Application of zero-emission wastewater evaporation technology in power plants

Water is an indispensable natural resource for human survival and national economic development. While North my country, Northeast China, Northwest China, and Eastern Inner Mongolia are rich in coal resources, they suffer from severe water shortages. Furthermore, the limited water resources available are polluted, and the water quality of some sources is deteriorating. Water scarcity and pollution have become significant factors restricting the development of electricity in water-scarce regions of my country.
IGCC power plants employ water-saving technologies and other measures to improve water use efficiency and reduce production water consumption. To achieve zero discharge of industrial wastewater, water-saving processes, equipment, and systems are used, and technologies such as reverse osmosis (RO), electrodialysis (EDR), ultrafiltration (UF), and membrane reactor (MBR) are fully utilized to recycle and reuse production wastewater. However, some high-salinity wastewater cannot be reused. This high-salinity wastewater can be treated using evaporation, becoming one of the effective methods for achieving zero discharge of wastewater throughout the plant. After evaporation treatment, 90%–95% of the distilled water byproduct with a salt content of 5–10 mg/L can generally be recovered. A small amount of remaining concentrated sludge can be further treated by crystallization and drying or discharged into an evaporation pond for natural evaporation. The final salt residue solids are generally treated as ordinary solid waste and can be recycled or disposed of by landfill depending on their composition. The core technology of the zero-discharge wastewater evaporation solution is "forced circulation mechanical vapor compression recirculation evaporation technology," which is one of the most reliable and effective technological solutions for treating high-salinity wastewater in the world. When using mechanical compression recirculation evaporation technology to treat wastewater, apart from the initial start-up requiring external steam, the heat energy required for evaporating wastewater during normal operation is mainly provided by the heat energy released or exchanged during steam condensation and condensate cooling. There is no loss of latent heat during operation. The only energy consumed during operation is the electrical energy consumed by the pumps, steam compressors, and control systems that drive the circulation and flow of wastewater, steam, and condensate within the evaporator. When using steam as heat energy, evaporating one kilogram of water requires 554 kcal of heat energy. With mechanical compression evaporation technology, the typical energy consumption is 30 to 60 kWh of electricity required to treat one ton of saline wastewater, meaning that evaporating one kilogram of water requires only 50 kcal or less of heat energy. In other words, the efficiency of a single mechanical compression evaporator is theoretically equivalent to a 15-effect multi-effect evaporation system. Multi-effect evaporation technology can improve efficiency, but it also increases equipment investment and operational complexity.
To achieve zero wastewater discharge for the IGCC power plant, zero-discharge wastewater evaporation technology was employed. This technology addresses the challenge of using high-salinity wastewater that cannot be reused in engineering projects while still requiring zero discharge. In short, zero-discharge evaporation technology provides a viable, effective, and reliable zero-discharge solution for large industrial and mining enterprises in extremely water-scarce, ecologically fragile, and environmentally restricted areas. In coal-rich but extremely water-scarce regions such as Inner Mongolia, Shanxi, Shaanxi, Ningxia, and Xinjiang, zero-discharge solutions will also help local governments and enterprises effectively address the challenges of balancing local economic development with water scarcity and stringent environmental emission restrictions.