What is the purpose of setting a flash before steaming?

The purpose of setting up flash evaporation before vaporization is to use the effect of flash evaporation to volatilize some of the ammonia, carbon dioxide, and water present in urine, thereby reducing the load on the first and second stage evaporation heaters and ultimately saving steam consumption.

The urine coming out of the low-pressure decomposition distillation tower enters a flash tank after being depressurized, allowing for more thorough separation of the ammonia and carbon dioxide remaining in the urine. The urine with a concentration of 72% (by mass) is then sent to a urine storage tank. The saturated vapor pressure of a solution is related to both the composition of the solution and the temperature. As the pressure decreases, the boiling point of the solution also drops; flashing utilizes this principle of reduced boiling point of solutions under vacuum for separation. At a pressure of 300 mm Hg, the boiling point of 75% urine is 92.6°C. Industrially, to prevent blockages, the temperature of the urine is usually maintained between 95 and 100°C; at these temperatures, satisfactory decomposition of residual methylammonium and elimination of free ammonia can be achieved. In actual production, the flash pressure is set at 350–450 mm Hg gauge (0.45–0.6 kgf/cm2 absolute pressure).

1. Further concentrate the urine; after flashing off the ammonia and carbon dioxide that are not to be recovered, recover those gases as well in order to reduce energy consumption. 2. Prevent the two pumps from vaporizing due to evaporation. 3. Reduce the evaporation load at the same time. This post was last edited by guizhou*aolong on 2009-2-3 22:01.]