Ultimate Analysis – Constituents of coal

Fossil Fuel Engineering – ERG 252 (1+1)

S.Vignesh – BTG-12-037

Introduction

A fossil fuel, coal forms when dead plant matter is converted into peat, which in turn is converted into lignite, then sub-bituminous coal, then bituminous coal, and lastly anthracite. This involves biological and geological processes that take place over a long period of time. Heat and pressure acts on it to finally convert into coal.

Ultimate Analysis

• Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulphur, oxygen, nitrogen.

• Ultimate analysis is also known as elemental analysis, it is the method to determine the Carbon,Hydrogen,Nitrogen,Sulphur and Oxygen content present in solid fuel.

Need For Analysis• It is essential to understand the properties of

biomass materials to evaluate their utility• As chemical feedstock's and also design suitable

gasifies systems. The analysis is carried out to find the oxygen required for combustion for efficient production of energy.

• Two types-proximate and ultimate analysis• Proximate-it determines moisture content,

volatile matter, ash and fixed carbon content of a fuel. It is reported as dry weight.

Determination of carbon & hydrogen

• About 0.2g of accurately weighed coal is burnt in oxygen in apparatus shown above.

• CCO2 & HH2O• KOH & CaCl2 absorb CO2 & H2O respectively.• Increase in weights of the tubes are noted.

% of C:increase in weight of KOH tube*12*100 weight of the coal sample taken*44

% of H:Increase in weight of CaCl2 tube*2*100 weight of coal sample taken*18

Determination of Nitrogen

• 1g of accurately weighed powdered coal is heated with conc.H2SO4 in kjeldahl flask.

• It is treated with excess KOH.

• Liberated ammonia is distilled over and absorbed in a known volume of standard solution of acid.

• Unused acid is determined by back titration with standard NaOH.

% of N is volume of acid used*normality*1.4

weight of coal sample taken

Determination of sulphur

• Sulphur is converted into sulphate.• The washings are treated with BaCl.• BaSO4 is precipitated.• Precipitate is filtered, washed and heated to

constant weight.• % of S= weight of BaSO4 obtained*32*100 233*weight of coal sample taken

Determination of ash and oxygen

• Coal sample of accurate weight in a crucible is heated in muffle furnace at 700+50 degree Celsius for ½ an hour. Crucible is taken out and cooled first in air and then in desiccators and weighed.• % of ash = weight of ash left*100 weight of coal taken• % of oxygen is 100-percentage of (O+H+S+N+Ash)

carbon hydrogen oxygen nitrogen Sulphur

55-60 6-6.5 30-35 1.5-2 0.6-1

Peat

Carbon hydrogen Oxygen nitrogen Sulphur

70-73 4.6-5.5 22-26 0.6-1.0 0.6-1.5

Lignite

Carbon Hydrogen Oxygen

80 6 15

Bituminous

Carbon Hydrogen Oxygen

93 4 3

Anthracite

• Fixed carbon+carbon present in volatile matter• High total carbon represents high calorific

value of the fuel.

Hydrogen• It increases calorific value-H2 remains as coke

oven gas• Associated with volatile matter of coal• Peat to bituminous contains 4.5-6% H2• Anthracite contains only 1-2%

Nitrogen• Present up to 1-3%• Comes from protein us matter in vegetable matter.• Inert nitrogen decreases calorific value.• As coal matures, extractable nitrogen decreases.• Its proportion does not depend on rank.• It varies from 1-2% in all.

Sulphur• It increases calorific value but is undesirable.• Its oxidization product in presence of moisture cause

corrosion of equipment and pollution.• When used in steel making it badly affects properties of

iron and steel.• Sulphur exists in 3 forms-pyritic, organic & sulphate• World coal contains 1 to 3% sulphur.

Oxygen• Less the oxygen-better is the coal.• Decreases from lignite to anthracite.• As oxygen content increases, moisture holding

capacity increases and caking power decreases.

Phosphorus• Undesirable in metallurgical as it badly affects

properties of metals.• Indian coking coals have less than 0.15%

phosphorus.

Fuels % C % H % O % N % S % Ash

Peat 23 10 59 1.5 0.5 6

Lignite 42 7 43 1 1 6

Bituminous 77 5 5 1.5 0.5 11

Sub-Bituminous

59 6 29.5 1 0.5 4

Semi-Anthracite

80 3.5 4.5 1.5 0.5 10

Anthracite 86.5 2.5 3 0.5 0.5 7

Ultimate Analysis – Constituents of Coal

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