Mobile Solutions solves consent to discharge problem at UK Power Station
While the 20’ containerised plants were being built and commissioned, Mobile Water Services provided a short term MODi trailer, ensuring that the station’s water supply was secured.
A 140MW oil fired open cycle gas turbine (OCGT) station based in Cornwall, UK. The Power Station was constructed in 1996 and, under the terms of the integrated pollution control application, it operates as a peak lopping station, which means that it runs only infrequently and predominantly in the winter months when demand is high.
The Client’s NeedsIn order to suppress NOx emissions, water is sprayed directly into the burner to reduce the flame temperature. This water evaporates leaving behind any dissolved salts which deposit in the burner and need to be removed regularly. In order to avoid such problems, the station uses deionised water of 0.1μS/cm conductivity and silica less than 20ppb, which is very low in dissolved salts.
During the summer, the station uses about 40m3 per day of deionised water, but in winter the demand rises to about 170m3/day. To produce this high quality water, an ion exchange plant with its associated regenerant chemicals and effluent discharge is required.
Project & Technology SolutionsThe company had purchased a 9m3/h Rapide deioniser from Veolia Water Technologies. The Rapide uses state-of-the-art ion exchange technology, with a highly efficient regeneration process that produces such a small quantity of effluent that it can be economically tankered off site to a merchant waste disposal facility.
Back in 1996, the site did not have a Consent to Discharge. So during the winter months when the demand for water is higher, tankering the water off-site becomes un-economical, so the station’s then owners, opted to use a mobile rental deionisation system with off-site regeneration and no on-site effluent discharge.
Process DescriptionVeolia operates a fleet of Mobile Water Services trailer mounted treatment plants that includes MODi deionisation units. These provide two streams of cation, anion and mixed bed ion exchange vessels housed in custom built, 45’ trailers together with automated controls, remote telemetry and all the necessary safety equipment.
Each MODi trailer is capable of producing in excess of 150m3/h of high purity water – more than enough for their needs. Once exhausted the complete trailer is returned their Stoke-on-Trent facility for regeneration, which means zero discharge on site and no problems of handling or disposal of regenerant chemicals. But the MODi trailers are intended mainly for emergencies or planned maintenance shutdowns and may not be the most cost effective solution for long term hire.
The Mobile Water Services Team carried out a detailed review of the site and concluded that, rather than a trailer-mounted mobile unit, a lower cost option would be to install a custom designed 30m3/h containerised, deionisation plant. They proposed two 20’ ISO containers each fitted out with a cation exchanger, two anion exchangers and a mixed bed polisher.
One container is also equipped with the controls, quality monitors and remote monitoring equipment needed for both streams. Rather than shipping the complete unit back to for regeneration when the resins are exhausted, the resin vessels are simply exchanged for regenerated ones by the Mobile Water Services team. Each containerised unit will treat about 1200m3 of mains water between regenerations; enough for a fortnight’s usage at average station generating capacity.
ResultsThis long term hire solution offered a big saving and the company signed up to a multi-year contract. While the 20’ containerised plants were being built and commissioned, Mobile Water Services provided a short term MODi trailer, ensuring that the station’s water supply was secured.
- Cost effective mobile plant
- Zero discharge
- Secure water supply