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.