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



A-Standard Inspection procedure for Dry & thorough inspection

  • Checking the registration number of the Boilers
  • Carryout thorough inspection of Boiler from both inside and out side
  • Check for defects like corrosion, erosion, bend, bulging, pitting, deformation, thermal expansion etc of pressure parts
  • Check thickness of pressure parts
  • Check the conditions of mountings & fittings
  • Witness non destructive tests if required

B-Standard procedure for ground inspection of pressure parts under erection

  • Verification of documents of pressure parts with relevant certificates
  • Verification of approved drawings
  • Checking pressure parts makers stamp & other identification marks with form no-II
  • Checking of leading dimension of the parts & comparing with approved drawings
  • Checking general condition of the pressure parts like dent marks, pitting, bend etc
  • Checking of fittings & mountings with relevant drawings

C-Standard procedure for material inspection

  • Verification of the approved drawings corresponding to the materials & documents
  • Checking of the pressure parts materials with relevant IBR certificate and  approved drawing.Check name of the material, its specification, heat no, cast no.class, size, identification number & stamping etc
  • Checking of leading dimension of the parts & comparing with approved drawings
  • Checking general condition of the pressure parts like dent marks, pitting, bend etc
  • Selection of samples for physical and chemical analysis/testing

D-Standard Procedure for weld set up inspection

  • Verification of approved drawing
  • Verification of Welder’s certificate
  • Verification of the certificates of welding consumables
  • Verification of the approval of contractor for particular job
  • Verification for the procedure of welding procedure
  • Verification for the site satisfactory  simulation test results
  • Verification of test results of pipe, tube or plates
  • Checking of root gap,weld groove profile and alignment of the pressure parts to be welded as per approved drawing
  • Ensure weld joint area to be welded is free from dust, dirt, oil & grease.And also ensure it is crack free
  • Check weld joint identification number.

E-Standard Procedure for welding joint inspection

  • Visual inspection of general condition of the weld joint like, slag, under cut, finish, surface crack, leg length etc
  • Check alignment of the pressure parts
  • Witnessing Dye penetrant test, magnetic particle inspection test & hardness tests if required
  • Selection of weld joints for NDT test like ultrasonic & radio graphic tests

F-Standard Procedure for Boiler Hydraulic tests

  • Verification of the satisfactory non destructive tests of the welding joints
  • Verification of PMI (Positive Material Identification) report of the weld joints
  • Verification of pressure parts calculation approval
  • Verification of all previous inspection reports and Post weld heat treatment (PWHT) charts
  • Check the calibration reports of pressure gauges using for hydraulic test
  • Witnessing Hydraulic test carried out as per IBR-1950
  • Checking of deflection, distortion and extension of pressure parts during hydraulic test
  • Thorough inspection of pressure parts for any leakages and sweating

G-Standard Procedure for Boiler steam tests

  • Verification of the provisional order of the Boiler
  • Witnessing the steam test carried out as per IBR-1950
  • Check, popping pressure, reset pressure, blow down, accumulation, chattering, lift
  • Checking of the performance of the mountings and fittings


Read more >>>> Power plant and calculations


How do you calculate the efficiency of Economiser in Boiler??


What is the Economiser in power plants?

It’s the heat exchanger used in Boilers to recover the heat from exhaust flue gases.

What are the functions of economisers in Boilers?

Functions of economisers:

It recovers the heat from flue gas leaving the boiler, there by reduces the losses

It helps in raising the feed water temperature, there by reduces the fuel consumption

It increases the Boiler efficiency

It lowers the power plant operation cost

What are the different types of economisers?

Types of economisers

Pressurized economisers

Non pressurized economisers

Steaming type

Non steaming pipe

What do you mean by steaming type economisers?

Economisers where only sensible heat is added to feed water

What do you mean by non-steaming type economisers?

Economisers where sensible heat and part of latent is added to feed water

Efficiency Calculations:

ηEco. = (Economiser outlet feed water temperature Two-Economiser inlet feed water temperature Twi)  X 100 / (Economiser inlet flue gas temperature Tfi- Economiser inlet feed water temperature Twi)


 Read APH efficiency calculation


Calculate the economiser effectiveness, whose feed water inlet & outlet temperatures are 160 Deg C & 240 Deg C respectively & flue gas inlet & outlet temperatures 390 deg C & 220 deg c respectively.




Twi = 160 deg C

Two = 240 deg C

Tfi = 390 deg C

Tfo = 220 deg C

ηEco = (Two-Twi) X 100 / (Tfi-Twi)

ηEco = (240-160 ) X 100 / (390-160)

ηEco= 34%


In an non steaming economiser of efficiency 51%, feed water inlet and outlet temperatures are 105 deg c & 160 deg C respectively, calculate the flue gas temperature entering the economiser



Twi = 105 deg C

Two = 160 deg C

Tfi = 370 deg C

Tfo = ? deg C

ηEco= 51%


ηEco = (Two-Twi) X 100 / (Tfi-Twi)

51= (160-105 ) X 100 / (Tfi-105)

Tfi X 51-105 X51 = 5500

Tfi = 212.8 deg C


A economiser inlet feed water & flue gas temperature are 125 deg C and 405 deg C respectively, calculate the feed water leaving the economiser, consider efficiency of economiser 43%



Twi = 125 deg C

Two = ? deg C

Tfi = 405 deg C

ηEco= 43%


ηEco = (Two-Twi) X 100 / (Tfi-Twi)

43= (Two-125 ) X 100 / (405-125)

12040 = 100 X Two-12500

Two = 245.4 deg C


For more calculations related to power plant read Powerplant & Calculations

Reasons for Priming, Foaming and carryover in Boilers



1. What do you mean by the term Priming?

Priming means carryover of water particle in the steam

2. What are the reasons for Priming?

Reasons for priming;

  • Improper design of Boiler and steam drum
  • Maintaining high drum level
  • Boiler load fluctuation
  • Sudden load raise due to steam demand
  • Foaming in feed water
  • Miss operation of Boiler
  • Sudden lifting of Boiler safety valve or start up vent CV
  • More impurities in Boiler water

3. What are the impacts of Priming?

Impacts of Priming;

  • Lower steam efficiency
  • Water hammering
  • Super heater coil failure due to thermal shock
  • Turbine high vibration & blade failure

How do you avoid priming in Boilers?

Priming can be avoided by;

  • Proper operation of boiler
  • Maintaining drum level in between 45 to 55%
  • Avoiding foaming
  • Avoiding sudden load fluctuation
  • Proper designing of Boiler


What do you mean by the term carryover?

Carryover is the carryover of solid, liquid & gaseous contaminants with water and steam leaving the drum due to incomplete separation of water and steam in steam drum.

What are the major reasons for carryover?

Reasons for carryover;

  • Defects in steam and water separators
  • Foaming
  • Boiler load fluctuation
  • Higher drum level
  • Boiler steam drum construction defects

What are the effects of carryover on Boiler components?

Contamination in steam leads to deposition of solid scale on Super heater coils & control and regulating valves.


What do you mean by the term foaming?

Foaming is the formation of unbroken bubbles on the surface of the boiler water inside the boiler drum.

The bubbles may be in thin layer with few bubbles overlying each other or it may build up throughout the steam space.

What are the reasons for foaming?

  •  High suspended solid concentration
  •  High alkalinity concentration
  •  High dissolved solid concentrations in the boiler water
  •  Oil and organic contaminants in the boiler water
  • High impurities
  • High dosage of chemicals
  • High water level

How do you avoid foaming?

  • Timely blow down & maintaining desired water quality
  • Maintaining constant load on Boiler
  • Avoiding high water level
For more articles read Power plant and calculations

Combustion air in Boilers and related calculations

1. What do you mean by combustion air?

The amount of air required for complete combustion of fuel in furnace is called as combustion air. The efficiency of the Boiler or furnace depends on efficiency of combustion system.

2. On what parameters the requirement of combustion air depends?

Combustion air requirement depends on;

  • Type of fuel burnt
  • Type & quantity of its elemental constituents
  • Type of Boiler and furnace
  • Amount of moisture content in it

3. What is the relation between moisture content in the fuel & combustion air required?

Combustion air requirement increases as the moisture content in the fuel increases and vice versa

4. What is the relation between carbon & Hydrogen content in the fuel & combustion air required?

Combustion air requirement increases as the % of carbon & Hydrogen content in the fuel increase and vice versa.

5. What is the relation between oxygen content in the fuel & combustion air required?

Combustion air requirement decreases as the % of oxygen content in the fuel increases and vice versa.

6. Do content of sulphur & Nitrogen in the fuel affect combustion air requirement?

Increase and decrease in sulphur & Nitrogen content in the fuel does not affect much on combustion air requirement.

7. What is meant by total air of combustion?

The total air supplied to the Boiler combustion chamber is divided into two parts Primary air and secondary air.

Primary air supports the flame and takes part in the initial combustion process. The second part is called as secondary air. Secondary air is admitted into the furnace from top to create turbulence in furnace and to ensure complete combustion of the fuel.

8. What are the functions of Primary and secondary air in Travelling grate, pulverized coal fired and FBC Boilers?

In case of travelling grate Boilers Primary air is supplied below the grate to support flame & combustion stabilisation. And secondary air from top of the furnace as over fired air to create turbulence for complete combustion. And also secondary air is used to spread the fuel in furnace

In case of Pulverized coal fired Boilers, Primary air is used to carry the pulverized coal into the furnace.

In case of FBC Boilers Primary air is used to carry fuel and fluidisation. Secondary air is supplied above the bed to ensure complete combustion

9-What is meant by theoretical air & excess air in combustion?

Theoretical air: Amount of air required to burn the fuel. It is stoichiometric air, it does not ensure complete combustion.

Excess air: Amount of extra air given for complete combustion

10-Calculate the Theoretical air required to burn imported coal having carbon 55%, Oxygen 8.2%, Hydrogen 3.3% and sulphur 0.32% in it

Theoretical air is calculated by using below formula

Thair = (11.6 X %C + 34.8 X (%H2-%O2/8) + 4.35 X %S)) / 100

Thair = (11.6 X 55 + 34.8 X (3.3-8.2/8) + 4.35 X 0.32)) / 100

Thair = 7.18 kg/kg of fuel burnt

In the above formula, you can vary the % of Carbon, Hydrogen & Sulphur to observe changes in air requirement

11-How do you measure % of excess air supplied?

Excess air is generally measured from Oxygen analyser installed at the out let of Boiler (Economiser)

It is to be noted that, excess air & excess oxygen are not same. Air has around 21% of oxygen in it by volume. So, 100% excess air is roughly equals to 10.5% of oxygen.

12-What is the significance of excess air?

For combustion, if less air is supplied it leads to incomplete combustion forming CO instead of Co2. And if more excess air is supplied it leads to reduction of combustion efficiency by cooling the furnace & carrying the heat through flue gas.

So, it is important to adjust the air supply in such a way that complete combustion will take place without much extra air.

13-Calculate the % of excess air required if oxygen measured in flue gas at economiser outlet is 5.5%.

Excess air = O2% X 100 / (21-O2%)

Eair = 5.5 X 100 / (21-5.5)

Eair = 35.48%

14-Calculate the total air required for complete combustion of coal if Theoretical air supplied is 7.1 kg/kg of coal and O2 measured in flue gas is 6.4%

Actual or total mass of air supplied = (1 + Excess air / 100) X theoretical air

We have

Excess air = O2% X 100 / (21-O2%)

Eair = 6.4 X 100 / (21-6.4)

Eair = 43.84%

Actual or total mass of air supplied = (1 + 43.84 / 100) X 7.1

Actual or total mass of air supplied = 10.21 kg/kg of coal

15-How do you control the excess air?

Excess air is controlled by;

  • Optimizing the moisture content in the fuel
  • Improving combustion chamber performance
  • Auto control of fuel feeding
  • Continuously monitoring O2 content in flue gas
  • Incorporating auto combustion control
  • Incorporating VFD drives to ID, FD, PA & SA fans

16-Among Bagasse, coal and Natural gas, which fuel needs more excess air?

Bagasse, since it has more moisture content

17-A boiler has supplied 27% excess air, calculate % of O2 in flue gas

Excess air = O2% X 100 / (21-O2%)

27 = O2% X 100 / (21-O2%)

27 X 21 -27 X %O2 = 100 X O2%

567= 127 O2%

O2% = 4.46

Read Powerplant & calculations

Reasons for priming, foaming and carryover in Boilers

Slop fired Boiler start up procedure



  • Ensure DM water storage tank, feed tank & Deaerator  level are normal
  • Ensure availability of start up fuel (wood) & main fuel (coal) and power supply with DG backup
  • Ensure maintenance & trial runs (healthiness) of all equipment including fuel handling, ash handling / auxiliaries, motorized valves, actuators, control valves and PRDS controls are completed successfully
  • Ensure that all interlocks / protection and controls are checked & taken in line.
  • Ensure expansion pointers are cleaned & tramps are in good condition.
  • Ensure Boiler manholes and flue gas path system manholes are boxed up.
  • Ensure availability of chemical dosing system and readiness of drum level gauge glass with illuminator assembly.
  • Ensure availability of cooling water, instrument air and service air.
  • Ensure Coal bunker is filled with required level
  • Ensure all rotary air lock valves of evaporator, economizer & bag filters are open
  • Ensure healthiness of all dampers and keep them in open/close marked positions as per requirement
  • Open all air releases/vent valves in boiler drum and open super heater header drains and its vent valves.
  • Ensure all boiler bottom ring header drains, blow down valves and main steam stop valves including its bypass valves are closed.
  • Ensure Boiler feed pump’s bearings oil level normal, minimum recirculation, balancing leak off valves & suction valves are open, cooling water pressure normal.

Boiler start up

  • Start the ACW pump, Instrument Air & Service Air Compressor
  • Start BFP from control room. Ensure suction pressure, balancing pressure & discharge pressure normal. Bearing temperature & Vibrations normal. Ensure motor draws current normal & sound normal. Shut the BFP immediately if any abnormal condition and check thoroughly before restart.
  • Start water filling the boiler drum through 30 % control valve and maintain the drum level up to 30%.
  • Start the Ash handling plant prior to light up the Boiler. Then start all hoppers RAV.
  • Ensure bag filter main damper is closed & bypass damper is open
  • Maintain the drum level about 40%.
  • Drum vent, super heater vent and main steam line drain should be kept open.
  • Start wood firing by spraying small quantity of diesel & slowly raise the furnace temperature
  • At furnace temperature > 150 deg C start ID & FD fans at minimum speed
  • Close drum air vent at 2.5 kg/cm2
  • At 3 kg/cm2, gibe blow down to CBD, IBD & bottom headers one by one for 30 sec to 45 seconds
  • At pressure > 4 kg/cm2, open start up vent 10% initially & close the top header drain valves & go on increasing the pressure
  • At furnace temperature around 250 deg C, start coal feeding by starting SA fan
  • Now slowly increase fuel feeding & FD air
  • When boiler pressure reaches 6 kg/cm2 & 150 deg C, charge the main steam line. Before charging the main steam line, open all the drains at 100 % and warm up vents at minimum opening and then open the MSSV bypass valve.
  • Start HP & LP dosing and maintain recommended drum water parameters of boiler. Keep the CBD at minimum opening to maintain recommended residual PO4 & conductivity of drum water
  • Check & record thermal expansion of boiler pressure parts and record the bearings temperature & vibrations of auxiliary equipment’s associated with Boiler
  • After ensured all condensate removed & color less steam comes through drains, keep all the drains in crack position, then open main steam stop valve and close the bypass steam valve
  • At Boiler pressure 9 kg/cm2 & temperature 180 deg C, charge Deaerator & SCAPH through PRDSH
  • At flue gas temperature > 180 deg C take bag filter into line
  • Observe seal air pressure, conveying air vessel pressure of AHP is normal.

Slop firing:

  • Ensure sufficient quantity of slop with required brix is available in slop tank
  • Ensure tank coil heater & steam tracing lines are charged & tank slop temperature is 70 to 80 deg C
  • Ensure slop pumps are healthy & agitator is running condition
  • After ensuring above all are normal, start slop transfer pumps & keep slop in recirculation mode for at least 2 to 3 hours before taking into boiler
  • As the Boiler reaches 50 to 60% of MCR & furnace temperature is 450 to 500 deg C open the atomizing steam line, slowly introduce the slop into furnace by opening SOV
  • Note: Before introducing slop into nozzle, keep open the steam connection line provided with respective nozzle.
  • Quantity of slop fired at MCR is 3.91 TPH & slop quantity should be reduced as the load demand reduces
  • Always maintain 20 to 25% supporting fuel on heat basis. Never start the Boiler with slop
  • During slop firing ensure supplement fuel is supplying continuously to avoid clinker
  • The soot blowers provided in economizer, evaporators are operated once in a shift & wall blowers twice in a shift

 Read more on Power plant & Calculations>>>>>



Questions & Answers on Ash handling system

1.What is Ash?

Ash is the remaining product of solid or liquid fuel after burning

2.What are the various components of Ash?

Ash has following components

  • Silica (SiO2)
  • Alumina (AlO3)
  • Iron Oxide (Fe2O3)
  • Sodium Oxide (Na2O)
  • Potassium Oxide (K2O)
  • Calcium Oxide (CaO2)
  • Magnesia (MgO)

3.Which fuel has more ash Liquid, solid or Gaseous fuel?

Solid, Liquid & Gaseous fuels are having more ash consecutively

4.What are the various types of ash produced in Boilers?

Bottom ash & Fly ash are generated in Boilers

5.Which ash is more in quantity?

Generally Fly ash is more around 70-80% & bottom ash is around 20-30%

6.What do you mean by Fly ash?

Ash which is carried out by flue gas is called fly ash.

7.What can fly ash could cause in downstream system of The Boiler?

  • If ash is more, it creates following problems in downstream of the Boiler
  • Improper heat transfer in Super heaters, economizers & APH
  • Erosion of pressure parts & flue gas ducts
  • If there is low velocity, ash deposits in ducts, APH ESP etc

8.Which type of Ash removal is more dangerous & why?

  • Bottom ash removal is more dangerous, because;
  • Bottom Ash is at higher temperature
  • Ash is high Abrasive & Corrosive in Nature
  • When it comes in contact with water high hot fumes are formed
  • Risk of frequent clinker formation

9.What are the different devices or systems used to separate Fly ash from flue gas before letting it into atmosphere?

  • Electrostatic Precipitator
  • Bag filter (Fabric separators)
  • Wet scrubber
  • Inertial separators (Settling chamber, Baffle chambers, Cyclone separator)
  • Fabric hybrid filter

10.Briefly explain the Fabric Separator type bag filters

In this system, fabric bags are used to filter the flue gas to separate the dust. Dust laden gases enter the bag house and passes through fabric bags which act as filter.The bags are woven with material nylon, fiber glass etc. Each bag is externally supported by steel/metal cage. The bag filter house is provided with an explosion vent to avoid explosion during abnormal operation conditions.

Further, the bag filter house consists of hoppers & ash handling system to remove fly ash separated in bag filters.

In bag filters, the dust collects at the outer surface of the bag since flue gas flow from out side to inside of the bag.

Mechanism of dust collection:

Gravity: Due to gravitational force & sudden lower velocity large sized dust/ash particles fall down into hopper due to Gravitational force.

Inertial collection: Due to inertial, heavy dust particles strike the bag filters placed in the flue gas path & fall down into the hopper, since they do not change their flow direction due to inertia.

Interception: Due to the fine mesh or size of the bag filters, dust or ash particles cannot cross the filters. Instead they hit filters & fall down into the hopper.

Electrostatic effect: Electrostatic force between dust particles & bag filter causes the dust to capture.

11.How do you remove dust particles from Bag filters?

  • Mechanical Shaker
  • Reverse air
  • Reverse Jet

12.What are the various materials of composition (MOC) of Bag filters?

Sl No.

Bag filter material

Operating temperature (0C)








Polyphenylene  sulphide or Ryton



Fibre glass



Fibre glass fabric coated with PTFE


13.What are the various factors considered for selection of Bag filters?

  • Flue gas temperature
  • Moisture level in flue gas
  • Dust or ash particles size
  • O2% in flue gas
  • Flue gas velocity
  • Dust or ash particles abrasiveness
  • Air to cloth ratio

14.What are the main functions of Ash handling system?

  • To remove the ash from Boiler furnace & other various ash discharge points
  • To convey this ash to nearby storage area like ash silo
  • Ash disposing

15.What are the various types of Ash handling systems used in Boilers?

Mechanical ash handling system: In this system chain, belt & screw conveyors are used to convey the ash from various ash termination points to ash silo.

Pneumatic ash handling system:

Pneumatic ash handling system is used widely in most of the Power plants. High pressure air is used to convey the ash to the suitable location.

16.What are the various types of Pneumatic ash handling systems used in Boilers/power plants?

  • Lean phase ash handling system
  • Medium phase
  • Dense phase

17.Why dense phase ash handling system is used in almost all Boilers Ash handling plant?

Because it has less air consumption due to volumetric ration of air & ash is more. Sometimes instead of pressurized air vacuum system is used to convey the ash.

Briefly explain the dense phase Ash handling system

In this system, Ash conveying system is placed just below the ash hopper. This system consists of Main ash hopper

  • Surge hopper with electromagnetic or Mechanical vibrators
  • Knife edge gate valve
  • SS expansion bellow
  • Dome valve assembly & operating mechanism
  • Ash & air conveying valves, solenoid valves
  • Pressure switches & limit switches
  • Conveying pipelines

If the temperature of the ash is more (Economiser & APH) surge hopper is made with water jacket for continuous circulation of water.

The system can be operated from local & remote in probe mode or timer mode.

Calculation part:

1. A Boiler is consuming 72 TPH an imported coal having ash % 8, calculate the total ash generated in a complete month. Assume there is no stoppages or load fluctuation

Total coal consumed in a month = 72 X 24 X 30 = 51840 MT

Total ash generated in a month = 51840 X 8 / 100 = 4147.2 MT

2. A boiler consumes 7 TPH of coal, calculate the total fly ash generated in a day if coal has 35% ash.

Total ash generated = 7 X 24 X 35 / 100 = 58.8 MT

We know that, fly ash is around 80% of total ash.

So total fly ash generated is 58.8 X 80 / 100 = 47.04 MT

3. A Boiler generates 20 MT of ash in a day, calculate total coal consumed in a day if coal has 5% of ash in it

Total ash generated =20 MT/day

Ash % in coal = 5%

Therefore total coal consumed = 20  / 5% = 400 MT


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Questions & Answers on steam Blowing

1.What is the purpose of steam blowing?

The purpose of the steam blowing is to remove any foreign materials from steam piping & super heater coils after completion of erection work.

2.What will happen if steam blowing is not done after erection or repair of Boiler?

If steam blowing is not done, considerable damage will happen to the steam lines & other end user applications like steam turbine, process heat exchangers due to scale, debris & other foreign materials present in the newly erected pipe lines/coils.

3.What is the basis behind steam blowing?

The basis behind the steam blowing is to create momentum equal to or preferably greater than that during normal operation. This will blow out all the debris from the steam lines

4.What are the two different methods of steam blowing?

Puff method & continuous method. In puff method thermal shock is created & in continuous steam blowing, constant steam purge is maintained

5.What are the requirements for steam blowing for newly erected Boilers?

  1. Steam blowing area is corned off & notice board or caution board should be displayed
  2. Ensure Boiler hydraulic test, alkali boil out & passivation procedures are completed before steam blowing
  3. All the temporary supports used during erection should be removed
  4. Steam pipe lines & valves used for steam blowing line should be equal to the maximum size of permanent pipe.
  5. Sharp elbows, bends & tees should be avoided in steam blowing pipe line to avoid more pressure drop
  6. Temporary pipe lines used for blowing should be well supported to withstand reaction forces created during steam blowing.
  7. Steam blowing line should be terminated outside the Turbine hall or process
  8. Sufficient allowance should be given to steam blowing line for thermal expansion
  9. Ensure steam line supports & hangers are erected & set properly
  10. Ensure control valves, steam nozzles & NRV flops are not installed during steam blowing
  11. Initially steam blowing is done at lower mass flow

6.What is the time gap between two steam blows?

For an un insulated steam pipe line blowing can be done at every 1 hr. And for insulated steam pile line the gap between two blows should be 3–4 hours

7.Which materials are used for target plates?

Aluminum & stain less steel

8.How do you decide the steam is clear after blowing?

 If there are only two or less than two recognizable impressions found on per square centimeter of target plate, then the target plate is said to be clean.

For Target Plate Made of Aluminum:

The piping considered clean if there are not more than 3 (Three) pitting of 0.5 mm to 1mm dia. in center area of 25 mm X 25 mm and shall not have any deformed edges. Besides this there shall be no pitting in the rim zone. Pitting below 0.5 mm may be ignored.

For Target Plate Made of Stainless Steel:

 The piping is considered clean if there are not more than five pitting of 0.1 mm dia to 0.5 mm dia. in center area of 50 mm X 50 mm & shall not have any deformed edges. Pitting below 0.1 mm may be ignored 

Read reference books for power plant O&M

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Power plant & Calculations

Boiler refractory dry out procedure


Why do you carryout refractory dry out for Boilers?

It is done to ensure proper drying & curing of refractory in furnace & other areas where refractory is applied. The refractory under goes chemical changes during initial heating. While heating there must be free air flow over the refractory to ensure complete removal of moisture.

Reference books for Power plant O&M

What are the rechecks carried out before refractory dry out?

Pre checks:

  • Ensure Boiler erection work is completed with all respect
  • Ensure Boiler official Hydraulic test is done
  • Ensure insulation work is completed
  • Ensure abundant quantity feed water is available
  • Ensure required quantity wood logs are available
  • Ensure sufficient & qualified operation staff is available
  • Ensure thermal expansion pointers are fitted at all required locations
  • Ensure steam drum & super heater vents are opened

Write down the standard procedure for refractory dry out

Refractory dry out is done as per OEM recommendation, too rapid heating of refractory may collapse the refractory material due to development thermal stresses. So it is recommended to heat the refractory for longer time at low temperature.

  • Cover all air & coal nozzles with bed materials, this will avoid the damage to the nozzles (This is not applicable for Travelling grate & dumping grate Boilers) while throwing wood logs into furnace
  • Select the required size wood logs generally 2 to 3” diameter & 2 to 3 feet length wood sizes are preferred. Ensure wood logs do not have nails, packing strip
  • Ensure wood logs have optimum moisture. Too dry or too wet woods are not good for dry out
  • Ensure refractory dry out is done on natural daft, no fans are necessary. Ensure all the suction & discharge dampers of fans are kept open
  • Put the woods on bed materials, spray the small amount of diesel & then fire the woods
  • Initially temperature raising should be slow at the rate of 25 deg c per hour for 3 to 4 hours
  • Then raise the boiler outlet flue gas temperature up to 100 deg C & hold for 8 to 10 hours (as recommended by OEM) for soaking the refractory inside the Boiler
  • Then raise the boiler outlet flue gas temperature up to 250 deg C & hold for 6 to 8 hours (as recommended by OEM) for soaking the refractory inside the Boiler
  • Finally raise the boiler outlet flue gas temperature up to 350 deg C & hold for 8 to 10 hours (as recommended by OEM) for soaking the refractory inside the Boiler
  • After completing the above process, firing is stopped & Boiler is allowed to cool naturally
  • After cooling down, Boiler must inspected for refractory damage/crack etc
  • Minor cracks formed during dry out procedure should be rectified with same quality refractory material


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 Questions & Answers on steam Blowing







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