Calculated Tolerance of a Large Electric Utility Gas Turbine to Erosion Damage by Coal Gas Ash Particles Available to Purchase

Erosion damage was estimated for the first stage of a large electric utility gas turbine based on projected particle distributions in the gas leaving the hot gas cleaning system of a pressurized fluidized-bed gasifier system. Based on the assumptions used in making the estimates, cleaning of the turbine expansion gas to a particulate concentration of 0.005 gram per standard cubic metre (0.002 grain per standard cubic foot) with particles larger than 6-μm diameter effectively removed should give satisfactory blade life from an erosion standpoint. Two stages of high-performance cyclone cleanup to 0.1 gram per standard cubic metre (0.5 grain per standard cubic foot) with 0.05 weight percent of 12-μm diameter particles remaining in the gas would wear stator vane trailing edges by 0.25 cm (0.1 in.) thickness (roughly equivalent to full wall thickness in upstream stage vanes) in 10000 h of operation.

The numerical results presented in this paper are based on the estimate that coal ash and sulfur sorbent particles will have, when impacting superalloy turbine materials under turbine conditions, 1/25th of the erosivity of silicon carbide particles impacting a nickel alloy at room temperature. The estimates do not account for the appreciable slowing of the 1- to 3-μm particles in the blade boundary layers before they reach the blading, even though these small particles account for most of the damage. The numerical results are in this way conservative. Actual data on the damage which coal gas particulates do to blade materials under turbine conditions are needed to establish the erosion tolerance of the turbine more accurately.