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==Typical refining of sugar==  
==Typical refining of sugar==  


Most of the sugar produced worldwide is derived either from [[sugarcane]] or [[sugar beet]]s. However, the sugar produced from sugarcane is at least twice the amount produced by sugar beets. For that reason, this section on the refining of sugar deals with sugar produced from sugarcane.
Most of the sugar produced worldwide is derived either from [[sugar cane]] or [[sugar beet]]s. 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 sugarcane into sugar has traditionally been done in two stages. The first stage is the production of a raw sugar by the milling of freshly harvested sugarcane, usually done locally in the sugarcane-producing regions. In a sugar mill, sugarcane is washed, chopped, and shredded by revolving knives. The shredded cane is mixed with water and crushed.
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.


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The juices (containing 10-15 percent [[sucrose]]) are collected and mixed with [[lime (mineral)|lime]] to adjust its [[pH]] to 7 which arrests sucrose's decay into [[glucose]] and [[fructose]], and precipitates out some 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. [[Centrifuge|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.
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 (mineral)|lime]] and with gaseous [[sulfur dioxide]] (SO<sub>2</sub>). The lime serves to adjust the [[pH]] of the juice to 7 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 fibrous solids, called ''bagasse'', remaining after the crushing of the shredded sugarcane, are burned for fuel which makes a sugar mill more than self-sufficient in energy. Any surplus bagasse can be used for animal feed, in paper manufacture, or burned to generate electricity for the local power grid.
The clarified juice is next concentrated in a [[multiple-effect evaporator]] to make a syrup with about 60 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 second stage is the processing is done in sugar refineries, often located in heavy sugar-consuming regions such as [[North America]], [[Europe]], and [[Japan]], to produce refined white sugar 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.  
The crystallized sugar is separated from the residual liquid syrup (''[[molasses]]'')s by [[Centrifuge|centrifuging]]. The end product is a white, crystalline sugar referred to as ''mill white'', ''plantation white'' or ''crystal sugar''.  


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.
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 referred to as the ''double sulfation (DS)'' process. There are other 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.


==The equipment used in refineries==
==The equipment used in refineries==

Revision as of 02:54, 16 January 2009

A refinery is an industrial manufacturing facility composed of a group of chemical engineering unit processes and unit operations[1][2] used for converting certain raw materials or into products of value or for the refining of partially converted raw materials into finished products.

Types of refineries

The various types of refineries include:

© Photo: Phillip Greenspun
A petroleum refinery.

A typical petroleum refinery

For more information, see: Petroleum refining processes.

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.[3][4][5][6]

Schematic flow diagram of a typical oil refinery
A natural gas processing plant

A typical natural gas processing plant

For more information, see: Natural gas processing.

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 +).[7][8][9][10][11]

Schematic flow diagram of a typical natural gas processing plant


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.

© Photo: Barritt & May
A sugar refinery in New South Wales, Australia.
(CC) Photo: Rufino Uribe
Cut sugar cane.
(PD) Image: Milton Beychok
Flow diagram of sugar refining process.

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 7 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 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 referred to as the double sulfation (DS) process. There are other 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.

The equipment used in refineries

Refineries utilize a great many different types of physical equipment such as:

References

  1. ↑ McCabe, W., Smith, J. and Harriott, P. (2004). Unit Operations of Chemical Engineering, 7th Edition. McGraw-Hill. ISBN 0-07-284823-5. 
  2. ↑ Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook, 8th Edition. McGraw-Hill. ISBN 0-07-142294-3. 
  3. ↑ Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics, 2nd Edition. Marcel Dekker, Inc. ISBN 0-8247-7150-8. 
  4. ↑ Guide to Refining from Chevron Oil's website
  5. ↑ Refinery flowchart from Universal Oil Products' website
  6. ↑ An example flowchart of fractions from crude oil at a refinery
  7. ↑ Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation to Market
  8. ↑ Example Gas Plant
  9. ↑ From Purification to Liquefaction Gas Processing
  10. ↑ Feed-Gas Treatment Design for the Pearl GTL Project
  11. ↑ Benefits of integrating NGL extraction and LNG liquefaction


See also


External links

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