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Coal and Crude Oil Fundamentals
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1
Question
Why is a high percentage of ash content in coal undesirable because it reduces calorific value?
Page 5
Answer
Ash is inorganic residue that does not combust; a higher ash percentage means less combustible material per unit mass, lowering the coal's calorific (heating) value.
2
Question
Why is a high percentage of ash content undesirable because it causes hindrance to heat flow?
Page 5
Answer
Ash forms an insulating layer on fuel and furnace surfaces that impedes heat transfer, reducing combustion efficiency and heat release to the furnace.
3
Question
How does ash in coal produce clinkers that block air supply and why is this undesirable?
Page 5
Answer
Certain ash components fuse during combustion to form hard lumps (clinkers) that accumulate and block air passages, disrupting airflow and combustion, lowering efficiency and causing operational problems.
4
Question
Why does high ash content increase transport, handling, storage and disposal cost for coal?
Page 5
Answer
Ash increases the non‑fuel bulk to be moved and stored, raises abrasive and corrosive handling problems, and creates additional waste that must be disposed of, all increasing operational costs.
5
Question
What is free moisture in coal?
Page 5
Answer
Free moisture is the amount of moisture that is lost from coal during air‑drying; it is surface or loosely held water that evaporates under normal drying conditions.
6
Question
What is inherent moisture in coal?
Page 5
Answer
Inherent moisture is the moisture not removed by air‑drying; it is water held within the coal matrix and is determined by heating an air‑dried sample under controlled conditions.
7
Question
How is the percentage of inherent moisture in coal experimentally determined?
Page 5
Answer
A weighed sample of air‑dried coal is heated in a weighed silica or porcelain crucible at \$105–110^\circ\mathrm{C}\$ for 1 hour; the percentage loss in weight of the coal is reported as inherent moisture.
8
Question
What is the formula for percentage of inherent moisture in coal?
Page 5
Answer
\$\text{Percentage of inherent moisture} = \dfrac{\text{loss in weight} \times 100}{\text{weight of coal}}\$
9
Question
Why is free moisture disadvantageous because it does not contribute to fuel value?
Page 5
Answer
Free moisture is not combustible, so it occupies mass in the coal sample without producing heat, effectively lowering the usable fuel fraction and reducing net energy output.
10
Question
Why does evaporating free moisture during combustion waste heat and lower the calorific value of coal?
Page 5
Answer
Energy from combustion must first evaporate the free moisture, consuming heat that would otherwise raise temperature or be available for useful work, thereby lowering the effective (net) calorific value.
11
Question
How does excessive free moisture make handling of coal difficult?
Page 5
Answer
High free moisture causes coal to clump, stick, and become heavier, complicating feeding, conveying, storage, and handling operations.
12
Question
What is fixed carbon in coal?
Page 5
Answer
Fixed carbon is the mineral (non‑volatile) matter originally present in coal that remains after volatile matter is driven off; it represents the solid combustible residue (elemental carbon) excluding ash and volatiles.
13
Question
What is the formula to calculate percentage of fixed carbon in coal?
Page 5
Answer
\$\text{Percentage of fixed carbon} = 100 - (\%\text{ moisture} + \%\text{ ash} + \%\text{ volatile matter})\$
14
Question
Why is a high percentage of fixed carbon desirable because it increases calorific value?
Page 5
Answer
Fixed carbon represents the stable combustible carbon fraction that produces heat on combustion; a higher fixed carbon percentage generally indicates higher calorific (heating) value of the coal.
15
Question
How does a high percentage of fixed carbon help in designing the furnace and the shape of the firebox?
Page 5
Answer
Knowledge of fixed carbon influences furnace design because it affects burnout characteristics, required air supply, residence time, and grate/firebox geometry to achieve efficient combustion and heat transfer.
16
Question
What is crude oil?
Page 8
Answer
Crude oil is a complex, naturally occurring liquid mixture primarily composed of hydrocarbons, with small amounts of other organic and inorganic compounds.
17
Question
What are paraffins (alkanes) in crude oil and why are they important?
Page 8
Answer
Paraffins (alkanes) are saturated hydrocarbons that typically make up \$30\% - 60\%\$ of crude oil; they are important feedstock for producing gasoline and light petroleum products.
18
Question
What are naphthenes (cycloalkanes) in crude oil and what do they contribute to?
Page 8
Answer
Naphthenes (cycloalkanes) are saturated cyclic hydrocarbons comprising about \$30\% - 60\%\$ of crude oil; they contribute to various refinery products including heavier residues.
19
Question
What are aromatics in crude oil and what is their usual proportion?
Page 8
Answer
Aromatics are unsaturated cyclic hydrocarbons containing one or more benzene rings, and they usually make up about \$15\% - 30\%\$ of crude oil composition.
20
Question
What are asphaltics (asphaltenes) in crude oil and how much do they typically comprise?
Page 8
Answer
Asphaltics are complex, high molecular weight compounds (often called asphaltenes) that typically make up the remaining approximately \$6\%\$ of crude oil.
21
Question
Which types of non-hydrocarbon organic elements are commonly found in crude oil?
Page 8
Answer
Non-hydrocarbon organic elements in crude oil commonly include sulphur, nitrogen, and oxygen-containing compounds.
22
Question
Why are sulphur compounds in crude oil particularly significant?
Page 8
Answer
Sulphur compounds (typically \$0.05\% - 6.0\%\$) are significant because of their corrosive nature and their negative impact on refining processes and product quality.
23
Question
What are typical concentration ranges for nitrogen and oxygen compounds in crude oil?
Page 8
Answer
Nitrogen compounds are typically present in the range \$0.1\% - 2\%\$, while oxygen compounds are typically present in the range \$0.05\% - 1.5\%\$.
24
Question
Which metals and inorganic salts are commonly found as traces in crude oil?
Page 8
Answer
Trace metals commonly found include vanadium, nickel, iron, and copper; common inorganic salts include sodium and calcium.
25
Question
What is the typical elemental composition of crude oil in terms of carbon and hydrogen?
Page 8
Answer
Typically, crude oil contains about \$83\% - 87\%\$ carbon and \$10\% - 14\%\$ hydrogen; the remainder consists of sulphur, nitrogen, oxygen, metals, and salts.
26
Question
How does crude oil typically appear in terms of colour?
Page 8
Answer
Crude oil varies in colour from colourless to black, but it commonly appears black, brown, or amber.
27
Question
What is API gravity and what value is assigned to pure water on the API gravity scale?
Page 8
Answer
API gravity is a scale used to measure the density of petroleum liquids relative to water; pure water is assigned a value of \$10^\circ\$ on the API gravity scale.
28
Question
How is 'light crude' defined by API gravity?
Page 8
Answer
Light crude is defined as having an API gravity greater than \$31.1^\circ\$.
29
Question
What API gravity range defines 'medium crude'?
Page 8
Answer
Medium crude has an API gravity in the range \$22.3^\circ\$ to \$31.1^\circ\$.
30
Question
What API gravity range defines 'heavy crude'?
Page 8
Answer
Heavy crude is defined as having an API gravity between \$10.0^\circ\$ and \$22.3^\circ\$.