Asia Power Week 2017

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Ash Deposition Control Technology: A Strong Enabler for Performance Upgrade in HFO CCGT Plants (Room Nile 2)

Heavy duty gas turbines (GT) are well known for their high energy performance and fuel flex. However, burning low grade fuels such as HFO in GTCCs results in strong performance penalties due to the fouling of the expansion turbine by ash deposits. There is actually a prospect for considerable performance gains, if one could suppress or reduce this adverse ash deposition effect. However, this represents a tricky technological challenge because the ash particles fly at very high speed across the expansion section of the machine and hit the GT hot parts. In contrast, in a boiler plant, the prime mover i.e. the steam turbine, is driven by high purity steam the quality of which is kept under strict control regardless of the quality of the fuel. A further difficulty faced when trying to reduce ash deposition in GTs lies in the additional fouling entailed by the “inhibition process” : the combustion of HFO requires the injection of a magnesium-based corrosion inhibitor to suppress the corrosion threat placed by the vanadium oxide originating from this type of fuel. This corrosion inhibitor substantially increases the amount of ash crossing the machine and aggravates the fouling effect. A joint initiative by LTL Holdings Ltd, GE Power & Water and the UTBM University has resulted in a feasible ash modification solution and the team has successfully tested a novel family of vanadium inhibitors that provides a considerable reduction in ash deposition. This new inhibitor family brings interesting improvements in terms of GT efficiency and plant availability as it enables reducing the frequency of the machine shutdowns that are periodically required to remove the ash deposits by water wash. In addition, it procures a strong soot suppression effect, a further significant added value of this technology.