Full-Scale Experimental Study of Groundwater Softening in a Circulating Pellet Fluidized Reactor

Abstract

The softening effect of a new type of circulating pellet fluidized bed (CPFB) reactor on groundwater was studied through a full-scale experiment. The operation of the CPFB reactor in the second water plant in Chang’an District in Xi’an China was monitored for one year, and the results were compared with those for the Amsterdam reactor in The Netherlands. The removal efficiency of Ca2+ in the CPFB reactor reached 90%; the removal rate of total hardness was higher than 60%; effluent pH was 9.5–9.8; the turbidity of the effluent and the turbidity after boiling were lower than 1.0 NTU; the unit cost was less than €0.064 per m3; and the softened effluent was stable. The pellets in the CPFB reactor were circulated, providing higher crystallization efficiency. The diameter of the discharged pellets reached between 3–5 mm, and the fluidized area height of the CPFB reactor was 4 m. The performance parameters of the CFPB reactor were optimized.

Pellet Softening Process for the Removal of the Groundwater Hardness; Modelling and Experimentation Modelling and experimental of groundwater shortening by a pellet reactor

“…The density of pellets decreased as bed height increased. This agrees with Hu et al [25] studies which showed that the highest dense pellets are settled at the bottom of the reactor while the least dense pellets are fluidized at the upper part of the reactor. Figures 14,15,and 16 show fair agreement between modeled and measured concentrations of Ca +2 ions.…”

“…Then, a comparison between crystal growth kinetics of low soluble salts and the lean fluidized -bed crystallizers was demonstrated. As a consequence, the two-step growth model was found to be convenient for the assessment of crystal growth rates in the design of a liquid fluidized bed reactor [8]. Schagen, et al [9] successfully simulated the pellet reactor and showed the effect of operational parameters (particle size and height of fluidized bed) on the removal efficiencies of the total hardness, calcium ions, and magnesium ions.…”

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

“…As shown in Figure 4, the total cost of the chemicals (NaOH + H 2 SO 4 ) per ton of water ranges between $0.06 and $0.10 when the removal rate of Ca 2+ varies between 75% and 90%. During actual operation, the hardness removal effect must be adjusted to reduce costs [11].…”

“…To replenish the circulating water, fresh water is first injected into the CPFB system and then discharged into the circulating-water pool, accompanied by the disposal of calcium carbonate particles. Details of the operating procedure and reaction processes can be found in existing literature [11]. The calcium carbonate particles disposed by the system are transported directly from the collection tank to the power plant’s desulfurization system to be used as a desulfurizer.…”

“…The chemical crystallization 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 the circulating water. For example, Hu et al applied CPFBs to soften groundwater and determined the operating parameters under specific water quality conditions [11]. They further studied the growth rate of the particles in Amsterdam’s crystallization fluidized bed reactor, as well as the relationship between the growth rate of the bed, rising flow rate, particle size, and supersaturation conditions on a pilot scale.…”