Limestone-gypsum Flue Gas Desulfurization Process Research Articles

Limestone-Gypsum Wet Flue Gas Desulfurization Wastewater Treatment

In this paper, chemical precipitation process is used for the treatment of the desulfurization wastewater generated by the waste gas treatment system of the limestone-gypsum flue gas desulfurization process of a thermal power plant. After one year of operation, the technology is reliable and stable. The removal rate of suspended matter, COD, fluoride, mercury and sulfate reached 99.5%, 98.3%, 87.5%, 99.8% and 85.6% respectively, and the corresponding effluent concentrations were 54 mg/L, 20 mg/L and 9.6 mg/L, 0.04 mg/L, 980 mg/L. Finally, the effluent quality of the system is better than the discharge requirements of “Discharge standard of wastewater from limestone-gypsum flue gas desulfurization system in fossil fuel power plants” (DL/T997-2006). In addition, the total electricity and chemical charges per ton of wastewater treatment were 6.50 yuan, which is lower than most of the engineering project under the same discharge requirements. Therefore, the process has certain engineering advantages.

Promotion of conversion activity of flue gas desulfurization gypsum into α-hemihydrate gypsum by calcination-hydration treatment

The massive accumulation of flue gas desulfurization (FGD) gypsum produced in the wet limestone-gypsum flue gas desulfurization process not only encroaches on lands but also causes serious environmental pollution. The preparation of α-hemihydrate gypsum (α-HH) is an important way to achieve high-value utilization of FGD gypsum. Although the glycerol-water solution approach can be used to produce α-HH from FGD gypsum under mild conditions, the transition is kinetically unfavorable in the mixed solution. Here, an easy pretreatment was used to activate FGD gypsum by calcination and hydration to readily complete the transition. The pretreatment deteriorated the crystallinity of FGD gypsum and caused it to form small irregular flaky crystals, which dramatically increased the specific surface area. Additionally, most of the organics adsorbed onto FGD gypsum surfaces were removed after pretreatment. The poor crystallinity, increased specific surface area, and elimination of organics adsorbed onto crystal surfaces effectively improved the conversion activity of FGD gypsum, thereby promoting dihydrate gypsum (DH) dissolution and α-HH nucleation. Overall, the phase transition of FGD gypsum to α-HH is facilitated.

Particle Separation with a Hydro-Cyclone Separator in a Wet Limestone Gypsum FGD Process

A hydro-cyclone was applied to the separation of gypsum, a byproduct of the wet limestone gypsum flue gas desulfurization (FGD) process, that uses limestone as the raw material. Using a high slurry concentration, similar to that used in an actual plant, the effect of the inlet shape and ceiling clearance of the hydro-cyclone was examined, and a model for predicting the efficiency of separation is proposed.The results indicate that the 50% cut size decreases when the inlet width ratio is decreased. Over the entire range of inlet width ratio, the limestone content of the blow-down flow decreased by approximately half, compared with that of the feed, and it was confirmed the purity of the gypsum could be improved by decreasing the limestone content.When the ceiling clearance of the hydro-cyclone was changed, an optimum ceiling clearance for obtaining a minimal cut size was found.A model for predicting the slurry concentration that is proportional to the solid throughput of a hydro-cyclone and the improvement in gypsum purity in an actual plant is proposed. The results of this calculation model agreed well with experiment data.

D304 DEVELOPMENT OF DOUBLE-CONTACT-FLOW SCRUBBER FOR FLUE GAS DESULFURIZATION

Chugoku Electric Power Co., Inc. and Heavy Mitsubishi Heavy Industries, Ltd. developed a new type of absorber, the Double-Contact-Flow Scrubber (DCFS). DCFS is an easily maintainable absorber of simple construction with low initial cost and low power consumption for the wet limestone-gypsum flue gas desulfurization process. Absorbent slurry is spouted up from special type of nozzles located at the bottom of the absorber, creating a pillar of absorbent slurry to achieve a good gas-liquid contact. The only internal components of the absorber are the header pipes and nozzles, resulting in the simplicity of construction with lower cost, as well as easy maintenance due to the lack of scale deposits. This paper shows the performance results of DCFS operation.

Effect of Ammonium Concentration on SO2 Absorption in a Wet Limestone Gypsum FGD Process.

To investigate the effect of the ammonium concentration on SO2 absorption with a chemical reaction in the wet limestone-gypsum flue gas desulfurization (FGD) process, the SO2 absorption rate in limestone slurry was studied by using a stirred tank reactor at a constant pH, high temperature (50°C) and under the presence of ammonium. An absorption model with a reaction plane and the presence of ammonium in the liquid based on the film model was also proposed for an actual FGD plant.For the SO2 absorption rate depending on the concentration of ammonium, the experimental values agreed quite well with the results calculated with the absorption model, taking the presence of ammonium in the liquid into consideration.

Catalytic oxidation of calcium bisulfite in the wet limestone–gypsum flue gas desulfurization process

A study on the oxidation of calcium sulfite catalyzed by Mn 2+ is presented in this paper. A laboratory-scale well-mixed thermostated reactor was used, with continuous feeding of both gas and liquid phase. The gas phase was a mixture of oxygen and nitrogen, with O 2 partial pressure varying from 5.1 to 40.5 kPa. The liquid phase was obtained by mixing inside the reactor two separate aqueous solutions, one obtained by dissolving Ca(OH) 2 into a SO 2 solution, and the other one containing manganous sulfate. The temperature was kept constant in all the experiments at 45°C. The results show that increasing catalyst concentration, the transition takes place from slow kinetic to slow diffusional and eventually to fast reaction regime.

Limestone-gypsum flue gas desulfurization process: Hiroshi Kuroda, Tsukasa Nishimura, Taiki Hashimoto, Masakatsu Nishimura, Osamu Kanda, Shigeru Nozawa, Kure, Japan assigned to Babcock-Hitachi Kabushiki Kaisha

Limestone-gypsum flue gas desulfurization process: Hiroshi Kuroda, Tsukasa Nishimura, Taiki Hashimoto, Masakatsu Nishimura, Osamu Kanda, Shigeru Nozawa, Kure, Japan assigned to Babcock-Hitachi Kabushiki Kaisha