PNEUMATICS Chapter 4 Primary Air Treatment RBTC-1359-01

Objectives Air Treatment Filtering Relative Humidity Effects of Moisture Water Removal Dew Point Moisture Separators

Objectives Continued Oil Scrubbers Air Dryers Air Receivers Deliquescent Adsorption Air Receivers

Introduction Chapter 4 All air, gas, oil, water and any other fluids require treating or processing to make then suitable for the purpose intended

Air Treatment Air is taken from various surroundings that make it unsuitable without treating or processing All air has contaminants All gas has variations The conditions vary from day to day Our job is to make the air suitable for our use Accessories fit the situation

Filtering Prior to compressing air requires filtering The filter removes most dirt and contaminants They are classed as: DRY – generally cartridges or socks Cotton or wire Generally washable (no gasoline) WET – Maze above oil The maze traps any particles coming from the oil Volume requirements dictate sizing

Relative Humidity The amount of moisture in the air Dependent upon temperature and weather RH = The amount in the air compared with the amount that it could hold 100% RH is saturated air The higher the temp the more water vapor it can hold TABLE 4-2 Page 45

RH Examples Room 10 x 10 x 10 = 1000 cu ft Temperature – as heated can contain more Can hold 1 pound (1 pint) of water at 66°F At 88°F it can hold 2 pounds of water Pressure – as increased can contain less Dew Point is the temperature at which the water vapor condenses Under heavy load the air will not reach DP Instead the moisture remains in the air Rapid pressure drop through equip causes DP

Effects of Moisture – Left off 9 28 Rust and corrosion – chem reaction Tanks, lines, vessels Even if it stays in vapor stage Common to reach DP and drop out Liquid “washes” out lube Plug small passages Damage equipment like paint sprayers

Effects of Moisture continued Oil can cause blockage Oil can pick up dirt and carry into system Emulsions – won’t lubricate if emulsified Hi T can cause sludge and acid Acids corrode everything Commonly oil exists in a mist Easy to remove Deteriorates hoses

Water Removal Methods Most common method – condensation 1) Condensation can be used for both water and oil – drop the temp with an aftercooler 2) Dryer

After Coolers Use either air or water Scrubbers follow coolers Air cooled – more economical in equipment Small and medium volumes – 1 or 2 stages Fin Fan Tube Water cooled – more economical in operation Best for high volumes and larger compressors Water removes heat faster Scrubbers follow coolers

Water Cooled Shell and tube – most common The air or gas gives up its heat to the tubes then the water Can work both ways Most heat exchangers work on counterflow Dependant upon volume, pres, temp

Dew Point As air cools it gives up water Dry air has a lower DP than moist air Low pressure air has a lower DP than hi P air Air/Gas expands as it cools – can reach DP Avoid the problem by removing the water before it expands First cool it and scrub it Refrigeration can be used TABLE 4-1 Page 49

Moisture Separators All moisture removed has to go somewhere Scrub it Mechanical separation Centrifugal force Velocity reduction Gravity Removes about 95% of liquids Floats and valves remove the liquid from seps

Oil Scrubbers Oil scrubbers ensure more water removal Usually large but simple Based on velocity drop Passes through bed of steel wool and moisture sticks to the steel – eventually dropping off Can be solvent washed when ΔP occurs

Air Dryers Pneumatic gauges, controls and sensors require very dry air Two types are used Absorption – Deliquescent – Chemical Use a soluble dessicant or liquid When the soluble dessicant dissolves it deliquesces Gas enters bottom and rises Adsorption – regenerative Use a dry dessicant

ADSORPTION Moisture adheres to the dessicant Only held on the surface Gas goes in top and usually out the bottom during dehydration cycle Reversed during regeneration

Air Receivers Used for storage Usually under pressure Volume needed determines size of receiver Peak usage time determines size