If the buffer tank’s volume is insufficient, the pumping pulses generated by the vacuum pump cannot be effectively dampened. These pulses will travel along the vacuum piping into the evaporation chamber, directly disturbing the gas-liquid interface and thereby reducing the demister’s actual separation efficiency. This issue is not due to damage to the demister itself but rather to a performance decline caused by abnormal system airflow conditions.

The periodic pumping action of the vacuum pump generates pressure pulses. A sufficiently large buffer tank can absorb these pressure oscillations, maintaining a relatively stable negative pressure environment within the evaporation chamber. If the buffer tank is too small and lacks sufficient buffering capacity, the attenuation of pressure pulses is limited, and pressure fluctuations are directly transmitted to the evaporation chamber, causing rapid, minor fluctuations in the vapor pressure inside the chamber. These repeated pressure changes directly act on the surface of the feed liquid, causing the liquid level to fluctuate in response to the pressure pulses. As the liquid surface is constantly disturbed, a large number of fine splash droplets are generated. Under normal steady-state conditions, only the foam produced by boiling vaporization needs to be captured by the demister; however, the pulsating disturbances generate a large number of additional microscopic droplets, causing the demister’s processing load to exceed its original design specifications.

The separation efficiency of a demister is based on the premise of relatively stable gas-phase flow velocity. Wire mesh demisters have a corresponding optimal gas velocity range; when the gas flow velocity is stable, droplets are captured by colliding with the wire mesh fibers due to inertia. When suction pulses occur, the gas-phase flow velocity in the piping and chamber fluctuates periodically between high and low levels, and the instantaneous peak gas velocity may briefly exceed the demister’s maximum allowable design gas velocity. During peak velocity phases, the liquid film already captured by the mesh is torn apart again by the high-speed gas flow, resulting in secondary entrainment. Liquid that had already been separated is carried away once more by the gas flow, leading directly to carryover. When the gas flow velocity drops during the trough of the pulse, some liquid flows back into the chamber, manifesting as intermittent fluctuations in condensate water quality—alternating between good and poor.

Pressure oscillations also alter the distribution of the upward steam flow field within the chamber. Under steady-state conditions, steam flows uniformly upward through the entire cross-section of the demister; under pulsating conditions, however, localized vortices and flow deviations form. In certain areas, the gas-phase velocity is significantly higher than the average velocity, leading to flow short-circuiting. Steam carrying liquid droplets passes directly through the demister from these high-velocity zones without being adequately intercepted by the wire mesh, resulting in a significant decline in separation efficiency. During many on-site inspections, demisters are disassembled to reveal that the wire mesh is intact with no blockages or damage, yet material leakage still occurs. In such cases, it is necessary to investigate whether the buffering capacity on the vacuum side is insufficient.

It is also important to distinguish between the characteristics of these phenomena: on the vacuum gauge, the pointer or digital display may be observed to fluctuate continuously in small increments; even if the set vacuum parameters remain unchanged, the actual vacuum within the chamber continues to oscillate within a narrow range; The higher the equipment’s evaporation load and the greater the steam volume, the more the interference caused by pulses is diluted, making the phenomenon less pronounced; during low-load operation, however, the vapor flow rate is inherently low, so the proportion of vacuum pump suction pulses is amplified, and liquid surface disturbances and carryover become more pronounced, often leading to misdiagnosis as a low-load foaming issue.

This leads to a chain reaction: the repeated action of pressure pulses causes the liquid film on the surface of the demister mesh to be repeatedly impacted, making localized fatigue deformation of the mesh prone to occur during long-term operation; as the pulses are transmitted to the pressure-taking lines, they also cause the vacuum sensor readings to fluctuate. The control system receives these fluctuating signals, which further drive the vacuum pump to adjust frequently, exacerbating the instability of the entire system.

Simply increasing the demister area or thickening the mesh cannot fundamentally resolve these issues; it only provides temporary relief. The root solution lies in matching a reasonable buffer volume, positioning the buffer tank as close as possible to the evaporation chamber to shorten the pulse transmission distance; where conditions permit, damping elements should be added to the vacuum piping to attenuate pulse amplitude, thereby controlling internal vapor pressure fluctuations within a reasonable range and maintaining the demister’s operation within the designed stable flow rate range.