Design of Multi-effect Evaporator for Sewage Treatment

Abstract

This paper takes chemical salt water treatment as an example, to describe the desigen process of multi-effect evaporation sewage treatment equipment. Using software to simulate and analyze the influence of different factors on the results. Using line graphs to show the results of operating conditions of Luoyang Sinopec Branch. Introduction Evaporation refers to the process of evaporating and concentrating the solution containing the non-volatile solute and the volatile solvent, mainly by heating to vaporize a part of the solvent in the solution [1]. The multi-effect evaporator uses the secondary steam produced in the evaporation production as the heat source of the next unit. Such as, liter film multi-effect evaporator, falling film multi-effect evaporator [2], steam recompression multi-effect evaporator[3]. Multi-effect Evaporator Design Select Design Software and Reasons Aspen Plus was used to establish a chemical salt water treatment system. (1) The model physical property database is complete and suitable for more complex process simulation. (2) Fast unit simulation is possible. (3) With advanced calculation methods, the model can be optimized. Setting the Composition of Salty Sewage It is difficult to determine accurate data for these substances, such as chemical formula, content, etc. Therefore, in the modeling verification, the sewage composition needs to be simplified. In this design experiment, according to the sewage component in the sewage data of Luoyang Sinopec Branch, it is assumed that the large particle insoluble sludge has been removed. Common electrolytes such as ions and potassium ions are used as impurities, and volatile impurities are not considered at present[4]. Determination of Multi-effect Evaporator Efficiency With the increase in the efficiency of the multi-effect evaporator, the amount of steam required is reduced and the operating cost is reduced with the same total evaporation,the equipment and infrastructure costs will increase[5]. Therefore, the multi-effect evaporation system referred to herein is three-effect evaporator. Design Evaporato The heat exchanger model HeatX in Aspen plus, the separator model flash and the pressure transmission module Valve represent the multi-effect evaporator. Design Condenser In multi-effect evaporation, using the HeatX model in the Aspen plus module library instead. The final multi-effect evaporator system is: Figure 1. Multi-effect Evaporation System. Determine the Convergence Method The current simulation convergence method selects the traditional WEGSTEIN method. Module Parameter Setting The system parameters simulated in this paper are as follows: Table 1. Parameters of the Simulated Plate. HeatX Stream flash Valve Calculation shortcut — — Pressure change parameter Hot fluid outlet gas fraction Flow rate temperature Outlet pressure Hot fluid outlet temperature temperature pressure — — ingredient — — — pressure — — According to the above table, the fluid parameters of the evaporation system designed in this paper are: Table 2. Parameters set by one-effect evaporation module. Hot stream Cold stream Heatx Valve Flash 120°C 60°C 0.5 — 116.2°C 0.3Mpa 0.12Mpa — 0.07Mpa 0.12Mpa 10kg/h 10kg/h — — — Table 3. Parameters set by two-effect evaporation module. Heatx Valve Flash 0.78 — 104°C — 0.04Mpa 0.07Mpa Table 4. Parameters set by two-effect evaporation module Heatx Flash 94°C 89.1°C — 0.04Mpa Model Verification Results After completing the above multi-effect evaporator model design work, the simulation software can be used to run the verification. Based on these data, the water generation ratio and heat exchange area of the multi-effect evaporator can be estimated. Simulation of the Effect of Evaporation Efficiency on the Process This simulation compares the water production ratios of one effect, two effects and three effects respectively. The data changes are shown in the figure 2. It can be seen from the above figure that under the condition that other process parameters remain unchanged, the water production rate increases significantly with the increase of effect, and the heat exchange area also increases with the increase of effect. However, with the increase of evaporation units, the increase rate of water yield decreases.