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Process

A brief description of the BPCL Mumbai Refinery Process Units is as follows - 

The list of various process plants as a simplified refinery flow diagram is enclosed as per Annexure I.

Crude Distillation Unit (CDU - 1)

The Crude Distillation Unit, comprising a series of distillation columns, separates crude oil into several groups of fractions viz. Refinery Gas (which is burnt in the refinery furnaces), Liquefied Petroleum Gas (Bharat Gas), Naphtha, Kerosene, Diesel Oil and Long Residue that is further processed in the Feed Preparation Units (FPU).

Heavy Crude Unit (CDU – 2)

The Heavy Crude Unit comprises of a distillation column wherein Heavy / Light Imported Crude separates into various fractions viz. Fuel gas, LPG, Naphtha, Kerosene, Gas Oil and Long Residue, which is further processed in Feed Preparation Units (HVU).

New Crude Distillation Unit (CDU – 3)

The new Crude Unit comprises of a distillation column wherein Heavy Imported Crude separates into various fractions viz. Fuel gas, LPG, Naphtha, Kerosene, Gas Oil and Long Residue, which is further processed in integrated Vacuum Distillation Unit (VDU) i.e. Feed Preparation Unit.

Feed Preparation Unit (FPU / HVU / VDU)

These units prepare feedstock for Catalytic Cracking Units by separating the Long Residue (from the Crude Distillation Unit and Heavy Crude Unit) into two components, a distillate known as Waxy Distillate and a heavy residue called Short Residue. The separation is carried out at pressures well below atmospheric pressure, which helps to reduce the temperature required for this separation. The Waxy Distillate is the feedstock for the Fluid Catalytic Cracking Units. Part of the Short Residue (of Imported crude origin) is processed further for the manufacture of Bitumen and the balance is diverted to Furnace Oil Blending. Bombay High Short residue becomes a component of LSHS.

Fluid Catalytic Cracking Unit (CCU / FCCU)

The distillation unit yields straight run products contained in the crude oil. However, some of these are not suitable in quantity and quality to meet the present requirements. For example, the quality of gasoline found naturally in crude oil does not satisfy car engine requirements. Also one needs higher yields of middle distillates, which the distillation unit alone cannot provide. These requirements of more middle distillates, better gasoline and more LPG, have resulted in the evolution of the Fluid Catalytic Cracking Units.

In these units, feedstock is charged to a Reactor in which it is contacted with hot catalyst, made of Silica-Alumina, that vaporizes this feedstock and at the same time brings about its chemical decomposition by cracking. The cracked vapors pass over to the Fractionator where they are separated into gas, gasoline, cycle oils and clarified oil.

During the cracking reaction, some carbon gets deposited on the surface of the catalyst, which is continuously removed by “burning” in the Regenerator. A Stripper that entrains and separates hydrocarbons by stripping with steam reduces the load on the Regenerator. Hot regenerated catalyst is then returned to the Reactor to renew the cycle.

The catalyst, in the form of a fine powder moves between the three main vessels as a fluid. Cracking produces higher quality gasoline and other valuable products. Gas is burnt in the refinery furnaces. LPG is sold to domestic and industrial customers. Cycle oils are blended to diesel and Clarified oil is blended with Short Residue from the Feed Preparation Unit to produce furnace oil / LSHS.

Hydro-Cracker Unit (HCR)

Products from distillation unit / Catalytic Cracking Unit does not meet all stringent qualities like sulfur, etc. Also one needs higher yields of middle distillates with better qualities, which the distillation / Catalytic Cracking Unit alone cannot provide that had resulted in the evolution of the Hydro-Cracker Units.

In these unit, feedstock is charged to a Reactor in which it is contacted with catalyst in presence of Hydrogen, cracking of feedstock and at the same time saturation takes place resulting valuable distillate meeting stringent qualities like low sulfur / high Cetane number gas oils etc. Stream ex Reactor pass over to the Fractionator where they are separated into gas, naphtha, Kerosene, Gas Oil cycle oils and unconverted Oil, which is the feedstock for LOBS unit.

Lubricating Oil Base Stock (LOBS)

In Feed Preparation Unit, unconverted Oil ex HCR is separated under vacuum as feedstock to meet three types of product, namely 100N, 150N & 500N. In block mode operation, feedstock as obtained is charged to a Reactor in which it is contacted with catalyst in presence of Hydrogen resulting Isomerization that improves viscosity index. Streams from reactor are separated as product and the rest is recycled back to Hydrocracker Unit for recovery of distillate.

Reformer Feed Unit (RFU)

Straight run Bombay High Naphtha from Distillation Unit is split in Reformer Feed Unit (RFU) to provide a narrow cut feedstock of 60-90°C, which has maximum potential of Benzene & Toluene and their precursors.

Naphtha Hydro-Desulphurisation Unit

The Naphtha Hydro Desulphurisation Unit comprises of a Catalytic reactor wherein the straight run Naphtha (60-90°C cut) from Reformer feed unit (RFU) is treated in presence of Hydrogen to reduce the Sulphur content to less then 0.5 ppm.

Catalytic Reforming Unit (CRU)

The desulphurised narrow cut Naphtha feedstock obtained from the Naphtha Hydrodesulphurisation Unit is then reformed in Catalytic Reforming Unit (CRU) to yield Reformate. This reformate is separated as middle reformate containing Benzene & Toluene and heavy reformate as blend component in gasoline pool to improve octane.

Aromatic Extraction Unit

Aromatic compounds (Benzene & Toluene) are extracted from the Middle Reformate using Sulpholene as solvent. This extract is then split into Benzene & Toluene, which are valuable petrochemical feedstocks.

New Solvent Unit (NSU)

In this unit, Naphtha is further processed to yield the required cut for the manufacture of special boiling spirit viz. SBP 55/115 and Food grade Hexane. This unit consists of two sections viz. Dearomatisation Unit (DAU) and Fractionator Section. Naphtha is first treated in DAU to reduce the Aromatic content. The DeAromatised Naphtha (DAN) is further processed in Fractionator section consisting of three Splitter Columns for the production of SBP 55/115 and Food grade Hexane (SBP 64/69). SBP 55/115 is widely utilized as a solvent in paint manufacturing and rubber industries while Food Grade Hexane is used in refining of vegetable oils.

Bitumen Blowing Unit (BBU)

The dark colored short residue stream obtained from the Feed Preparation Units of Imported crude oils is almost solid at ambient temperature. Yet, it is not hard enough to be used as road asphalt and thus necessitates further processing.

The above operation is carried out in the Bitumen Plant, where short residue is blown using air at high temperature in order to harden short residue. By altering the operating conditions, different bitumen grades of varying degrees of hardness are produced. Bitumen is filled in drums and despatched by road and rail to distant locations. Bitumen is also delivered in road tankers as a hot liquid for direct application without further heating.

Methyl Tertiary Butyl Ether (MTBE) Unit.

MTBE unit has been installed with a view to provide Lead free gasoline to Mumbai Metro. In this unit, C4 stream from the C3 / C4 separation unit is mixed with Methanol and routed through two reactors in series with MTBE unit, wherein the Isobutylene in the C4 streams reacts with Methanol in the presence of catalyst to produce MTBE. The reactor products are then separated into MTBE & Raffinate. The MTBE product is sent to storage to be blended with MS for Octane boosting and Raffinate is routed to LPG, after recovering water and Methanol, which are recycled.

Diesel Hydrodesulphurisation (DHDS) Unit

High Speed Diesel (HSD) contains contaminants like organic sulphur, nitrogen and metal compounds which contribute to increased levels of air pollution, equipment corrosion etc. The Diesel Hydrodesulphurisation (DHDS) Unit converts this sulphur in the presence of Hydrogen (H2) to H2S so that sulphur level in HSD is reduced to less than 100 ppm. The unit utilizes a fixed bed catalyst process to upgrade the quality of petroleum distillate fractions by decomposing the contaminants with a negligible effect on the boiling range of the feed.

The hydrogen required for this purpose is obtained by Steam Naphtha reforming. The hydrogen unit utilizes either Light Naphtha or High Aromatic Naphtha as feedstock. The raw feedstock utilized to generate hydrogen is first desulphurised in the Final Desulphurisation Unit (FDS) to sulphur level of less then 0.05 ppm. The sweet feed (free of sulphur) is then Prereformed to convert higher hydrocarbon to methane. The methane rich feed is then reformed. The hydrogen obtained by reforming is around 70 % pure. The Pressure Swing Adsorption (PSA) Unit further enhances the purity of hydrogen to 99.99 % volume.

H2S gas from DHDS is treated with Amine to enrich it and then the H2S rich gas is treated in Sulphur Recovery Unit (SRU) to obtain Sulphur as a by-product. The sulphur is obtained by Clauss process. The acid gas from the Clauss reactor is treated in Maximum Clauss Recovery Concept (MCRC) unit to recover Sulphur to the maximum possible extend.

Sulphur Recovery Unit (SRU)

Off-gases from CCU / FCCU / DHDS / HCR and Cracked LPG from Gas Concentration Units (GCUs) are treated in an Amine Treating Unit to remove H2S and CO2. The later are absorbed in Diethanol amine absorbers and stripped in an Amine Regenerator. This H2S rich gas is then fed into the Sulphur Recovery Unit where H2S is converted to SO2 by combustion process. The residual H2S combines with SO2 to produce elemental Sulphur. A thermal stage followed by two catalytic stages is used to achieve the desired yield.

Treating Units

In addition to the hydrocarbons, crude oils also contain small quantities of substances, which are harmful and must therefore be removed before use. Compound such as Mercaptans present in motor gasoline component cause corrosion. These are removed from gasoline by Merox treatment.

LPG is also treated to remove deleterious compounds by caustic soda / Merox treatment to produce Bharat Gas. A small quantity of harmless Mercaptans is added to give a distinct smell for easy detection of leakage.

Utilities Network

The utilities system which is the heart of refinery consists of Gas turbines (cogeneration mode), electricity receipt / distribution, steam generation / distribution, compressed air station, fresh water and sea cooling water supply & circulating system. The fresh water received is treated in the Demineralization plant before feeding to the three boilers & Heat Recovery Steam Generators (HRSG’s).

Waste Water Treatment Plant

The effluent treatment plant is designed to process the effluent from various units like CDU, FPU, FCCU, DHDS, CCU, Aromatics etc.. This facility is designed to process 240 M3/hr of effluent containing pollutants like oil sulphides, phenolics, BOD and suspended solids. Here, the process effluent is given a Powdered Activated Carbon Treatment (PACT), which is a highly effective process to meet the stringent Minimal National Standards (MINAS).

Tertiary Treatment Plant (TTP)

In TTP, the WWTP (MINAS) effluent is processed further, to recover desired quality of water for recycle to DM plant- thus conserving raw water.

TTP is designed for processing 1000 m3/d of effluent with 70 % recovery. The unit consists of a pre-treatment section followed by a suite of Reverse Osmosis (RO) membranes. Permeate from the RO membrane is diverted to DM plant for further processing thereby reducing the raw water requirement for the Refinery.