Refinery Procucts and processes Notes

Key Functions of Modern Refineries

• Fractionate crude oil into separate boiling range products.

• Shift products from less desirable to more desirable boiling ranges.

• Alter product quality to meet commercial and regulatory requirements.

• Product specifications are important for meeting customer requirements, protecting equipment, meeting performance criteria, and meeting environmental and safety regulations.

Refinery Products Overview

• Light Naphtha: < 30^{\circ}C, from distillation crude oil.

• Heavy Naphtha: 30.

• Liquefied Petroleum Gas (LPG): Gas Plant/Fuel Gas Propane/Butane.

Low-Boiling Products

• Fuel Gases.

• Liquefied Petroleum Gases (LPG).

Gasoline

• Light Naphtha.

• Heavy Naphtha.

Distillate Fuels

• Jet Fuels (kerosene).

• Automotive Diesel Fuels.

• Heating Oil.

Fuel Oils

• Marine Fuel, Shipping fuel.

Asphalt

Low-Boiling Products Details

• Methane (C_1): Used as refinery fuel or for hydrogen production via steam reforming.

• Ethane (C_2): Used as refinery fuel or petrochemical feedstock for ethylene production in steam cracking.

• Refinery C_3s:

  • Propane: Used as refinery fuel or sold as LPG.

  • Propylene: Used in refineries (70% purity) or polymer manufacture (99%+).

• Refinery C_4s:

  • Normal Butane (n-C_4): Valued as gasoline blending component or sold as LPG.

  • Iso-butane (i-C_4): Used for alkylation or MTBE units.

Gasoline Details

• Complex mixture of hydrocarbons with boiling ranges from 38 to 205^{\circ}C.

• Finished product is a blend of several streams.

• Most refiners produce regular and premium grades.

• Important properties:

  • Reid Vapor Pressure (RVP) - Volatility.

  • Sulfur Content.

  • Benzene (Aromatics) Content.

  • Engine Knock Properties (Octane Rating).

Distillate Fuels Details

• Fuels in the 150-450^{\circ}C range.

• Primary sources: straight run distillate range, light gas oil from FCC and other processing units.

• Blended from refinery streams to meet desired specifications.

  • Three types:

  • Jet and turbine fuels.

  • Automotive diesel fuels.

  • Final use, BP range, and specifications are important.

Jet and Turbine Fuels

• Blend of Hydrocarbons (177-288^{\circ}C).

• Used for commercial (Jet-A, A-1) and military (JP-5, 8) aircraft.

• Main fraction is straight-run kerosene.

• Primary difference between jet fuels is freezing point.

Automotive Diesel Fuels

• No. 1 (super-diesel): Made from virgin or hydrocracked stocks, cetane over 45, used for high-speed engines (182-316^{\circ}C).

• No. 2: Wider boiling range than No. 1, blended from naphtha, kerosene, FCC and coker light oil.

  • Cetane is a key property: Measure of ignition quality; higher number, easier to start diesel engine.

Residual Fuel Oil

• Composed of heaviest crude oil parts, generally vacuum unit fractionating tower bottoms.

• Used as power plant fuel, bunker fuel, or processed to make asphalt.

• Types:

  • HSFO: Sells for low price (70% of crude oil).

  • LSFO: Very low sulfur heavy fuel oils (price of crude).

Catalytic Cracking

• Conversion of heavy oils into lighter, more valuable products like gasoline.

• Lowers average molecular weight and produces high yields of fuel products.

• Has almost completely replaced thermal cracking due to higher gasoline and olefins yields.

• Produces carbon (coke) that lowers catalyst activity; catalyst is regenerated by burning off coke with air.

• Classified as moving bed or fluidized bed units (FCC).

Fluidized Catalytic Cracking (FCC)

• Upgrades heavy, low-value petroleum streams like vacuum gas oil (VGO) into higher value products, mainly gasoline.

• Circulates a catalyst with feed vapors into a riser-reactor for a few seconds.

• Cracked products are separated, and the catalyst is circulated back to the regenerator where coke is burned off.

• Coke combustion generates heat required for the endothermic reaction in the riser.

FCC Reaction and Regeneration Zones

• Reaction Zone (endothermic):

  • Fresh feed combined with catalyst and steam in riser.

  • Cracking produces HCs, cokes catalyst.

  • Separation of coked catalyst and flue products (cyclones).

  • Vapors taken overhead to fractionator.

  • Deactivated catalyst to regenerator.

• Regeneration Zone (exothermic):

  • Steam stripping to remove remaining oil.

  • Controlled combustion (air) to remove carbon.

  • Separation of catalyst and flue gases (cyclones).

  • Hot regenerated catalyst back to reactor.

FCC Unit Types

• Two basic types: ‘‘Side-by-side’’ and “Orthoflow or stacked”.

• The fluidized catalyst is circulated continuously between the reaction zone and the regeneration zone and acts as a heat carrier from the regenerator to the oil feed and reactor.

FCC Reactor

• Riser reactor is a tall cylindrical unit where reactions occur in the vapor phase.

• Preheated feed is injected through atomizers or nozzles for rapid vaporization.

• Heat for vaporization comes from hot regenerated catalyst particles.

• Vaporizing temperature depends on the feed, usually between 350 and 450^{\circ}C.

• Catalyst temperature at reactor entry is an important parameter.

FCC Regenerator

• Catalyst leaving the stripper needs regeneration before being recycled to the riser reactor.

• Adsorbed coke and hydrocarbons are burned off in the regenerator.

• Functions:

  • Restoring catalyst activity.

  • Supplying heat for the reactor.

• Air is used to fluidize catalyst particles and for combustion.

• Coke is converted to carbon monoxide and carbon dioxide.

• The ratio between CO_2 and CO is related to temperature control of regenerator.

• If CO is produced, a CO incinerator may be used to convert CO to CO_2

FCC Design Features

• Short contact time cracking: Maximizes valuable product production by minimizing re-cracking and thermal cracking effects.

• High efficiency feed injectors: Optimize product distribution by efficient feed atomization and effective mixing with hot regenerated catalyst.

• Efficient spent catalyst stripping: Minimizes valuable products carryover to the regenerator.

• Effective catalyst regeneration: Optimizes regeneration of spent catalyst due to its reactor cracking result impact.

FCC Operating Conditions

• Typical riser temperature: 480-550^{\circ}C.

• Regenerator temperature: 650 – 760^{\circ}C

• Reactor pressure: generally limited to 15 to 20 psig.

• Initial catalyst charge: about 3-5 tons per 1000 bbl.

• Catalyst circulation rate: about 1 ton/min.

• Residence time in the riser: 2–10 s.

• Feed conversion: about 70% and the catalyst to oil ratio is about 7

FCC Feedstock

• Atmospheric & vacuum gas oils are primary feeds.

• Considerations due to chemical species:

  • Aromatic rings typically condense to coke.

  • No hydrogen added to reduce coke formation.

  • Amount of coke formed correlates to carbon residue of feed.

  • Feeds normally 3‐7 wt% CCR.

• Catalysts sensitive to heteroatom poisoning by nitrogen & metals (nickel, vanadium, & iron). Feeds may be hydrotreated

FCC Reactions

• Products formed in catalytic cracking are the result of both “primary” and “secondary” reactions

• Reactions are acid site catalyzed cracking & hydrogen transfer via carbonium mechanism

FCC Products

• Dry gas, liquified petroleum gas (LPG), gasoline, light cycle oil (LCO), Heavy coker oil (HCO), and coke.

• LPG contains propylene, butylenes and are used as feed for alkylation

• Gasoline is the desirable product and its yield can be increased by increasing catalyst to oil (C/O) ratio or operate at maximum possible temperature

Residue Upgrade Processes

• Resid refers to the bottom of the barrel, atmospheric or vacuum tower bottoms rich in sulfur, nitrogen, and metals.

• Due to environmental regulations, resid must be converted to produce fuels blending stocks.

Hydroprocessing

• Used to denote processes to reduce boiling range and remove impurities (metals, sulfur, nitrogen, high carbon forming compounds).

• Techniques:

  1. FIXED BED PROCESSES (low to medium metal content)

  2. EBULLATED BED PROCESSES (high metal content)

  3. MOVING BED PROCESSES (high metal content)

Hydrotreating Catalyst

• A porous alumina matrix impregnated with combinations of cobalt (Co), nickel (Ni), molybdenum (Mo) and tungsten (W).

  • Cobalt and molybdenum oxides on alumina catalysts are in most general use because they have proven to be highly selective, easy toregenerate, and resistant to poisons