Thermal concentration and reduction technology for high concentration saline wastewater and its application

The treatment and comprehensive utilization of high concentration saline wastewater is a major environmental issue facing industrial development at present. Choosing a reasonable treatment process can not only achieve certain economic benefits, but also generate environmental and social benefits. This article mainly focuses on the company's current main products and processes, and combines past successful cases to discuss the technology and application of thermal concentration and reduction of high salt wastewater.

Multi effect evaporation technology (MED)

The main working principle of Multi Effect Evaporation Technology (MED) is to use the secondary steam generated by the previous stage evaporator as the heat source for the subsequent stage evaporator to achieve multiple utilization of steam thermal energy, thereby improving the thermal energy utilization efficiency. The power steam heats and condenses the first effect evaporator before being reused. The wastewater is evaporated and concentrated by the first effect evaporator to form secondary steam as the heat source for the second effect evaporator. The concentrated wastewater enters the second effect evaporator for further concentration, and the secondary steam formed serves as the heat source for the third effect evaporator. Similarly, the concentrated wastewater enters the next evaporator for further concentration. Finally, the steam from the final effect evaporator enters the condenser and condenses into water, which is the distilled water after desalination. This condensed water has good water quality and can be used as circulating water for cooling towers or even boiler feed water; The final concentrated brine can continue to enter the subsequent concentration system or be directly subjected to solid-liquid separation through thickeners and centrifuges.

Normally, the energy-saving rate of multi effect evaporation increases with the increase of the number of effects, but the energy-saving effect becomes less significant when the number of effects is increased after the fifth effect. As the number of effects increases, the equipment investment cost of the MED system will also increase, and the heat transfer temperature difference loss for each effect will also increase, resulting in a decrease in effective heat transfer temperature difference and a decrease in equipment production intensity. Therefore, considering cost savings and energy consumption reduction, multi effect evaporation generally only achieves four effects, and the evaporation effect after four effects is relatively poor.

Although multi effect evaporation uses the secondary steam generated by the previous effect as the heating steam for the subsequent effect, the first effect still requires continuous supplementation of fresh steam. The multi effect evaporation process requires a large amount of steam consumption, and the evaporation treatment of 1 ton of water requires approximately 0.3 to 1 ton of steam. Due to the secondary steam generated by the final effect requiring condensation of water, the entire multi effect evaporation system is quite complex.

At present, our company's Multi Effect Evaporation Technology (MED) has been successfully applied in the fields of new energy industry, metal recycling and resource regeneration industry, pharmaceutical and chemical industry, food processing, and desulfurization wastewater in the power industry.

Steam mechanical recompression technology (MVR)

Steam mechanical recompression technology (MVR) refers to the process of compressing the secondary steam generated by the evaporator, which originally needs to be condensed by cooling water. After being compressed by a compressor, the pressure and saturation temperature are increased, the enthalpy is increased, and then sent to the evaporator as a heat source, replacing fresh steam for recycling. The latent heat of the secondary steam is fully utilized, and the secondary steam cooling water system is eliminated, saving a large amount of cooling water and achieving the goal of energy conservation and reducing operating costs.

The MVR evaporator consumes 25-55 kWh of electricity per ton of water evaporated. Compared to traditional multi effect evaporation technology, it saves 50-60% energy for the same solution. The energy consumption and production cost of MVR are significantly lower than those of conventional evaporators.

MVR evaporators have a wide range of applications, and all conventional evaporator applications are suitable for MVR evaporators. MVR evaporators have low evaporation, small temperature differences, and mild evaporation, making them more suitable for thermosensitive solutions. The solution has a short flow and residence time in the evaporator, and the solute should not deteriorate.

MVR evaporator is an energy-saving technology promotion project of the National Development and Reform Commission's Science and Technology Commission, which conforms to the scope of national energy-saving, emission reduction, and environmental protection high-tech promotion. At present, our company's MVR evaporation technology has been successfully applied in the new energy industry, environmental water treatment industry, rare and precious metal recycling and other fields.