Single and simultaneous absorptions of lean SO2 and NO2 into aqueous slurries of Ca(OH)2 or Mg(OH)2 particles.

Abstract

The absorption rate of lean SO2 and/or NO2 into aqueous slurries of fine Ca(OH)2 or Mg(OH)2particles was measured using a stirred vessel with a plain gas-liquid interface at 25°C and 1 atm. The absorption process of lean SO2 into Ca(OH)2 slurries was found to be almost gas-film controlled under the partial pressures considered here. On the other hand, for SO2-Mg(OH)2slurry system, the diffusion of the reactant across the liquid film was significant and the absorption rate was increased with solid concentration. The observed enhancement factors were compared with the theoretical prediction according to the previously proposed model to estimate the dimensionless parameter concerning solid dissolution. For NO2-slurry system, the reaction between NO2and the aqueous slurry may satisfactorily be considered the reaction between NO2and water. The hydrolysis was found to be second-order in NO2and the secondorder rate constant was derived as 5.0X107//molà"sec.The absorption rate of NO2 with coexistence of SO2into aqueous slurries of Mg(OH)2greatly exceeded that of NO2alone into clear solutions with the same sulfite concentrations, which may be due to the solid-surface reaction in a region from the interface to the reaction plane. Introducti onThe elementary processes involved in chemical absorption into slurry are (i) diffusion of solute gas in the liquid film, (ii) chemical reaction and (iii) dissolution of solid (one of the reactants of Ca(OH)24)5) and absorption of SO2 into aqueous slurries of Mg(OH)23) using a stirred-tank absorber with a plain gas-liquid interface. But in our previous work3>5), the gas-phase composition of solute gases was restricted to percentorder of magnitude. The concentration of SO2 in the flue gases emitted from stationary combustion sources is generally less than several thousand ppm by volume. Therefore, it is necessary to discuss the absorption mechanism of lean SO2 by aqueous slurries.The present work was undertaken to check the applicability of the proposed model to the chemical absorption of such lean solute gas as is encountered in flue gases. To this end, absorption of SO2 by aqueous slurries of Ca(OH)2 and Mg(OH)2 was carried out using a stirred vessel with a plain gas-liquid interface.An aqueous Mg(OH)2 slurry has an advantage of yielding high scrubbing capacity for the removal of SO2 as a result of the presence of more soluble reaction product, MgSO3, than the corresponding Casalt. Dissolved MgSO3 in a slurry solution is also favorable for the absorption of NO2. In considering this, the simultaneous absorption of lean SO2 and NO2 into aqueous slurries of Mg(OH)2 was in

Integration of reverse osmosis and membrane crystallization for sodium sulphate recovery

“…[1] SO 2 is mainly generated by combustion of fossil 9 fuels or by industrial processes, such as the manufacture of ZnO from ZnS, and 10 emitted to the atmosphere as byproduct. Different strategies for SO 2 emission control 11 and gas desulphurization have been studied.…”

“…Examples 20 include the use of water enriched with DMA, trying to minimize the use of DMA 21 Page 3 of 43 A c c e p t e d M a n u s c r i p t 3 while improving the rate of absorption of SO 2 in water, [6] and application of inorganic 1 solutions, such as alkaline slurries of Ca(OH) 2 / Mg(OH) 2 . [10,11] However, the 2 chemical reaction between Ca(OH) 2 / Mg(OH) 2 and SO 2 results in large quantities of 3 solid waste as CaSO 3 /MgSO 3 . Sodium citrate (Na 3 Ci)/citric acid buffer solutions have 4 been also investigated for absorbing SO 2 ; in this approach, SO 2 can be recovered from 5 the Na 3 Ci solution by forming Na 2 SO 3 .…”

“…[12] Na 3 Ci is a non-toxic reagent and the 6 process is characterized by the absence of fouling problems and low oxidation losses 7 of SO 2 but the recovery of dissolved SO 2 involves stripping by steam or further 8 reaction of the absorbed solution with H 2 S to produce sulfur. [13] This requires 9 additional energy for the production of steam or H 2 S. NaOH in aqueous solution has 10 been also proposed as an efficient way to remove acid gases, such as CO 2 and SO 2 11 from flue gas. [14][15][16] When an aqueous NaOH solution is used as absorbent for SO The main focus of this work is to develop a process that allows the production of 1 Na 2 SO 4 as a reusable compound for further industrial application as raw material.…”

“…2 Membrane crystallization and reverse osmosis are employed to fulfill this objective. 10 Integration of membrane-based systems has shown clear benefits in desalination, [32, 11 33] concentration of protein solutions, [34] waste water treatment, [35] and NaCl 12 crystallization. [18,36] In this work, membrane crystallization is used to crystallize In both sets of experiments, the permeate is recycled in order to keep the 1 concentration of the feed solution constant.…”

Mathematical Modeling of Wet Magnesia Flue Gas Desulphurization Process

“…The dimensionless positions of two reaction planes, x 1 and x 2 , can be determined by the following equations [10]:…”