Hans T. Karlsson

Treatment of dye wastewater containing acid orange II using a cell with three-phase three-dimensional electrode

The removal of color and chemical oxygen demand (COD) from simulated dye wastewater containing Acid Orange II was experimentally investigated using coagulation-electrooxidation. Two kinds of coagulation methods, ferrous-mediated coagulation and electrocoagulation were tested as pretreatment. The electrooxidation was carried out in a cell with a three-phase three-dimensional electrode using granular activated carbon as particle electrodes. Particular attention was paid to probe the effect of cell voltage, airflow rate, solution conductivity and treatment time on the electrochemical treatment efficiency. The experimental results showed that the coagulation-electrooxidation process could efficiently remove the color and the COD from the simulated dye wastewater. The overall COD and color removal efficiencies reached as high as 99% and 87%, respectively, by ferrous coagulation (molar rate of Fe(II)/ dye: 0.5) and 30-min electrolysis (cell voltage: 20.0 V and airflow: 0.1 m3 h(-1)).

Modeling the absorption of SO2 in a spray scrubber using the penetration theory

A model based on the penetration theory has been developed to calculate the dynamic absorption rate of sulfur dioxide into a droplet of limestone slurry. The model includes both instantaneous equilibrium reactions and reactions with finite rates; limestone dissolution, sulfite oxidation, gypsum crystallization and the hydrolysis reaction of CO2. The model has been used to quantify the mass transfer within a spray scrubber and to estimate the impact of the reactions with finite rate of the SO2 mass transfer. The variations within the physical mass transfer conditions of a spray scrubber have been simulated by assuming high mass transfer coefficients close to the nozzles and low coefficients below the spray region. The developed concentration profiles of the diffusing species and the depth of penetration have been determined for different penetration times. The calculations show that the absorption of SO2 into a limestone spray scrubber to a large extent is liquid-side controlled. Only at the very top of the absorber, where the partial pressure of SO2 is low, is the gas film resistance above 50%. Limestone dissolution close to the gas-liquid interface has been shown to be of significance at low pH and in the parts of the absorber where the internal circulation inside the droplets is low. The impact of the hydrolysis reaction of CO2 on the absorption rate of SO2 has been studied by varying the reaction rate constant. Simulations show that the rate constant has a large impact on local absorption rates. Depending on the length of the contact time between the gas and the liquid, the assumption of an instantaneous hydrolysis reaction has an impact on the overall SO2 absorption rate

Performance of three-phase three-dimensional electrode reactor for the reduction of COD in simulated wastewater-containing phenol

The removal of chemical oxygen demand (COD) from wastewater-containing phenol was investigated using three-phase three-dimensional electrode reactor. Special attention was paid to experimentally probe the performance of the reactor in COD removal in the process of repeated batch runs. The experimental results showed that the reactor could remove COD from phenol-containing wastewater much more efficiently than both granulated activated carbon (GAC) adsorption bed and conventional three-dimensional electrode. For 200th batch run, the three-phase three-dimensional electrode reactor with an airflow of 5 l min(-1) and a cell voltage of 30 V could remove 1350 ppm COD from the wastewater in 30 min while conventional three-dimensional electrode reactor with a same cell voltage and GAC adsorption bed with a same airflow only could remove 610 and 1000 ppm, respectively, at the same reaction duration. Although it was found that COD removal decreased with increasing repeated batch runs in our experimental range, due to adsorption saturation of GAC and electrode passivation, the extent of decrease for the three-phase three-dimensional electrode is much less than those for conventional three-dimensional electrodes and GAC adsorption beds. The passivated reactor could be partly re-activated by electrolysis in the presence of MnO2.

Absorption of NO in an Aqueous Solution of NaClO2

A packed column has been used to study the absorption of nitrogen oxide in an alkaline solution of sodium chlorite. The reactions taking place during the absorption have been examined and a lumped reaction model has been used to estimate rate constants from experimental data. Several parallel and consecutive reactions were found to take place during the absorption. NO was found to be oxidized to NO2 and/or to NO2-, and ClO2- was reduced to Cl- and/or to ClO-. The pH value of the absorbing liquid was found to have a great impact both on the absorption rate and on the extent of the different redox reactions within the liquid. Experimental results indicate that sodium chlorite mainly works as an agent to oxidize NO to NO: and that the major part of the nitrogen oxides are absorbed via the hydrolysis of N2O3 and N2O4. (Less)

A KINETIC STUDY OF THE DRY SO2-LIMESTONE REACTION AT LOW TEMPERATURE

The dry reaction between SO2 and limestone has been investigated at low temperatures. The study was focused on the wet-dry scrubbing application. Parameters investigated included: temperature: 313–353 K, SO2 concentration: 50–4000 ppm, oxygen concentration: 0–9 percent, carbon dioxide concentration: 0–10 percent, relative humidity 0–92 percent, limestone panicle diameter: 4–100 microns, and limestone conversion: 0–95 percent. The study has revealed that the relative humidity, the particle diameter and the limestone conversion have the most dramatic impacts on the reaction rate. A suggested reaction mechanism is outlined in great detail.

Similarities between lime and limestone in wet—dry scrubbing

Lime is utilized as a sorbent in most commercial wet—dry scrubbing processes for SO2 control, while limestone is not considered to be sufficiently reactive for such a purpose. Faced with the fact that limestone is potentially the least expensive sorbent for SO2 control, a study was conducted to uncover ways to increase the reactivity of this sorbent in order to use it in wet—dry scrubbing applications. The study was focused on a comparison of the reactivity of lime and limestone during the dry reaction period. The conditions which have a major impact on the reactivity include the sorption capacity of water vapour, the BET surface area, the relative humidity and the sorbent utilization. The experiments revealed several similarities between the two sorbents, which led to a number of ways to obtain increased limestone acitivity.

Limestone based spray dry scrubbing of SO2

Spray dry scrubbing for emissions control has emerged during recent years. Worldwide, more than fifty spray dry scrubbers are in operation or under construction for the control of SO2 on coal fired boilers. Virtually all of these units utilize a slurry of slaked lime as a reactive agent for SO2 capture. The cost of lime is several times the cost of limestone, so it would be a great advantage if limestone could be used in the process. Research on spray dry scrubbing has been underway for over six years at our department. The investigation on which the present paper is based was undertaken to study the prospects for spray dry scrubbing of SO2 by utilizing a slurry of finely ground limestone. The experiments were performed in a 0.5 MWth pilot plant, consisting of a spray dryer and a fabric filter system. The slurry was prepared from limestone ground to various particle sizes. Parameters investigated were the approach to the adiabatic saturation point, the stoichiometric ratio (CaCO3/SO2), and the addition of CaCl2, which would result from the chlorine in the coal. Furthermore, the impact of the pressure drop over the fabric filter on SO2 removal was studied. The experimental results showed that ground limestone can remove SO2 efficiently in a spray dry scrubber system. A significant contribution to the removal occurs in the fabric filter. The removal increases as the surface area of the limestone increases due to grinding. However, a limiting value of the removal over the spray dryer is obtained at quite modest surface areas. This is caused by agglomeration of smaller particles at low pH values; as the droplets are contacted with the flue gas, the pH drops due to hydrogen ion production from hydrolysis of SO2. This was seen by measuring the paricle size distribution at different pH values. Hence, while the gas—solid reaction in the fabric filter depends on the surface area, the rate for the gas—liquid—solid reaction in the droplets depends on the particle or agglomerate size.

Microorganisms for desulphurization of coal: the influence of leaching compounds on their growth

An investigation was undertaken to outline how microorganisms suggested for use in coal desulphurization are affected by compounds leached from coal. Three species of the genus Sulfolobus were studied. Sulfolobus acidocaldarius was seen to be affected by compounds leached from coal more negatively than Sulfolobus brierleyi and Sulfolobus solfataricus. It was observed that certain conditions during leaching, such as pH, temperature and leaching time, were important for the concentration of compounds leached from coal. It was seen that compounds leached from coal, in some cases, can improve the growth yield for the microorganisms.

Adsorption of Hydrochloric Lime for Flue Gas Clean Up

The reaction between hydrochloric acid and solid slaked lime was investigated by passing simulated flue gas through a fixed bed reactor. The influence of CO2 and H2O present in the flue gas was studied, as well as the influence of the reaction temperature in the range 423 to 673 K. The reaction was found to be of first order with respect to the two reactants. Expressions to account for the temperature and the CO2 and H2O concentrations were derived from the experimental data.

Oxidation of pyrite by Acidianus brierleyi: Importance of close contact between the pyrite and the microorganisms

Experiments were done in order to study the thermophilic archaebacterium Acidianus brierleyi during oxidation of pyrite (FeS2). The microorganisms were grown both separated from the pyrite by a membrane and in close contact with the pyrite. From the results it can be concluded that direct contact is needed for good growth of the strain studied. The obtained results indicate that the direct contact mechanism may be applied to oxidation of sulfidic minerals by A. brierleyi.