The air intake valves shall be spring loaded or check type and be provided/mounted on fly ash branch pipe for air entry as may be required for necessary assistance to ensure the ash extraction. The exact number and size shall be as per system requirement. The valve body shall be made of Cast Iron/Gun Metal/Cast Steel and disc shall be constructed of SS or Gun Metal. All air intake valves shall be provided with suitable rain-hood protection.
The air activated gravity conveyors provided for Fly Ash extraction system and/or for silo aeration for flat bottom silos, shall consist of a trough shaped lower section (Plenum chamber) and at inverted trough shaped upper section (Material chamber). These two sections shall be separated lengthwise by a porous media. The porous media shall be sealed and retained by longitudinal bolting of the two chambers.
The porous media shall be woven/non woven fabric of natural organic mineral/synthetic fibres/suitable combinations as is suitable for service conditions in various zones of Ash Handling Plant. Ceramic porous tiles or aluminium oxide porous plates are not acceptable.
The angle of inclination of air activated gravity conveyors shall be greater than angle of repose of aerated fly ash.
The air activated gravity conveyors are to be accommodated with the head room available. It is a mandatory requirement that all the fly ash handling plant equipments is to be located above ground. Therefore, location the air activated gravity conveyors or any other associated equipment below the ground level is not allowed.
2.8.12 Fluidizing Air Blower
Low pressure air shall be used to fluidize the fly ash and thus to reduce the angle of repose of fly ash.
The air flow required to convey the fly ash shall be estimated based on fluidization characteristics of the fly ash.
The air pressure must be adequate to overcome the resistance in fan piping, air plenum, porous media and fluidized fly ash in the air activated gravity conveyors.
The activating air may be supplied at any point along the conveyor plenum.
To prevent the blockage of the porous media and fan suction filters due to the accumulation of atmospheric dirt on the underside, Bidder shall pay special attention for selection of the suction filter on the air supply unit and shall bring out in their bid special features of filters to be provided.
The fluidising air shall be supplied from a centrifugal fan or a blower, in case of fly ash extraction system and from air blowers in case of silo aeration for flat bottom silos.. The capacity of the blower/fan shall have at least 10% margin.
Suitable heating arrangement shall be provided at the discharge of centrifugal fans (if fans are envisaged for fly ash extraction) to raise the temperature of air atleast 50°C above the water vapour dew point. Schemes shall also include for thermal insulation of all air pipe work from the fan outlet to the point of contact of fly ash.
The fluidising air on the conveying side of the porous media shall be vented anywhere along the length of the conveyor. However system design and constructional features of Air Activated gravity conveyors and vent piping shall ensure minimum dust emission from joints as acceptable to statutory authorities.
For supplying air to Air activated gravity conveyors and vent lines fabricated GI ducting can be used. The thickness of duct sheet steel shall increase with the size of duct. Vent lines shall be fabricated from sheets of thickness at least two (2) gauges higher than air supply lines.
Material of construction shall be as follows
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Air Slides |
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Lower & Upper trough |
14 gauge carbon steel. |
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Porous media |
Woven/non-woven fabric of natural organic/mineral/ synthetic fibres/suitable combination to suit service conditions in various zones of Ash Handling Plant. |
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Fan/Blowers |
|
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Type |
Centrifugal Fan Blowers |
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Capacity and Static Pressure |
Adequate to meet system requirement. 10% margin shall be provided in capacity. |
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Numbers |
Four (4) nos. per unit (2 nos. working + 2 nos. standby) for fly ash extraction and Three (3) nos. (2 working + 1 standby) for flat bottom silo aeration. |
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Filter |
|
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Capacity |
To match with individual fan/blower capacity. |
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Numbers |
Numbers should be selected based on a face velocity of 2M/sec. |
Ash Transporter/Air Lock/Pump Tank
Two numbers of ash transporter/air lock/pump tank for each intermediate surge hopper/buffer tank shall be provided. Design pressure of the ash transporter/air lock/pump tanks shall be the maximum pressure the vessel is subjected to during any operating conditions. In any case it shall not be less than 1.5 times the rated pressure of the associated Air Blowers/Compressors.
Ash transporter /air locks/pump tanks shall be provided with necessary inlet and outlet valves.
The ash transporter /air locks/pump tanks vessel shall be constructed with tested quality mild steel plates as per IS:2062. They shall be able to withstand the abrasive action and hot condition of fly ash. The Ash transporter /Air locks/pump tanks shall be supported independently on steel columns.
The air locks/pump tanks shall be sized for the ash removal rates as specified.
The chamber itself shall be provided with an access door.
Aeration pads, if felt necessary by the bidder to assist the flow of ash through the air-lock valves shall be provided.
Air locks/pump tanks shall be vented to inlet of flue gas duct. Connection of vents directly to collection chutes is not acceptable.
The fly ash conveying lines from the fly ash collection chute outlets to the intermediate surge/buffer hoppers or continuous dust separators, and from buffer hoppers to dry ash storage hoppers silos etc. shall be designed to withstand the expected wear from the pneumatic transport of fly ash.
The piping layout should, within the limitation, of the specifications, reduce to a minimum the expected wear and abrasion. In general, every effort should be made to utilise straight sections as much as possible.
All the pipelines and supports shall be capable of withstanding all possible pressure/vacuum and loads that may result during various normal and abnormal conditions of operations.
shivajichoudhury