In the complex production process of the alumina industry, the problem of alkali carryover in secondary water often troubles many manufacturers. When this issue arises, the first reaction of many people is to seek solutions from the defoamer. However, is the truth really that simple? Today, we will uncover the key factors behind vapor-liquid separation through a real-case example!

一、"Unexpected" production hides crises

Previously, a manufacturer selected a 330-ton evaporator. Initially, the design planned to use 3 kg steam flashed from hot water in another area as the heat source. However, during actual operation, it was found that there was not as much hot water as expected, so the manufacturer directly switched to 6 kg live steam. This change subsequently led to a dramatic shift in the original situation — the larger temperature difference caused the water evaporation capacity of the evaporator to far exceed expectations. Surprisingly, the manufacturer found that this 330-ton evaporator could even achieve a water evaporation capacity of 460 tons!

However, while the manufacturer was （immersed in）the joy of "overfulfilling the task", problems quietly emerged — the phenomenon of alkali carryover in secondary water became severe. The expected efficient production, due to this issue, might affect product quality, increase subsequent treatment costs, and even pose environmental risks, plunging the manufacturer into anxiety.

二、The defoamer "takes the blame", but the problem remains unsolved

Faced with the dilemma of alkali carryover in secondary water, the manufacturer's first thought was to start with the defoamer. In the understanding of many people, the defoamer is a "sharp tool" for solving vapor-liquid separation problems, so the manufacturer decisively replaced it with a wire mesh defoamer, expecting it to turn the situation around. However, the result was unsatisfactory, and the alkali carryover problem still existed. This (can't help but make people wonder): Why does the seemingly professional defoamer appear so "powerless" in solving the problem of alkali carryover in secondary water?

In fact, the defoamer is merely an auxiliary device in the vapor-liquid separation process! It acts like a "little helper" that can assist in separating tiny mist droplets to a certain extent, but it cannot fundamentally solve the problem of insufficient separation. Its scope and capacity are limited—akin to patching a leaky bucket by merely sticking a small patch over the hole, without truly addressing the source of the leak.

三、The Separation Chamber: The Neglected "Unsung Hero"

So, what is the key to vapor-liquid separation? The answer lies in the separation chamber! The diameter of the separation chamber and the superficial gas velocity are the core factors determining whether vapor and liquid can be sufficiently separated.

The superficial gas velocity refers to the average flow rate of gas in the separation chamber. Simply put, the lower the superficial gas velocity and the longer the separation path, the more sufficient the vapor-liquid separation will be. A larger diameter and higher height of the separation chamber can effectively reduce the superficial gas velocity and extend the separation path. Just like on a wide and long road, vehicles (gas) and pedestrians (liquid) have enough space and time to diverge, naturally achieving better separation.

In the above case, the diameter of the evaporator separation chamber of the manufacturer was designed according to a 330-ton evaporator. When the water evaporation capacity increased to 460 tons, the gas flow rate significantly increased, but the size of the separation chamber remained unchanged, resulting in a substantial increase in the superficial gas velocity. As a result, the vapor and liquid did not have enough time for sufficient separation in the separation chamber and were "hurriedly" carried out, leading to the phenomenon of alkali carryover.

四、Identify the Right Direction to Effectively Solve Problems

Therefore, when solving problems like alkali carryover in secondary water, we should not solely focus on the defoamer. It is crucial to pay attention to parameters such as the size, length, and area of the separation chamber. Only by fundamentally reducing the superficial gas velocity and extending the separation path can we truly achieve sufficient vapor-liquid separation and avoid issues like alkali carryover.

In actual production, manufacturers can reasonably plan the specifications of the separation chamber during the design phase according to production requirements. If problems have already arisen, they can also improve the vapor-liquid separation effect through technical modifications, such as appropriately expanding the diameter and increasing the height of the separation chamber. At the same time, while the defoamer cannot solve the root problem, its rational selection and installation can serve as a complementary measure to further enhance the separation efficiency.

It is hoped that today's case sharing can provide new ideas and directions for solving similar problems in chemical production. If you have any other questions or content you would like to know, welcome to consult and communicate online!