Odour control at Northumbrian Water
Feb 27 2009
For waste water treatment companies, wet chemical scrubber circulation applications for odour control provide essential environmental control systems. To be truly effective they demand a high plant availability at all times, which means that the mechanical components must offer high reliability and operating integrity.
At Northumbrian Water’s (NW) Howdon sewage treatment works, great reliance is placed on the efficiency and performance of the re-circulating scrubber liquor pumps which handle 25% Sodium Hydroxide (caustic) and 17% Sodium Hypochlorite (Hypo). The eight Wernert pumps supplied by AxFlow Limited (UK) were installed when the wet chemical scrubber plant entered service in 1998 and a decade on the same pumps are still giving the levels of service demanded by NW.
The plant was designed to remove H2s and sulphur based compounds through the use of a re-circulated liquor made up of softened water. The Wernert NEPO pumps return liquor from ground level to a height of around four metres to allow the liquor to dose the odorous air before it leaves the vessel stack. The chemicals are dosed directly into the liquors and are controlled and monitored using Prominent control technology
The Wernert NEPO pump, fitted with a bellows-type axial face seal has a long track record within the waste water and effluent treatment industry where it has to convey various chemicals. For NW, specification of the pumps back in 1998 was based on previous experience with Wernert pumps on scrubber circulation operations.
AxFlow reports that other than periodic inspection, the eight pumps used in the scrubber circulation application have performed well. In fact it has only been on four or five occasions that any remedial work has been undertaken for all eight pumps, which is not as frequent as similar pumps on other scrubber systems on the Howdon site.
Certified to ATEX 100a, the Wernert NE range has robust completely metal encased thick-walled casing parts made from high performance plastics such as ultra-high molecular weight polyethylene (UHMPE - RCH1000), PVDF and PTFE / PFA, which ensure that the pump is safe for pressure rating to 16barG. The choice of pump process contact parts depends on temperature, abrasion and corrosion associated with the process fluid. In the case of the pumps supplied to NWL, the pumps are fitted with highly abrasion and corrosion resistant UHMPE. If necessary, the “rear pullout” pump design allows a quick exchange of the hydraulic side of the pump, without detaching the flanges or dismounting of the electric motor. Temperatures of up to 165ºC can be handled.
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