It is of significance to intensively investigate the solid-liquid equilibrium of the NH3-CO2-SO2-K2SO4-H2O system to assess the novel aqueous NH3 based CO2 and SO2 combined capture process proposed in our previous work. In this work, the solubility of K2SO4 in aqueous NH3 at various temperatures, CO2 and SO2 loadings, and NH3 concentrations was predicted using Aspen Plus with a developed thermodynamic model package, which can accurately simulate the vapor-liquid equilibrium and the solid-liquid equilibrium of the combined CO2 and SO2 capture system. The results indicate that the solubility of K2SO4 increases with temperature and CO2 loading, but decreases with NH3 concentration. The precipitation starting point of K2SO4 shift to higher temperature with the increasing of SO2 loading and NH3 concentration. It is favorable to collect K2SO4 precipitates at lower CO2 loading and temperature, and higher SO2 loading and NH3 concentration.

•The vapor–liquid equilibrium of CO2 in CO2 and SO2 loaded aqueous ammonia (NH3–CO2–SO2–H2O system) was investigated.•The electrolyte NRTL model was carried out to predict the vapor–liquid equilibrium data of the NH3–CO2–SO2–H2O system and the comparison between experimental results and model predictions shows good agreement.•The detailed analysis of the aqueous ammonia based CO2 and SO2 capture process shows CO2 absorption capacity and driving force are reduced, but the CO2 desorption capacity and driving force increase with SO2 loading.Vapor–liquid equilibrium (VLE) of CO2 in CO2 and SO2 loaded aqueous ammonia (NH3–CO2–SO2–H2O system) was investigated in this study. The effect of SO2 loading (mol SO2/mol NH3 in solvent) on VLE of CO2 was measured in the range of 0.1–0.3 mol SO2/mol NH3 in 2.5–7.5 wt.% aqueous ammonia at 20 °C, 40 °C and 60 °C, using a Fourier transform infrared (FT-IR) gas analysis method with a pressure determination stirred tank apparatus. The equilibrium vapor pressures of CO2 in the aqueous ammonia with no SO2 content were compared with experimental data in the public domain. The electrolyte NRTL model was carried out to predict the VLE data using Aspen Plus. The comparison between experimental results and model predictions showed good agreement. The total equilibrium pressure, NH3 equilibrium partial pressure and liquid speciation in the NH3–CO2–SO2–H2O system were calculated and analyzed. It was found that the total equilibrium pressure decrease slightly at lower CO2 loading (mol CO2/mol NH3), but increase sharply at higher CO2 loading with SO2 loading. The NH3 equilibrium partial pressure, and the NH3 and NH2COO− molar concentrations decrease with SO2 loading. However, the NH4+ and HCO3− molar concentrations increase with SO2 loading. Further CO2 equilibrium partial pressure analysis shows that the driving force and solvent capacity of CO2 absorption decrease with SO2 loading, while the desorption capacity and driving force of CO2 at high temperature significantly increases with SO2 loading, which has the potential to reduce the regeneration energy of CO2.

CO2 capture from coal-fired power plants using a monoethanolamine (MEA) solution is one of the most promising technologies for CO2 abatement. The MEA absorption process for CO2 capture from power plants is an inherently dynamic system that is affected by the load variations in the upstream power plant because of fluctuations in electricity demand. This paper presents an experimental study of the dynamic behavior of a stripping column after various disturbances. Tests of negative and positive steps of different magnitudes in the reboiler heat duty were conducted to determine the process gain and time constant. The dynamic behavior of the desorption process was also investigated using ramp tests of different magnitude in the reboiler heat duties and feed solvent temperatures. The results show that the desorption process response to the heat duty could be approximated as a first-order time delay model. The solvent holdup time in the reboiler was the dominant factor controlling the system response time. The results also show that the CO2 capture is a nonlinear process.

An aqueous solution of 2 M 1,4-butanediamine (BDA) blended with 4 M 2-(diethylamino)-ethanol (DEEA) has been proven to be a promising solvent in previous work, and BDA is a potential amine to accelerate the reaction rate of DEEA with CO2. In the present work, kinetics of CO2 absorption into aqueous solutions of BDA, DEEA, and their mixtures were studied using a wetted wall column (WWC) at 25, 40, and 60 °C with the driving force of 3–35 kPa. The BDA concentrations were 1, 2, and 3 M, with DEEA concentrations of 2, 3, 4, and 5 M, while those of the BDA/DEEA mixtures were 1 M BDA/4 M DEEA, 2 M BDA/3 M DEEA, 2 M BDA/4 M DEEA and 2.54 M BDA/2.73 M DEEA. The results show that the reaction rate constant of BDA is larger than most of the amines but lower than piperazine. BDA can largely accelerate the reaction of solvents with CO2, and the overall reaction of their mixtures can be regarded as a reaction between CO2 and DEEA in parallel with the reaction of CO2 with BDA.

Densities of and N2O solubilities in aqueous solutions of 1,4-butanediamine (BDA), 2-(diethylamino)-ethanol (DEEA), and their aqueous mixtures were measured at (298.15, 313.15, and 333.15) K, and viscosities were measured at (298.15, 303.15, 313.15, 323.15, and 333.15) K. The experiments cover the mole fraction ranges (1.95–14.3 mol %) BDA, (2.01–19.3 mol %) DEEA, and (3.63–16.7 mol %) BDA + (2.62–22.2 mol %) DEEA in the blended solutions. The results were compared with available data in the literature. The experimental density and viscosity data were correlated using two semi empirical correlations in the literature as functions of temperature and concentration of BDA and DEEA.

Acidic impurities in the flue gas, such as SO2 and NOx, are supposed to promote amine degradation in the amine scrubbing process for CO2 capture. This work investigates the effect of these acidic gases on thermal degradation of MEA (monoethanolamine) by preloading additives, which are Na2SO3, SO2, H2SO4, and HNO3, respectively. MEA concentration was 4.4 mol/kg. CO2 loading was 0.4 mol/(mol of MEA). Experiment temperature varied from 120 to 150 °C. Ion chromatography (IC) is the main analytical method. The results show that the MEA thermal degradation rate was not affected by these additives. Ammonium became an important product in the experiment with SO2 or HNO3 loading. Sulfate was stable in the experiment. In the experiment with SO2 loading, most of the sulfur remained dissolved in the solution after degradation but could not be detected by IC. A lower pH value will speed up sulfite degradation.

A lab amine-based chemical absorption pilot plant for CO2 capture from coal-fired power plants was built. The character of CO2 capture of the new blended amine absorbent was studied in the pilot plant, under the condition of prolonged operation. Three campaigns were conducted. One campaign was the baseline experiment to evaluate the cyclic absorption and desorption character of the absorbent during 500 h with 12 vol % CO2 and 18 vol % O2. Other two campaigns were performed to evaluate the influence of SO2 on the absorption character of the absorbent, with 214 and 317 ppm SO2, respectively. The CO2 reaction rate and mass transfer behavior were analyzed for the three campaigns. The results show that the CO2 removal efficiency is in inverse proportion to reaction time, and the results of amine degradation and heat stable salts formation are in accordance with it. The SO2 removal efficiency is almost 100%. After the addition of SO2 to the simulated flue gas, there is more serious amine degradation and more heat stable salts formation. Four kinds of organic acid salts, such as formate, acetate, oxalate, and glycolate, were detected with and without SO2. The analysis on mass transfer and CO2 reaction rate indicates that the free amine concentration reduction is the main reason for the CO2 removal efficiency decreases. The combination of SO2 with amine results in the decrease in free amines.

We used Raman spectroscopy to systematically and comprehensively measure the concentrations of the main ion components (NH2COO−, HCO3−, and CO32−) in the CO2−NH3−H2O system for an initial total ammonia concentration [A] = 0.69, 0.88, 1.09, 1.34, 1.60, and 2.10 mol·L−1 and CO2 loading [C]/[A] = 0.18, 0.35, 0.43, 0.50, and 0.67, respectively. The experimental data were processed using two existing theoretical methods, and the analysis on results allowed us to propose a number of improvements based on these theoretical methods. Experimental results show that upon increasing [C]/[A], the ratios of [NH2COO−] and [CO32−] to total carbon decrease linearly, whereas the ratio of [HCO3−] to total carbon increases linearly. The reaction process can be divided into three steps. Considering the impacts of experiment errors, [A] has little effect on the relative composition of the system in the range we studied. Results calculated with a revised theoretical method are in better agreement with the experimental data.

•FGD gypsum can be used to ameliorate saline-alkali soil, which has been applied for around 120 km2 in China.•The application of FGD gypsum in saline-alkali soil can enhance the productivity of the plants grown on it, and improve the physical and chemical properties of the soil.•The concentrations of the heavy metals in FGD gypsum, soil, and plants grown on the soil are accord with the national standard.•Soil organic carbon content increased a lot in the saline-alkali soil after amelioration.Flue gas desulfurization (simplified as FGD) gypsum, a kind of byproduct from wet FGD process of coal-fired power plants, was used to ameliorate saline-alkali soil. The FGD gypsum can react with the main content of saline-alkali soil to improve the soil properties. The technology has been applied for around 120 km2 in China with impressive results. Detailed field studies showed the productivity of the plants grown in the ameliorated soil increased a lot, and also the physical and chemical characteristics of the soil improved evidently. Both field and laboratory studies showed the technology is safe considering the heavy metal concentration in the soil and plants grown on it. The SOC (soil organic carbon) analysis revealed that the saline-alkali soil amelioration can fix more carbon, so contributing to the global warming mitigation. It was concluded that the saline-alkali soil amelioration with FGD gypsum is a promising technology, and worthy of widely application in the world.

•A new application of aqueous NH3 based combined CO2 and SO2 process was proposed.•A thermodynamic model simulated the heat of absorption and the K2SO4 precipitation.•The CO2 content can be regenerated in a stripper with lower heat of desorption.•The SO2 content can be removed by K2SO4 precipitation from the lean NH3 solvent.A new application of aqueous NH3 based post-combustion CO2 and SO2 combined capture process was proposed to simultaneously capture CO2 and SO2, and remove sulfite by solid (K2SO4) precipitation method. The thermodynamic model of the NH3-CO2-SO2-K2SO4-H2O system for the combined CO2 and SO2 capture process was developed and validated in this work to analyze the heat of CO2 and SO2 absorption in the NH3-CO2-SO2-H2O system, and the K2SO4 precipitation characteristics in the NH3-CO2-SO2-K2SO4-H2O system. The average heat of CO2 absorption in the NH3-CO2-H2O system at 40 °C is around −73 kJ/mol CO2 in 2.5 wt% NH3 with CO2 loading between 0.2 and 0.5 C/N. The average heat of SO2 absorption in the NH3-SO2-H2O system at 40 °C is around −120 kJ/mol SO2 in 2.5 wt% NH3 with SO2 loading between 0 and 0.5 S/N. The average heat of CO2 absorption in the NH3-CO2-SO2-H2O system at 40 °C is 77, 68, and 58 kJ/mol CO2 in 2.5 wt% NH3 with CO2 loading between 0.2 and 0.5 C/N, when SO2 loading is 0, 0.1, 0.2 S/N, respectively. The solubility of K2SO4 increases with temperature, CO2 and SO2 loadings, but decreases with NH3 concentration in the CO2 and SO2 loaded aqueous NH3. The thermodynamic evaluation indicates that the combined CO2 and SO2 capture process could employ the typical absorption/regeneration process to simultaneously capture CO2 and SO2 in an absorber, thermally desorb CO2 in a stripper, and feasibly remove sulfite (oxidized to sulfate) content by precipitating K2SO4 from the lean NH3 solvent after the lean/rich heat exchanger.Download high-res image (167KB)Download full-size image