Pyrometallurgy 2 (terms) Flashcards
- Statement of the energy balance of a given system
o It is less abstract than the formal thermodynamic treatment
o It accounts for the input and output
o Based on the 1st Law of Thermodynamics
Metallurgical Heat Balance
Items in a Heat Balance
◦ Heats of reaction (exothermic reactions)
◦ External heat supply
Input terms
Items in a Heat Balance
◦ Heat absorbed by endothermic reactions
◦ Heat absorbed in bringing input materials to the reference temperature
◦ Heat loss to surroundings
Output terms
Supply the necessary amount of heat to attain the satisfactory temperature level
Heat Utilization
associated with any change of state in a material is a change in the heat content of the system
◦ Exothermic Reaction
Chemical Energy
maybe solid, liquid or gaseous
*liquid fuels: petroleum, oil, alcohol
*gaseous fuels: natural gas
*solid fuels are: coal and coke
*mined from tar sands and oil shale and methane hydrates
*further requires distillation and upgrading to produce crude and petroleum
Hydrocarbon Fuels
◦ advantage is that there is no contamination of the charge by the fuel
Electricity
◦ energy which has been produced in another part of the plant and recycled within the plant
◦ Heat exchangers, flue gases
Conserved Heat
Heat Utilization
◦ the temperature required to carry chemical reaction effectively
◦ For processes producing a slag, it is the minimum temperature with which slag flow is achieved
Critical Process Temperature
Heat Utilization
◦ the maximum temperature theoretically attainable assuming complete combustion of fuel under adiabatic conditions
◦ The temperature of the combustion products when the reaction is carried out without any loss of heat
Adiabatic Flame Temperature (AFT)
◦ the total input from the combustion of fuel, less the sensible heat in the combustion products at the critical temperature
◦ the heat given up by the combustion products to the furnace and its contents when cooled from AFT to critical temperature
◦ proportional to (TAFT – T crit)
◦ anything that increases the AFT also increases the gross available heat
Gross Availability Heat
◦ the gross available heat less the net losses in the furnace
Smelting Power:
◦ the maximum furnace throughput
◦ net available heat generated per unit time divided by the net required available heat per unit throughput
Net Availability Heat
◦ sensible heat from flue gas represents considerable amount of fuel cost, and any heat recovered would improve the profitability of a given process
Uses of recovered heat:
◦ preheat of combustion gases/fuel
◦ conversion to steam power
◦ drying of ore
Heat Recovery from Flue Gas
rate of heat flow and temperature at any position does not vary with time
Steady State
continuous type, wherein both fluids are flowing continuously through the system being separated only by walls through which heat transfer occurs
Heat Recuperators
contain heat storage elements which alternately absorb heat from the flue gas and then give up heat to the cold air being preheated
Heat Regenerators
rate of heat flow and temperature at any position vary with time
Unsteady State
heat flow through a body without displacement of particles in the body; heat flows in a stationary medium
Conduction
heat flow through a body which involves displacement of particles; heat flows in liquid and gases
Convection
heat flows in vacuum
Radiation
Uno sini na law?
◦Rate of heat flow is proportional to the difference in temperature
Fourier’s Law
◦ Constant cross-sectional area ⊥ to the direction of heat flow
◦ One (1) dimension «_space;other two (2) dimensions
Neglect end effects
Slabs
◦ Cross-sectional area changes with position
◦ Heat transfer through r and θ
Cylinders
◦ Molecules are agitated
◦ Atoms easily collide with neighboring atoms to the right
◦ Process continues until all molecules transfer their kinetic energy to those in the cold wall
Hot Wall
