double-effect evaporation
Thread Content
Our company uses double-effect evaporation; the design specifies a pressure of 0.04 MPa and a temperature of 85°C for the first effect, while the pressure for the second effect is 0.06 MPa with a temperature of 75°C. The steam from the first effect can be used to heat the second effect. However, there is a problem: only one vacuum pump is connected to the two evaporators. When the vacuum pump is turned on, the pressures in both evaporators become identical, ending up at 0.06 MPa. As a result, the temperature does not reach 80°C, and there is hardly any change in the conditions in the second evaporation chamber. I would like to ask why the pressures of these two evaporation chambers are controlled differently? Solve
A high pressure in the first effect, along with a high vapor pressure and high condensation temperature, is required to serve as a heat source for the second effect.
With evaporators connected in series, a pressure difference is naturally created, and the last stage is connected to a vacuum system! Will heating with a 10-degree temperature difference work? Doubt!
Why are the pressures of the two evaporators the same as soon as I start the vacuum pump? No matter what I do, it remains the same
I want to ask how to control different vacuum levels. When I turn on the vacuum pump, the vacuum pressures of the two areas are the same; no matter what I do, I can’t change that
The pressure difference between the two evaporators is too small, as is the pressure difference in the pipelines; as a result, the vacuum level is almost identical； With almost the same vacuum level, the evaporation temperature is naturally almost the same. If the pressure is adjusted manually in different ways, the evaporation temperature will vary; for example, by using valves to regulate the pressure in the intermediate pipes! It indicates that there is a problem with the evaporator design!
When the vacuum level is almost the same, the evaporation temperature is the same
Double-effect evaporation involves using raw steam to heat the heating chamber in the first effect, while the secondary steam from the first effect is used to heat the heating chamber in the second effect. Vacuum is created in the second effect, which enables the existence of temperature differences and pressure differences.
I’ve also seen a set like yours; the effect of it isn’t very good.
This design has issues: a temperature difference of only 10°C between the two stages results in low heat exchange efficiency, and the heat exchange area is too large. It would be better to design it such that the absolute pressure is higher in the first stage and lower in the second stage, thereby allowing for a larger temperature difference. Valves can be added to the vacuum pipes in the first stage to increase resistance. It is necessary to conduct thorough calculations to determine whether the secondary steam used in the second stage of evaporation is sufficient, as well as whether the final amount of vapor produced meets the requirements. Problems of this kind that arise during operation should be addressed with guidance from the manufacturer
With double-effect evaporation, the pressure difference between the two tanks is too small. After the vacuum pump is turned on, it should be connected to the evaporation tank of the subsequent stage; by shutting off all non-condensable gases, a pressure difference will be created.