Oil & Gas

Question 1

What is meant by natural gas?

Answer 1

Associated with petroleum oil deposits, coal seams or decay of organic matter.

Question 2

Give four examples of manufactured gas.

Answer 2

Wood, peat, coal, oil shale.

Question 3

Discuss use of hydrogen.

Answer 3

Combustible gas of moderate CV. Constituent of the manufactured gases.

Question 4

Discuss GCV and NCV.

Answer 4

GCV includes the latent heat of condensation of the water produced, this is the value used when costing gas.

Question 5

Define the Wobbe Number.

Answer 5

GCV/(Specific Gravity)^0.5

Question 6

Define the Weaver Flame Speed Factor.

Answer 6

The flame speed of the gas relative to H2, which is given an arbitrary value of 100.

Question 7

Define the Gas Modulus.

Answer 7

(P)^0.5 / Wobbe No.

Question 8

What is the autoignition temperature?

Answer 8

Lowest temperature at which the substance spontaneously ignites in normal atmosphere without an external source of ignition.

Question 9

Discuss flammability limits.

Answer 9

Mixture composition must be within the flammability limits in order to combust.
Below the lower limit, the mixture is too lean to support combustion.
Above the upper limit, the mixture is too rich to propagate flames.

Question 10

Discuss ignition energy.

Answer 10

An ignition energy is to be applied in a minimum volume of mixture in order to give rise to a continuing flame through the rest of the mixture.

Question 11

Discuss the H/C ratio of fuels.

Answer 11

Ratio in fuel gases is substantially greater than that of alternative fuels. Also, latent heat of the combustion products is higher.

Question 12

What is combustion always accompanied by?

Answer 12

1) Heat release
2) Dynamic flow changes.
3) Transformation of multiple chemical compounds.

Question 13

What are the three stages of chain reactions?

Answer 13

1) Initiation
2) Propagation
3) Termination

Question 14

Define the term “burning velocity”.

Answer 14

The velocity with which a plane of flame moves, normal to its surface through the adjacent unburnt gas.

Question 15

Discuss different factors of the burning velocity.

Answer 15

Increases with oxygen concentration.
Increases with increasing temperature.
Increases with decreasing pressure.

Question 16

What is the adiabatic flame temperature?

Answer 16

Maximum temperature achievable in the combustion. Usually between 2000-3000 K.

Question 17

Name 4 sources of fuel oils.

Answer 17

Crude petroleum, oil shales, coal, biomass.

Question 18

Discuss viscosity of fuel oil.

Answer 18

Viscosity decreases as temperature rises, becomes almost constant above 120C.
Decreased viscosity facilitates the flow of oil and atomisation in the burner, however decreased density results in less weight being delivered.

Question 19

What is the cloud point?

Answer 19

Temperature at which a haze appears when an oil is cooled. Indicates the onset of formation of wax crystals.

Question 20

What is the pour point?

Answer 20

Several degrees below the cloud point. Temperature which is 2.8K above the temperature at which the oil just fails to flow when cooled.

Question 21

What is the flash point?

Answer 21

Temperature at which the vapour pressure of the substance gives a concentration of vapour in the air which corresponds to the lower flammability limit.

Question 22

What is the fire point?

Answer 22

Lowest temperature at which the liquid, when placed in an open container, will give sufficient vapour to continue to burn when ignited.

Question 23

Discuss petrol, diesel and jet fuel.

Answer 23

Petrol: mixture of light distillate HCs from refined crude oil.
Diesel: Straight run products obtained from the distillation of crude oil.
Jet Fuel: Straight run products, not limited by antiknock.

Question 24

What is the difference between engines which use gasoline compared to diesel?

Answer 24

Gasoline: Fuel and air is combined, then ignited by spark plugs.
Diesel: Air is compressed first, the fuel is injected and ignited by the compression.

Question 25

How does knocking occur?

Answer 25

Gasoline knocking occurs when unburnt fuel burns rapidly, forming pressure waves.
Diesel knocking occurs due to a delay between injection of the diesel fuel into the compressed air and its ignition.

Question 26

Why is spray combustion used?

Answer 26

Increases the fuel surface area. Increases the vapourisation and combustion rate.

Question 27

Name three types of spray nozzles.

Answer 27

Simple pressure, air/steam atomization, swirl.

Question 28

Discuss the jet break up mechanism.

Answer 28

Suggested by Rayleigh. Column of liquid is unstable and breaks into droplets if the length is greater than the circumference.

Question 29

What does BLEVE stand for?

Answer 29

Boiling Liquid Expanding Vapour Explosions.