Indonesian Journal of Environmental Management and Sustainability p-ISSN: 2598-6260 e-ISSN: 2598-6279 http://ijoems.com/index.php/ijems Research Article Received: 3 November 20117 Accepted:12 March 2018 *Corresponding author email: DOI: 10.26554/ijems.2018.2.11-1411 CFD Analysis Of Flue Gas Streamline Through Varied Of Flow Straightener Inclination Pramadhony1, Dewi Puspitasari2, Ellyanie2, Marwani2, Rizki M. R. Sihombing 3 1Master Program of Mechanical Engineering, Sriwijaya University, Palembang 30139, Indonesia 2Mechanical Engineering Departemnt, Sriwijaya University, Inderalaya, OI, 30662, Indonesia 3Undergradulate Program of Mechanical Engineering, Sriwijaya University, Inderalaya, OI 30662, Indonesia ABSTRACT Air emission, generated by industrial sector, is one of the main contributors of ambient air quality degradation. In order to minimize the impact to its surrounding, the company regularly should conduct an air emission monitoring activity by measuring the hazardous compound concentration. The sample should be taken in a reference plane located two diameter from the outlet. The sampling of air emission by using isokinetic method cannot be conducted when the swirling flow is existed; the streamline is also should be uniform and vertical. Flow straightener with difference inclination angles, 0°, 15°, and 30°, are suggested to condition the streamline and ful- fill the requirements. A computational simulation conditions with no flow straightener and with three flow straighteners are conduct- ed to overview the influence of flow straightener inclination. Based on the analysis these inclinations are effectively improving the uniformity of velocity at reference plane. In other side these inclinations are causing the increasing of helicity as well as streamline inclination. Keyword: Flow Straightener, Inclination angle, Helicity 1. INTRODUCTION Industrial sector is one of the main emission contributors in Indo- nesia. One of processes is generated by the combustion process. The amount of emission load is determined by the amount of fuel and the quality of equipment used. In 2014 industrial sector is became the largest consumer of energy with a percentage of 48% [1]. Considering the significant impact, the government has been regulating the industrial sector to implement the monitor- ing/ measurement of air emission quality. This study is aimed to analyze the chimney which it’s sampling point does not meet the 8D-2D criteria, where the chimney has 6D of height. The sam- pling point/reference plane is measured at some distances from the outlet, they are: 2D, 1.5D and 1D from flue outlet. Particulate emission is measured by isokinetic method, where the sample is taken at some points along two traverse points in the reference plane [2][3]. This method cannot be used when a swirling flow is occured. Because of that a vertical flue gas flow with small angle streamline is required. This swirling flow can lead an error for the measurement of exhaust emissions, particu- larly related to the increasing of measurement deviation which is reaching of -7.05% [4]. In addition, the uniformity of flow should also be a concern, because the uniformity of velocity is influenc- ing the measurenment result. 2. EXPERIMENTAL SECTION 2.1.Geometry The geometry of chimney and flow straightener are created with the dimension is resemble to the previous research [5]. The flue gas is flowing through the inlet of chimney in a certain angle which produces a swirling flow. The flow straightener is designed with the height of 0.45 D stack diameter. The detail of dimension is shown in Figure 1. The modification of flow straightener di- mension is focused on the inclination angle of flow straightener. So the flow straightener is designed with inverse conical shape (downward position) with the angle of 0°, 15° and 30° as shown in Figure 2. 2.2. CFD Simulation Having created the geometry, the next process is creating the hex- ahedron mesh. The size of mesh inside the flow straghtener is arrenged to be 0.015 D, while the others is arranged to be 0.05- 0.1D. The flue gas flow and the influence of flow straightener installation was analyzed computationally by using software of fluent. The flue gas temperature is assumed 190°C and with the composition as shown in Table 1 [6]. The average velocity of flue gas at the reference plane is set to be 17.5 m/s [7]. This simula- tion is using K-Epsilon (reliazable) viscous model with pressure based solver. Author, year | Indones. J. Env. Man. Sus. 1 (1) 2017: xx - xx DOI: 10.26554/ijems.2018.2.11-1412 3. RESULTS AND DISCUSSION 3.1. Helicity Helicity is a scalar value obtained by projecting the vorticity to axial velocity of flue gas as shown by the equation (1). The mag- nitude is directly proportional to the rotational / vortex movement that is occured inside the chimney. 𝐻𝐻 = (�̅�𝑉𝑥𝑥�⃗�𝑉 ) ⋅ �⃗�𝑉 ........................................(1) The resume of helicity value for four-simulation conditions is shown in Table 2. While contour of helicity inside the chim- ney is shown in Figure 3. According to simulation results, the installation of flow straightener is able to reduce helicity. The helicity reduction is inversely proportional to the increase of flow straightener inclination. This relation is occured due to the flow straightener inclination which tends to direct the flue gas to be rotated in counter-clockwise direction. 3.2 Streamline Inclination The streamline inclination of flue gas is shown by the angle be- tween radial velocity and vertical velocity. The smaller angle indicates the more vertical streamline which is influencing the measurement accuracy as shown in Table 3. The results show that 30° flow straightener produces the largest streamline angle with a maximum and average value of 8.01° and 1.62°. These results show that the more angle of flow straightener inclination, the more angle of flue gas streamline occured. These streamline in- clinationss are directly proportional to the value of helicity. Based on the contour of streamline inclination, the largest streamline an- gle is occured on the left side of chimney (x-negative axis) which generally has a lower vertical velocity. Details of streamline incli- nation can be seen in Figure 4. 3.3 The Uniformity of Velocity Figure 5 shows the velocity profile of flue gas from inlet to outlet of chimney and the velocity profile in the reference plane where located at 2D, 1.5D and 1D from the outlet. This pictures show that by increasing the inclination angle of flow straightener, it will cause the increasing of velocity in the right side of chimney (x-positive axis). Then it increases the uniformity of velocity. The method used to calculate the uniformity of velocity is taken by calculating the Coefficient Variation (CV). The coefficient of var- (a) (b) Figure 1. Fixed dimensions of the geometry (a) Chimney (b) Flow Straightener (a) (b) (c) Figure 2. isometric figure of flow straightener (a) with 0o angle (b) with 15o angle, (c) with 30o angle. Table 1. Composition of flue gas [8] Substance Volume fraction (%) Mass fraction (%) Carbon Dioxide (CO2) 11 16,66 Argon (Ar) 1 1,32 Water vapor (H2O) 6 3,97 Oxygen (O2) 6 6,57 Nitrogen (N2) 76 72,81 Other substances Near zero Near zero Table 2. Helicity values at the reference planes Simulation Condition Maximum Heli- city (m/s2) Average Heli- city (m/s2) With no flow straightener 733.37 385.32 With 0° flow straightener 667.58 45.42 With 15° flow straightener 717.81 53.59 With 30° flow straightener 873.72 67.18 Table 3. The Maximum and Average Streamline Inclination in reference plane Simulation Condition Maximum (°) 2D from outlet 1.5D from outlet 1D from outlet With no flow straight- ener 43.34 38.84 35.57 With 0° flow straight- ener 6.42 5.16 2.97 With 15° flow straightener 7.09 3.98 3.07 With 30° flow straightener 8.01 4.6 3.29 Simulation Condition Average (°) 2D from outlet 1.5D from outlet 1D from outlet With no flow straight- ener 17.47 16.46 16.05 With 0° flow straight- ener 1.41 0.97 0.78 With 15° flow straightener 1.45 0.98 0.78 With 30° flow straightener 1.62 1.01 0.82 Author, year | Indones. J. Env. Man. Sus. 1 (1) 2017: xx - xx DOI: 10.26554/ijems.2018.2.11-1413 iation is calculated by the following formula: 𝐶𝐶𝐶𝐶 = |𝑣𝑣−�̅�𝑣|�̅�𝑣 𝑥𝑥100%..................................(2) B y taking the average value of CV, then it obtain the CV value of each simulatin as shown in Table. 4. Based on the result, the 30° flow straightener is able to generate the most uniform velocity at the reference planes. These results also show that the closer plane to the chimney outlet, the more uniform velocity is obtained. CONCLUSION Computational simulations have been performed to exemine the effect of flow straightener inclination to the flue gas flow at the reference plane. The reference planes are located at a distance of 2, 1.5 and 1 times diameter of flue outlet. The velocity profile and streamline inclination are presented in contour form. Meanwhile the uniformity of velocity is determined by calculating the aver- age value of the coefficient of variation. Based on the results, these modifications are effectively im- proving the uniformity of velocity in some reference planes. The best variation coefficient is generated by 30° flow straightener with value of 35.05% located 2D before outlet, 33.58 % located 1.5D before outlet and 32.37% located 1D before outlet. On the other hand the increasing of flow straightener inclination is caus- ing the increasing of helicity. Where this increasing of helicity is proportional to the increasing streamline inclination. The highest streamline inclination which is generated by 30° flow straightener is located in the area near chimney wall. Since the inclination angle is relatively low and the emission measurement do not be taken in the area near to the wall, it is predicted that the stremline (a) (b) (c) (d) Figure 3. The helicity contours from inlet to outlet of chimney (a) with no flow straightener, (b) with 0o flow straightener (c) with 15o flow straightener, (d) with 30o flow straightener. Reference plane location 2D from outlet 1.5D from outlet 1D from outlet (a) (b) (c) (d) Figure 4. The contour of streamline inclination at reference plane (a) with no flow straightener, (b) with 0o flow straightener (c) with 15o flow straightener, (d) with 30o flow straightener Tabel 4. Average of variation coefficient for each simulation Simulation condition Reference plane location (%) 2D from outlet 1.5D from outlet 1D from outlet With no flow straightener 21.61 18.54 16.4 0° With flow straightener 36.91 35.11 33.78 With 15° flow straightener 36.33 34.73 33.4 With 30° flow straightener 35.05 33.58 32.37 Author, year | Indones. J. Env. Man. Sus. 1 (1) 2017: xx - xx DOI: 10.26554/ijems.2018.2.11-1414 inclination do not give a significant impact on the measurement results. Finally, experimental analysis is still needed to determine the accuracy of these particulate emissions measurements. ACKNOWLEDGEMENT We would like to thanks to DIPA BLU of Sriwijaya University, Ministry of Research, Technology and Higher Education, which has provided financial support in this research. REFERENCES [1] BPPT, “Outlook Energi Indonesia 2016,” Jakarta, 2016. [2] U. Karnik, W. M. Jungowski, and K. K. Botros, “Effect of Turbulence on Orifice ieter Performance,” J. Offshore Mech. Arct. Eng., vol. 116, no. May 1994, pp. 77–85, 1994. [3] U.S. EPA Method 1, “Sample and Velocity Traverses for Sta- tionary Sources,” 1996. [4] J. J. S. Shen, “Characterization of Swirling Flow and Its Ef- fects on Orifice Metering,” 1991. [5] A. Scarabino, F. Bacchi, R. J. Filace, and M. Raviculé, “Com- putational Fluid Dynamic Analysis of a Heater Chimney with and without a Flow Straightener,” J. Sci. Eng. Res., vol. 2, no. 2, pp. 79–93, 2015. [6] V. Seshendra and K. Karri, “A Theoretical Investigation of Efficiency Enhancement in Thermal Power Plants,” vol. 2012, no. August, pp. 106–113, 2012. [7] B. J. J. Carter, R. L. Petersen, and B. C. Cochran, “Designing Exhaust Systems to minimize energy costs,” vol. 47, no. 7, 2005. [8] R. Zevenhoven and P. Kilpinen, Flue gases and fuel gases. 2001. (a) (b) (c) Figure 5. Contour of velocity profile (a) with no flow straighten- er, (b) with 0o flow straightener (c) with 15o flow straightener, (d) with 30o flow straightener