关键词: 废液焚烧, 积灰结渣, 挥发/非挥发元素, 低熔点共晶体, 腐蚀

Abstract: 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.

Key words: wastewater incineration, fouling and slagging, volatile/non-volatile elements, eutectic mixture, corrosion