Indian Queens Gets the Best Deal
25 September 2007 10:07
ELGA Process Water assists power station without consent to discharge
International Power plc is a growing, independent power generation company with 18GW net ownership of capacity worldwide (30GW gross). Last year, it acquired the 140MW Indian Queens oil fired open cycle gas turbine (OCGT) station in St Austell, Cornwall. Indian Queens Power Station constructed in 1996 operates as a peak lopping station, which means that it runs only infrequently and predominantly in the winter months when demand is high.
In 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, Indian Queens uses de-ionised 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 de-ionised 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. Back in 1996, Indian Queens did not have a Consent to Discharge and, since the station would operate with a very low utilisation, its then owners opted to use a mobile rental de-ionisation system with off-site regeneration and no on-site effluent discharge.
The ten year rental contract allowed Indian Queens Power to obtain de-ionised water from any source available during the summer months. Water costs were reviewed every year and, when the economics moved in favour of on-site regeneration, the company purchased a 9m³/h ELGA Process Water Rapide de-ioniser. 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. During the winter months this becomes un-economical and the station reverts to the mobile rental solution.
The ELGA Process Water plant had performed well, so when the rental contract was due for renewal, ELGA was given a chance to bid. ELGA operates a fleet of AQUAMOVE mobile trailer mounted treatment plants that includes MODI de-ionisation units. These provide two streams of cation, anion and mixed bed ion exchange vessels housed in custom built 45ft trailers. Each MODI trailer is capable of producing in excess of 150m³/h of high purity water. Once exhausted the complete trailer is returned to ELGA's Stoke-on-Trent facility for regeneration, which means zero discharge on site. But the MODI trailers are intended mainly for emergencies and are an expensive option for long term hire.
ELGA Process Water’s AQUAMOVE Team carried out a detailed review of the Indian Queens 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 20ft 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 ELGA Process Water for regeneration when the resins are exhausted, the resin vessels are simply exchanged for regenerated ones by the AQUAMOVE service team. Each containerised unit will treat about 1200m³ of mains water between regenerations; enough for a fortnight’s usage at average station generating capacity.
This proposal offered a big saving by comparison with mobile trailers and International Power signed up to a five-year contract.
For more information on this company:
ELGA Process Water - Industrial Water Treatment
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