Microsoft Word master thesis report fina doc

2.3.4. Wellman-Lord process 
The Wellman-Lord process consists in the SO
2
neutralisation by a sodium-based solution 
which is then regenerated. The following chemical reactions occur: 
SO
2
capture: 
SO
2
+ Na
2
SO
3
+ H
2
O → 2NaHSO
3
Na
2
SO
3
+ ½ O
2
→ Na
2
SO
4
Regeneration: 
2NaHSO
3
→ SO
2
+ Na
2
SO
3
+ H
2
O 
SO
2
-rich gas treatment: 
2SO
2
+ 6H
2
→ 2H
2
S + 4H
2
O 
2H
2
S + SO
2
→ 3S + 2H
2
O 
The final effluent is sent to the Claus unit. 
This process has been often used for utility and industrial boilers. It has the advantage to 
regenerate the scrubbing solution and to produce a saleable product. However, installation and 
maintenance costs are higher than lime, limestone or dual-alkali systems. 
2.4. Control techniques for particulate matters emissions 
For large boilers, a good design and good maintenance can minimize soot and condensable 
organic compounds emissions. However, fly ash is still emitted, and in this case a 
postcombustion PM control is needed. Four common methods are described below. 
2.4.1. Inertial collectors 
Inertial collectors allow separating particles from gas thanks to mechanical forces such as 
centrifugation, gravitation or inertia. The three major types of inertial collectors are settling 
chambers, baffle chambers and centrifugal chambers. 
2.4.1.1. Settling chambers 
A settling chamber is a large box which, by a large size, reduces the speed of the gas stream. 
Thus, heavier particles settle down. 
Figure A-2-1: Settling chamber 
This technique is quite simple and easily manufactured, however it needs a large space and it 
has a low efficiency. 

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2.4.1.2. Baffle chambers 
In baffle chambers, gas stream changes its direction. Heavier particle do not follow the stream 
and settle down. 
Figure A-2-2: Baffle chamber 
This technique is better used as precleaner. 
2.4.1.3. Centrifugal collectors 
Centrifugal collectors use the cyclonic action to separate particles from the gas stream. 
Particles, which are heavier, are directed towards the wall of the cyclone and fall down. 
Figure A-2-3: Cyclone 
Single or multicyclones are available.