Process Anomalies Caused by an Excessively Narrow Liquid Level Buffer Range

1. Frequent start-stop cycles in the feed and circulation logic, resulting in severe fluctuations in flow rate

In staged concentration, the feed valve is controlled by the difference between high and low liquid levels; however, with a narrow buffer range, even slight changes in liquid level trigger the feed valve to open or close:

Frequent valve cycling causes water hammer, leading to sudden fluctuations in pipeline flow rate and off-center flow on the product side of the plate heat exchanger;

The total volume of material in the chamber fluctuates slightly and continuously, causing unstable loads on the circulation pump. Localized flow rates across the heat exchange plates vary erratically, making it prone to localized salt accumulation and scaling.

2. Continuous Disturbances in Evaporation and Boiling Conditions, with Frequent Vacuum Drift

A stable liquid level is required to form a steady boiling layer; however, an excessively narrow buffer range causes frequent fluctuations in the liquid level:

The volume of the vapor space changes repeatedly, disrupting the rhythm of steam generation;

With the vacuum pump’s pumping speed remaining constant, steam production fluctuates erratically, causing the negative pressure to continuously fluctuate. This amplifies vacuum disturbances caused by gas leaks in the piping and fluctuations in fan cooling.

3. Foam and mist entrainment continue to worsen

As the liquid level fluctuates, the boiling surface repeatedly approaches and recedes from the demister screen:

When the liquid level is too high, foam comes into direct contact with the mesh, carrying a large amount of material; after a sudden drop in liquid level, the vapor phase in the chamber suddenly expands, causing the gas flow velocity to increase instantly, tearing droplets into fine mist that penetrates the demister;

In the late stages of concentration, in systems containing salts and colloids, even slight fluctuations in liquid level can cause foam to overflow, contaminating the condensate and clogging the vacuum lines.

4. Alternating wet and dry conditions on heat transfer surfaces accelerate under-scale corrosion and fouling

Rapid fluctuations in liquid level cause the plate heat exchanger plates and chamber sidewalls to repeatedly switch between wet and dry states:

At the liquid surface, salt solution dehydrates and crystallizes, forming a hard scale layer that creates a corrosive environment;

Newly precipitated microcrystals do not have time to be washed away by a steady water flow and quickly adhere to the plate surface, shortening the acid washing cycle.

5. Frequent drift in conductivity and temperature readings leads to program misjudgments

Conductivity and temperature probes are fixed within the liquid level range:

When the liquid level is low, parts of the probes are exposed to the gas phase; when high, they are fully submerged, causing frequent changes in the measurement environment;

Instrument readings fluctuate, causing the concentration switching points for staged concentration to occur too early or too late, resulting in over-concentration, oversaturation of the mother liquor, and massive crystallization.

6. Accelerated Fatigue Wear of Pumps, Valves, and Seals

Feed valves and circulation pumps undergo repeated start-stop cycles within short intervals:

Valve gaskets age and leak due to high-frequency impact; frequent start-stop cycles of the circulation motor subject the windings to impact, increasing the failure rate;

Manhole and flange sealing surfaces are subjected to steam impact caused by liquid level fluctuations, increasing the probability of micro-leakage and further deteriorating the vacuum.

7. Loss of control during stage switching, posing a risk of blockage due to excessive concentration

When the buffer margin is insufficient and feed replenishment cannot keep up with the rate of water loss during evaporation, the liquid level drops rapidly, and the program cannot switch to the discharge stage in time:

The mother liquor becomes continuously overconcentrated, with salinity far exceeding the saturation point; large amounts of salt crystals precipitate instantaneously, rapidly clogging the narrow flow channels of the plate heat exchanger, causing the pressure differential to spike and the system to shut down.