Corrosion and Energy Quiz

Water Purification Methods - Industrial Applications

• Zeolites (principle, process, advantages, disadvantages)
• Ion-exchange resins (double/mixed bed) (principle, process, advantages, disadvantages)
• Reverse osmosis (principle, process, advantages, disadvantages)
• Fuels and combustion
  • LCV, HCV, Bomb calorimeter (numerical)
• Corrosion
  • Prevention of Corrosion, cathodic protection (Sacrificial anodic protection and Impressed current cathodic protection)

Water Softening Methods

• Zeolite (Permutit process)
• Ion-exchange
• Mixed bed ion-exchange
• Reverse Osmosis

Permutit or Zeolite Process

• Zeolite is a hydrated sodium aluminum silicate (Na2OAl2O3.xSiO2.yH2O)
• Exchanges Na+ ions for Ca2+ and Mg2+ ions
• Common zeolite is Na2OAl2O3.3SiO2.2H2O (natrolith)
• Other materials used for water softening include glauconite, green sand (iron potassium phyllosilicate)
• Artificial zeolite (Permutit) has a higher softening capacity than green sand
• Prepared by heating china clay (hydrated aluminum silicate), feldspar (e.g., KAISI3O8, NaAlSi3O8, CaAl2Si2O8) and soda ash (Na2CO3)

Natural Zeolites

• Natrolite (Na2O.Al2O3.4SiO2.2H2O)
• Laumontite (CaO.Al2O3.4SiO2.4H2O)
• Harmotome [(BaO.K2O).Al2O3.5SiO2.5H2O]
• Capable of exchanging Na+ ions

Permutit or Zeolite Process - Softening Method

• Na2Ze + Ca(HCO3)2 → 2 NaHCO3 + CaZe
• Na2Ze + Mg(HCO3)2 → 2 NaHCO3 + MgZe
• Na2Ze + CaSO4 → 2 Na2SO4 + CaZe
• Na2Ze + CaCl2 → 2 NaCl + CaZe

Permutit or Zeolite Process - Regeneration

• CaZe (or) MgZe + 2 NaCl → Na2Ze + CaCl2 or MgCl2 + Brine solution

Zeolite Process - Advantages

• Residual hardness of water is about 10 ppm only
• Equipment is small and easy to handle
• Time required for softening of water is small
• No sludge formation, clean process
• Zeolite can be regenerated easily using brine solution
• Any type of hardness can be removed without modifications

Zeolite Process - Disadvantages

• Coloured water or water containing impurities cannot be used without filtration
• Water containing acidic pH cannot be used due to acid destroying zeolite

Ion-Exchange Process

• Resins are cross-linked long chain polymers with microporous structure
• Functional groups are responsible for ion exchange properties
• Acidic functional groups (-COOH, -SO3H) exchange H+ for cations
• Basic functional groups (-NH2, =NH) exchange OH- for anions
• Cation-exchange resins (RH+): styrene divinylbenzene copolymers
• Anion-exchange resins (R'OH): styrene divinylbenzene copolymers or amine formaldehyde copolymers with NH2, QN+, QP+, QS+, groups

Ion-Exchange Process - The Process of Ion-exchange

• 2 RH+ + Ca2+/Mg2+ → R2Ca2+/R2Mg2+ + 2 H+
• R'OH + Cl- → R' + Cl- + OH-
• 2 R'OH- + SO42- → R'2 SO42- + 2 OH-
• 2 R'OH- + CO32- → R'2 CO32- + 2 OH-

Ion-Exchange Process - Regeneration

• Saturated resins are regenerated
• R2Ca2+/R2Mg2+ + 2H+ → 2RH+ + Ca2+/Mg2+
• R'2 SO42- + 2 OH- → 2 R'OH- + SO42-

Mixed Bed Deionizer

• Single cylindrical chamber with anion and cation exchange resins
• Hard water is passed through the bed, removing cations and anions
• Effectively passes hard water through a series of resins
• Soft water contains less than 1 ppm of dissolved salts, suitable for boilers

Regeneration of Mixed Bed Deionizer

• Mixed bed is backwashed (upward water flow)
• Light-weight anion exchanger rises to top
• Anion exchanger is regenerated with NaOH solution and rinsed
• Lower cation exchanger is washed with dilute H2SO4 and rinsed
• Beds are remixed with compressed air

Mixed Bed Deionizer - Advantages/Disadvantages

• Advantages: Suitable for highly acidic/alkaline water, low residual hardness (2 ppm)
• Disadvantages: Expensive equipment/chemicals, turbidity needs treatment, skilled labor needed

Reverse Osmosis

• Reverse osmosis membrane filters have very small pore size (0.0001 micron)
• Removes organic molecules, viruses, most minerals
• Removes monovalent ions, leading to desalinated water
• Osmosis is the movement of solvent across a semipermeable membrane from a less concentrated solution to a more concentrated one

Fuels and Combustion

• Fuel is a combustible material producing a large amount of heat for both domestic and industrial purposes
• Combustion involves oxidation of elements in the fuel (carbon, hydrogen, etc.) forming CO2, H2O, releasing heat
• Primary fuels include coal and petroleum oils, considered fossil fuels

Classification of Fuels

• Primary or natural fuels: solid (wood, coal, dung), liquid (crude oil), gaseous (natural gas)
• Secondary or derived fuels: solid (coke, charcoal, coal briquettes), liquid (tar, kerosene, diesel, petrol, fuel oil, LPG), gaseous (coal gas, water gas, oil gas, biogas, coke oven gas, blast furnace gas)

Calorific Value of Fuels

• Calorific value: the amount of heat released when a unit mass or volume of fuel burns completely
• Important property of fuels
• Measured in kJ/kg
• Different fuels have different values

Calorific Value of Common Fuels

• Give examples of fuels and their calorific values

Characteristics of a Good Fuel

• High calorific value
• Moderate ignition temperature
• Low moisture content
• Low non-combustible matter content
• Moderate combustion velocity
• Non-harmful combustion products
• Inexpensive
• Easy to transport
• Easy to control combustion
• Low storage costs
• Uniform size (solid fuels)

Comparison of Solid, Liquid, and Gaseous Fuels

• Advantages/Disadvantages for each fuel type
• Summarize each fuel's properties (transport, storage costs, combustion, etc.)

Corrosion

• Any process of deterioration of a solid metallic material by chemical or electrochemical attack from the environment
• Types of corrosion: Dry/chemical corrosion vs Electrochemical corrosion. Subtypes of corrosion are listed for each type.
• Factors affecting corrosion: Nature of the metal, position in galvanic series, overvoltage, purity of metal, relative areas of anode and cathode, nature of surface film, the passive character of the metal, and solubility of corrosion products.
• Environment factors: Temperature, humidity, presence of impurities, suspended particles, pH, silicates, conductance, formation of O2 concentration cell, flow velocity.
• Forms of corrosion include uniform corrosion, galvanic corrosion, concentration cell corrosion, pitting corrosion, crevice corrosion, filiform corrosion, intergranular corrosion, stress corrosion cracking, corrosion fatigue, fretting corrosion, erosion corrosion.

Cathodic Protection

• Principle: protecting the main metal as cathode by connecting to a highly active metal such as Zn, Mg, etc
• Methods:
  • Sacrificial anodic protection
  • Impressed current cathodic protection

Sacrificial Anodic Protection

• Anodic metal sacrifices itself (corrosion) while protecting the main metal from corrosion
• Anodic metals: Zn, Mg, Al and alloys
• Used for underground pipelines, ship hulls, and marine devices

Impressed Current Cathodic Protection

• Directs a current through the main metal, making it the cathode
• Uses an insoluble anode (e.g., graphite) immersed in a conductive solution (e.g., coke, gypsum, bentonite, sodium sulphate)
• Protects underground pipelines, oil pipelines, transmission lines, ships, etc

Additional Information

• Include tables of galvanic series and electrode reactions
• Diagrams for sacrificial anodic and impressed current cathodic protection methods