What is upward film evaporation of urea (using steam directly, without a heat recovery section)?
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What happens during the evaporation of urea? 74% of the urine, at 84 degrees Celsius, is sent to a first-stage evaporator (where the operating pressure and temperature are 33 kPa and 130 degrees Celsius?) ) After import, first the sensible heat stage heats it from 84 degrees to 130 degrees, and then the latent heat stage – does evaporation occur at a constant temperature of 130 degrees? But at 130 degrees, isn’t the saturated vapor pressure corresponding to 95% urine 33 kPa? ?
How does this evaporation process take place? ? Constant temperature? ? Variable temperature? ?
Urine evaporation is a process of evaporation with variable temperature and concentration. When urine is heated, the water evaporates, resulting in an increased concentration; the boiling point rises while the saturated vapor pressure drops, until equilibrium is reached with the operating pressure and no more water evaporates. The saturated vapor pressure of urine is related to temperature and concentration; at a given temperature and operating pressure, the concentration of urine remains the same after evaporation. A period of evaporation generally achieves a concentration of around 95%, but based on the data provided by the original poster, this level cannot be reached.
Let me explain: this temperature of 130 degrees refers to the temperature at the bottom end of the ’U’-shaped tube, which is different from the temperature at the outlet of the heater. I hope everyone will participate in the discussion. The material balance sheet I received indicates that by raising the temperature from 84 degrees to 130 degrees, 74% of the urine can be purified to 95%.
In the evaporation section, the urine is heated to about 140 degrees, causing a large amount of water to evaporate and absorb heat; as a result, the temperature of the urine at the outlet drops to 130 degrees
I would like to discuss with you: after urine is evaporated and concentrated in an evaporator, its temperature cannot drop to 130 degrees, otherwise the molten urea will crystallize and solidify, as its melting point is 132.6 degrees. Of course, if the temperature is inaccurate, that’s another matter.
Reply to 6# lxq700918: I can say one paragraph; two paragraphs is definitely not possible, around 137