Use of Zero-Discharge Technology to Recycle Salt in Desulfurization Wastewater

Abstract

As a series of laws and regulations governing the water drainage in coal-fired power plants have been implemented in China, the discharge requirements of desulfurization wastewater from coal-fired power plants are becoming increasingly stringent. Conventional desulfurization wastewater treatment can no longer satisfy the needs of the current zero-discharge policy. It is imperative to develop advanced desulfurization wastewater treatment technology. Low-temperature flue gas waste heat concentration and desulfurization wastewater technology, a current low-cost zero-discharge technology, has attracted the wide attention of the industry. When the wastewater is concentrated nearly 8–15 times, the concentration of chloride ions in the concentrated wastewater can be increased to nearly 240 g/mL. Moreover, the wastewater has strong acidity, and the pH is nearly 1.0–2.0. The effective use of this concentrated waste liquid is the key to the success of low-temperature flue gas waste heat concentration desulfurization wastewater treatment technology. Accordingly, this study suggests that the compound water purifying agent of polymeric ferric chloride (PFC) and polymeric ferric sulfate (PFS) can be prepared through the reaction of concentrated high-chlorine wastewater with red mud, and PFC and PFS have a synergistic effect on water purification. The prepared water purifiers outperform PFS or polyaluminum ferric sulfate (PAFS) in selectivity, sensitivity, and cost-effectiveness. Water purifier preparation experiments and flocculating effect comparison experiments were performed. The resource utilization of salt was achieved in the concentrated waste liquid. This technical route provides a novel insight into the reasonable transfer of salt in desulfurization wastewater and the preparation of compound water-purifying agents. This study proposes a technical process for zero discharge of desulphurization wastewater coupled with the preparation of a water purifier which changes the conventional preparation method of water purifiers. It solves the problems of high concentrations of chlorine salt and the large use and cost of pharmaceuticals in high-salt wastewater from power plants. Moreover, it used red mud and industrial waste acid resources to turn waste into a valuable resource and solved the problem of misplaced and wasted resources. Low-temperature flue gas waste heat was adopted to concentrate desulfurized wastewater, such that the concentration of chloride ions in wastewater was concentrated into high-chlorine wastewater. The compound water purifier of polymeric ferric chloride and polymeric ferric sulfate was prepared by the reaction of concentrated low-pH and high-chlorine wastewater with red mud and waste acid. The compound water purifier was used for sewage pretreatment to reduce turbidity and chemical oxygen demand (COD) content of sewage.