2.8.7 Expansion Joints for Fly Ash Handling System

2.8.7  Expansion Joints for Fly Ash Handling System

 

                        To the extent possible, the fly ash handling system loads shall be supported from the respective collection chutes and other structure in the area.

 

                        Expansion Joints in the fly ash handling system shall be of the metallic bellow type with replaceable liners. The expansion joints shall be designed to suit the duty conditions and constructed as per EJMA standard and shall have a minimum cyclic life of 5000 cycles.  The replaceable liners shall be an abrasion resistant material with a minimum hardness of 300-350 BHN.

2.8.8 Vacuum Pumps for Fly Ash Extraction

2.8.8  Vacuum Pumps for Fly Ash Extraction

 

                        The vacuum pump shall be of the low speed liquid ring type driven by an electric motor.  The vacuum pumps shall be of proven capacity, preferably in similar applications.

 

                        A minimum margin of 10% over the above capacity shall be considered for sizing of the vacuum pumps.

 

                        Silencers shall be provided so that each vacuum pump complies with the noise level limits stipulated in GTC. Separator silencers shall be provided to separate liquid and air and to reduce noise.

 

                        The vacuum pumps shall be designed to handle highly abrasive dust laden hot air under continuous operation mode.  The design shall also take into account the possibility of vacuum pumps sucking in flue gas con­taining SO₂ and SO₃ from the ash collection chutes.  The material of construction of various components and the type of seal liquid shall accordingly be selected.  Bidders shall also indicate in their bid the inlet dust loading that has been considered in the design of their vacuum pumps.

 

                        The vacuum pumps shall be of single or double stage and shall not cavitate under all operating conditions.  Bidder, if considers necessary, shall incorporate arrangements for cooling of inlet air to achieve the desired level of performance and life.

 

                        Bidder shall bring out in their proposal necessary arrangement provided to keep particulate loading in seal water low to avoid contamination of seal water/liquid ring.

 

                        All vacuum pumps and their drives shall be interchange­able.

 

2.8.8.1              Instruments

 

                        Each Vacuum pump shall be provided as a minimum of following :

 

                        (a)        Vacuum gauge                                                               :           1 No.

 

                        (b)        Pressure gauge in the working fluid

                                    make up/seal water line                                                  :           1 No.

 

                        (c)        Pressure switch in the working fluid

                                    make up/seal water line                                                  :           1 No.

 

                        (d)        Flow meter in the working fluid

                                    make up/seal water line                                                  :           1 No.

 

                        (e)        Flow switch in the working fluid

                                    make-up/seal water line                                                  :           1 No.

 

                        Each set of main & standby vacuum pump shall be provided with following:

 

                        (a)        Remote (control room mounted) vacuum

                                    indicator alongwith a vacuum transmitter

                                    in the common line of two vacuum

                                    pumps                                                                          :           1 No.

 

                        The bidder shall include any other instrument required to make-up the system safe, efficient and reliable.

                                   

                        Material of construction of various components shall be as follows:

Material of Construction
Casing	Cast Iron
Shaft	Carbon Steel EN8
Impeller	Stainless Steel
Shaft Sleeves	Stainless Steel
Type of coupling between Pump & Motor	Flexible suitable guards or V Belt drive alongwith beltguards.
Accessories	Necessary separator silencer adjusting valves and orifices  piping, strainers, heat exchangers for seal water system   ( if applicable) and other equipments as necessary and as required
Location	Outdoor
Duty	Continuous.
Motor rating at 50 °C Ambient	Continuous motor rating shall have at least 10% margin above the maximum load demand of the driven equipment in the entire operating range to take care of system frequency variation.
Inlet seal water temperature	36 °C

2.8.9 Fly ash branch feed valves and segregation valves.

2.8.9   Fly ash branch feed valves and segregation valves.

 

                        One number fly ash feed valve under each fly ash collection chute,  i.e. ESP and flue gas duct collecting hoppers and one no. fly ash branch segregation valve for each branch pipe  for vacuum system shall be provided.

 

                        The valve shall be totally enclosed type and shall be designed for no air leakage.

 

                        (a)        Branch segregation valves shall be used in fly ash extraction and transport piping to isolate the pipe line sections as also to isolate extraction/transportation equipment (if necessary) from the conveying (extraction and transportation) piping.

 

                        (b)        Fly ash feed valve shall be provided under each fly ash collection chute/hopper.

 

                        The valve shall be totally enclosed type and shall be designed for no air leakage.

 

                        The type of the valves shall be swing type or slide plate type for vacuum system and plate type/butterfly/dome/cone type in case of pressure system.

 

                        The valve shall be solenoid operated pneumatic actuated type consist­ing of a double acting air cylinder, a 4-way solenoid control valve with manual override facility.

 

                        Valves shall be provided with suitably located rodding port/access plug/panel if applicable.

 

                        The material of construction for valves on vacuum/pressure system shall be

 

Body	Alloy Cast iron, with hardness of 250 BHN (Min.)
Plate/Disc	3 mm thick stainless steel with 300-350 BHN hardness for fly ash segregation valve and 10 mm thick SS with 300-350 BHN hardness for fly ash feed valves.
Seat	Replaceable type Alloy C.I. or SS smooth finished with minimum 250 BHN hardness.
	Material of construction for valves on Pressure system
Plate/Disc/Dome/Cone	Minimum 10mm thk. S.S/Alloy   C.I.-300-350 BHN.
Seat (wherever applicable)	Replaceable type Alloy CI or SS smooth finished. Hardened to 250 BHN (min.)

Vacuum Breaker

 

                        Vacuum breaker shall be employed to open automatically at the end of fly ash handling operation, to prevent any residual vacuum prevailing in the ash trans­port  pipeline.

 

                        The vacuum breaker shall be mounted on the pneumatic ash transport line.

 

                        The vacuum breaker shall be of slide plate type with a pneumatic cylinder and piston assembly with solenoid valve. The body shall be made of Alloy Cast Iron with a hardness of 250 BHN (min.) and the plate be min. 3 mm thick SS of 300 – 350 BHN Hardness.

 

2.8.10 Air Intake Valves

 

                        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.

 

2.8.11 Fluidising Pads/ Air Activated Gravity Conveyors

 

                        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

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.

 

2.8.13 Pneumatic Ash Conveying Pipe Line

 

                        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.