Tuesday, December 23, 2008

TYPE OF AIR POLLUTANTS



· Carbon monoxide - a colorless and odorless poison, it is a gas produced when fuel is not completely burned in engines, furnaces and space heaters. A major source of this is the vehicles.

· Carbon Dioxide - a product by normal combustion. Although it is not a serious pollutant, it is believed that the continuous build up of this gas in the atmosphere would cause a "green house effect" by reducing the flow of heat from earth back into the space, thus causing the warming of the earth.

· Sulfur dioxide - one of the most dangerous of all air pollutants. The major sources of these pollutants are factories and electric power plants that use sulfur-containing coal or oil as fuel. In the air, some sulfur dioxide is converted to sulfuric acid, which is then deposited into the earth's surface, usually by rain. This acid rain has caused damage to the environment in many parts of
the world.

· Nitrogen oxides - are mildly poisonous brown gases. These are produced in automobile engines and other devices where combustion takes place. During thunderstorms, heat energy that has been released by lightning causes nitrogen and oxygen in the air to react to form nitrogen oxides. Gas ranges are a major source of nitrogen oxides. These oxides dissolve in water to form acid rain.

· Hydrocarbon pollutant - produced by unburned fuel and is emitted mostly by motor vehicles. This also contributes to smog.

· Particulate matter - tiny liquid or solid particles in the air. Particulate matter includes smoke, dust, and soot, which may contain toxic substances like asbestos, fluorides, lead, and mercury. Tobacco smoke is one of the major sources of particulate matter.

· Chlorofluorocarbons (CFC's) - are synthetic substances that have has a variety of industrial uses. It is believed that CFC's can also contribute to a "greenhouse effect" resulting in the warming of earth. Some scientists also believe that CFC's are destroying ozone that absorbs potentially harmful ultraviolet radiation from the sun.

· Radon - is a naturally occurring radioactive gas formed in varying concentrations in the ground. The waste products of radon enters building from the ground, in place where there is a high concentration of radon, dangerous level of this gas may accumulate in building where there is poor ventilation.

· Methane – is a colourless and odourless gas. it is produced from decaying matter and the decay of rubbish in landfills. It is an important greenhouse gas.

Thursday, December 18, 2008

FRACTIONAL DISTILLATION OF AIR

The air is the main source of oxygen, nitrogen and noble gases. These are separated by first liquefying the air and then separating the components of liquid air by fractional distillation. The process can be divided into various stages:

Stage 1: The air is filtered to remove any dust

Stage 2: Any carbon dioxide or water vapour in the air must be removed, otherwise when the air is cooled they would solidify and block up the pipes. Carbon dioxide is removed by passing the air through an alkali like sodium hydroxide.

Sodium hydroxide + carbon dioxide -> Sodium Carbonate + water.

Water is removed in a drying tower by using a drying agent such as silica gel

Stage 3:The air is then compressed to 200 atmospheres. On compression, the air gets hotter. This compressed air is then suddenly allowed to expand. This causes the temperature of the air to drop. The cold air is then returned to the compressor. Here is mixes with more incoming air and helps to lower its temperature. This process of expansion and compression continues till the temperature of the air falls to -200 degrees Celsius. By this time most of the all the gases in the air have been liquefied, except neon and helium.

Stage 4:The liquid air is pale blue in colour due to the presence of liquid oxygen. It is passed through the fractionating column where it is slowly heated. The first gas to boil off is nitrogen at -196 degrees Celsius. When all the nitrogen has been converted to gas, the temperature begins to rise again. Argon boils at -186 degrees Celsius. Oxygen boils at -183 degrees Celsius. Each gas is collected and stored separately in cylinders under pressure.

(Before processing, air is pretreated to remove impurities that will clog the cryogenic piping. Once pretreated, the air is submitted to fractional distillation. In the fractional distillation process, the components are gradually separated in several stages. Because all distillation processes work on the principle of boiling a liquid to separate one or more of the components, a cryogenic section is required to provide the very low temperatures needed to liquefy the gas components. Once the liquid oxygen is separated, it is purified and stored. )

Tuesday, December 16, 2008

THE COMPOSITION OF AIR



99.998% of air
COMPONENTS; VOLUME
- Nitrous Oxide
0.5 per million parts
- Xenon
0.09 per million parts
- Ozone
0.07 per million parts
- Nitrogen Dioxide
0.02 per million parts
- Iodine
0.01 per million parts
- Carbon monoxide
Trace
- Ammonia
Trace


the other 0.001% of air
COMPONENTS; VOLUME
- Neon
18.2 per million parts
- Helium
5.2 per million parts
- Krypton
1.1 per million parts
- Sulfur Dioxide
1.0 per million parts
- Methane
2.0 per million parts
- Hydrogen
0.5 per million parts
- Nitrous Oxide
0.5 per million parts
- Xenon
0.09 per million parts
- Ozone
0.07 per million parts
- Nitrogen Dioxide
0.02 per million parts
- Iodine
0.01 per million parts
- Carbon monoxide
Trace
- Ammonia
Trace