Microsoft Word master thesis report fina doc

 
Lock hopper depressurization 
 
Media 
Gas 
Origin 
Lock hopper
Destination 
Atmosphere 
Quantity 
Can be found in process book
Composition 
N
2
, possible presence of alumina dust 

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3.6.3. Solid wastes
Catalyst 
Media 
Solid 
Origin 
Reactors 
Destination 
Regeneration, metal recovery 
Quantity 
Depends on reactor size
Composition 
Contaminated catalyst 
 
Catalyst from reforming process is regenerate every 6 to 24 months for SR process and 
continuously for CCR. Catalysts used are generally very expensive so precautions are taken to 
ensure a long lifetime and losses. When the catalyst has lost its activity, metals are recovered 
off-site.
3.7. Emissions reduction proposals 
3.7.1. Air emissions 
Air emissions from isomerization unit 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 
(see part A of this report). 
Concerning process heaters, old furnaces that produce NOx, SOx and particulate matters 
should be replaced with emission controls furnaces. 
3.7.2. Solid wastes 
Concerning the catalyst, source reduction methods are those that extend its life. Currently, 
recycling of the spent catalyst by sending to metals reclamation is a common practice since 
the catalyst is platinum and other expensive metals. 
3.7.3. Spent caustic 
In order to minimize spent caustic, contact between caustic and gas must be optimized. 
3.8. Dioxins emissions 
According to limited testing performed in the United States, catalyst regeneration in the 
reforming process is a potential source of PCDDs/PCDFs. 
During the reforming process, coke formation onto the catalyst lower its activity. This coke 
can be removed by regeneration via burning at temperatures around 400°C followed by a 
reactivation at temperatures around 500°C using chlorine or chlorinated compounds. This 
coke burning produces exhaust gases that are vented to the atmosphere or scrubbed with 
caustic or water. 

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Studies have been conducted in order to determinate PCDDs and PCDFs concentrations in 
waste streams. However no regulation law has been emitted by European or American 
legislation concerning dioxins in petroleum industry. 
Once dioxins are produced, it is difficult to eliminate them as treatment methods or disposal 
systems just transfer dioxins from a medium to another (for example, to scrub a gas transfer 
dioxins to liquid). Decomposition of dioxins seems to not be widely used. 
A better option would be to prevent dioxins formation, which is also difficult as formation 
mechanisms are not well-known and chlorinated compounds are necessary in this process. 
4. Hydrogenation in olefin plants 
 
Hydrogenations are simple and relatively similar units present in olefin plants. They are 
purification steps whose aim is to selectively hydrogenate dienes, alkynes and olefins which 
are unstable compounds into olefins and alkanes. These processes generally do not produce a 
lot of effluents. The main issue is basically effluents produced during the catalyst 
regeneration. Axens has a strong experience with all types of hydrogenation. 
4.1. Purpose of units 
The C
3
hydrogenation unit is a sub-process in an olefin plant. It is designed to selectively 
hydrogenate Methylacetylene (MA) and Propadiene (PD) contained in the C
3
stream from the 
depropaniser overhead, before it is fed to Propylene Towers. Indeed, in addition to up to 90% 
propylene, the raw C
3
cut contains a non negligible quantity of MA and PD that have to be 
removed in order to meet the propylene product specification. The reactions involved are 
hydrogenations of MA and PD with hydrogen. The MAPD hydrogenation to propylene can be 
carried out in either the vapour or liquid phase. All modern steam crackers for which the C
3
cut is separated before hydrogenation ("tail end hydrogenation") use liquid-phase 
hydrogenation as it requires lower investment and has lower operating costs compared to gas-
phase processing. 
The C
4
hydrogenation unit is a sub-process in an olefin plant. It is designed to selectively 
hydrogenate butadiene contained in the C
4
stream from the debutanizer overhead, before it is 
fed to isobutylene and butane-1 removal units. The reaction involved is hydrogenation of 
butadiene with hydrogen. 
The gasoline hydrogenation unit is a sub-process in an olefin plant. It is designed to totally 
hydrogenate raw pyrolysis gasoline (RPG) which is the bottom product of the ethylene plant 
debutanizer. The purpose of this unit is to eliminate unstable components such as diolefins 
and styrenics, and olefins in order to meet the product specification. Indeed cracked gasoline 
typically exhibits high aromatics content, about 50% being benzene. It is an ideal feedstock 
for benzene production. However, treatment steps with adequate fractionation facilities are 
required upstream of the benzene process in order to meet sulphur, olefins and diolefins 
content specifications. The treatment process operates in two stages. About 90 first stages and 
60 second stages of gasoline hydrogenation have been licensed by Axens. 

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4.2. Raw materials and resources input characteristics