take place because burning reaction is sensitive to flow fluctuation in case of gas burning. When oscillatory burning is conducted, vibration noise is generatedon specific frequency, combustion efficiency is decreased and related equipments are damaged. Oscillatory burning

in boiler isHelmholtz type oscillatory burning and acoustic resonance type oscillatory burning.

(6) Premixed flame

When flammable premixed gasis ignited, flame is produced extremely thin flame and propagated in premixed gas. This flame is reacted chemically immediately, temperature and gas concentration are changeddrastically. Burning velocity depends on type, composition, temperature and pressure of premixed gas. Burning velocity of turbulent premixed flame is increased in connection with Reynolds number and is not depended on type of gas.

(7) Turbulent (jet flow) diffusion flame

Fuel and air are jetted out separately and they are burned. Flame is produced at boundary face between fuel and air, fuel and air are supplied to this boundary face by diffusion and flame is kept. Burning velocity depends on diffusion mix velocity.

(8) Stabilization of flame

Flame is stable and not extinguished when fuel flowelocityv and air ratio are within proper range. There is a possibility that premixed flame is generated back fire when fuel flow velocity is decreased, generally jet flow diffusion flame is not generated back fire. It is necessary that balance point with mixed gas flow velocity and burning velocity is produced to steady flame. In general, this balance point is base of flame.

2. Exhaust gas composition

It must be paid attention to emission gas from power plant to prevent environmental pollution. It must be referred to Part6 of Vol.2 design technical regulation regarding emission control regulation when identifying industrial emission and sulfur in natural gas in regulation of power plant.

Chapter 3 Pulverized Coal Processing

Article 131. General Provision

Starting mode for coal pulverizer is normal starting mode and starting with remaining coal mode. When boiler is stopped emergency, coal pulverizer emergency is stopped leaving coal in it. This is

Acceptable stop time for coal pulverizer with remaining coal (sample) is shown in Table 131-

1. It must be referred to actual experience of each power plant and ’smanufacture recommendation when it is defined at each power plant.

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Table 131-1 Acceptable stop time for coal pulverizer with remaining coal (sample)

(2) Concrete countermeasures

It must be following countermeasures within above acceptable time to prevent a fire. 1) Starting with remaining coal of coal pulverizer

Process flow of starting with remaining coal is shown as follows; a. Preparation before starting

(a) It must be confirming following provisions as preparationfore bestarting with remaining coal.

a)Starting condition of relevant oil burner is formed.

b)Each measuring gauge and recorder is normal.

c)Control air pressure is normal.

d)Following equipments are turned on power and in automatic mode.

-Coal pulverizer

-Coal feeder

-Rotating classifier

-Primary air fan

-Related damper and pumps

-Coal gate etc.

e)Each control source is turned on power. And others b. Process flow of staring

(a)It must be started starting system of coal pulverizer with remaining coal.

(b)It must be confirmed operation status of following equipments.

a)Lubricant oil pump : Starting

b)Roller pressure pump : Starting

c)Rotating classifier : Starting

d)Igniter : Ignition

e)Hot air damper : Full close

f)Cool air damper : Full open

g)Seal air damper : Open

h)Cut damper : Open

i)Primary air shutoff damper : Open

j) Primary air control damper : Stipulated opening etc.

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(c)It must be confirmed following operation condition is met with acceptable value.

a)Primary air flow volume

b)Differential pressure of roller seal

c)Differential pressure of table seal

d)Lubricant oil temperature

e)Inlet lubricant oil pressure of coal pulverizer reduction gears and others

(d)It must be confirmed starting condition of motor of coal pulverizer is formed and it is started.

(e)It must be confirmed coal feeder is started.

(f)It must be confirmed initial stipulated coal feed rate.

(g) It must be confirmed outlet temperature of coal pulverizer is met with acceptable value and initial feeding coal is completed.

(h)It must be confirmed relevant igniters are extinguished.

2)Purging with remaining coal of coal pulverizer

It must be supplied remaining coal to boiler by purging of coal pulverizer. It must be referred to Article 137 of this guideline.

3) Removing from coal pulverizer inside

When coal pulverizer is stopped longer than acceptable stop time shown in Table 1311,- it must be removed remaining coal by hand to prevent a fire. It must be taken appropriate countermeasures of removed coals.

Photo 131-1 Coal pulverizer

Article 132.

(Nothing)

Article 133. Starting up system

When confirming trouble and defects in coal pulverizer, it must be stopped and maintained it immediately to keep stable operation of power plant. It must be confirmed following provisions to operate coal pulverizer system safely before restarting it after stopping it over 72 hours.

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1.It must be confirmed following equipments are in good condition.

(1)Interlock and protection system

1)Emergency stop

2)Starting and stopping conditions for loading hydraulic pressure pump of coal pulverizer

3)Starting and stopping conditions for lubricant oil pump of coal pulverizer

4)Starting and stopping conditions for coal feeder

5)Starting and stopping conditions for rotating classifier

6)Opening and closing conditions for coal gate

7)Opening and closing conditions for cut damper

(2)Measuring instruments

1)Coal pulverizer outlet temperature

2)Differential pressure in coal pulverizer

3)Lubricant oil pressure of coal pulverizer

4)Lubricant oil level of coal pulverizer

5)Vibration of coal pulverizer

6)Bearing temperature of each motor

7)Roller loading hydraulic pressure

8)Casing metal temperature of coal pulverizer

9)Differential pressure of roller seal

10) Differential pressure of table seal And others

(3)Lubricant oil equipment of each bearing of coal pulverizer and coal feeder

(4)Cooling water equipment of following equipments

1)Lubricant oil equipment of each reduction gears

2)Roller loading hydraulic pressure equipment

3)Each motor cooler

(5)Automatic system

(6)Signaling system

(7)Remote control system

2.It must be confirmed control air pressure is normal.

3.It must be confirmed there are sufficient quantities coals in coal bunker to operate power plant stably.

4.It must be referred to Article 137 of this guideline regarding purging of coal pulverizer.

Article 134. Check during operation

When operating pulverized coal processing system, it must be checked following items by daily patrol, daily inspection and monitoring from control room;

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1. Feeding of fuels for pulverizer

It must be checked feeding of fuels for pulverizercarefully because No flow coal at bunker chute and lack of coal at coal feeder causes emergency trip of coal pulverizer. Countermeasures for no flow coal at bunker chute and lack of coal at coal feeder are shown as follows ;

(1) No flow coal at bunker chute

No coal flow at bunker chute

Figure 134-1 Process flow of no flow coal at bunker chute

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(2) Lack of coal at coal feeder

Lack of coal at coal feeder

Figure 134-2 Process flow of Lack of coal at coal feeder

2.Amount of raw coal and pulverized coal must not be lower or higher than amount stipulated in regulations of power plant.

Amount of raw coal and pulverizedcoal are calculated based on output of power plant and heating value etc. When amount of raw coal and pulverized coal are lower or higher than amount stipulated in regulations of power plant, output of power plant is lower or higher thanrated output. It must be supplied coal to boiler according to regulations of power plant to operate power plant stably.

3. Temperature of pulverized coal in the system must not be over the stipulated limit

When temperature of pulverized coal in the system is increased, there is a possibility that a fire of coal pulverizer is occurred. Therefore, it must be monitored outlet temperature of coal pulverizer carefully. The reason and countermeasures when outlet temperature of coal pulverizer is high are shown as follows ;

(1)Reason

1)Control failure of cool and hot air damper

2)Rapid decreasing of coal feed rate

3)Failure of temperature switch

(2)Countermeasures

1)Manual adjustment of cool and hot air damper Adjustment by control drive

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2) Confirming of no flow coal at bunker chute and lack of coal at coal feeder

Refer to above paragraph 1 “Feeding of fuels for pulverizer”.

Opening cool air damper manually when coal feed rate is deceased rapidly and outlet temperature of coal pulverizer is increased.

3)Inspection and maintenance of temperature switch

4.Heat insulation and tightness of all parts of equipment. Holes which cause the air and pulverized leakage must be sealed immediately.

It must be checked eath insulation and tightness of all parts of equipmentat daily patrol and inspection. When detecting pulverized coal leakage, it must be maintained immediately referring to following items to prevent a fire.

(1)Pulverized coal leakage from coal piping (pin hole)

1)It must be started standby coal pulverizer and stopped one to be maintained.

2)It must be removed piping to be maintained and cleaned pulverized coal in it.

3)It must be welded leakage place and close the hole properly. It must be referred to Article 138 of this guideline regarding welding.

4)It may be used metal repairing materials such as Devcon and Multi Metal etc. instead of welding.

5)It must be installed maintained piping.

6)It must be started maintained coal pulverizer and stopped standby one.

(2)Pulverized coal leakage from flange of coal piping

1)It must be tightened bolts of flange and confirmed that pulverized coal leakage is completed.

5.Clogging of a coal bunker, pulverized coal bunker and mixing bunker

Because clogging of coal bunker, pulverized coal bunker and mixing bunker causes decrease of coal feed rate and makes power plant unstable operation, it must be checked it carefully by daily patrol and inspection and monitoring from control room of power plant. When confirming no flow coal of this bunker, it must be referred to above paragraph 1 “Feeding of fuels for pulverizer”.

Article 135. Adjustment pulverized coal system

Several type of coals are supplied to some coal fired boiler due to cost down, fuel security and burning characteristics etc. . When type of coal is changed,fineness and primary air weight in terms

of coal at coal pulverizer outlet. And, it is importantto confirm fineness and primary air weight in terms of coal at coal pulverizer outlet regarding operation management of power plant because combustion of boiler,unburnt combustible content in ash andslagging characteristics are changed significantly. Moreover, fineness of pulverized coal is deteriorated as power plant operates. Therefore,

it must be conducted sampling of pulverized coal and measuring of fineness periodically.

1.Main process flow for sampling of pulverized coal

(1)Preparation of sampling devices and installation of them

(2)Measuring of flow velocity of pulverized coal (please refer to Photo 135-1.)

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(3)Calculation of average of isokinetic sampling flow

(4)Installation of sampling tube

(5)Sampling of pulverized coal

(6)Measuring of fineness and flow volume of pulverized coal (please refer to Photo 135-2)

Joint

Flow of pulverized coal

U-tube manometer

Figure 135-1 Configuration of measuring of flow velocity

Dehumidifier

Flow meter

Figure 135-2 Configuration of sampling

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Article 136. Pulverized coal processing system with heater

Primary air fan system has Cold Primary Air Fan method and Hot Primary Air Fan method according to temperature of primary air. Please refer to Figure 136-1.

-Cold PAF (Primary Air Fan) method: PAF is installed upstream of AH and supplies cold air.

-Hot PAF (Primary Air Fan) method : PAF is installed downstream of AH and supplies hot air.

Comparison between Cold Primary Air Fan method and Hot Primary Air Fan method is shown as follows;

1. Power consumption

In high load operation with many coal pulverizers operation, Cold PAF method has high efficiency of

fan because small numbers of fans supply primary air to all coal pulverizers and small power consumption because it supplies cold air.

On the other hand, in low load operation with few pulverizers operation, Hot PAF method has small power consumption because PAF of stopped coal pulverizer can be stopped.

2. Operational evaluation

When load of coal pulverizer and moisture in coal are changed, inlet air temperature of coal pulverizer

is changed. In this case, Hot PAF method is affected by temperature change directly and operating pint of PAF is fluctuated. On the other hand, when inlet air temperature of coal pulverizer is changed, air flow and wind pressure fluctuation to PAF is small and controllability is high.

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Article 137. Purge of pulverized coal system

It must beexhausted coal dust from thepulverized coal system when topping system longer than stipulated time and before having boiler overhaul. Purge process of this system is shown as follows;

1.Preparation before purging

(1)It must be confirming following provisions as preparation before purging.

1)Starting condition of relevant rotating classifier is formed.

2)Starting condition of relevant oil burner is formed.

3)Another coal pulverizer is not under purge.

4)Some primary air fans are operated.

5)Seal air pressure of flame detector is normal.

6)Coal pulverizer system is automatic mode. And others

2.Process flow of purging

(1)It must be started purging system of remaining coal.

(2)It must be confirmed operation status of following equipments.

1)Lubricant oil pump : Starting

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2)Roller pressure pump : Starting

3)Rotating classifier : Starting

4)Igniter : Ignition

5)Hot air damper : Full close

6)Cool air damper : Full open

7)Seal air damper : Open

8)Cut damper : Open

9)Primary air shutoff damper : Open

10)Primary air control damper : Stipulated opening

(3)It must be confirmed following operation condition is met with acceptable value.

1)Primary air flow volume

2)Differential pressure of roller seal

3) Differential pressure of table seal And others

(4)It must be confirmed starting condition of motor of coal pulverizer is formed and it is started.

(5)It must be confirmed coal feeder is started.

(6)It must be confirmed alarm of lack of coal and coal feeder is stopped after stipulated time.

(7)It must be confirmed motor of coal pulverizer is stopped after stipulated time.

(8)It must be confirmed following equipments are stopped after stipulated time.

1)Roller pressure pump

2)Rotating classifier

(9)It must be following dampers are closed fully after stipulated time.

1)Primary air control damper

2)Primary air shutoff damper

3)Cut damper

4)Seal air damper

(10)It must be confirmed coal bunker pouring water valve is opened for stipulated time and igniters are extinguished.

Article 138. Safety on welding

When welding of pulverized coal processing system, it must be paid attention to following provisions to weld properly and keep safety for power plant staff and stable operation of power plant. Moreover, it must be referred to Part 7 Welding of Vol.2 design guideline regarding further details about welding.

1.It must be conducted preparation and welding according to procedures developed by each power plant.

2.It must be removed inflammable materials around welding place to prevent a fire.

3.It must be cleaned groove face and removed coal, pulverized coal and dust to prevent improper welding.

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