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

TE

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

M

ECONOMISER

CH

EM

ICA

L

DO

SIN

G

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