Experiments investigating transformation

deposition and corrosion behaviour of ash were carried out in a large-scale wastewater incineration plant.Ash deposited samples were collected from the surfaces of heat transfer tubes after operating period of 15 d and characterized using analytical techniques such as X-ray fluorescence spectrometer(XRF)

scanning electron microscope coupled with energy dispersive spectroscopy(SEM-EDS)and X-ray powder fluorescence(XRD)

to determine their chemical composition

morphology and mineralogy.The results show that Na which volatilizes during wastewater incineration has an even distribution on whole region flue gas flows

while non-volatile elements

Ni and Fe which are transported by ash particles have strong deposition trends at region of high temperatures.Element S is significantly enriched at region of low temperatures.Release and transformation of numerous Na and S as well as heat transfer process during incineration are the key issues for fouling/slagging and deposits growth in the HRSG.Condensation of Na species on surface of heat transfer tube forms a sticky deposition layer

which increases sticking probability of ash particles.At region of high temperatures

main components in ash deposits are Na2SO4

NiO and Fe2O3.While at 660-900℃

eutectic mixtures with much lower melting temperatures

such as sodium iron sulfate(Na3Fe(SO4)3)

nickelblodite(Na2Ni(SO4)2·4H2O)are formed.They are temperature-dependent and can enhance formation of sintered deposits.Acidic salt sodium sesquisulfate Na3H(SO4)2 is generated at low temperatures and should be responsible for the initiation of low temperature corrosion.