Refining Processes

Alkylation

Alkylation is a process for chemically combining isobutane with light olefinic hydrocarbons, typically C3 and C4 olefins, (e.g.propylene, butylene) in the presence of an acid catalyst, usually sulphuric acid or hydrofluoric acid. The product, alkylate (an isoparaffin) has a high-octane value and is blended into motor and aviation gasoline to improve the antiknock value of the fuel.

The light olefins are most commonly available from the Catalytic crackers.

Alkylate is one of the best gasoline blending components because it is a clean burning, very low sulphur component, with no olefinic or aromatic compounds and with high octane and low vapour pressure characteristics.

The Indian scenario is unique, in that on the one hand, the relative gasoline consumption is much lower vis a vis the developed counter parts, on the other hand, the C3 and C4 components, which are otherwise used in alkylation as a feedstock, offer much higher value alternative, i.e. LPG.

LPG is in large deficits in India, and to meet its demand, Reliance's configuration is designed to maximize the production of LPG. Hence the processing scheme currently does not include Alkylation.

Bottom of the Barrel Processing

"Bottom of the barrel" is a term used to refer Vacuum residue (VR) boiling above 5650C. It is produced from bottom of the Vacuum Distillation Column. Traditionally this material, high in sulphur, asphaltenes and metals has been blended into heavy or industrial fuel oil.

Outlets for high sulfur fuel oil are becoming increasingly scarce, with stringent emission norms for SOx and NOx . In the most parts of the world, increasing switch over from heavy fuel oil to clean combustion natural gas for power generation is already evident. The process of displacing high sulfur fuel oil is expected to gather further momentum as further switching from fuel gas to natural gas takes place for environmental and availability reasons.

There are several options for the bottom-of-the barrel processing including Delayed Coking, Visbreaking and Resid Desulfurization. Reliance has selected Delayed Coking for upgrading the "bottom of barrel".

Catalytic Cracking

Catalytic cracking is a process which breaks down the larger, heavier, and more complex hydrocarbon molecules into simpler and lighter molecules by the action of heat and aided by the presence of a catalyst but without the addition of hydrogen. In this way, heavy oils (fuel oil components) can be converted into lighter and more valuable products (notably LPG, gasoline and middle distillate components). The catalytic cracking unit is known as the Fluidized Catalytic Cracking or FCC.

The FCC is the most widely used secondary conversion process in the refinery industry. Traditionally, the FCC units have been operated on either the maximum gasoline mode or the maximum distillate mode, dependent largely on the seasonal product demand pattern.

Of late, a third mode is gaining importance, that of a maximum olefin mode which maximizes LPG, propylene and butylene. In India, FCC in the max olefin mode is suitable for maximum value addition because LPG and propylene are among the highest value petroleum products. Reliance operates the Jamnagar FCC in the max olefin mode, to maximize LPG and propylene. FCC in the max olefins mode also produces isobutylene which can be used for

MTBE, isobutane and butylene which can be processed into alkylate and isoamylene which can be used for TAME. MTBE, Alkylate and TAME are principal gasoline additives used to improve gasoline quality. Reliance utilizes the isoamylene from the FCC as a feedstock to produce TAME in the Jamnagar Refinery.

The FCC feed is also known as vacuum gas oil (VGO) because it is generally a product from the Vacuum Distillation Column. The FCC feed can be of three types:-

• VGO
  
  
• Hydrotreated VGO
  
  
• VGO mixed with VR (Process is known as Resid FCC or RFCC).

The VGO material for the FCC feed is generated from the Vacuum Distillation Column in the CDU/VDU and from the Coker.

Delayed Coking

Delayed Coking is a high severity "Bottom of the barrel processing" scheme by which heavy crude oil fractions can be thermally decomposed under conditions or elevated temperatures to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units or blended into products. The coke can be used either as a fuel or in other metallurgical applications such as the manufacturing of steel or aluminum.

The Delayed Coking process achieves approximately 70% of residue conversion to lighter products compared to only about 30% in Visbreaking. Reliance has selected Delayed Coker to maximize conversion to higher products.

Reliance, with a large Delayed Coker to handle 100% of Vacuum Residue, is able to achieve much higher value addition and "zero fuel oil production".

Distillation (Atmospheric and Vacuum)

This is the first stage in the refining for separating crude oil components at atmospheric pressure by heating, and subsequent condensing, of the fractions (unfinished petroleum products) by cooling. Distillation under reduced pressure (less than atmospheric) i.e. Vacuum Distillation lowers the boiling temperature of the liquid being distilled permitting the production of distillates at lower temperature than would be necessary in atmospheric distillation, thus avoiding coke formation.

The Jamnagar Refinery has a combined Crude Distillation Unit / Vacuum Distillation Unit (CDU / VDU) to separate the crude oil into primarily fractions of LPG, Naphtha, Kerosene, Gasoil, Vacuum Gas Oil and Vacuum Residue. The combined CDU/VDU maximizes energy integration to minimize the energy required for primary separation.

Hydrotreating

Hydrotreating is used for treating petroleum fractions in the presence of catalysts and substantial quantities of hydrogen. Hydrotreating results in desulphurisation, (removal of sulphur), denitrification (removal of nitrogen compounds) and conversion of olefins to paraffins.

Reliance has the highest Hydrotreating Capacity relative to crude distillation which enables it to produce world class products and high value addition.

Oxygenates

Oxygenates are ethers which are used as gasoline additives to improve the gasoline. Two principal oxygenates are Methyl Tertiary Butyl Ether (MTBE) and Tertiary Amyl Methyl Ether (TAME).

Reforming

Reforming Process rearranges hydrocarbon molecules in the naphtha (or naphthatype) feed, thereby converting paraffinic and naphthenic type hydrocarbons into aromatic type hydrocarbons, suitable for blending into finished gasoline. Since its product, reformate, is richer in aromatics than its feed, naphtha, this process is also used to produce aromatic petrochemicals (Benzene, Toluene and Xylene).

The Reforming process requires high temperature and catalyst to facilitate the reaction.The Reforming catalyst contains Platinum. The Platinum based catalyst has to be protected and hence reformer feed has to be sulphur free.

Thermal Cracking

In this process, heat and pressure are used to break down, rearrange, or combine hydrocarbon molecules. Thermal cracking includes vis-breaking, delayed coking, fluid coking, and other similar processes.

Vis-breaking

Vis-breaking is a relatively mild thermal cracking process in which heavy atmospheric or vacuum-distillation bottoms are cracked at moderate temperatures to make light products and produce a lower viscosity residue than the initial feed to the unit.

Vis-breaking process achieves about 30% of residue conversion to lighter products. Vis-breaking is one of the least costly upgrading processes, and is common where there is still a relatively large use of heavy fuel oil. But with the problems of suRelianceus fuel oil compounding the world over, the importance of this process is expected to decline.

Sweetening The petroleum products should be free of mercaptans (a form of sulphur compound) because otherwise it emits foul odour on burning. Sweetening is a process of mercaptan removal by oxidation. This sweetening process is also better known by the patented process name of Merox or mercaptan oxidation. Reliance has 4 sweetening units to remove mercaptans from :-

• Saturated LPG
  
  
• Unsaturated LPG
  
  
• Gasoline
  
  
• Kerosene