2.8.12 Fluidizing Air Blower

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

                       

Air Slides
Lower & Upper trough	14 gauge carbon steel.
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.
Fan/Blowers
Type	Centrifugal Fan Blowers
Capacity and Static Pressure	Adequate to meet system requirement. 10% margin shall be provided in capacity.
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.
Filter
Capacity	To match with individual fan/blower capacity.
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.

 

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