Presentation by Dave Lees (Bedford Pumps) Mellish Kett (Severn Trent)
Largest Sewage Treatment Works in Severn Trent Extensive Process Modifications New Pumping Station Entire Works Flow to Full Treatment Settled Sewage Maximum Flow 12,400 l/s Approximate Head 3.5m
Whole Life Cost Review Civil Cost M & E Cost Power Consumption Maintenance Lineshaft/Volute Pumps £5M Archimedean Screw Pumps £5.48M Submersible Bowl (Canister) Pumps £4.12M
Bedford Pumps invited to participate No formal Specification Non – Framework Free sharing of ideas Costing of various options Competitive tender reviews not required Ability to react to design changes
Maximum Flow: 12,400 l/s Average Flow: 5,700 l/s Minimum Flow: 3,500 l/s Total Head (approx): 3.8m
Design 5+1 Pumps: 2,480 l/s each Nine alternatives. Two subjected to WLC. Diurnal Flows considered. Final Pump selection made.
Open – top Canister Pump Arrangement: Ease of installation removal (H & S) Lowest friction loss No pipework or valves Clearly defined static lift
Additional Return Flows: Maximum flow now 13,150 l/s Part gravity flows after two years Introduction of BNR (Biological Nutrient Removal) Plant, from 2012: Potential increase of 2m on the pump head Phase 1: 13,150 l/s at 2.8m Phase 2: 11,050 l/s at 2.8m Phase 3: 11,050 l/s at 5.1m Same Pump and Motor.
Model Test commenced. Two sets of three pumps, so half station modelled. Minimum excavation required. Station designed to run at a relatively constant low sump level. Benching required as shown to optimise inlet conditions into the pump bellmouth.
Discharge chamber also modelled. Original design was for 1.8m canister outlet diameter. This was changed to 2.4m diameter, to prevent splashover into adjacent units. Also resulted in a reduced “weir” over canister lip. Pump centre spacings now fixed.
Flows finalised. Minor adjustments to levels and heads taken into account. Results of model test incorporated into design. Final tender submitted 25 th October, following several estimates.
Contract awarded in January. All six pumps given full Grade 1 works performance test. Both contract inverter and in-house inverter used. Guarantee pump efficiency 86.1%. Tested efficiency 88-89%. Pumps delivered December 2008, commissioned March 2009.
Six Pumps (Five Duty, one Standby) Total station Flow: Max 13,150 l/s (2,630 l/s each) Maximum flow/Pump: 2,630 l/s Maximum Speed: 424 rpm Guarantee duty: 1,200 l/s each at 2.88m (5 units) Guarantee Efficiency: 86.1% Motors: ATB Morley 160 kW 14-pole Pump/motor weight: 6,100 kg
Six Pumps , canisters, sitework, etc. Total contract Value: £650,000 Production man-hours: 7,000 Installation man-hours: 200 Castings: UK Machining: UK Testing: UK Canisters: UK Motors: UK
Change of Plan.. Plan was to install 55,000m 3 tank Replaced with advanced Liquor Treatment and increasing depth of existing ASPs SSPS Future duty BNR reduced from ASP 7 5.1m to 3.25m
Best Laid Plans.. Remove and replace canister Was there a cheaper way? How are we actually going to do this with the walkway obstruction?
Ideas New Canister Difficult to remove and would require removal and disconnection of pump
Ideas Adding to Top Difficult to manufacture 2.4m ring to join and seal
Ideas Add to bottom Would have to remove Pump to add Coupling, unless… Split Coupling
How it was done Week without rain Shut Penstocks to isolate one cell
How it was done Pump down
How it was done • Scaffold out • Lift in Couplings • Lift Canister • Bolt together
OUTCOMES Collaboration Plan Ahead Plan Ahead More
Questions?
(Video)
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