petroleum refinery
DESCRIPTION
Solution ManualTRANSCRIPT
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Petroleum Refining
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Petroleum Refining is the process of taking crude oil and reprocessing it into a number of different products
Crude Oil - a yellow/black liquid found underneath the surface of the earth which contains various hydrocarbons and other liquid organics
Typical refineries are very large industrial complexes made up of many primary and auxiliary units
No two refineries are identical in that each handles varying amounts of crude oil and produces vary amounts of products depending on location and demand
What is it?
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ProductsLight Distillates
Liquid Petroleum Gas (LPG)
Gasoline (Petrol)
Light and Heavy Naphtha
Middle Distillates
Kerosine
Diesel Fuels
Heating Fuels
Other Light Fuels
Heavy Distillates
Heavy Fuel Oils
Bunker Fuel Oil
Others (not all listed)
Petroleum Naphthas
Solvents
Elemental Sulfur
Petrochemicals
Asphalt and Tar
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General Flow DiagramSince gasoline is the most desired product, that is what a majority of the crude oil is used to produce
Aside from air and water, hydrogen gas and H2S are frequently used and are thus produced on site
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Crude Oil Distillation UnitThis is the first step for all refineries
The crude oil is heated up until it boils, and then, by using fractional distillation, the heavier hydrocarbons (higher BP) can be separated from the light ones (lower BP)
As the gases travel up the column, they will condense and can be pumped out
No reactions occur within the distillation column
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Crude Oil Distillation UnitThe products by temperature range and chain length are:
< 40 oC - Petroleum Gas (C1 - C3)
40 - 200 oC - Gasoline (C4 - C12)
200 - 250 oC - Kerosene, Jet Fuel (C12 - C16)
250 - 300 oC - Heating Oils (C15 - C18)
300-370 oC - Lubricating Oils (C19 +)
370+ oC - Residue, Asphalt (C25 +)
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Vacuum DistillationVacuum distillation units are found in 80+% of refineries
At very low pressure, the leftovers from the initial distillation tower can be vaporized without cracking
These oils can later be cracked with the aid of catalysts to control the product formation
They are primarily used to produce addition gasoline
No reaction occur during vacuum distillation
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Naphtha HydrotreaterNaphtha - a flammable oil made up of various hydrocarbons with sulfur atoms
By treating the naphtha fraction with hydrogen, refineries are able to desulfurize the hydrocarbons
The purpose of this is to reduce the SOx emissions generated from using the fuels produced
Nitrogen and Olefins will be removed as well
Primary Reactions
C-S + 3/2 H2 > R-C-H + H2S
C=C + H2 > H-C-C-H
C-N + 2 H2 > C-H + NH3
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Catalytic ReformingCatalysts are used to convert the desulfurized naphtha into higher-octane molecules know as reformates
N.B. - Octane rating measure the compression which can be withstood before ignition
The reformates are rearranged and cracked versions of the hydrocarbons
These are a component of the final gasoline product
Primary Reactions:
R-R + H2 > R-H + R-H
R-C-R > C-R-R (and similar rearrangements)
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AlkylationConversion of isobutane and butylene into alkylate, another high-octane component of the gasoline product
The process is typically done in sulfuric acid of hydrofluoric
The product alkylate can either be used directly or farther alkylated in order to produce a higher premium product for aviation fuels
Primary Reaction: butene + isobutane > 2,2,4 - trimethylpentane
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IsomerizationThe two distinct isomerization process are butane isomerization and pentane/hexane isomerization
In this process, the straight chains are catalyticlly rearranged into their branched isoparaffins of a higher octane number
For low temperature butane isomerization, aluminium chloride and HCl are typically used, whereas with high temperature isomerization, platinum or other metal catalysts are used
The reaction is simply a catalytic rearrangement similar to the following: R-C-R > C-R-R
The above is a generic sense of the rearrangement. The catalyst will determine the exact isomerization product
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Distillate HydrotreaterSimilar to the Naphtha hydrotreater, it uses hydrogen gas to desulfurize other fractions of the crude oil distillate in order to reduce the production of Sox gases from use
It will also remove nitrogen and aromatics; exactly what depends on the feed
Primary Reactions:
C-S + 3/2 H2 > R-C-H + H2S
C-N + 2 H2 > C-H + NH3
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Merox (Mercaptan Oxidizer)
These units also desulfurize fraction of the crude oil distillation, specifically liquid petroleum gas, kerosene, and jet fuels, but by oxidizing undesired mercaptans (also known as thiols, the R-S-H group)
The overall reaction can be written:
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Amine Gas Treater & Claus UnitThese two units are used in conjunction to create elemental sulfur from the H2S byproduct of the hydrotraters
This process makes up the majority of all sulfur production worldwide
The Amine Gas treater also reduces the CO2 levels, which when present in gas, sharply reduces its markability
Primary Reactions:
RNH2 + H2S > RNH3+ + SH- (Amine Gas Treater)
2 H2S + O2 S2 + 2 H2O (Claus Unit)
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Fluid Catalytic CrackingConverts heavy, high-boiling fractions into lighter products with a higher octane rating to be used in gasoline
This used to be done by thermal cracking, but the catalytic cracking allows the refineries to control the product they produce, and as such is now the common method
Carbon is deposited on the catalyst in this process and reduces the performance of the catalyst
This catalyst coke is burnt off in a regenerator
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HydrocrackerUses hydrogen gas to break large carbon chains into smaller ones of a higher octane rating
The process works by pumping the hydrogen gas and crude oil distillate at high pressures over towers of catalyst
The main products of this are jet fuel and diesel
Primary Reaction:
R-R + H2 > R-H + RH
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VisbreakerThis unit is responsible for thermally cracking the heavy residual oils of the vacuum distillation into more valuable products with a reduced viscosity
While they are old, straight forward units, they will continue to be present in refineries for many years to come with more modernized designs that help decrease energy losses and increase conversion efficiencies
Thermal Cracking Reaction:
2C-C > [ 2C+
+ C-C ] > 2C + C=C
The initial and final molecule will be longer than ethyls and methyls, but it is the same idea
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Delayed CokingConverts heavy residual oils into petroleum coke, a carbonaceous solid, in addition to naphtha and other gas oils
The coke is referred to as fuel grade, meaning it is high in sulfur and metals) and anode grade (low in sulfur and metals)
Coke that is primarily carbon can be sold for use in fuel, whereas anode grade coke sees use in the aluminium and steel industries
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Sourceshttp://www.elmhurst.edu/~chm/vchembook/513refining.html
http://www.pavementinteractive.org/article/asphalt-production-and-oil-refining/
http://www.eia.gov/todayinenergy/detail.cfm?id=9130
http://www.eoearth.org/view/article/149994/
http://www.eoearth.org/view/article/153923/
http://www.pescova.com/oil_recovery/hydrotreating_system.shtml
http://www.uop.com/?document=uop-the-role-of-the-merox-process-in-ultra-low-sulfur-transport-fuels-production-tech-paper&download=1
http://www.newpointgas.com/amine_treating.php
http://www.eia.gov/todayinenergy/detail.cfm?id=9150
http://www.refiningnz.com/visitors--learning/classroom--learning-resources/learning-centre/how-it-works---the-refining-process/hydrocracker.aspx
http://www.sciencedirect.com/science/article/pii/S1026309812000612#
http://www.punjlloydgroup.com/landmark-projects-gallery/visbreaker-unit-and-sulphur-block