Preliminary study of water methyl ester separation via Aspen-HYSYS

Transcription

1 aper Code: sp TIChE International Conference 2 November, 2 at Hatyai, Songkhla THAILAND reliminary study of water methyl ester separation via Aspen-HYSYS Wilaiporn Sawangpon *, Sutham Sukmanee, ornsiri Keawpradit Department of Chemical Engineering, Faculty of Engineering, rince of Songkla University, Songkhla, 92, Thailand * sawangpon.w@hotmail.com Abstract A separation of water methyl ester after biodiesel purification by water washing relies conventionally on a gravity technique, which requires considerable consumption of time and further causes discontinuous biodiesel production. Since Liquid-Liquid Hydrocyclone (LLHC) is inexpensive equipment, easy to install and operate, and spend short operation time consequently giving continuous production. It is currently an alternative separation unit for purifying methyl ester in the biodiesel production process. This work then focuses on a preliminary study of LLHC application via using a commercial simulation program such as an HYSYS. Four operating variables have been evaluated by considering separation efficiency effects. Simulation results have shown that pressure differential ratio (DR) and droplet size distribution have significantly effects on the separation efficiency, while the inlet flow rate and the inlet temperature have barely effects. Keyword: Liquid-Liquid hydrocyclone, ASEN HYSYS, Separation, Biodiesel

2 TIChE International Conference 2 November, 2 at Hatyai, Songkhla THAILAND. Introduction Biodiesel is an alternative energy made from vegetable oil such as palm oil products, jatropha, coconut and sunflower etc. A palm biodiesel production is commonly achieved by an acid-transesterification reaction as shown in fig including of the following steps: () a pretreatment of palm oil, (2) a mixing of alcohol and acid/base-catalyst, () transesterification reaction, (4) a separation of glycerol, () biodiesel purification by water washing, and () water removal. alm biodiesel production is usually produced by transesterification of triglycerides (palm oil) to produce mono-alkyl ester (biodesel) and glycerol, as shown in fig 2. Methanol is widely employed, and alkaline catalyst NaOH/KOH are commonly suggested [, 2]. Conventional glycerol separation techniques are filter technology, centrifugal technology and decanter system. production. In addition, it is a compact device and requires low maintenance. This work then focuses on applying LLHC for a water-methyl ester separation via using a commercial simulation program such an HYSYS (HYprotech SYStem) ASENTech V7.. The objectives of this present study are to understanding LLHC behavior and to design for purifying methyloleate (MO) which is a suitable major component of biodiesel [2]. Four effects of pressure differential ratio (DR), inlet flow rate, droplet size distribution, and inlet temperature on separation efficiency are evaluated. 2. Liquid-Liquid Hydrocyclone Methyl Ester Overflow retreatment of staple oil Mixing of alcohol and catalyst Methyl Ester/ Water Reverse flow Overflow Transesterification Glycerol separation Glycerol Feed Recirculation Zones urification by Washing Water removal alm Methyl Ester Fig. Schematic of palm biodiesel production Underflow Water Fig.. Hydrocyclone flow behavior. A liquid-liquid hydrocyclone (LLHC) utilizes centrifugal force to separate methyl ester from the continuous fluid. The pressurized fluid is injected into the hydrocyclone body in a tangential direction causing the swirling motion. The fluid consequently develops a flow pattern consists of inner and outer spiral moving with the same circular direction as shown in fig. The inner forced vortex is produced in the region close to LLHC axis delivering the reverse flow of the methyl ester through the overflow outlet. While the water flow moves downward to the underflow outlet resulting of the outer forced vortex appearance in the wall region []. Fig. 2 Transesterification of triglyceride and alcohol After the biodiesel purification step, the product is fed into a settling vessel providing two phases of water and methyl-ester (biodiesel). The phase of water is further drawn off easily from the bottom of the vessel. However, it has been found in literatures [] that a water separator requires considerable consumption of time (about -8 hours) and construction space, causing discontinuous biodiesel production. Because a liquid-liquid hydrocyclone (LLHC) can separate two immiscible liquid phases, spends short operation time, and consequently cause a continuous 2.. LLHC Geometry The LLHC shape proposed by [] as seen in fig. 4 has been applied in this work with mm diameter of cylindrical inlet section called a characteristic diameter (D c ) and the inlet diameter (D i ) of 7.8 mm. The inlet section is followed by the taper cones with angles of 2º and.º respectively. Subsequently the cylindrical tail section of LLHC has the underflow diameter (D u ) of 2 mm and the overflow diameter (D o ) of 4 mm. Total length of LLHC is 7 mm. sp-2

3 Differiential ressure (ka) TIChE International Conference 2 November, 2 at Hatyai, Songkhla THAILAND Di = 7.8 mm Do = 4 mm D = mm 2 mm 7 mm. variables are evaluated on separation efficiency including of pressure differential ratio (DR), inlet flow rate, droplet size distribution, and inlet temperature. Figure shows the diagram of the separation process simulated via Aspen-HYSYS Flow Split Ratio Du = 2 mm Fig. 4. LLHC dimension details A flow split ratio is defined as the ratio of overflow flow rate to the inlet flow rate, as given in eq : qoverflow F () q inlet where, F is the flow split ratio, q overflow is the overflow volumetric flow rate, and q inlet is the inlet volumetric flow rate. 2.. ressure Differential Ratio (DR) ressure drop ratio (DR) is a fundamental ratio defined as the ratio of overflow to underflow pressure drops (as shown in eq 2). Inlet r essure Overflow r essure DR (2) Inlet r essure Underflowr essure 2.4. Separation Efficiency The separation efficiency of the hydrocyclone vessel is widely calculated by the ratio of outlet to inlet amounts of oil, as given in eq : FoCo ε % () F C i where F o and F i are the mass flow rate of outlet and inlet respectively, C o and C i are the mass concentration (ppm) of oil concentrations.. Water-Methyl ester Separation The main objectives of this study are to understanding LLHC behavior and to design for purifying methyl ester in the final step of the palm biodiesel production. The simulation is carried out via using HYSYS ASENTech V7.. Since methyl-oleate (MO) is a major component of biodiesel [2], two phases of water and MO are simply selected. Effects of four i 2 4 Fig.. Diagram of a water-methyl ester separation (-methyl ester tank, 2-water tank, -centrifugal pump, 4-mixer, - pressure gauge, -flowmeter, 7-hydrocyclone) 4. Simulation Results and Discussion 4.. Effect of ressure Differential Ratio (DR) DR Fig.. Effect of DR on oil separation efficiency Underflow DR Fig. 7. profiles according to DR variation Figure shows effect of various DR on separation efficiency of LLHC. In this case, the simulation is carried out with the inlet flow rate of.9 m /hr and inlet pressure of 7 ka. The concentration of MO is % by wt. It can be seen that the efficiency of LLHC primarily increases from.9% to 4.% by increasing DR from. to.8. This is because the underflow pressure-drop ( ) decreases continuously (as seen in Overflow y = 4.7x 2-2.7x R² =.987 sp-

4 ressure Drop (ka) Flow Rate (m/hr) Oil Concentration (%) Overflow Oil urity (%) TIChE International Conference 2 November, 2 at Hatyai, Songkhla THAILAND fig 7) causing the increment of the axial pressure gradient. However, the efficiency gradually decreases afterward due to the insufficient underflow causing the absent of the inner forced vortex DR Fig. 8. Oil Concentration profiles according to DR variation The simulation also shows as given in fig 8 that MO is purified 99.9% in all range of DR. In this case, the maximum separation efficiency is 4.% at DR.8 giving.24% oil concentration in the underflow stream. The highest overflow flow rate is 2.7 m /hr as well as the highest split ratio is.% in this case Effect of Inlet Flow rate Overflow Oil Concentration Underflow Oil Concentration 2 4 Fig. 9. Effect of inlet flow rate on efficiency Effect of inlet flow rate is further evaluated on the efficiency of MO separation. The simulation is carried out under the inlet pressure of 7 ka, flow split ratio of.%, and DR.8. The results are presented in fig 9-, it has been found that the feasible range of the inlet flow rate in this case is in range of m /hr. The inlet flow rate change has slightly effects on the seperation efficiency which is about 4.%. The efficiency and product purity insignificantly decreases by increasing the inlet flow rate. The maximum oil purity is 99.99% under the minimum inlet flow rate, 2.7 m /hr and the minimum purity is 99.9% under the maximum inlet flow rate,.9 m /hr. As seen in fig 2, the overflow as well as underflow flowrates and pressure drops ( ) increases by increasing the inlet flow rate. The results present that higher flow rate provides higher centrifugal force and but lower efficiency due to lower product purity. It is noted that the results corresponds to ones obtained by [] Fig.. Oil purity profile according to variation of inlet flow rate 4 2 y =.28x R² = Underflow flow rate y =.9472x R² = Overflow flow rate 2 4 Fig.. Flow rate profiles according to variation of inlet flow rate 4 2 o u Fig. 2. profiles according to inlet flow rate variation sp-4

5 Effciency (%) Mixture Density (kg/m) TIChE International Conference 2 November, 2 at Hatyai, Songkhla THAILAND 4.. Effect of Droplet Size Distribution Oil droplet distribution is greatest impact on efficiency separation of LLHC [,]. In this case, the system is operated under the inlet pressure and flow rate of 7 ka and.9 m /hr, flow split ratio of.%, and DR.8. The simulation result has shown that the efficiency increases by increasing in median droplet size (d) as seen in the fig. That can be intuitively expects as larger droplet size coalesce faster than smaller ones. The proposed LLHC can reach the maximum efficiency, 4.% with the valid range of the droplet size..4 mm Droplet, d (mm) Fig.. Effect of droplet size distribution on efficiency 4.4. Effect of Inlet Temperatures y = -.7x R² = Temperture (C) Fig.4. Effect of inlet temperatures on efficiency In this case, the simulation is operated under the inlet flow rate.9 m /hr and inlet pressure 7 ka. The DR and flow split are kept constant at.8 and.% respectively. The inlet temperature is adjusted in range 2 C. The inlet temperature has barely effect on the efficiency as shown in the fig, but it has significantly effect on mixture density as seen in fig. Increasing inlet temperature causes the decrement of the mixture density providing lower density difference of water and MO Inlet Temperture (C) Fig.. Mixture density profile according to inlet temperature variation. Conclusions and Recommendation A liquid-liquid hydrocyclone (LLHC) has been designed by modifying from one presented by [] for the separation of water methyl oleate system. Four operating variables have been evaluated by considering separation efficiency effects, i.e. pressure differential ratio (DR), inlet flow rate, droplet size distribution and inlet temperature. Simulation results have shown that DR and the droplet size distribution have significantly effects on the separation efficiency, while the inlet flow rate and the inlet temperature have barely effects. For LLHC design, it is recommended that the optimum DR as well as optimum flow split ratio should be firstly determined, and valid range of droplet sizes, inlet flow rate and inlet temperature are further evaluated. References [] C. Tongurai, S. Klinpikul, and C. Bunyakan, Biodiesel roduction from alm Oil, Department of Chemical Engineering, Faculty of Engineering, rince of Songkla University, Hat Yai, Songkhla(2). [2] G. Knothe, Designer Biodiesel: Optimizing fatty ester composition to improve fuel properties, Energy & Fuels, 22 (28) 8-4. [] T. Husveg, O. Rambeau, and T. Drengsitg, erformance of a deoiling hydrocyclone during variable flow rates, Mineral Engineering, 2 (27) [4] G.A.B. Young, W.D. Wakely, and D.L. Taggart, Oil-waer separation using hydrocyclone: An experiment search for optimum condition, etroleum Science & Engineering (994) 7-. [] C. Gomez, J. Caldentey, and S. Wang, Oil-Water Separation in Liquid-Liquid Hydrocyclones (LLHC) Experiment and Modeling, SE Annual Technical Conference and Exhibition. 2, New Orleans, Louisiana, Sep -Oct, 2, aper No. SE 78 [] Schütz. S, Gorbach. G, and iesche. M, Modelling fluid behavior and droplet interactions during liquid-liquid seperation in hydrocyclones, Chemical Engineering Science 4(29) sp-