With 2,160 megawatts, RWE npower’s power plant near Pembroke in South Wales, which was built by Alstom Power Systems, is one of the largest and most efficient gas and steam power plants in Europe. It can supply close to three million households with electricity. An important component of the plant is the generation of ultrapure water from surface water, which is fed into the water/steam cycle. This requires, among other things, a demineralisation system. Alstom Power Systems awarded this contract directly to H+E. The removal of organic impurities from the water played a key role in the process selection, since they need to be kept away from the water/steam circuit for corrosion-chemical reasons.
With the various treatment stages, the water quality improves continuously along the entire process. The deionised water conductivity must be less than 0.10 μS, and the TOC less than 200 μg/l. In order to ensure compliance with the TOC, the H+E team opted for a membrane plant combination with redundant design. This enables parallel operation and allows the power plant operator to fill the water/steam cycle with double-installed plant capacity and to quickly put it back into operation.
For complete desalination of the surface water, H+E connected the following process stages in succession: first a prefiltration, followed by inline flocculation, which destabilises colloidally dissolved substances. Ultrafiltration removes solids and lowers the fouling potential before the water flows through an antiscalant dosing system. The permeate-stepped reverse osmosis unit with NaOH dosing serves as the penultimate process step for the main desalination and for the removal of TOC and carbonic acid. Fine desalination is carried out by the final mixed-bed ion exchanger system.
Facts & figures:
- Full desalination for one of the largest gas and steam power plants in Europe
- A reliable, redundant system concept
- Ultrapure water quality even with large fluctuations in the raw water composition
- A low number of CIP cleanings per year