Day 3 MELE (Paolo's Version)

Refractory and Fuel Science, Metallurgical Laws and Ethics

fuel

a substance that gives energy as heat and light when burned with air, in a way that can be used efficiently and economically: the heat is enough to be useful, combustion is efficient, and the energy is cheap enough to use.

Metallurgical fuels

are burned to supply heat at usable temperatures for metallurgical processes on a commercial scale.

Hydrocarbon fuels

can be solid (coal, coke), liquid (petroleum, oil, alcohol) or gaseous (natural gas). They are also mined from tars ands, oil shale and methane hydrates and need distillation and upgrading.

solid fuel

fuel type that is:

• Cheap. Some uses need its special mix of physical and chemical properties.

• Ash forms. Hard to control during operation.

liquid fuel

fuel that is:

• Easy to handle, store and transport. Highest calorific value of all fuel types (by mass or volume).

• Expensive

gas fuel

fuel type that is:

• Clean and ash-free. Easy to control and handle. Flexible, with good combustion characteristics.

• Low calorific value per volume

liquid > solid > gas

Calorific power of fuel, highest to lowest

liquid › gas › solid

ease of transport of fuel types

solid › gas › liquid

Cost of fuels, cheapest to most expensive

coking coal

The most important metallurgical fuel

coal

forms in the earth when geologic forces act for a long time on accumulated plant matter. It is the largest single energy source of the metallurgical industry.

wood, peat, lignite, bituminous, anthracite, graphite, diamond

coalification sequence

rational analysis

identifies individual compounds by solvent leaching, destructive distillation at various T, chemical attack and microscopy. It is used for basic coal studies only.

petrographic analysis

a microscopic study that treats coal as a rock made of constituents (macerals) with different optical properties.

proximate analysis

is empirical: moisture, VM, ash, FC.

ASTM D271

astm standard for proximate analysis

ultimate analysis

gives the elements C, H, O, N, S. It is used for element balances and calorific power.

calorific power

the heat given off by complete combustion of a unit quantity of fuel under set conditions. It is −ΔH of combustion with O2, starting at 25 °C and 1 atm and with the products brought back to the same T and P. Because most fuels contain H, its value depends on the reference state of water.

Gross (high) CV, GCV

liquid water is the reference. It includes the latent heat released when H2O in the products condenses at 25 °C.

Net (low) CV, NCV

water vapour (100 °C) is the reference. It does not include the latent heat.

coke

manufactured fuel made by destructive distillation (pyrolysis) of coal without air. It is the coherent cellular residue of bituminous (coking) coal.

beehive oven

batch coking oven

by-product oven

continuous coking oven

fuel oil

has the highest CV by weight or volume

lighter grades

have the highest heating value per weight.

Heavier grades

have the highest per volume.

atomization

the oil is forced at high pressure through an orifice with compressed air or steam.

producer gas

Air (+ steam) through hot coal or coke. C + 1⁄2O2 → CO and CO + 1⁄2O2 → CO2 (net C + O2 → CO2, ~900 °C), then C + CO2 → 2CO (~1200 °C). Ideal: 34.6% CO + balance N2. Gas CV ≈ 70% of the coal's. Used when gas is needed but only coal is available.

Blast-furnace gas

Large-volume by-product of the iron BF. Mostly CO (+N2). Burned in Cowper stoves to preheat the blast.

Coal gas / coke-oven gas

Non-condensable gases from destructive distillation of coal in coke ovens

Water gas

Steam over a hot bed of coal or coke: C + H2O → CO + H2. C + 2H2O → CO2 + 2H2. C + CO2 → 2CO.

Carburetted water gas

water gas enriched with hydrocarbons from cracked oil, giving a higher CV.

Oil gas

Thermal decomposition of oil into gaseous hydrocarbons

Natural gas

Trapped at great depth and pressure. Often found with petroleum, where it was once flared as waste

Ignition temperature

is the lowest temperature of a gas–air mixture at which rapid, self-sustaining combustion occurs

Limits of inflammability

the range of gas–air compositions in which a flame propagates by itself. The lower limit is the minimum % fuel gas and the upper limit is the maximum % fuel gas that supports combustion.

Flame velocity

the linear speed at which a flame travels through a gas–air mixture. If the mixture's velocity in the burner is below the flame velocity, the flame travels back into the burner (backfire). If it is much greater, the flame lifts off (blow-off).

grate firing

lump coal burned on grates

pulverized-coal firing

a fine coal + air mixture blown into the chamber

Type 1 gas burners

mixes gas and air in the combustion chamber.

Type 2 gas burners

gas burner inspirator type

Type 3 gas burners

gas burner premixed type

Critical process temperature

the T needed to carry out the reaction effectively. For slag-producing processes it is the minimum T at which the slag flows.

thermodynamic, kinetic, mechanical

angles in which CPT is viewed

Adiabatic flame temperature

highest temperature theoretically possible with complete combustion under adiabatic conditions, i.e., the temperature of the products when no heat is lost.

Actual flame temperature

Usually 48–75% of the AFT, because real conditions are not adiabatic

fuel type, moisture, preheating, oxygen enrichment

Factors affecting the AFT

Gross available heat

total heat input from burning the fuel minus the sensible heat in the products at the critical temperature.

Net available heat

GAH minus the furnace's net losses.

Smelting power

the highest possible furnace throughput: net available heat generated per unit time ÷ net available heat required per unit throughput.

heat regenerators

contain heat-storage elements (checker brick or a rotating matrix) that take up heat from the flue gas, then give it to the cold air. The flows alternate or rotate. Examples are Cowper (hot-blast) stoves and open-hearth checkers.

Heat Recuperator

exhaust gas from the process flows through the tubes. Atmospheric air enters from the top, crosses outside the tubes, and leaves as preheated air. The tube walls separate the two streams, so they never mix and the flow is steady.

furnace structure, refractory, fuel

three parts in the furnace

crucible furnace

Charge is held in a refractory or metal “pot” (crucible). Heated externally or internally. For small batches only (class I)

hearth furnace

The widest class. May be fixed, tilting or rotating. The charge lies on the floor (hearth) and is heated from the top (flame/arc/radiation from the roof). (class II)

shaft furnace

Cylindrical or rectangular shaft. The solid charge flows down by gravity against rising gases, and the product collects at the hearth. (class III)

retort

Closed vessel heated from outside. Distinguished by volatile products that are taken off (e.g. coke-oven gas, Zn vapour).

Converter

High-temperature vessel in which gas (air/O2) is blown through liquid metal.

refractory

a material used to contain heat and to “refract” it back to the burden.

fusion

the refractory has melted. This is rare and usually means the wrong refractory was chosen.

Slag action

one of the most common causes of failure. Refractory and slag oxides are essentially the same, so attack cannot be prevented, only slowed.

Slag erosion

the wearing away of the surface by the washing action of moving slag.

Expansion or shrinkage

caused by thermal changes and by deformation under load

3–4%

A volume shrinkage of _counts as failure

Spalling

cyclic fracture of the hot face. Material keeps flaking off and exposing new surface until the lining fails.

Thermal spalling

temperature gradients cause unequal expansion, which sets up shear and tensile stresses. Heating–cooling cycles also cause it.

Mechanical spalling

external forces, e.g. a wall built without allowance for thermal expansion.

Over-loading

applied stress exceeds the load-carrying capacity, often because of slag contamination or misapplication

Abrasion

scouring by moving solids (e.g. descending BF charge, rising coal ash and coke dust), washing by slag, and erosion by dust-laden gases.

Shell-type construction

A thick refractory lining inside a steel shell (furnace construction type)

Masonry construction

Brickwork held together by exterior structural steel binding (furnace construction type)

P.D. 1536

old law of metallurgical engineering

RA 10688

new law of metallurgical engineering

P.D 1536

"Metallurgical Engineering Law of the Philippines"; Signed by Pres. Ferdinand E. Marcos, Manila, 11 June 1978. "Shall take effect immediately." It created the Board of Metallurgical Engineering and repealed the parts of Act No. 2985 that covered metallurgy.

Act No. 2985

repealed by PD 1536

Mineral Processing & Extractive Metallurgy

covers the "scientific, engineering, environmental and economic aspects" of preparation, separation, extraction and purification.

Adaptive and Physical Metallurgy

adds the adaptation and application of metals: melting, casting, forging, rolling, extrusion, welding and other metal working and finishing.

Fuel Technology

covers washing, flotation and heavy- media separation, including carbonization, gasification and coking. The 1980 Rules add "as applied to metallurgical processes".

at least 1 RMetE

persons directly engaged 10–25, entire operation

1 RMetE + 1 RMPF, or 2 RMetEs

persons directly engaged >25–50, entire operation

at least 1 RMetE per shift

persons directly engaged 10–25 per shift

1 RMPF + 1 RMetE each shift

persons directly engaged >25–50 per shift

+1 RMPF + 1 RMetE per shift

persons directly engaged: Each 50 above the first 50 per shift

RMetEs

All superintendents (or equivalent) must be _

Atomic number

number of protons in the nucleus. In a neutral atom, protons = electrons.

Isotopes

atoms of the same element (same Z) with different masses because they have different numbers of neutrons, e.g. 1H, 2H, 3H.

Atomic weight

weighted average of the atomic masses of the naturally occurring isotopes.

Atomic mass

mass of protons + neutrons (mass number). It is written AZM (A = mass number, Z = atomic number).

n principal

Total energy, distance from the nucleus, size of the orbit. Lower _ = more stable.

l orbital (azimuthal)

Subshell. Angular momentum. Shape of the orbital.

ml magnetic

Number of energy states (orbitals) in each subshell. Component of angular momentum along a given direction.

ms spin

Spin of the electron about its own axis

Pauli exclusion principle

each electron state (orbital) holds at most 2 electrons, and they must have opposite spins (+1⁄2, −1⁄2). No two electrons share all four quantum numbers.

Aufbau principle

"A maximum of two electrons are put into orbitals in order of increasing orbital energy. The lowest-energy orbitals are filled before electrons are placed in higher-energy orbitals."

lower left

metallic character trend

lower left

atomic radius trend

upper right

1st IE trend

upper right

electronegativity

Metallic

Elements with 1–3 valence electrons give them up. This leaves an array of positive ion cores in a "sea of electrons", and the electrons act as glue.

Covalent

Atoms share valence electrons. Electrons of opposite spin pair in overlapping, spatially directed orbitals, so neither atom gains or loses electrons.