Thursday 15 March 2012

A short view about Feed water heater, Air Pre heater, Economizer, Super heater, Re heater

Feed water heater 
        A feed water heater is a power plant component used to pre-heat water delivered to a steam generating boiler. In a steam power plant (usually modeled as a modified Rankin cycle), feed water heaters allow the feed water to be brought up to the saturation temperature very gradually.
Types
Open feed water heater
Closed feed water heater

 




Feed water heater with T-S diagram


Advantages 

Preheating the feed water reduces the irreversibility's involved in steam generation
Improves the thermodynamic efficiency of the system
Reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle.
Air prehater
   The purpose of the air pre heater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas.
Types:
ØTubular type
ØRegenerative air pre heater 
 
Schematic diagram

 

Sunday 11 March 2012

Child Labor


  
        The International Labor Organization (ILO) has estimated that 250 million children between the ages of five and fourteen work in developing countries—at least 120 million on a full time basis. Sixty-one percent of these are in Asia, 32 percent in Africa, and 7 percent in Latin America. Most working children in rural areas are found in agriculture; many children work as domestics; urban children work in trade and services, with fewer in manufacturing and construction.
It Depends:
Child labor ranges from four-year-olds tied to rug looms to keep them from running away, to seventeen-year-olds helping out on the family farm. In some cases, a child's work can be helpful to him or her and to the family; working and earning can be a positive experience in a child's growing up. This depends largely on the age of the child, the conditions in which the child works, and whether work prevents the child from going to school.
Children who work long hours, often in dangerous and unhealthy conditions, are exposed to lasting physical and psychological harm.
Working at rug looms, for example, has left children disabled with eye damage, lung disease, stunted growth, and a susceptibility to arthritis as they grow older.
Children making silk thread in India dip their hands into boiling water that burns and blisters them, breath smoke and fumes from machinery, handle dead worms that cause infections, and guide twisting threads that cut their fingers.

Children harvesting sugar cane in El Salvador use machetes to cut cane for up to nine hours a day in the hot sun; injuries to their hands and legs are common and medical care is often not available.



Of nearly 250 million children engaged in child labor around the world, the vast majority—70 percent, or some 170 million—are working in agriculture. Child agricultural workers frequently work for long hours in scorching heat, haul heavy loads of produce, are exposed to toxic pesticides, and suffer high rates of injury from sharp knives and other dangerous tools. Their work is grueling and harsh, violating their rights to health, education, and protection from work that is hazardous or exploitative.
         According to the ILO's new report on child labor, the number of children working in agriculture is nearly ten times that of children involved in factory work such as garment manufacturing, carpet-weaving, or soccer-ball stitching. Yet despite their numbers and the difficult nature of their work, children working in agriculture have received little attention compared to child labor in manufacturing for export.