NOx - Wikipedia
The concentration of oxygen in water is crucial to aquatic animals that depend on What is the concentration of N2 in water under a pure nitrogen atmosphere?. High altitude can also be a problem for people with cardiopulmonary disease, Although the percentage of oxygen in inspired air is constant at different oxygen and nitrogen, and also the partial pressure of water vapour ( kPa at 37 °C). The question library on air related issues The air in the atmosphere consists of nitrogen, oxygen, which is the life-sustaining substance for animals and.
The weight of 22,4 dm3 of dry air is 28,96 grams. When the air contains sufficient amounts of water it is called humid. Humid air is lighter less dense than dry air. Apart from the elements that have been summed up earlier, other elements are also present in air.
However, the percentages of these elements are very low. Aerosols can be found in air. These are dust particles that are blown off the earth's surface by wind, or emitted during volcanic activity.
When burning processes take place, ashes and grime particles also end up in the air. The composition of air varies greatly with height. Over ninety kilometres above the earths' surface oxygen molecules fall apart and only oxygen atoms are left. Over one hundred kilometres above the earths' surface, nitrogen molecules also decompose. At this height the air does not have the composition we know. The atmosphere is completely different there.
All chemical elements can be found in several different states phases. One of these phases is the gaseous phase.
Apart from gaseous an element can also be solid or liquid.
Water is called ice when it is solid, it is wet when it is liquid, and when it is gaseous it exists merely as gas or steam. When temperatures rise, the molecules of a substance part, causing the substance to become gaseous and less visible.
This phase change causes air to be invisible. When temperatures fall air molecules are closer together and a substance eventually becomes solid.
The temperatures at which each 'phase-change' takes place differs for each substance. Where on earth do we find air?
We can state that air can be found everywhere on earth exept where there is water. Air is even located in the surface layer of the earth; in the soil. Air is not only located on earth, it is also located around the earth in an air layer called the atmosphere. The atmosphere can be divided up in separate layers depending on temperature and height. These lines are not clearly separated by straight borders; they gradually overflow one another. The first layer of air, which is located closest to the earth is called the troposphere.
This layer is 11 kilometres in height. When moving up in the troposphere temperatures fall six or seven degrees per kilometre. Consequentially the weather on earth is mainly determined by circumstances within the troposphere.Solubility of Gases
The upper layer of the troposphere is called tropopause. Near the Antarctic, the tropopause layer is located eight to ten kilometres above earth.
However, at the equator the tropopause layer is located at seventeen to eighteen kilometres above earth. The second layer of air above the troposphere is called stratosphere. Temperatures stop decreasing in the lower part of this layer. The temperature is around degrees Celsius here. In the higher stratosphere temperatures are rising to zero degrees Celsius at forty-seven kilometres above earth. Within the stratosphere solar radiation creates ozone O3 from oxygen O2between twenty and forty kilometres above the earth's surface.
This reaction causes this part of the stratosphere to be referred to as 'ozone-sphere'. The upper part of the stratosphere is called stratopauze.
Oxygen, nitrogen and the rare gases
The third layer of air is called the mesosphere. Since air separation plants operate at low temperatures, construction materials have to be chosen carefully. Aluminium alloys and stainless steel are frequently used.
They do not become brittle at low temperatures. Efficient plant insulation is necessary to make the process economic and safe.
Perlite an expanded rockglass wool and vacuum jacket techniques are commonly used Figure 5. Pressure swing adsorption can provide this and produce up to about tonnes a day. To produce oxygen, a stream of clean air is passed through a bed of alumina to dry the gas and then through a bed of zeolite molecular sieve.
Nitrogen is preferentially retained adsorbed leaving an oxygen-enriched gaseous stream to pass through Figure 7. When the zeolite becomes saturated with nitrogen it is necessary to regenerate it.
This can be achieved simply by reducing the pressure, whereupon the nitrogen is released desorbed back into the gaseous phase and rejected as waste. The sieve is totally regenerated in this way and is ready to repeat the cycle.
Two beds are usually used in rotation. One is used to produce the oxygen while the other is being regenerated. The full cycle time can vary between 2 and 8 minutes depending upon actual performance requirements.
Instead of using a zeolite as in the manufacture of oxygen, nitrogen is produced from air using beds of carbon molecular sieve CMS. Clean, dry, compressed air is passed through a bed of CMS typically at 7-I2 atm. Oxygen is adsorbed on the surface of the CMS and nitrogen passes through to storage.
When oxygen saturation is reached a second bed is brought on-stream, retaining continuity of supply and the first vented to atmosphere to desorb the oxygen and hence regenerating the CMS prior to the next cycle. Similar to the production of oxygen by PSA, the full cycle time for nitrogen varies between 2 and 8 minutes. This process is more expensive to build but it is more efficient to run. The sieve is more effectively regenerated and as a result, more oxygen is obtained from a given amount of air.
Oxygen and carbon dioxide diffuse more rapidly than nitrogen and argon and this allows the remaining gas to become richer in nitrogen and argon. The polymer used for the membrane is often made of poly methylpentene. Air, at pressures of between 7 and 12 atm and heated to to K, is passed through the membranes.
Chapter Combustion (Updated 5/31/10)
The waste gases permeate through the membrane and are vented to the atmosphere. When very high grade This plant removes residual oxygen by mixing the gas stream with hydrogen and passing the mixture over a catalyst. Oxygen combines with hydrogen and the water formed is removed by passage through a molecular sieve.