Simulative Research On Feasibility Of Double-Effect Distillation And Its Applications In Industry Examples As Paralleled Double-Effect Schemes

Distillation is a high energy intensive unit operation with large residual heat. Thelarger momentum, heat and mass transfer driving force is in the system, the largerenergy loses. Energy efficiency is currently low in chemical industries of China, onlyat the level of advanced industrial countries in the late1970s. During theenergy-saving transformation process in the chemical and oil refining industry, theeconomic benefits created by the distillation process energy-saving ranks first amongall the devices. Energy-saving technology of distillation process has great significancefor saving the investment in equipment, reducing energy consumption, loweringproduction cost and protecting the environment.Double-effect is an important means of improving energy efficiency indistillation process. This scheme can reduce energy consumption of distillation byextending technical process. Its basic principle is to reuse the energy which issupplied to column to improve thermodynamic efficiency. The overhead vapor of thepressured column is used to heat the reboiler of column at lower pressure. For a longtime, it is often based on experience to determine what kind of distillation process isfitness for double-effect. A standard for judgment does not exist. In this paper, on thebasis of detailed analysis of double-effect theory, two criteria are proposed to analyzefeasibility of double-effect, that is, the sensitivity of relative volatility to pressure andthe sensitivity of overhead vapor dew point to pressure. Then, parallel double-effect,which is a new form of double-effect, is put forward. The overhead vapor of pressuredcolumn integrates with several atmospheric columns simultaneously. Compared withthe multi-effect, parallel double-effect can reduce the amount of pressured column.In order to apply the feasibility of double-effect and parallel double-effectdistillation to process design, industrial four-column methanol distillation andnine-column organosilicon distillation are simulated using Pro/Ⅱ8.0simulationsoftware. A new five-column double-effect methanol distillation scheme is proposed.Then feasibility analysis of double-effect is applied to methanol distillation andorganosilicon distillation process, and trying to apply the concept of paralleldouble-effect to the two distillation processes. Finally, the parallel double-effect methanol distillation scheme and the parallel double-effect organosilicon distillationscheme are achieved, which have good energy saving effect.To further analyze the advantage of parallel double-effect distillation, exergyanalysis of methanol and organosilicon distillation process is performed. The totalexergy loss of the five-column parallel double-effect methanol scheme is decreased33.1%in comparison to the four-column scheme. If compared with the newfive-column double-effect methanol scheme, exergy loss can decrease14.3%. Paralleldouble-effect organosilicon scheme presents40.4%less exergy loss than the normalscheme. The effect of energy-saving is significant.