Showing posts with label Boiler. Show all posts
Showing posts with label Boiler. Show all posts

On line water & steam leakage arrester and sealants

 

Lucifer Waterproof Rubberized Adhesive Sealant Tape Stop Leaks Seal Sealant Repair Tape




2-Buyyart Polyimide Heat Resistant/High Temperature Adhesive Tape (10mm)



                                               

3-RUDRA Waterproof Adhesive Sealant Tape Stop Leaks Seal Repair Tape



                                               `

4-Online Transformer Oil Leak Sealant



                                                         

5-THEMISTO - built with passion RT1 Royal Tools Silicon Sealant Gun



                                        

6-J-B Weld 8281 Professional Size Steel Reinforced Epoxy


                                                     

7-Blue Magic 16002TRI QuikSteel Steel Reinforced Epoxy Putty Repair


                                              

Challenging situations & troubleshooting during Boiler light up & start up

 

1-Unavailability of start-up equipments/Competent Man power etc:

As we aware after long shutdown or after maintenance activities, we face following common problems

  • Not closing of work permits,
  • Not normalizing equipment like Boiler fans, Fuel feeding system equipments from electrical department
  • No trial of equipments prior to Boiler light up.

Solution:

  • Preparation of check lists for pre light up of Boiler
  • Equipments trial & interlock testing
  • Ensuring competent persons for light up activities

2-Boiler light up failure:

The main reasons for Boiler light up failure are;

  • Improper selection of fuel (coal, bagasse) : High moisture content fuel may lead to late light up or complete failure
  • Foreign materials in fuel may lead to clinker
  • Improper fuel: air mixture can lead to clinker formation
  • Following wrong SOP of light up
  • Not achieving 3T’s of combustion (Temperature. Time & Turbulence)
  • Failure of fuel feeding system
  • Choke up of fuel feeding system

Solution:

  • Following SOP
  • Selecting good quality fuel
  • Deputing competent person for Boiler light up

3-Drum level fluctuation:

The reasons for drum level fluctuations are;

  • Not following boiler pressure raise curve (Fast raising of Boiler pressure)
  • Sudden opening or closing of start-up vent control valve
  • Improper controlling of blow down valve
  • Improper Boiler loading
  • Uncontrolled & uneven firing rate

Solutions:

  • Following Boiler start up SOP
  • Maintaining good control over Start up vent control valve & IBD valves
  • Deputing competent Boiler Engineer for operation

4-Air Pre Heater (Tubes jamming):

Reasons for APH tubes jamming;

  • Not bypassing the APH during initial start-up (Some Boilers have 100% APH bypass arrangement & some Boilers have 25-30%).If APH not bypassed during Boiler light up, cold FD air will cause condensation of flue gas passing through APH tubes. Initially APH inlet flue gas quantity & temperature is less and FD air quantity will be more. This causes condensation of flue gas in tubes resulting into tubes jamming.
  • Maintaining lower flue gas temperature at APH inlet
  • Leakages in APH tubes: APH tubes leakage may also lead o jamming
  • Operating Boiler at more excess air

Solutions:

Bypassing the APH during light up & start ups.Generally APH is taken online when APH outllet flue gas temperature crosses 140 Deg C

5-Draft fluctuation & Boiler back fire:

Initially there will not be any control systems working in Auto mode, so controlling the draft & combustion is totally based on communication with field people

Probable reasons are;

  • Unbalanced draft
  • Poor communication of field people & control room engineers
  • Uncontrolled fuel feeding

Solutions:

Maintaining proper communication of field & control room engineer is good remedy to control back fire & draft fluctuation

6-Incomplete & Secondary combustion:

Incomplete combustion is mainly due to poor air fuel mixture leading to more unburnt & secondary combustion at Super heaters, APH & ESP.

Incomplete combustion is also due to not achieving 3T’s of combustion (Lower bed temperature, over feeding, low excess air)

Power plant safety Questions & Answers

Solutions:

  • Maintaining 3Ts during boiler light up & start up
  • Maintaining balanced draft to avoid secondary combustion due to carryover of fuel
  • Ensure OFA nozzles are open & dampers opening is optimized as per requirement

7-Flue gas duct explosions:

This is mainly due to more negative draft, carry-over of fuel particles & secondary combustion. Secondary combustion at the lack of O2 lead to formation of CO, this CO when exposed to rich oxygen leads to explosion.

How CO formation leads to explosions??

During Light up & start-ups unburnt fuel particles get carryover & accumulate at corners of ducts (APH, ESP etc).As we know incomplete combustion leads to formation of Co instead of Co2.This CO formed by unburnt particles when comes in contact with oxygen start to burn (combustion), due to low volume at ducts corners, ESP , this combustion leads to sudden explosion.

Solution:

  • During light ups & start up maintain balanced draft, or draft slightly positive (up to + 2 to 4 mmwc) in furnace.
  • Maintain sufficient turbulence for combustion
  • Ensure all flue gas & air ducts are clean & free from obstacles
  • Get feedback from field people on furnace draft, combustion & chimney condition etc.

Note: More black smoke at stack outlet shows unburnt carryover & incomplete combustion or insufficient air

8-No water flow to Boiler:

This condition exists;

  • On tripping of pumps,
  • Instruments malfunctions
  • Faulty flow meter
  • Stuck up of control valve etc
  • BFP suction strainer choke up

Solution:

  • Ensure pre start up checks have been followed properly
  • Keep standby equipments healthy & should be available readily

9-Stuck up of Main Steam Stop valve (MSSV):

  • Main steam valves stuck up due to long shutdown & no frequent operation
  • Unequal pressure at inlet & outlet of MSSV
  • Problems related to actuator (low torque set)
  • Not operating MSSV bypass valve before opening MSSV

Solution:

  • Carryout preventive maintenance (PM) of MSSV periodically
  • If PM not conducted, follow valve operation schedule during long shutdowns
  • Ensure actuator open & close torques have been set properly
  • Before opening the Main valve, do open the bypass line valve (1” or 1.5”), which helps for pressure equalization at inlet & out let side of main valve.

Note:

Functions of Main steam line bypass line:

  • Pressure equalizer
  • Initial line charging

10-Main steam line hammering

Steam line hammering is the phenomenon when steam & water mix at high pressure. Water hammer is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change).

As soon as steam leaves the boiler, it starts losing heat. As a result, steam stats condensing inside the pipe work. The rate of condensate formation is high particularly during the start ups when the system is cold. As a result of the condensation, the droplets of water are formed. These droplets of condensate get built up along the length of steam pipework forming a solid slug. When this slug encounters any obstacle such as a bend, it will be brought to a halt abruptly. All the kinetic energy of the condensate slug will get converted into pressure energy which has to be absorbed by the pipe work. This gives rise to the phenomenon of water hammer.

Understanding the term water hammer:

After condensate is formed, the flow inside the pipe has two components, steam and the condensate. The flow velocity of steam is much higher than that of the condensate. During such dual phase flow, the heavy condensate which flows at the bottom of the pipe is pulled by high speed steam. This results in formation of water slug which is much denser than steam travelling with the velocity of steam. When this slug is stopped by any abruption like a bend or equipment, the kinetic energy of the slug will be suddenly converted into pressure energy which will create a shock wave in the entire pipework. The pipework will keep on vibrating until this energy is dissipated in the structure.

Solution:

  • Charge main steam line by opening bypass valves only, if line is cold give sufficient time to warm the line
  • Keep open all drains of main steam line & ensure condensate is draining from those line
  • Ensure operator opens the valve very slowly (if MOV is not provided)
  • Ensure all steam traps are working properly
  • Ensure all steam lines are covered with insulation to avoid steam condensation
  • Ensure NON return valves of attemperator (desuper-heating line) water line is working properly

11- Boiler & steam line uneven thermal expansion:

This condition exists when;

  • Boiler light up & start-ups are not done as per OEM recommendation
  • Quick light up & start ups
  • Improper refractory during carrying out maintenance activities
  • Obstacles or foreign material left in Boiler during maintenance
  • Damage of steam line supports or stuck up
  • Overloading the Boiler or steam line

Solution:

Following post shutdown Boiler maintenance checks

  • Ensuring proper refractory during shutdown
  • Ensuring no any pressure parts are welded with external parts of boilers like platform, columns, beams etc. which do not undergo thermal expansion
  • Conduct preventive maintenance steam line supports & spring hangers
  • Strictly following SOPs for Boiler light up & start-ups as per time curve given by manufacturer

12-Not achieving the Boiler rated parameters (Pressure, temperature & load)

This is condition is due to;

  • Improper combustion
  • Selecting improper fuel (high moisture. High ash content fuel)
  • Problems related to combustion system
  • Improper air & fuel distribution
  • Choked fuel feeding system
  • Choked air nozzles
  • Leakages in & out of the Boilers
  • Not operating the Boilers as per SOP

Solution:

  • Check issues related to combustion system like proper opening of air & flue gas duct dampers, direction of rotation of FD, PA & ID fans
  • Check & ensure field & DCS instruments are showing correct readings
  • Check & ensure proper air & fuel distribution in furnace/bed
  • Arrest leakages.

13-Frequent jamming of fuel feeding system

  • This is due to wet fuel
  • Operating the fuel feeding at lower speed
  • Not providing sufficient air pressure
  • Foreign materials in fuel

Solution:

  • Ensure correct moisture fuel is being used for Boiler light up
  • Ensure proper air pressure for fuel distribution

14-Pressure parts failure

During initial start-up of Boilers there is more chances of failure of super heater coils & water wall tubes.

This is due to;

  • Less steam flow through super heater coils: This happens if pressure rising is done without opening the start-up vent valve, or super header drains.
  • Low water level
  • High firing rate
  • High drum level (>100%) can cause water hammering in super heater coil & eventually failure

Solution:

  • Follow Boiler light up & start up SOP
  • Ensure enough steam is flowing through super heater coils coils during boiler start up
  • Control firing rates
  • Ensure proper water level & cross check DCS level with local gauges

15-Clinker formation:

  • Reasons for clinker formation;
  • Improper air fuel mixture
  • Not achieving 3TS during light up
  • Foreign materials in coal
  • Foreign materials in bed material or poor quality bed material

Solution:

  • Using low moisture coal
  • Maintaining proper air fuel mixture
  • Achieving proper combustion
  • Using coal with no foreign materials
  • Avoiding frequent startups and stops
  • Use coal with high ash fusion temperature

Other General problems associated during Boiler light up & start-ups are

  • Fuel handling chutes jam due to wet coal
  • Coal crusher jamming
  • Low water level in DM storage tanks
  • Power supply constraints for running WTP & other BOPs
  • Ash handling chutes & hoppers jam

 

 Questions & Answers on Spent wash Boilers

Troubleshooting guide for Boilers

 

 Viva Questions & Answers on Boiler Safety Valves

 

 

 

 

 

Factors considered for Boiler Engineering & Design

Factors considered for Boiler engineering/Boiler Design

1-Boiler Design code: IBR 1950 with latest all amendments

2. Ambient air temperature: Depends on the location of the plant, in India Generally 30 to 45 Degree C is considered.

3. Relative humidity for performance: (Normal: 60% to 70%, Maximum: 80% & Minimum: 20%).Generally it depends on site condition

4. Wind Velocity & direction for structure design: as per IS 875 (39 m/sec)

5. Seismic coefficient As per Is 1893 Zone-I

6. Wind velocity for insulation: generally 1 m/sec

Why & How these in Boilers??

7-Maximum Continuous Rating (MCR) required for particular process or use: It is the capacity of the Boiler in TPH or Kg/hour required.

8-Operating pressure & temperature: Operating pressure & temperature of the Boilers depends on the requirement of process of prime mover. Higher the operating parameters higher will be the Boiler efficiency & lower will be the fuel consumption. For high pressure Boilers water quality required is

9-Type of fuel: It depends on the easily availability of fuel, for example: Sugar based cogeneration Boilers are designed for bagasse fuel. Utility Boilers are designed for Briquettes & Indian/ Indonesian coal. Thermal power plant Boilers are designed for coal.

Gujarat state area Boilers are designed for natural gas fuel. Middle yeast country Boilers are designed for Oil fuel.

While designing the Boilers & combustion system fuel GCV, ash & moisture contents are considered.

Questions & Answers on Fuel consumption

10-Peek Capacity of the Boiler: It is the maximum allowable load on Boiler for short period. Generally it is kept 110% of MCR.Peak capacity is allowed 30 minutes in 8 hours.

11-Range of load variation/Steam temperature control range: It is the range of load (as % of MCR) during which Main steam temperature is maintained constant. Generally it is around 60-100%.

12-Percentage of excess air or Excess air coefficient at Boiler furnace & Boiler outlet

13-Circulation ratio

14-Feed water temperature at economiser inlet: In order to achieve desired efficiency & fuel consumption, feed water at economiser inlet is very must. Higher the feed water temperature, lower will be the fuel consumption & Vice versa.

14a-Feed water quality like pH, conductivity, TDS, Silica, hardness, Alkalinity etc

15-Steam temperature drop at Super heater coils: In order to get the desired main steam temperature at super heater outlet, need to maintain the ∆T across super heaters.

16-Flue gas temperature drop: While engineering Boilers, flue gas temperature drop at every zone (Super heaters, Bank zone, Economiser, APH etc) should be considered.

17-Combustion air temperature: FD & SA air temperatures after APH should be optimum. More air temperature leads to formation of clinker & less air temperature leads to less combustion efficiency.

18-Air & Flue gas ducts sizing: In order to avoid pressure drops in ducting proper sized ducts have to be considered. Flue gas pressure drop is very important for considering heat transfer at APH, Economiser, Bank zone & Super heaters.

Material of MS material (IS 2062) for air ducting is of 5 mm & for flue gas ducting is 6 mm

19. Fuel feeding system: Considerations of No. of fuel feeding system & their individual capacity is necessary for operating the Boilers at MCR & Peak loads at varying fuel parameters. If the fuel GCV, moisture & ash content vary then fuel consumption will also vary. So while engineering the Boilers fuel feeding capacity is considered 25 to 30% more.

Turn down ratio of fuel feeding system. Maximum moisture handling capacity of the system

20. Heat released in Furnace: This important factor for designing the furnace height, width & breadth

21. Heat released on Grate/Bed: This important factor for designing the furnace & combustion compartments, grate materials etc

Power plant equipments efficiency calculation

Boiler calculations for Boiler operation engineer (BOE) exam

Viva Questions & answers for preparation of BOE exam & interview

22. Flue gas velocity at various zones of Boilers: This is very important factor to be considered while designing the Boilers. Higher velocity of flue gas leads to erosion of pressure parts & ducting, lower flue gas velocity leads to poor heat transfer.

Generally for AFBC, Travelling grate, WHRB, oil fired Boilers ducting are designed for 18 m/sec velocity.

23. Percentage of combustion air flow through FD & SA. Generally from FD 60 to 70% and from SA 30 to 40%

10-Tips to reduce Unburnt in Boilers

24. Steam pressure drop in all stages of Super heater coils

25. Velocity of feed water & saturated water at each pressure part

26. Overall heat transfer co-efficient & LMTD in super heater, economiser, Bank zones

27. APH: Overall heat transfer co-efficient & LMTD .Pitching of tubes along & across the air flow. Heating surface area

28. Pitching of super heater coils along & across the flue gas flow: Wide pitching of super heater to minimize fouling.

29. Desuperheating spray water quantity at MCR & other various loads

30. Maximum steam temperature at each super heaters

31. Maximum allowable metal temperature at each Super heaters

32. Pressure parts thermal expansion calculations & Maximum/minimum tolerances

Thermal expansion in Boilers

33. Grate or Bed area loading in mm Kcal/M2/Hr

34. Dust concentration at Boiler outlet in gram/NM3

35. Quantity of flue gas produced

36.No.of Safety valves installed Boiler safety valves QnA

 

 Power plant Maintenance calculations

 

 10-Tips to reduce LOI in Boilers


Opportunities for energy conservation in power plant

 

 Challenging situations & troubleshooting during boiler light up & start up

 


25-Questions & Answers on AFBC Boilers

 

1-What do you mean by AFBC Boiler?

Atmospheric Fluidized Bed Combustion (AFBC) boilers are those, which have the potential to use alternative fuel sources such as coal, wood, or waste or any other low grade fuel, and are able to reduce and control nitrogen oxide (NOx) and sulphur dioxide (SO2) emissions.

2-List down the advantages of FBC boilers over other boilers?

  •          FBC boilers have higher combustion efficiency.
  •          Any low grade fuel can be burnt in FBC Boilers
  •          Boiler size is compact as compared to travelling grate & pulverized boilers.
  •          Different variety of fuels can be burnt
  •          Very high ash content fuel can be burnt
  •          Over & under feed fuel feeding system availability
  •          Higher turn down ratio

3-Briefly explain the process of fluidisation?

When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized.” With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid “bubbling fluidized bed” desirable for good heat transfer and intimate contact. If sand particles in a fluidized state is heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840 °C to 950 °C.

4-Explain the different types of Fluidization in FBC boilers

Boiler Gauge Glass Line Up Procedure

Fluidization: At low velocity air flows through the porosity of bed. Once the velocity of air increases, the air starts moving in a turbulent state & causes particles of bed to attain turbulence along with the air. Here bed materials move like fluid, so called Fluidization.

Different types of fluidization are:

When gas flow introduced through the bottom of the bed of solid particles, it moves upward through the bed via the empty spaces between the particles.

During low air velocity bed remains under stable fixed state, this condition is called Pseudo Fluidization

Minimum Fluidization:

At higher air velocity, the aerodynamic drag forces begins to counteract the gravitational forces causing the bed to expand in volume as the particles move away from each other. Further increasing the air velocity, it reaches the critical value at which upward drag forces exactly equal to the gravitational forces causing particles to remain in suspended within the fluid, this is called minimum fluidization.

Maximum fluidization or bubbling fluidization:

Further increasing the air velocity, the bulk density of the bed continues to decrease and its fluidization becomes more violent, until the particles no longer form a bed and are conveyed upwards by the gas flow. This is called bubbling fluidization.

Questions & Answers on Boiler Troubleshooting

5-What the bed plate is consisting of?

Bed plate is the partition plate between wind box & furnace. It consists of Bed nozzle, coal feed nozzle & ash drain pipes. Generally bed plates are made up of stainless steel materials.

6-What are the different types of nozzles used in AFBC Boilers

Fluidizing nozzles:

These are the stainless steel or alloy steel nozzles fitted on bed plate. It has 2 to 5mm holes around it, through which FD air enters rom wind box to furnace. It is manufactured by machining a solid SS/alloy steel bars.

Coal feeding Nozzles:

Coal with primary air enters into the furnace through these nozzles.4 to 6 nozzles or depending on Boiler capacity are fitted in each compartments. Coal feeding nozzles are fitted in bed plate to distribute coal uniformly

7-What is the function of Ash drain pipes?

Generally Ash drain pipes are fitted in bed plates & extended outside. These are terminated to bed ash cooler where ash is getting cooled by air before discharges through ash conveying system.

How to convert air /gas flow from M3/hr to Nm3/hr or Sm3/hr??

What do you mean by IBE & IBSH in FBC Boilers?

IBE: In Bed Evaporating Coils

In some FBC Boilers, complete furnace is covered with evaporator coils. Coils are generally fitted in 2 nos inner & outer. To prevent erosion due to fluidizing materials, coils are covered with refractory materials.

IBSH: In bed Super heater coils

One SH coil is placed inside the bed, it is just placed right angle of IB coil & generally installed from last compartment & extended up to second compartment. To get rated main steam temperature at lower loads, sometime these are installed in 1st compartment also.

Why & How these in Boilers??

8-What do you mean by DP test in AFBC Boilers?

It is the test carried out before the light up of Boiler to ensure the healthiness of air nozzle & bed plate.

9-Write down the potential reasons to carryout DP test

To check the condition of air nozzles that is to identify the nozzles are clean, choke free & correct hole size

  • To identify the leakages in bed plate
  • To check the maximum FD air flow for each compartment
  • To identify air leakages in APH
  • To check problems associated with each compartment

10-Briefly explain the procedure of DP test

DP test is done on clean bed

Pre-checks

  • Ensure bed is clean
  • Ensure all maintenance works of air nozzles, bed etc are completed
  • Ensure FD fans are healthy & can be run at its full flow capacity (Air flow is allowed in each compartment from 25% to 100% of its capacity)

Procedure:

  • Start ID fan & then FD fan at minimum RPM initially
  • Take APH in line
  • Increase air flow gradually from 25% to 100%
  • Note down wind box pressure at each stage
  • Repeat this procedure for remaining all compartments
  • The wind box pressure values should match commissioning or design values
  • Now take all the compartments together & increase FD air flow up to 100% & again check wind box pressure & FD fan discharge pressure

Interpretation

  • If the DP test results (wind box pressure) are 10 mmwc more or less than commissioning values, nozzles& bed plates are said to be in good condition
  • If result data shows higher value, then nozzles are blocked
  • If the results show less value, then nozzles or damaged or holes are enlarged
  • Higher pressure drop in APH indicates tubes leakage

11-What is the fluidization air velocity in AFBC Boilers?

It is around to 1.5 to 3.7 m/sec

12-What do you mean by Elutriation in AFBC Boilers?

Process of separation & escaping of fine bed materials with the air during fluidsation is called Elutriation.

13-What do you mean bed level?

It is the height of the bed above the bed plate

Power plant maintenance Calculations

14-How do you calculate the Bed level?

Bed level = wind box pressure-DP across the bed nozzles

What is the function of Over Fire Air (OFA) in AFBC Boilers?

OFA is given at height around 5 to 8 meter above the bed to achieve complete combustion

15-What is the standard size of Bed materials used in AFBC Boilers?

Bed material is Crushed refractory of size around 0.85 to 2.36 mm & having fusion temperature > 1300 Deg Cdf

16-What is the density of refractory material?

It is around 1100 kg/m3

17-What are the standard compositions of Bed materials?

Sl No.

Chemicals Compositions

Limits

1

SiO2

55-60

2

Al2O3 37-40 , Min 30% required

37-40 , Min 30% required

3

FeO

<2.0

4

TiO2

1.67

5

MnO

Small traces

6

CaO

0.54

7

MgO

0.23

8

P2O5

0.08

9

Na2O + K2O

< 3.0

 Questions & Answers on Spent wash fired Boilers

18-What are the startup fuels used for AFBC boiler light up?Write down the procedure for AFBC boiler start up

Charcoal & Light Diesel Oil (LDO) are used as start fuels for AFBC boiler light up

Light up & Start up procedures

  • Before filling bed material into the furnace FD air nozzles must be cleaned by admitting maximum FD air into the furnace by opening FD air compartmental damper (PA air damper remaining closed) for 10–15 minutes.
  • Fill bed material into the furnace so that bed height should be about 250–300 mm above air nozzles or 280–300 above the distribution plate.
  • The bed material below the air nozzles remains static all the time and should be counted as bed height.
  • Spread the bed material uniformly by admitting sufficient fluidized air through the bed and bed height can now be measured physically after putting off air. During fluidizing PA dampers should remain closed.
  • After uniform spreading of bed material and maintaining required bed height start the startup compartment by varying the air flow gradually so that bed material begins to fluidize.
  • Slowly increase the air flow so that small bubble formation takes place over the bed material and incoming air escape the bed as small bubbles. Note down the air flow at the stage known as bubbling stage.
  • Again increase the air flow so that the bed become turbulent and complete mixing of top and bottom layer of bed material take place. Note down the air flow at this stage. This is the amount of air required fir mixing during start up.
  • Now stop the fans and boiler can be taken for startup.
  • Maintain the drum level about 40%.
  • Drum vent, super heater vent, startup vent and main steam line drain should be kept open.
  • Desired quantity of dry charcoal is to be spreaded uniformly over the bed in the start up compartment. Generally 1 to 3% of bed material
  • Desired quality of Diesel mixed charcoal is spreaded over the dry charcoal. Generally Diesel must be 10-15% of total charcoal. Out of total charcoal 70-75% should be dry & spreaded at the bottom & 25-30% should be wet & spreaded over top of dry charcoal
  • Initiate the fire using diesel soaked cotton. Ensure fire is spreaded uniformly
  • After some times start ID, FD & PA fans as per sequence and open their discharge dampers then suction damper. Keep at minimum RPM if there is VFD if not then control the flow by discharge & suction dampers.
  • Maintain PA header pressure up to 500 MMWC initially
  • Now check physically and ensure when the flame is in bluish condition mixing should be done with mixing air flow for 10–15 second
  • Now bed temperature will start rising and after getting bed temperature up to 450 Deg C start the coal feeding by increasing PA header pressure up to 900-1000 mmwc
  • Now slowly increase fuel feeding & FD air
  • Close drum air vent at 2.5 kg/cm2.
  • Close super heater drain at 20 kg/cm2 pressure and open start up vent control valve.
  • Open MSSV (main steam stop valve) after the prior and proper charging through equalizer valve (MS bypass valve).
  • In order to increase the load on Boilers take 2nd, 3rd etc compartments as per requirement

19-What is the size & GCV of Charcoal used for light up

Charcoal size is around 15 to 25mm & GCV is around d 6500 to 7000 Kcal/kg

20-What are the important parameters in AFBC boilers?

  • Fuel size
  • Bed material size and specification
  • Bed height and FD air pressure
  • Bed temperature and furnace temperature

21-What action you will take if bed temperature increases?

  • Increase bed material
  • Reduce load
  • Control the bulk density of fuel

22-What are the reasons for drop in bed temperature?

Poor quality of bed material

Sudden reduction of boiler load

Moisture in fuel

More excess air

23-Why do you add Lime in AFBC boilers?

Lime is added to absorb the moisture from coal

24-Explain the process of sulphur dioxide absorption by lime

Lime stone (CaCo3) on heating gets converted to slaked lime

CaCo3 + Heat = Cao + Co2

Sulphur on heating gets converted into Sulphur di-oxide

S + O2 = SO2

Slaked lime reacts with Sulphur dioxide & converts into Calcium sulphur

Cao + SO2 + ½ O2 = CaSO4

25-How do you decide the quantity of sulphur required for desulphurization of coal?

Around 3.3 kg of lime is required for 1 kg of sulphur in coal or 2 kg of sulphur dioxide

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