Energy Sources - Comprehensive Notes

ENERGY SOURCES

• Fuel contains mainly carbon ('C') which undergoes combustion, liberating large amounts of heat energy.

• Fuel + Combustion -> Heat energy + Light energy + Combustion products

• $C + O<em>2 \rightarrow CO</em>2 + \text{heat}$

• Combustion is burning a substance (in the presence of $O_2$) or oxidation of a compound; it's exothermic

CLASSIFICATION OF FUELS

• Primary or Natural Fuels
  • Solid: Wood, coal, lignite
  • Liquid: Crude oil
  • Gaseous: Natural gas
• Secondary or Derived Fuels
  • Solid: Coke, charcoal, petroleum
  • Liquid: Petrol, kerosene, diesel
  • Gaseous: Coal gas, water gas, biogas

Characteristics of a good fuel

• High Calorific Value
• Moderate ignition temperature
• Low moisture content
• Low non-combustible matter
• Combustion products should not be harmful
• Low cost
• Easy to transport
• Should undergo spontaneous combustion
• Should leave less carbon residue

SOLID FUELS

• Coal: Found in the Earth's crust; formed from plants subjected to high temperature and pressure, and bacterial action.

• Coal Classification: WOOD -> PEAT -> LIGNITE -> BITUMINOUS COAL -> ANTHRACITE COAL

• Coalification: Process of conversion of wood to coal

• Carbonification: Process of conversion of wood to charcoal

• Charcoal: Used to absorb gases and for discoloration of sugar.

Ranking of Coal (Based on Carbon, Hydrogen, Moisture, Calorific Value)

• Dry Wood

  • Carbon: 48-50 %
  • Oxygen: 42-44 %
  • Hydrogen: 5-6%
  • Traces of minerals
  • Calorific value: 4000-4500 Kcal /Kg

• FUEL % of Carbon Calorific Value ( Kcal) Main application

• Wood 50 4000-4500 Domestic Fuel

• Peat 50-60 4125-5400 If deficiency of high rank coal is prevailing

• Lignite 60-70 6500-7000 Steam generation in thermal power plant , production of producer gas

• Bituminous 80-90 8000-8500 Making of coal gas , metallurgic coke , steam generation

• Anthracite 90-98 8650-8700 Households , metallurgic where no smoke and high heat is required

Analysis of Coal

• Helps in ranking, price fixation, commercial classification, industrial utilization, etc.
• The quality of coal can be analyzed via proximate and ultimate analysis

Proximate Analysis

• Determines moisture, volatile matter, ash, and fixed carbon.

• Determination of Moisture Content

  • A known amount of powdered coal is taken in a crucible.
  • The crucible is placed in an electric hot air-oven at $105^o$ to $110^oC$ for 1 hour.
  • The crucible is then cooled and weighed.
  • The weight loss provides information about moisture.
  • \text{% of moisture} = \frac{\text{Weight loss due to moisture}}{\text{Weight of sample}} \times 100
  • Lesser moisture content indicates better fuel quality.

• Determination of Volatile Matter

  • The moisture-free coal sample is taken in a crucible, covered with a lid, and placed in a muffle furnace at $950^oC$ for 7 minutes.
  • Then cooled and weighed again.
  • Loss in weight indicates the presence of volatile matter.
  • \text{% of volatile matter} = \frac{\text{Loss in weight due to volatile matter}}{\text{Weight of sample}} \times 100
  • Low quantity of volatile matter indicates better coal quality.

• Determination of Ash Content

  • The residual coal sample is heated without a lid in a muffle furnace (in the presence of air) at $750^oC$ for an hour.
  • The process of heating, cooling, and weighing are repeated until a constant weight is obtained.
  • \text{% of ash} = \frac{\text{Weight of ash}}{\text{Weight of sample}} \times 100
  • Ash is a non-combustible substance that reduces the calorific value; low ash content is desirable.

• Determination of Fixed Carbon: Determined indirectly.

  • \text{% of fixed carbon} = 100 - (\text{% of moisture} + \text{% of volatile matter} + \text{% of ash})
  • Greater calorific value corresponds to a higher percentage of fixed carbon.

Ultimate Analysis

• Measures C, H, N, S, and O.
• Carbon and Hydrogen: Coal sample is burnt in oxygen, converting C and H into $CO<em>2$ and $H</em>2O$ respectively.
  • The gaseous products are absorbed in KOH and $CaCl_2$ tubes of known weights.
  • $C + O<em>2 \rightarrow CO</em>2$
  • $2KOH + CO<em>2 \rightarrow K</em>2CO<em>3 + H</em>2O$
  • $H<em>2 + \frac{1}{2}O</em>2 \rightarrow H_2O$
  • $CaCl<em>2 + 7H</em>2O \rightarrow CaCl<em>2 \cdot 7H</em>2O$
  • $\% \text{ of Carbon } = \frac{\text{Increase in weight of KOH tube}}{\text{Weight of coal sample}} \times \frac{12}{44} \times 100$
  • $\% \text{ of Hydrogen } = \frac{\text{Increase in weight of } CaCl_2 \text{ tube}}{\text{Weight of coal sample}} \times \frac{2}{18} \times 100$
• Determination of Nitrogen
  • Powdered coal is heated with concentrated $H<em>2SO</em>4$ and $K<em>2SO</em>4$ (catalyst) in Kjeldahl’s flask.
  • Nitrogen is converted into ammonium sulphate.
  • Ammonium sulphate is treated with excess NaOH to liberate ammonia.
  • The liberated ammonia is distilled and absorbed in a known volume of standard (N/10) $H<em>2SO</em>4$ solution.
  • $N<em>2 + H</em>2SO<em>4 \rightarrow (NH</em>4)<em>2SO</em>4$
  • $NaOH + (NH<em>4)</em>2SO<em>4 \rightarrow 2Na</em>2SO<em>4 + 2NH</em>3 + 2H_2O$
  • $2NH<em>3 + H</em>2SO<em>4 \rightarrow (NH</em>4)<em>2SO</em>4$
  • The volume of unused $H<em>2SO</em>4$ is determined by titrating against standard NaOH solution (N/10).
• Calculate amount of $H<em>2SO</em>4$ required to neutralize ammonia:
  • Amount of acid $= N/10 V<em>1 – N/10 V</em>2 = 0.1 (V<em>1 – V</em>2)$ mili equivalents
  • Where $V<em>1$ = Volume of standard $H</em>2SO<em>4$ (N/10) solution and $V</em>2$ = Volume of standard NaOH (N/10) solution
  • $\% \text{ of Nitrogen } = 0.1 (V<em>1 – V</em>2) \times \frac{14}{W}$
• Determination of Sulphur: Coal sample is burnt in a bomb calorimeter in the presence of oxygen.
  • Sulphur is converted into $SO<em>2$ and $SO</em>3$.
  • The ash is extracted with dil. HCl.
  • Acid extracts are treated with Barium chloride solution to precipitate sulphates as Barium sulphate.
  • Precipitate is filtered, washed, dried, and heated to constant weight.
  • $S \rightarrow BaSO_4$
  • Weight of sulphur $= \frac{32}{233} \times \text{weight of } BaSO_4$
  • $\% \text{ of sulphur} = \frac{\text{Weight of sulphur}}{\text{Weight of coal sample}} \times 100$
• Determination of Ash: Percentage of ash is calculated by the method in proximate analysis.
• Determination of Oxygen: Calculated by subtracting the sum of total % of carbon, hydrogen, nitrogen, sulphur, and ash from 100.
  • $\% \text{ of Oxygen} = 100 – [\% \text{carbon} + \% \text{hydrogen} + \% \text{nitrogen} + \% \text{sulphur} + \% \text{ash}]$

Liquid Fuels

• Ex: Petroleum (Crude Oil)
• Composition:
  • Carbon: 80-85%
  • Hydrogen: 11-15%
  • Sulphur: 0.1-3.5%
  • Nitrogen: 0.4-0.9%
  • Oxygen: 0.1-0.9%
• Origin of Petroleum:
  • Carbide theory/Mendeleev’s theory (inorganic theory of petroleum)
    • $Ca + 2C \rightarrow CaC_2$ (high t)
    • $4Al + 3C \rightarrow Al<em>4C</em>3$
    • $CaC<em>2 + 3H</em>2O \rightarrow Ca(OH)<em>2 + C</em>2H_2$
    • $Al<em>4C</em>3 + 12H<em>2O \rightarrow 4Al(OH)</em>3 + 3CH_4$
  • Engler’s theory: Organic matter, animals, vegetation, and marine animals died and accumulated in the sea, decomposing under high temperature to give petroleum.

Refining of Petroleum

• Crude oil contains soluble and insoluble impurities that must be removed.

• Refining is the process of separating crude oil into various useful fractions by fractional distillation and converting these into desired products.

• The industry where refining occurs is called an oil refinery.

• Stages Involved in Refining of Petroleum:

  • Removal of sulphur compounds: Treated with copper oxide to convert sulphur into insoluble copper sulphide, which is removed by filtration.
  • Removal of water (Cottrell’s process): Crude oil passed between two charged electrodes to destroy emulsion films, causing water droplets to coalesce and separate from the oil.
  • Fractional distillation: Heating crude oil to around $400^oC$ in an iron retort produces hot vapours passed through a fractionating column.
    • The column is a tall cylindrical tower with horizontal stainless trays at short distances with small chimneys.
    • Vapours cool gradually as they go up, causing fractional condensation.
    • Higher boiling fractions condense first later the lower boiling fractions.

• Fraction Name, Boiling range, Approximate composition, Uses

  • Uncondensed gas Below $30^oC$ C1 to C4 A domestic or industrial fuel
  • Petroleum ether $30^oC - 70^oC$ C5-C7 As a solvent.
  • Gasoline or petrol $40^oC -120^oC$ C5-C9 As motor fuel, solvent, in dry cleaning
  • Naphtha or solvent spirit $120^oC -180^oC$ C9-C10 As solvent, in dry cleaning
  • Kerosene $180^oC - 250^oC$ C10-C16 As an illuminant ,Engine fuel
  • Diesel oil $250^oC - 320^oC$ C10-C18 Diesel engine fuel
  • Heavy oil $320^oC - 400^oC$ C17-C30 Gasoline by cracking
  • Lubricating oil As lubricant
  • Petroleum jelly As lubricant and in cosmetics and ointments
  • Paraffin wax In candles, boot polishes
  • Greases As lubricant
  • Residue (asphalt, petroleum coke) Used for making tar roads, water proof roof

Cracking

• The process of breaking and converting higher molecular weight long chain hydrocarbons with high boiling points to lower molecular weight hydrocarbons with low boiling points.
• Catalytic cracking:
  • Fixed bed catalytic cracking
  • Fluid bed catalytic cracking or moving bed catalytic cracking
• Fluid bed catalytic Cracking
  • The heavy oil is heated first passed through a preheater upto 425-$450^oC$
  • The preheated oil vapours are then passed through finely powdered catalyst maintained a temperature of $500^oC$.
  • Cracked oil Vapours are passed to fractionating column.
  • The vapors condenses heavy oil is separated.
  • This is then sent to dissloved gases
  • a cooler where where heavy oil is separated.