Re: TIG welding of Large dia SS Pipe

In current technology, the adsorbers are on the warm side. This is different rom the "old days" of reversing exchangers. The guts of the whole thing is the main air compressor, everything else is static. Quite amazing that it is so easy to liquefy what you breathe, actually.

It's not so bad to design for these circumstances once you get used to it. Jacques Cousteau did some of of the background work on it. If you look into it a bit further, you'll see that the process ("Claude") has been refined over the years.

The most interseting part is how pure gases can be used.

Here's the basics:

From
<a href="http://school.discovery.com/homeworkhelp/worldbook/atozscience/l/3">http://school.discovery.com/homeworkhelp/worldbook/atozscience/l/3</a> 26000.html:

Liquid air is a product made by greatly reducing the temperature of air until it turns into a fluid. Air becomes liquid at about -190 °C. The liquid is bluish and looks like water. Liquid air, like the air we breathe, consists of about 78 percent nitrogen, 21 percent oxygen, and 1 percent argon.

Scientists use liquid air in cryogenics, the study of temperatures -100 °C and lower (see Cryogenics). Liquid air is considered a cryogenic fluid because of its extremely low temperature. It is a primary source of liquid forms of nitrogen and oxygen. Scientists use liquid nitrogen in biology, chemistry, and physics research. It is also used in refrigerating and processing food. Liquid oxygen is used in compact, high-energy fuels for rocket engines that power spacecraft. It is also used to make explosives for blasting.

Properties. Liquid air affects different substances in a variety of ways. Liquid mercury becomes as hard as steel when liquid air is poured over it. A tennis ball dipped in liquid air will shatter when bounced. A lead bell, which normally makes a dull sound, will temporarily produce a clear tone when it has been exposed to liquid air.

Scientists use liquid air to study the effects of extremely low temperatures on the strength of certain substances. Such materials as iron and plastics temporarily become brittle after being dipped into liquid air. However, copper and brass become tougher upon immersion in the fluid. Exposure to liquid air also makes metals better conductors of electricity and increases the strength of certain types of magnets.

Scientists measure the temperature of liquid air with special thermometers because mercury and alcohol thermometers cannot be used. Mercury and alcohol freeze at temperatures much higher than that of liquid air. The most accurate and widely used thermometer that measures the temperature of liquid air is the platinum resistance thermometer. It measures temperature by determining its effect on the electrical resistance of platinum. Platinum becomes a better or poorer conductor of electricity as its temperature changes. A constant-volume gas thermometer measures the effect of temperature on the pressure of a gas kept at a certain volume. Such gases as helium or neon are used to measure the temperature of liquid air because they turn into liquid at lower temperatures than air does.

Nitrogen and oxygen, the two major parts of air, can be separated and used in their liquid form by distilling liquid air (see Distillation). When liquid air is heated, the nitrogen turns into a gas before the oxygen does because the boiling point of nitrogen is lower. After the nitrogen has been removed, the remaining substance consists mostly of liquid oxygen. The high oxygen content of the undistilled liquid could cause an explosion if a flammable material came in contact with it.

Making liquid air. The process of making liquid air is based on the fact that compressed air becomes cooler when it expands. This cooling effect was described in detail in 1853 by two British physicists, James Prescott Joule and William Thomson, and it later became known as the Joule-Thomson effect. In 1877, Louis-Paul Cailletet, a French physicist, liquefied air for the first time.

In 1895, the German chemist Carl von Linde invented a commercial process for liquid air production based on the Joule-Thomson effect. Linde's method is still used today but with many improvements. Compressors raise the air pressure in a chamber to about 3,000 pounds per square inch (20,600 kilopascals). Compression heats the air, and so water jackets on the compressor, plus a device called a heat exchanger, are used to lower the compressed air's temperature before it is liquefied.

Air can be liquefied in one of two ways. In one method, called Joule-Thomson expansion, the compressed air flows through a series of throttling valves into increasingly larger chambers. The pressure and temperature of the air decrease in each chamber as the air expands. In the final chamber, some of the air has become cold enough to condense into liquid. The cold vapor from this chamber is circulated around the other chambers to help cool the air that is still going through the liquefying process.

In 1902, Georges Claude, a French engineer, developed the second method of liquefying air. It resembles Joule-Thomson expansion but is more efficient because it makes use of work done by expanding air. In the Claude method, compressed air enters a chamber and pushes a piston as it expands. As the piston moves, the volume of the chamber increases, and the chamber's air pressure and temperature decrease. The air is sent through a series of these piston-equipped chambers, called expansion engines, until it becomes liquid.

Special containers called Dewar flasks protect liquid air from heat and evaporation. A Dewar flask is a bottle made of two layers of glass. There is space between the layers of glass to insulate the contents. The flask may be coated with silver to reflect heat. Large quantities of liquid air for industrial use are stored in huge insulated tanks.

• Original Message ----- From: SARE, RALPH H

> working in the cold boxes are real pain. Imagine a handfull of
piping,
> valves, adsrobers and braze heat excnagers. put 'em in the box
and then fill
> her up with perlite. all the handwheels that are sticking out
require a
> rubber boot to contain the "heat" then u worry also about the
penetration
> seal for the piping. Access is very limited and perlites are
flying
> everywhere during maintenance work. Its amazing how people can
design those
> piping cramp in a box...
Received on Thu Jun 28 08:25:00 2001