Synthesis, characterization and application of a highly selective adsorbent for the removal of corrosive sulphur compounds from mineral insulating oils and a new method for the assessment of oil corrosiveness against silver

[J. U. Janković]

119 listova

Tehnološko inţenjerstvo - Hemijsko inţenjerstvo / Technological engineering - Chemical engineering

Cilj istraţivanja ove disertacije je sinteza, karakterizacija i primena visoko selektivnog adsorbenta (VSA) za uklanjanje korozivnih jedinjenja sumpora iz mineralnih izolacionih ulja, pre svega elementarnog sumpora (S8) i razvoj nove metode za ocenu korozivnosti mineralnih ulja prema srebru. VSA, sintetisan u posebnom postupku nanošenja vodenog rastvora jona srebra i amonijum jona na nosaĉ adsorbenta na bazi silicijum-dioksida, predstavlja nov, mezoporozni materijal visoke efikasnosti u uklanjanju S8 iz ulja procesom hemisorpcije. Nakon tretmana, dobija se nekorozivno ulje sa poboljšanim karakteristikama za dalju upotrebu. Primena VSA ispitana je perkolacionim postupkom regeneracije ulja, u laboratoriji (lab-scale set up) i na pilot postrojenju (pilot-scale set up). Proces je verifikovan na terenu, u mobilnom postrojenju (on-site), na ulju iz 35 kV energetskog transformatora. Izvršena je teksturalna, strukturno-morfološka i fiziĉko-hemijska karakterizacija VSA. Ustanovljeno je da je adsorpcija spontana i endotermna, da kinetiĉki model pseudo-drugog reda najbolje opisuje proces adsorpcije i da Langmirov model izoterme najviše odgovara dobijenim eksperimentalnim rezultatima sa maksimalnim kapacitetom adsorbenta od 4.84 mgS8/gads na 353 K. Drugi pravac istraţivanja bio je razvoj nove, unapreĊene ASTM D 1275-15 metode korozije srebra u uslovima povišenog sadrţaja kiseonika, kao glavnog faktora koji promoviše formiranje naslaga srebro-sulfida. Prikazani su rezultati novorazvijenog testa na uljima koja sadrţe dibenzil-disulfid (DBDS) u širokom rasponu koncentracija (od 40-200) mg/kg iz pet transformatora u pogonu, koji imaju komunikaciju sa atmosferom preko konzervatorа i koja su prema standardnom ASTM D 1275-15 testu bila ocenjena kao nekorozivna. Nakon novog testa ulja su bila korozivna prema srebru, što je potvrĊeno EDX merenjima. Nova metoda znaĉajno će unaprediti procenu rizika eksploatacije transformatora sa korozivnim uljima i doprineće pravovremenom planiranju primene efikasnih tehnika za rešavanje problema korozije srebra kod energetskih transformatora.

The aim of this dissertation is synthesis, characterization and application of a highly selective adsorbent (HSA) for the removal of corrosive sulphur compounds from mineral insulating oils, particularly elemental sulphur (S8) and development of a new method for silver corrosion assessment. The HSA, synthesized in a novel procedure of deposition of silver ions and ammonium ions, from aqueous solution, on the silicon dioxide support, represents a new, mesoporous material with high efficiency in removal of S8 from the oil by chemisorption. Non-corrosive oil with improved characteristics is obtained after the treatment for further use. The application of VSA was tested using percolation process of oil regeneration, in the laboratory (lab-scale set up) and on a pilot scale system (pilot-scale set up). The process was verified using large scale mobile unit (onsite) on oil from 35 kV power transformer. The textural, structural, morphological and physicochemical characterization of the HSA was performed. It was found that the adsorption is spontaneous and endothermic process, that the pseudo-second-order kinetic model best describes the adsorption process and that Langmuir isotherm model fits better to the obtained experimental results with the maximum capacity of the adsorbent of 4.84 mgS8/gads at 353 K. Second research area of the thesis covered development of a new, improved ASTM D 1275-15 method for silver corrosion assessment in conditions of higher oxygen content, as a crucial parameter for promoting the formation of silver sulphide deposits. The newly developed method was demonstrated on oils containing dibenzyl disulfide (DBDS) in a wide range of concetrations (from 40-200) mg/kg from five free-breathing power transformers in service, which remained non-corrosive following the standardized ASTM D1275-15 silver strip test. After the new test, the oils were corrosive to silver, which was confirmed by EDX results. The new method will contribute to improved diagnostics and assessment of the oil corrosivity against silver and to timely planning of the application of efficient mitigation techniques for silver corrosion problem in power transformer.

energetski transformator, mineralno izolaciono ulje, korozivni sumpor, dibenzildisulfid, elementarni sumpor, srebro(I)-sulfid, korozija srebra, visoko selektivni adsorbent, hemisorpcija

power transformer, mineral insulating oil, corrosive sulphur, dibenzyl-disulfide, elemental sulphur, silver sulphide, silver corrosion, highly selective adsorbent, chemisorption

544.723.21:621.314.2:665(043.3)

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