Investigation of the Motive Steam Pressure Effect on Performance and Reverse Flows in Sugar Factory Thermo-compressor: Validation and Numerical Study

Abstract

IntroductionThermo-compressors or ejectors are used to enhance the vapor enthalpy in the process industry. The low costs of construction and maintenance, and simple structure, have increased by using this equipment in relevant fields of industry and agriculture. The thermo-compressor's inlet parameters, including the thermodynamic properties of the motive steam and suction vapor, are the foremost affecting factor of a thermo-compressor.The steam used in processing factories loses its capability after passing through evaporators due to the reduction of pressure and temperature, gets cooled again, and returns to the boiler despite having a moderate energy level. Therefore, the use of vapor-recovery equipment can increase the efficiency of energy systems. That will lead to a significant reduction in greenhouse gas emissions and harmful environmental effects, which increase the lifetime of energy resources.Materials and MethodsThe realizable k-ε turbulence model is used to simulate turbulence within the flow. The thermo-compressor geometry has meshed in 2D and 3D modes to apply the conservation laws. For this purpose, quadratic (quad) and hexahedral (hex) types are used for two and three-dimensional meshing, respectively. Structured meshes have a high ability to obtain numerical results due to creation of structural meshes in the flow direction.The axisymmetric structure of the thermo-compressor leads to a half simulation of geometry. The thermodynamic properties of the input flows and their variations in the output, such as pressure, velocity, Mach number, and mass ratios for different motive steam pressure are extracted and discussed.Results and DiscussionDifferent levels of meshes are examined to investigate the mesh-independence test. In axisymmetric two-dimensional analysis, these levels include 33460, 51340, 78620, and 103590 cells, respectively. The relatively insignificant difference in motive flow for the third and fourth mesh levels (which proves less than 5%) clearly shows the independence of the results from the mesh size. Regarding the time considerations, the grid with 78,620 meshes was used in the simulations.The experimental data from the article by Sriveerakul et al. (2007) are used to validate the numerical results of the present work. Validation shows that the results obtained from the simulations are in good agreement with the experimental data. Since the final results of the two-dimensional analysis are very close to the three-dimensional one, the first one is selected due to the time considerations and higher computational costs of the three-dimensional mesh analysis.Considering the problem conditions, pressures of 10 and 15 bars are appropriate for practical application. Since the 15 bar motive stem creates a longer development length in the diffuser section, it is a better choice. At this level (15 bar), the temperature field within the thermo-compressor is well distributed in the presence of ideal temperature conditions. The ideal velocity distribution within the thermo-compressor and the uniformity of the motive and suction flows indicate the high performance of the thermo-compressor in these operating conditions. Applying the motive steam of 15 bars, the values of 0.59 and 0.41 for the motive and suction mass ratios of the diffuser output were achieved, respectively.ConclusionGeometrically, the study was examined in asymmetrical two-dimension and three-dimension. It was observed that there is a slight difference between the two analysis modes by comparing the velocities along the longitudinal line of the thermo-compressor. Therefore, to save computational and time costs, results are presented for the axisymmetric two-dimensional mode.The effect of 4 levels of motive steam pressure on the thermodynamic properties within the computational domain, including pressure, temperature, velocity, Mach number, mass ratios of both motive steam, and suction vapor are evaluated. Finally, the values of the performance curve for steam with motive pressures of 3.7, 5, 10, and 15 bars are presented.

Keywords

• entrainment ratio
• mach number
• suction flow
• sugar processing