Application of Chemical Crystallization Circulating Pellet Fluidized Beds for Softening and Saving Circulating Water in Thermal Power Plants

Abstract

The circulating pellet fluidized bed (CPFB) softening method is a highly efficient and environmentally friendly softening technology that can be used to reduce water hardness during the pretreatment process of circulating water in thermal power plants. The performance of chemical crystallization CPFB reactors was tested for increasing the concentration ratio and softening the circulating water in a thermal power plant in Dingzhou, Hebei. The results show that usage of CPFB reactors removed water hardness and Ca2+ ions with efficiencies exceeding 60% and 90%, respectively. The size of the particles discharged from the reactors was approximately 1–3 mm, and the content of CaO in these particles was found to be greater than 50%. All the discharged particles were reused in the desulfurization system in the power plant. The operational cost of the CPFB system is US$0.074 per cubic meter of water. After adopting the proposed CPFB softening method in the Dingzhou Power Plant, the concentration ratio of the circulation cooling water was increased from 4.5 to more than 9. In addition, the amount of replenished water and sewage discharge were both reduced by 150 m3/h, and the amount of scale inhibitor used in the system was reduced by more than 30%. These improvements contribute to approximately US$200,000 in annual savings in the power plant. In summary, the CPFB softening method demonstrated a high hardness removal rate, strong economic benefits, and remarkable environmental and social benefits. Therefore, this method seems ideal for softening replenished circulating cooling water, increasing the concentration ratio of the water and achieving zero liquid discharge (ZLD) in thermal power plants.

Review of Techniques to Reduce and Prevent Carbonate Scale. Prospecting in Water Treatment by Magnetism and Electromagnetism

“…On the other hand, addition of acids such as sulphuric acid to the fluid during the water pre-treatment process in refrigeration systems is another technique which prevents scale precipitation because it converts calcium bicarbonate into more stable and soluble calcium sulphate; it also contributes to the formation of CO 2 [40]. Other techniques based on the addition of compounds with metals are no longer used, such as molybdate, which reacts with other organic and inorganic compounds.…”

Numerical Investigations of Hydrodynamics in a Liquid-Solid Fluidized Bed

“…The water hardness degree is an important water quality indicator, expressed in terms of the calcium carbonate (CaCO3) concentrations. Indeed, a total hardness concentration above 4 mg/L can affect human and animal health, power generation, and equipment corrosion rate [1,2]. The water softening process is an efficient method to reduce the concentrations of hard ions (Ca 2+ and Mg 2+ ) in water, thus becoming increasingly important for economic, operational, and safety concerns [3,4].…”