Power plant and calculation site basically includes the detailed study of power plant operation and maintenance, its related all calculations and thumb rules. It also involves detailed troubleshooting guides for operation and maintenance of power plant system/equipments like Boiler, fans, compressors, belt conveyors, ash handling system, ESP, steam turbine, cooling tower, heat exchangers, steam ejectors, condensers WTP. etc. Heat rate, efficiency
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
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
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
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
Opportunities for energy conservation in power plant
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.
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 |
18-What
are the startup fuels used for AFBC boiler light 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
Read related articles
Viva Questions & answers for preparation of BOE exam & interview
Factors considered for Boiler Engineering
Boiler Feed Pumps Design factors & Pump Capacity calculation
Challenging situations & troubleshooting during boiler light up & start up
Why does Boilers main steam temperature increases more than design?
Slop fired Boiler bag filter commissioning & shutdown procedure
Practical Approach to Power Plant Operation and Maintenance
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