Numerical Simulation of Square Section Venturi Scrubber with Horizontal Spray

Numerical Simulation of Square Section Venturi Scrubber with Horizontal Spray

Available online at www.sciencedirect.com ScienceDirect Procedia Computer Science 107 (2017) 117 – 121 International Congress of Information and Com...

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Available online at www.sciencedirect.com

ScienceDirect Procedia Computer Science 107 (2017) 117 – 121

International Congress of Information and Communication Technology (ICICT 2017)

Numerical Simulation of Square Section Venturi Scrubber with Horizontal Spray Zhenhui Luan*, Xiao Liu, Meng Zheng, Libo Zhu College of Mechanical Engineering, Anhui University of Science & Technology, Huainan 232001, Anhui, China * Corresponding author: [email protected] Tel.: 8613909645247

Abstract In order to improve of tar removal efficiency of venturi tube, the authors synthetically analyzed a variety of tar removal methods, put forward square section venturi scrubber with horizontal spray for removing the tar from the gas, modeled the tube through the software CATIA, choosed the physical model, carried out the numerical simulation by the software ANSYS-FLUENT, and obtained the velocity contours, pressure contours and turbulent kinetic energy. The results show that the square section tube has such advantages as big velocity pulsation, big pressure loss, big turbulent kinetic energy and so on. And so it has a high efficiency of tar removal, and has a broad application prospect in engineering project. Keywords: venturi scrubber, square section, horizontal spray, numerical simulation.

1. Introduction Biomass gas has attracted the attention of people. In process of biomass gasification, it is inevitable to produce by-products, among which the most important is the tar. Tar has a larger viscosity, and it will clog the pipe. In order to purify biomass gas, scholars have used many methods [1]. The venturi tube is physical wet decoking equipment, and it is an important part to improve the efficiency of removing tar [2, 3]. In this paper, the authors put forward a square tube with horizontal spray, established a physical model, selected some structural parameters, simulated the flow field, obtained some pressure contours, velocity features of the tube.

1877-0509 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 7th International Congress of Information and Communication Technology doi:10.1016/j.procs.2017.03.066

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Nomenclature D1 D0 D2 L0

α1 α2

the side length of the square entrance the side length of the throat the side length of the square export the length of the throat contract angle of converging section diffusion angle of diverging section

2. The model of the venturi screbber 2.1. The physical model Venturi tube is currently composed of 3 sections of a converging, a throat and a diverging part, as shown in Fig.1. According to the cross section of the tube, the venturi scrubber can be divided into circular tube and square s tube. According to the position of the nozzle, the venturi scrubber can also be divided into downstream spray tube and horizontal spray one. In downstream spray tube, there is one nozzle which is fixed in the center of the converging part, and scrubbing solution is sprayed by a nozzle into biomass gas [4]. In horizontal spray tube, there are at least two nozzles which are fixed in throat of the tube, and scrubbing solution is sprayed by two nozzles traversing the gas. This paper fixed two nozzles on two sides of the throat of the square section venturi scrubber symmetrically. Literature [5] has researched the circular tube, accordingly this paper determined the geometrical dimensions of squaretube shown in table 1, and built a 3D model shown in Fig.2. Table 1. Main parameters of square tube. parameter numeric

D1(mm)

D0(mm)

D2(mm)

100

50

100

α1(°)

α2(°)

22

6

L0(mm) 100

2.2. The mathematical model There are many models to describe the motion of fluid, because of the complexity of the large of the fluid in venturi scrubber, this paper selected the standard 䭉䈟!ᵚ᢮ࡠᕅ⭘ⓀDŽ model, and details please see [2].

Fig.1. the physical model

Fig.2. The 3D model of square section venturi scrubber

Zhenhui Luan et al. / Procedia Computer Science 107 (2017) 117 – 121

3. Numerical simulation This paper set the inlet velocity as 12 m/s, set the outlet as free flow and wall conditions as no slip, set the gas as a continuous phase, set tar and scrubbing solution droplet as a dispersed one, selected Q235 as tube material, selected the inlet temperature as 50ć and the outlet temperature as 30ć. Biomass gas density is 1.1757kg/m3 䭉䈟! ᵚ᢮ࡠᕅ⭘ⓀDŽ, dynamic viscosity is 1.4919u10-5kg/ms 䭉䈟!ᵚ᢮ࡠᕅ⭘ⓀDŽ. There are two nozzles in the throat symmetrically. When the continuous phase achieved the throat, set injections from the two nozzles for washing liquid discrete phase, selected the surface type, selected the wall effect of liquid particles, selected the inner wall as trap type, and selected the gas exports as escape type, and iterated this process until convergence [6]. 4. Simulation analysis 4.1. Velocity contours Fig.3 is a velocity contours of the square tube, Fig.4 is velocity contours of a circular tube. Because of converging part, velocity of the flow has a change. As geometrical dimension of the pipe reduces rapidly, velocity of the flow increases. When it is in throat, it reachs maximum velocity. After throat of the tube, the velocity reduces rapidly as the pipe dimension increases. Velocity variation uniformity in square tube is poorer than that in circular tube (see Fig.3 and Fig.4).

Fig.3. The velocity variations of square tube

Fig.4. The velocity variations of circular tube

4.2. Pressure characteristics Fig.5 was pressure variations of square tube, Fig.6 was the pressure variations of a circular tube. There is a gradient variation features with a sharp decline at the beginning. When the flow reached throat the pressure reduced to the minimum. After the throat, the pressure recover slowly. In the inlet of the tube, the pressure of the flow can achieve lower pressure (negative pressure), so the square tube will have a strengthening decoking effect.

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Fig.5. Pressure variations of square tube

Fig.6. Pressure variations of circular one

4.3. Wall shear stress Fig.7 was wall shear stress of square tube, Fig.8 was one of circular tube. Every part of the venturi has wall shearing action by biomass gas flow, and in the throat the stress achieves to maximum.

Fig.7. The wall shear stress of square venturi tube

Fig.8. Stress of a circular one

5. Conclusion The authors established a physical model of the square venturi tube, selected some structural parameters, simulated the features of flow field, got some velocity features, pressure features and wall shear stress of the square tube with horizontal spray. By comparing the velocity, the pressure and the wall shear stress to those of the downstream spray square tube, the square tube with horizontal spray has bigger velocity pulsation and greater pressure loss, and its decoking purification efficiency is higher than that of the downstream spray square tube. So it would have a broad application prospect in engineering project.

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References 1. Chen Lianguo, Chen Zhili, Yu Jingchun, et al. Application Status of Biomass Carbonization and Pyrolysis Technologies. Gas and Heat, 2013,33(11):32-34 (In Chinese). 2. Zhenhui Luan, Libo Zhu. Numerical simulation of Biomass Gas Purification of Square Section Venturi Scrubber. 2015 International Power, Electronics and Materials Engineering Conference, May 16-17, 2016. Dalian, China: 546-550. 3. Wang Yan, Chen Wenyi, Sun Jiao, et al. Research progress in biomass gasification equipment. Chemical Industry and Engineering Progress. 2012,31(8):1656-1664 (In Chinese). 4. Zhang Changqing, Ding Decheng. Process Calculation for Venturi Scrubber. SP˂BMH RELATED ENGINEERING, 2011(6):6-10 (In Chinese). 5. Dang yuchun, Liu hongbin, Ding qingguo. Effects of geometric parameters on venture scrubber purifying biomass gas. Journal of Chinese Agricultural Mechanization, 2014,35(2):115-118 (In Chinese). 6. Libo Zhu. Research on Numerical Simulation of Rectangular Section Venturi Scrubber. Anhui University of Science and Technology, 2016.5 (In Chinese).

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