Study On Particle Sedimentation In Electric Heaters In Small Ethylene Glycol Desalination Plants

In order to solve the key problem of removal of monovalent salt in ethylene glycol regeneration process, the laboratory established a smalll dynamic experimental device which removed monovalent salt from lean glycol. Considering the thermal oil system too complicated to use in the laboratory, there is a big security risk, we have to choose the electric heater to provide heat circulation for the flash tank. However, during the experiment, the deposition of salt particles appeared in the electric heater, which affected the normal process of the experiment. The deposition of salt particles is closely related to the internal structure and flow field distribution of electric heater. In order to reduce the deposition of particles in the electric heater, in this paper, by means of numerical simulation, changing the internal structure and operating parameters of the electric heater, and the heat transfer coefficient and the pressure drop along the path of the electric heater are synthetically considered.In this paper, the particle size of NaCl crystal was measured, and the average diameter of salt particles is 58?m. Then, this paper introduces the basic theory of particle and fluid movement and the numerical model of solid-liquid two-phase flow, and establishes the mathematical model of the solid-liquid two-phase flow in electric heater. Three-dimensional geometric model of electric heater was built by CATIA software, and the simulation grid was divided by ICEM software, and the deposition of particles in the electric heater with segmental baffles and the electric heater with helical baffles was simulated by Fluent. The grid adopts hexahedral structured mesh. The solid-liquid two-phase flow in electric heater is calculated using Euler-Euler model and RNGk-? model, and the surface power density of the electric heating tube was determined to be 11 KW/m2. The main conclusions are as follows:(1) For electric heater with segmental baffles, The increase of the number of baffles can reduce the particles at the bottom of the electric heater, and increase heat transfer coefficient, but the pressure drop is increased, and the comprehensive performance increases at first and then decreases. With the height of baffles increased, the particles in front of the baffle at the bottom of electric heater are decreased, and the particles in the rear area of the baffle are increased, at the same time, the heat transfer coefficient and pressure drop are increased, and the comprehensive performance increases first and then decreases. The increase of the inclination angle of the electric heater can reduce the particle deposition near the baffle at the bottom of the electric heater and the pressure drop, but the solid volume fraction at the end enclosure is increased, and the heat transfer coefficient increases at first and then decreases.(2) For electric heater with helical baffle:With the increase of helical angle, the particles at the bottom of electric heater are increased, the heat transfer coefficient and pressure drop are decreased, and the comprehensive performance increases first and then decreases.(3) For these two kind of electric heaters:When the inlet of the electric heater is above the housing and the outlet is below the housing, it is advantageous to reduce the particles at the bottom of electric heater and the pressure drop, and to improve heat transfer coefficient and comprehensive performance. The increase of circulation flow rate can both reduce the particles near the baffle at bottom of electric heater and increase heat transfer coefficient, but the pressure drop is increased, and the comprehensive performance is decreased.(4) For these improved two electric heaters:With the increase of particle size and solid volume fraction, the particles at the bottom of electric heater are increased, and the particles near the baffle at bottom of the improved structure of electric heater with segmental baffles (with helical baffles) when particle size is 95?m (75?m) are still much less than that of the original structure when the particle size is 58 ?m, and the increase of the proportion of particle deposition near bottom baffles is not so obvious. When the flow rate is 1.5m3/h, the particle size is average and the solid volume fraction is 0.04, the particles at the bottom of the helical-baffle electric heater are less than that of the segmental-baffle electric heater. Under the same conditions of the flow rate, the pressure drop, the heat transfer coefficient and the comprehensive performance of electric heater with helical baffles are larger than that of electric heater with segmental baffles.