Research On Energy Saving In Hydrazine Refining Process

Hydrazine hydrate, a fuming, colorless oily liquid having an ammoniacal odor, is widely used in the field of fine organic synthesis. Because of its strong reduction char-acteristic, it is reckoned as one of the most important chemical raw materials and inter-mediates. Currently, there are four processes of industrialized production technologies, among which, urea-based process is much more popular in our country. This process has advantages of mature technology and simple equipment, however, the lower con-centration of hydrazine hydrate and large amount of by-product salts in raw hydrazine brought the problems of high energy consumption in the refining process, complicated solid-liquid separation operations and increasing equipment. In fact, high energy con-sumption in the refining process of raw hydrazine has already been the bottleneck of urea-based process.A reliable gas chromatography method to analyze the concentration of hydrazine hydrate in aqueous solution was established. We measured, at atmospheric pressure, the vapor-liquid equilibrium (VLE) data of hydrazine-water binary system and hydra-zine-water-sodium chloride ternary system with apparent sodium chloride mass frac-tions at 0.05,0.10,0.15 respectively. We employed NRTL and Electrolyte NRTL models to regress experimental data, obtained the relationship between temperature and interac-tion energy of molecule-molecule of N2H4-H2O and molecule-ion of N2H4-(Na+, Cl-). Our study showed that for hydrazine-water system, the presence of Na+, Cl- would lead to a rise of equilibrium temperature and an increase of equilibrium concentration of hy-drazine in vapor phase in comparison with systems containing no Na+, Cl- Those VLE data also provides the basic data for relevant chemical processes simulation and reactor design.We simulated the refining process of urea-based process with Aspen Plus software. An energy-saving process by intergration of heat pump technique, distillation process and evaporation process was studied. In the advanced process, the vapor distillate from the top of distillation column is compressed to a higher thermal grade and then is used partially as the heat source of the reboiler and partially as the heat source of the preve-nient evaporation section. Simulation result shows that the novel heat pump-distillation-evaporation integrated process saves 88.83% operating energy comsumption, namely saves 20187.25t of standard coal, equivalently 50266.26t CO2 emmision in comparison with the conventional refining process every year.