SIMULATIONS AND OPTIMIZATIONS OF VOLATILE ORGANIC COMPOUNDS REMOVAL FROM WASTE STREAMS

V magistrski nalogi smo izvedli modeliranje, simulacijo in optimizacijo procesa odstranjevanja HOS iz odpadnih vod s tehniko prepihovanja z zrakom (angl. air stripping). V prvem delu naloge smo ugotavljali vpliv ključnih procesnih parametrov na učinkovitost odstranjevanja. Rezultati kažejo, da se z višanjem temperature, razmerja volumskih pretokov zrak/voda, višine polnila in premera kolone, učinkovitost odstranjevanja povečuje. Sorazmerno s tem se povečujejo tudi skupni letni stroški procesa. Zaradi tega smo izvedli ekonomsko optimizacijo procesa, da bi dosegli zakonsko dovoljeno koncentracijo posameznih HOS v pitni vodi ob čim nižjih stroških. Enačbo odvisnosti skupnih letnih stroškov od posameznih procesnih spremenljivk smo pridobili z uporabo programa SuperPro Designer. Proces smo nato simulirali in optimizirali v programih Aspen Plus in GAMS. Rezultati optimizacije kažejo, da ima največji vpliv na stroške procesa temperatura, na katero mora grelnik segreti vodo pred vstopom v kolono. Simulator tako v vseh primerih optimizacije vzdržuje ta parameter na najnižji dovoljeni vrednosti, želene učinkovitosti odstranjevanja pa skuša dosegati predvsem s spremembo višine polnila. V primerih, ko to ne zadostuje, se spreminja tudi pretok zraka in s tem posledično razmerje volumskih pretokov zrak/voda. Simulator spreminja tudi premer kolone, ki pa je omejen na ozkem območju zaradi nevarnosti poplavljanja kolone, tako da ta parameter nima tako izrazitega vpliva. Optimizacijo smo izvedli za pet HOS: benzen, toluen, kloroform, etilbenzen in klorobenzen. Učinkovitosti, ki smo jih dosegli, so zelo visoke in znašajo tudi nad 99,95 %. Izračunani skupni letni stroški znašajo okoli 400 000 €/a, odvisno od zahtevane učinkovitosti odstranjevanja in od HOS, ki jo odstranjujemo iz odpadne vode. Rezultati kažejo, da se komponente z višjimi Henry-jevimi konstantami (etilbenzen, benzen, toluen) odstranjujejo lažje kot komponente z nižjimi vrednostmi teh konstant (klorobenzen, kloroform), ki za dosego enake učinkovitosti odstranjevanja zahtevajo višje letne stroške procesa.The paper discusses the modeling, simulation and optimization of the process of removing VOCs from wastewater with the air stripping technique. In the first part we determined the impact of the key process parameters on the removal efficiency. The results indicate that by raising the temperature, the ratio of the flow rates of air/water, the packing height and the diameter of the column, removal efficiency increases. Proportionally with it, the total annual costs of the process increase. For this reason, we carried out an economic optimization of the process, the aim of which was to achieve a legally permissible concentration of individual VOCs in drinking water at the lowest possible costs. The equation of dependence on the annual costs of individual process variables was obtained by using the SuperPro Designer program. The process was then simulated and optimized in the programs Aspen Plus and Gams. Optimization results show that the temperature at which the heater heats the water prior entering the column has the greatest impact on the costs of the process. In all cases of the optimization the stimulator maintains this parameter to the minimum permitted value, while the desired removal efficiency is trying to be achieved by changing the packing height. In cases where this is not sufficient, the air mass flow changes and with it the ratio of flow rates of air/water. The simulator has also changed the diameter of the column, which is limited to a narrow range due to the risk of flooding the column, so that the impact of this parameter is not as significant. The optimization was carried out for five VOCs: benzene, toluene, chloroform, ethylbenzene and chlorobenzene. The achieved efficiencies are very high and rate up to 99.95%. The calculated annual costs come up to around €400,000/a, depending on the efficiency of the removal and on the nature of VOCs, which are removed from wastewater. The results show that components with higher values of Henry’s constants (ethylbenzene, benzene, toluene) are removed more easily than components with lower values of these constants (chlorobenzene, chloroform), which for achieving the same removal efficiency require higher annual costs of the process