2007-07-25 - ABB has been contracted to supply packaged analytical systems to Alstom Power for installation on two new gas fired power stations. Comprising a host of analytical equipment, the systems will be used to monitor the purity of water throughout the power plant's water & steam circuits.
Analytical systems are essential for the efficient operation of the water and steam circuits in a power plant. The quality of water and steam within the boiler needs to be continuously monitored to avoid corrosion and the build up of deposits. The efficiency of the boiler and turbine can be seriously impaired if deposits are allowed to build up unchecked.
In the UK, Centrica Energy is building a new combined cycle power plant at their Langage Energy Centre near Plymouth. Rated at 847 MW, this is the first new power plant to be constructed in the UK for a number of years.
The second system will be supplied for a 412MW combined cycle power plant being built for Gas Natural in Malaga, Spain. The 6m long system cabin, which incorporates pH, conductivity and sodium analyzers, is scheduled for shipment from ABB’s manufacturing plant in Stonehouse, Gloucestershire during September 2007. The new power plant will come on stream during 2008.
The Langage analytical cabin is scheduled for delivery to site in December 2007. It will be housed in a 13.5m long, air conditioned cabin – and will be one of the longest to be supplied from Stonehouse.
The cabin will include primary coolers and a secondary chiller section to ensure that the sample temperature is at a nominal 250C before it enters the analytical instruments. Here it is monitored for key parameters such as conductivity, pH and sodium content.
This system incorporates two novel features. The pH measurement of the condensate and feed water is inferred (rather than measured) using ABB AX411 analysers and the VGB standard directive number 450L model calculation. This produces a more cost effective solution compared to actual pH measurement and reduces maintenance requirements.
Secondly, to minimise steam wastage and give greater plant efficiency, the conductivity level of the high pressure steam lines (traditionally analyzed for before and after cation conductivity) has the addition of ‘Degas’ conductivity. Because modern plant have multiple start ups and shut downs carbon dioxide dissolves in the make up water tank and this can influence the conductivity of the sample. This measurement gives the conductivity value of the steam after the dissolved carbon dioxide has been removed from the sample. The resulting reduced conductivity level so achieved allows the steam to be routed to the steam turbine as quickly as possible after start up of the plant.