Electrocoagulation to Remove Silica from Cooling Towers Water

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Villegas Mendoza et al Electrocoagulation to Remove Silica from Cooling Towers Water. a portion of the water is discarded to avoid Sivakumar 2009 Chuang et al 2006 reported. precipitation in heat transfer equipment If X is that the removal efficiency was about 7 4 mg. a reference substance then Al2O3 mg SiO2 when dosing poly aluminium. chloride PACl or alum in a range from 30, CC concentration of X in blowdown to 150 mg L as Al2O3 this represents a 4 1. concentration of X in makeup water 1 aluminium silica mass relationship There are. other methods that can remove silica efficiently, RW in a CT can be calculated using Eq 2 these include nanofiltration reverse osmosis. if the drift figure 1 is considered near to zero ion exchange and electro deionization. Nevertheless the costs of these methods are,higher than those for chemical methods Zeng. RW E CC CC 1 2,et al 2007,Electrocoagulation EC is an electrochemical. Where E is the amount of evaporated water technique that has been suggested as an. and CC represents the concentration cycles alternative to conventional coagulation and. On the other hand cooling tower blowdown is characterized by its low sludge production. water CTBW can be estimated with Eq 3 no addition of chemicals and easy operation. Emamjomeh and Sivakumar 2009 P rez, CTBW RW CC 3 Castrej n et al 2012 The main difference.
between EC and ChC is the manner in which, According to these equations if CC metal ions are added to water EC produces. increases the required RW diminish and so flocks of metal hydroxides by electro. does CTBW Seneviratne 2007 Figure 1 dissolution of soluble anodes usually made up. illustrates the main currents in a CT of iron or aluminium while ChC promotes the. Several treatment methods exist to remove formation of hydroxides by using metal salts. silica however the most common one has been such as aluminium sulfate or ferric chloride. chemical coagulation ChC This treatment is Comninellis and Chen 2010. efficient in the removal of soluble and colloidal Several studies using EC to remove silica. silica Sheikholeslami and Bright 2002 but have been carried out Den and Wang 2006. has inherent problems in the cost maintenance Kin et al 2006 Wang et al 2009 Liao et al. and production of sludge Emamjomeh and 2009 Schulz et al 2009 however only the. last two authors worked with representative,cooling tower water On the other hand up. to our knowledge there are not studies where,the convenience of treating replacement water. Ciencias del Agua vol V n m 3 mayo junio de 2014,with respect to treat cooling tower blowdown. water is analyzed,This paper presents the results of treating.
make up water from wells RW and cooling,tower blowdown water CTBW at a pilot small. scale The results were used to determine the,technical and economic feasibility of treating. RW or CTBW in an EC process combined with, Figure 1 Mass balance of water for a cooling tower. a conventional clarification system for silica,Tecnolog a y. Villegas Mendoza et al Electrocoagulation to Remove Silica from Cooling Towers Water. Methodology Description of experimental equipment and. response variables,Type of water used,The experiments were carried out using a.
The water used in this study was obtained pilot small scale EC system with a plug flow. from two water supply wells RW1 RW2 the electro chemical reactor attached directly to a. water quality is different as they come from three stage mechanical flocculator followed by. two distinct locations On the other hand two a high rate settler and a gravity fed sand filter. different blowdown cooling tower samples The reactor was made from acrylic having. coming from two different industries CTBW1 the shape of a rectangular parallelepiped with. CTBW2 were the other studied matrices The a dimension of height 10 cm length 78 cm and. relevant quality parameters of the four sources width 15 cm Placed inside the reactor were 60. of water are shown in table 1 aluminium electrodes measuring 8 x 4 x 0 5. The RW1 matrix has been extensively cm each connected like deflecting screens in a. studied by our working group under different monopolar arrangement figure 2 forcing the. conditions of operation consistent previously water to behave like a flow plug throughout. obtained results ensures us that the system the reactor The space between the electrodes. is stable and that the results are statistically was 0 6 cm and the total active anodic area of. reproducible Villegas Mendoza 2009 2011 the electrodes was 0 19 m2 The hydraulic head. Gelover Santiago et al 2012 RW2 and CTBW1 loss in the reactor was measured by a mercury 43. come from the same cooling tower differential manometer allowing an evaluation. Table 1 Quality of analyzed water,RW1 RW2 CTBW1 CTBW2. pH 7 8 64 8 6 7 13,Conductivity S cm 200 795 1 625 1 290. Silica mgL 1 50 83 164 195,Sulfates mgL 1,25 2 83 250 298. Chlorides mgL 1,8 38 43 1 111 338,Turbidity NTU 0 05 0 05 14 35 1. Ciencias del Agua vol V n m 3 mayo junio de 2014,Figure 2 Electrochemical reactor.
Tecnolog a y, Villegas Mendoza et al Electrocoagulation to Remove Silica from Cooling Towers Water. of the blockage caused by the formation of Molybdate methods respectively The pH was. deposits on the surface of the electrodes determined with an Orion 420A potentiometer. The electrical power required to establish model and the conductivity with an Orion 145. the desired theoretical concentration of Al3 Model. in each one of the experiments was calculated The film in the passivated electrodes was. using Faraday s law Comninellis and Chen characterized using a X Ray diffractometer. 2010 P rez Castrej n et al 2012 It was Rigaku DMAX 2200 with a radiation K alfa. supplied using a Sorensen DLM 40 15 model of cupper Intensities were measured in the. power source and the polarity of the electrodes 2 range between 3 to 100 with a two theta. step of 0 02 and a scanning velocity of 1 min,was shifted every hour The current density. 36 kV and 30 mA The identification of crystal,and flow rate of operation were 71 Am 2 and. phases was carried out with the software Jade,1 7 Lmin 1 respectively In order to remove. 6 5 and the database of the powder diffraction,deposits formed during the preceding tests at.
patterns PDF of the International Centre for,the beginning of each experiment the reactor. Diffraction Data ICDD,was chemically washed with a solution at 30. of commercial product with hydrochloric acid Tests description. as the active ingredient The response variables, were Effect of water quality on silica removal Having. Efficiency of aluminium to remove silica found the best conditions of pH and velocity. 44 mgl 1 dosed Al3 mgl 1 of removed silica gradients in the reactor and the flocculator. after settler and filter Villegas Mendoza 2011 data not shown in. Efficient removal of dosed aluminium this paper continuous runs were performed. after settler and filter for each type of water using the EC small pilot. Hydraulic head loss indirect measurement The values of pH that optimize aluminum. of the obstruction by deposits in the flocks formation and consequently silica. reactor removal were as follows RW1 7 RW2 6, Voltage variation indirect measurement of CTBW1 5 5 and CTBW2 5 it was noticed. the passivation of the electrodes that as sulphate concentration increases pH. value should decrease in order to achieve the, The data of silica removal efficiency were highest aluminium hydroxide precipitation.
statistically analyzed First of all the data for The aluminium dose was set at 60 mgl 1. which corresponds to the highest concentration,RW1 were compared with data previously. that can be obtained with the power source,published by our group Gelover Santiago et al. used This was done in order to analyze the,2012 for the same water matrix RW1 using. efficiency of high doses of aluminium to,the same pilot plant aluminium cathodes and. remove silica The response variables were,anodes applying similar current densities and.
measured every one or two hours along the,Ciencias del Agua vol V n m 3 mayo junio de 2014. switching the polarity during the test After duration of the tests which provided between. this a Student s t test for media comparison 6 and 8 operation data in a steady state system. was applied to contrast the values for silica This allowed to obtain enough data to carry out. removal for the four types of water considered a statistical analysis applying a Student s test. comparison of two means and to compare, Analytical determinations the results among the different kinds of water. As the head loss in the EC reactor began to, The concentration of silica and aluminium was increase figure 3b the flow was increased in. determined by colorimetry with a DR 2010 order to drag hydraulically deposits that form. Hach spectrophotometer by the Aluver and on the electrode surface except in the case of. Tecnolog a y, Villegas Mendoza et al Electrocoagulation to Remove Silica from Cooling Towers Water. CTBW2 that was used as reference to see what Results and discussion. is the result when this operating condition was, not implemented Analysis of the effect of water quality.
The operation of the system was stopped, when the voltage began to increase The The four types of water were tested using. increasing in the voltage is considered as an continuous EC small pilot system between. indicative of the electrodes passivation The eight and ten hours per day and the data were. increase in head loss suggests mechanical plotted with respect to real hours of work. obstruction in the reactor Figure 3a shows the voltage with respect to. Cost of treatment Once the behavior of the time of operation This voltage is the necessary. four types of water was analyzed the energy supplied voltage to guarantee the required. costs for the oxidation of aluminium as well electric current for the aluminium production. as those of aluminium foil itself and chemicals pursued Two observations can be done. needed to set pH at the optimum values of according to the tendency of this variable the. operation were calculated for each matrix voltage with clean electrodes depends inversely. These factors were considered because they on the conductivity and the passivation starts in. are the main contributions and can widely vary general after approximately 10 hours of work. depending on the water quality characteristics The passivation is a phenomenon characterized. The cost for aluminium oxidation depends on by the gradual increase in the electrical power. voltage which is a function of the conductivity required to set the desired current in the 45. The required doses of aluminium depend on electrolytic cell during the operation of the. the silica concentration and the amount of acid system In this case the passivation does not. necessary to reach the pH to maximize the depend significantly on the quality of the. silica removal depends on characteristics of the water but may depend on the current density. water such as alkalinity that was a fixed parameter similar for the four. The following data were considered for types of water. cost calculation a electric energy US 0 12 Figure 3b shows the hydraulic head loss. KW h b aluminium plates US 4 85 kg measured with the mercury manometer with. aluminium c Hydrochloric acid to adjust pH respect to time of operation In all the tests the. US 0 16 L at a rate exchange of 14 00 head loss increased significantly between the. MXN 1 US fourth and sixth hour of operation Once the. Ciencias del Agua vol V n m 3 mayo junio de 2014, Figure 3 Variation of a voltage and b hydraulic head loss in relation to operation times. Tecnolog a y, Villegas Mendoza et al Electrocoagulation to Remove Silica from Cooling Towers Water. head loss increased we look to push it down function of time Only data from the second. by hydraulic flushing increasing drastically hour and beyond have been considered for. the flow of operation for 10 seconds except the statistical analysis because the hydraulic. in the CTBW2 test where this washing residence time for the treated water in the. method was not implemented as a measure system is around 2 h As can be observed in. of comparison This allowed a temporary figure 4b due to the optimization performed. recover of the initial head loss and the cleaning with the settler filter looking for concentrations. off of most of the soft and spongy deposits below 0 2 mgl 1 the aluminium was almost. present on the electrodes however it did not totally removed in every case corresponding. help to stop the passivation process indicating to a removal efficiency of more than 99. that this phenomenon is associated with the From the Gelover Santiago et al study. presence of deposits strongly adhered to the 2012 the values for the relation mgl 1 dosed. electrode surface Through studies of powder Al3 mgl 1 of removed SiO2 measured at the. X ray diffraction the main component of exit of the settler were in the interval 1 22. the inlay was identified as bayerite insoluble 0 12 while for the present job were 1 36 0 05. Al OH 3 when we used well water in the tests According to the t test both media values. This second type of deposit can be partially belong to the same interval at a 95 level. removed with chemical washing and can of confidence This is an indication of the. be completely removed only by mechanical reproducibility of the system. Electrocoagulation to Remove Silica from Cooling Towers Water Water Technology and Sciences in Spanish Vol V No 3 May June 2014 pp 41 50 This paper presents the results of a study carried out about the effect of water quality on the removal of dissolved silica using an electrocoagulation process with aluminum elec trodes Silica is found in replacement water RW usually known as

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