The rate of corrosive wear in superheaters of boilers for supercritical parameters of steam

The paper prepares models of corrosion processes in superheaters of supercritical boilers. The models presented enable a quantitative description of steam-side and flue gas-side oxidation as a function of the design and operational parameters of the heating surface. In the latter part of the paper, example calculations were performed for the final stages of a superheater and reheater in a supercritical PF (hard coal) boiler. The calculations show that if the boiler under analysis is fired with coal of low susceptibility to the creation of corrosion scale and the material of the tubes is adequately chosen, then the rate of tube thickness loss in the final stages of superheaters is sufficiently small to expect undisturbed operation of these surfaces for at least a dozen years. The use of alloys with a relatively high oxidability (e.g., the replacement of TP347HFG with its coarse-grain variation TP347H) poses the danger of a loss of metal that is several times faster.

► Cofiring of agricultural biomasses and wastes with coal increases the external corrosion rate of tubes.
► Quality of alloy is of basic importance to the progress of superheater/reheater corrosion.
► The rate of oxides growth is significantly higher in reheaters.
► Substantial spread of steam temperatures in the particular coils of superheater stages is a serious threat.