(C) Dr. Payal Joshi

` Substances that undergo combustion in presence of air to produce a large amount of heat

` Used economically for domestic & industrial purpose like heating & generation of power

(C) Dr. Payal Joshi

(C) Dr. Payal Joshi

` High calorific value: Amount of heat liberated & temperature attained thereby depends on the calorific value

` Moderate ignition temperature: ◦ Ignition temperature: Lowest temperature at which the fuel

must be pre-heated so that it starts burning smoothly ◦ Low Ignition temperature– dangerous for storage, transport–

fire hazard ◦ High Ignition temperature—difficulty in igniting fuel– safe

during storage ` Ideal fuel with moderate Ignition temperature

(C) Dr. Payal Joshi

` Low moisture content ◦ Presence of moisture content of fuel reduces heating value

` Low non-combustible matter content ◦ Non-combustible matter (ash) remains cause reduction in

heating value ` Products of combustion - Objectionable gases– CO, SO2,

H2S, PH3

` Easy control on combustion: Spontaneous ignition lead to fire hazard

` Low cost, easy to transport ` Fuel should burn in air without smoke formation

(C) Dr. Payal Joshi

` Total quantity of heat liberated by burning a unit mass or volume of fuel completely

` Gross calorific value (High calorific value) ◦ GCV/HCV ◦ Total amount of heat produced when a unit mass/volume

of fuel is burnt completely & products of combustion is cooled to room temperature (150C or 60oF)

(C) Dr. Payal Joshi

` Calorific value of fuels is determined theoretically by Dulong’s Formula (Dulong-Petit’s formula)

Where, C, H, O, S are % of Carbon, Hydrogen, Oxygen and Sulfur respectively

𝐆𝐂𝐕 =𝟏

𝟏𝟎𝟎 𝟖𝟎𝟖𝟎 × 𝐂 + 𝟑𝟒𝟓𝟎𝟎 𝐇 −𝐎𝟖 + 𝟐𝟐𝟒𝟎 × 𝐒 𝐤𝐜𝐚𝐥/𝐤𝐠

(C) Dr. Payal Joshi

` Net Calorific value/ Low Calorific value ` NCV/LCV ` Net heat produced when unit mass/volume of

fuel is burnt completely and products are permitted to escape

NCV = GCV– 0.09 u % H u 587 cal/g or kcal/kg

𝐍𝐂𝐕 = 𝐆𝐂𝐕 − 𝟗 ×𝐇 %𝟏𝟎𝟎 × 𝐥𝐚𝐭𝐞𝐧𝐭 𝐡𝐞𝐚𝐭 𝐨𝐟 𝐬𝐭𝐞𝐚𝐦

(C) Dr. Payal Joshi

` British Thermal Unit (B.T.U/lb): Heat required to raise the temperature of one pound of water from 60qF to 61qF.

` Calorie: Heat required to raise the temperature of one kg of water from 15qC to 16qC.

(C) Dr. Payal Joshi

Bomb Calorimeter

(C) Dr. Payal Joshi

` Let x = mass in g of fuel taken in crucible ` W = mass of water in calorimeter ` w = water equivalent in g of calorimeter, stirrer, thermometer,

bomb etc. ` t1 & t2 are initial & final temperatures of water in calorimeter ` L = HCV of fuel in cal/g or kcal/kg ` Then heat liberated by burning of fuel = xL ` Heat absorbed by water & apparatus = (W+w) (t2-t1) ` But heat liberated = heat absorbed ` so, xL = (W+w)(t2-t1) On Rearranging the above expression,

` GCV (L) = 𝑾+𝒘 (𝒕𝟐−𝒕𝟏)𝒙

cal/g or kcal/kg

(C) Dr. Payal Joshi

` If H = % of hydrogen in fuel ` 9H/100 g = mass of water from 1 g of fuel= 0.09H g ` So heat taken by water in forming steam = 0.09H×587cal/g ` LCV = HCV - 0.09 H × 587 cal/g or kcal/kg ` By considering fuse wire correction, acid correction &

cooling correction L = [{(W+w)(t2-t1+ cooling corr)}- {acid +fuse corr}]

x Units : cal/g or kcal/kg

(C) Dr. Payal Joshi

(C) Dr. Payal Joshi

Proximate analysis is easy and quicker and it gives a fair idea of the quality of coal.

Ultimate analysis is essential for calculating heat balances in any process for which coal is employed as a fuel.

(C) Dr. Payal Joshi

` Determination of Moisture content 1 g air dried powdered coal in Si Crucible 1 Heat in hot air oven (105-1100C) for

1 hr

Cool and determine loss in weight

% of moisture = Loss in weight x 100 weight of coal sample taken

High percentage of moisture reduces the calorific value of coal It quenches fire in the furnace Lesser the moisture content, better the quality of fuel

(C) Dr. Payal Joshi

` Determination of volatile matter

Moisture free coal from Step 1 is taken in the Crucible 2. Cover it with a lid partially

Placed in muffle furnace Heated to 925 +/- 200C for 7 min

Cooled in air, desiccated & weighed again Loss of weight as volatile matter on % matter

% Volatile Matter = (Loss in weight due to removal of volatile matter / weight of coal sample taken) x 100

Volatile matter present in form of combustible gases like H2, CH4 & lower hydrocarbons Presence of VM gives long flames, high smoke, relatively low heating Higher the VM, greater the combustion space required– dictates the furnace design

Lesser the VM, better the rank of coal

(C) Dr. Payal Joshi

` Determination of Ash

Residual coal in Crucible 2 Heated at 700 – 750C for 30 min

Cooled in air, desiccated Heating and cooling repeated Until a constant weight of residue is obtained

% of Ash = (Weight of residue left/weight of coal taken) x 100

Presence of ash reduces calorific value of coal Lower the ash content, better the quality of coal

(C) Dr. Payal Joshi

` Determination of Fixed Carbon

% of Fixed Carbon =100 - % of (Moisture + VM + Ash)

Higher the % of Fixed carbon, greater the calorific value of coal, better the quality of coal It is this Fixed carbon that burns in solid state Helps in determining the furnace design

(C) Dr. Payal Joshi

Carbon and Hydrogen ` 1-2 g coal (pre-weighed) burnt in current of O2. ` C + O2 Æ CO2 ; 2H2 + O2 Æ 2H2O

Combustion Apparatus

Combustion gases absorbed in KOH & anhy. CaCl2. Increase in weight of KOH represents weight of CO2 Increase in weight of CaCl2 represents weight of H2O

(C) Dr. Payal Joshi

% Carbon =Increase in wt of KOH bulb × 12

wt of coal sample × 44 × 100

% Hydrogen =Increase in wt of CaCl2 bulb × 2

wt of coal sample × 18 × 100

(C) Dr. Payal Joshi

` Determination of Nitrogen ◦ 1 g powdered coal heated with H2SO4 & K2SO4 in flask ◦ Clear solution treated with excess of KOH/NaOH; Liberated NH3

distilled over acid solution ◦ Unused acid back titrated against NaOH. From volume of acid used

by liberated NH3, % N can be estimated

(C) Dr. Payal Joshi

Mass of Coal = X gm Volume of acid in which NH3 is passed = V1 ml Volume of acid unused = V2 ml Volume of acid consumed by NH3 = (V1-V2) ml 1000 ml of 1N HCl ≡ 1 mole of NH3 ≡ 14 g of N2

Thus, (V1 – V2) ml of 0.1 N HCl = 14 × (V1-V2) × 0.1 g of N2

1000 x 1 X g of coal sample contains = 14 × (V1-V2) × 0.1 g of N2

1000 x 1

% 𝑵 = 𝟏𝟒 𝑽𝟏−𝑽𝟐 𝑵𝒐𝒓𝒎𝒂𝒍𝒊𝒕𝒚 𝒐𝒇 𝑯𝑪𝒍 𝟏𝟎𝟎𝟎 𝒙 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒄𝒐𝒂𝒍 𝒔𝒂𝒎𝒑𝒍𝒆 𝑿𝒈

x 100

(C) Dr. Payal Joshi

` Determination of Sulfur ◦ Known amount of coal burnt in bomb calorimeter in a

current of oxygen ◦ Sulfur gets oxidized to sulfates ◦ Acid extract treated with BaCl2 Æ BaSO4 ppt formed ◦ BaSO4 ppt filtered, washed, dried and heated until

constant weight

% 𝐒𝐮𝐥𝐟𝐮𝐫 =𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐁𝐚𝐒𝐎𝟒 𝐩𝐩𝐭 × 𝟑𝟐

𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 × 𝟐𝟑𝟑 × 𝟏𝟎𝟎

(C) Dr. Payal Joshi

` Ash determination as per proximate analysis ` Oxygen Determination % Oxygen = 100 – percentage of (C+H+N+S+ash)

Significance: •Higher % of C & H : Greater calorific value of coal; better is the quality of coal •Higher % O, lower is calorific value. •% of S, though contributes to calorific value, is undesirable due to polluting properties as it forms SO2 on combustion.

(C) Dr. Payal Joshi

` Combustion is a process in which oxygen from the air reacts with the elements or compounds to give heat.

` As the elements or compounds combine in indefinite proportions with oxygen, we need to calculate minimum oxygen or air required for the complete combustion of compounds.

(C) Dr. Payal Joshi

` From the equations, quantity of oxygen & air can be calculated for complete combustion of fuels

1. C + O2 o CO2 2. 2H2 + O2 o 2H2O 3. S + O2 o SO2 4. 2CO + O2 o 2CO2 5. CH4 + 2O2 o CO2 + 2H2O 6. 2C2H6 + 7O2 o 4CO2 + 6H2O 7. C2H4 +3O2 o 2CO2 + 2H2O 8. 2C2H2 + 5O2 o 4CO2 + 2H2O 9. C3H8 + 5O2 Æ 3CO2 + 4H2O CO2, moisture, Nitrogen, ash do not take part in combustion-Ignore these factors while solving

(C) Dr. Payal Joshi

Weight of air required for complete combustion of fuel = 100/23 [C × 32/12 + H × 32/4 +S × 32/32 – O] Volume of air required for complete combustion of fuel= 28.94 g of air = 22.4 litres of volume of air at NTP

(C) Dr. Payal Joshi

` Petroleum/ Crude Oil (petra = rock, oleum = oil) ` Dark, greenish-brown viscous oil found in deep

Earth crust ` Mainly composed of various hydrocarbons ` Crude Oil Æ Unprocessed petroleum

(C) Dr. Payal Joshi

` Petroleum resulted from partial decomposition of marine animals, vegetable organisms from prehistoric forests.

` Changes in Earth (volcanic eruptions) had buried these materials underground—subjected to intense pressure & heat during ages of time.

` Conversion of these materials into various hydrocarbons has been on either under the influence of radioactive substances (Uranium) or by bacterial decomposition in anaerobic conditions.

(C) Dr. Payal Joshi

Petroleum floats over salt water (brine) and natural gas (CH4=70-90%, C2H6=5-10%, H2=3%, CO+CO2=rest) surrounds the porous rocks containing petroleum (Crude oil). Hydraulic pressure of natural gas allows gushing of petroleum from the Earth’s crust to the surface conveyed thro’ pipelines to refinery.

(C) Dr. Payal Joshi

` Problem with Crude Oil: It contains hundreds of different types of hydrocarbons; all mixed together.

` You have to separate different types of hydrocarbons to have useful fractions

` Different hydrocarbon chain lengths have progressively higher boiling points, so they can be separated by distillationÆ Fractional Distillation

(C) Dr. Payal Joshi

` Step 1: Separation of Water (Cottrell’s Process) ` Crude oil is an emulsion of oil & salt water ` Process of freeing oil from water involves passing

crude oil to flow between two highly charged electrodes ` Colloidal water droplets coalesce to form larger drops

which separate from oil ` Step 2 : Removal of harmful sulfur compounds ` Oil + CuO Æ CuS (removal by filtration)

(C) Dr. Payal Joshi

` Step 3: Fractional Distillation ` Crude oil heated to about 400C in

iron retort ` Hot vapors passed into

fractionating column ` Continuous contact of vapors

and liquid at bubble caps ` Substance with lowest bp will

condense at highest point in column;

` Substances with higher bps. will condense lower in the column

(C) Dr. Payal Joshi

Name of Fraction Boiling Range Approx comp of hydrocarbons

Uses

Uncondensed gas < 300C C1-C4 Domestic fuel (LPG)

Petroleum ether 30-700C C5-C7 Solvent Gasoline/Petrol 40-1200C C5-C9 Motor fuel, solvent Naphtha/Solvent

Spirit 120-1800C C9-C10 Solvent

Kerosene Oil 180-2500C C10-C16 Engine oil, laboratory gas preparation

Diesel Oil/Fuel Oil 250-3200C C15-C18 Diesel engine fuel Heavy Oil 320-4000C C17-C30 For getting gasoline by

cracking process Lubricating oil - - Lubricant Petroleum jelly - - Cosmetics, medicine

Grease - - Lubricant Paraffin Wax - - Candles, boot polish

Residue (asphalt) >4000C C30 & above Water proofing Petroleum coke Fuel

(C) Dr. Payal Joshi

Chemical Processing Rather than continually distilling large quantities of

crude oil, oil companies chemically process some fractions from the distillation column to make gasoline

` One can change the fractions from distillation as follows: oBreaking large hydrocarbons into smaller pieces

(cracking) oCombining smaller pieces to make larger ones

(unification) oRearranging various pieces to make desired hydrocarbons

(alteration)

(C) Dr. Payal Joshi

` Decomposition of bigger hydrocarbon molecules into simpler valuable lower boiling hydrocarbons of lower MW

` Process of thermal/catalytic decomposition Æ Cracking

` Objective: To obtain greater yields of improved gasoline. Cracked gasoline gives better engine performance

` Higher saturated hydrocarbons are converted to simpler molecules like paraffinic & olefinic hydrocarbons, eg,

(C) Dr. Payal Joshi

Thermal Cracking ` Heavy oil is subjected to high temperature & pressure until

they break apart to lower hydrocarbons ` Yield is generally from 7-30%

◦ Liquid phase cracking ◦ Vapor phase cracking

Catalytic Cracking ` Uses catalyst to speed up the cracking reaction at much

lower temperatures & pressures (300C-4500C; 1-5kg/cm2) ◦ Fixed Bed catalytic cracking ◦ Fluid Bed/ Moving bed catalytic cracking

(C) Dr. Payal Joshi

Liquid Phase Cracking ` Heavy oil/gas oil is cracked at 420-5500C at pressure of

100 kg/cm2

` Cracked products are separated in fractionating column.

Vapor phase cracking ` Oil is first vaporized & then cracked at 600-6500C at

pressure of 15-20 kg/cm2

(C) Dr. Payal Joshi

` T =425-4500C; P = 1.5 kg/cm2

` Catalyst : Artificial Clay and ZrO ` Pure Gasoline

(C) Dr. Payal Joshi

` Catalyst is kept agitated by vaporized heavy oil feed stock and can be pumped as a fluid. This allows close contact between catalyst & reactant, resulting in efficient reaction

` T= 5300C at P = 3-5 kg/cm2

` Catalyst regenerated (600C) ; pure gasoline obtained (C) Dr. Payal Joshi

• Process of bringing about structural modifications in the components of straight run gasoline (direct obtained on distillation)

• Primary objective of improving its anti knock characteristics.

• Aromatization : Conversion of open chain (aliphatic) hydrocarbons and/or cycloalkanes in presence of a catalyst, into aromatic hydrocarbons (arenes) containing the same number of carbon atoms.

• It is carried thermally (T=500-6000C at P=85 atm) or catalytically [Pt (0.75%) supported over Alumina (T=460-5300C, P=30-35 atm)].

(C) Dr. Payal Joshi

(C) Dr. Payal Joshi

` Knocking Æ related to the internal combustion engine working on petrol.

` Four stroke engine: Intake, compression, combustion and exhaust (Otto cycle)

` Mixture of gasoline vapors and air is compressed and ignited by electric spark.

` Due to combustion, gases are formed which moves the piston down the cylinder.

` The movement of the piston must be even/uniform without any vibration.

(C) Dr. Payal Joshi

` Sometimes, pressure of piston causes air and fuel mixture to ignite prematurely during compression cycle creating uneven movement of the piston with rattling noise in the engine.

` It is called as knocking of the engine.

` Knocking results in the loss of efficiency of I.C. engine & damage to the piston and cylinder

(C) Dr. Payal Joshi

` Petrol is a mixture of various lower hydrocarbons and the knocking of the engine depends upon the structure of hydrocarbons, present in petrol.

` Thus, tendency of gasoline to knock is in the following order,

Straight chain paraffins > Branch chain paraffins > Olefins > Cycloparaffins > Aromatics.

(C) Dr. Payal Joshi

Octane number of a fuel is defined as, the percentage of iso-octane in a mixture of iso-octane and n-heptane that has the same knocking characteristics as the fuel under question.

(C) Dr. Payal Joshi

Sr. No.

Parts of Octane

Parts of n-heptane

Knocking Octane Number

1. 100 Zero Minimum 100 2. Zero 100 Maximum Zero 3. 78 22 Moderate 78

4. 85 15 Less 85

Antiknocking Agents/Compounds : Antiknocking agents are the compounds which help to increase the octane number of the fuel or decreasing the knocking. By the addition of these agents, the gasoline/ petrol can be improved in its quality. Some of the compounds used are TEL, i.e. Tetra Ethyl Lead [(C2H5)4 Pb].

(C) Dr. Payal Joshi

` Petrol whose octane number is increased without addition of lead compounds is called unleaded petrol.

Methyl tertiary butyl ether (MTBE) ` MTBE is most preferred since, it contains oxygen in

form of ether group and supplies oxygen for the combustion of gasoline in the IC engines

` This reduces extent of peroxy compound formation & it increases contents of molecules having branched and aromatic ring structures.

(C) Dr. Payal Joshi

` Compression ignition engines- no spark plug

` Air is pumped in suction stroke and compressed till 5000C.

` Fuel is then injected into the engine, vaporizes and undergoes self-ignition and burns.

` If there is lag between vaporization and combustion – ignition delay-diesel knock

(C) Dr. Payal Joshi

` Cetane number (performance of diesel engines) is

defined as percentage by volume of cetane in a

mixture of cetane and D-methyl naphthalene

which exactly matches in its ignition delay

characteristics with the diesel under test

` Cetane value of diesel can be improved by adding

about 2% doping substances like ethyl nitrite, isoamyl

nitrite and acetone peroxide

(C) Dr. Payal Joshi

Sr. No

Parts of Cetane C16H34

Parts of D-methyl Naphthalene

Ignition Delay Cetane Number

1. 100 Zero Minimum 100

2. Zero 100 Maximum Zero

3. 55 45 Moderate 55

4. 45 55 Moderate 45

(C) Dr. Payal Joshi

` Natural gas compressed to high pressure of 1000 Atm. ` Steel cylinder containing 15kg of CNG contains about

2x104 l of natural gas at 1 Atm pressure ` Calorific value of 13000 kcal/m3

` Substitute to petrol, diesel ` During combustion, no C, S or N gases released. No

unregulated pollutants – smoke, SO2, SO3, benzene, HCHO, hence CNG is considered as better fuel for automotives

(C) Dr. Payal Joshi

` Mixture of n-butane, isobutane, butylene and propane (trace of organic sulfides – mercaptans- to identify leak)

` It is bottled gas supplied under pressure in cylinders. ` Calorific value = 27,800 kcal/m3 ` Used as domestic & industrial fuel ` Odorless, colorless gas ` Explosive range of 1.8% to 9.5% volume of gas in air.

This is considerably narrower than other common gaseous fuels- making it hazardous gas

` Auto-ignition temperature of LPG is around 410-580 deg. C and hence it will not ignite on its own at normal temperature.

(C) Dr. Payal Joshi