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

Procedure for Boiler Gauge glass line up & Flushing

Boiler Gauge glass: is a transparent glass of shape tubular, flat or square blocks fitted to the boiler steam drum to facilitate a visual indication of the water level of a steam drum. These types of glasses are manufactured by borosilicate glass which is robust, temperature & chemical resistant.

 



Line up of Gauge glass:

  • Ensure all tools & required PPEs are taken to operate the valves (Hand gloves, Safety goggles, “F” rods etc)
  • Ensure steam & water side valve of gauge glass are healthy & operating properly
  • Ensure there are no any leakages
  • Ensure steam side & water side valves are closed
  • Ensure gauge glass drain valve is open & drain is connected/extended to safe location
  • Now crack open the steam valve & check for any leakages in gauge glass. Wait for some times until system heats uniformly.
  • Then crack open the water side valve, wait for some time for stabilization
  • Then close the drain valve
  • Open the steam valve & water valve fully
  • Observe water collected in glass & showing the level
  • Cross check the level glass with other side level glass or control room transmitter reading or with Hydra step

Factors considered for Boiler Engineering

Flushing of gauge glass

Ensure all tools & required PPEs are taken to operate the valves (Hand gloves, Safety goggles, “F” rods etc)

Step-I

  • Close the water side valve & open the drain valve for flushing, wait for some time
  • Then close the drain valve & open the water side valve

Note: After opening the water side valve, water level should retain its normal operating level, if not then there might be blockages in valve or line

Step-II

  • Close the steam side valve & open the drain valve for flushing, wait for some time
  • Then close the drain valve & open the steam side valve

Note: After opening the steam side valve, water level should retain its normal operating level, if not then there might be blockages in valve or line

Questions & Answers on AFBC Boiler





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16-Perfect reasons for more fuel consumption of Boilers

Following are the 16-reasons for increase in Boilers fuel consumption

1. Decreased economiser inlet feed water temperature:

On every 6-8 deg C decrease in Economiser inlet feed water temperature causes the rise in Boiler fuel consumption by 1%.

2. Increased Boiler outlet  flue gas  temperature:

On every 22 deg C increase in flue gas temperature causes the reduction in Boiler efficiency by 1% & hence boiler fuel consumption increases for generating same steam.

3. Increased moisture content in the fuel

Boilers fuel consumption increases as the moisture in the fuel increases. As it requires more excess air & reduces combustion efficiency leading to unburnt losses

4. Increased excess air

10-Tips to reduce LOI in Boilers

Increase in excess air causes dry flue gas loss & hence more fuel consumption. And also leads to more auxiliary power consumption.

5. Increased unburnt loss

Unburnt fuel or incomplete combustion of fuel leads to increased consumption of fuel. Unburnt is due to improper air fuel mixture or unbalanced draught or variation in the fuel quality

6. Higher blow down

Blow down water carries saturated water/steam through it, so leads into more fuel consumption. Maximum acceptable blow down rate for normal Boiler operation is 0.5 to 1%.

7. Operating the Boiler at lower or partial loads

Operating the Boilers on partial load requires more excess air & leads to incomplete combustion forming unburnts.

Calculated reasons for for SSC of Turbine

Boiler calculations for Boiler operation engineer (BOE) exam

Viva Questions & answers for preparation of BOE exam & interview

8. Operating the boiler at non-standard operating parameters

Operating the Boilers at non standard parameters like pressure, temperatures, flow etc will lead to the higher fuel consumption

9. Leakage into & out of the Boilers

Air & flue gas leakages into the Boiler & out of the Boiler will reduce the working efficiency there by increasing the boiler fuel consumption

10. Steam leakage

It is a direct cause for higher steam consumption. Generally steam leakage is from vent & drains valves, welding & flange joints

11. Boiler heating surfaces internal scaling

Pressure parts namely water wall tubes, economiser tubes & super heater coils internal & external scaling will result into poor heat transfer, which increases fuel input to produce required amount of steam.

Pressure parts internal scaling can damage the pressure parts by over heating

12. Radiation & Convection losses

Radiation & convection losses in the boiler causes increased fuel consumption. These losses may be due to uninsulated or unlagged surfaces of boiler

13. Lower combustion air temperature

On every 20 Deg C decrease in combustion air temperature leads to Boiler efficiency reduction by 1%

14. More ash content in the fuel

More ash content in the fuel takes away heat associated with it during discharging through hoppers. Especially bed ash is having more temperature. Also higher ash fuel are having lower GCV

Guide for Boilers troubleshooting


Why does Boilers main steam temperature increases more than design?

15. More Volatile matters (VM) in the fuel

Calorific value of the fuel reduces as the VM increases. Boilers using Lower GCV fuel consume more fuel

16. Other potential reasons for increased fuel consumption of a Boiler are;

Boiler design related issuers

Wrong selection of auxiliaries like fans & fuel feeding system

Low quality of Bed materials

Defects in fuel burners & fuel spreaders

Over refractory on internal heating surfaces

Faulty field instruments

Factors considered for Boiler Engineering

Also read Why & How these in Boilers???



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Why do the Boilers explode???

 



Now days, we are hearing more on explosion in Boilers & related auxiliaries. This is harming man, machines & system and creating unrecoverable situations in power plant. Upon thinking on this following major causes or reasons come into picture.

The main reasons for Boiler explosions are;

  • Operating the Boiler more than the design pressure for long time
  • Operating the Boilers at lower water level in drum
  • High furnace pressure
  • Poor water quality
  • Poor maintenance of Boilers in shutdowns
  • Ignoring the aging factors of Boiler parts
  • Operating the Boilers at higher main steam or metal temperature

1-What are the reasons for operating the Boilers at more than operating pressure?

  • Malfunction of pressure transmitter or leakages in its impulse line
  • Faulty local pressure gauges
  • Faulty safety valves or safety valves set at higher pressure
  • Improper control of combustion system
  • Operating the Boiler at higher pressure set point
  • Varying fuel quantity & quality
  • Frequent load fluctuation on Boiler
  • Leakages
  • Improper spreading of fuel or no control on fuel feeding system

2-What are the potential reasons for low or no water level in the boilers?

  • Feed water pump is not running, but showing running indication in DCS
  • Mis-operation of feed water control valve or control valve is not opened as per requirement
  • False reading from feed water or steam flow meters
  • Malfunction of drum level transmitters/controllers
  • Low water level in Deaerator or mal function of Deaerator level sensors
  • Feed water discharge pump is closed
  • More load on Boiler than design
  • Under capacity feed water pumps
  • Cavitation or steaming in feed water pumps
  • Steaming in Economizers
  • Long time lifting of Boilers safety valves-(Higher blow down of Safety valves)
  • Wrongly set Boiler safety valves (Super heater line safety valve should be set at lower pressure than drum safety valves)
  • Heavy passing in blow down valves
  • Bypassing the instrument process interlocks like alarm value, low level trips etc

3-How does no water in pressure parts lead to explosion?

No water in pressure parts for long time leads into overheating of pressure parts & eventually failure.

Sudden entry of cold water into no water operating parts leads to flashing of water resulting into high volume steam. This high volume steam suddenly lead to explosion, as there is no sufficient space for steam to expand.

4-How do wrongly set Boiler safety valves lead to explosion?


POWER PLANT PROTECTIONS & INTERLOCKS

Requirement is SH outlet Steam line safety valve is to be set at lower pressure than steam drum safety valves.

If drum safety valves set at lower pressure, on lifting of drum safety valves before lifting of SH line safety valves lead to starvation of super heater coils leading to overheat & eventually explosion.

Questions & Answers on AFBC Boilers

5-What are the reasons for high furnace pressure?

  • High furnace pressure is due to;
  • No control on FD fans
  • Bypassing or not working of Fans interlocks
  • Sudden closure or miss-operation of ID fans dampers
  • Variation of fuel moisture
  • Improper spreading of fuel into furnace
  • Wrongly set over fired air
  • Draught transmitter malfunction & its impulse pipe leakages
  • Choke up of open portion transmitter

6-How the Boiler does lead into explosion due to high furnace pressure

Boiler calculations for Boiler operation engineer (BOE) exam

High furnace pressure leads into damages to the sealing, buck stay & membranes if exceeds leads to furnace & duct explosion.

7-How does the poor quality of feed water lead into Boiler explosion?

Poor quality of feed water leads to scaling & corrosion of pressure parts.

Scaling will lead into poor heat transfer & overheating of tubes, this over heating of tubes cause failure of pressure parts followed by explosions.

8-What are the reasons for overheating of pressure parts?

  • Low water level
  • Continuous flame impingement on particular area of pressure parts
  • Localized heating
  • Fuel (Coal) deposition on pressure parts area
  • Pressure parts choke up
  • Poor material quality
  • More Excess air than requirement
  • Internal scaling
  • Lower feed water temperature at economizer inlet

9-What is the significance of shutdown maintenance of Boilers to avoid explosions?

  • In order to take proper care on Boilers to avoid damages & explosion, need to concentrate on following listed areas of maintenance
  • Thorough cleaning of pressure parts
  •  Inspection of pressure parts thickness & replacement of less thickness
  • Proper setting of air & gas nozzles
  • Proper setting of mechanical spreaders to avoid direct hitting of coal particles to rear wall tubes
  • Inspection of steam line spring hangers
  • Cleaning & inspection of buck stays
  • Safety valves maintenance & proper floating
  • Removing all obstacles & temporary supports in boilers for boilers free expansion
  • Proper setting of burners & air nozzles to avoid localized heating & flame impingement
  •  Cleaning & inspection of ducts
  • Overhauling of steam drum gauge glasses
  • Maintenance & calibration of pressure & level transmitters, pressure gauges & temperature gauges
  • Proper maintenance of soot blowers 
Note:Bend lance tube inside the furnace/SH zone/Economiser can harm the pressure parts
Lance tubes if not rotating may damage the pressure parts by continuous impingement of steam jet.

Why & How these in Boilers???

10-What are the reasons for Boiler back end flue gas ducts explosion?



It is due to secondary combustion & formation of carbon monoxide at ducts such as APH & ESP.

During start up or abnormal operation of Boilers, fuel will carry through flue gas  & settle into APH & ESP ducts, where its incomplete combustion starts & form CO gas.CO is very explosive gas, when external Oxygen combines with this gas results into explosion.


Also read 16-Perfect reasons for increasing the fuel consumption of Boilers

11-What precautions can be taken to avoid high metal temperature operation?

  • Installation of metal skin temperature sensors for Super heater coils
  • Avoiding wet fuel intake into the furnace
  • Avoiding more excess air than design for long time
  • Maintain required or designed feed water temperature at economizer inlet
  • Operate boilers more than 50% of its MCR

  

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Basic Questions & Answers on Slop/Spent wash fired Boilers



1-What do you mean by Slop or Spent wash?
Slop or Spent wash also known as Vinasse is an acidic effluent produced in Distillery unit. Slop is formed on fermentation of Sugar cane molasses in distillery.
2-Why do you treat Slop as a Hazardous effluent?
Because it is an acidic effluent having pH around 4 to 5
3-What are the standard parameters of Slop or Spent wash?
  • Colour : Brown
  • Odour : Pungent
  • pH : 4 to 5
  • Solids: 9 to 12%
  • BOD : 45000 to 60000
  • COD : 110000 to 1350000
4-What are the various methods of Slop disposal?
  • Disposal methods:
  • Biomethanation
  • Composting
  • Incineration Technology

5-What is the purpose of using incineration technology for Slop disposal?
Incineration technology method leads to Zero Liquid Discharge, where spent wash is concentrated by heating it in specially designed Boilers.
6-What are the benefits of burning Slop in Boilers?

TOP-6 BEST POWER PLANT O&M BOOKS

Slop fired Boiler start up procedure
Benefits:
  • Zero liquid discharge (ZLD) or Zero effluent discharge (ZED)
  • Steam generated in Boilers can be used for Distillery process
  • Power generation to fulfil auxiliary power of distillery, hence reduction in production cost.
  • Ash generated is of potash reach which is good manure


7-What are the challenging situations for designing the Spent wash Boilers?
  • Slop & its ash characteristics
  • Design of combustion system for Slop
  • Design of combustion system for supporting fuel
  • Design of pollution control equipments
8-Why it is being challenging task to burn the spent wash?
Because it is a liquid fuel having very low GCV up to 1800 kcal/kg & high ash & moisture content.
9-What are the various supporting fuels used in Incineration Boilers?
  • Spent wash + Coal (Indian/Imported)
  • Spent wash + Rice husk
  • Spent wash + Bagasse
10-What type of Boilers are used in Incineration Technologies?
  • Travelling grate Boiler: Rice husk & Bagasse
  • AFBC Boiler: Indian & Imported coal
11-What are the features of AFBC boilers used in Incineration Technology?
AFBC Boiler:
  • Bottom supported
  • Single drum
  • Over bed feeding
  • 3-pass flue gas construction
  • Combustor is located in pass-1 & Super heater, Evaporator; Economiser & Super heaters are located in Pass-3

12-Briefly explain the combustor & fuel feeding system in AFBC boilers?
Combustor:As discussed above, Combustor is located in Pass -1, fabricated with high temperature refractory material, enclosed by steel casing and supporting structure. Combustor is divided into various compartments & for all compartments ash drain system is provided.
Coal feeding system: consists of coal bunker, VFD screw feeders to feed the coal. Coal is distributed inside the combustor by pneumatic spreading system.
Spent wash feeding system: Concentrated and pre-heated Spent wash from the storage tank is conveyed to boiler through variable speed pump. Spent wash is sprayed over the fluidising bed at first pass through spray guns.

13-Where do the Secondary air & spent wash nozzles are provided in AFBC Boilers?
Secondary air system is provided at 2 to 3 locations at various heights at furnace. And spent wash nozzles provided just below the secondary air nozzles
14-What are the various online cleaning mechanisms are provided for pressure parts?
Mechanical rapping systems for super heaters
Soot blowers for Evaporators
Sonic soot blowers for Economisers
15-How do the spent wash concentration (Brix) & its calorific values are related?
GCV of the spent wash increases with increase in its concentrations
Sl No.
Brix (%)
GCV (Kcal/kg)
1
40
850
2
45
1200
3
50
1400
4
60
1800

16-How do you increase the Brix of Spent wash?
Spent wash Brix can be increased by heating
17-What parameters of Brix are recommended for efficient burning?
  • Brix: 55 to 60%
  • Moisture: 40 to 50%
  • Ash: 18 to 20%
  • GCV: 1550 to 1750 kcal/kg


18-Write down the ultimate analysis parameters of Spent wash
  • Ultimate analysis report:
  • Carbon: 18.5 to 23%
  • Hydrogen: 1.5 to 2.5%
  • Oxygen: 12 to 15%
  • Nitrogen: 1.5 to 2%
  • Sulphur: 0.5 to 0.7%
19-What are the various contents of spent wash?
Ash contents analysis by weight is as follow
  • Silica (SiO2) : 2.3 to 2.8%
  • Iron Oxide (Fe2O3) : 2 to 2.5%
  • Calcium Oxide (Cao) : 12 to 16%
  • Magnesium oxide (MgO) : 6 to 7%
  • Sulphate, SO3: 15 to 17%
  • Phosphate (P2O5) : 8 to 12%
  • Potassium Oxide (K2O) : 45 to 50%
  • Chlorides: 0.8 to 1.2%

20-What is the quantity of steam generated per square meter of heating surface in Spent wash AFBC boilers?
It is around 8 to 10 kg of steam is generated per square meter of heating surface
21-What is the quantity of steam generated per square meter of heating surface in Spent wash Biomass (Bagasse, rice husk etc) fired boilers?
It is around 10 to 12 kg of steam is generated per square meter of heating surface.
Note: For incineration:AFBC Boilers have more heating surface as compared to Biomass fired Boilers
22-Why do the Spent wash Boilers have taller furnaces?
Because;
  • To maintain higher residence time in furnace up to 8 seconds
  • To maintain optimum flue gas temperature at super heaters inlet to avoid coils fouling due to alkali ash property and to avoid corrosion of super heater coils due to chlorides (1%) in ash
23-What is the design configuration of APH in spent wash fired Boilers?
In spent wash Boilers APH are designed for air flow through tubes & flue gas outside to avoid choking of tubes
24-What is the flue gas temperature that we get at APH outlet for spent wash fired Boilers?
It is around 180 to 200 Deg C
25-What is the size & density of refractory materials used in Spent wash AFBC Boilers?
Size of refractory materials is around 0.8 to 2.5mm. And density is around 1000 to 1100 kg/m3
26-What are the main compositions of Refractory materials?

Questions & Answers on AFBC Boilers
  • Silica 55 to 60%
  • Alumina 35 to 40% & small traces of Feo, Mno, Cao, Mgo, P2O5 etc
27-What is the optimum temperature of spent wash at the nozzle inlet?
It is around 70 to 80 deg c
28-What is the maximum efficiency that we can get for spent wash & Rice husk fired Boilers?
It is around 72%

Also read:Troubleshooting in Boilers



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How do you preserve the power plants equipments in long shutdown??

POWER PLANT EQUIPMENTS LONG SHUTDOWN PRESERVATION METHODS
SL NO.
EQUIPMENT
PRESERVATION METHOD
A
MECHANICAL

1
Boiler
1-Wet preservation (If shutdown period is up to one month)
Maintain pH: 10-10.5
Hydrazine concentration :> 200 ppm
Note: Check water sample at various locations like steam drum, mud drum, super heater, economiser & Water wall tubes. Concentration should be same at all collection points
2-Dry Preservation (If shutdown period is more than one month)
2
Deaerator & Surge tanks
Wet preservation
Maintain pH: 10-10.5
Hydrazine concentration :>200 ppm
3
Travelling grate (TG)
After cleaning, inspection & Maintenance, keep run TG at least 10-15 minutes on every 6-7 days to avoid shaft jam in bush/bearings
4
ESP
After cleaning & Inspection, close all the man hole doors air tight & keep lime trays at various locations to avoid moisture accumulation on internals
5
APH & Economiser
After cleaning & Inspection, close all man hole doors air tight & keep lime trays at various locations to avoid moisture accumulation on internals
6
Boiler fans
After cleaning & Inspection..close all man hole doors air tight
Change the shaft orientation at every 10-15 days by rotating shaft manually to avoid shaft sagging/bending
7
Boiler feed pumps
Keep suction valve open
Change the shaft orientation at every 10-15 days by rotating shaft manually to avoid shaft sagging/bending
8
Air Compressors
Operate Air compressors at least 10-15 minutes at every 7-8 days or else rotate the flywheel one complete rotation
9
Main & Auxiliary cooling water pump
Rotate the shaft on every 10-15 days to avoid impeller jam in wear ring
10
Steam Turbine
1-Turbine dehumidification by blowing hot air through Turbine HP suction to LP suction & ensure relative humidity in Turbine is <40%
2-Put turbine on barring gear for 20-30 minutes at every 6-7 days
3-Operate HP & LP valves from 0 to 100% at every 15 days
4-Operate ESV at every 15 days
11
Turbine lub oil system
Keep "ON" oil centrifuge at least twice in a week
12
Ash handling system
Ensure all ash handling & storage systems are clean to avoid rusting/corrosion
13
Fuel feeding system
Maintain fuel feeding system internals clean to avoid corrosion & rusting
B
E&I

1
Generator
Keep "ON" Generator space heaters for 8-10 hours if atmosphere temperature is very less (In rain & winter seasons)
2
Power Transformer
Charge transformers at least 6-8 hours at every week to avoid moisture formation in oil
3
VFD drives
Keep charged all VFD drives continuously
Note: Avoid interruption of power supply to VFDs
4
Batteries
Inspect battery voltages regularly (twice in a month)
5
UPS & AVR
Check Healthiness of redundancy systems regularly
6
Motors
1-Cover all motors terminals by polythene covers to avoid entry of rain water
2-For higher KW motor keep "ON" space heaters
7
MCC & PCC
Keep lime trays at MCC, PCC to avoid moisture formation
8
DCS
Ensure DCS healthiness regularly
Note: If DCS kept OFF, inspect the panels regularly to ensure rats/lizards are not entering into the panels
C
WTP

1
RO plant
Preserve RO membranes with 2-3% SMBS or other chemical for 30-40 days. After that drain  the preserved water & perform membrane flushing on every 7-8 days
2
Cooling tower
If CT is not necessary in shutdown, drain the cooling tower ,clean the sumps & apply lime
3
Cat ion & Anion Resin
Maintain normal water level in vessels
Replace the vessels water at every 10-15 days
D
SAFETY

1
Fuel yard & Fuel handling
Depute a particular person to have daily round to avoid fire incidents due to saturation of coal/bagasse or any other fuel
2
Fire fighting system
Conduct fire fighting pumps trial (especially Diesel fire fighter pump & Main fire fighter pump) to ensure healthiness
3
Plant fire alarm system
Check Healthiness of fire alarm systems  regularly
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