The core efficiency of low-temperature wastewater evaporation equipment hinges upon three fundamental dimensions: mass and heat transfer efficiency, vacuum environment stability, and the inherent characteristics of the wastewater itself. Concurrently, the structural design of the equipment, operational conditions, and routine maintenance directly influence efficiency levels. In essence, evaporation efficiency represents the quantity of wastewater converted into water vapour per unit time under low-temperature vacuum conditions. All influencing factors revolve around the principle of ‘maximising contact between wastewater and the heat source to facilitate rapid vaporisation’.

Approaches to enhancing evaporation efficiency correspond to these influencing factors. Targeted adjustments across four levels—wastewater pretreatment, optimisation of equipment operating parameters, structural adaptation of equipment, and routine operational maintenance—can achieve significant efficiency gains. Below is an analysis of specific influencing factors and corresponding enhancement methods, balancing practicality and technical expertise:

I. Core Factors Influencing Evaporation Efficiency (Categorised into Four Groups, from Primary to Secondary)

(1) Primary Determinant: Mass and Heat Transfer Efficiency (Evaporation is fundamentally a heat exchange process)

This is the most critical factor affecting efficiency. The rate at which wastewater absorbs heat and the contact area with the heat source directly determine the vaporisation rate. Key associated factors include:

Heat exchange area and method: Smaller heat exchange surfaces and insufficient contact between wastewater and heat source result in lower efficiency. For instance, spray/falling film evaporators have significantly greater contact areas than static systems, yielding over 30% higher efficiency.

Temperature differential between heat source and wastewater boiling point: The heat source temperature (from heat pumps/heating systems) must exceed the wastewater boiling point by 5–10°C (e.g., boiling point 50°C requires heat source 55–60°C). An insufficient differential slows heat exchange, while an excessive differential wastes energy and risks localised overheating and scaling.

Cleanliness of heat exchange surfaces: Salt deposits, oil films, or contaminants on surfaces drastically reduce thermal conductivity (e.g., oil films decrease efficiency by over 40%), constituting the most common cause of operational efficiency decline.

(2) Critical Foundational Factor: Vacuum Environment Stability (Prerequisite for Low-Temperature Evaporation)

Vacuum level directly determines wastewater boiling point. Fluctuations in vacuum cause erratic boiling point variations, disrupting heat exchange equilibrium. Core associated factors:

Vacuum precision: A deviation in chamber absolute pressure from the set value (e.g., set at 0.085 MPa but rising to 0.095 MPa) causes the boiling point to shift from 50°C to 40°C. This disrupts the temperature differential between the heat source and wastewater, resulting in a sharp decline in evaporation rate.

Equipment Sealing Integrity:

Leaks at evaporation/condensation chamber junctions or pipe connections cause the vacuum pump to continuously draw air to compensate for pressure loss. This prevents stable negative pressure maintenance, increases pump energy consumption, and indirectly reduces efficiency.

Non-Condensable Gas Content:

Dissolved gases in wastewater or gases produced by organic decomposition, if not promptly vented, accumulate within the chamber. This occupies heat exchange space, reduces vacuum level, and impedes vaporisation.

(3) Critical External Factors: Intrinsic Wastewater Characteristics (Necessity of Pretreatment)

Untreated wastewater containing substantial interfering impurities directly impedes evaporation. Key associated factors:

Wastewater Viscosity and Concentration: Excessively high TDS and COD levels increase viscosity (e.g., in high-salinity wastewater), impairing fluidity. This prevents uniform coverage of heat exchange surfaces, leading to localised dry-out and uneven heating.

Suspended solids and oil content: Excessive SS may clog spray nozzles/heat exchange tubes, while oils form films enveloping the wastewater, hindering heat absorption and water vaporisation. This also readily generates foam entraining impurities.

Foam content: Surfactants in wastewater generate substantial foam, which occupies evaporation chamber space. The heat exchange efficiency of foam layers is significantly lower than that of liquid wastewater, and foam readily enters the condensation chamber with steam.