Formation Of Emissions

Question 1

CO Carbon monoxide

Answer 1

C+O2 =2CO

usually formed with incomplete combustion.

Can be prevented by control of residence time in chamber, air/fuel ratio and temperature.

Question 2

Sulphur dioxide

Answer 2

S+O2=SO2

Almost always released to the gas phase during combustion.
Organic sulfur :usually bonded to hydrocarbons.
Inorganic sulfur imbedded in coal as loos pyrite.
Mostly in coal & oil

Question 3

NOx formation mechanisms

Answer 3

1. Thermal NO
2. fuel NO : volatiles NO and char NO
3. Prompt NO

Question 4

Thermal NO

Answer 4

It is formed when Nitrogen combines with O and OH radicals.
N2+O= NO+N
N+O2= NO +O
N+OH=NO +H

the formation is entirely dependent on temperature. The higher the temperature the more NOx is formed.
It also relies on time and pressure.

Question 5

What is the key to lower NOx formation?

Answer 5

Reducing the temperature in combustion chambers is the key to lower NOx formation.

Question 6

Fuel NO

Answer 6

When nitrogen is chemically bonded to fuels it all turns into NOx .
This typically found in solid and liquid fuels .
Fortunately refineries that remove sulfur remove NOx as well.

Question 7

Prompt NO

Answer 7

Even when thermal and fuel NOx are removed NOx can still be formed . This formation is through the atmospheric oxygen bonding with combustion radicals.

CH+N2=HCN+N
N+OH= NO+H
N+O2=NO+O
HCN +O2 = NO +CO + H

Question 8

Is Prompt NOx temperature dependent ?

Answer 8

No it is not and it only becomes important after the other mechanisms have been suppressed.

PROMPT NOx HAS NO WAY TO BE REDUCED ! hence focus is placed in the other two.

Question 9

Formation of organic compounds

Answer 9

These include volatile (have a high vapor pressure point even at room temperature and easily evaporate into air) ,semi volatiles(moderate vapor pressure and evaporate more slowly that volatiles ) and condensable organic compounds (they exist in the gas phase but can also condense into liquid or solid under certain conditions like changes in temperature or pressure).

Emissions of these compounds are dependent on combustion behavior ie. temperature,residence time , air/fuel ratio.
Particularly present during the start up of a cold combustion unit

Question 10

Formation of particulate matter

Answer 10

There are different particles formed depending on the combustion precursor

1. Combustion particles formed from gas precursors:
   a. At high temperatures: soot (formed from incomplete combustion , inorganic particles.
   b. At exhaust temperature: condensation of sulfuric acid and organic material.
2. Particle matter formed from liquid or solid precursors:
   Fly ash

Question 11

Soot formation mechanism

Answer 11

It is formed under fuel rich conditions
The most critical step is the formation of the first aromatic ring after that is formed growth continues with formation of PAH (polycyclic aromatic hydrocarbons.