Air Supply System arrangement of an Opposite Fired Boiler :

1

Typical Power Plant Centrifugal Fan

2

Coal Burner Details:

This shows a schematic of a burner. The flame shape is very important for proper combustion, flame

detection and NOx formation. The secondary air distribution in the burner is controlled by manual

adjusters at the burner front.

3

The concept of burning coal that has been pulverized into a fine powder has come out from the belief

that if the coal is made fine enough, it will burn almost as easily and efficiently as a gas. The feeding rate

of coal according to the boiler demand and the amount of air available for drying and transporting the

pulverized coal fuel is controlled by computers. Pieces of coal are crushed between balls or cylindrical

rollers that move between two tracks or "races." The raw coal is then fed into the pulverizer along with

air heated to about 650 degrees F from the air heater. As the coal gets crushed by the rolling action, the

hot air dries it and blows the usable fine coal powder out to be used as fuel. The powdered coal from

the pulverizer is directly blown to a burner in the boiler. The burner mixes the powdered coal in the air

suspension with additional pre-heated combustion air and forces it out of a nozzle similar in action to

fuel being atomized by a fuel injector in modern cars. Under operating conditions, there is enough heat

in the combustion zone to ignite all the incoming fuel.

Typical layout of a horizontal economizer: Tubes could be about 1” diameter with 1” gaps between

circuits. Tube bank spacing increases for the sections closer to the furnace to reduce the chance of

plugging and because the volumetric flow rate is higher where the gas is hotter.

4

The water walls are tubes that are welded to spacers between the tubes to form a gas-tight wall. The water

flows up through the walls as it turns to steam.

5

This is the traditional PC unit I have been showing. Coal is ground up and mixed with air. Heat is

released at the burners.

Notice that below the burners there is not much going on – just a water-cooled hopper that is sealed in a

water trough. The ash drops out and is taken away by drag chain or a water sluice system.

Water is boiled in the water walls (mostly by radiant heat transfer), and then the flue gas goes through the

backpass to give up its heat to the various tube banks (much like an HRSG).

Then (unlike an HRSG) the flue gas gives up the remainder of its available heat to the incoming air in the

air heater.

6

The air heater is a key part of a fossil plant design. The air heater captures much of the heat leaving the

boiler and sends it back to the furnace.

Air heaters can be tubular (shell and tube) or regenerative as shown here.

Flue gas goes from ~730° F to ~220° F and heats the air from ambient to ~680° F, some of the air leaks

over into the gas stream. An important parameter to monitor is AH cold-end average temp (the average of

the to-gas streams on the cold side) This must stay above a certain number depending on the sulfur in the

coal, ~150° F for low sulfur PRB.

Boiler fittings and accessories

Safety Valve: It is used to relieve the excess boiler pressure and avoid the possible explosion of

the boiler

Water level indicators: They show the operator the level of fluid in the boiler, also known as a

sight glass, water gauge or water column is provided.

Bottom blow down valves: They provide a means for removing solid particulates that condense

and lay on the bottom of a boiler. As the name implies, this valve is usually located directly on

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the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push

these particulates out.

Continuous blow down valve: This allows a small quantity of water to escape continuously. Its

purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation

would lead to foaming and cause water droplets to be carried over with the steam - a condition

known as priming

Priming (steam engine)

Priming is a condition in the boiler of a steam engine in which water is carried over into the

steam delivery. It may be caused by impurities in the water, which foams up as it boils, or

simply too high a water level....Hand holes: They are steel plates installed in openings in

"header" to allow for inspections & installation of tubes and inspection of internal surfaces.

Steam drums internals, A series of screen, scrubber & cans (cyclone separators).

Low- water cutoff: It is a mechanical means (usually a float switch) that is used to turn off the

burner or shut off fuel to the boiler to prevent it from running once the water goes below a

certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or

catastrophic failure.

Surface blowdown line: It provides a means for removing foam or other lightweight non-

condensible substances that tend to float on top of the water inside the boiler.

Circulating pump

A pump is a device used to move fluids, such as gases, liquids or Slurry. A pump displaces a

volume by physical or mechanical action. One common misconception about pumps is the

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thought that they create pressure....: It is designed to circulate water back to the boiler after it

has expelled some of its heat.

Feed water check valve A check valve, clack valve, non-return valve or one-way valve is a

mechanical device, a valve, which normally allows fluid to flow through it in only one

direction.... or clack valve: A non return stop valve in the feed waterBoiler feedwater is

water used to supply a boiler to generate steam or hot water. At thermal power stations the

feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded

into the boiler by a boiler feedwater pump.... line. This may be fitted to the side of the boiler,

just below the water level, or to the top of the boiler. A top-mounted check valve is called a top

feed and is intended to reduce the nuisance of lime scale.Limescale is the hard, off-white,

chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained

hot-water central heating systems.... It does not prevent lime scale formation but causes the

lime scale to be precipitated in a powdery form which is easily washed out of the boiler.

De-super heater tubes or bundles: A series of tubes or bundles of tubes, in the water drum but

sometime in the steam drum that De-superheated steam. This is for equipment that doesn't

need dry steam.

Chemical injection line: A pipe line to add chemicals for controlling the feed water pH is a

measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of

dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured

experimentally, so they are based on theoretical calculations....pH

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Steam accessories

Main steam stop valve:

o A steam trap is a device used to discharge condensate and non condensable gases

while not permitting the escape of live steam. Nearly all steam traps are nothing more

than automatic valve....Main steam stop/Check valve: It is used on multiple boiler

installations.

Combustion accessories

Fuel oil system:

Gas system:

Coal system:

Burning Coal in Power Plants – Calorific Value and Moisture

Coal is the primary fuel for producing Electricity. Some of the characteristics of coal have profound

influence on the day to day working and economics of the power plant. This article discusses two of the

important characteristics – Calorific Value and Moisture.

Calorific Value or Heating Value

This is the most important parameter that determines the economics of the power plant operation.

It indicates the amount of heat that is released when the coal is burned. The Calorific Value

varies on the geographical age, formation, ranking and location of the coal mines. It is expressed

as kJ/kg in the SI unit system. Power plant coals have a Calorific Value in the range of 9500 kJ/kg

to 27000 kJ/ kg.

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The calorific value is expressed in two different ways on account the moisture in the coal. Coal contains

moisture. When coal burns the moisture in coal evaporates taking away some heat of combustion which

is not available for our use.

When we say Gross Calorific Value or Higher Heating Value it is the total heat released when

burning the coal.

When we say Nett Calorific Value or Lower Heating Value it is the heat energy available after

reducing the loss due to moisture.

The Heating Value determines how much fuel is required in the power plant. Higher the Calorific Value

lesser the amount of the coal required per unit of Electricity. Higher Calorific value also means the cost

of the coal is higher but is offset by the lower cost of logistics, storage and ash disposal.

Moisture

The coal when mined contains moisture. The moisture is in two forms. First is the inherent moisture

which is entrapped within the structure of the coal. Second is the external moisture that is outside of

the coal structure. The amount of moisture depends again on the geographical age, location and

condition in the mines. A part of this moisture can easily evaporate in atmospheric conditions during its

transfer from the mines, storage at the power plant and finally feeding to the boiler in the power plant.

Depending on where and when you determine the moisture, values will be different for the same of

coal.

The amount of moisture determines how much of heating is to be done to dry the coal before it is

burned in the boiler.

Reporting Coal Properties

Moisture in coal is expressed as % by weight. So the change in the moisture content changes the

proportion of the other coal constituents and the Calorific Value.

‘As Received’ coal, is the coal received in the power plant premises. The payment to the coal

companies are normally made based on the ‘As Received’ coal properties.

‘As Fired’ coal is the coal entering the boiler system. The performance of the boiler and power

plant is based on the ‘As Fired’ coal properties.

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‘Air Dried’ coal is what is used in the laboratory for analysis. This coal is dried in atmosphere and

has the lowest amount of moisture. Laboratory results are reported as ‘Air Dried’ coal

properties.

The difference between the above three conditions is the proportion of the Moisture. The Calorific

Value and other coal constituents analysed in the laboratory on ‘Air Dried’ basis is converted to ‘As

received’ or ‘As Fired’ basis proportional to the moisture content.

Combustion Characteristics of Low Grade Coal

Background

At present, bituminous coal that burns well with a high calorific value in the range of 6,500 to 7,000

kcal/kg and with a fuel ratio (weight ratio of fixed carbon to volatile matter) of 1.0 to 2.5 is used to

pulverized coal fired power stations in Japan. As the demand for coal is likely to increase worldwide,

particularly in developing countries, it is hoped that low grade coal that has not yet been used in

thermal power stations can be utilized to reduce the power generation cost by reducing the fuel cost.

The types of coal that should be considered for use are low grade coal with a low calorific value and a

high moisture content or high ash content, and high fuel ratio coal which is difficult to ignite and which

has a narrow stable combustion range.

Objectives

To clarify the combustion characteristics of low grade coal that have a calorific value in the range of

3,000 to 5,000 kcal/kg and a high moisture content or high ash content and high fuel ratio coal that has

a fuel ratio of 5 or greater with a pulverized coal combustion test furnace (combustion capacity of 0.1

t/h).

Principal Results

1. Low Grade Coal

(1) The NOx conversion ratios of lignite coal (weight ratio of moisture content to coal supply amount as

dry ash free = 1.5) and subbituminous coal (same ratio = 0.3) were compared with that of low moisture

coal under similar conditions to pulverized coal fired power plants. It was found that the NOx conversion

ratio of lignite coal was slightly lower than that of low moisture coal while that of sub-bituminous coal

was higher (Fig. 1). As lignite coal has a high moisture content, the latent heat of vaporisation is high.

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This reduces the flame temperature. As a result, the oxygen consumption near the burner is slowed and

NOx production is suppressed. On the other hand, the oxygen consumption of sub-bituminous coal is

fast near the burner and the formation of NOx is promoted. As the reactivity of both types of coal after

the evaporation of moisture is high, the uncombustion fraction of these types of coal are lower than

those of low moisture coal.

(2) The greater the ash content, the higher the uncombustion fraction and NOx conversion ratio. As the

reactive area decreases and the consumption of oxygen near the burner is slowed with a higher ash

content, the formation and decomposition of NOx are delayed (Fig. 2).

(3) As coal with a high moisture content has a higher reactivity than coal with a high ash content, the

uncombustion fraction of coal with a high moisture content is lower. It is believed that coal with a high

moisture content is easier to use for power generation purposes. Unfortunately, as this sub-bituminous

coal tends to generate a large amount of NOx, it is necessary to develop a combustion technology that

can suppress NOx emission.

2. High Fuel Ratio Coal

(1) The higher the fuel ratio of coal, the harder it is to ignite. Studies show that by using a burner

designed to create re-circulating currents to lengthen the time that coal particles stay in the high

temperature region near the burner, ignition can be improved and the range of stable combustion can

be widened (Fig. 3).

(2) Both the concentration of NOx and concentration of unburned carbon in fly ash are higher for high

fuel ratio coal than for bituminous coal. The NOx conversion ratio of high fuel ratio coal, like that of

bituminous coal, increases as the fuel ratio increases or as the nitrogen content decreases although the

tendency is not as pronounced (Fig. 4). On the other hand, the uncombustion fraction rises fairly sharply

as the fuel ratio increases.

(3) It is believed that among the latest pulverized coal fired power plants designed to meet

environmental regulations, high fuel ratio coal with a fuel ratio of up to 5 can be used with slight

modification of the burners.

Coal Blending in Power Stations

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Coal blending in power stations is mainly adopted to reduce the cost of generation and increase the

availability of coal. The low-grade coals can be mixed with better grade coal without deterioration in

thermal performance of the boiler thus reducing the cost of generation.

In many nations, the blending of high grade imported coal with low grade high ash coals has long been

adopted. Many methods may be used. The blending can occur at the coal mine, preparation plant, trans-

shipment point, or at the power station. The method selected depends upon the site conditions, the

level of blending required, the quantity to be stored and blended, the accuracy required, and the end

use of the blended coal. Normally in large power stations handling very large quantities of coal, the

stacking method with a fully mechanized system is followed.

To decide to blend or not, it is very important to understand the composition of the coals that are to be

blended. This means one will have to understand the origin of coal, the organic and inorganic chemistry

of coal, and the behavior of the coals in questions. It has been established that coals produced by the

drift theory of coal formation and coals formed by the swamp theory of coal formation have to be

blended with caution. The main difference is that coal formed by drift theory exhibits pronounced

regional variation in thickness and quality of seams. They also have enormously high ash content with

varying inorganic chemistry. The organics of drift origin coal also present problems mainly because the

vegetation that lead to the forming of the coal are drifted from different places having different kind of

vegetation. In contrast, the coals formed by the swamp theory have much more uniform organic

properties and much lower ash content with consistent inorganic chemistry.

During combustion, it is necessary to understand the physical conditions and coal properties during

heating of the particles, devolatalisation, ignition and combustion of the volatile matter, and ignition and

combustion of the char. It is also equally important to know the phase changes in mineral matter and

other inorganics present in coal. The combustion efficiency and carbon loss will have to be also

addressed during blending of coals. It is also necessary to look into the aspects of slagging, fouling, and

emission characteristics like NOx, Sox, and particulates.

For more about the complexities of mixing and burning coal, continue reading on the next page. For

more basic information, read about how coal power plants generate electricity by burning coal and

interesting facts about the process.

Because of the complexity of the combustion process and the number of variables involved (which are

still not fully understood), it is difficult to extrapolate small scale results to a full scale power plant. Thus,

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operational experience with a wide range of plant configurations with a variety of coal feedstock is

essential for determining the practical significance of results from bench – and pilot – scale tests. More

published research about how the behavior of the coals and coal blends utilized in tests differ from their

actual performance in power station boilers is required.

Predicting the risk of spontaneous combustion of coal stocks is another aspect of current fuel quality

research. In addition to the inherent dangers, uncontrolled burning can lead to the release of pollutants.

The economic issues associated with the loss of a valuable energy resource are also a concern.

The presence of trace elements in coal combustion has also received increased attention throughout the

world during the last few years, with elements such as mercury of particular concern. One way to reduce

trace element emissions is cleaning the coal prior to combustion. The use of cleaner coals – those with

lower ash and sulfur content – can have the added advantage of substantially reducing operating costs.

Again, however, some effects may be detrimental (ash deposition may be exacerbated, and the effects

on corrosion and precipitator performance are uncertain), which makes testing vital.

It has been found from field data that even if the blended coal closely resembles the design coal for the

boiler, the blend need not perform the same way. This is mainly due to the transformation of inorganic

particles during combustion and the way in which the organics are dispersed in coal. A limitation to

blending coals is the compatibility of the coals themselves, and problems are more likely when blending

petrographically different coals or coals with different ash chemistry. Non-additive properties make

blend evaluation for power generation inherently complex. More work is required on understanding

how the inorganic components of coals in the blend interact and how it affects ash behavior including its

emissivity, reflectivity, and thermal conductivity.

Blending decisions should be based on the knowledge of the specific behavior of a given pair of coals,

rather than an assumption of linear variation of properties with blend traction. The ever more stringent

constraints placed on coal-fired power stations worldwide and the continuing development of new

technologies means that the issue of fuel quality improvement will remain a primary factor.

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Predicting Combustibles in Pulverized Coal Fired Boilers - Fly Ash and Bottom Ash

Predicting the percentage of combustibles in fly ash in a tangential fired boiler using proximate analysis

of coal gives boiler designers an edge during the proposal and contract stages. Here is how to predict fly

ash and bottom ash combustibles in order to compute carbon loss in a boiler.

In boilers with pulverized firing systems, about 80% of the ash in coal being fired is carried as fly ash. The

other about 20% get collected as bottom ash. During the combustion of coal, some portion of the

hydrocarbon, mainly char, leaves the furnace as unburned particles. The amount of such unburned

particles leaving the furnace depends on many factors like the coal property, the type of burning system,

the resident time available in the furnace, the ash percentage in coal, the calorific value of coal, the fuel

ratio, the operating conditions, etc. The existence of unburned carbon in ash decreases not only the

combustion efficiency, but also the grade of fly ash for commercial sale.

Carbon loss is influenced by the following: (1) coal preparation and grinding, such as changes in ash and

maceral content ; mean, standard deviation, and higher moments of the particle size distribution;

moisture remaining in the pulverized coal, (2) properties of the pulverized coal and its char like heating

value, char yield on pyrolysis, char structure, char reactivity, ash content and composition, and

characteristics, and (3) adjustments of the burners and furnace such as air preheat, excess air, mixing,

residence time, and furnace temperature.

Hottel and Stewert (1940) were the first to consider the interaction between furnace design and coal

properties in the determination of carbon conversion, analyzing the effects of grind, reactivity,

temperature, excess air, and residence time on unburned carbon loss.

With the estimated values of percentage combustibles in fly ash as well as bottom ash, the carbon loss

can be calculated by using the formula given in BS_EN_12952, ASTM, PTC 4 and any other International

Standards.

Boiler designers during the design stage have only proximate analysis, ultimate analysis and ash

composition of coal. Carbon loss calculation involves calculating the carbon loss in fly ash and bottom

ash. This article provides a tool for the designers and others to predict the percentage of combustibles in

fly ash and bottom ash in a tangential fired boiler using proximate analysis of coal and the residence

time in the boiler furnace. Based on combustibles in flyash and bottom ash, it is possible to compute the

carbon loss in a boiler.

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Fly ash unburned prediction

The major portion of carbon loss in a boiler is from unburned carbon in fly ash. A method was developed

by me after a large volume of data was subjected to analysis and validation. It is seen from the analysis

and literatures that the fuel ratio i.e. the ratio of fixed carbon and volatile matter in coal has a very

significant effect. The ash in coal is a burden for combustion and can cause large problems during and

after combustion. Deposits and slagging in boiler furnaces using high amounts of medium slagging and

slagging coals are common. After combustion they can foul the heat transfer surface in the convection

region. So it is seen that log of ash % correlates well with fly ash combustibles. Coal calorific value

indicates the heat value of the coal being fired hence has to be taken into account when we want to

predict the fly ash combustibles. The calorific value of the coal in question divided by the calorific value

of carbon gives meaning to the factor. This indicates the relative stage where the coal in question lies

with respect to its ultimate transformation and also is an indirect indicator of the difficulty to ignite and

burn. I would not like to call it as reactivity as the same has not been studied / understood much with

respect to this ratio of coal. Inverse of residence time is another major factor which affects the fly ash

combustibles. As boilers are operated within a close range of excess air and fineness of coal, these

variables do not affect the unburned to any significant level.

A factor combining all the parameters is evolved which is used for fitting a curve with percentage

combustibles in fly ash. The factor is defined as

[{(FC/VM) + (HVV/8080)*100+Log (A)}/Res^2]

The equation governing the curve fitted on a fourth order polynomial is

Y = -3E-06 X4 + 0.0004 X3 - 0.0161 X2 + 0.2969 X - 0.9438

with a ‘R square’ value of 0.8824.

As this predictive equation is only made for a pulverized coal tangentially fired boiler, this has to be

verified for pulverized coal wall firing, down shot firing, opposed firing, etc. However, more than 50% of

the pulverized coal fired boilers in the world are equipped with tangential firing system.

Bottom ash unburned prediction

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The single most independent variable affecting the bottom ash combustibles is the plus 50 mesh size of

pulverized coal. A plot of percentage bottom ash combustible plotted against percentage plus 50 particle

sizes has a fourth order polynomial curve with an R2 value of 0.9412. The equation governing this fit is

Y1 = 0.0233X14 - 0.3925X1

3 + 1.9277X12 - 0.1593X1 + 0.2357

where, Y1 is percentage combustibles in bottom ash and X1 is plus 50 mesh particle percentage in the

pulverized coal.

It is seen that this percentage plus 50 in the pulverized fuel should be retained below 2% to minimize

the percentage combustible in bottom ash. This is generally recommended by boiler manufacturers.

Boiler design considerations

The goal of a boiler designer is always to ensure the efficiency of a boiler that shall be fabricated with

minimal capital investment and occupies less floor space.

It must also be capable of quick start up with considerable allowance to escape from certain limitations

such as thermal stress cracking.

The boiler thus designed should meet unwarranted load fluctuations that arise out of process

compulsions in industries. Specific consumption of fuel, power, boiler water treatment chemicals,

manpower costs etc should be as low as possible per tonne of steam generation. Heat loss to

atmosphere must be within the allowable limits keeping in mind that all heat can never be recovered

from flue gases owing to cold end corrosion in Gas-Air heaters and blowdown requirements.

Another aspect of boiler design includes enabling easy maintenance during shut-downs. Therfore, a

boiler must be light and simple in construction, its tubes and various joints must be away from direct

flame impact and they should be readily accessible for inspection which calls for the provision of

necessary man-holes.

Circulation and heat transfer: Before proceeding, it would be handy to know what Nucleate boiling and

departure from nucleate boiling (DNB) mean and how they affect the system.

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In DNB a "film of steam" layers the inner surface of the water tube due to insufficient turbulence

created in the flow of boiler water or steam or mixture of water and steam. This layer reduces heat

transfer between furnace gases and waterside substantially. The tubes get overheated and may fail in

due course.

The mass velocity of the fluid inside the tubes and tube roughness affects the turbulence either

positively or negatively. The engineers are aware of these while designing the boiler. Sufficiently high

mass velocities, but not too high, shall provide necessary turbulence to the fluids. Thus the water+steam

mixture is subjected to nucleate boiling, a desirable outcome as far as the circuation and heat transfer

are concerned.

The helical ribs on the inner surface of the tubes create a swirling motion of fluids and directs the

contents toward inner area. Steam film is thus avoided. Internal spiral grooves in tubes help produce

nucleate boiling with sufficient mass velocities. High pressure boilers need this arrangement to escape

the wrath of DNB.

Circulation of water or steam through the heated tubes is to ensure that they are cooled sufficiently

thereby preventing overheating and high skin temperatures of metal. Why should the waterwall tubes

be cooled as much as needed? High temperatures invite corrosion inside the tubes, overheat and

overstress them and ultimately metals crack. Heat from the metal, therefore, needs to be absorbed by

the water or steam or a mixture of both.

There are three types of circulation in boilers:

Natural circulation: Boiler water flows through downcomers by gravitation from steam drum to

mud drum or any other collecting header in the bottom and rises to the top through integrated

risers and furnace wall tubes agin back to the top of steam drum. In the steam drum water plus

steam mixture is separated by appropriate mechanisms like baffle plates or cyclone separators.

The saturated steam routes itself to superheater system for further heating. The success of

natural circulation entirely depends on the difference between the mean density of boiler water

in downcomers and the mean density of steam, water mixture in water wall tubes or risers.

Downcomer tubes start from the bottom of the steam drum and risers join at the top.

Forced circulation: In this circulation loop a pump is introduced in between steam drum and

collecting header or mud drum on the downcomer portion. Hence, it is 'forced' circulation.

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Once-through system: In this system the entire feed water that enters boiler system i.e., water-

wall tubes leaves as steam. No circulation is involved here. So there is no need for a steam

drum.

F urnace chamber design:

The designers of a furnace chamber or combustion chamber take into view the following points:

Combustion requirements

Properties of fuel

Emission standards of flue gases or solid particles as prescribed by the Law of the land, ash

content etc

The path the gas flow should take before leaving bank tubes to gas-air heaters and other heat

recovery systems so that the fluid in water wall tubes, front wall and real wall tubes completely

absorbs the heat.

Metal temperatures

The surface area exposed to heat. It should be borne in mind that heat transfer area is different

for different fuels though the pressure, temperature, and steaming capacity are same.

Other design considerations are of :

1) Super heaters 2) Reheater 3) Hot and cold gas air heaters 4) Economizers 5) Safety 6)Boiler

Protections, interlocks, instrumentation, electrical systems etc

Boiler Efficiency Calculations

To calculate the efficiency of a boiler, there are two methods of computation.

First method is simply dividing the output heat equivalent of the steam generated by the heat input to

the boiler through the fuel burnt. In this method the efficiency what we get will be very near to accuracy

because of the probable minor errors in the measured quantities of steam generated and the fuel

supplied to the boiler and also any minor errors in the measurement of pressure and temperature of the

steam generated, considered to arrive at the equivalent output heat in the steam generated.

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Second method is to calculate the various percentage heat losses occurring in the boiler, which are

computed based on the chemical reactions taking place in the process of combustion and deducting the

total percentage losses from hundred to get the percentage boiler efficiency. This method is more

accurate for computing the boiler efficiency and hence adopted.

The following are the various kinds of losses occurring in the boiler:

1. Dry Gas Loss.

2. Loss due to the combustibles present in the ash.

3. Wet Loss due to the moisture and hydrogen present in the coal.

4. Loss due to the sensible heat in the ash.

5. Radiation Loss.

6. Loss due to Air Moisture

Total % Losses: 1+ 2 + 3 + 4 + 5 + 6

% Boiler Efficiency: 100 – Total % Losses

For computing the various losses occurring in the boiler certain boiler parameters are to be noted

maintaining steady state conditions on the unit at full load. Soot blowing operations and bottom ash

clearing operations shall be completed before taking the observations. Mill rejects also shall be collected

at the end of the test period. The duration of test period will be one hour during which period the boiler

parameters will be noted once in every fifteen minutes. The average of the parameters will be taken into

calculations to have better results in obtaining the performance. The chemist also will conduct flue gas

analysis by orsat apparatus during the period of test.

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