Lecture 18 resources 9 coal Flashcards
trends in coal production
rapid increase in the 1800’s with a decline in the 1900 - now we use very little coal and most is imported.
- moved from natural resource to a commodity.
where is coal found?
- found almost everywhere in the world - recoverable reserves in 70 countries.
Top - china
- india
- USA
what are the properties of coal
high content of Carbon and hydrogen
- coals rich in volatiles are easy to ignite - Smokey flame
- coals low in volatiles - harder to ignite, burn with smoke free flame.
Coking properties: carbonized residue after volatile removal in the absence of air.
Calorific value - amount of heat liberated under standard conditions.
What is calorific value
calorific value increases with rank.
carbon content increases
volatile matter decreases
15-25 kJg Low rank Lignites - rich in volatiles and easy to ignite
31-35 kJg Bituminous coals
30-33 kJg Anthracites (high rank coals)
What are the uses of coal
lignite and sub-bitumous coal - power generation and industrial uses.
Bitumous coals - Linked to steel industry
Anthracite - domestic and industrial
Where is coal found in the present day?
Humus - fresh decayed organics in upper soil profile eventually oxidised
peat - plants more resistant to decay; anaerobic conditions: generally colder climate. freshwater swaps and bogs - some tropical mangrove swamps.
sapropel - subaqueous; shallow to deep marine basins lagoons, lakes, deltas - mostly phytoplankton from upper water levels.
Note - peat layers decrease in thickness by a factor of 10 during coalification. this requires enormous thicknesses of peat to generate coal seams between 2-10 metres thick.
where to coal deposit forms
Mires - habitats which peat accumulates
A freshwater ecosystem - there is a net accumulation of organic matter
organic matter found - swamps, swamp forest, floating swamps, Fen, Marsh and Bog
What are Macerals and what types are there
Macerals = organic constituents (material)
Maceral group:
vitrinite: plant debris - wood and bark
Inertinite: woody tissue (oxidised wood or bark), fungi, fine organic debris
Liptinite: Spores, cuticle, resin algae
The nature of the coal is determined by the Maceral group that is present.
What conditions are needed for generation of coal
Landcape where rocks formed are in the manine/non-marine interface
- shallow swamp like environment.
What happens to the layers as temperature and pressure change (coal formation)?
Move towards carbon apex
move upwards from peat to Anthracite
Top = Anthracite
bitumen
sub-bitumen
lignite
bottom = peat
low volatility at the apex
How is coal formed - two ways.
1) biochemical decomposition
- accumulation of dead plant material - action of bacteria and fungi
- loss of volatiles CO2, H20, CH4
- results in compacted structureless compounds enriched in carbon = peat.
2) Coalification
- when accretion of peat deposits is arrested by burial beneath mud, sand and silt.
- involves physical and chemical changes imposed by increasing temp and pressure and time.
- Stages of change referred to as rank - pear to carbon apex.
what are the geochemical characteristics of coal types - what happens with depth and pressure.
peat (bottom) to anthracite (top)
volatility decreases
carbon increases
Vitrinite reflectance increases
calorific value increase
these are the changes that occur in coalification
Explain the age of Coal
no coal before 400ma
- first coal - carboniferous
two major periods of coal formation
carb - E triassic (200Ma)
Jurrassic - E tertiary (50Ma)
younger coals - brown coals and liginites
older coals - bitumous and anthracites (because need more time, temp and pressure to convert them)
what do we think about historic coal formation - why it is found where it is? (carboniferous paleogeography)
if reconstruct the patterns of continents at time of carboniferous - located around the equator.
UK coal formation
All coal mined in the UK is carboniferous
- generates significant areas of coastal swamp - coincide with current coal fields.
The anthracitic coal - from deformation phase in the south
bituituous in the north
