/28/2019 Boiler Operating Course

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OPERATION OF BOILERS

OPERATION OF BOILERS........................................................................................................................... 4

1.1 PREPARATION BEFORE OPERATION OF BOILERS ........................................................................... 4

1.1.1 Boiler Hydrostatic Pressure Test................................................ 4

1.1.2 Scope of Hydrostatic Test and Requirements on Water............................ 4

1.1.3 During the hydrostatic test, water filled in different equipment is not the same: ........ 4

1.1.4 Preparations for Hydrostatic Test ............................................... 5

1.1.5 Procedures of Hydrostatic Test ................................................. 6

1.2 CHEMICAL CLEANING ................................................................................................................... 8

1.2.1 General ..................................................................... 8

1.2.2 Chemical cleaning scope...................................................... 8

1.2.3 Chemical cleaning medium .................................................... 8

1.2.4 General steps of chemical cleaning ............................................. 9

1.3 BOILER STEAM PURGE ................................................................................................................ 10

1.3.1 Range of boiler steam purging ................................................ 10

1.3.2 Steam purge mode .......................................................... 11

1.3.3 Steam purge requirements ................................................... 11

1.3.4 Precautions for steam purge .................................................. 11

1.4 FEED WATER AND BOILER WATER TREATMENT .............................................................................11

1.5 DRUM BOILERSTARTUP ............................................................................................................. 12

1.5.1 General Introduction for Boiler Startup.......................................... 12

1.5.2 Characteristics of Drum Boiler Startup.......................................... 12

1.5.3 Boiler startup state classification............................................... 13

1.5.4 Essential Conditions for Boiler Startup.......................................... 14

1.5.5 Necessary Conditions for Boiler Startup ........................................ 14

1.5.6 Cold State Startup of Boiler................................................... 15

1.5.7 Warm State Startup (The Warm State Startup Curve Refers to Fig. 3.) .............. 19

1.5.8 Thermal State Startup (The Curve for Thermal State Startup Refers to Fig. 4.) ....... 20

1.5.9 Extremely Thermal State Startup (The Curve of Extremely Thermal State

Startup Refers to Fig. 5) ............................................................... 20

1.5.10 Boiler Thermal State Startup ................................................. 20

1.6 BASIC OPERATION FORWATERDRAINAGE AND STEAM EXHAUST............................................. 21

1.6.1 Basic Principles ............................................................. 21

1.6.2 Operation for Drainage and Steam Exhaust Valves at Cold Startup ................. 22

1.6.3 Suggestions for the Operation of Drainage and Steam Exhaust Valves at Warm

State startup. 23

1.6.4 Suggestions for the Operation of Drainage and Steam Exhaust Valves at

Thermal State Startup................................................................. 24


Extremely Thermal State Startup: ....................................................... 26

1.7BOILERSOOT BLOWING ..................................................................................................................... 27

1.8 BOILERBLOWDOWN AND WATERDRAINAGE .................................................................................. 28

2. BOILER OPERATION ADJUSTMENT ................................................................................................. 29

2.1CONTENT OF BOILEROPERATION ADJUSTMENT ................................................................................. 29

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2.2THE INFLUENCE OF WORKING CONDITION CHANGES ON BOILERPARAMETERS ................................ 29

2.3BOILERSTEAM TEMPERATURE CONTROL AND ADJUSTMENT ............................................................. 30

2.3.1 The Influence of Steam Temperature on the Safe and Economic Operation of

the Unit 30

2.3.2 Heat-Transfer Characteristics of Boiler Heating Surfaces ......................... 31

2.3.3 Drum Boiler SH Steam Temperature Control and Adjustment ...................... 32

2.4CONTROL AND ADJUSTMENT OF REHEATED TEMPERATURE ............................................................... 33

2.4.1 The Characteristics of Reheated Temperature................................... 34

2.4.2 Factors influencing the temperature variety of reheating........................ 34

2.4.3 Adjusting method for reheated steam temperature ............................... 35

2.5CONTROL AND ADJUSTMENT OF BOILERLOADING AND STEAM PRESSURE ....................................... 36

2.5.1 The Impact of Steam Pressure Swing .......................................... 36

2.5.2 The Reasons of Steam Pressure Variation ...................................... 36

Reasons for causing the steam pressure of boiler are plenty; mainly in two aspects:

one is the external factor of the boiler; the other is the internal factor. ........................ 36

2.5.3 The Adjustment of Boiler Loading and Steam Pressure......................... 37

2.5.4 Steam pressure adjustment................................................... 38

2.6THE CONTROL AND ADJUSTMENT OF DRUM LEVEL ........................................................................... 39

2.6.1 The Importance of Keeping Steam Drum Normal Level ........................... 39

2.6.2 The Main Factors for Impacting the Drum Level Swing ........................... 39

2.6.3 Control and Adjustment of Boiler Steam Drum Level ............................. 40

2.7BOILERCOMBUSTION ADJUSTMENT .................................................................................................. 41

2.7.1 Purpose and Target of Combustion Adjustment .................................. 41

2.7.2 The factor influencing the combustion and measures intensifying combustion........ 41

2.7.3 Adjustment of Burner........................................................ 42

2.7.4 Principles of Combustion Control: ............................................. 43

3. SHUTDOWN OF BOILER....................................................................................................................... 46

3.1THE SHUTDOWN MODE AND PREPARATION OF BOILER........................................................................ 46

3.1.1 Shutdown mode of boiler..................................................... 46

3.1.2 Preparation for the shutdown of boiler.......................................... 46

3.1.3 Shutdown of Nature Cycle Steam Drum Boiler................................... 47

3.2MAINTENANCE AFTER SHUTDOWN ..................................................................................................... 51

3.2.1 Principle of storage .......................................................... 51

3.2.2 Maintenance method selection of shutdown ................................... 513.2.3 Method of boiler storage ..................................................... 51

3.2.4 Selection of storage method after boiler shutdown ............................... 52

4. SAFETY OPERATION OF BOILER ...................................................................................................... 54

4.1THE ATTRITION AND ATTACK OF BOILER HEATING SURFACE................................................................ 54

4.1.1 Fly ash erosion of boiler heating surface........................................ 54

4.1.2 Cold end corrosion of heating surface of boiler.................................. 54

4.1.3 Hot corrosion of heating surface of boiler....................................... 54

4.1.4 Internal Corrosion of the Boiler................................................ 55

4.2 SAFETY OPERATION OF HEATING SURFACE OF BOILER...................................................................... 55

4.2.1 Safety operation of water cooling wall, coal economizer......................... 55



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4.2.2 Safety operation of superheater and reheater................................... 58

4.2.3 Precaution measures on leakage and burst of boiler four pipes .................... 60

4.3 SAFETY OPERATION OF BOILER PRESSURE PARTS........................................................................ 62

4.3.1 Safety devices for boiler super-pressure issues.................................. 62

4.3.2 Boiler hydrostatic test and Super-Hydraulic Test ................................. 62

4.3.3 Prevent pressure parts from being over-pressed during boiler operation ............ 63

4.4PREVENT BOILER AND TUBES FROM WATER IMPACT............................................................................ 63

4.4.1 Water impact caused by steam passing through steam tubes...................... 63

4.4.2 Water impact caused by low-temperature water getting into steam ................. 64

4.4.3 Water impact caused by sudden drop of steam temperature....................... 64

4.5 COUNTERMEASURE FOR EXPLOSION ON BOILER......................................................................... 64

4.5.1 Principle on furnace explosion ................................................ 64

4.5.2 Preventive measures to furnace explosion ...................................... 64

4.6 SLAGGING IN FURNACE .............................................................................................................. 65

4.6.1 Principle of slagging ......................................................... 65

4.6.2 In accordance with factors that will result in slagging, preventive measures are

described as follows: ................................................................. 66

APPENDIX VARIOUS START-UP CURVES AND OTHERS.................................................................. 66



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Operation of Boilers

1.1 Preparation before Operation of Boilers

1.1.1 Boiler Hydrostatic Pressure Test

Upon completion of erection or maintenance of the boiler steam and water system, an

overall hydrostatic pressure test shall be performed in cold state to test the tightness

of all pressure parts, to check them for residual deformation and to determine if they

have sufficient strength. During the test, the pressure system is filled internally with

pressurized water, the pressure of which may be evenly distributed to each location.

In case of any tiny hole or gap on the pressure parts, or if weld, flange or valve plug is

not well sealed, leakage will occur. If the weak points of pressure parts can not

withstand high pressure during test, they will be subject to permanent deformation or

even cracking. Therefore, measures are to be taken in a timely manner to correct the

defects of leakage, deformation or damage found in the test. In this way the

purpose for inspection of boiler pressure parts can be achieved.

1.1.2 Scope of Hydrostatic Test and Requirements on Water

As a principle, the scope of hydrostatic test for boilers shall cover all the pressureparts in the heating surface system, i.e. all the pipes, valves, the drainage and

discharge system, the attemperating water system, temperature and pressure

measuring points as well as instruments and fittings from boiler feed water isolating

valve to primary isolating valve at main steam outlet. The test scope for the reheating

steam system shall be from the turbine HP cylinder steam exhaust to the low

temperature reheater inlet, through the high temperature reheater outlet and then to

the IP cylinder combined steam valve. As pressures are different, tests for primary

steam system and reheating steam system are separately performed.

1.1.3 During the hydrostatic test, water filled in different equipment is not the same:

l) For the drum and water wall, slightly treated water may be filled as they may

discharge completely. And it will certainly be better if demineralized water is

used;

2) For the superheater system, demineralized water must be used to avoid

internal sedimentation and local corrosion;

3) For stainless steel parts, the water filled shall be removed from natrium,



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kalium, chloride and sulphide, otherwise alloy pit corrosion, intergranular

chemical corrosion and stress corrosion cracking will occur.

For simplified operation, demineralized water obtained by addition of ammonia

or hydrazine is often used for hydrostatic test: hydrazine at a concentration of 200pp,

PH value at about 10.

4) Water temperature for hydrostatic test is usually determined by the following

factors:

(1) The temperature shall be above dew point, otherwise it will be difficult to

tell the actual occurrence of leakage;

(2) Excessively high temperature is likely to cause evaporation, which

would make it difficult to identify leakage;

(3) The temperature of water for test of alloy steel parts shall be higher than

that of the fracture appearance transition temperature;

(4) The temperature between water into drum and drum wall shall be no

more than 28 .

In summary, the water temperature for hydrostatic test is usually between

20C and 70C, and the metal temperature at heating surface should be no less

than 20C. The ambient temperature shall be above 5 when performing test,

otherwise anti-freezing measures must be in place.

1.1.4 Preparations for Hydrostatic Test

l) All the joints and welds shall be exposed for inspection during the test. Close

connection shall be maintained for the equipment subject to pressure test, while

low pressure pipes and all other equipment requiring no pressure test shall be

isolated by proper means.

2) Before filling water to drum, water wall and superheater, it shall be ensured that

all the sundries, welding slag and contaminants in drum and header are cleaned,

and that steam separator inside the drum is properly installed.

3) The drainage and discharge pipes, air valves and steam exhaust pipes shall be

free. The valves shall be easily operated with good seals. Due pressure gauges,

instrument pipes and relevant valve fittings are installed in the hydrostatic test

system. Electrically operated valves and regulation valves shall be calibrated

and the power supply shall be energized.

4) During the test, at least two certified calibrated pressure gauges shall be

provided on the boiler for cross reference during boosting operation. The test



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pressure read from the pressure gauge at outlet header of drum or superheater

shall prevail.

5) Before water pressure is increased above rated operating pressure, hydrostatic

test plugs shall be installed for all the safety valves according to instructions of

manufacturers. If the test pressure is equal to or below the rated operating

pressure, it is only required to shut off the safety valves.

6) Chemical water in sufficient quantity shall be prepared for hydrostatic test.

1.1.5 Procedures of Hydrostatic Test

Hydrostatic test for boiler is classified into two types: operating pressure test and

excess operating pressure test. The former is usually performed after minor repair,

overhaul of boiler or maintenance of pressure parts, while the latter is usually

performed after erection of new boilers. The test pressures are given in Table 8-1:

System

Operating

pressure test

(MPa)

Excess operating

pressure test (MPa)

Primary steam

system

18.87 23.59

Secondary steam

system3.98 5.97

Table 8-1: Pressures in regular pressure test and excess pressure test

In general, the procedures of hydrostatic are as follows:

1) Before filling water to the boiler, all the air valves shall be open and all the

secondary valves in drainage and discharge systems as well as in the scope

of boiler proper shall be turned off.

2) Start the feed water pumps or the pumps specially provided for hydrostatic

test, and slightly open the boiler water inlet valves to allow slow inflow.

Check frequently for air leakage at the drum air valve during this process

until three to five minutes after water starts to leak without air bubble. Take

water samples from the air valve for chemical analysis, and close all the air

valves if the impurity content in water is compliant with relevant

requirements.3) Fill the reheater in the same way as used for superheater (for which special



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joint shall be installed) and take water samples for chemical analysis when

water spills from the reheater air valve. Close the air valves when the water

is compliant.

4) As the water is filled, raise the pressure at a rate of 0.2-0.3MPa/min to 10%

of the maximum allowable operating pressure. Hold for a while to perform

initial inspection. Continue the boosting procedure if no leakage is found.

5) When the pressure is increased to 80% of the minimum setting pressure of

safety valve, halt the process and maintain at a stable pressure. Press the

safety valves of drum, superheater and reheater, and then continue to

increase the pressure to regular pressure. Close the water inlet valves and

record the pressure fall after five minutes. Maintain the pressure for overall

inspection, and record the discovered defects and problems.

6) If the inspection results of regular pressure test allows for excess pressure

test, increase the pressure to the intended test value at a rate below

0.1MPa/min after disconnecting water levels and evacuating all workers.

Then stop the process, observing that the pressure shall at least maintain

for 10 minutes. It shall be noted that the excess pressure may not be over

6% of the regular test pressure.

7) Reduce to the rated operating pressure and continue the overall inspection

of both internal and external pipes of the boiler. During this period the

pressure shall be able to maintain stable with the metal temperature not

exceeding 49C.

8) Reduce the pressure at a rate of 0.3-0.5MPa/min by means of continuous

blowdown or drainage valves. Open the air valves and drainage valves to

drain water after the pressure is reduced to 0MPa, when the devices

pressing safety valves are to be removed.

9) If the boiler is to be put into operation after the hydrostatic test and the wateris eligible, the drum may be fed to ignition level, however, the water in

superheater, main steam pipe and reheater shall be discharged. If the boiler

is not to be in operation in short term, reliable maintenance measures shall

be taken.

10) Eligibility Criteria for Hydrostatic Test

1) Within five minutes after closure of inlet valves, the pressure drop of primary

steam shall be no more than 0.5MPa and of secondary steam shall be no

more than 0.25MPa;



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2) The external metal wall and welds of pressure parts shall be free of any

water drop and moisture signs;

3) After excess pressure test, the pressure parts are identified free of obvious

residual deformation by visual check.

Boiler water volumem3

StateEconomizer

systemDrum

Water cooling

systemSH system RH system Total

Hydrostatic test 101 66 197 372 333 1069

Normal operation 101 33 197 / / 331

1.2 Chemical cleaning

1.2.1 General

Boiler chemical cleaning is a necessary measure to upgrade water quality of power

plant, preventing heating surfaces from scaling and being eroded. The chemical cleaning

method generally includes alkali cleaning and acid cleaning. The former is mainly used to

remove dirt which has been brought into boiler during fabrication and installation, such as

lubricant, oil, rust etc. The latter is mainly used to remove dirt, sediment, oxidation scale and

corrosive product which arise from the contact between heating surface and water. It is

necessary to prevent the cleaned heating surface from being eroded again.

The specific cleaning steps shall follow the GUIDELINE FOR THERMAL POWER

PLANT BOILER CHEMICAL CLEANING (JB/T794-2001).

1.2.2 Chemical cleaning scope

Chemical cleaning shall be performed for economizer, drum and water wall prior to

putting them into operation and after them operating for certain period. Superheater and

reheater systems generally only need to be water washed.

1.2.3 Chemical cleaning medium

Chemical cleaning medium shall be selected according to the scale composition, boiler

structure style, metal material, cleaning effect, corrosion inhibit effect and requirements of



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economical efficiency and environmental protection. Hydrochloric acid, citric acid,

hydrofluoric acid or EDTA (Ethylene Diamine Tetraacetic Acid) can be selected as resolvent.

Meanwhile an appropriate corrosion inhibitor shall be selected to protect tube wall against

corrosion.

1.2.4 General steps of chemical cleaning

System chemical cleaning process: water flushing-alkaliine boilout-water flushing after

alkaliine boilout-acid cleaning-water flushing after acid cleaning-rinsing-passivation.

1.2.4.1. Preparation before chemical cleaning

Before feeding the dose, all glass instruments easy to be eroded shall be separated.

Saline water or condensed water shall be fed into the system before chemical cleaning to

prevent superheater from being contaminated by cleaning liquid.

1.2.4.2. Alkaline boilout

The selected dose is suggested to be mixed with water in order to keep the even

concentration of alkali solution in the whole boiler. The time span of boilout depends on the

amount of oil and grease inside. The boiler shall be cooled down slowly and drained after

boilout, rinsing out residues, and then the cleanliness is checked up. Acid cleaning shall be

conducted after this boilout is acceptable.

1.2.4.3. Acid cleaning

Acid cleaning for boiler shall be conducted as per the stipulated procedure. Acid liquid

temperature shall be strictly controlled, or cannot be exceeding to avoid corrosion inhibitor

being damaged.

Acid liquid shall be squeezed out by injecting nitrogen gas to prevent metal surface

from secondary corrosion, and then water flushing shall be performed. Twice rinsing shall

be generally enough.

There is possibility that the superheater is corroded by cleaning liquid since it is close to

drum. If the superheater has been contaminated, cleaning process shall be suspended, and

water flushing shall be performed to get rid of contamination. The boiler shall be never

ignited prior to removing contamination completely.



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1.2.4.4. Passivation

After the completion of rinse, alkaline solution such as ammonia watershall be fed

into the boiler to neutralize the residuary cleaning medium. After that, passivator shall be

ejected to passivate metal surfaces so as to prevent them from being rusted. Solution in the

system shall be drained after deactivation. Nitrogen gas may be fed into the system if

necessary.

1.2.4.5. Precautions for chemical cleaning:

1) The temperature, flow rate, concentration of the acid alkaline liquor shall be

strictly controlled during the entire chemical cleaning process. For the release of

cleaning liquor, proper measures shall be taken to avoid the occurrence of

environmental pollution.

2) Combustion input cannot be increased before the acid solution is not removed

from the system, otherwise the passivator may be damaged.

3) During rinsing process, the water in superheater which might contain acid

alkaline solution shall be replaced or cleaned by demineralized water or

condensed water.

4) Boiler chemical cleaning shall be performed nearly before steam purging stage.

If the interval between chemical cleaning and boiler steam purging is too long,

heating surfaces may be eroded again.

5) The drainage time of cleaning liquor shall be controlled within certain scope to

prevent dirt from attaching to the lower header again.

1.3 Boiler steam purge

Boiler purge is an indispensable stage before the startup of the whole unit, it is a way to

remove impurities by using steam. Since dirt is easily accumulated in the lower ends of

U-type superheater or reheater pipes during acid cleaning to cause blockage. Besides, acid

cleaning has corrosion effect on alloy metal material, so steam purge is generally performed

for superheater and reheater.

1.3.1 Range of boiler steam purging

SH and RH systems, desuperheating water pipelines, water drainage pipelines and

final steam exhaust pipelines of boiler SH and RH systems etc.



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1.3.2 Steam purge mode

Steam generated from boiler ignition may be used as purging medium. Decompression

purging method shall be done for SH, RH and their steam pipelinesMain steam system may

be purged separately or main steam system and RH system are purged in series.Steam

parameter of purge could be decided by calculation in advance.

1.3.3 Steam purge requirements

During purge process, it shall be guaranteed that the steam kinetic energy in the

pipeline is higher than the steam kinetic energy under BMCR condition. Take a section of

heating surface as an example, the pressure drop of heating surface inlet and outlet during

purge shall be higher than that of heating surface inlet and outlet under full load, i.e. purge

coefficient K1 (K= P blowpipe / PBMCR 1). In this way it is possible to guarantee

the cleanness inside the SH and RH pipelines.

1.3.4 Precautions for steam purge

Boiler various heating surfaces and pipelines (particularly thick wall component) will be

affected by intensive thermal impact during steam purge, so boiler purge times shall be

reduced provided the purge quality is guaranteed.

The design parameter of provisional purge pipeline shall guarantee there is no

overheating or overpressure during the boiler purge process.

During purge under the ignition of boiler oil guns, furnace outlet gas temperature shall

not be over 540 to prevent the occurrence of SH/RH dry combustion.

During steam purge, water level fluctuation of boiler drum may be great. When the

temporary purge gate is opened, the water level will rise quickly with the descent of

pressure, but it will soon fall below the low level. Therefore, once the temporary purge gate

is opened, feed water amount shall be increased to insure that the drum water level will not

be too low.

During each purge, the pressure drop value of drum shall be strictly controlled, and the

saturated temperature drop value shall not be over 42 .

1.4 Feed water and boiler water treatment

Feed water and boiler water shall be chemically examined to meet certain water quality

requirements. Feed water quality shall meet relevant stipulations of DL /T561-95 STEAM



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WATER CHEMICAL TEST GUIDE RULE FOR POWER PLANTAND GB /T12145-1999

STEAM WATER QUALITY STANDARD FOR POWER PLANT UNIT AND STEAM

GENERATING EQUIPMENT.

1.5 Drum Boiler Startup

1.5.1 General Introduction for Boiler Startup

The modular unit is generally started up in a mode of combining boiler with turbine,

which means that, the boiler and turbine shall be started up simultaneously. During startup,

the steam whose temperature increases gradually with the rising boiler parameters will

warm pipes, start up and warm turbines under load. Therefore, this mode of startup is also

known as startup with variable parameters which improves the startup condition of turbines,shortens the time for startup and increases the flexibility of grid dispatching. Currently, the

startup with variable parameters of 600MW units is usually pressure startup with variable

parameters.

1.5.2 Characteristics of Drum Boiler Startup

1 Thermal Stress Problem

The startup process is a heating process for every part of the boiler, but the heating

process is uneven. Therefore, large temperature differences exist among boiler parts,

which may cause thermal stress to damage the equipment. When other conditions are

identical, the greater wall thickness of the parts to be heated, the larger temperature

differences between the inner wall and the outer wall, and accordingly, the greater the

thermal stress. The drum, header, main steam pipes and some valves of drum boilers are

thick-wall parts. Starting up these parts may cause their thermal stress to reach a

dangerous degree if no control measures for temperature rising rate is adopted during

startup.

2Metal Over-temperature Problem

During startup, the working medium inside heating surfaces cannot flow normally,

with little or even no flow in some heating surfaces, resulting in insufficient cooling of the

heating surfaces. In such condition, overheating will make the metal wall temperature

become excessively higher than its tolerance limit and thus be damaged. These heating

surfaces includes partial water wall before water circulation is established, SH tubes when



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Cold state startup 48t72 P0.5 T150

Warm state startup 8t48 0.5P9.0 150T300

Thermal state startup 2t8 9.0P14.0 300T400

Extremely thermal state

startup

t


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2) Dynamic balance calibration for air fans;

3) Resistance adjustment test for boiler coal pipes;

4) Dynamic field test for air inside boilers;

5) Air leakage test in cold state for air preheaters;

6) No-load step-up test for electrostatic precipitator;

7) Protection check for electric interlock and thermal machine of auxiliary

boilers.

1.5.5.2 The following boiler equipment have all been electrified: all auxiliary boilers and

accessories, all instruments and instrument panels, electric control valves & regulating

valves, solenoid valves, moving blades and stationary blades conditioning devices of air

fans, air door dampers, all automatic devices, sequencers, data loggers, computer

systems, boiler protective systems, alarm signals and related boiler lightings.

1.5.5.3 Boilers steam/water systems, attemperating water systems, water drainage

systems, flame detecting cooling air systems, turbine bypass systems and the valve

positions of thermodynamic instruments have met the requirements prior to startup.

1.5.5.4 The sight holes, access doors and inspection doors of boiler combustion chamber

and air & gas duct have been closed with seals being complete. All soot blowers have

been withdrawn.

1.5.5.5 Boiler cooling water systems, compressed air systems, fuel atomization steam

systems have been put into operation; hopper heating systems of electrostatic

precipitators and air heating systems are already in hot standby status.

1.5.5.6 Boiler fuel oil and coal reserves can meet the requirements; light oil and heavy oil

have formed a circulation; and the fuel system with hot steam has operated normally.

1.5.5.7 Ash handling systems, deslagging systems, ash sluice water systems, shaft

sealing water systems and electrostatic precipitators, pre-heaters, air fans, pulverizing

systems and their ancillary equipment are all ready for operation.

1.5.5.8 Various boiler interlocks and protective devices have satisfied the startup

requirements; DCS systems have met the operation requirements; steam turbines and

generators have been qualified for startup; and relevant systems and equipment such as

fuel and chemicals have satisfied the requirements of startup.

Except for meeting the above requirements, it is required that the operating personnel

have already known change situations and startup measures of the equipment. The

operating personnel on duty shall have been orderly arranged with clear division so as to

conduct the startup smoothly.

1.5.6 Cold State Startup of Boiler

Cold state startup of the modular unit can be classified into four stages with the



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following main characteristics: boiler ignition, turbine startup, grid integration of power

generators and unit load rising. During these stages, turbine startup and generator

synchronization require less boiler operation, while the other two stages require much

more boiler operation. As such, the main working of natural circulation drum boilers

during startup can be subdivided into the following five stages: boiler water filling, furnace

purge, boiler ignition, boiler heating-up and pressure boosting-up, unit startup and

synchronization and boiler load rising to rated value.

1.5.6.1 Boiler Water Filling

1) After completion of all inspections and tests required by boiler startup, the boiler can

then be filled with water in accord with the following requirements:

u The water shall pass the examination before water filling: PH: 9.0-9.5;

hardness5.0moL/L; dissolved oxygen30g/L; hydrazine: 1050g/L

u Inlet water temperature shall be from 20 to 70 ; temperature differences

between feeding water and lower drum wall shall be less than 28 ; and the

metal temperature of heating surfaces shall be no less than 20 .

u The average temperature differences of drums upper-lower wall shall be no

more than 56 .

u Time for water filling: no less than 2 hours for summer and 3 to 4 hours for

winter

When water was seen in the local water level gauge,, it is necessary to reduce the

inlet water flow and fill water until the drum water level is kept within -300mm. Then stop

water filling by closing electric control valves and regulating valves for main feedwater and

open the recirculating valves of economizers.

2) When boiler water filling is completed, chemical test of boiler water quality is required. If

verified to be unqualified, the boiler water shall be fully released and refill water till the

water quality is proved up to standards.

3) Why natural circulation drum boilers have relatively strict requirements for filling water

lies in that the drums are large pressure parts. During water filling, the warm water will

heat the inner wall of the drum by contacting its walls, which leads to temperature

differences between the inner/outer walls and upper/lower walls of the drum. Thermal

stress caused by temperature differences will affect the service life of the drum. Therefore,

when water filled to drum boilers, the water filling temperature and time shall be strictly

controlled. When water filling is finished, it is required to record every 30 minute the wall

temperature and temperature differences at all points of the drum.

4) After water filling, it is required to heat from the bottom of the boiler:



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u The bottom of the boiler shall be heated slowly; the temperature rise rate of

boiler water saturation temperature shall be equal to or less than 28 /h; the

upper-lower wall temperature differences of the drum shall be less than

56 .

u During the heating process, when the drum water level is +100mm higherthan normal water level, it is required to open the emergency water drainage

valves and close them after it dropping to +50mm.

u Detected by thermocouples, when the wall temperature at downcomers is

higher than 95 or when the drum pressure is greater than 0.125MPa, the

heating work for the boiler bottom can be stopped.

1.5.6.2 Furnace Purge

Furnace purge is generally performed by FSSS system. Furnace purge asks for aseries of conditions and only when all conditions are satisfied at the same time, can the

purge control system send a signal ofpurge allowed. Shall any unsatisfied condition be

found, the signal will not be sent. The boiler requires for the following 15 conditions in

general:

1) No conditions exist for MFT( losses of all f lame are excluded);

2) DCS has no power failure;

3) The pressure of instrument gas source shall be normal, namely, within 0.5

0.8MPa; 4) At least one FD fan shall be running and its corresponding baffles be opened;

5) At least one ID fan shall be running and its corresponding baffles be opened;

6) The pressure inside furnace is normal;

7) The two air preheaters shall be running;

8) 25%40%BMCR air flow of the furnace shall be maintained;

9) The front quick open-and-close valves of furnace inlet oil main tubes, return oil

main tubes and all oil guns shall be closed;

10) All primary air fans, mills and coal pulverizers have tripped;

11) All primary air doors on coal pipes have been closed;

12) The drum water level is normal;

13) No signal offlame existence in furnaces;

14) All air door dampers of burners are in adjustable status and at the position of

purge;

15) The leak test has been accomplished.

1.5.6.3 Boiler Ignition



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1) Before cold state start up, all drainage valves, steam exhaust valves and dampers

shall be at the position of boiler ignition.

2) After the oil guns have been ignited, at least 30% BMCR air flow shall be maintained.

3) Drainage valves and steam exhaust valves shall be adjusted according to relevant

requirements from boiler ignition to synchronization (being incorporated into the grid).

4) The oil guns corresponding to the first row of burners (on the lower layer of front wall)

shall be ignited. It is recommended that full load ignition of the oil guns shall be

performed.

5) If necessary, the secondary row of burners (on the lower layer of rear wall) shall be

started up and their input heat may be adjusted according to boiler load requirement.

1.5.6.4 Boiler Heating-Up and Pressure Boosting-Up

After the boiler has been ignited normally, the temperature of all heating surfaces will

increase gradually; the boiler water temperature and steam pressure will increase

accordingly; and the saturated water and steam will coexist in the drum. Because of

one-to-one relationship between temperature and pressure in saturated state, boiler

heating-up will be accompanied by pressure boosting-up, that is, temperature heating up

and pressure boosting up will happen simultaneously. In order to avoid greater thermal

stress resulted from fast rate of temperature rise and large temperature differences, it is

usually to control the temperature rise rate by controlling pressure rise rate. Generally, the

temperature difference between the drums upper and lower wall shall be not more than

56 ; the boiler water temperature rise rate shall be 28 /h before boiler pressure

rising; after pressure rising, it is necessary to control the temperature rise rate by

controlling pressure rise rate (Fig. 8-2):

Drum Temperature ( ) Pressure rise rate (MPa/min)100184 0.0150.020

184265 0.0600.080

265312 0.160.18

>312 0.20

The setting of drainage valves shall be adjusted according to boiler startup mode.

The steam discharging valve and bypass system at the main steam safety valve pipe

section shall be adjusted to make the boiler steam parameters meet the requirements for

turbine startup.



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Air fans of combustion system are started up in sequence.

When the warming-up time and rotation speed of turbine reach the stipulated

requirements, the turbine can be incorporate into the grid, with certain load exerted.

The mill system is started up. In cold condition start up, the mills corresponding to the

lower row, the medium row and the upper row of burners shall be started in sequence

(from the front wall to the rear wall). Mill shutdown sequence shall be based on boiler

shutdown mode and in combination with operation experience. For boiler warm, thermal

and extremely thermal state startup, the startup sequence of mills shall be based on

actual operation requirements.

The first mill is started up and the secondary air door damper is manually adjusted.

More mills are started up continually according to boiler load rising requirement.

Before mill startup, it is necessary to confirm that the oil guns of burners corresponding to

that mill are ignited in advance. Subsequently, mill outlet air temperature, secondary air

door, coal feeder may be switched to automatic control mode until all of the five mills have

entered into automatic control mode. For the combustion of check fuel, all of the six mills

must be put into service to reach full load.

OFA air door damper shall be in manual mode and in closing position. OFA air door

damper may be switched to automatic operation mode when boiler reaches proper load.

The adjustment of oxygen amount may be switched to automatic operation mode after two

mills have been put into service.

The adjustment of superheated steam temperature and reheated temperature may

be switched to automatic operation mode at proper load.

Boiler master control system may be switched to automatic operation mode, and

corresponding operation mode shall be selected (such as constant pressure operation or

variable load operation).

The following parameters shall be monitored closely during the whole boiler startup

process such as boiler combustion condition, boiler pressure rising speed, temperature

difference of drum and temperature difference of RH/SH wall.

1.5.7 Warm State Startup (The Warm State Startup Curve Refers to Fig. 3.)

1) Before warm state startup, boiler drum water level shall reach the preset positionnamely150mm below normal water level.



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2) The boiler shall be started up as per the same sequence as cold state startup

mode.

3) During warm startup mode, drainage valves and steam exhaust valves shall be

operated according to corresponding sequence.

1.5.8 Thermal State Startup (The Curve for Thermal State Startup Refers to Fig. 4.)

1) Before thermal state startup, drum water level shall reach the preset position, i.e.

drum normal water level.

2) The boiler shall be started up as per the same sequence as cold state startup

mode, but generally the medium row of burners shall be ignited first.

3) For thermal state startup, water drainage valves and steam exhaust valves shall

be operated in the same sequence as that of thermal state startup.

1.5.9 Extremely Thermal State Startup (The Curve of Extremely Thermal State

Startup Refers to Fig. 5)

1) Before extremely state startup, drum water level shall reach the preset position,

i.e. drum normal water level.

2) The boiler shall be started up as per the same sequence as that of cold state

startup, but generally the medium row of burners shall be ignited first.

3) For extremely thermal state startup, water drainage and steam exhaust valve

shall be operated as per the same sequence as that of thermal state startup.

1.5.10 Boiler Thermal State Startup

1) Extremely thermal state startup (The curve of extremely thermal state startup

refers to Fig. 5)

2) Before extremely state startup, drum water level shall reach the preset position,

i.e. drum normal water level.

3) The boiler shall be started up as per the same sequence as that of cold state

startup, but generally the medium row of burners shall be ignited first.

4) For extremely thermal state startup, water drainage and steam exhaust valve

shall be operated as per the same sequence as that of thermal state startup.



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1.6 Basic Operation for Water Drainage and Steam Exhaust

1.6.1 Basic Principles

1) It is necessary to confirm that condensed water in the back pass (BP) lower

circular header and convection SH inlet header (partition wall outlet header) is

drained when they are started up,

2) When the boiler is started up or its load is decreased under constant pressure

condition, condensed water may form inside BP lower circular header and

convection SH inlet header. If such water has not been drained before ignition or

under relatively lower pressure (less than 5 MPa) after ignition, this condensed

water will baffle steam flow in heating surface tubes, thus resulting in uneven

heating of enclosure wall, partition wall and convection SH. The condensed

water may also be carried in other heating surface pipes to block steam flow

there. Consequently, the tube temperature at the steam blockage area is too low

while its downstream tube temperature is too high. This will results in large

temperature difference of membrane walls, thus causing tube leakage or tube

rupture.

3) The condensed water in platen SH and finishing SH shall be fully evaporated

before being taken away.4) Because heating surfaces of platen SH and finishing SH are not fully of drainable

configuration, during boiler shutdown, condensed water will deposit in the tube

bundles. (For example: after hydraulic test, the tubes are full of water, while at

extremely thermal state startup little water deposits in the tubes.) Cooling of

these suspended heating surfaces starts from the bottom of tube platen to the

platen header. Before boiler startup, the wall temperature of platen bottom will be

the lowest (150~200 lower than the header connected with the tube platen) and

the wall temperature of the header will be the highest (close to the temperature

of normal operation before thermal state startup). Hence, during boiler startup,

the introduction of condensed water into the outlet header will result in abrupt

cooling of the nozzles and shell of header to cause the occurrence of crack at the

joint between the header and its nozzles. More condensed water is brought away

by steam, greater the cooling degree of steam is. And it is possible that the

steam temperature before turbine main steam valve cannot reach the required

value, thus causing the temperature difference of valve.

5) We could deduce gas temperature based on the platen heating surface metal



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wall temperature detected by thermocouples. When the metal wall temperature

reaches the preset value, we affirm the condensed water in the tubes has been

vaporized. The condensed water in the platen heating surface tubes will

generate steam during heating process. This heating process may be detected

by thermocouples. When the vaporization of condensed water begins, the metal

wall temperature detected by thermocouples dropswhen the vaporization of

condensed water decreases or stops, the metal wall temperature rises again.

6) It is necessary to guarantee the acquisition of appropriate steam temperature

and steam pressure during boiler startup process.

7) To guaranteed the acquisition of appropriate steam temperature and steam

pressure during boiler startup process, it shall be confirmed which row of burners

are firstly put into service besides water drainage and steam exhaust by

operating relevant valves to process . For cold state startup, the lower row of

burners shall be put into service at first so as to supply heat to the lower furnace,

thus raising pressure and maintaining relatively lower steam temperature. For

thermal state startup, the medium row of burners shall be ignited at first to

maintain steam temperature.

8) It is necessary to guarantee combustion input is stably increased during boiler

startup process.

During boiler startup, either maintaining combustion input or decreasing combustion

input will lead continual descent of steam temperature. If the steam flow through heating

surface is increased continually without combustion input increased, the steam

temperature will drop. The steam temperature cannot be maintained unless combustion

input is increased before increasing boiler steam flow. Therefore, during boiler startup

process, especially when starting up turbine and incorporating it into the grid, the steam

temperature must be monitored closely to prevent the abrupt drop of temperature of the

steam entering into turbine, which may lead the cooling and shrinkage of high, medium

and low rotors, thus resulting in turbine failure and its shortening of service life.

1.6.2 Operation for Drainage and Steam Exhaust Valves at Cold Startup

SequenceOperation

ModeDescription

1Initial

Position

Enclosure wall circular header drainage valve, (partition

wall lower header) convection superheater inlet header

drainage valve, main steam outlet release valve shall be all

opened.



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2 Manual

5 oil guns corresponding to the lower row of burners on

the front wall and rear wall are ignited respectively, with

approximately 5%BMCR heat inputted.

3 Automatic

When the pressure rises up to 1.0MPa.a, enclosure wallcircular header drainage valve shall be closed; the drainage

valve shall be opened for 30 seconds every other 30 minutes

before the pressure rises up to 5.0MPa.a.

4 Automatic

When the pressure rises up to 1.2MPa.a, LT SH inlet

header drainage valve shall be closed; the drainage valve

shall be opened for 30 seconds every other 20 minutes

before the pressure rises up to 5.0MPa.a.

5 Automatic When the pressure rises up to 1.6MPa.a, main steamoutlet steam exhaust valve shall be closed.

6Manual/

automatic

The automatic mode of bypass is selected. Ignite more

oilguns corresponding to the lower row and the middle row of

burners on the front & rear wall until the boiler heat input

reaches 15%BMCR, and steam parameter meets the

requirements of steam turbine (pressure: 6.0MPa.a ).

1.6.3 Suggestions for the Operation of Drainage and Steam Exhaust Valves at Warm

State startup.

Sequence Operation

Mode

Description

1 Initial

Position

Rear enclosure wall circular header drainage valve, (division

wall lower header) convection superheater inlet header

drainage valve, main steam outlet exhaust valve shall be all

closed.

2 Manual Ignite oil guns corresponding to the lower row and the

middle row of burners on the front & rear wall until the boiler

heat input reaches 15%BMCR, and steam parameter meets

the requirements of steam turbine.



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Sequence Operation

Mode

Description

3 Automatic Lower enclosure wall circular header drainage valve,

convection superheater inlet header drainage valve, mainsteam outlet exhaust valve shall are opened.

4 Automatic When the initial pressure is lower than 4.5MPa.a:

When the pressure reaches the value of initial pressure

plus 0.5MPa, close rear enclosure wall circular header

drainage valve, then open it for 30 seconds every 15 minutes

until the pressure reaches 5MPa.a.


plus 0.7MPa, close LT SH inlet drainage valve, then open it for30 seconds every other 10 minutes until the pressure reaches

5MPa.a.

When the initial pressure is higher than 4.5MPa.a:


plus 0.5MPa, enclosure wall circular header drainage valve

shall be closed.

When the pressure reaches the value of initial pressureplus 0.7MPa, LT SH inlet header drainage valve shall be

closed;

5 Automatic When the pressure reaches the value of initial pressure plus

1.0MPa, main steam outlet steam exhaust valve shall be

closed.

6 Manual/

automatic

Bypass is switched to automatic mode. Adjust the boiler

combustion input to make steam parameters meet the

requirement of steam turbine.


Thermal State Startup

SequenceOperation

ModeDescription



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SequenceOperation

ModeDescription

1 Initial Position

Rear enclosure wall circular header drainage valve,

(division wall lower header) LT SH inlet header drainagevalve, main steam outlet steam exhaust valve shall be all

closed.

2 Manual

Ignite oil guns corresponding to the upper row and the

middle row of burners on the front & rear wall until the boiler

heat input reaches 15%BMCR, and steam parameter meets

the requirements of steam turbine.

Note: The higher superheater outlet parameter is required

at thermal state startup, which is fulfilled by igniting the oilguns corresponding to the upper row and the middle row of

burners on the front & rear wall (if necessary).

3 Automatic

After the first oil gun has been ignited for a certain

time(about 3 minutes), enclosure wall circular header and LT

SH inlet header drainage valves shall be opened (100%

opened).

Note: When Item 4 and 5 are performed, the temperature

measured by thermocouples on platen SH outlet and HTSH outlet tube panels (measured by thermocouples) shall

not decline, otherwise the operation shall be stopped, and

not be continued until the measured wall temperature rises

up to the original level. The drop of HT SH outlet steam

temperature will cause the drop of main steam pipe

temperature, and delay turbine operation.

4 ManualGradually close drainage valve of enclosure wall circular

header.

5 Manual Gradually close drainage valve of LT SH inlet header.

Note: Item 6 and 7 shall be performed in sequence.

6 AutomaticOpen high pressure bypass inlet stop valve and main

steam pipe lower point drainage valve.

7 Automatic The warming valve on main steam pipeline is opened.

Note: Item 6, 7 and 8 shall be performed synchronously.



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SequenceOperation

ModeDescription

8

Manual/

automatic

Bypass is switched to automatic mode (The pressure

value shall be 10Mpa.a for high pressure bypass, and0.7Mpa.a for low pressure bypass.)

9 Manual

Combustion input shall be regulated to insure that turbine

startup parameter is met. Bypass flux, pressure and

temperature shall be verified to meet the requirement for

main steam parameter.


Extremely Thermal State Startup:

Sequence Operation Mode Description

1 Initial Position

Rear enclosure wall circular header drainage

valve, (division wall lower header) LT SH inlet

header drainage valve, main steam outlet steam

exhaust valve shall be all closed.

2 Manual

Ignite oil guns corresponding to the upper row

and the middle row of burners on the front & rear

wall until the boiler heat input reaches 15%BMCR,

and steam parameter meets the requirements of

steam turbine.

Note: The higher superheater outlet parameter is

required at extremely thermal state startup, which is

fulfilled by igniting the oil guns corresponding to the

upper row and the middle row of burners on the

front & rear wall (if necessary).

Note: Item 3, 4, 5, 6 and 7 shall be performed in

sequence.

3 Automatic

LT SH inlet header drainage valve shall be

immediately closed after opening the enclosure

circular header drainage valve.

4 Automatic Open the high pressure bypass drainage valve.



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5 AutomaticOpen the main steam pipeline low drainage

valve.

6 AutomaticOpen the main steam pipeline electric warming

valve.

7Manual

automatic

Bypass is switched to automatic mode (The

pressure value shall be 14.5Mpa.a for high

pressure bypass, and 0.7Mpa.a for low pressure

bypass.)

8 Manual

Combustion input shall be regulated to insure

that turbine startup parameter is met. Bypass flux,

pressure and temperature shall be verified to meet

the requirement for main steam parameter.

1.7 Boiler Soot Blowing

1.7.1 Periodic soot blowing shall be conducted for the heating surfaces of the new unit put

into operation so as to keep the outer walls of heating surfaces clean and prevent

the occurrence of slagging and insure good heat transfer performance and low gas

emission temperature. Only by this means could boiler economic operation be

guaranteed.

1.7.2 The soot blowing system of the unit is designed, fabricated and provided by

Daimengde Electric Power Machinery (Hubei) Co., Ltd. The company shall also

provide site service during installation. Relative commissioning requirements and

operation instruction shall be strictly followed.

1.7.3 Before soot blowing, the soot blower shall be drained and warmed. The water

drainage valve could be closed only after the medium temperature has reached the

setting value. After soot blowing, steam feeding shall be stopped and water drainage

valves shall be opened to prevent the formation of condensed water in the piping

system.

1.7.4 Soot blowing shall not be conducted at low load or unstable combustion condition.

Generally, soot blowers shall be out of service when boiler load is lower than 50%.

Soot blowing shall be performed before boiler shutdown.

1.7.5 Boiler soot blowing shall start from the furnace to the rear part along flue gas flow

direction. Soot blowers are symmetrically arranged and shall be put into operation at

the same time.

1.7.6 During boiler startup or low load operation, the steam source for soot blower of air

preheater may be substituted by steam out of the auxiliary steam system.



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1.7.7 Any soot blower that failed shall be immediately repaired to keep it in good condition.

The soot blower shall not be out of service for long time.

1.7.8 The soot blowing procedure shall be optimized according to slagging conditions of

each boiler part during operation to improve soot blowing efficiency and prevent the

occurrence of damage caused by soot blowing. During low load operation, soot

blowing frequency for the rear part of boiler shall be increased to prevent ash

deposition.

1.8 Boiler Blowdown and Water Drainage

1.8.1 To make the steam/water quality meet the requirements and stipulations inQuality

criterion of water and steam for thermal power plant and steam power equipment,

boiler blowdown shall be conducted. This boiler is designed with the periodic

blowdown system and the continuous blowdown system. The periodic blowdown

starts from boiler waterwall lower header while the continuous blowdown starts from

boiler drum. The blowdown pipeline shall be warmed to prevent the occurance of

water impact before blowdown. Drum water level shall be properly increased before

periodic blowdown, and blowdown shall be performed one loop after another. Two or

more points blowdown cannot be performed at the same time to keep the stability of

drum water level and safety of water circulation. Periodic blowdown shall be

conducted as fast as possible under stable load.

1.8.2 During boiler normal operation, the open degree of continuous blowdown control

valve and blowdown time shall be properly adjusted according to steam/water

quality control requirements and results of their tests. Periodic blowdown is mainly

used to control boiler water and steam quality in short term. Continuous blowdown

can be used to control boiler water and steam quality in both long term and short

term.

1.8.3 When boiler operation is abnormal or accident occurs (except excessive high water

level) or the blowdown system fails, blowdown shall be stopped.1.8.4 The water drainage and steam exhaust system of boiler proper are mainly used for

drainage and pressure/temperature control during boiler startup or shutdown. The

water drainage of convection SH inlet header and BP circular header are mainly

used for drainage of accumulated condensed water during boiler startup or

shutdown.

1.8.5 Steam discharge valve at SH outlet is mainly used for steam temperature/pressure

control when safety valve rejects motion.



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2. Boiler Operation Adjustment

2.1 Content of Boiler Operation Adjustment

1) Make the boiler parameters reach the rated values and meet the requirements of

unit loading.

2) Keep stable and normal steam temperature and pressure.

3) Balance water feeding and maintain the normal drum water level.

4) Keep qualified boiler water and steam.

5) Keep good combustion, reduce heat losses and improve boiler efficiency.

6) Adjust boiler operation conditions in time to ensure the unit runs safely and

economically under the best operation conditions.

7) Reduce the emission of NOx.

2.2 The Influence of Working Condition Changes on Boiler Parameters

2.2.1.1 Boiler Parameters

The boiler conditions, namely, its operating conditions, are reflected by a series of

relevant operating parameters. These reflection parameters are as follows: evaporation

capacity reflecting boiler capacity, pressure and temperature reflecting steam quality, and

fuel flow rate, air flow, oxygen content, drum water level, flue gas pressure & temperature

etc. Among these parameters, some are used as governing objects; some are used to

reflect the conditions of various matters entering boilers; and some are to reflect the

economy and safety of boilers.

2.2.1.2 The Influence of Working Condition Changes on Boiler Parameters

By the dynamic characteristics of the boiler, we can see that the stability of boilers

main operating parameters depends mostly on the following two balances: balance

between turbine power and boiler evaporation capacity, and balance between fuel and

feedwater of once-through boiler, or between evaporation capacity and feedwater flow of

drum boiler. To maintain the first balance will be able to guarantee the stability of boiler

steam pressure, while to maintain the second can keep superheated steam temperature

of the once-through boiler or water level of the drum boiler. When changes happen to

working conditions, the balance will be disturbed and will cause changes in operating

parameters, if not adjusted timely. Whether the disturbance is internal or external, it will

lead to changes in the boiler conditions, which ultimately manifested as changes in

operating parameters. Whats worse, a change factor will usually cause changes in a

number of relevant parameters at the same time.



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2.2.1.3 Boiler Operation Economy

Continuously improving the economy of boiler operation is an important part of boiler

operation adjustment. For the modular unit, the boiler operation adjustment is not only to

improve the boiler thermal efficiency, but also to improve the thermal efficiency of the

whole unit. According to the relevant introduction, when 600MW units boiler is working at

rated conditions, changes of some of the major parameters have the following influence

on coal consumption for power generation of the whole unit as shown in the following

table:

Parameters Unit VariationAffecting Coal Consumption of the

Generating Unit (g/kWh)

Main Steam Temperature 1 0.19

Main Steam Pressure MPa 0.1 0.24

Reheat Steam

Temperature 1 0.16

Flue gas temperature 1 0.17

The contents of boiler operation adjustment can generally be classified into three

aspectsi.e. combustion adjustment, parameter adjustment and operation modes. In

terms of enhancing the operation economy, the purpose of combustion adjustment is to

reduce the losses of a variety of incomplete combustion in the furnace; the purpose of

parameter adjustment is to reduce the boiler flue gas heat losses and improve the

thermodynamic cycle efficiency of the whole unit; the purpose of operation mode

adjustment is to optimize the combination of auxiliaries, and reduce their power

consumption and auxiliary water & steam consumption.

In order to improve the thermal efficiency of the boiler and the whole unit, the

following shall be followed: a relatively high steam temperature and pressure shall be

generally maintained during normal operation; rational air distribution shall be ensured;

the combination of burners shall be optimized; low oxygen combustion mode shall be

adopted; appropriate fineness of pulverized coal shall be maintained; "The leakage of

seven substance phenomena" shall be eliminated; the valve throttling losses and RH

attemperating water supply shall be minimized; air leakage in all parts of the boiler shall

be reduced; regular sootblowing of the heating surfaces according to the requirements

shall be conducted and variable-pressure operation mode shall be adopted.

2.3 Boiler Steam Temperature Control and Adjustment

2.3.1 The Influence of Steam Temperature on the Safe and Economic Operation of



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the Unit

The SH and RH steam temperature of this boiler are 541 .

When the steam temperature is too high, it will cause superheaters, reheaters, steam

pipes and metals on steam turbine cylinders, valves and rotors to weaken in strength,

resulting in shortened service life of equipment, or even serious equipment trouble

accidents. When the steam temperature is too low, it will cause several turbine blades of

the final class to increase in humidity, and even cause serious water hammer to rupture

the turbine blades. In addition, it will also cause the turbine rotors to suffer from increased

axial thrust. All the above consequences will seriously threaten the safe operation of the

steam turbine.

If significant changes happen to SH and RH steam temperatures, except for the

greater thermal stress and fatigue of the boiler tubes and related components, they will

also result in differential expansion between turbine cylinders and rotors, or even serious

dynamic and static friction between turbine blades and diaphragms, causing a strong

vibration of steam turbine. When the steam temperature difference on the turbines both

sides is too large, it will lead to uneven heating and uneven thermal expansion on the

sides, threatening the safe operation of the unit.

2.3.2 Heat-Transfer Characteristics of Boiler Heating Surfaces

According to mode of heat transfer, boiler heating surfaces can generally be

classified into three types, namely, radiation heating surfaces, semi-radiation heating

surfaces and convection heating surfaces. The water wall evaporating surface, the front

platen and the wall enclosure tube heating surface, etc. belong generally to the radiation

heating surface in that the radiant heat accounts for the major proportion. The rear platen

superheater belongs to semi-radiation heating surfaces for the following reasons: on the

one hand, it absorbs the convection heat transfer of flue gas; on the other hand, it absorbs

the radiation heat transfer of flue gas in furnace and tubes. Heating surfaces of

economizers, and SH/RH in the convection pass belong generally to the convection

heating surface on the ground that the convective heat constitutes the major proportion.

With the changes in boiler load, the furnace radiant heat and convective heat

distribution ratio will change accordingly. When the boiler load increases, the heat transfer

share of the convection heating surface will increase, and the heat transfer share of the

radiation heating surface will decrease comparatively while the semi-radiation heating

surface will be less affected. Refer to Figure 4-2-1.



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2.3.3 Drum Boiler SH Steam Temperature Control and Adjustment

2.3.3.1 Influence Factors for Drum Boiler SH Steam Temperature Changes:

1) Changes in the nature of the fuel

2) Changes in air flow and its distribution ratio

3) Changes in burner operation modes

4) Temperature changes in feedwater

5) Changes in cleanliness of heating surfaces

6) Changes in boiler load

7) Changes in saturated steam temperature and attemperating water flux

2.3.3.2 Natural Circulation Drum Boiler SH Steam Temperature Control and

Adjustment.

This drum boiler adopts the primary attemperation installed at the inlet of platen SH

as the chief means for regulating SH steam temperature. In case of emergency, the

secondary attemperation at the outlet of platen SH can be used to adjust SH steam

temperature. The attemperating water flux for original design coal and various working

conditions is shown in the following table:

Item Unit B-MCR TRL THA 70%TRL 50%TRL 30%BMCR

The SH primary

attemperating water f lux

t/h 19.50 21.69 16.49 54.94 66.07 51.93

Figure4-2-1 Relation curve between boiler load and the amount of heat

absorbed for each heating surface

Q-The amount of heat absorbed per unit of working medium

D-Boiler load -Radiation heating surface

-Convection heating surface -Semi-radiation heating surface



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The SH secondary

attemperating water f lux

t/h 13.00 14.46 10.99 36.63 44.06 34.62

a. Under Constant pressure operation (60 ~ 100 % B-MCR), rated temperatures of

superheated steam and reheated steam shall be kept, and under sliding pressure

operation (45~100% B-MCR)rated temperatures of superheated steam and reheated

steam shall be kept, 5 temperature difference permitted.

b. Two-stage spray attemperation shall be adopted to adjust superheated steam

temperature. The primary attemperation shall be arranged at the inlet of platen SH for

coarse adjustment, while the secondary attemperation shall be arranged at the inlet of

finishing SH for fine adjustment. When the high pressure heaters are out of service,

large amount of spray water must be fed via the primary attemperator to protect the

platen SH and finishing SH from being overheating.

c. For The secondary attemperation, temperature drop value may be set as 7 . In order

to prevent the occurrence of steam condensation and water forming after

attemperation, the steam temperature after the primary attemperation shall not be

under the saturation temperature plus one degree (margin) under operation pressure

D . When the pressure is less than 12.1Mpa, D shall be at least 28 . When

the pressure is more than 17.6Mpa, D shall be at least 14 . Under intermediate

pressure, D value may be calculated by linearity difference. In case the primary

attemperation could not meet the steam temperature requirement, then the

desuperheating extent of the secondary attemperation may be enlarged.

d. Under 20%BMCR, the primary attemeration shall be out of service, and under

10%BMCR, the secondary attemperation shall be out of service.

In short, during the regulation of steam temperature, it shall be firstly adjusted by

combustion, seeking for non-deflection flame and avoiding partial coking, and then by fine

adjustment of SH steam temperature. Within the limits of all levels of wall temperature,when attemperating water flux become inefficient for stable adjustment of steam

temperature, combustion adjustment shall be considered as the measures and methods

for steam temperature adjustment.

2.4 Control and Adjustment of Reheated Temperature

Reheated temperature of this boiler reached 541 , steam pressure is 3.9MPa.



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2.4.1 The Characteristics of Reheated Temperature

Because of the characteristics of construction and lay out of SH, the characters of

steam temperature are:

1) Capacity of SH is big enough, so flow velocity of working medium is relatively low,

and the location of SH is in smoke low temperature area, so there has low temperature

differences of heat transfer. Therefore, when the condition changes, reheat

temperature will take relatively long retarded time to change.

2) Because of the low reheated steam pressure and specific heat, when unit

working medium changes at the same caloric receptivity, the variation of reheat

temperature will be larger than that of superheated steam temperature. Convection

section of RH is located in relatively low gas temperature area, because of the heat

transfer characteristic of convective heating surface and low specific heat of reheated

steam, so there is a smaller effect to reheated temperature.

3) Reheated temperature is sensitive to heat deviation. Because of its low pressure

and specific heat, under the same heat deviation condition, derivation of reheated

temperature will be larger than superheated steam temperature.

4) Operating condition of RH suffer not only from the operating condition of boiler,

but also from operating condition of steam. Flow rate of reheat steam changes with

unit load, class one and two extraction flow of turbine and open/close status of boiler

safety valve and steam discharging valve. While unit working in constant pressure

modes, turbine HP cylinders exhaust temperature (cold RH input temperature) will

have substantially change as unit load is change. So change of RH input temperature

and working medium flow rate will change reheat temperature.

2.4.2 Factors influencing the temperature variety of reheating

For the characteristics of the structure and layout of RH, there are various factors

for influencing the temperature variety of reheating. Mainly as the followings:

1) Impact of high pressure cylinder steam exhausting temperature variation

2) Impact of RH heat absorption capacity variation

3) Impact of reheated steam flow variation

4) Impact of reheated desuperheater water flow variation



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2.4.3 Adjusting method for reheated steam temperature

Flue gas side adjustment is the main adjusting method for the reheated steam of

this furnace (to adopt fuel gas damper adjusting, changing the height of center flame

of furnace), then operate with desuperheater water adjusting mode.

a. Adjustment of Flue Gas Temperature Adjusting Damper

The open degree of the rear flue gas adjusting damper changes with the

loading swing of boiler; and the recommended open degree of the damper of SH

and RH see drawing 7. Shut down one side flue gas damper, when adjustment of

flue gas damper towards to the stop is needed, dont simultaneously close the flue

gas adjustment damper of SH and RH.

The open degree of back pass gas damper shall be adjusted according to

boiler load fluctuation. The recommended open degree is shown in Fig. 7.

b. When RH steam temperature is low, the flue gas damper at convection RH

side shall be adjusted toward open side, meanwhile the flue gas damper at

convection SH side shall be adjusted toward close side. When RH steam

temperature is high, the flue gas damper at convection RH side shall be adjusted

toward close side, meanwhile the flue gas damper at convection SH side shall be

adjusted toward open side.

c. RH spray attemperator outlet steam temperature shall not be less than the

saturation temperature plus 14 under operation pressure. When the boiler load

is lower than 40%BMCR, RH spray attemperator shall not be put into service.

d. The heat absorption ratio of radiation and convection surface can be

modified via altering the central height of furnace flame to fulfill the temperature



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adjustment of reheating steam. Factors that influencing the furnace flame central

height are plenty; the furnace flame central height can be decreased by lowering

the loading of upper burner and adding the loading of lower burner, properly

decreasing furnace pressure and increasing the secondary wind of the upper and

reduce the secondary wind of the lower etc; for the convection RH, the reheating

steam temperature will be lower when the furnace flame center dropping.

Otherwise, the reheating steam temperature will be upper when the furnace flame

center rising.

2.5 Control and Adjustment of Boiler Loading and Steam Pressure

The work of boiler loading and steam pressure adjustment is actually

maintaining the balance between boiler duty and quantity of steam that steam

turbine required while sustaining the outer electrical loading.

Under normal operation (rated working condition), SH outlet steam pressure

shall be 17.40.2Mpa.g.

2.5.1 The Impact of Steam Pressure Swing

High economic benefits of the units will be realized by a high sustaining degree of

the boiler main steam pressure within the allowable variation scope. However, the

steam pressure over the allowable range will severely harm the body and equipment.

If the steam pressure fluctuated frequently, it will cause the metal of the boiler

heating surface under the action of repeated stress, in addition to other factors such

as temperature stress; finally the heating surface metal will have fatigue damage.

For the drum boiler, when the temperature dropping, the water volume inside of

the drum boiler will expand; and the drum level will rise. Otherwise, when steam

pressure rising, the water volume shrinking; the drum level will go down. This untrue

water level will cause water level accidents such as full water level or water shortage

in the violent steam pressure variation. Additionally, suddenly steam pressure

dropping or rising will also cause the vaporization of down pipe inlet working medium

or lowering the circulation ratio to impact the water cycle safety of boiler.

2.5.2 The Reasons of Steam Pressure Variation

Reasons for causing the steam pressure of boiler are plenty; mainly in two

aspects: one is the external factor of the boiler; the other is the internal factor.



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1) External factor: boiler external factor is also called external disturbance,

means the disturbance caused by the equipment or operation outside of the

boiler.

Loading swing of the outside:

High pressure heater suddenly out of operation for fault

The quality changing of fuel:

2) Internal factor:

Internal factor of boiler is also called internal disturbance, usually means the

disturbances caused by the equipment and operation of the boiler itself.

a) The alteration of combustion conditions:

b) Equipment fault:

2.5.3 The Adjustment of Boiler Loading and Steam Pressure

1Adjusting method for boiler loading and steam pressure

The modular unit with rated pressure operation, the adjusting method for

loading and steam pressure normally could be classified by three modes; they are

boiler following mode (also called Lugenji mode), turbine following mode (called

Jigenlu mode) and coordinating mode.

a. Boiler following mode

In the boiler following adjustment system, pressure set is drawing upon the

boiler main control, manually adjust the opening degree to fulfill the loading; the

main control of the boiler adjusts the main steam pressure.

b. Turbine following mode

In the turbine following adjustment system, pressure set works on the turbine.

The control valve of the turbine will be set in compliance with the pressure to fulfill

the pressure set.

c. Coordinating mode

Coordinating mode boiler main control mainly controls steam pressure, steam

turbine main control mainly control loading. Through the co-working and effect,

the set requirement of the loading and steam pressure can be fulfilled.



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2.5.4 Steam pressure adjustment

a. Main steam pressure shall be adjusted by increasing or decreasing fule

on the premise that the stable combustion cannot be affected . Safety valve and

steam exhaust shall not be used to decrease the steam pressure under

non-accident working condition. Under superpressure operation, the electric

discharge valve shall be first opened to release pressure due to its low setting

pressure.

b. If the steam pressure reaches the action value of safety valve, the safety

valve still rejects action while the

boiler operating course

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