Coal Properties

Hello, I welcome you all in this course on Power Plant Engineering. Now we have discussed

boilers and the performance of the boilers in the previous lectures. Now the coal is

used in the thermal power plant. Coal is the main fuel which is used in the thermal power plants. And today we will discuss about the properties of coal.

And we will discuss topics to be covered today are first of all discuss about the coal, analysis

of coal, classification of coal, we will talk about the Indian coal and coal beneficiation.

Now, regarding the coal is the oldest fuel which is used in the power plant. Actually

oldest fuel is the wood; I mean which is used for heat generation or in power plant also

earlier the wood was used, but coal is the main I mean for the commercial power generation

the coal is the oldest fuel. And the earth has sufficient reserve for the coal for the

another let us say 20, 30 years. So, still we can go for the coal based power plants.

Shifting earlier many of the power plants were running with using oil as the fuel with

there certain power plants thermal power plants which run with oil. There are certain power plants which run with the gas also they are known as gas based power plants or oil based

power plants. But what happened in 1973, when this there was a sudden hike in the price

of the oil the shifting of power plants from oil to coal started. And again let us say

for example, in our country 60 % of the power is generated is through thermal power plants

and upto 2050; I mean we have sufficient reserves and we can afford to have thermal based thermal

power plants up to net coming 20 30 years. Coal is very reliable source of energy. It

has the certain disadvantage of course, it has certain disadvantages also and hydrogen

content is more in the coal. If you look at the development of the civilization forget about the power generation, if you look for the source of energy thermal energy where

initially wood was used. So, wood was used I mean it has it has low hydrogen content then came the coal. Coal had higher hydrogen content then LPGs.

Nowadays we are using LPGs for the cooking purpose. It has more hydrogen content. Perhaps

in the future we will use pure hydrogen. Hydrogen is the fuel of the future, but it will take

time, it will take a lot of time. Yeah I mean meanwhile at present coal is the best alternative

for power generation because we cannot go as a country we cannot go for the oil based

power plants because our import bill of oil we are I mean we are importing 150 % of our

oil; I mean import coal import bill is approximately 45 % of the total import bill of oil.

So, oil import because everybody is moving with a motorized vehicle. So, that is why

the oil consumption is very high and we are importing a lot of oil. And regarding the coal production we rank 7 . The first is USA. USA is the highest. First is USA, second is

Russia or USSR right and Russia, second is Russia, third is China, fourth is Poland.

Poland has a lot of coal reserve then UK and then sixth is India.

We have coal reserves in I mean Bihar, West Bengal. Most of the coal reserves are in Bihar

and West Bengal and still it is advisable to go for coal based power plant; because

oil based power plant we cannot afford I mean already we are importing 150 % of the requirement

by importing oil and oil based plants are costly also.

So, for the when we are using coal. So, we should start with the analysis of the coal

analysis. So, there is a method which is known as a proximate analysis proximate analysis.

In proximate analysis, we estimate the moisture, moisture in the coal, volatile material, ash

content. Ash content in the coal can be as a 30 % right. Indian coal has very high ash

content that is coal which is generated in India has very high ash content then fixed

carbon. So, this is, these values are estimated in approximate analysis.

Now, regarding moisture we will start with the moisture. So, in the moisture there are

two types of moistures in the coal. One is inherent moisture and second is free moisture.

Now inherent moisture is because when the formation of coal was taking place inside

the earth moisture was trapped in the coal so, it is in the pockets right.

And another moisture is which absorbed by the coal. It is just taken from the atmosphere

or some other sources. So, which is inherent in moisture that the moisture which is I mean

which is trapped in the or the water body water which is trapped in the coal during the formation right. So, this moisture can also be removed, but

for the removal of this moisture the coal has to be exposed to nitrogen right; because

we cannot use any other oxidize or any other we cannot use air because air has oxygen it will oxidize coal. So, normally nitrogen is used because it is easily available at 110

?. So, it is passed through the coal so, inherent moisture can be removed by this process. Free moisture can be removed by any I mean by air

at 50 ? air or it is simply drying the coal. So, if you pass this 50, 60 ? air through

the coal, it will remove the moisture from the coal. So, for, but for the purpose of

removing the inherent moisture we have to pass, we have to flow make we have to use

nitrogen at 110 ?. Now, moisture not only it affects the performance

of the boiler it has other additional cost also. Suppose a coal has 10 % moisture is

not very high. 10 % moisture means, if you are carrying 100 kg of coal you are carrying

10 kg of water also. So, effectively you are carrying 90 kg of coal; because 10 kg of moisture

is of no use right. So, it increases the transportation cost. Number 1 moisture increases the transportation

cost. Or in addition to that, it increases the handling

cost handling cost is also increased because more bulk of the coal has to be handled by

the handling units and it increases the storage cost also. You are paying for 100 kg, but

90 kg of coal is stored. So, storage cost is yours and it does not play any useful role

in the entire process in the entire process of power generation right. Because part of

this is carried away by the heat and it quenches fire also. So, in this moisture is undesired

in a coal, but some %age of moisture is also present in the coal so, it cannot be avoided.

So, the second component of the coal is volatile matter. Now, volatile matter means combustible

gases combustible gases right hydrogen right methane,

carbon monoxide or hydrocarbons also right they are volatile matter which can be oxidized.

And through these volatile metals matters the power is generated.

Now, here interesting thing is hydrogen. Hydrogen forms a water hydrogen oxide and presence

of water is not required. So, in fact we should not have hydrogen in the in the coal right,

but hydrogen is very much required if you look at the calorific value of the coal if you look at the calorific if you want to calculate calorific value of the fuel you will have

to go by this formula 8080C. This C is the %age of carbon +34500(H - O/8) + 2240S). This

is the formula for calculating calorific value right. So, here you can see, that the burning of hydrogen a lot of heat is generated. So, presence

of hydrogen is also required because a lot of heat is generated by burning the hydrogen.

And at the same time you should get a sulphur, sulphur is not required, sulphur is not desired

because some part of heat is added by burner of sulphur also, but sulphur has many harmful

effect in the boiler. It creates the acidic medium and it causes the corrosion and erosion of the boiler so, but in any case hydrogen presence of hydrogen

now from here you can see the presence of hydrogen is very much required in the combustion.

Some in combustible gases are also there like CO2 and nitrogen also is also present right.

Now, after this the most I mean undesired part in the coal is that is ash right. There

are two types of ashes that is the fixed ash and the free ash. The fixed ash has come from

the original vegetable matter. I mean when the coal was found below the earth due to

the formation of the coal the this fixed ash has come into the coal right.

And the free ash it constitutes clay it constitutes shales, it constitutes pyrites and the ashes

undesired because it forms the clinkers. When at around 1,000 degree centigrade the ash it melts and it forms clinker on the coal surface and these clinkers they act as a thermal

barrier. They do not allow heat to be transmitted and sometimes in the in the crate or in the

combustion chamber they block the air passage also. So, DE clinkering is all periodically

required in the boilers, DE clinkering is in periodically required in the boiler.

And another type of analysis of the coal this is proximate analysis. Another analysis of

the coal is ultimate analysis. Normally Orsat apparatus is used for the ultimate analysis

right and ultimate analysis we measure the carbon. Carbon in the coal can be in a range

of 50 to 90 %or more than that it hydrogen ultimate analysis hydrogen it present 2 to

40 %, oxygen 2 to 40 %, sulphur 0.5 to 3 %. But sulphur is not desired as I said earlier

because it causes corrosion and what we will call the formation of the clinkers oh sorry

it also promotes the formation of clinkers in the boiler then nitrogen 0.5 to 7 % and

ash which is 2 to 30 % right. Now, if you classify the coal because there are different

varieties of coal which are available. So, if you take in order of increase in the heat value. So, first comes the peat coal.

It is the lowest quality of coal. It is then comes the lignite coal. Lignite coal there

are lot of lignite mines in India so, lignite coal. Third one is bituminous; bituminous

coal and last one is anthracite coal anthracite coal. There are four types of coals right

if you look at the composition of these coals. Now we will start with the we will we will make a table peat coal, lignite coal, bituminous

coal and anthracite coal starting with the moisture. In peat coal the moisture is 20

%. It can go up to 20 %. Lignite it is up to 15 %, bituminous 2 %, anthracite 1 %. So,

you just see the difference in the moisture, here it is 1 % and here is in 20 %. So, if

you are carrying 100 kg of peat coal effectively you are carrying 80 kg of peat coal only ok. Now, the carbon contents now the carbon is peat coal it is only 43 %, lignite 56 %, it

is 74 % and it goes upto 90 %. So, carbon content of because carbon content decides

carbon contents mainly decide how much heat will be generated by the coal. So, anthracite coal it is it goes up to 90 % here it is 43 % almost half of this. So, if you are burning

2 kg of peat coal it will be equivalent to approximately 1 kg of anthracite coal. Now, hydrogen content it is 6.4 %, 5.7 %, 6 % and 3.3 %. So, anthracite coal has a little

less hydrogen, oxygen 44 %, 32 %, 13 % and 2.5 %. Ash content which is of major concern

it has 4 %, 4.25 %, 4.75 %, 2.97 %. Lower calorific value 13.4 %. Sorry no 13.4

MJ/kg, 10.3 MJ/kg ,low CV MJ/kg. It is 30.5 and it

is 33.5. So, for bituminous and anthracite coal the calorific value is quite high.

Now, after this coal processing is also done which is known as coal benefication, coal

benefication; for example, cleaning of coal. Cleaning of coal is required it can be done

during the mining or post mining also the benefication it can be done for cleaning the

coal the best media is water. So, water jets the coal the coal is clean. So, the best is

water. It helps in removing the sulphur also. The sulphur which is sticking on the surface

of the coal the if you wash the coal with the water the sulphur will be removed.

And there are certain coal cleaning equipment also, I mean it is not simply spraying the water. The coal is put into the cleaning equipment and where the cleaning of coal takes place.

Then coal drying is done because most of the moisture has to be removed from the coal after

washing because unnecessarily the we will be carrying the weight of the coal so, drying has to be done. Then the coal sizing is also important.

Sizing means proper the coal has to be in a particular range for proper burning in the

combustion chamber of the boiler. If the size is too big, incomplete combustion will be there. So, proper sizing of the coal has to be done.

So, for sulphur removal sulphur removal can be done by not only by washing it can be done

by hand picking also. And organic sulphur which is present in the coal which is in built

in the coal it cannot be even it cannot be done any physical process. I mean some chemical

process has to be adopted normally it is not done. Sulphur is removed either by hand picking, cleaning the coal or by cleaning coal with

the water which is sulphur which is sticking on the surface of the coal will be washed away.Now, the for washing the coal it is not simply I as I said earlier it is putting part

or washing with the water, water jigs are used right.

And water jigs are I will I will show draw a sketch. Water jigs are like this. It is

tapering below and this side it is filled with water, it is filled with water right

and here this is put under vibrations and the movement of the fluid is like this right

and small particles they have high density because big size of the coal if the coal size

is big it will have some trapped air also. So, density will be lower right and high density

particles are accumulated at the bottom, low density particles will go up.

So, after stratification here of the low density particles periodically they will be removed,

but what happens slowly density gradient will be formed. You will not know from where to

remove the settlement. Initially you will find a distinct distinction between the high

density and the lower density, but in due course of time with continuous use you will get a get a get a very smooth variation in the density and then it becomes difficult

where from to coal is removed. And for this purpose, if feldspar bed is provided

in the in the cone itself in the cone itself cone itself. A feldspar bed is provided which

separates the low density and high density particles. So, in fact the coal which is used

for the burning will fall in the category of low density fine particles are the high

density particles. So, they have to be removed from the coal. So, that is the one method.

Another method is two stage cyclone. two stage cyclone is also used for separation of I mean

fine particles from the coal. So, that is the stage one. So, that is stage one. This is a cyclone. So, stage one raw coal is they will enter

from here raw coal will enter from this side. High density due to centrifugal force high

density for particles will stick to the surroundings and it they will drain down right and the

low density particles they will go up with the swirl and leave the cyclone. No they will

leave the cyclone and they will be collected somewhere else. So, the hard density the high density particles they will again go to another cyclone right.

And secondary process is done and here also those particles which are refused they will

come here and they will drain down here; because as they are draining from here they will drain

down here and this will go this part will go again here and again it will be processed.

So, it is a two way two stage separation of high density low density particles. We need

low density low density coal or particles which is low.

So, first the raw coal will enter it will go the first cyclone to do centrifugal process

because small particles are high density. They will stick to the surface of the cyclone

and they will be drained from the bottom. Coal which is low density big size particles

which are which we require they will leave from the center with the swirl will go up and they will be accumulated at one place. This is excepted lot.

Now, again the exit of this is low density high density particles leaving the first cyclone

they will enter second cyclone ok. Again they will be filtered and the low density particles

they will not be accepted initially they will go back again for the same process right. So, there is a two stage process of clearing the coal.

Now, what are the advantages of preparation of the coal? The advantages of number one

transportation cost is reduced, if we refine the coal then coal if we do the preparation

of the coal the transportation cost is reduced. Quality of the coal is improved quality of

the coal is improved. Boiler performance of the boiler performance is also improved. Fourth

is less ash less ash has to be handled; because ash handling is also a big issue in the thermal

power plant nowadays because it causes the pollution. So, less ash will have to be handled

in the boiler power plant. Now, sulphur removal have its one advantages because sulphur is also not desirable because it has corrosive nature. So, that is also

that is the benefit of having the coal preparation. Now, blending of coal is also because we do

not get coal from the same source. We are getting coal from different sources in the

thermal power plant right. So, if we inject one coal for one source the efficiency of

the boiler is different from the from the fact that when we inject coal from another source right. So, in order to have uniform performance of

the boiler blending of the coal is done blending of the coal is done. So, the for

coal blending let us say we have coal from 10 sources right. So, we will take part of

say 5 % or 10 % from all source and mix them and feed to the boiler. So, say one source

we have very superior coal another source we have a little I mean inferior coal. So,

by mixing we will get some average performance and this performance because for the boiler maintaining constant performance is important right.

So, the boiler perform so the system also remains in balance. So, for that purpose the

blending of coal is done. There are several methods bed blending on a bed the blending

is done, on a conveyor belt also the blending is done and there are automatic blending is

also done. I mean their machines where we can say 5 % of a coal, 10 % b, 20 % c automatically

it will blend the coal, but coal blending is important and unavoidable.

Nowadays, there is a another type of oil is available which is known as shale oil. You

must have heard oil shale. They are carbanions rocks. Shale oil because shale oil nowadays

it has been discovered abundance in USA. Shale gas they call it shale gas and shale oil and

that is why it is affecting the other methods of power generation like nuclear power or

the coal based power plants. So, it is a carbonic rock and the from carbonic rocks cracking

is done cracking is done around 400 to 500 degrees centigrade.

So, after cracking the oil is extracted from the rocks. It is known as shale oil it is

very popular point of discussion because shale gas, shale oils has been discovered in abundance

in USA, it is a discovered in Canada and Brazil also. And this is hampering the progress of

other fuel based industries; because the government is switching to the oil shale because it is I mean the extraction is cheaper right. And another is tar sand. This is again bituminous

sand oil. This is also getting the fuel the sand oil sand oil is especially in the Canada

a lot of sand oil has been discovered and the oil companies are focusing there for the extraction of the sand oil. It is known as tar sand.

So, switching from now let us go back to the switching of oil based power plants to the

coal based power plants. So, there is a hybrid type of technique which is known as where

slurry emulsion type of fuel is used. Emulsion is made between oil and the fine particles

of coal right and this emulsion is fed into the oil based power plants right and used

for power generation. The benefit of is because if you change from oil base to the coal based

power plant a capital investment is required first of all it is storage cold storage coal handling for this capital investment has to be made. So, instead of that a slurry is made

emulsion slurry is made with oil with the coal oil and coal. So, these this capital cost investment can be reduced. It is a it is a sort of a hybrid

type of arrangement. And advantage is immediate shift improves the quality of the burn first

of all it improves the quality of the burn. It keeps the boiler clean because even if

you burn the oil boiler is cleaner, but if you mix the coal with the oil if you use some slurry also the boiler remains clean, pollution is reduced right and increases the efficiency

increases. And fourth is and the fifth is which is very important existing pumps and

pipelines. Pumps may have to be replaced because we are dealing with the slurry, but the pipelines

existing pipelines can be used for the movement of slurry right. Now, slurry emulsion mixture they are different type of mixture like coal oil, mixtures which

is known as COM coal water mixture is also there C sorry CWM coal oil, coal water coal

methane right CMM. So, slurry emulsion type of fuel is also used in power plants . That

is all for today. Thank you very much.