Multi-tasking sludge pumps

ITT Flygt has supplied centrifugal pumps to Newton Aycliffe WwTW for various sludge-handling applications. Tony Price explains.

Newton Aycliffe is west of Middlesbrough, between Darlington and Bishop Auckland. Its industrial estate accommodates Northumbrian Water's sewage treatment works which handles an average inflow of 26 megalitres/day. The N pumps at Newton Aycliffe STW were selected not just to handle sewage sludges containing rags and grit, but because they reduce downtime. The N pump can handle sewage sludges of up to 8% total dry solids.

A complaint from operation and maintenance staff is lack of availability of pumping equipment, due to product failure, which can be apportioned to blockage, reduced performance due to wear or extended delivery of critical spare parts.

The STW's sludge thickener building, housing the belt press, is the hub of the thickening process. Three sets of Flygt pumps handle an array of sludges, all dry well mounted in the vertical "T" configuration using N technology. These are imported sludge transfer pumps, washout pumps and thickened sludge transfer units. The transfer pumps draw from a well receiving tankered sludges from the surrounding minor works, as well as farms and local businesses. The nature of imported sludge is such that grit, rag content and dry solids content cannot be controlled or guaranteed.

The NT3153.181 with a 455 impeller was chosen as it gives operational staff the knowledge that the imported sludge at Newton Aycliffe will be handled problem free, and require minimal downtime, without the need for ongoing spares.

The pumps draw from the imported sludge chamber and pump to the sludge consolidation tank situated some 30m away outside. The pumps have to perform a static lift of 5m plus losses in the discharge pipework, giving a flow rate of 32ls-1 at a total delivery head of 14m. Next to the imported sludge pumps is a 2m-deep chamber with three washout pumps. These handle return liquors, screen washdown and water from the primary tanks which give a variable solids concentration of 0.5-2%. The pumps discharge into the same sludge consolidation tank fed by the imported sludge pumps. The pumps used here are NT3171.180 with 434 impellers, employing a drive of 18.5kW running at 4 pole speed. Each pump delivers 92ls-1 against a total head of 10.2m. This is made up of 7m static plus the losses in the 200mm-diameter pipework leading to the sludge consolidation tank.

The primary sludge introduced to the sludge consolidation tank is 3% dry solids, while the thickened sludge from the gravity belt thickener is in the order of 5-6% dry solids. The resultant sludge to be fed to the digester from the sludge consolidation tank is about 4-4.5% dry solids content.

Raw sewage
The digesters are 350m from the thickener building. The pumps feeding the digesters are thickened sludge transfer pumps. The requirement here is for pumps that will give trouble and blockage free operation, eliminating downtime and the requirement for costly spares.

The N pump was again used here - the requirement is to deliver the sludge consolidation tank's contents to the digester. The pumps selected were the NT3153HT, fitted with a 453 impeller, driven by 13.5kW 4 pole speed drives. The duty point of these pumps is 32ls-1 at 17.4m total delivery head, comprising 14m static plus the losses in the 200mm rising main taking the consolidated sludge to the digester.

No. 4 Pumphouse is the collection point for Humus sludges and receives raw sewage from Aycliffe Village's pumping stations. Two sets of pumps are housed here - the Humus Return Pumps and the Tertiary Sludge Pumps. The Humus Return Pumps feed back up the site to the inlet. These are single vane channel impellers mounted in the vertical plane. Although on single vane impellers, the sludge dry solids content of 2% is handled by this technology. The pumps are CT3152s with 431 impellers.

The drive units are 13.5kW electric motors, running at 4 pole speed. These operate at 22ls-1 delivering the flow to the works inlet for treatment.

Sharing Pumphouse No 4 with these pumps are the Tertiary Sludge Pumps horizontally-mounted Z configuration N Pumps to take humus liquor from the final effluent well and deliver back to the treatment work's biological filters.

These are NZ3301.180 fitted with 622 impellers. The drive is rated at 55kW; full load speed 985rpm.These pumps operate via a variable frequency drive, giving an adjustable flow rate to about 400ls-1. The digester building, where thickened sludge is delivered and fed into the digesters. Three N pumps to circulate sludge from the digesters to the clarifiers.

The suction pipelines of the digesters are 60m in length, 100mm in diameter and run from the two digesters to the pump house. The digesters run on an alternating duty basis.

Three digester recirculation pumps each handle sludge with a dry solids content up to 8%. These are NT3127 with 489 impellers. The pumps then pass sludge back to the clarifiers. The suction line is 60m long with six bends and a suction lift of 1m, on the discharge; the pumps work against a total head of 6m giving a flow rate of 35ls-1

Tony Price is Flygt's specialist sludge market manager.
T: 0115 940 0111.

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