25
1.7. Emissions reduction proposals
Air emissions from naphtha hydrotreating in normal operations arise from process heaters,
vents and fugitive emissions.
In order to reduce fugitive emissions, a leak detection and repair program can be established
(refer to part A of this report).
Concerning process heaters, old furnaces that produce NOx, SOx and particulate matters
should be replaced with emission controls furnaces.
During catalyst regeneration, waste vapor is sent to the atmosphere. These vapors contain
coke, VOC and carbon monoxide in trace amount and carbon dioxide. Before being released
in the atmosphere, this gas should be treated. For example, it could go through a first boiler to
burn carbon monoxide and VOCs, and then through a particulate matters removing apparatus,
such as an electrostatic separator or a cyclone separator.
2. Naphtha isomerization
10,14,15,16,17,18,19
Isomerization is a conversion process which aim is to raise octane number by transforming
straight chains C
5
-C
6
paraffins into branched paraffins (isoparrafins). Axens offers a complete
range of isomerization solutions that can increase C
5
-C
6
naphtha cut octane number up to 92.
Isomerization schemes available are once-through, recycle with diisopentanizer or with
deisohexanizer, advanced recycle (IPSORB
®
, HEXORB
®
). The choice of the process depends
on criteria such as feed composition or desired octane number.
2.1. Purpose of the unit
The purpose of the unit is to produce high-octane number isoparaffins by isomerising normal
C
5
-C
6
paraffins. The isomerization unit can also include a benzene hydrogenation step in the
first reactor. Naphtha isomerization unit is located after the hydrotreating unit because the
catalyst is very sensitive to impurities. The product obtained (isomerate) enters in gasoline
composition.
2.2. Raw materials and resources input characteristics
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