Search Results (8)

This work used piperazine (PZ) as a base solvent, blended individually with five amines, which were monoethanolamine (MEA), secondary amines (DIPAs), tertiary amines (TEAs), stereo amines (AMPs), and diethylenetriamine (DETA), to prepare mixed solvents at the desired concentrations as the test solvents. A continuous bubble-column scrubber with one stage (1 s) was first used for the test. Six parameters were selected, including the type of mixed solvent (A), the ratio of mixed solvents (B), the solvent feed rate (C), the gas flow rate (D), the concentration of the mixed solvents (E), and the liquid temperature (F), each one having five levels. Using the Taguchi experimental design, only 25 runs were required. The outcome data, such as the absorption efficiency (E_F), the absorption rate (R_A), the overall mass-transfer coefficient (K_Ga), and the absorption factor (φ), could be determined under steady-state conditions. The optimal mixed solvents were found to be A1 (PZ + MEA) and A2 (PZ + DIPA). The parameter importance and optimal conditions for E_F, R_A, K_Ga, and ϕ were determined separately; the verification of all optimal conditions was successful. This analysis found that the importance of the parameters was D > C > A > E > B > F, and the gas flow rate (D) was the most important factor. Subsequently, multiple-stage scrubbers were used to capture CO₂. Comparing 1 s and 3 s (three-stage scrubber), E_F, R_A, K_Ga, and φ increased by 33%, 29%, 22%, and 38%, respectively. The desorption tests for the four optimal scrubbed solutions, including multiple stages, showed that the heat of regeneration for the three scrubbers was 3.57–8.93 GJ/t, in the temperature range of 110–130 °C, while A2 was the best solvent. Finally, the heat regeneration mechanism was also discussed in this work. Full article

This study used monoethanolamine (MEA) as an amine-based solvent, which was blended with secondary amines (DIPA), tertiary amines, stereo amines, and piperazine (PZ) to prepare mixed amines at the required concentrations, which were used as the test solvents. To search for the best-mixed amines, a continuous bubble-column scrubber was adopted to explore the performance of mixed solvents presented in this study. The solvent regeneration test was also carried out at different temperatures. The selected factors included the type of mixed amine (A), the ratio of mixed amines (B), the liquid feed flow (C), the gas flow rate (D), the concentration of mixed amines (E), and the liquid temperature (F), each having five levels. Using the Taguchi experimental design, the conventional experimental number could be reduced from 15,625 to 25, saving much time and cost. The absorption efficiency (E_F), absorption rate (R_A), overall mass-transfer coefficient (K_Ga), and absorption factor (ϕ) were estimated as the indicators. After the Taguchi analysis, E, D, and C were found to play important roles in the capture of CO₂ gas. Verifications of optimum conditions were found to be 100%, 19.96 × 10⁻⁴ mole/s·L, 1.2312 1/s, and 0.6891 mol-CO₂/L·mol-solvent for E_F, R_A, K_Ga, and ϕ, respectively. The evaluated indexes suggested that MEA + PZ was the best-mixed amine, followed by MEA and MEA + DIPA. The solvent regeneration tests for the scrubbed solutions performed at different optimum conditions showed that the heat of the regeneration sequence was in the order of MEA > MEA + PZ > MEA + DIPA with minimum energy required at 110 °C. The individual energy required was also analyzed here. Full article

In this work, sodium aluminate alkaline solution was used to capture CO₂ in a continuous bubble column scrubber and aluminum tri-hydrate (ATH) precipitates were produced. As the sodium carbonate could be recycled after the filtrated solution was crystallized by evaporation, a novel CO₂ capture process was developed successfully. There were five experimental operation variables, including solution flow rate (A), concentration of the solution (B), gas flow rate (C), CO₂ gas concentration (D), and liquid temperature (E), with four levels to each variable. The influence of each variable on absorption efficiency (EF), absorption rate (R_A), absorption factor (φ), mass transfer coefficient (K_Ga), and precipitation rate (R_P) in a steady state was explored in this study. The Taguchi experimental design was adopted, and 16 experiments were performed; as the optimum operating conditions found in Taguchi analysis required further verification, there were a total of 21 experiments in the end. According to S/N analysis, the overall order of importance was D > A = B > C > E, meaning D (CO₂ concentration) was most important and E (liquid temperature) was least important. In addition, the result also showed that the Rp was 1.25–2.0 times higher than the RA. The obtained powder was mainly ATH according to XRD analysis, with the crystal size ranging between 8.14 and 27.97 nm. However, the BET analysis showed its particle size range being 17.6–283.7 nm, indicating agglomeration for primary particles. The SEM analysis showed that there were flower-like, irregular, urchin-like, elongated, and amorphous particles. The solutions from five groups of optimum conditions were used to recycle the sodium carbonate experiments. After evaporation and crystallization of the filtrated solutions, the energy loading was found to be 1.70–2.56 GJ/t-solvent, illustrating the superiorities of low energy consumption. The precipitated powders were verified to be sodium carbonate by FTIR, which is a valuable constituent. Full article

There have been studies recently on bubble-column scrubbers with low cost and high efficiency for the absorption and treatment of hazardous gases in the event of a chemical spill. Bubble columns are vulnerable to freezing at temperatures below zero because the absorbents generally do not circulate. To address this issue, this study focused on the applicability, absorbed amount, and performance of brine as an absorbent. Under three different temperatures, i.e., −5 °C, −8 °C and −10 °C we examined brine (NaCl, CaCl₂, and MgCl₂) by varying the concentration required at each temperature. Following the experiments, CaCl₂ brine was determined as the optimal brine for its absorption performance and affordability. Based on the experimental results, the absorption performance for ammonia, ethylene oxide, and methylamine, which are hazardous and water-soluble gases among accident preparedness substances (APS), was tested by using ASEPN PLUS. Our results suggested although the efficiency dropped by about 5% to 25% when brine was used as an absorbent, it can be used at the low temperatures because the gas solubility increased with decreasing temperature. Therefore, if brine, as an alternative, is used at temperatures about 15 °C, it can operate efficiently and stably without deterioration in the absorption performance. Given our experimental results and design data on the absorbed amount and absorbent replacement period for major hazardous gases are utilized to prevent bubble columns from freezing, it can be commercially used for small and medium-sized enterprises because it can help reduce installation and operation costs. Full article

In order to select the best mixed amines in the CO₂ capture process, the absorption of CO₂ in mixed amines was explored at the required concentrations by using monoethanolamine (MEA) as a basic solvent, mixed with diisopropanolamine (DIPA), triethanolamine (TEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ). Here, a bubble column was used as the scrubber, and a continuous operation was adopted. The Taguchi method was used for the experimental design. The conditional factors included the type of mixed amine (A), the ratio of the mixed amines (B), the liquid feed flow (C), the gas-flow rate (D), and the concentration of mixed amines (E). There were four levels, respectively, and a total of 16 experiments. The absorption efficiency (E_F), absorption rate (R_A), overall mass transfer coefficient (K_Ga), and scrubbing factor ($\varphi$) were used as indicators and were determined in a steady-state by the mass balance and two-film models. According to the Taguchi analysis, the importance of the parameters and the optimum conditions were obtained. In terms of the absorption efficiency (E_F), the absorption rate (absorption factor) (R_A/$\varphi$), and the overall mass transfer coefficient (K_Ga), the order of importance is D > E > A > B > C, D > E > C > B > A, and D > E > C > A > B, respectively, and the optimum conditions are A1B4C4D3E3, A1B3C4D4E2, A4B2C3D4E4, and A1B1C1D4E1. The optimum condition validation results showed that the optimal values of E_F, R_A, and K_Ga are 100%, 30.69 × 10⁻⁴ mol/s·L, 1.540 l/s, and 0.269, respectively. With regard to the selection of mixed amine, it was found that the mixed amine (MEA + AMP) performed the best in the CO₂ capture process. Full article

This study used the solvent monoethylamine (MEA)/CaCl₂/H₂O to investigate CO₂ absorption and CaCO₃ crystallization in a bubble column scrubber. The variables explored were pH, gas flow rate, gas concentration, the liquid flow rate of the solution to absorb CO_2, and CaCO₃ crystallization. Under a continuous mode, the solution of CaCl₂ was fed continuously, and the pH dropped after CO₂ absorption. To maintain the set pH value, there was an automatic input of the MEA solvent into the bubble column. In addition to maintaining the pH, the solution could also absorb CO₂ and produce CaCO₃ crystals, which served two purposes. The results showed that there were mainly vaterite crystals. At different pH values, the lower the pH, the higher the precipitation rate of vaterite (F_p), and vice versa. However, under different gas flow rates, the F_p decreased as the pH value increased. Additionally, the process variables also affected the absorption rate (R_A) and the overall mass-transfer coefficient (K_Ga) generally increased with increasing pH, gas concentration, and gas flow rate. However, it slowed down under operating conditions at high pH and high gas flow rate. Finally, correlation equations for R_A, K_Ga, and F_p were also obtained and discussed in the study. Full article

This study used sodium glycinate as an absorbent to absorb CO₂ in the bubble column scrubber under constant pH and temperature environments to obtain the operating range, CO₂ loading, and mass transfer coefficient. For efficient experimentation, the Taguchi method is used for the experimental design. The process parameters are the pH, gas flow rate (Q_g), liquid temperature (T), and absorbent concentration (C_L). The effects of the parameters on the absorption efficiency, absorption rate, overall mass transfer coefficient, gas–liquid molar flow rate ratio, CO₂ loading, and absorption factor are to be explored. The optimum operating conditions and the order of parameter importance are obtained using the signal/noise (S/N) ratio analysis, and the optimum operating conditions are further verified. The verification of the optimum values was also carried out. The order of parameter importance is pH > C_L > Q_g > T. Evidence in the ¹³CNMR (Carbon 13 Nuclear Magnetic Resonance) spectra shows that the pH value has an effect on the solution composition, which affects both the absorption efficiency and mass transfer coefficient. There are 18 experiments for regeneration, where the operating temperature is 100–120 °C. The heat of regeneration was measured according to the thermodynamic data. The CO₂ loading, the overall mass transfer, and the heats of regeneration correlation are also discussed in this work. Finally, an operating policy for the CO₂ absorption process was confirmed. Full article

A lab-scale bubble-column scrubber is used to capture CO₂ gas and produce ammonia bicarbonate (ABC) using aqueous ammonia as an absorbent under a constant pH and temperature. The CO₂ concentration is adjusted by mixing N₂ and CO₂ in the range of 15–60 vol % at 55 °C. The process variables are the pH of the solution, temperature, gas-flow rate and the concentration of gas. The effects of the process variables on the removal efficiency (E), absorption rate (R_A) and overall mass-transfer coefficient (K_Ga) were explored. A multiple-tube mass balance model was used to determine R_A and K_Ga, in which R_A and K_Ga were in the range of 2.14 × 10⁻⁴–1.09 × 10⁻³ mol/(s·L) and 0.0136–0.5669 1/s, respectively. Results found that, R_A showed an obvious increase with the increase in pH, inlet gas concentration and gas temperature, while K_Ga decreased with an increase in inlet gas concentration. Using linear regression, an empirical expression for K_Ga/E was obtained. On the other hand, ammonia bicarbonate crystals could be produced at a pH of 9.5 when the gas concentration was higher than 30% and γ (=F_g/F_A, the gas-liquid molar flow rate ratio) ≥ 1.5. Full article