Coal and Petroleum - Lec 4

Coal and petroleum

• Are formed as a result of degradation of ancient plant life which lived millions of years ago.
• These dead plant matter started to pile up, eventually forming a substance called peat.
• Over time, heat and pressure from geological processes transformed these materials into coal.
• Since these are formed from essentially fossils, they are also known as fossil fuels.

Coal

One of the most important primary fossil fuels, a solid carbon-rich material that is usually brown or black and most often occurs in stratified sedimentary deposits.

Is defined as having more than 50 percent by weight (or 70 percent by volume) carbonaceous matter produced by the compaction and hardening of altered plant remains—namely, peat deposits.

Property of coal: Density

Is slightly denser than water (1.0 mega gram per cubic meter) and significantly less dense than most rock and mineral matter (e.g., shale has a density of about 2.7 mega grams per cubic meter and pyrite of 5.0 mega grams per cubic meter).

Property of coal: Porosity

• Coal density is controlled in part by the presence of pores that persist throughout coalification.
• Measurement of pore sizes and pore distribution is difficult; however, there appear to be three size ranges of pores:
(1)macropores (diameter greater than 50 nanometres),
(2)mesopores (diameter 2 to 50 nanometres), and
(3)micropores (diameter less than 2 nanometres). (One nanometre is equal to 10−9 metre.)

Properties of coal: Reflectivity

• An important property of coal is its reflectivity (or reflectance)— i.e., its ability to reflect light.
• Reflectivity is measured by shining a beam of monochromatic light (with a wavelength of 546 nanometers) on a polished surface of the vitrinite macerals in a coal sample and measuring the percentage of the light reflected with a photometer.

Properties of coal

• Hardness, grindability, ash-fusion temperature, and free-swelling index (a visual measurement of the amount of swelling that occurs when a coal sample is heated in a covered crucible), may affect coal mining and preparation, as well as the way in which a coal is used.
• Hardness and grindability determine the kinds of equipment used for mining, crushing, and grinding coals in addition to the amount of power consumed in their operation. Ash-fusion temperature influences furnace design and operating conditions.
• The free-swelling index provides preliminary information concerning the suitability of a coal for coke production.

Types of coals

Depend on the amount of oxygen, carbon and hydrogen they contain, they are:

1. Lignite
2. Subbituminous
3. Bituminous
4. Anthracite

Lignite

1. Lowest rank of coal
2. Show the original woody structure of the element
3. Highest content of volatile matter and moisture
4. Light brown to very dark brown in color

Subbituminous

• Black and shows no traces of woody substance in naked eye
• 40% Carbon and 25% moisture

Bituminous

• Fixed-carbon content exceed 70% moisture content is less than 15%
• Soft coal- it catches fire easily with yellow flame
• It produces odor depending on the amount of ash and sulfur it contain

Anthracite

• Highest rank of coal- 90% fixed carbon and very little moisture
• Burns longer than other kinds of coal
• Produces a blue flame
• No smoke and very little odor

Coalification

• Process of coal formation
• The general sequence of coalification is from lignite to subbituminous to bituminous to anthracite.
• Since microbial activity ceases within a few meters of Earth’s surface, the coalification process must be controlled primarily by changes in physical conditions that take place with depth.
• Some coal characteristics are determined by events that occur during peat formation—e.g., charcoal-like material in coal is attributed to fires that occurred during dry periods while peat was still forming.

Petroleum

• Is crude oil, a naturally occurring liquid that can be refined to make gasoline (or petrol), diesel fuel, jet fuel, home heating oil, lubricating oil, wax, asphalt, and many other valuable products.
• The word petroleum comes from Latin, in which petra means rock and oleum means oil.
• As a technical term, petroleum also includes natural gas, a naturally occurring gas with a similar chemistry to crude oil that also occurs in subsurface deposits.

Properties of petroleum

• Consists basically of compounds of only two elements, carbon and hydrogen.
• Because these elements combine in a large variety of complex ways, however, crude oils vary greatly in their chemical composition.
• Their physical properties such as color, specific gravity, and viscosity also vary widely.

Asphalt

Based crude oils are usually black. When refined, they produce a relatively large amount of high-quality gasoline and asphalt.

Paraffin

Based crude oils are black with a greenish tinge. When refined, they produce a relatively large amount of paraffin wax and high-quality motor lubricating oil.

Mixed

Base crude oils are a natural blend of asphalt- and paraffin- based crude oil.