refinery

A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.

Types of refineries

Different types of refineries are as follows:

• oil refinery, which converts crude oil into high-octane motor fuel (gasoline/petrol), diesel oil, liquefied petroleum gases (LPG), jet aircraft fuel, kerosene, heating fuel oils, lubricating oils, asphalt and petroleum coke;
• sugar refinery, which converts sugar cane and sugar beets into crystallized sugar and sugar syrups;
• natural gas processing plant, which purifies and converts raw natural gas into residential, commercial and industrial fuel gas, and also recovers natural gas liquids (NGL) such as ethane, propane, butanes and pentanes;
• salt refinery, which cleans salt (NaCl), produced by the solar evaporation of sea water, followed by washing and re-crystallization;
• metal refineries refining metals such as alumina, copper, gold, lead, nickel, silver, uranium, and zinc; and
• vegetable oil refinery

An oil refinery

A typical oil refinery

The image below is a schematic flow diagram of a typical oil refinery depicting various unit processes and the flow of intermediate products between the inlet crude oil feedstock and the final products. The diagram depicts only one of the hundreds of different configurations. It does not include any of the usual facilities providing utilities such as steam, cooling water, and electric power as well as storage tanks for crude oil feedstock and for intermediate products and end products.^[1][2]

Schematic flow diagram of a typical oil refinery

A typical natural gas processing plant

A natural gas processing plant

The image below is a schematic block flow diagram of a typical natural gas processing plant. It shows various unit processes converting raw natural gas into gas pipelined to end users.

The block flow diagram also shows how processing of the raw natural gas yields byproduct sulfur, byproduct ethane, and natural gas liquids (NGL) propane, butanes and natural gasoline (denoted as pentanes +).^{[3][4][5][6][7]}

Schematic flow diagram of a typical natural gas processing plant

Sugar refining

Harvested sugar cane ready for processing.

Sugar is generally produced from sugarcane or sugar beets. However, the global production of sugar from sugarcane is at least twice the production from sugar beets. Therefore, this section focuses on sugar from sugarcane.

Milling

Sugarcane is traditionally refined into sugar in two stages. In the first stage, raw sugar is produced by the milling of freshly harvested sugarcane. In a sugar mill, sugarcane is washed, chopped, and shredded by revolving knives. The shredded cane is mixed with water and crushed. The juices (containing 10-15 percent sucrose) are collected and mixed with lime to adjust pH to 7, to prevent decay into glucose and fructose and precipitate impurities. The lime and other suspended solids are settled out, and the clarified juice is concentrated in a multiple-effect evaporator to make a syrup with about 60 weight percent sucrose. The syrup is further concentrated under vacuum until it becomes supersaturated, and then seeded with crystalline sugar. Upon cooling, sugar crystallizes out of the syrup. Centrifuginging then separates the sugar from the remaining liquid (molasses). Raw sugar has a yellow to brown color. To produce a white sugar, sulfur dioxide is bubbled through the cane juice before evaporation so as to bleach color-forming impurities into colourless ones. Sugar bleached white by this means is called mill white, plantation white, and crystal sugar. It is the form of sugar most often consumed in the sugarcane-producing countries.

The fibrous solids, called bagasse, remaining after the crushing of the shredded sugarcane, are burned for fuel, which helps a sugar mill to become self-sufficient in energy. Any excess bagasse can be used for animal feed, to produce paper, or burned to generate electricity for the local power grid.

Refining

Sugar refinery in Arabi, Louisiana, United States

The second stage is often executed in heavy sugar-consuming regions such as North America, Europe, and Japan. In the second stage, white sugar is produced that is more than 99 percent pure sucrose. In such refineries, raw sugar is further purified. It is first mixed with heavy syrup and centrifuged to wash away the outer coating of the raw sugar crystals, which is less pure than the crystal interior. The remaining sugar is then dissolved to make a syrup (about 70 percent by weight solids), which is clarified by the addition of phosphoric acid and calcium hydroxide that combine to precipitate calcium phosphate. The calcium phosphate particles entrap some impurities and absorb others, and then float to the top of the tank, where they are skimmed off.

After any remaining solids are filtered out, the clarified syrup is decolorized by filtration through a bed of activated carbon. The purified syrup is then concentrated to supersaturation and repeatedly crystallized under vacuum to produce white refined sugar. As in a sugar mill, the sugar crystals are separated from the molasses by centrifuging. To produce granulated sugar, in which the individual sugar grains do not clump together, sugar must be dried. Drying is accomplished first by drying the sugar in a hot rotary dryer, and then by blowing cool air through it for several days.

Equipment in refineries

A refinery consists of different types of equipment such as:

• centrifuges
• compressors
• cooling towers
• crushers
• crystallizers
• distillation towers and other pressure vessels
• electric power generators, transformers and electric motors
• electrolysis cells
• evaporators
• filters
• furnaces
• gas flares
• mixers and blenders
• monitoring and control systems
• piping and valves
• pumps
• steam generators
• steam turbines and gas turbines
• storage tanks
• wastewater treatment

See also

• Alumina
• Bagasse
• Bayer process and Hall-Héroult process (used to produce aluminium from bauxite ore)
• Falconbridge Ltd. (large mining and metals refining company)
• Liquefied Natural Gas (LNG)
• Liquefied petroleum gas (LPG)
• Natural gas
• Oil refinery
• Petroleum
• Sugar cane
• Sugar beet

References

1. ^ Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics (2nd Edition ed.). Marcel Dekker, Inc. ISBN 0-8247-html Refinery flowchart] from Universal Oil Products' website. 
2. ^ An example flowchart of fractions from crude oil at a refinery
3. ^ Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation to Market
4. ^ Example Gas Plant
5. ^ From Purification to Liquefaction Gas Processing
6. ^ Feed-Gas Treatment Design for the Pearl GTL Project
7. ^ Benefits of integrating NGL extraction and LNG liquefaction

External links

• Complete, detailed oil refinery description
• Processing natural gas
• Aluminum production process flow sheets
• World LP Gas Association
• National Propane Gas Association, USA
• Liquefied Natural Gas (LNG) Overview
• Making sugar
• Sugar refining
• Searchable United States Refinery Map
• Interactive map of UK refineries