BS 6754:1986 download free.Specifications and testing of compressed air dryers [ISO title: Compressed air dryers — Specifications and testing].
IEC Publication 51, Recommendations for direct acting indicating electrical measuring instruments and their accessories.
IEC Publication 651, Sound level meters.
4 Definitions
4.1
moisture content (gram per cubic metre)
ratio of water and water vapour by mass to the total volume
4.2
vapour concentration (gram per cubic metre)
ratio of water vapour by mass to the total volume
NOTE Vapour concentration was earlier called “absolute humidity” and has been used to describe what is more correctly termed “water load”, i.e. the water content of the desiccant expressed as a mass ratio.
4.3
vapour ratio
mass ratio of water vapour (gram) to dry air (gram)
NOTE It is not recommended to express the vapour ratio in parts per million (PPM). When parts per million are used (at very low dew points) it should be clearly stated whether it is on a mass or a volume ratio basis.
4.4
partial pressure (millibar)
absolute pressure exerted by any component in a mixture
4.5
saturation pressure (millibar)
total pressure at which moist air at a certain temperature can coexist in neutral equilibrium with a plane surface of pure condensed phase (water or ice) at the same temperature (see Annex B)
4.6
relative vapour pressure
ratio of the partial pressure (millibar) of the water vapour to its saturation pressure (millibar) at the same temperature
NOTE Relative vapour pressure is often called rclativc humidity”.
4.7
relative vapour concentration
ratio of the actual water vapour concentration (gram per cubic metre) (see 4.2) to its saturation value (gram per cubic metre) at the same temperature and pressure
4.8
relative vapour ratio
ratio of the actual vapour ratio (see 4.3) to the saturation vapour ratio at the same temperature
4.14 Absorption
Process of attracting one substance into the mass of another, so that the absorbed substance disappears physically.
4.14.1
liquid absorption
drying of air or gas by means of a liquid desiccant (for example, triethyleneglycol or sulfuric acid)
4.14.2
deliquescence
spontaneous process whereby a soluble solid material absorbs water and becomes liquid
4.15
drying by cooling
method of liquifying part of the condensable vapours by reducing the temperature
4.16
drying by overcompression
method of drying air by compressing it to a pressure
higher than the intended working pressure
5 Types of compressed air dryers
5.1 Absorption dryers
5.1.1 Compressed air dryers, which extract water vapour from the compressed air, where the absorbent combines chemically with the water vapour and goes into solution. The hydrous solution is drained off; the absorbent is normally not recovered.
5.1.1.1 Liquid desiccant
5.1.1.2 Deliquescent substances
5.2 Adsorption dryers
5.2.1 Compressed air dryers, which extract water vapour from the compressed air by attraction and adhesion of molecules in a gaseous or liquid phase to the surface of a solid. The adsorbent can be regenerated by removing the adsorbed water.
5.2.1.1 heatless: Regeneration is achieved with non-heated, expanded, previously dried air. 5.2.1.2 directly heated: Regeneration is achieved by heating elements applied to or embedded in the desiccant.
5.2.1.3 regeneration air heated: Regeneration is achieved by passing heated ambient air through the desiccant.
5.2.1.4 regeneration: Achieved by adsorption and absorption.
7 Specification
The data given in Table 4 shall, when applicable, be stated when specifying and inspecting a compressed air dryer. Other relevant details such as explosion proof properties, hazardous area. etc. shall also be included.
8 Data for performance comparisons
The data to be stated for performance comparisons and for technical acceptance are listed in Table 5.
9 Performance measuring and testing
9.1 Test conditions
To obtain valid test results, constant operating conditions (inlet air pressure, inlet temperature, inlet pressure dew point, etc.) are required. These conditions shall be listed in the test report. Testing should be carried out under operating conditions specified in Table 2. Performance data should then be compared to selected performance rating parameters, with adequate consideration given to measuring instrument tolerances.
9.2 Conversion of test results
Test conditions and results sometimes do not agree exactly with the reference conditions and the selected performance rating parameters. The precise conversion details shall therefore be agreed between the supplier and user.
9.3 Test report
The test report form is given in Annex A. 9.4 Test system for air dryers
A diagram of a typical testing system for air dryers (see Figure 1) and notes on the symbols used are given in Annex B.
9.5 Saturation pressure and density of pure water vapour
Extracts from the Smithsonian Meteorological
Tables and the National Bureau of Standards and
National Research Council of canada: Steam Tables
are given in Annex C.
9.6.7 Refrigeration dryers
The total input power to the complete unit shall be measured in accordance with 9.6.5 over a suitable period.
9.6.8 Heatless dryers
The bleed air volume and the dump losses together with other energy requirements shall be measured while operating under constant working conditions.
9.6.9 Heat regenerated dryers
When electricity, steam, hot water, etc. are used as source of regeneration heat, the energy consumption shall be reported in kilowatt hours per full drying cycle, and the nominal cycle time stated. Bleed flow rate and total consumption of bleed air shall be stated.
9.6.10 General examination
The unit under pressure shall be examined for resistance to damage and leakage and the results shall be included in the report in conformity with relevant national regulations.
9.6.11 Noise level
If noise level readings are required, by agreement between the supplier and user, it is recommended that the noise level should be measured using a sound level meter of type 1 in compliance with IEC Publication 651, and the results expressed in the form suggested in ISO 131 using the preferred frequencies of ISO 266.
9.6.12 Acceptance test
The extent and cost of any such test shall be agreed in writing between the supplier and user at the time of the contract.
10 Acceptance deviations from rated values
10.1 The usable flow-rate of a new dryer, when delivering the rated pressure dew point and working at the specified conditions, shall not fall below the rated value by more than 5 04
10.2 The total energy requirement of a new dryer, divided by the corresponding usable volume delivered, shall not exceed the value calculated from the rated performance by more than 5 %.
10.3 The pressure drop over the complete dryer shall not exceed the rated value by more than 10 %.