W9- Downstream Processes Flashcards
Overall stages of refining
Pre-treatment, separation, conversion, treatment
Desalting (Pre-treatment)
Hot water for extraction agent and electrostatic potential difference (electrostatic separator).
Remove salt, water, sediments, and suspended solids
Problem if salts not removed from crude oil
fouling and corrosion in pipes downstream
O&G Separation
Split crude oil feeds into HC cuts, with light HC vaporising and rising up and heavier drawn at bottom
Fractional Distillation (ADU) (Separation)
Straight-run cuts from different boiling fractions separated: light & heavy naphtha, kerosene, atmospheric gas oil and residue.
Fractionator collects separate crude cuts as they condense on tray at Temp below BP.
Fractionator internals (Separation)
Bubble caps (prevent condensate flowing down, allow vapour flow up)
Downcomers (ensure vapour/liquid flow separately)
Income/outcoming weirs (prevent waves on each tray)
Valve trays (collect condensed liquid)
Vacuum Distillation (VDU) (Separation)
Separates high BP material from ADU residue & avoids too high temp in separating the residue.
Higher temps would result in thermal cracking
Conversion & types
Increase yield of high-value HC products.
Cracking, catalytic reforming, isomerization, oligomerization (alkylation & polymerisation).
Steam Cracking (Conversion)
Steam used to produce unsaturated HCs from alkanes
Products: ethylene, alkenes/alkynes.
Hydrocracking (Conversion)
Cracks lighter waxes in crude with H2 to produce high-demand lighter oil fractions.
Wax is hydrotreated before cracked & S removal to ensure sweet (low S).
Products: Naphtha, diesel oil, gas oils.
Fluid Catalytic Cracking (FCC) (Conversion)
High temp and zeolite-based catalyst to crack heavy gas oils & wax (ADU residue and vacuum gas oil) into lighter fractions and components for blending.
Feedstock is pre-heated and vaporizes in contact with a hot catalyst.
Products: Naphtha, gas oils, fuel oil
Coking (severe thermal cracking) (Conversion)
Thermal cracking (heavy wax upgrade to lighter cuts)
Converts VDU residue to lighter valuable distillate products, off-gas and petroleum coke.
Heavy product remains as solid coke- periodically removed.
Products: Naphtha, gas oil, coke
Catalytic Reforming (Conversion)
Improve naphtha quality by enhancing aromatic content - increase of ON.
(Aromatics=high ON, paraffins = low ON)
Isomerization (Conversion)
Chemical transformation of molecule to other form, with same molecular formula (normally branched).
Increase ON as branched molecules = high ON
Oligomerisation (Alkylation & Polymerisation) (Conversion)
Combine light gaseous HCs to increase MW and ON.
Hydrotreating (Treatment)
Removes harmful components (s-N2-O2-metals) from HCs using H2 over a metal catalyst.
What happens if S left/burnt?
Toxic gas oxides yield corrosive acids that destroy catalysts, equipment etc.
Hydrosulpherisation (Treatment)
Catalytic HC vapour hydrogenation/S removal.
Amine Gas Treater (Treatment)
Gas sweetening to remove CO2/H2S from gases via aqueous amine solutions (absorption column).
Claus Sulfur Units (Treatment)
Sulfur recovery from previously captured H2S in amine gas treater.
H2S converted into sulfuric acid/S to be sold as feedstock for fertilisers, medicine etc.
Ethylene & Olefins Production & source
Steam cracking process using light HCs (Mainly Naphtha, else ethane, propane, butane).
Steam transports HC feedstock into heaters and cracked -> ethylene, H2, other olefins
Ethylene derivatives
Plastics: polymerisation with catalyst for ethylene into PE;
Intermediates, reactive/flammable feed (converted for stability first)
