Seeking help regarding faults in the three-effect counterflow II and III effect forced-circulation evaporation systems
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This post was last edited by sunjl1981 on 2013-1-6 at 22:44. Our company uses a three-effect counter-current evaporation system, with forced circulation in effects II and III. The impellers of the forced circulation pump in effect II have suffered significant wear recently, resulting in a reduced circulation volume of the alkaline solution within that effect. During recent production operations, after two days of operation, an amount of 0.4 g/l of alkali was found in the secondary steam from effect II, and the pH of the condensate water rose to 9, which affected the operation of the condensate water recovery pump. I’m not sure whether it’s caused by the forced pump, or by damage to the swirl plate at the top of the evaporator or by inadequate cleaning. # + + .
I’ll answer this question myself; I hope that peers in the same industry who encounter similar issues can find some help here. After analysis and tracking last week, the fault was ultimately located in the impeller of the forced circulation pump. The main issues were as follows: 1. After two days of operation, the secondary air pressure in the second effect unit decreased, and negative pressure sometimes occurred. 2. The effect of Stage III is ideal: the vacuum level is high, the temperature of the secondary vapor phase decreases, and the material temperature drops by 2 degrees. The temperature difference between the gas phase and the liquid feed is 20 degrees. 3. The temperature difference during discharge is difficult to control. 4. In the second effect, false liquid levels often occur and salt formation is likely to happen (mainly because the first effect works well and the temperature of the feed liquid is high, while the circulation efficiency in the second effect declines; the mixture of materials in the heating chamber and the evaporation chamber is uneven, the temperature of the materials in the evaporation chamber is low, and flash evaporation occurs after the material passes through, a phenomenon commonly referred to as the \"pu pot\" effect). ) The top of Effect II is under negative pressure, which makes it easy for alkali foam to be carried into the heating chamber of Effect III. For this reason as well, sometimes a roaring sound is heard inside the second-effect evaporation chamber during material transfer, mainly due to a pressure difference. The impeller has been in use for three and a half days after replacement, and so far there has been no occurrence of alkaline condensate; moreover, the production per shift has increased by nearly 10 M3.
Additional note: Once the circulation pump is functioning properly, the circulation volume and speed increase significantly, enabling uniform mixing of the materials within the effectors; salt extraction in the second effector also returns to normal. The alkalinity content of the material produced by double-discharge centrifuges decreases. The entire system enters a positive cycle.