Search Results (8)

Zero-liquid discharge (ZLD) of desulfurization wastewater from coal-fired power plants is a critical challenge in the thermal power industry. Flash evaporation technology provides an efficient method for wastewater concentration and the recovery of high-quality freshwater resources. In this study, numerical simulations of the high-temperature and high-pressure spray flash evaporation process within a flash tank were conducted using the Discrete Phase Model (DPM) and a self-developed heat and mass transfer model for superheated droplets under depressurization conditions. The effects of feedwater temperature, pressure, nozzle spray angle, and mass flow rate on spray flash evaporation characteristics were systematically analyzed. Key findings reveal that (1) feedwater temperature is the dominant factor, with the vaporization rate significantly increasing from 19.78% to 55.88% as temperature rises from 240 °C to 360 °C; (2) higher pressure reduces equilibrium time (flash evaporation is complete within 6 ms) but shows negligible impact on final vaporization efficiency (stabilized at 33.93%); (3) increasing the spray angle provides limited improvement to water recovery efficiency (<1%); (4) an optimal mass flow rate exists (0.2 t/h), achieving a peak vaporization rate of 42.6% due to balanced evaporation space utilization. This work provides valuable insights for industrial applications in desulfurization wastewater treatment. Full article

Zero Liquid Discharge (ZLD) is a wastewater management strategy that eliminates liquid waste while maximizing water use efficiency. This article reviews the primary ZLD technologies used for desulfurization wastewater (DWW) treatment in coal-fired power plants. These technologies include the thermal process and the membrane process. The thermal process includes “concentrated crystallization” technology and “gas evaporation and drying” technology. The paper also highlights recent advances in membrane technology for power plant wastewater treatment. The advantages and limitations of each technique are discussed. Membrane technology is considered a promising solution for wastewater recycling, while thermal technology offers easy operation and maintenance without the need for pretreatment. Finally, the paper outlines possible future directions for the treatment of DWW. Full article

Desulfurization wastewater is industrial wastewater with a high salt content, high metal ions, and high hardness produced by flue gas desulfurization of the limestone-gypsum method in coal-fired power plants. This paper summarizes the source of desulfurization wastewater, water quality characteristics, water quality impacts, and other factors, combined with the current status of research worldwide to introduce the advantages and shortcomings of the existing desulfurization wastewater treatment technology. In addition, zero liquid discharge technology as a novel method to treat desulfurization wastewater is also summarized. It mainly includes evaporation and crystallization, flue gas evaporation, membrane distillation removal, etc. Finally, this manuscript looks forward to the future development direction of desulfurization wastewater based on its existing technology and emission standards. Full article

Spraying flue gas desulfurization wastewater into flue ducts is an emerging technology that is receiving extensive attention in thermal power plants. In order to study the evaporative performance of wastewater-atomizing droplets under variable working conditions, a combined Euler–Lagrange model was developed to demonstrate the thermal behavior of FGD wastewater spray evaporation in flue gas. The effects of several control factors under various operating conditions were numerically determined and validated against experimental data. Due to the complicated parameters and various other conditions, a least-square support vector machine (LSSVM) model relying on numerical results was used to anticipate the evaporation rate of the droplets. We prove that the LSSVM model has high prediction accuracy for the evaporation rate at different cross-sections of flue under a different operating situation. The conclusion is that for the sake of improving the quality of evaporation, the spacing between two adjacent nozzles should be increased while increasing the flow rate. However, using a higher flue gas temperature, higher initial temperature and smaller diameter of droplets can shorten the time and distance of complete evaporation. In summary, this research analysis can be used effectively to determine the design of the FGD wastewater flue gas evaporative process in thermal power plants. Full article

The desulfurization wastewater evaporation technology with flue gas has been widely applied to dispose of desulfurization wastewater. This paper investigates the effect of flue gas flow rate and temperature, wastewater flow rate and initial temperature, and droplet size on the evaporation performance of the desulfurization wastewater in a spray drying tower without deflectors. The results show that the flue gas flow rate and temperature affect the evaporation performance of desulfurization wastewater. The larger flow rate and higher temperature of flue gas correspond to the faster evaporation speed and the shorter complete evaporation distance of the wastewater droplet. Decreasing the flow rate and increasing the initial temperature of the desulfurization wastewater is advantageous to enhance the evaporation speed and shorten the complete evaporation distance of the wastewater droplet. Reducing the droplet size is beneficial to improve the evaporation performance of the desulfurization wastewater. The orthogonal test results show that the factors affecting droplet evaporation performance are ranked as follows: flue gas flow rate > wastewater flow rate > flue gas temperature > wastewater initial temperature > droplet size. Considering the evaporation ratio and the complete evaporation distance, the optimal setting is 14.470 kg/s for flue gas flow rate, 385 °C for flue gas temperature, 0.582 kg/s for wastewater flow rate, 25 °C for wastewater initial temperature, and 60 μm for droplet size. These studied results can provide valuable information to improve the operational performance of the desulfurization wastewater evaporation technology with flue gas. Full article

Wet flue gas desulfurization (WFGD) wastewater treatment is a key problem in coal-fired plants. Traditional chemical precipitation methods cannot reach zero-liquid discharge (ZLD). In this paper, a new technology using the low-rank heat from flue gas to concentrate the wastewater for ZLD is proposed. A scrubber was built to verify the concentrating process, and the characteristics of the concentrated water were analyzed. The concentrated water was neutralized by adding Ca(OH)₂ to raise the pH value. The wastewater can be concentrated 10~25 times to reduce the flow rate. The characteristics of the concentrated wastewater were studied by dosing lime. Then, liquid and solids were separated by filter pressing, the liquid was mainly composed of CaCl₂, which accounts for 73.6%. The sludge is composed of CaSO₄ and Mg(OH)₂, depending on the lime consumption of the dosing process. Finally, the filter liquor after the filter press was mixed with ash to reach zero liquid discharge, and the sludge could be burnt after mixing with the coal or disposed by third-part vendor. This technology is demonstrated in one 600 MW unit and shows a high system reliability. The clean water is recycled by the WFGD wastewater during the evaporation. Binding on the environmental policies and large market demand of the WFGD wastewater, this technology shows a great application prospect in the future. Full article

As an advanced treatment of desulfurization wastewater, centrifugal spray drying technology, which can achieve a zero liquid discharge target, has attracted wide attention and great interest in recent years. However, the results of previous studies were based on the laboratory-scale centrifugal spray dryer. In order to study the evaporation characteristics of desulfurization wastewater and the parameter optimization of the dryer, the evaporation model of wastewater droplets was established. The effects of parameters such as the angle of the deflectors, gas–liquid ratio and atomizer speed on droplet evaporation were studied by numerical simulation. The results show that with the increase in the angle of the deflectors, the swirl effect of flue gas flow field is more obvious and the time and axial distance required for the complete evaporation of the droplets are shorter. Reducing the gas–liquid ratio will make the average evaporation time longer. Moreover, a higher atomizer speed is helpful for the evaporation of the droplets. The optimum gas–liquid ratio and rotational speed are found to be 9300 m³/Nm³ and 16,000 rpm, respectively. Full article

Limestone-gypsum wet flue gas desulfurization (WFGD) often produces a certain amount of wastewater with complex water quality and heavy metal pollution which should be treated properly before release. Spaying the desulfurization wastewater into flue duct and using exhausted flue gas heat for evaporation is a promising and economical technology for achieving zero wastewater discharge in thermal power plant. To enable a more in-depth understanding on evaporation of FGD wastewater spray, a visual wind tunnel test rig based on the atomized droplet laser measuring system was built to reveal the impact factors on droplet thermal-fluid behavior. The dominant impact factors such as compressed air pressure and flow rate in air-blast spray nozzle, hot air temperature and velocity in the evaporation tunnel were analyzed to discuss the droplet size distribution and evaporation performance through alternating operate condition. A discrete mathematical model that combines both Eulerian and Lagrangian framework was established to validate the experiment result. It is concluded that introducing high pressure compressed air into the nozzle can contribute to the dispersion of droplets and enhance the evaporation rate. Proper flow rate in spray nozzle is required to avoid incomplete droplets evaporation. Air temperature and velocity in the evaporation tunnel apply positive impact on droplet size distribution and evaporation performance. Numerical simulation results of both dominant factors impact on evaporation behavior and total evaporation rate showed consistency with the experimental outcome. Full article