Challenge

At the Knostrop wastewater treatment plant, Yorkshire Water was required to provide an odour control facility to improve the air quality from their sludge treatment processing plant and surrounding area of the works. The solution had to address possible odour complaints from nearby neighbourhoods, meet stringent statutory legislation requirements to reduce nuisance odours, and reduce installation and operational costs. There was also a challenge with the physical space allowed. The system had to fit into this space whilst still providing the high level of odour control treatment expected. 

Solution

To resolve these problems, Yorkshire Water installed a LO/PRO® system from Siemens. The system is a “once-through” patented unitary design wet chemical LO/PRO® packaged odour control scrubbing system. The three-stage wet chemical system consists of a two vertical counter-current stages and one co-current stage of gas absorption.  After the system has removed H2S from the hydrogen sulphide- producing plant process areas, the deodourised air is exhausted at high level. The unit was designed for an odour level of 201ppm H2S plus other odorous constituents.

The LO/PRO® scrubber’s footprint is approximately two-thirds smaller than that of conventional packed tower systems, which helps address Yorkshire Water’s concern about required installation space and associated civil engineering costs. The system also has a much smaller overall height and does not require expensive interconnecting ductwork between the various stages.

Unlike its conventional counterparts, the LO/PRO® unit’s patented design significantly reduces the amount of chemcial used in the third stage of the unit. The first stage uses NaOH to remove up to 80% of the H2S. The second stage performs 70% removal of the remaining H2S using NaOH, with the third stage using NaOH and NaOCI to remove the remaining H2S and organic odours. This multi-chemistry system reduces chemical costs to less than half that required by conventional packed tower scrubbers.

Results

The LO/PRO® was successfully commissioned in December 2008. The system treats 56,534 m3/hr of odorous air extracted from domestic and industrial wastewater process treatment areas. At this first major installation of a LO/PRO® in the UK, Siemens will help the plant meet removal efficiencies in excess of 99% and minimise chemical usage rates. The system runs to guaranteed levels that, whilst encompassing odour levels, also includes water, chemical and power consumption.

Yorkshire Water’s custom-designed system was factory assembled and tested prior to delivery. This customisation ensures maximum efficiency as well as significantly reducing the onsite installation time, tooling and effort over more conventional odour systems.

Black & Veatch were the principal contractor for the project.

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