A boileris an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam.When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost care The hot water or steam under pressure is then usable for transferring the heat to a process.
There are different types of boilers based on different fuels and with various capacities. (Questions to audience) What type of boilers do you know of? What kind of boilers do you use in the industry where you work? (Discussion)(Click once and boiler types will appear) We will look closer at the following types of boilers: Fire Tube Boiler, Water Tube Boiler, Packaged Boiler, Fluidized Bed Boiler, Stoker Fired Boiler, Pulverized Fuel Boiler and Waste Heat Boiler.
To begin with, we will look at the fire tube boiler:This is generally used for relatively small steam capacities and at low to medium steam pressures. The steam rates for fire tube boilers are up to 12,000 kg/hour with pressures of 18 kg/cm2. Fire tube boilers can operate on oil, gas or solid fuels. The figure illustrates how a fire tube boiler works. The fuel is burned and heats up the water to steam which is turn channeled to the process. Today, most fire tube boiler are in a packaged construction for all fuels.
We will now look at boiler efficiency.Thermal efficiency of a boiler is defined as the percentage of heat energy input that is effectively useful in the generated steam. There are two different methods to assess boiler efficiency. (Click once) They are direct and indirect method.(Click once) In the direct method, the energy gain of the working fluid, that is the water and steam, is compared to the energy content of the boiler fuel.(Click once) In the indirect method, the efficiency is calculated as the difference between the losses and energy input.We will start with looking at the methodology of the direct method of calculating boiler efficiency.
The direct method of determining boiler efficiency is also known as the “input-output” method. This is because it only needs the useful output, which is steam, and the heat input, which is fuel, in order to evaluate the efficiency. The efficiency is evaluated by using this formula where hg is the enthalpy of saturated steam and hf is the enthalpy of feed water.(Click once) The parameters to be monitored for the calculation of boiler efficiency through the direct method are: Quantity of steam generated per hour; the quantity of fuel used per hour; the working pressure and superheat temperature if any; the temperature of feed water; the type of fuel and gross calorific value, GVC, of the fuel.
Now, we will look at the indirect method. This is also referred to as the heat loss method. The boiler efficiency can be calculated by subtracting the heat loss fractions from 100 as shown here. The principle losses that occur in a boiler are due to: Dry flue gas; evaporation of water and evaporation of moisture in fuel; moisture present in combustion air; unburnt fuel in fly ash; unburnt fuel in bottom ash, radiation and other unaccounted losses.
The data that is required to calculate boiler efficiency according to the indirect method include: Ultimate analysis of fuel in terms of H2, O2, S, C, moisture content and ash content. Percentage of oxygen or CO2 in the flue gas; flue gas temperature; ambient temperature and humidity of air; as well as GCV of fuel. In case of solid fuels, the percentage combustible in ash and GCV of ash.
A better understanding of the properties of steam may be achieved by understanding the general molecular and atomic structure of matter and applying this knowledge to ice, water and steamA molecule is the smallest amount of any element or compound substance still possessing all the chemical properties of that substance which can exist. Molecules are made up of even smaller particles called atoms, which define the basic elements such as hydrogen and oxygenOne such compound is represented by the chemical formula H2O, having molecules made up of two atoms of hydrogen and one atom of oxygen.Most mineral substances can exist in the three physical states (solid, liquid and vapour), which are referred to as phases. In the case of H2O, the terms ice, water and steam are used to denote the three phases respectively.
Steam today is an integral and essential part of modern technology. Without it, our food, textile, chemical, medical, power, heating and transport industries could not exist or perform as they do. Steam provides a means of transporting controllable amounts of energy from a central, automated boiler house, where it can be efficiently and economically generated, to the point of use. Therefore as steam moves around a plant it can equally be considered to be the transport and provision of energy. For many reasons, steam is one of the most widely used commodities for conveying heat energy. Its use is popular throughout industry for a broad range of tasks from mechanical power production to space heating and process applications. Reasons for using steam include:Steam is efficient and economic to generateSteam can easily and cost effectively be distributed to the point of useSteam is easy to controlEnergy is easily transferred to the processThe modern steam plant is easy to manageSteam is flexibleThe alternatives to steam include water and thermal fluids such as high temperature oil. Each method has its advantages and
An understanding of the basic steam circuit or ‘steam and condensate loop’ is requiredNote to the trainer: a detailed description is in the chapter. Below are the summarized points onlyAs steam condenses in a process, flow is induced in the supply pipe. The steam generated in the boiler must be conveyed through main pipes, or 'steam mains‘ and then smaller branch pipes. Heat is transferred from the steam to the pipe, so the pipe work will begin to transfer heat to the air.Steam on contact with the cooler pipes will begin to condense immediately. On start-up of the system, the condensing rate will be at its maximum and is commonly called the ‘starting load’. Once the pipe work has warmed up, the condensing rate is minimal and commonly called the ‘running load’.The resulting condensation (condensate) falls to the bottom of the pipe and will then have to be drained from various strategic points in the steam main.When the valve on the steam pipe serving an item of steam using plant is opened, steam flowing from the distribution system enters the plant and again comes in contact with cooler surfaces. The steam then transfers its energy in warming up an equipment and product (starting load), and, when up to temperature, continues to transfer heat to the process (running load).There is now a continuous supply of steam from the boiler. More water (and fuel to heat this water) is supplied to the boiler to make up for the water which has previously been evaporated into steam. The condensate formed in both the steam distribution pipework and in the process equipment is a convenient supply of useable hot boiler feedwater.
Pipe material: Pipes for steam systems are commonly manufactured from carbon steel to ANSI B 16.9 Al06. The same material may be used for condensate lines, although copper tubing is preferred in some industries. For high temperature superheated steam mains, additional alloying elements, such as chromium and molybdenum, are included to improve tensile strength and creep resistance at high temperatures. Typically, pipes are supplied in 6-meter lengths.Pipeline sizing: The objective of the steam distribution system is to supply steam at the correct pressure to the point of use. Pipeline sizing is an important factor.Oversized pipework means:Pipes, valves, fittings, etc. will be more expensive than necessary.Higher installation costs will be incurred, including support work, insulation, etc.For steam pipes a greater volume of condensate will be formed due to the greater heat loss. This in turn means that either more steam trapping is required or wet steam is delivered to the point of use.Undersized pipework means:A lower pressure may only be available at the point of use. This may hinder equipment performance due to only lower pressure steam being available.There is a risk of steam starvation.There is a greater risk of erosion, water hammer and noise due to the inherent increase in steam velocity.The required pipeline size can be calculated based on pressure drop and velocity. Note to the trainer: if time allow you can use the chapter to explain how each of these calculation methods work
A filter used in a steam system typically consists of a sintered stainless steel filter element.Filters are used to remove smaller particles than strainers, for example, in the following applications:When there is direct injection of steam into a process, which may cause contamination of the product. Example: In the food industry, and for the sterilization of process equipment in the pharmaceutical industry.Where dirty steam may cause rejection of a product or process batch due to staining or visible particle retention. Example: Sterilizers and paper/board machines.Where minimal particle emission is required from steam humidifiers. Example: Humidifiers used in a “clean” environment.For the reduction of the steam water content, ensuring a dry, saturated supply.
Performance assessment of boilers,steam system,insulation & refractories
PERFORMANCE ASSESSMENT OF
What is a Boiler ?
Vessel that heats water to become hot water or steam.
At atmospheric pressure water volume increases 1,600
Hot water or steam used to transfer heat to a process.
PERFORMANCE ASSESSMENT OF
TYPES OF BOILERS
Water Tube Boiler
Fluidized Bed (FBC) Boiler
Fire Tube Boiler
Stoker Fired Boiler
Pulverized Fuel Boiler
Waste Heat Boiler
FIRE TUBE BOILER
Relatively small steam
Low to medium steam
pressures (18 kg/cm2)
Operates with oil, gas or
ASSESSMENT OF A BOILER
Boiler Efficiency :
Thermal efficiency: % of (heat) energy input that is
effectively useful in the generated steam.
1) DIRECT METHOD: 2) INDIRECT METHOD:
The energy gain of the
working fluid (water and steam)
is compared with the energy
content of the boiler fuel
The efficiency is the
different between losses
and energy input
BOILER EFFICIENCY : DIRECT
Boiler efficiency ( ) =
x 100 =
Q x (hg – hf)
Q x GCV
hg -the enthalpy of saturated steam in kcal/kg of steam
hf -the enthalpy of feed water in kcal/kg of water
Parameters to be monitored:
- Quantity of steam generated per hour (Q) in kg/hr
- Quantity of fuel used per hour (q) in kg/hr
- The working pressure (in kg/cm2(g)) and superheat
temperature (oC), if any
- The temperature of feed water (oC)
- Type of fuel and gross calorific value of the fuel (GCV)
in kcal/kg of fuel
BOILER EFFICIENCY : INDIRECT
Efficiency of boiler ( ) = 100 – (i+ii+iii+iv+v+vi+vii)
i. Dry flue gas
ii. Evaporation of water formed due to H2 in fuel
iii. Evaporation of moisture in fuel
iv. Moisture present in combustion air
v. Unburnt fuel in fly ash
vi. Unburnt fuel in bottom ash
vii. Radiation and other unaccounted losses
Required calculation data
• Ultimate analysis of fuel (H2, O2, S, C, moisture content, ash
• % oxygen or CO2 in the flue gas
• Fuel gas temperature in C (Tf)
• Ambient temperature in C (Ta) and humidity of air in kg/kg of
• GCV of fuel in kcal/kg
• % combustible in ash (in case of solid fuels)
• GCV of ash in kcal/kg (in case of solid fuels)
PERFORMANCE ASSESSMENT OF
What is Insulation?
Insulation, or more correctly thermal insulation , is a general
term used to describe products that reduce heat loss or heat
gain by providing a barrier between areas that are
significantly different in temperature.
It make your home warmer in winter and also helps
keep it cooler in summer.
Air is a poor conductor of heat, so the tiny pockets of
air trapped in insulation minimise the amount of heat
which can pass between the inside and outside of your
HOW INSULATION WORKS?
Building insulation refers broadly to any object in a
building used as insulation for any purpose.While the
majority of insulation in buildings is for
(1)thermal purposes, the term also applies to (2)
acoustic insulation, (3) fire insulation, and (4)impact
Thermal insulation can refer to material used to reduce
the rate of heat transfer or the methods and processes used
to reduce heat transfer.
Heat or thermal conduction is the spontaneous transfer
of thermal energy through matter to equalize temperature
differences. It is also described as heat energy transferred
from one material to another by direct contact.
DIFFERENT KINDS OF MATERIAL
USED IN INSULATION
The different materials used in the Insulation process
Glass mineral wool (glasswool)
Rock mineral wool (stone mineral wool)
TYPES OF INSULATION
Structural Insulated Panel
Blanket batts and roll
Loose fill-in and blow-in
STRUCTURAL INSULATED PANEL
Structural insulated panels (SIPs), also called stressed-skin
walls, use the same concept as in foam-core external
doors, but extend the concept to the entire house. They
can be used for ceilings, floors, walls, and roofs.
The panels usually
plywood, OSB, sandwich
ed around a core of
, polyisocyanurate, compr
essed wheat straw, or
Insulated Concrete Forms
ICFs are hollow, light-
weight "stay in
place" forms made
of two Expanded
panels which are
forms are stacked to
the desired height
then filled with
stable, durable and
Oriented strand board, (OSB) or Sterling
board (UK), is an engineered wood product
formed by layering strands (flakes) of wood in
Cellulose is 100% natural and 75-85% of it is made from
a. Fibrous Type – from mineral wool rock, glass wool, slag
wool or vegetable fiber usually of wood fiber.
or ground vegetable
Sound Insulation (Soundproofing)
is any means of reducing
the intensity of sound
with respect to a specified
source and receptor.
sound in two different
reduction and noise
PERFORMANCE ASSESSMENT OF
What is steam?
Molecule: smallest of any compound
Water = H2O
◦ two hydrogen atoms (H)
◦ one oxygen atom (O)
Three physical states :
◦ solid: ice
◦ liquid: water
◦ vapour: steam
Why do we use steam?
Transport and provision of energy
•Efficient and economic to generate
•Easy to distribute
•Easy to control
•Easily transferred to the process
•Steam plant easy to manage
Steam saturation curve:
MOST IMPORTANT COMPONENTS
2. Drain points
3. Branch lines
7. Steam traps
8. Air vents
9. Condensate recovery
Pipe material: carbon steel or copper
Correct pipeline sizing is important
Size calculation: pressure drop or velocity
Ensures that condensate can reach steam trap
Consideration must be give to
• Distance between drain points
• Diameter of drain pipe
Take steam away from steam main
Shorter than steam mains
Pressure drop no problem if branch line < 10 m
Handles high pressures
Lower dirt holding
capacity: more cleaning
Consists of sintered stainless steel filter element
Remove smallest particles
– Direct steam injection – e.g. food industry
– Dirty stream may cause product rejection – e.g. paper machines
– Minimal particle emission required from steam humidifiers
– Reduction of steam water content
Separators remove suspended water droplets from steam
Water in steam causes problems
o Water is barrier to heat transfer
o Erosion of valve seals and fittings and corrosion
Selection depends on steam trap’s ability to
oVent air at start-up
oRemove condensate but not steam
oMaximize plant performance: dry steam
AIR VENTS : Effect of air on heat transfer
CONDENSATE RECOVERY SYSTEM
What is condensate
– Distilled water with heat content
– Discharged from steam plant and equipment through steam
Condensate recovery for
– Reuse in boiler feed tank, desecrator or as hot process water
– Heat recovery through heat exchanger
Insulator: low thermal conductor that keeps heat confined within or
outside a system
Reduced fuel consumption
Better process control
Fire protection of equipment
PERFORMANCE ASSESSMENT OF
What are the refractories?
Any material can be described as a refractory, if it can
withstand the action of abrasive corrosive solids, liquids
or gases at high temperature.
A good refractory lining inside a furnace can help life of
a blast furnace from 4-5 yrs or 10-15 yr.
Refractories can be classified
-on the basis of chemical composition
-method of manufacture
-according to their refractoriness.
These are used in areas where slag and atmosphere are acidic.
They are stable to acids but attacked by alkalis.
e.g. fire clay, silica, Quartz, Zirconia.
These are used on areas where slags and atmosphere are
basic, stable to alkaline materials but reacts with acids.
e.g. Magnesia , Alumina, Dolomite.
On the basis of chemical composition
• Neutral refractories
These are used in areas where the atmosphere is either acidic or
basic and are chemically stable to both acids and bases.
e.g. Chromate, Carbide, Mullite.
Based on refractoriness
Low heat duty refractories
For low temperature environment i.e. 1520 —1630 ºC
Medium heat duty refractories
For temperature ranging from 1630—1670 ºC
High heat duty refractories
For temperature ranging from 1670—1730 ºC
Super duty refractories
For temperature above 1730 ºC
Transportation of Raw material
Wet Mixing (14-20% water)
Dry Mixing ( < 5% water)
Hand Moulding (Wet Mixed)
Machine Moulding (Dry and Semi wet Mixed)
Avoids high shrinkage and gives strength.
Make refractories safe for handling.
Removes water of Hydration,
30% Shrinkage in Volume
SELECTION OF REFRACTORIES
Area of application
Extent of abrasion and impact
Stress due to temperature gradient
Heat transfer and fuel conservation
Refractories are meant to sustain at high temperature so
the very common applications are Used in furnaces such as blast furnac
and coke oven.
Used in boilers.
Mostly used in cement industry in