In alumina production, the evaporator is a key piece of equipment, and its stable operation is directly related to production capacity, costs, and equipment service life. Many industry practitioners know that an area margin of approximately 10% is reserved for evaporators during the design phase. Does this mean the evaporator can operate at a 10% overload for a long time? Recently, Industry Expert Director Ju conducted an in-depth explanation on this issue, helping us uncover the "invisible costs" of evaporator overload operation.

First, Understand: Why a 10% Margin Is Designed, Yet Overload Operation Is Not Recommended?

"The 10% margin reserved for evaporators is intended to address short-term fluctuations in production, rather than serving as a 'license' for long-term overproduction," Director Ju clarified his core viewpoint right at the beginning.

From the perspective of design logic, the 10% margin is a "buffer space" reserved by engineers based on factors such as equipment safety and operating condition fluctuations — for instance, when there are temporary changes in raw material concentration or short-term needs for production capacity rushes, the equipment can temporarily withstand slight overpressure and overproduction. However, if this part of the margin is regarded as "regular production capacity" and the equipment is forcibly operated at overload for a long time, it will instead disrupt the equipment's balanced state and trigger a series of cascading problems.

Caution! The 3 Core Hazards of Evaporator Overload Operation

Combining his practical operation and maintenance experience, Director Ju broke down the three key hidden risks of overload operation, and each of these directly affects production indicators and equipment service life:

Hazard 1: Steam-water ratio increases, leading to an "invisible increase" in energy consumption costs

When the evaporator is forcibly operated at overload (e.g., by means of increasing the feed amount), the most direct change is the rise in the material temperature of the first effect and the increase in temperature difference.

"The rise in the material temperature of the first effect essentially means consuming more heat from live steam to maintain operation," Director Ju explained. This directly leads to an increase in the "steam-water ratio" (the ratio of the amount of secondary steam generated to the amount of live steam consumed) — meaning that to produce the same amount of products, more investment in steam costs is required, and in the long run, this will significantly increase enterprises' energy consumption costs.

Hazard 2: Scaling in the First Effect Accelerates, Compromising Equipment Service Life

Another chain reaction resulting from the increased temperature difference and higher material temperature is the accelerated scaling rate in the first effect.

The first effect of the evaporator is a key link in heat transfer; excessively high material temperature causes solutes in the solution to precipitate more easily and form scale on the surface of heat exchange tubes. Scale formation not only further reduces heat transfer efficiency (creating "thermal resistance") but also forces enterprises to increase the frequency of acid cleaning — each acid cleaning process causes a certain degree of corrosion to the equipment's metal materials, and long-term, high-frequency acid cleaning will directly shorten the service life of the evaporator and increase equipment maintenance and replacement costs.

Hazard 3: Excessively High Empty Tower Gas Velocity, Leading to Excessive Alkali Carry-over in Secondary Water

Modern large-scale evaporators' separation chambers are all designed with precise calculations, and the matching degree between their space dimensions and gas flow velocity is extremely high. When the equipment is operated at overload, the empty tower gas velocity in the separation chamber will exceed the design threshold.

Excessively high gas velocity disrupts the balance of gas-liquid separation, causing the alkaline solution (or other solutes) in the solution to be carried by the gas flow into the secondary water system, resulting in "alkali carry-over in secondary water". This not only affects the recycling and reuse of secondary water (which requires additional treatment to meet standards) but also may cause contamination to the equipment in subsequent processes or product quality, increasing production risks.

Director Ju provided operation and maintenance recommendations: In the short term, the buffer (margin) can be relied on; in the long term, operation at the rated capacity is a must.

In response to the short-term production capacity needs of some enterprises, Director Ju has also provided

flexible recommendations: "Short-term and occasional overload operation (such as single-day production capacity rushes) is acceptable, but long-term overproduction must be avoided."

From the perspective of long-term operation and maintenance, Director Ju emphasized: "Evaporators should operate as much as possible at the rated capacity (≤ not exceeding the design capacity)." This not only ensures the stability of the steam-water ratio and controls energy consumption costs, but also reduces scaling and acid cleaning frequency to prolong equipment service life. At the same time, it avoids the problem of alkali carry-over in secondary water, ensuring that both production indicators and environmental requirements meet the standards.

Conclusion

The 10% margin of an evaporator is a "safety buffer" rather than a "production capacity bonus". Standardized operation and respect for design thresholds are the key to ensuring the evaporator operates with high efficiency, long service life, and low cost.