SCOPE

The scope of this section comprises the supply, erection, testing and commissioning double skin construction wet scrubber units, conforming of these specifications and in accordance with Drawings and of the Schedule of Quantities.

TYPE

The evaporative cooling units shall be of double skin construction draw – thru type comprising of various sections such as filter section, wet scrubber section, fan section as per details given drawings and Schedule of Quantity.

CAPACITY

The air handling capacities, maximum motor H.P., Static pressure shall be as shown on Drawing and in Schedule of Quantity.

HOUSING / CASING

The housing/casing of the unit shall be of double skin construction.  The frame work shall be of Extruded Aluminum hollow sections. All the frame shall be assembled using pressure die cast aluminum/nylon joints to make a sturdy, strong and self supporting frame work for various section.

25/43mm thick Double Skin Panels shall be made of 0.6mm Pre-coated GSS on outside and 0.6 mm Galvanized sheet inside with CFC/HCFC free Poly Urethane Foam of 38-40 kg/cum. in-house injected in between.  These panels shall be screwed from inside on to the frame work with soft rubber gasket in between to make the joints air tight.

Frame work for each section shall be joined together with soft rubber gasket in between to make the joints air tight.  Suitable air tight access doors/panels with Nylon hinges and locks shall be provided for access to various sections for maintenance.  The entire housing shall be mounted on heavy gauge GSS/heavy duty aluminium frame work having pressure die cast aluminium jointers.

FILTERS

Each unit shall be provided with a factory assembled filter section containing washable metallic type grease filters having extruded aluminum frame.  Filter shall fit so as to prevent by pass. Filter face velocity shall not exceed 2.5m/sec Holding frames shall be provided for installing a number of filter cells in banks.  These cells shall be held within the frames by sliding the cells between guiding channels.

WET SCRUBBER

Wet scrubber shall be of double bank type with brass nozzles to spray water. Water piping shall be of GI with necessary flow control valves. Mist eliminator in PVC construction with multiple bends shall be provided as a screen between wet scrubber section and fan section.

WATER SUMP

The water sump below the wet scrubber section shall be constructed out of 18 G. Stainless Steel with welded joints. The tank shall be complete with make up, quick fill, overflow and drain connections. A brass float valve shall be provided for make up water line.

PUMP

Water circulating pumps shall be single phase mono-block pump. The capacity and head shall be adequate for the intended duty. The suction portion shall be at the bottom with proper seal arrangement to directly pick up water from the sump. The pump shall be suitable to operate at 415+10% V, 50 Hz, AC supply.

Necessary water bleeding arrangements shall be incorporated with separate drain connection provided in the sump to bleed small percentage of total circulated water in order to ensure compulsory water change over during running of the system. The pumps shall have following specifications:

Casing                       –           CI

Impeller                      –           Bronze

Shaft                          –           High tensile steel

Shaft sleeve              –           MS / Bronze

Bearing                      –           Heavy duty ball / roller

Base plate                 –           Fabricated MS

Packing                      –           Graphite Asbestos

FAN

The fan shall be AMCA certified backward curved, double inlet, double width type.  The fan shall be imported, factory tested and assembled by original manufacturer. The Wheel & housing shall be fabricated from heavy gauge galvanized steel.  The fan impeller shall be mounted on a solid shaft  supported to housing spider frame

and heavy duty ball bearings.  The impeller & fan shaft shall be statically and dynamically balanced.  The fan shall be selected for a noise level less than 80db(A). The fan outlet velocity shall not be more than 12.0m/sec.  Fan housing with Motor shall be mounted on a common extruded aluminum base mounted inside the air handling housing on anti-vibration mounts.  The fan outlet shall be connected to casing with the help of fire retardant fabric, mounted on aluminium extruded channels, acting as a flexible connection for anti-vibration.

MOTOR AND DRIVE

Fan motors shall be 415 ï 10% volts, 50 cycles, 3 phase, squirrel – cage, totally enclosed fan cooled with class F Insulation and IP – 55 protection.   Motor shall be especially designed for quiet operation and motor speed shall not exceed 1440 RPM.  Drive to fan shall be provided through belt drive arrangement.  Belts shall be of the oil-resistant type. 

SAFETY FEATURES

Each Air handling Unit must have safety features as under:

1. The fan access door shall be equipped with micro-switch inter locked with fan motor to enable switching off the fan motor automatically in the event of door opening.
2. The Access Door shall further have wire mesh screen as on added safety feature bolted on to the unit frame.
3. Fan section shall have weatherproof light for illumination.
4. Fan and motor base shall be properly earthed from the factory.
5. All screws used for panel fixing and projecting inside the unit shall be covered with PVC caps to avoid human injury.

PERFORMANCE DATA

Wet Scrubber units shall be selected for the lowest operating noise level of the equipment.  Fan performance rating and power consumption data, with operation points clearly indicating shall be submitted and verified at the time of testing commissioning of the installation.

TESTING

Exhaust Capacity of various wet scrubber unit models shall be computed from the measurements of air flow.  Flow measurements shall be by an anemometer. 

Computed results shall conform to the specified capacities and quoted ratings.  Power consumption shall be computed from measurements of incoming voltage and input current.