2.8.27 Horizontal Centrifugal Pump

2.8.27               Horizontal Centrifugal Pumps

 

                        The ash slurry pumps for combined B.A. and F.A. disposal, B.A. Cooling water over flow pumps, BAHP pumps, BALP pumps, flushing water pumps seal water pumps, for ash slurry pumps, dust suppression, ash conditioning and seal water pumps in main storage silo area and cooling water pumps for cooling various equipments of ash handling plant shall essentially be horizontal and centrifugal type.

 

                        The equipment shall be capable of developing the required head at rated capacity for continuous operation.

 

                        All centrifugal pumps shall have a drooping characteristics curve, with the head continuously increasing with decreasing flow to maximum head at zero flow and the pumps shall preferably be non-overloading type beyond rated duty point.

 

                        The characteristics curves of each set of pumps shall match each other for equal load sharing in case of parallel operation and such pumps shall be identical and all parts shall be fully interchangeable.

 

                        Standard type pumps with a proven record of reliability shall only be provided.

 

                        Specific Design Requirements for Slurry Pumps

 

                        The ash slurry sump geometry and configuration shall be such as to minimise ash settlement, formation of vortices and air entrainment in the slurry as this may affect the operation of the slurry disposal pumps.  To minimise the ash settlement adequate number of high velocity water jetting nozzles shall be provided in the slurry sumps.

 

                        The rating of the ash disposal pumps shall be based on the stipulations con­tained herein as given under:

 

                        A)        F.A. and B.A. Handling

 

                                    The maximum velocities in slurry transformation lines for both F.A. and B.A. shall be limited to 2.8 m/sec.

 

                                    The maximum concentration of B.A. and F.A. slurries when being

                                    handled independently or combined shall be as under:-

 

                                    i)          B.A.                                         -           25% (W/W)

 

                                    ii)         F.A.                                          -           30% (W/W)

 

                                    iii)        Combined B.A. & F.A.              -           25% (W/W)

 

                        B)        Combined Ash Slurry Disposal System

 

                                    The combined ash slurry disposal system shall meet the following mandatory requirements :

 

a)                Not more than (2) pump streams shall be employed for handling the total bottom and fly ash slurry generated from the two units when the bottom ash is extracted either intermittently and fly ash is extracted at the specified  removal rates.

 

                                    b)         Minimum make up water should be required at the slurry sump during the operating condition when only one unit is operating or during the periods in a shift of 8 hours when fly ash slurry is being received continuously and the bottom ash slurry is being received intermittently since these operating modes are also considered as normal operating modes.

 

                                    c)         The concentration of the ash (combined bottom and fly ash in the sump) in the slurry handled by the ash slurry disposal pumps shall not exceed 25% (W/W) and the flow velocity in the ash slurry disposal pipeline shall not exceed 2.8 m/sec. during any operational mode of the system.  The bottom ash and fly ash slurry concentration under any mode of operation shall be decided considering the rated capacity of respective extraction systems.

 

                                    d)         The ash slurry disposal system should also be designed to cater to the operating conditions as when only the F.A. handling system for both the units is working (i.e. when B.A. and economizer ash evacuation is over), the slurry concentrations under such condition shall not exceed 30% (W/W) and the flow velocity in ash disposal pipe line shall not exceed 2.8 m/sec.

 

                                                            The fly ash slurry concentrations under this mode of operation, shall be decided, considering the rated capacity of the extraction system.

 

To maintain the concentration limit and to run the ash slurry disposal pumps effi­ciently a provision shall be made for make-up water pipe connections complete with motor operated gate valves and manual gate valves.

 

                        Minimum 10% margin shall be considered for ash slurry pump sizing over and above the total slurry disposal head requirement comprising the straight pipe line frictional loss and bends loss.  The value of the constant ‘C’ in William-Hazen equation, shall be considered as 140 for calculating the system head.

 

                        An additional flow of 100 m³/hr (continuous) shall be considered on ash slurry pump capacity to take into account sludge disposal from clarifier units to be pumped by ash slurry disposal pumps to the disposal area.  Bidder may take advantage of this additional quantity of sludge (the density of solids in sludge may be taken as 1.1 and the concentration as 5%) while arriving at ash slurry concentration for the combined ash disposal pumps.  Apart from the working streams one standby and one maintenance standby shall be provided for the ash slurry disposal system.

 

                        The slurry pumps shall essentially be slow rpm pumps. The rotational speed of the impeller at design point shall not exceed 1000 rpm.

 

                        The first stage of slurry disposal and transportation pumps shall be provided with variable speed hydraulic coupling of robust design for setting the optimum operating speed of the pumps based on actual site requirements after the system is installed.  Minimum (+) 10% and (-) 45% speed variation with respect to speed at rated  design point shall be provided in the first stage of combined ash slurry disposal pumps and ± 20% for bottom ash transportation and BA overflow water pumps. The slurry pump motor speed shall not exceed 1500 rpm.

 

                        To minimise the drive losses in the first stage of slurry disposal and transportation pumps, a constant speed reduction gear box shall be provided.  The gear boxes to be employed shall be suitable for heavy duty application and of such reputed make which have proven established record of trouble free service under heavy load transmission duties.

 

                        For the subsequent slurry disposal and transportation pump stages, the drive shall be transmitted through belt drive arrangement.  If in future, the operating speed of these pumps is also required to be changed, the Owner intends to carry out this change by replac­ing the existing belt-pulley with a pulley of different diameter to allow a future variation of ± 10%.  Pump and motor layouts in the pump house shall be accordingly decided to take care of this requirement.

 

                        Continuous motor rating (name plate rating) at 50°C for ash slurry pumps shall have atleast 20% margin above the maximum load demand of the driven equipment at the rated duty point. The maximum load demand shall be calculated considering slurry density, efficiency of pump when handling slurry and the complete drive losses in the transmission (fluid coupling, gear box, etc.). For selecting the motor, the maximum pump efficiency to be considered shall be 70%. To ensure interchangeability, all the pumps & motors of the pumping streams shall be of similar rating and the pumps shall be designed for + 10% and – 45% speed variation.

 

                        Pumps shall be single stage, end suction design provided with heavy duty impellers suitable for highly abrasive duty application.

 

                        All the wear parts of pumps, impellers and liners etc. shall have a minimum guaranteed life of 8000 hrs. of operation.

 

                        Provision shall be made for adjustment to take up wear by axial movement of the shaft.

 

                        The seals shall be water flushed packed glands, fed from an external clean water supply source.

 

                        The impeller tip speed at the rated parameters shall not be more than 1676 metres/min.  Bidders shall make selection of the pump size such as to limit the tip speeds to above specified limits.

 

                        The passages and clearances in pump components shall be properly designed, considering the size of ash and clinker to be handled.

 

                        The pumps shall have flooded suction inlet and shall be located indoors.  Howev­er, pumps shall be suitable for operating with upto 2 metres suction lift.

 

                        The glands of the pumps should be suitably designed to prevent clogging of ash particles.

 

2.8.27.1            Specific Requirements for Seal Water and other Horizontal Water Pumps

 

                        (a)        Seal water system, taking suction from water supply terminal points, shall be provided to supply gland sealing water for ash slurry disposal pumps, bottom ash slurry transportation pumps, BA overflow water pump, sludge pump, sump drainage pumps, clinker grinders, submerged scraper conveyors and cooling water for air compressors, blowers, vacuum pumps, fluid couplings, etc. Any other cooling/seal water requirement for the plant shall also be included in this seal water system.

 

                        (b)        To meet the gland sealing requirement in combined ash disposal pump house and bottom ash transportation pump house (if applicable). The pumps will take suction from  clarified water storage.  Separate pump sets shall be provided for meeting the sealing water requirements in each of the above mentioned buildings and 100% standby pumps shall be provided for each of these duties.

 

                                    For sealing requirement of clinker grinders, SSC’s (if applicable) in the boiler area and sump drainage pumps in bottom ash transportation pump house the water shall be tapped from the  clarified water storage.

 

                                    All the necessary piping and valving shall be in the scope of supply.

 

                        (c)        Additionally One (1) no. tank shall be provided in the ash storage silo area for meeting the water requirements of ash conditioning, dust suppression, cooling water for silo aeration blowers (if any) and seal water for sump drainage pumps.  Necessary pumps (as specified and as required) shall be provided to meet these requirements which will take suction from this tank.  Bidder may combine the requirements of dust suppression, cooling water for blowers and seal water for sump drainage pumps (depending upon the pressure/flow requirements) in which case the cooling water requirement for silo aeration blowers (if any) and water requirement for dust suppression shall be considered as simultaneous requirement.  The pumps shall be suitably designed to take care of the varied water requirements.

 

                        (d)        The design of the seal water system for supplying water to gland sealing to various ash slurry pumps shall be such as to have the gland sealing water system for maximum of two (2) stages of the working streams supplied from one seal water pump and shall have its own 100% standby pump.  For the balance stage (stages) of the working streams separate seal water pump shall be provided with its own 100% standby facility.  The seal water pump shall be sized for meeting the seal water requirements of pumps in working streams and one (1) no. additional stream which will be in flushing mode.

 

                        At least 15% margin shall be provided in the pump capacity over and above the maximum seal water/cooling water and other flow requirements. For calculating the system head, the value of constant ‘C’ in William Hazen equation shall be considered as 100.

 

                        Continuous motor rating (name palte rating) at 50°C for seal/cooling water pumps and other horizontal water pumps shall have at least 15% margin above the maximum load demand of the driven equip­ment in the complete operating range to take care of the system frequency varia­tion.

 

                        Seal water/cooling water and other horizontal water pumps shall be direct driven with speed not exceeding 1500 rpm.

 

2.8.27.2            Construction Features

 

            ●          Casing

 

                        i)          The casing shall be structurally sound to provide housing for the pump assembly and shall be designed hydraulically to minimise radial loads at part load operations.         

 

                        ii)         With the exception of the slurry pumps, pump casings shall preferably be horizontal split type, with the top casing and internals being removable without disturbing the main pipework connections.  In general all pumps shall be designed such that the rotating assembly can be withdrawn without removing the motor. The casing shall be finished to smooth surfaces as far as possible.  Casing drain and vent connection with plugs and valves shall be provided where required. Casing shall withstand without expansion joints, the usual moment and thrusts.

 

                        iii)        In case of ash slurry pumps, these shall be of either twin casing construc­tion or single casing with metal lining construction or single volute casing construction. The pressure casing (or outer casing) shall be generally in accordance with the stipulation of API-610. The thickness of inner casing in case of single casing with metal lining pumps and the wear margin in case of single volute casing pumps shall not be less than 35 mm.

 

            ●          Impeller

 

                        i)          The complete rotor assembly shall be statically and dynamically balanced and designed with critical speed substantially abvoe the operating speed.

 

                        ii)         Impellers shall be made in one piece and securely fixed to the shaft.  Means shall be provided to prevent loosening during operation including rotation in reverse direction.

 

                        iii)        Impeller fastening nuts (if provided)shall be of cap type and shall tighten in direction of normal rotation.

 

                        iv)        For ash slurry pumps, the minimum impeller thickness shall not be less than 30 mm and shroud cover thickness shall not be less than 35 mm.

 

            ●          Impeller/Casing Wearing Rings (Where applicable)

 

                        Replaceable type wearing rings shall be provided at suitable locations for each pump. The rings shall be so fitted as to prevent turning while the pump is in opera­tion.

 

            ●          Shaft

 

                        i)          The shaft shall be finished to close tolerance at the impeller, coupling, pulley and bearing diameters. The impeller, pulley and shaft sleeves shall be firmly secured to the shaft by key and/or nuts.  Slurry pump impellers may be screwed on the shaft (threads to tighten during normal pump rota­tion).         

 

                        ii)         The shaft shall be adequately sized to withstand all stresses from rotor weight and hydraulic loads etc. and ground and polished to final dimen­sions.

 

                        iii)        The design of the shaft shall also take into consdieration the critical speed of the shaft which shall be at least 20 percent above the maximum operating speed or about 60 to 75 percent of the lowest operating speed.

 

            ●          Shaft Sleeve

 

                        Pumps shafts shall be protected by renewable type shaft sleeves which shall extend well beyond the pump glands. The sleeves shall be highly  polished and shall be securely fastened to the shaft to prevent any loosening.

 

            ●          Bearings

 

                        i)          Heavy duty ball, roller (tapper roller wherever required)or sleeve bearings, adequately designed for the type of service specified and for long and trouble free operation, shall be furnished. Sleeve type bearing shall not be supplied for slurry handling liquids.

 

                        ii)         The design of oil lubricated bearings shall be such that the bearing lubricat­ing oil does not contaminate the liquid being pumped.

 

                        iii)        Grease lubricated ball bearings are acceptable, if the pumps is specifically designed for grease lubrication and if shaft speed is less than the speed limit recommended by the bearing manufacturer and the fluid temperature does not exceed 65.5 deg.C (150 deg.F).

 

                        iv)        Each bearing housing shall have drain plug.

 

            ●          Thrust Bearings

 

                        Adequately designed thrust bearings to absorb pump end thrust or other unbal­anced forces, if any, shall be provided wherever required. Suitable arrangement for adjusting clearances shall be provided.

 

            ●          Stuffing Boxes & Sealing

 

                        i)          Stuffing boxes of packed ring construction or of mechanical seal type as applicable shall be provided. Packed ring stuffing boxes shall be properly lubricated and sealed as per service requirement and manufacturer’s stand­ard.

 

                                    If lantern rings are provided between the packages, these shall be complete with inlet and outlet piping connections.  Lantern rings shall be axially split type.

 

                        ii)         For pumps handling clear cool water if external gland sealing is required, it shall be done from the pump discharge or from any intermediate stage.

 

                        iii)        For pumps handling sandy/muddy water or slurry, external clear water sealing shall be provided. The design should also provide for flushing of the clearance between pump rotation and stationary parts continuously by trickle clear water flow.

 

                        iv)        The Bidder shall provide the necessary piping, valves, boosters, fittings, etc. for the gland sealing connection.

 

                        v)         For mechanical seals, the mating surfaces shall be suitably hard faced to ensure long life.

 

            ●          Couplings

 

                        i)          The pump & motor shaft shall be connected with a suitably designed flexi­ble coupling of approved design preferably with a spacer to facilitate dismantling of the pump without disturbing the motor.  Necessary expand­ed metal coupling guards for the coupling shall also be furnished.

 

i)                 Other arrangements for coupling the pump with prime mover may be employed only in case the same is categorically specified.

 

ii)                For pumps handling abrasive slurry or where fast wearing of pumps is likely due to the particular service conditions, variable speed drive shall be employed, thus enabling operation of pumps within specified ranges of speed with respect to pump speed at rated operating point. Pumps shall be suitable for operation at such higher speeds. The variable speed drive shall be the variable speed hydraulic coupling as specified.

 

            ●          Base Plates

 

                        i)          The base plates shall be of fabricated steel and of rigid construction, proper­ly ribbed as required.  Driplip with drain tap based on type of service speci­fied shall be furnished.

 

                        ii)         All directly coupled pump motor sets shall be supplied with common base plates.

 

                        iii)        For pumps coupled with motor through the variable speed drive transmission system, separate base plates for pumps and motors are acceptable.

 

                        iv)        The common base plate together with all foundation bolts and nuts shall be supplied by the Contractor.

 

            ●          Connections/Nozzles

 

                        Cast iron flanges shall be flat faced. Flanges shall be full or spot faced on the back side also.

 

                        All accessories required for proper and safe operation of the complete pump motor set shall be furnished.

 

                        Each pump shall be provided with drain, vent and a priming connection at suitable location, wherever applicable.

 

                        Pumps are required to operate for some period with discharge valve closed. The pumps shall be suitable for zero-flow operation for a reasonable period.

 

            ●          Accessories

 

                        The following accessories shall be supplied for all pump motor sets:

 

                        i)          Foundation bolts and nuts for pumps.

 

                        ii)         Foundation bolts and nuts for motors.

 

                        iii)        Foundation bolts and nuts for base plates.

 

                        iv)        Foundation bolts and nuts for slide rails, if slide rails are provided.

 

                        v)         Base plate for all pump-amotor sets.

 

                        vi)        Transmission guard for flexible coupling/vee belt transmission etc. as ap­plicable.

 

                        vii)       Slide rails for motors if variable pitch, set of vee belts or flexible coupling as applicable.

 

                        viii)       Suitable connection for sealing/cooling/flushing water supply, if applicable.

 

                        ix)        Lubrication fittings as necessary for proper and easy lubrication of the equipment.

 

                        x)         Drain and vent cocks as required.

 

                        xi)        Priming funnel or overhead tank, as required.

 

                        xii)        Foundation bolts for hydraulic coupling.

 

                        xiii)       Suitable adopter for pumps suction and discharge, if required.

 

                        xiv)       Anchor Bolts, Sleeves, Inserts, Lifting Lugs, Eye Bolts etc.

 

                                    The Bidder shall supply all anchor bolts, foundation plates, sleeves, nuts inserts etc. to be embedded in concrete for the equipment to be supplied.  The length of foundation bolts shall be liberally sized to reach below the reinforcement level.

 

                        xv)       Any other accessories mentioned elsewhere in this specification.

 

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