Fly ash immobilization with vitrification

Raziskali smo možnost imobilizacije letečega pepela iz sežiga komunalnih odpadkov. Leteči pepel smo skupaj s slovenskim odpadnim steklom stalili in ulili v kovinske kokile, da je nastal pretežno amorfen produkt, tj. steklo, ki smo ga toplotno obdelali, da se je tvorila steklokeramika. Leteči pepel je bil sestavljen iz delcev velikosti <1 m, ki se povezujejo v aglomerate velikosti okrog 180 m. Tali se pri temperaturi okoli 1300 °C in se v tekočem stanju dobro meša z odpadnim steklom. Steklo, nastalo pri litju, se pretvori v steklokeramiko pri žarjenju v temperaturnem območju med 700 °C in 950 °C, pri čemer se tlačna trdnost poveča za dvakrat. Vrednosti izluževanja težkih kovin iz vzorčnega letečega pepela prekoračujejo predpisane mejne vrednosti za odlaganje na odlagališčih za nevarne odpadke, medtem ko so vrednosti za nastalo steklo in steklokeramiko pod predpisanimi vrednostmi. Zasteklen leteči pepel lahko odložimo kot stabiliziran in nereaktiven odpadek na odlagališčih nenevarnih odpadkov, mogoče pa bi ga bilo tudi predelati in uporabiti v koristne namene.The possibility of fly ash immobilization was investigated. Municipal solid waste fly ash mixed with waste glass cullet was melted and poured into metal moulds. Mainly amorphous glass product was formed, which was then heat treated to obtain glass- ceramics. Fly ash consisted of particles with size <1m, normally joined to larger agglomerates (r180 m). Its melting temperature was around 1300 °C and it mixed well with the glass cullet in the liquid state. Glass formed during solidification was transformed into the glass-ceramics after heat treatment in the temperature range between 700 °C in 950 °C, that doubled the compressive strength. Leaching of heavy metals from fly ash exceeded the allowed values for dumping dangerous waste in landfill, whereas the values for the produced glass and glass-ceramics were under the allowed values. The produced glass and glass-ceramics can be landfilled as a stabilised and unreactive waste in landfills for nonhazardous wastes. Their properties also offer the possibility for manufacturing useful products

Thermal treatment of municipal solid waste incinerator fly ash

Pri sežigu komunalnih odpadkov nastajajo večje količine produktov, ki jih moramo ustrezno zajeti in obdelati do te stopnje, da ne bodo negativno vplivali na okolje in ljudi. Med temi produkti sta zelo pomembna pepel iz kotla in iz odpraševalnih naprav (leteči pepel). Vsebujeta namreč velike količine težkih kovin in nevarnih kemikalij, (As, Pb, Sb, Sn, Sr, Cd, Cr, Cu, Hg), pa tudi sledi organskih polutantov (poliklordibenzo-dioksini in furani), zato imata lastnosti nevarnega odpadka. Teh odpadkov ni mogoče odlagati v okolje ali jih koristno in varno za okolje in ljudi uporabiti za druge uporabne produkte brez stabilizacije ali celo inertizacije. Kemijska sestava in fizikalne lastnosti letečega pepela so odvisne predvsem od sestave vhodnega materiala — torej od komunalnih odpadkov, ki pa variira in se spreminja v odvisnosti od sezone in sestave odpada. V splošnem pa leteči pepel vsebuje SiO2, Al2O3, CaO in spremenljive količine MgO, Na2O, K2O, žveplo (kot SO3),… - podobne sestavine, kot se uporabljajo v steklarski industriji za pripravo stekla — zato je bil osnovni cilj magistrske naloge preveriti zmožnost visokotemperaturnega taljenja letečega pepela sežigalnice v Augsburgu, Nemčija in iz prašnega pepela izdelati kompaktne masivne dele po treh različnih postopkih (taljenje + naknadna kristalizacija vzorcataljenje + mletje materiala + stiskanje + sintranje vzorca in stiskanje + sintranje vzorca). Pri taljenju se tvori steklu podobna, amorfna snovleteči pepel se zatali, postane steklast oz. se vitrificira. Če nastalo steklo naknadno toplotno obdelamo - z namenom pridobitve boljše kemijske obstojnosti in višje tlačne trdnosti - nastalo steklo kristalizira (se razstekli oz. devitrificira), nastane steklokeramika. Raziskane so bile relacije in odvisnosti med temperaturo taljenja letečega pepela, tlaka, s katerim stisnemo vzorec pred sintranjem in temperaturo toplotne obdelave dobljenega produkta, z namenom pridobiti produkt z najoptimalnejšimi lastnostmi. Na podlagi meritev različnih fizikalnih in kemijskih lastnosti izdelanih vzorcev smo ugotavljali, po kateri od teh tehnologij lahko iz prašnega letečega pepela izdelamo kompaktne dele s primerno trdnostjo in kemijsko obstojnostjo, kar bi omogočilo njihovo varno in neškodljivo odstranjevanje oziroma uporabo v praktične namene (kot npr. nasipni material oz. kot material za tlakovanje).During the incineration of municipal waste, large amounts of residues are formed. They have to be safely disposed due to serious environmental impact on people and animals. Among these residues, electrostatic fly ash and boiler ash have the same composition – they contain large amounts of heavy metals and undesired elements (As, Pb, Sb, Sn, Sr, Cd, Cr, Cu, Hg) as well as traces of organic pollutants (polychlordibenzo-dioxins and furans). Because of high environmental standards and strict regulations in force fly ash is considered to be a dangerous waste and should consequently be landfilled under strict conditions or in dormant chambers as fillers. Chemical composition and physical properties of the fly ash depend mainly from the composition of the input waste which is variable and dependable from the season and composition of the waste material. Main components of the fly ash are SiO2, Al2O3, CaO and variable amounts of MgO, Na2O, K2O, sulphur (as SO3),… - same components as in the glass industry for making glass – thats why an ability of fly ash from incineration plant in Augsburg, Deutschland for thermal treatment was applied. Massive, glassy-like amorphus product was formed, fly ash melts itself and it becomes glassy (vitrified). If this produced glass is subsequently heat treated – in order to get better chemical resistivity and higher compressive strenth – glass crystallizes (is devitrified), and the glass-ceramics is formed. Three different methods for thermal and heat treatment of fly ash were applied (melting + crystallization, melting + grinding + pressing + sintering and pressing + sintering) in order to obtain product with the most optimal properties. Relations between temperature of the melting, temperature of heat treatment and pressure were analysed and discussed. Main purpose of this master thesis was considering the ability of producing compact solid massive parts from dusty fly ash under three different processes and on the ground of measuring different physical and chemical properties of produced material select the best technology for producing the material, that is chemicaly durable and compressive strengthened for safe and harmfull landfilling or use as a material in practical way (as a gravel material or as a pavement)