drain the chambers. Each chamber shall be provided with stainless
steel screens at the inlet and the outlet to contain the desiccant
bed, pressure gage, and safety valve. Normal air flow during
drying shall be upward through the desiccant chamber.
Desiccant
shall be spherical activated alumina.
b.
Regeneration: Accomplish by depressurizing the chamber on
reactivation and purging with a portion of the dry outlet air from
the chamber on stream. Purge air flow shall be downward. Maximum
allowable purge flow rate at design conditions shall be 10 percent
of design capacity of dryer. Purge system shall be controlled by
a cam timer such that each desiccant bed is regenerated as
required.
Provide a flow control valve, flow indicator, and
exhaust muffler for the purge system.
c.
Controls: Cam timer, switches and relays shall be housed in a
NEMA 12 control panel, mounted as part of the dryer. Provide
interconnecting wiring in accordance with Division 16. In the
case of electrical power failure, automatic valves shall fail in
the open position to allow the wet gas to pass through the
chambers.
Provide gages to indicate pressure in each chamber.
d.
Accessories: Dryer shall be complete with necessary solenoid
operated control valves, check valves, and interconnecting piping.
Mount equipment on a steel base plate suitable for floor
mounting.
[Provide pressure reducing valve to reduce pressure to
suit desiccant dryer.]
e.
Prefilter: Provide prefilter upstream of dryer to remove oil
vapor, liquid water, and solid particles. Prefilter shall have
greater than 99 percent efficiency in removing both 0.5 micron
diameter solid particles and 0.5 micro diameter oil aerosol.
Filter shall have replaceable oil absorbing filter element which
turns red to indicate saturation with oil and which shall be
mounted in a transparent cast methyl methacrylate tube for
visibility and inspection while on stream. Protect transparent
acrylic tube by a safety shield.
f.
Afterfilter: Provide an additional afterfilter for instrument
air. Filter shall combine three filter mechanisms - mechanical
separation, coalescence and absorption in a single, cartridge type
unit. Filtration efficiency shall be greater than 99.99 percent
at 0.5 micron particle size for oil and other contaminants. A
visible color change shall indicate when element should be
replaced.
[2.7.3.2
Compressed Air Refrigerated Air Dryer
**************************************************************************
NOTE: Choose this subparagraph or the above
subparagraph entitled "Compressed Air Desiccant Air
Dryer."
**************************************************************************
**************************************************************************
NOTE: The refrigerated air dryer is limited with an
atmospheric dew point of approximately minus 23
degrees C 10 degrees F equivalent to minus 12
degrees C plus 10 degrees F at 172 kPa (gage) 25 psig
SECTION 15502N
Page 84
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