1. AAAR 2009 Conference
An Optimum Swirl Generator Devises for Gas Cooling Towers of Cement Plant Ali Kalantarifard (1), Omid Abouali (1), Mohammad Mehdi Alishahi (1), Goodarz Ahmadi (2) 1Dept. of Mechanical Engineering, Shiraz University, , Shiraz, Iran 2Dept. of Mechanical Engineering, Clarkson University, , Potsdam, NY, USA
Abstract
The aim of this study is analyze the SGD (Swirl Generator device) effects on the Gas Cooling Towers (GCT) of the cement plants. In these towers the temperature of hot exhaust gas of the preheater furnace is reduced by water injection. Also entering flow includes dust which some parts of that are being collected at the GCT walls and exit of tower. The motion, vaporization and heat transfer of the droplets in GCT are being analyzed in this research. SGD is being used at the inlet of the tower to swirl the flow and gives the flow more time to be cooled. In this research various tower sizes, mass flow rates, inlet temperature and SGD angles have been investigated.
For these aims the 3-D forms of continuity and Navier Stokes equations have been solved to obtain flow field inside the GCT. Then the motion of droplets in the tower walls has been analyzed with a Lagrangian approach. Because of the energy exchange between gas and vaporized droplets, the equation of energy has been solved with an Eulerian approach simultaneously with droplet motion equations. Comparing the results for various cases an optimum SGD for gas cooling towers is presented which results to a complete evaporation of the droplets and appropriate temperature for the gas at the exit temperature.
Figures 14 to 17 show the droplets paths for various SGD angles.
Figures 1 to 5 show the reversed flow region for various SGD angles.
Figure1.Angle 30º
Figure2.Angle 40º
Figure3.Angle 50º
Figure4.Angle 60º
Figure5.Angle 70º
Figures 6 to 10 show the radial velocity at the diffuser outlet for various SGD angles.
Figure15.Angle 50º
Figure16.Angle 60º
Figure17.Angle 70º
Figure14.Angle 40º
Conclusions
Due to the different angles of SGD, the reversed flow region has different position.
Thus the any droplets will have different paths in the tower that depends directly on the reversed flow location. For high SGD angles (70 and 60) the reverse flow region is in the middle of the diffuser and cause the droplets move near the wall. So by using the high SGD angle the droplets will face the wall and makes the tower wall wet. This increases the dust build up on the tower wall and it should be avoided. By decreasing the size of the SGD angle, the reversed flow region gradually vanishes in the middle of the diffuse (at angle 50) and then moves towards the diffuser wall and gets larger (at angle 30). Thus the low SGD angles ( 30,40) which all droplets are vaporized and also move far from the tower wall are preferred.
Figure6.Angle 30
Figure7.Angle 40
Figure8.Angle 50
Results
Flow field
The results of this study shows that one of the most important parameter on the performance of a GCT is the SGD angle. As it is shown in figures 1 to 5 as the SGD angle increases, the reversed flow in the middle of the tower and diffuser gets larger. Nevertheless it seems in the low SGD angles (30° and 40°) the reversed flow region moves towards the walls of the tower and diffuser. Thus for the large SGD angles, droplets have to move near the tower wall. The results also show that the large SGD angles have more effect on the flow radial velocity at the diffuser outlet (figures 6 to 10). So some droplets move near the tower wall.
The second important parameter on the performance of GCT is the inlet mass flow rate which causes various inlet velocities. This parameter changes the temperature distribution (figures 11 to 13).
Vaporization of the droplets
In this study the effect of water injection through the nozzles on the temperature distribution along a gas conditioning tower including a SGD was studied. The effects of different parameters such as GCT dimension, SGD angles and mass flow rate were investigated. The results show that the position of the reversed flow region is the most important parameter in the motion of the droplets (figures 14 to 17).
Figure9.Angle 60
Figure10.Angle 70
Figures 11 to 13 show the temperature distribution for different inlet velocities.
Figure13. V =17.32m/s
Figure11. V =11.55m/s
Figure12. V =14.43m/s