What are the main changes in changing the two-stage evaporation to three-stage evaporation? What's the difference

This post was last posted by Xishui on 2010-1-20 22:23 Editors, everyone knows that due to the double boiling point of urea solution under low pressure, two-stage evaporation is required to concentrate urine with a water content of about 30% to a water content of 0.5%. So whether to choose two stages or more than two stages of evaporation depends on the heat source. If there is a low-energy heat source, three-stage evaporation is feasible. If you want to increase production and want to reduce the heat load in the latter stage, it is also good to add one stage of evaporation in front. Yes, if it were not for the above situation, I thought about it and there is no need to set up three stages of evaporation. The process is complicated and takes up space. Compared with the conventional process, an additional stage of evaporation is required. Evaporation heaters, separators, condensers, ejectors, pipelines, instrument controls and other equipment must be added. As far as the evaporation process is concerned, the pressure (absolute) of one stage is lower/the temperature is higher/the urine concentration is higher than the other stage, and finally you can achieve the goal you want.

The analysis by water conservation experts on the 2nd floor is very accurate and can be used as a reference for the poster. In actual engineering applications, three-stage evaporation generally refers to: In addition to the original first and second stages of evaporation, a flash heater is added to the original flash evaporation tank to use by-product low-pressure steam, other higher-temperature steam condensates, or higher-temperature process media as heat sources to preconcentrate the urine before entering the first stage of evaporation.

The explanation of the three-stage evaporation on the 3rd floor is very correct. In addition to the first and second stages of evaporation, a flash heater is added to the original flash evaporation tank. The by-product low-pressure steam, or other higher-temperature steam condensate, or higher-temperature process medium is used as the heat source to preconcentrate the urine before entering the first stage of evaporation. The aqueous solution circulation method for small urea is mostly designed by the Fourth Chemical Engineering Institute. After technical modification, most of the 4wt production capacity can reach 12-15wt. The evaporation load in one stage is heavy, and the water content of the evaporated urine in the first stage is unqualified. It is often forced to raise the temperature by two points, which results in high pressure and analysis pressure in the second stage. At the same temperature, the steam consumption in the second stage is high. After changing to three-stage evaporation, the first-stage evaporation load can be effectively reduced, and the overall steam consumption is reduced. Therefore, the three-stage evaporation is very practical for small urea.