Dehydration of Waste Edible Oil by Hydrocyclones.pdf

This article was downloaded by: Xian Jiaotong University On: 13 March 2013, At: 00:54 Publisher: Taylor Dehydration; Waste edible oil INTRODUCTION The amount of waste edible oil collected in all the European Union was estimated to be about 400,000 tons. However, it is predicted that the collection of vegetable oil will rise and may reach amounts between 700,000 and 1,000,000 tons, and 90% of those edible oils will be dumped as refuse without collection (Ayhan, 2007; Pinto et al. 2005). It is unreasonable from the viewpoint of resource saving that most of the waste edible oil is dumped without being utilized (with the exception that a small percentage of waste edible oilisrecycledasarawmaterialofsoap).Moreover,whenthewasteedibleoilisincinerated together with combustible refuse, a large amount of suspended particulate matter, such as SOx,NOx,CO2,andCO turning to airpollutants are produced,and it isreported that deadly poisonous dioxin may be produced. On the other hand, when the waste edible oil is buried together with noncombustible refuse, soil pollution occurs. A part of the waste edible oil dumpedfromrestaurants,foodplantsandhomesisactuallydischarged intoriversandlakes and is one of the major causes of water pollution. Inthissense,transesterificationofwasteedibleoilstoproducebiodieselcoulddecrease thewastedisposalproblem.Thewasteedibleoilsservingasrawmaterialincludewrapeseed oil, sesame oil, soybean oil, maize oil, sunflower oil, palm oil, palm kernel oil, coconut oil, International Journal of Green Energy, 6: 184191, 2009 Copyright ? Taylor Tanaka, 2004; Tirmizi et al. 1996), magnetic handling method (Freeman et al. 1994;Shen et al., 1990), and direct current hydrocyclone method (Pratarn etal.2005;Pratarnetal.2006).Butthosetechniqueswerelessusedinindustrialproduction because of the complexity of the equipment and low reliability. Then a new process of waste edible oil dehydration that is based on hydrocyclone technology was designed. Preliminary experiments have been carried out to prove the feasibility of dehydration using hydrocyclone. We demonstrate here that water was being removed successfully in waste edible oil through hydrocyclones. FUNDAMENTALS OF DEHYDRATION WITH HYDROCYCLONE Principle of Hydrocyclone Separation A hydrocyclone is a device that causes the centrifugal separation of materials contained in the liquid fed to it (Bai et al. 2006; Cullivan, et al. 2003; Firth 2003; Habibian et al. 2008). These materials are normally in the form of solid particles but may also be gas bubbles, oil, or others. The feeds are separated by the induced centrifugal force inside the hydrocyclone body and mainly according to their density, size, and shape. Unlike other centrifugal machines, hydrocyclones have no moving parts. The separa- tion driving force comes from the transformation of the static energy of the fluid (fluid pressure) into dynamic energy (fluid velocity). A hydrocyclone body consists of two parts: a cylindrical part and a conical part. Design depends on both the nature of the separation and the quality of effluent desired. The applications of hydrocyclones are principally the separation of solid suspended matter and the clarification of liquid phases. Figure 1 shows the operation of a hydrocyclone designed for liquid-liquid separation. The fluid is injected tangentially at the top of the hydrocyclone and cause centrifugal forces to accelerate particles toward the walls. As the fluid passes through the hydrocyclone in a spiral fashion, large or dense particles are forced against the wallandmigratedownwardstotheunderflow.Fineorlowdensityparticlesaresweptintoa second inner spiral that moves upward to the overflow. Flow Split and Pressure Drop Ratio Flow split of the hydrocyclone is defined the ratio of the volume flow of the under- flow to feed, i.e., R Qu=Qi 100%(1) where R is the flow split, and Quand Qiare individually the volume flow of the underflow and feed. Under normal operating conditions, there are two distinct pressure drops across the hydrocyclone separator: DEHYDRATION OF WASTE EDIBLE OIL BY HYDROCYCLONES185 Downloaded by Xian Jiaotong University at 00:54 13 March 2013 ?pio pi? po(2) and ?piu pi? pu(3) where pi, po, puare the pressure in the feed, overflow, and underflow, respectively. The relationshipbetweenthe twopressure drops is also important and canbe used for control purposes. The pressure drop ratio PR ?pio=?piu. Reynolds Number The hydrocyclone characteristic Reynolds number could be described as follows: Re ?Dv ? (4) where D isthe hydrocyclone diameter; ? and ? are the density and viscosityof liquid, respectively; and v is the hydrocyclone characteristic velocity 4Qi ?D2 . Euler number ThehydrocycloneoverflowcharacteristicEulernumbercouldbedescribedasfollows: Eu pi? po ?v2=2 (5) Underflow Overflow Feed Inner Spiral Outer Spiral Figure 1 Fluid flow in hydrocyclone. 186BAI, WANG, AND TU Downloaded by Xian Jiaotong University at 00:54 13 March 2013 Dehydration Efficiency The separationcapability of a hydrocyclone isstronglydetermined by the capacity of handling the amount of material reporting to the oversize flowstream and the size distribu- tion of the feed. Although the nominal diameter is the most important parameter in hydrocyclone separation efficiency, the other parameters such as feed diameter, overflow diameter, and underflow diameter still influence the separation efficiency. The expression used to calculate the overall separating efficiency for W/O separa- tions with classical hydrocyclones is E 1 ? go gi 100 (6) where goand giare the volumetric fraction of water in the overflow and feed, respectively. EXPERIMENTAL Materials Table 1 shows the properties of waste edible oil. Hydrocyclone Geometry The swirl chamber diameter D of the hydrocyclone was 35 mm, the cone angle was 10?.DimensionsofhydrocycloneisshowninTable2.Hydrocyclonehavetwosymmetrical rectangular inlet (5mm 10mm). Flow Diagram The schematic diagram of the experimental apparatus is illustrated in Figure 2. Wastewater and contaminants are discharged from the bottom of hydrocyclones to the wastewater treatment facility. The dehydration edible oil is continuously drawn from the top of hydrocyclones and sent to the next procedure. Dehydration efficiency was deter- mined by measuring water concentration in the feed dispersion as well as in the overflow and underflow. Table 1 Properties of edible oil. MaterialDensity/Kg?m-3Viscosity/mm2?s-1Water concentration /% Waste edible oil875 (25?C)6.210.53.0 Table 2 Geometry of hydrocyclone. Do/DDu/DLs/DL/DLu/D 0.4290.2860.28610.888.56 Note: 1. D, Do, Durefer to the diameters of swirl chamber, tail pipe, and underflow orifice respectively. 2. Ls, L, Lurefer to the lengths of swirl chamber, taper, and tail pipe respectively. DEHYDRATION OF WASTE EDIBLE OIL BY HYDROCYCLONES187 Downloaded by Xian Jiaotong University at 00:54 13 March 2013 RESULTS AND DISCUSSION Pressure Characteristics Pressure drop ratio vs. Reynolds number. The relationship between pressure dropratio andReynoldsnumberisshowninFigure3. Forthe same flowsplit R,an increase in the Reynolds number will decrease the pressure drop ratio. When a Reynolds number is more than 6,000, as the Reynolds number increases, the decrease in pressure drop ratio is gentle. This shows that the value of two pressure drops is approaching with the increase of flow rate. Euler number vs. Reynolds number. The relationship between Euler number and Reynolds number is shown in Figure 4. As can be seen, with an increase in Reynolds number, Euler number increases gradually. This shows that an increase of flow rate will increase the value of ?pio. Separating Performance Effect of Reynolds number on dehydration efficiency. The Reynolds num- berisakeyoperatingcharacteristicandhasadistincteffectonthedehydrationefficiencyof the hydrocyclone. Figure 5 shows the relationship between the Reynolds number and dehydration efficiency. Under the condition that the Reynolds number is less than 5,400, an increase in Reynolds number will improve the separating efficiency. The separating efficiency will reachits maximum when the Reynolds number is close to 5,400.Further increases in the Reynolds number will cause performance deterioration. This occurs for the following reasons: Edible oil Dehydration edible oil Oily wastewaterHydrocyclone Figure 2 Diagram of crude desaltingdevice in atmospheric and vacuum distillation unit. 300040005000600070008000 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 PR Re R=1% R=3% Figure 3 Pressure drop ratio vs. Reynolds number. 188BAI, WANG, AND TU Downloaded by Xian Jiaotong University at 00:54 13 March 2013 1. Atveryhighflowrates,intenseemulsificationoccurred.Itisattributedtotheshearforce that caused size reduction among the liquid particles. When emulsification occurs, the function of the hydrocyclone is reduced to separating a dense emulsion from a lighter emulsion of an essentially homogeneous mixture. 2. A certain minimum flow rate is necessary to set up the vortex motion and to establish centrifugal separation forces that grow in intensity as the flow rate increases and improve the separating efficiency. Effect of Euler number on dehydration efficiency. Figure 6 shows the rela- tionship between Euler number and dehydration efficiency. Typically, as the Euler number increases, the efficiency of separation increases and reaches maximum when Euler number is 1,800. Further increases in Euler number will eventually cause the efficiency to drop sharply. From the results of dehydration present in Table 3, it can be seen that dehydration efficiency range from 80% to 94% with a feed flow rate of 2.7,3.0 m3/h. The water concentrations can be reduced to the range of 0.100.30 vol.%. 3500 40004500 5000 5500 60006500 7000 800 1000 1200 1400 1600 1800 2000 2200 2400 Eu Re Figure 4 Euler number vs Reynolds number. 4000440048005200560060006400 78 80 82 84 86 88 90 92 E/% Re Figure 5 Reynolds number vs. dehydration efficiency. DEHYDRATION OF WASTE EDIBLE OIL BY HYDROCYCLONES189 Downloaded by Xian Jiaotong University at 00:54 13 March 2013 CONCLUSIONS In the present article, a new process of waste edible oil dehydration based on hydrocyclonetechnologyisdesigned.Preliminaryindustrialexperimentshavebeencarried out to verify the process. It is found that the Reynolds number has a distinct effect on the dehydrationefficiencyofthe hydrocyclone.UndertheconditionofaReynoldsnumberless than 5,400, an increase in Reynolds number will improve the separating efficiency. The separating efficiency reaches its maximum when the Reynolds number is close to 5,400, beyond which further increases in Reynolds number will cause performance deterioration. Under the condition that the Reynolds number of inlet is ranging from 5,000 to 5,800, the water concentrations can decrease from 0.53.0 vol.% to less than 0.30 vol.%. It is demonstrated that the water can be removed successfully from waste edible oil through hydrocyclones. REFERENCES Ayhan, D. 2007. Recent Developments in Biodiesel Fuels. International Journal of Green Energy 4 (1): 1526. Bai,Z.-andH.Wang.2006.Theexperimentsfordesaltinganddewateringofcrudebyhydrocyclones. Chinese Acta Petrolei Sinica 22 (4): 5660. Cullivan, J. C., R. A. Williams, and C. R. Cross. 2003. New insights into hydrocyclone operation. Particulate Science and Technology 21: 83103. Firth, B. 2003. Hydrocyclones in dewatering circuits. Minerals Engineering 16: 115120. 800 1000 1200 1400 1600 1800 2000 2200 2400 70 75 80 85 90 95 E/% Eu Figure 6 Euler number vs dehydration efficiency. Table 3 Results of waste edible oil dehydration. No.Qi/m3?h-1gigoE/% 12.960.80.1088 22.811.60.1591 32.922.70.1594 42.852.30.291 52.932.50.2490 190BAI, WANG, AND TU Downloaded by Xian Jiaotong University at 00:54 13 March 2013 Freeman, R. J., N. A. Rowson, T. J. Veasev, and I. R. Harris. 1994. Development of a magnetic hydrocycloneforprocessingfinely-groundmagnetite.IEEETransactionsonMagnetics30(6): 46654667. Guu, Y. K., Y. W. Lin, and C. H. Chiu. 1997. Separation and recovery of oily wastewater from the edible oil refinery with ceramic membranes. Bulletin of National Pingtung University of Science and Technology 6 (3): 195206. Habibian, M., M. Pazouki, H. Ghanaie, and K. Abbaspour-Sani. 2008. Application of hydrocyclone