Utjecaj tehnologije raspršivanja na performanse apsorbera u H2O/LiBr apsorpcijskom rashladnom uređaju

For major thermal engines used in industrial sectors, the use of chillers has been growing steadily over the previous decades. Indeed, this is linked strongly to their large energy performance despite their investment costs, which are still high, in particular for low powers. Performance coefficients for absorption chillers are relatively low, and their profitability depends on the costs of the main equipment and more particularly on the price of the absorber. Several studies focusing on the development of mass contactors are underway with the principal objective of further improving their performance of mass and energy transfer. Relating to the mass and heat transfer, it is specified that the contact between the phases in circulation is ensured by different types of contactors. The transfer performance is correlated with the heat and mass transfer coefficient on the one hand, and the specific exchange area, i.e., the exchange area per unit volume of the contactor on the other hand. These contactors are distinguished by their mode of contact between phases (bubbling, spraying, falling film, etc.). While the exchange coefficient depends on the hydrodynamics regime in the contactor (flow regime and physicochemical properties of phases), the specific exchange area is dictated by its operating mode. Any limitation of its use for a specific application (physicochemical phenomena, such as crystallisation, deposited dust, etc.) requires research and development of better devices more adapted. Moreover, the most used contactors in chemical engineering are plate columns, packed columns, falling film columns, spray columns, etc. In order to intensify exchanges, a new absorber of the pulverised type is to be explored in relation with the physicochemical properties of the phases, and of their hydrodynamic flow conditions in the sprayed column. Therefore, an experimental study of the influence of operating variables (nozzle diameter, fluids flow rate, their concentrations, size of droplets, etc.) on the overall coefficient of mass transfer in gaseous phase in the absorber of the absorber chiller was conducted. After having fixed the pressure in the absorber, the first part of the study allowed developing new correlations linking the experimental results of the KG ∙ a to all operating variables (L, C, dd, etc.). The second part was devoted to the simulation of the absorption chiller functioning by introducing the concept of energy and exergy yields based on the mass transfer correlations.Posljednjih desetljeća vidljiv je stalan porast upotrebe rashladnih uređaja kod glavnih toplinskih motora koji se upotrebljavaju u industrijskim sektorima. Koeficijenti učinka apsorpcijskih rashladnih uređaja relativno su niski, a njihova isplativost ovisi o troškovima glavne opreme, točnije o cijeni apsorbera. U tijeku je nekoliko studija razvoja kontaktora masa usmjerenih na poboljšanje prijenosa tvari i energije u kontaktorima. Vezano uz prijenos tvari i topline, specificirano je da se kontakt između cirkulirajućih faza ostvaruje različitim tipovima kontaktora. Učinak prijenosa koreliran je s koeficijentom prijenosa tvari i topline s jedne strane te specifičnom površinom izmjene, tj. površinom izmjene po jedinici volumena kontaktora, s druge strane. Kontaktori se razlikuju po načinu kontakta faza (mjehurići, raspršenje, padajući film, itd.). Dok koeficijent izmjene ovisi o hidrodinamičkom režimu u kontaktoru (režim protoka i fizikalno-kemijska svojstva faza), specifična površina izmjene ovisi o njegovu načinu rada. Ograničenje njegove uporabe na neku određenu primjenu (fizikalno-kemijske pojave poput kristalizacije) zahtijeva istraživanje i razvoj uređaja koji bi više bili prilagođeni spomenutoj primjeni. Štoviše, najčešće upotrebljavani kontaktori u kemijskom inženjerstvu su kolone s pliticama, kolone s punilima, kolone s padajućim filmovima, kolone za raspršivanje, itd. S ciljem povećanja izmjena, istražit će se novi praškasti apsorber i to s obzirom na fizikalno-kemijska svojstva faza i njihove hidrodinamičke uvjete strujanja u koloni za raspršivanje. Stoga je provedeno istraživanje utjecaja radnih varijabli (promjera mlaznice, protoka fluida, koncentracije fluida, veličine kapljica, itd.) na ukupni koeficijent prijenosa tvari u plinovitoj fazi u apsorberu rashladnog uređaja. Nakon fiksiranja tlaka u apsorberu, prvi dio istraživanja omogućio je razvoj novih korelacija koje povezuju eksperimentalne KG ∙ a rezultate sa svim radnim varijablama (L, C, dd, itd.). Drugi dio bio je posvećen simulaciji rada apsorpcijskog rashladnog uređaja uvođenjem koncepta energetskih i eksergijskih prinosa temeljenih na izrazima za prijenos tvari

Electrocoagulation in a packed bed reactor-complete treatment of color and cod from real textile wastewater

This paper deals with the efficiency of electrocoagulation (EC) for the abatement of COD and absorbance (i.e. color) from real textile wastewater using a packed bed electrochemical reactor in a unique design, not previously encountered in the literature for the treatment of textile wastewater by electrocoagulation. The cylindrical iron reactor was used as a cathode while the packed bed formed from wrapped iron wire netting was used as an anode. Various operating parameters, such as current density, initial pH, wastewater recirculation flow rate and continuous flow regime, were examined for intensifying the performance of the process. Also, calculation of electrical energy consumption and the characterization of sludge formed during electrocoagulation have been performed. The initial COD concentration of 1953mg/L was reduced to 61mg/L with a removal efficiency of 96.88%, while the color of the wastewater was almost completely removed. The experimental results, throughout the present study, have indicate that electrocoagulation of textile wastewater using a uniquely designed reactor was very effective and direct dischargeable effluent, complying with legal requirements, was obtained. The XRD analysis of the sludge produced during EC reveals that maghemite (Fe2O3) is the main by-product formed after EC. © 2013 Elsevier Ltd

Electrochemical conversion of sulfur dioxide with a rotating cylinder electrode working as anode or cathode

BACKGROUND: A batch electrochemical reactor with a rotating cylinder electrode is analysed for the transformation of sulfur dioxide into either sulfuric acid or colloidal sulfur. RESULTS: Potentiostatic experiments carried out at 30 °C and 500 rpm with 5 g L-1 SO2 in 0.5 mol L-1 H2SO4 conclude that -0.7 V, against SCE, represents an appropriate potential for the sulfur production at a 316 L stainless steel cathode. The figures of merit were: 0.15 kg m-3 h-1 space time yield and 39.7 kWh kg-1 for specific energy consumption. Galvanostatic experiments at 30 °C and 1000 rpm with three-dimensional electrodes identify graphite felt as a promising anodic material. Using a gas phase of 5% SO2 in nitrogen and 0.5 mol L-1 H2SO4 as supporting electrolyte, a macrokinetic current density of 100 mA cm-2 represents an appropriate value, being the space time yield 7.58 kg m-3 h-1 with 2.86 kWh kg-1 specific energy consumption. CONCLUSION: An electrochemical reactor with a rotating cylinder electrode showed a good performance for the production of colloidal sulfur. Sulfur dioxide was also converted into sulfuric acid including a separator in a reactor with a three-dimensional rotating cylinder anode and co-current gas and liquid flows.Fil: Fornes, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: González, Gabriel A.. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Bisang, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentin

Electrocoagulation of food waste digestate and the suitability of recovered solids for application to agricultural land

Digestates from anaerobic digestion (AD) of food waste contain fertiliser nutrients (such as P and N) which are valuable for agricultural purposes and can be environmentally hazardous if disposal is uncontrolled. Here, we applied electrocoagulation (EC) for treatment of digestates, to separate liquids and nutrient-rich solids. Coagulant-dosing electrocoagulation (CDEC) was used to compare Al and steel anodes for treatment of digestate from AD fermenters fed a controlled diet representative of food waste. When applying metal dosing concentrations of 0–4.66 mM, Fe was found to be up to 29.8 % superior to Al in terms of aiding removal of chemical oxygen demand (COD). To mitigate plate fouling, the digestate was diluted to 0.25 and 0.1 concentrations to enable successful treatment by continuous-flow electrocoagulation (CFEC). The highest recovery of soluble P per Fe added by CFEC was 22.4 mg-P g-Fe−1. This was achieved when using 2.33 mM Fe to treat a 0.25 dilution of digestate. In comparison to a control, these optimal conditions also caused a reduction of 4.5 mg L−1 (or 87.7 %) of soluble P and the removal of 254 mg L−1 (33.2 %) of COD in the filtrate. The NH4+ concentration in filtrate was not influenced by EC treatment. Analyses of a range of known toxic elements (Cu, Ni, Zn, As, Cd, Cr, Mo and Pb) indicates that the solids recovered by CFEC could be suitable for application to land