Boiler Basics.ppt
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Transcript of Boiler Basics.ppt
TRAINING MODULE ON
BOILER BASICS
Boiler is an closed vessel in which water is heated to produce steam.
This steam shall be used for process / Power Generation.
BOILERAIR + FUEL
WA
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RST
EA
M
What is Steam Boiler.?What is Steam Boiler.?
Steam boilers under IBR means any closed vessel which is used for
generating steam
Exceeding 22.75 liters in capacity.
Having pressure > 1 Kg/cm2.
Includes any mounting or other fitting attached to such vessel which
is wholly or partly under pressure when the steam is shut off.
IBR – Indian Boiler RegulationsIBR – Indian Boiler Regulations
Boilers are classified into different types based on Type of combustor,
Steam pressure, Fuel fired etc., Main two classifications are
Fire or Smoke Tube boiler.
- Low Pressure system.
Water Tube boiler.
- Low & High Pressure system.
Boiler ClassificationBoiler Classification
Fire or Smoke Tube Boiler:
Water gets heated outside the tubes while the hot gases flows inside the
tubes.
Water Tube Boiler:
Water flows inside the tubes and the hot flue gases flow outside the
tubes.
Basics of Steam
• If we take 1 Kg of water at 0°C and if we add 100 Kcal of heat then the temperature of water will increases to 100°C.
• This rise in temperature can be detected and is called Sensible Heat (Specific Enthalpy - Water)
Steam - BasicsSteam - Basics
• At normal atmospheric pressure, any further addition of heat to water at 100°C will not increase the temperature but will convert some of the water into steam.
• In order to convert water into steam 539Kcal/kg of additional heat must be added.
• This cannot be detected as a rise in temperature and is called the Latent Heat of Vaporization (Specific Enthalpy - Evaporation).
Steam – Basics (Contd)Steam – Basics (Contd)
At atmospheric condition
•Specific weight of water at saturation point = 958.38 Kg/m3.
•Specific weight of steam at saturation point = 0.58 Kg/m3.
The volume of water expands 1650 times when it is converted into steam at
atmospheric condition.
Specific weight of steam and waterSpecific weight of steam and water
Importance of Fuel
Air Dried Basis (ADB):
Samples sent to lab are kept open to lab ambient condition for equilibrium
moisture. Datas reported on this basis is ADB basis.
As Received Basis (ARB):
Data reported on the basis of as received moisture at laboratory. Such
samples are sent to lab in a tightly packed covers.
As Fired Basis (AFB):
This has relevance to boiler performance. The sample is collected in feeder
area just before it enters into furnace. The data reported is AFB.
Dry Basis (DB):
Data expressed on moisture removed basis is called Dry basis.
Reporting Fuel AnalysisReporting Fuel Analysis
Calorific value is the heat produced by the combustion of a unit quantity of
fuel in a bomb calorimeter with oxygen under a specified set of conditions.
GCV – Gross Calorific Value:
In GCV all the vapor produced in combustion process is fully condensed. The
latent heat is added to GCV and thus GCV is higher to NCV.
NCV – Net Calorific Value:
Net calorific value informs that the water is removed as vapor with the
combustion products.
Calorific ValueCalorific Value
Surface Moisture:
- The moisture which is present on the surface of the fuel particle.
- Can be removed easily when it is exposed to atmosphere.
Inherent Moisture (IM):
- The moisture which is held inside the molecular structure of the fuel.
- Difficult to remove.
Total Moisture (TM):
- Surface Moisture + Inherent Moisture.
“Higher the moisture, lower will be the GCV”
MoistureMoisture
Calorific Value ConversionCalorific Value Conversion
1. Find the AS FIRED GCV:
GCVADB = 5300 Kcal/Kg.
Total Moisture = 30 %.
Inherent Moisture = 10 %.
GCVAFB = …….. Kcal/Kg.?
2. Find the AS FIRED GCV:
GCVDB = 5888.89 Kcal/Kg.
Total Moisture = 30 %.
GCVAFB = …….. Kcal/Kg.?
Calorific Value Conversion - ExampleCalorific Value Conversion - Example
Higher the moisture, lower the efficiency of boiler.
Creates jamming problem in bunker chutes and in feeders.
It chokes the APH tubes and starts corroding from inside the tubes.
Corrodes the back hand equipments like Dust collecting system, ID fan
flue gas ducting & steel chimney when it condenses.
Effects of Moisture in FuelEffects of Moisture in Fuel
Ash
- Higher the ash content lower the GCV & high ash handling cost.
Sulphur Content
- Corrodes the back hand equipments due to Sulphur condensation.
Fuel Size
- Lower the fuel size, higher the surface exposed to flame and better the
combustion.
- Higher the fines, more will be the carryover of fuel with ash.
Other ParametersOther Parameters
What is the fuel used in 16 TPH boiler.?
Imported Coal:
GCV (AFB) : <5000 Kcal/Kg.
Total Moisture : <30 %.
Coffee Spent:
GCV (AFB) : <3000 Kcal/Kg.
Total Moisture : >50 %.
Boiler - Working
ESP
Flue Gas flow
Air flow
SA Fan FD Fan
ID Fan
Moving Grate Boiler – Air & Flue Gas CircuitMoving Grate Boiler – Air & Flue Gas Circuit
DEAERATOR STORAGE TANK
MU WATER CONDENSATE
ST
EA
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ECONOMISER
CH
EM
ICA
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SIN
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F.P:01
F.P:02
TO PROCESS
Moving Grate Boiler – Water & Steam CircuitMoving Grate Boiler – Water & Steam Circuit
Deaerator is used for the removal of oxygen (O2) and non condensable gases.
Oxygen promotes pitting corossion. It affects the heat transfer in equipment
Deaerator
As the temperature increases, the solubility of oxygen in water decreases.
The concentration of dissolved oxygen in water is very less at 100 Deg C. Hence the temperature is maintained more than 100 Deg C in Deaerator.
Temp Vs Dissolved Oxygen
0
2
4
6
8
10
12
1 32 50 65 82 100
Temperature in Deg C
Dis
solv
ed O
xyge
n in
ppm
Deaerator (Contd)
Heat Recovery Equipment.
It adds sensible heat to the incoming feed water.
It enhances the efficiency of the boiler by abstracting the heat from flue gases.
Economiser
It is the tube nest connecting Steam drum and Mud drum.
In this zone some quantity of water is converted into steam.
Water is transferred to waterwall panels through Downcomer.
Boiler Bank
It is the zone where water partially converted into steam.
The arrangement is of tube and fin construction so that it forms a gas tight chamber.
It ensures the flue gas gets cooled down before entering boiler bank zone.
Membrane/Waterwall Panel
The Air Preheater is the last heat recovery equipment which is situated last in the flue gas path.
It is a cross flow heat exchanger which provides hot air for combustion.
Air Preheater
Air In
Air Out
Fittings or Devices which are necessary for safety and controls are known as Mountings.
Fittings or Devices which are provided to increase the efficiency of boiler and help in smooth running of boiler is known as Accessories.
Boiler Mountings & Accessories
Safety Valve.
Water Level Gauge.
Pressure Gauge.
Fusible Plug.
Blowdown Valve.
Feed Check valve.
Air Vent Valve.
Boiler Mountings
Economiser.
Air Preheater.
Superheater.
Boiler Feed Water Pumps.
Pressure Reducing Valve.
Moisture Separator.
Steam Traps.
Boiler Accessories
Boiler Basic Calculation
Feed water consumption:
Feed Water
Make Up Water
Steam to Deaerator
Condensate
Feed Water Consumption = Make Up Water + Condensate + Steam (To Deaerator)
Percentage of Blowdown:
Example : 01
Feed water TDS : 250 PPM.
Boiler water TDS maintained : 2500 PPM.
Blowdown % : …….%
Example : 02
Feed water TDS : 100 PPM.
Boiler water TDS maintained : 2500 PPM.
Blowdown % : …….%
Evaporation Ratio:
Example:
Steam Generated : 200 Tons/Day.
Fuel Consumed : 38500 Kg/Day.
Evaporation Ratio : ……..
Boiler Direct Efficiency:
Boiler Indirect Efficiency:
Boiler Indirect Efficiency = 100 – Total Heat Losses.
Heat Losses:
HL 1 : Heat loss in dry flue gas.
HL 2 : Heat loss due to formation of water from H2 in fuel.
HL 3 : Heat loss due to moisture in fuel.
HL 4 : Heat loss due to moisture in air.
HL 5 : Heat loss due to unburnt in bed / bottom ash.
HL 6 : Heat loss due to unburnt in fly ash.
HL 7 : Heat loss due to partial combustion of C to CO.
HL 8 : Heat loss due to radiation.
Dust Collecting System
The purpose of dust collector is to trap the dust particles and to allow
only pure gases into the atmosphere.
Dust CollectorDust Collector
Cyclone Separator
Wet Scrubber
Bag Filter
Electrostatic Precipitator (ESP)
• In cyclone separator, the dust particles are removed by means of gravity and rotation.
• The light weight particles travel at cyclone path and the heavy weight particles will get settle down in the hopper.
Cyclone SeparatorCyclone Separator
Gas I/L
Gas O/L
Wet ScrubberWet Scrubber
• The water is sprayed over the dust laden gas particles which is flowing upward.
• The heavy dust particles will acquire weight and settles down.
• Bag filter consists of bags with cages.
• The bags consists of micron size holes which allows only minute size of gas particle to pass inside.
• Purging air supplied frequently to remove that adhered particles on bag surface.
Bag FilterBag Filter
High voltage is applied to electrode plates.
The oppositely charged ions particles are attracted by electrode plates.
Rapping is applied to remove the dust particles which is adhered to electrode plates.
The precipitation process involves the following process.
ELECTROSTATIC PRICIPITATORS (ESP)ELECTROSTATIC PRICIPITATORS (ESP)
Bottom Ash
Fly Ash
Ash
ASH HANDLING SYSTEMASH HANDLING SYSTEM
Hot Ash collected from traveling grate of Boiler furnace is collected directly in to water filled
trough, where in a moving belt is installed to take out Wet Ash from the trough.
Bottom AshBottom Ash
Pneumatic Handling is an effective method of conveying dry bulk material through
pipes by means of compressed Air as a conveying medium.
Fly AshFly Ash
Boiler Water Quality
Parameters Feed Water Boiler Water Condensate
pH at 25 Deg C 8.5 – 9.5 10.5 - 11 6.5 – 7.5
Hardness Nil Nil Nil
TDS <50 PPM <2000 PPM Nil
Water parameters to be maintained
Waterside problems in boilers
CARRYOVER
Ca & Mg Hard scales,Silica Scales
etc.
Low pH Pitting Corrosion due to
Dissolved Gases,Under Deposit corrosion,
Caustic Corrosion etc.
High TDS
CORROSION
SCALING
pH
pH is the measure of degree of acidity or basicity of solution.
pH < 7 - Acid
pH = 7 - Neutral
pH > 7 - Base
Chemical Dosing:
NaOH, Sodium hydroxide is used to elevate the pH in feed water.
Morpholine/Ammonia are volatile chemicals used for pH improvement in feedwater.
Dissolved Oxygen
Dissolved gases depend on source of water.
Dissolved gases such as oxygen and CO2 are naturally occurring.
It leads to pitting corrosion.
At high temperature, even a small O2 leads to high rate of corrosion.
The Dissolved oxygen can be removed by
Mechanical De aeration &
Chemical Dosing.
Chemical Dosing:
Hydrazine (Should be handled with care)
Sodium Sulphite.
Total Hardness
Hardness is composed primarily of calcium and Magnesium minerals.
These are primarily responsible for scale formation.
External Water Treatment:
Softener Plant.
Internal Water Treatment:
Can be controlled by dosing phosphate.
Total Dissolved Solids
When water is converted into steam only pure steam is formed and the
dissolved solids will settle down. Hence the dissolved solids concentration will
increases in the steam drum over a period of time.
It causes foaming and Carryover.
External Water Treatment:
RO Plant & DM Plant.
Internal Water Treatment:
By proper Blowdown.
Common problems in Pressure parts due to water quality
Hydrogen Attack – Low pH Corrosion – Dissolved O2
Scale Deposit – Hardness Carryover – TDS
Thank YouThank You