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Composition 
Light fuel gas, H
2
S (see material balance) 
 
Off-gases are very rich in hydrogen sulphide and light hydrocarbons. It is typically sent to the 
sour gas treatment unit and sulfur recovery unit. 
 
Flue gas from furnaces 
 
Media 
Gas 
Origin 
Fuel oil or fuel gas combustion in heaters 
Destination 
Atmosphere 
Quantity 
Can be known from process data 
Composition 
CO
2
, SOx, NOx, PM, VOCs, metals - Calculated with Emission 
Factors 
 
These emissions are indirect emissions from the process. They come from the fuel 
combustion in heaters. These emissions can be estimated thanks to Emission Factors. They 
depend on the type of fuel burned, firing practice and post combustion controls. The choice of 
fuel oil or fuel gas burned in furnaces depends on the fuel available on-site.
 
 

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Sour waters 
Media 
Liquid 
Origin 
Separators 
Destination 
Sour waters treatment 
Quantity 
6 to 12 % of the charge 
Composition 
Salts (≈5%) 
Sour waters come from stripping steam injected after reactors. Sulfur is converted into H
2
S 
and mercapts, nitrogen compounds are converted into NH
3
and cyclic hydrocarbons are 
converted into phenols. These waters are sent to sour waters treatment. 
1.6.2. Intermittent operations 
Spent caustic stream from catalyst regeneration 
Media 
Liquid 
Origin 
Separator drum 
Destination 
Spent caustic treatment unit 
Quantity 
Estimated in process book 
Composition 
Estimated in process book – H
2
O (≈92%), Salts ((≈8%), HC < 50 wt 
ppm 
During regeneration, a spent caustic stream is drained from the separator drum and sent to the 
spent caustic treatment unit. 
Waste vapor from catalyst regeneration