Prediction of inlet SO2 concentration of wet flue gas desulfurization (WFGD) by operation parameters of coal-fired boiler

Circulating fluidized bed (CFB) boilers with wet flue gas desulfurization (WFGD) system is a popular technology for SO₂ removal in the coal-fired thermal power plant. However, the long response time of continues emission monitoring system (CEMS) and the hardness of continuously monitoring the coal properties leads to the difficulties for controlling WFGD. It is important to build a model that is adaptable to the fluctuation of load and coal properties, which can obtain the SO₂ concentration ahead CEMS, without relying on coal properties. In this paper, a prediction model of inlet SO₂ concentration of WFGD considering the delay between the features and target based on long-short term memory (LSTM) network with auto regression feature is established. The SO₂ concentration can be obtained 90 s earlier than CEMS. The model shows good adaptability to the fluctuation of SO₂ concentration and coal properties. The root-mean-squared error (RMSE) and R squared (R²) of the model are 30.11 mg/m³ and 0.986, respectively. Meanwhile, a real-time prediction system is built on the 220 t/h unit. A field test for long-term operation has been conducted. The prediction system is able to continuously and accurately predict the inlet SO₂ concentration of the WFGD, which can provide the operators with an accurate reference for the control of WFGD.

O3 oxidation combined with semi-dry method for simultaneous desulfurization and denitrification of sintering/pelletizing flue gas

With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies, the emission of pollutants such as SO₂ and NO_x has received unprecedented attention. Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process, several semi-dry desulphurization technologies such as flue gas circulating fluidized bed (CFB), dense flow absorber (DFA) and spray drying absorption (SDA) are briefly summarized. Moreover, a method for simultaneous treatment of SO₂ and NO_x in sintering/pelletizing flue gas by O₃ oxidation combined with semi-dry method is introduced. Meantime, the effects of key parameters such as O₃/NO molar ratio, CaSO₃, SO₂, reaction temperature, Ca/(S+2N) molar ratio, droplet size and approach to adiabatic saturation temperature (AAST) on denitrification and desulfurization are analyzed. Furthermore, the reaction mechanism of denitrification and desulfurization is further elucidated. Finally, the advantages and development prospects of the new technology are proposed.

Study on sulfur migration in activated carbon adsorption-desorption cycle: Effect of alkali/alkaline earth metals

Activated carbon (AC) has been widely used in the removal of SO₂ from flue gas owing to its well-developed pore structure and abundant functional groups. Herein, the effect of alkali/alkaline earth metals on sulfur migration was investigated based on the dynamic adsorption and temperature programmed desorption experiment. The adsorption and desorption properties of six types of AC (three commercial and three laboratory-made) were carried out on a fixed-bed experimental device, and the physical and chemical properties of samples were determined by X-ray fluorescence, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray, and X-ray photoelectron spectroscopy analysis. The experimental results showed that the adsorbed SO₂ cannot be completely desorbed by increasing the regeneration temperature (350 - 850°C), while the SO₂ fixed in the AC combines with the Ca-based minerals in the ash to form a stable sulfate. For different samples, higher ash content, higher CaO content in the ash and a more developed pore structure lead to a higher SO₂ fixation rate. Moreover, the multiple adsorption-desorption cycles experiment showed that the effect of SO₂ fixation is mainly reflected in the first cycle, after which the adsorption and desorption amount are approximately the same. This study elucidates the effect of alkali/alkaline earth metals on the adsorption-desorption cycle of AC, which provides a deeper understanding of sulfur migration in the AC flue gas desulfurization process.

Ultrasonic Power to Enhance Limestone Dissolution in the Wet Flue Gas Desulfurization Process. Modeling and Results from Stepwise Titration Experiments

The goal of this work is to assess the application of ultrasonic power to the reactive dissolution of limestone particles in an acidic environment; this would represent a novel method for improving wet Flue Gas Desulfurization industrial systems. In this study a stepwise titration method is utilized; experiments were done by using different particle size distributions with and without the application of ultrasound. The use of ultrasonic power sensibly affected the reaction rate of limestone and its dissolution; a major difference could be observed when samples from the Wolica region in Poland were studied. In this case, the overall dissolution rate was found to increase by more than 70%. The reactive dissolution of limestone does not follow the same mathematical model when sonication is in effect; in this case, an extra Ultrasonic Enhancement Constant was introduced. It was demonstrated that the dissolution is proportional to an Effective Reaction Surface and, therefore, surface interactions should also be taken into consideration. For this purpose, a study is presented here on the Z-potential and electrophoretic mobility of limestone samples measured in aqueous dispersions by means of Laser Doppler Micro-Electrophoresis.

Wet flue gas desulfurization using alkaline agents

The continued great dependency on fossil fuels entails increasing SO

A new concept of desulfurization: the electrochemically driven and green conversion of SO2 to NaHSO4 in aqueous solution

A new concept of desulfurization was developed by designing a series of electrochemical reactions to drive an SO2 absorption-and-conversion process in aqueous solution, hence the SO2 in gas was eventually converted to a valuable chemical of NaHSO4. A model experiment of chemically substantiating this concept includes two steps: (I) absorption of SO2 gas by aqueous solution and oxidation of the absorbed SO2 to SO4(2-) by air and (II) transformation of the SO4(2-) to NaHSO4. The experiment demonstrated that in Step I, the cathodic reduction of 02 from ambient air scavenged the H+ released due to the SO2 absorption and its further oxidation, which thereby were accelerated. Meanwhile H2O2 as a cathodic product further enhanced the SO2 oxidation. In Step II, the anodic oxidation of H2O supplied H+ and allowed the NaHSO4 formation through balances of electrons and mass. Thereafter, a pH range of 5.0-6.0 for the SO2 oxidation was optimized, and an electrochemically driven process for the SO2 conversion to NaHSO4 was proposed. Sustainability evaluation indicated that this concept complies with the principles of green chemistry and potentially enables the SO2 conversion from flue gas to NaHSO4 as a value-added process.