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Refineries are industrial manufacturing facilities composed of a group of chemical engineering unit processes and unit operations used for the conversion certain raw materials such as petroleum crude oil, mined ores, sugar or salt into finished products of value or for the refining and purification of partially converted raw materials into finished products.

Types of refineries
The various types of refineries include:


 * Petroleum refinery: Converts petroleum crude oil into high-octane motor fuel (gasoline/petrol), diesel oil, liquefied petroleum gases (LPG), jet aircraft fuel, naphtha, kerosene, heating fuel oils, lubricating oils, asphalt and petroleum coke.
 * Natural gas processing plant: Purifies and converts raw natural gas into residential, commercial and industrial fuel gas, and also recovers byproduct sulfur and natural gas liquids (NGL) such as ethane, propane, butanes and pentanes.
 * Sugar refinery: Converts sugar cane and sugar beets into crystallized sugar and sugar syrups.
 * Salt refinery: Converts salt (NaCl), produced by underground mining, the solar evaporation of sea water (or other water ponds) or by solution mining and vacuum evaporation, into crystallized salt used for cooking and the  flavoring of food, as well as for various industrial uses (notably for the production of chlorine).
 * Various metal refineries converting metallic ores into end product metals such as alumina, copper, gold, lead, nickel, silver, uranium, and zinc.

A typical petroleum refinery
Petroleum refineries are very large industrial complexes that involve a great many different processing units and auxiliary facilities such as utility units and storage tanks. Each refinery has its own unique arrangement and combination of refining processes largely determined by the refinery location, desired products and economic considerations. There are most probably no two refineries that are identical in every respect.

The image below is a schematic flow diagram of a typical oil refinery that depicts the various unit processes and the flow of intermediate product streams that occurs between the inlet crude oil feedstock and the final end products. The diagram depicts only one of the literally hundreds of different oil refinery configurations. It does not include any of the usual refinery 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.





A typical natural gas processing plant
There are a great many ways in which to configure the various unit processes used in the processing of raw natural gas. The image below is a generalized, schematic block flow diagram of a typical natural gas processing plant configuration. It shows the various unit processes used to convert raw natural gas into sales gas pipelined to the end user markets.

The block flow diagram also depicts how processing of the raw natural gas yields byproduct sulfur, byproduct ethane, and natural gas liquids (NGL) such as propane, butanes and natural gasoline (denoted as pentanes +).



Typical refining of sugar
Most of the sugar produced worldwide is derived either from sugar cane or sugar beets. However, the sugar produced from sugar cane is at least twice the amount produced by sugar beets. For that reason, this section deals with sugar produced from sugar cane.

The refining of sugar cane into sugar is usually done in two stages. The first stage is the preparation and milling of freshly harvested sugar cane. In some cases, the preparation and milling may be done locally where the sugar cane is grown and harvested. In the milling stage, the sugar cane is first washed, chopped, and shredded by revolving knives. Then the shredded cane is mixed with water and crushed to produce a sugar juice.

As shown in the above schematic flow diagram, the juice (containing 10 – 15 percent sucrose) is heated to about 65 – 70 °C and mixed with lime and with gaseous sulfur dioxide (SO2). The lime serves to adjust the pH of the juice to about 7.0 – 7.1 which arrests sucrose's decay into glucose and fructose, and precipitates out some impurities. The sulfur dioxide serves to decolorize the juice. The juice is then further heated to about 100 – 105 °C and sent through a clarifier where the precipitated impurities and other solids are settled out and removed.

The clarified juice is next concentrated in a multiple-effect evaporator to make a syrup with about 60 – 65 weight percent sucrose. The syrup is again treated sulfur dioxide for further decolorization and then is further concentrated under vacuum until it becomes supersaturated with sugar. Upon cooling, sugar crystallizes out of the syrup.

The crystallized sugar is separated from the residual liquid syrup (molasses)s by centrifuging. The end product is a white, crystalline sugar referred to as mill white, plantation white or crystal sugar. To produce granulated sugar, in which the individual sugar grains do not clump together, sugar must be dried. Drying is accomplished by first drying the sugar in a hot rotary dryer, and then by blowing cool air through it for several days.

The refining process described in this section is sometimes referred to as the Double Sulfation (DS) process. There are other refining processes that use calcium phosphate (instead of lime) to remove impurities from the sugar juice (and/or the sugar syrup) and treatment with activated carbon (rather than gaseous sulfur dioxide) for decolorization.

The fibrous solids, called bagasse, remaining after the crushing of the shredded sugar cane, are burned for fuel within the sugar refinery. Any surplus bagasse can be used for animal feed, in paper manufacture, or burned to generate electricity for the local power grid.

Salt production
There are three different methods used for the production of salt: solar evaporation of saline water, underground salt mining and mechanical evaporation of solution mined salt.

Solar evaporation
Solar salt (sodium chloride or NaCl) is produced by using sunlight and wind to evaporate saline saline ocean water, open water ponds or saline lakes. This is the oldest method of producing salt and has been used since salt crystals were first observed in trapped ponds of sea water. It requires a climate where there are steady prevailing winds and the evaporation rate of open water exceeds the rate of rainfall for long time periods. Some examples of solar salt production are:

The water in the San Francisco Bay salt ponds is not as saline (i.e., salty) as the Pacific Ocean seawater because it is diluted by fresh water from local rivers, creeks and other sources. The bay water first flows into the intake set of ponds and is subsequently moved progressively through other ponds. In the first stage of ponds, evaporation over time reduces the water volume by about 70 percent which increases the salinity and impurities such as calcium sulfate precipitate. As the water is subsequently moved through the other pond stages, other impurities preciptate out and 95 percent of the water is eventually evaporated before the water is moved into the final ponds (referred to as the crystallizing ponds) where the sodium chloride precipitates out at about 40 tons per acre and is then mechanically harvested.

The colors of the salt ponds reflect the interaction of plants, aquatic life and varying salinity. In the low-salinity ponds, algae creates a green color. In the moderate-salinity ponds, Dunaliella algae proliferates and the color of this ponds become a lighter shade of green. In the mid-salinity ponds, tiny bay shrimp produce an orange color. In the high- salinity ponds, the Dunaliella algae produce a red color and halophylic bacteria contribute a purplish-red color.

The equipment used in refineries
Refineries utilize a great many different types of physical equipment such as:


 * Centrifuges
 * Compressors
 * Cooling towers
 * Control valves
 * Crushers
 * Crystallizers
 * Distillation towers and other pressure vessels
 * Electric power generators, transformers and electric motors
 * Electrolysis cells
 * Evaporators
 * Filters
 * Flare stacks


 * Furnaces
 * Mixers and blenders
 * Monitoring and control systems
 * Piping and valves
 * Pumps
 * Relief valves
 * Rotary dryers
 * Steam generators
 * Steam turbines and gas turbines
 * Storage tanks
 * Wastewater treatment