Outsourced treatment supplies ultrapure water for power plant

By Shiraz Butt

In June 2004, Ecolochem International Ltd began operating its new water purification plant at the Spalding Energy Power Station in the UK.

Ecolochem trailer supplements demineralised water needs during power plant commissioning.

The plant will provide a dependable supply of demineralised water, which is essential to operate the power station. The 24-hour cover and monitoring of the site provides outsourced benefits for Intergen, the joint venture company of Royal Dutch/Shell Group and Bechtel, that is constructing the power station, according to Project Engineer Howard Crooks of Intergen. The US company Ionics Incorporated of Watertown, Massachusetts, acquired the UK company Ecolochem International in February 2004.

Under the terms of an 18-year service agreement, Ecolochem International built the water treatment plant and will now operate, service and maintain it to produce ultra pure water to the required specification and quantity. The initial phase of the contract also includes the commissioning of the power station, where typically ten times the water needed for running the power station is required. The main processes of hydro testing, flushing, cleaning and steam blows need large quantities of steam before the plant begins operations.

Ultra pure water is required at the combined cycle gas turbine (CCGT) power station for make-up for the boiler/heat recovery steam generator (HRSG) in addition to NOx control. Power station boilers create the steam and pass it through a steam turbine to generate electricity. The waste heat energy from gas turbines is also used to create steam, making the overall plant more efficient. The demineralised water (DI) produced is fundamental to prevent damage to the major plant components and more importantly to reduce make-up requirements on the steam cycle, as used steam is condensed and returned to the HRSG for reuse.

The water is treated with granular activated carbon (GAC) for de-chlorination and polishing filtration and then ion exchange softening resin to remove total hardness which would scale the downstream reverse osmosis (RO) membranes. The softened water is fed to a two-pass RO unit containing polyamide (PA) membranes before being passed through a double pass gas transfer membrane (GTM) system to reduce carbon dioxide and oxygen and finally to an Ecolochem MobileFlow® DI trailer for ion exchange polishing to DI quality.

The US company Bechtel constructed the Spalding Energy power station for Intergen, which will also initially use the ultra pure water to assist during the commissioning phase of the station. The water being treated is municipal water with almost a 500µS/cm Total Dissolved Solids (TDS) content. The quality of water produced is <0.1µS/cm TDS, <20ppb Silica and <10ppb Sodium.

The water treatment plant is a combination of containerised and trailer-mounted mobile equipment. The regeneration of ion exchange resin off site means no chemical handling or discharge issues for power station owners. Additionally, the mobile equipment reduces the need for space required by the water treatment plant. The flexibility of this system is advantageous during plant commissioning where trailers can come to site, produce the water and leave to be replaced by a new trailer— no space problems and no discharge issues.

Once the power station is fully operational, the water treatment plant will operate using an automated system devised by Ecolochem. Company field service engineers will visit the site on a weekly basis. Director of Operations for Ecolochem Colin Wright explained that the automated system at this site will use equipment that allows company engineers to continually monitor and fine-tune the water treatment plant as the need occurs from Ecolochem headquarters in Peterborough.

Author's Note
Shiraz Butt is the marketing manager of Ecolochem International Ltd, located in Peterborough, England, UK.