Cooling the air at the inlet to a compressor

[desi]

Could anyone give me possible information about the cooling of the air at the inlet to a compressor. Is it worthwhile adding a refirgeration cycle. Is there a certain lower temperature at which the air would be harmful to the compressor.If so why?
Any ideas or links to any websites with information about this topic would be greatly appreciated.

 

[ceesjan]

desi,

cooling or humidify (!) inlet air will decrease the amount of compressor power. so if u can cool inlet air it is advisible however a refrigeration cycle will need power which will influence the total efficiency (probably lower).
For swirl flash technology see:

http://www.alphapowersystems.nl

 

[ardilesd]

The point is that air density is increased, so there is more capacity for the same power.
However the limit must be in the condensation of water content in the air. You need to separate this before entering into the machine or cool down w/o entering into the dangerous zone.
Check the psicrometric chart to be in the safe side with your typical humidity and temperature in differntes seasons.

 

[Windward]

For reducing the power required to drive the compressor, or to increase its capacity, humidification of the inlet air can be much more effective than merely cooling it with a refrigeration coil. A low degree of humidification is about equivalent to using a cooling coil only. All of the water is evaporated before it enters the compressor. A higher degree known as overspray allows liquid water to enter the compressor in very small droplets. This method not only cools the inlet air but takes advantage of the high latent heat of vaporization of the liquid water. As it passes through the compressor it evaporates, reducing the temperature rise of the air/water mixture and therefore the power required to compress it. The main disadvantage of humidification systems is that they require pure water to avoid damage to the compressor and turbine blades. I have heard of desperate operators injecting water into the compressor inlet air with a fire hose to get more power out of their turbine. This will work a few times, but bad water and big droplets will destroy the gas turbine before long.

The earliest article I have found about overspray is "Value of Wet Compression in Gas-Turbine Cycles" by R.V Kleinschmidt, MECHANICAL ENGINEERING, vol. 69, 1947, pp. 115-116. The ultimate technology in this field is the hydraulic compressor. It compresses a gas such as air with a flow of water. It is the closest thing to an isothermal compressor that I know of. Those wanting an introduction to this device should read "Marmy Snorkels Some Green Stuff", one of the Marmaduke stories by Steve Elonka in POWER. I am sorry I don't know the edition of the magazine in which this story was published, but it is circa 1960. An Israeli company claims to have invented an isothermal compressor using a proprietary sealing technique in a vane compressor. They are not generous with details, however. Search under "isothermal compressor" on the web.

Caldwell Energy is one manufacturer of inlet air cooling systems.

An arrangement in which an isothermal compressor supplies compressed air to a recuperated gas turbine would be as efficient as a combined cycle plant. It would also be much simpler. General Electric was awarded U.S. Pat. 4,569,194 in 1986 for an application of this technology. There are several other patents in this field. I suggest that the technology of isothermal air compression will become widespread before long, because it can substantially increase the efficiency of both power generation and power use.

 

[Yench]

You did not state the type of compressor, but gas turbine cooling is quite common and offers a relatively quick payback in certain geographical regions. Check out Turbo Refrigeration as one site. There are several methods of refrigerated cooling, so find out which is best for your application.

 

[radomir]

In case of stationary gas turbines (industrial or marine) having two-spool gas generator (meaning low and high pressure compressors, each powered by its own turbine) air intercooler could be encountered. Increases efficiency of the compressor (which is axial in most of the cases) reducing specific work of compression (work required to compress a unit of air mass flow to a certain ratio). It is also beneficial reducing Turbine Entry Temperature (TET) for the same energy (heat) input. This reduces turbine thermal load, for the same level of power, increasing lives of gas turbine hot section components.

Cooling media can be a fuel (if heavy oil is utilized, making it less viscous and gaining some heat input) and/or water (could be used to heat fuel in tanks or for any other heating need or just to negligibly raise temperature of seas and oceans - some military ship installations). Aircraft gas turbines having weight as one of the major limiting factors (high specific thrust = thrust per unit of weight required) are without such devices.

Stationary gas turbines usually operate with large airflows, for example Marine Spey (19.5 MW unit) maximum airflow is: »53 normal m^3 per second (65.7kg/s). Obviously cooling intake (inlet) air is not practicable, the reason why water injection is utilized instead.

I haven’t even heard of inlet air cooled piston compressors (having rather small airflows). Although it looks like possible and practicable to do again only interstage cooling of partially compressed air is rather common.