Experiment on moisture content in Coal

EXPERIMENT NO : 4 AIM : Determine the moisture and ash content in a given coal sample. THEORY : Coal is a fossil fuel which occurs in layer in the earth crust. It has been formed by the partial decay of plant material accumulated million’s years ago and further altered by the action of heat and pressure. Coal is highly carbonaceous matter and an important fuel. The process of conversion of wood into coal can be represented as – WOOD →

PEAT

→

LIGNITE

→

BITUMINOUE → ANTHRACITE

The coal is classified accordingly to the rank which measure of the change it has undergone in the transition from wood to anthracite. Peat, the youngest phase has the lowest rank and anthracite has a high rank. The classification according to rank is largely based on the carbon content. The composition of coal varies widely and hence it is necessary to analyze and interpret the results from the point of view of commercial classification, price fixation and proper industrial utilization. The following methods of analysis can be used for the selection of coal. 1.

THE PROXIMATE ANALYSIS : Which includes the determination of moisture, volatile matter, ash and fixed carbon. This gives quick and valuable information regarding commercial classification and determination of suitability for a particular industrial use.

2.

THE ULTIMATE ANALYSIS : Which includes the estimation of ash, carbon, hydrogen and sulphur, nitrogen and oxygen. The ultimate analysis is essential for calculating heat balance in any process for which coal is employed as a fuel.

SIGNIFICANCE OF PROXIMATE ANALYSIS : a)

MOISTURE: -

Increases the transport cost.

-

Reduces the calorific value.

-

Considerable amount of heat is wasted in evaporating the moisture during combustion. Hence, high % of moisture is undesirable.

2

b)

VOLATILE MATTER : -

The volatile matter is not a constituent of coal, but consists of a complex mixture of gaseous and liquid products resulting from the thermal decomposition of the coal substances.

-

The volatile matter content of a coal is related to the length of the flame, smoke forming tendency and the ignition characteristic.

-

High volatile matter coal gives long flames, high smoke and relatively low heating values.

-

Coal with low volatile matter content burns with shorter flame. Thus the higher volatile matter content the larger the combustion space required. Hence the volatile matter content of coal influences the furnace design.

-

High volatile matter content coal is preferable in coal gas manufacturing and in carbonization plants, particularly when the main objective is the by – product recovery.

-

For manufacturing metallurgical coke, a coal with low volatile matter content and high fixed carbon is preferred.

-

It is important to note that, volatile matter % gives some idea about coking property of the coal .

c)

ASH : -

Ash is useless and non combustible matter, usually consists of silica, alumina, iron oxide and small quantity of lime, magnesia etc. its composition is of considerable importance in metallurgical operations. As it affects the slag, metal composition and consequently its prime consideration in selecting the flux.

-

It decreases the heating value of a coal.

-

It may forms clinkers during burning, clinkers may block interspace of the grate on which coal is being burnt.

-

It also increases the cost of storage, handling and disposal of ash.

3

-

d)

It also causes early wear of furnace wall and burning apparatus.

FIXED CARBON : -

Higher the % of fixed carbon greater is its calorific value and better the quality of coal.

-

From fixed % of carbon design of fire box, furnace can be decided.

PROCEDURE FOR PROXIMATE ANALYSIS : 1. -

MOISTURE : Moisture is generally determined by heating a known quantity of air dried coal from 105 to 110 0C for one hour and calculating the loss in weight as percentage.

-

Take about 1.0 gm of the air dried coal sample in a previously weighted silica crucible.

-

Heat the partially covered silica crucible in an electric oven at a temperature of 105 to 110 0C for one hour.

-

Cool the crucible first in air and then in a desicator. Weight the crucible. The loss in weight corresponds to the moisture.

2. -

ASH : Weight about 1 gm of the finely powdered air dried coal sample in a previously weight silica crucible.

-

Place the crucible without lid on a pipe clay triangle and heat carefully in muffle furnace at 700 ± 50 0C until all the carbonaceous matter is burnt off; stir the residue and ignite it for 30 minute. Cool first in air and then in a desicator and weight.

-

Repeat ignition, cooling and weighing till a constant weight is obtained. Note the constant weight.

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OBSERVATION AND CALCULATION : 1.

MOISTURE : i)

Weight of the empty crucible = W1 = ------------gm.

ii)

Weight of the crucible + Coal sample = W2 = ----------gm.

iii)

Weight of the crucible + Coal sample, after heating = W3 = ---gm.

∴ % of moisture = W2 – W3 / W2 – W1 x 100 = -------------- % 2.

ASH : iv)

Weight of the empty crucible = W4 = ------------gm.

v)

Weight of the crucible + Coal sample = W5= ----------gm.

vi)

Weight of the crucible + Coal sample, after heating = W6= ---gm. ∴ % of ash

= W5 – W6 / W5 – W4 x 100 = -------------- %

RESULT : 1)

Percentage of moisture = ------------ %

2)

Percentage of ash

= ------------ % D. V .NIGHOT ( LECTURER IN CHEMISTRY )