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More than cleanliness, food hygiene is
It is the process of separation of components of comparable volatility. Production of vapor by boiling liquid mixture and condensing the vapor and allowing part of condensed liquid to still is the working principle of rectification.
In every distillation process, vapor formed in kettle is richer in more volatile component than in remaining liquid. However, the vapor contains certain amount of both components and distillate is rarely a pure substance. In order to increase concentration of volatile component in vapor and to separate the less volatile one, vapor is brought into contact with the stream of boiling liquid that runs down the column.
A stream of liquid with high concentration of volatile component is introduced at the top of the column. The most volatile components are concentrated in vapor phase and least volatile in liquid phase. This way vapor becomes richer in volatile component as it goes up the column, while liquid phase becomes richer in heavier component as it descends the column and separation is achieved.
Separation of mixtures depends upon relative volatilities of components, number of contact stages and reflux ratio. Rectification unit consist of
Typical diagram for rectifying column is shown as below.
In the above figure, feed is introduced into the column ‘A’ at the point that is nearly its center. The plate on which feed enters is called feed plate. All plates above the feed constitute rectifying section. The plates below the feed, including the plate itself constitute stripping section.
The feed flows down the stripping section to the bottom of the column in which definite level of liquid is maintained. Liquid flows by gravity to reboiler ‘B’. Reboiler generates steam (vapor) and returns it to the bottom of the column, which then passes up to entire column.
At one end of reboiler is a weir (dam) and downstream side of this weir collects bottom product which is withdrawn and passed through cooler ‘G’. This cooler also preheats the feed by heat exchange with the hot bottoms. The vapors rising through rectifying section are completely condensed in condenser ‘C’ and the condensate is collected in accumulator ‘D’.
Reflux pump ‘F’ takes liquid from accumulator and delivers it to the top plate of tower. This liquid stream is called ‘external reflux’.
Condensate not picked up by reflux pump is cooled in heat exchanger ‘E’ called product cooler and withdrawn as overhead product.
About Author
Name : Pratiksha Shrestha
pratiksha.shrestha2001@gmail.com
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.
It is group of practices and procedures intended to control risk and hazard throughout the handling of food. Hazard can be
Foundation of food safety management system: Read more
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Azeotropes or constant boiling mixtures is a mixture of two or more liquid which cannot be separated by simple distillation. This happens because when azeotrope is boiled, vapor has same proportion of constituents as unboiled mixture.
Maximum boiling azeotropes:
These are obtained from solution that shows negative deviation from ideal solution. We know, vapor pressure is inversely proportional to boiling point. Since first type of mixture showing negative deviation have lowest vapor pressure, they form maximum boiling azeotropes. Here the mixtures will boil at the temperature above boiling temperature of components from which they are made and the mixture will boil undistilled. Read more
Person may suffer from different diseases and therefore need to adopt different diet plan to recuperate form the ailment. Different food have different functions and thus the same diet cannot benefit all diseased condition. Special care should be given in diet when suffering from body illness like fever, hypertension, diabetes etc. There are diet that should be strictly prohibited in certain diseases while some food are highly recommended for recuperating the disease or fighting the disease. Also care should be taken about recommended dietary allowances of nutrients for specific age group and gender and particular diseases. Read more
1. When peeling skin of vegetables do peel as thinly as possible. The nutrients in fruits and vegetables are concentrated just below the skin.
2. Do not cut vegetables into very small cubes as the surface area f vegetables interact with oxygen and destroy vitamins
3. Do not soak vegetables in water to prevent discoloration (browning). 40% of water soluble vitamins are lost during soaking. If you must soak, use the soaked water t knead dough and prepare soup and gravies.