Combustion Flashcards
Briefly describe inerting.
CO2, N2, H2O and Ar act as a coolant on the flame. This reduces the flame temperature and reactivity of the flame.
What does the effectiveness of an inert gas depend on?
Its ability to absorb heat, therefore Cp.
What is LOC?
Limiting Oxygen Concentration.
What is the minimum oxygen concentration?
Maximum oxygen concentration that will be non-combustible in any mixture of fuel, oxygen and inert gas.
What is the effect of pressure on inerts?
Increases the rich limit with little effect on the lean limit. More inert needed as pressure increases.
How does pressure affect LOC?
LOC decreases as pressure increases.
How does pressure affect the stoichiometric flame temperature.
Pressure increases the stoichiometric flame temperature due to the reduction of dissociation.
What is the criteria for an explosion?
1) O2 presence
2) Fuel in sufficient quantity.
3) Ignition source.
What is meant by loss of load expectation?
Average expected number of hours per year in which supply is expected to be lower than demand.
What are three options for CO2 control from coal combustion?
- Carbon capture and storage
- Efficiency improvement
- Capacity reduction.
What are the two sources from which NOx can be formed?
Molecular N2 in air, and fuel nitrogen found in fuel source.
Describe thermal NO.
Formed through Zeldovich mechanism.
Slow at low temperatures due to high activation energy.
Practically insignificant at temperatures below 1700K.
Increases at an exponential rate with an increase in temperature.
Describe prompt NO.
Hydrocarbon radicals react with molecular nitrogen to form amines or cyano compounds that from NO. Usually very fast,
What is the air-fuel equivalence ratio?
Ratio of the actual air fuel ratio to the stoichiometric air fuel ratio.
Describe furnace air staging.
Allows deprivation of O2, less mixing of fuel and air in the main combustion zone. Results in a cooler flame therefore less thermal NO.
