Numerous factors influence the effectiveness of low-temperature evaporators in treating high-salinity wastewater, primarily encompassing wastewater characteristics, operating conditions, equipment design, and maintenance. Specific details are outlined below:

Wastewater Characteristics

Salinity: Excessively high salt content in wastewater elevates the solution's boiling point, necessitating higher temperatures and greater energy input during evaporation. Concurrently, high salt concentrations increase solution viscosity, impairing fluid flow properties and heat transfer efficiency, thereby reducing the evaporator's processing efficacy.

Salt Composition: Different salt types exert varying effects on evaporators. For instance, salts such as calcium sulphate and calcium carbonate exhibit low solubility at low temperatures, readily crystallising and precipitating on heat transfer surfaces to form scale deposits that diminish heat transfer efficiency. while corrosive salts like chlorides can corrode evaporator materials, shortening equipment lifespan.

Organic Content: Organic matter in wastewater may form foam during evaporation, impairing evaporation efficiency and normal equipment operation. Furthermore, organics can deposit as fouling on heat transfer surfaces, reducing heat transfer coefficients while also increasing wastewater viscosity and affecting fluid flow properties.

Wastewater pH: The pH of wastewater significantly impacts evaporator performance. Highly acidic or alkaline effluents accelerate equipment corrosion, particularly under high-temperature and high-salinity conditions where corrosive effects are accentuated. Furthermore, pH influences the solubility and crystallisation behaviour of certain salts, thereby affecting scaling patterns.

Operating Conditions

Evaporation Temperature and Pressure: Low-temperature evaporators operate at reduced temperatures and pressures, though specific parameters require optimisation based on wastewater characteristics and treatment objectives. Excessively low temperatures may result in sluggish evaporation rates and diminished efficiency, while excessively high temperatures risk significant salt crystallisation and equipment corrosion. Pressure control is equally critical, as inappropriate levels can disrupt vapour condensation and evaporation equilibrium, thereby compromising treatment efficacy.

Wastewater Flow Rate: The velocity of wastewater within the evaporator significantly impacts treatment efficacy. Excessively low flow rates may cause salt deposition on heat transfer surfaces, leading to scaling; conversely, excessively high flow rates increase energy consumption and equipment wear. Therefore, an optimal flow rate range must be determined to ensure effective heat transfer while minimising scaling and equipment deterioration.

Heating Medium Temperature and Flow Rate: The temperature and flow rate of the heating medium directly affect the evaporator's heat transfer efficiency. Excessively high temperatures or flow rates may cause localised overheating, accelerating salt crystallisation and equipment corrosion. Conversely, insufficient temperatures or flow rates fail to provide adequate heat, preventing the evaporation process from proceeding normally.

Evaporation Duration: The length of evaporation determines the concentration level of the wastewater. Excessively prolonged evaporation may cause over-concentration of salts, increasing the risk of scaling and blockages; conversely, insufficient evaporation time fails to achieve the desired treatment effect, resulting in effluent that remains non-compliant with discharge standards.

Equipment Design and Maintenance

Evaporator Type and Structure: Different types of low-temperature evaporators—such as falling film, scraped surface, and plate evaporators—exhibit distinct heat transfer performance, fluid flow characteristics, and resistance to scaling. Selecting an appropriate evaporator type and optimising its structural design—including heat transfer tube diameter, length, and arrangement—enhances treatment efficacy and operational stability.

Heat Transfer Area: The size of the heat transfer area directly impacts the evaporator's heat transfer capacity. Sufficient area ensures adequate heat exchange between wastewater and the heating medium, improving evaporation efficiency. However, excessive heat transfer area increases capital investment and footprint; whilst insufficient area may fail to meet treatment requirements.

Material Selection: Given the corrosive nature of high-salinity wastewater, material selection for evaporators is critical. Utilising corrosion-resistant materials such as stainless steel, titanium alloys, or polytetrafluoroethylene extends equipment lifespan and ensures reliable operation. Inappropriate material choices may lead to corrosion damage, compromised treatment efficacy, or even safety incidents like leaks.

Equipment maintenance: Regular servicing of low-temperature evaporators—including cleaning deposits and scale from heat transfer surfaces, inspecting seals, and replacing worn components—is vital for preserving performance and treatment efficacy. Neglecting maintenance gradually reduces heat transfer efficiency, exacerbates scaling and corrosion, and ultimately compromises treatment outcomes.