Amitava Bandyopadhyay

SO2 SCRUBBING IN A TAPERED BUBBLE COLUMN SCRUBBER

SO2 emissions from various sources are found to occur in various concentrations and quantities. Abatement of SO2 emission, therefore, assumes significant importance over the decades. Wet scrubbers offer great advantage over other devices for gas cleaning. That is the reason that compliance with SO2 standards will in many cases result in the installation of scrubbing devices. This article presents results of a study on the scrubbing of SO2 (initial concentration ranging between 400 and 1780 ppm) in a tapered bubble column scrubber using water and dilute sodium alkali. Preliminary studies reveal that the tapered bubble column is capable of generating higher fractional gas holdup than a standard bubble column under similar situations. Moreover, the tapered bubble column has generated bubbles with less power consumption than the existing columns under comparable hydrodynamical conditions. Experimental results indicate that almost 100% SO2 removal (i.e., zero penetration) can be achieved in the scrubber developed in alkali scrubbing at an optimum QL/QG ratio of 3.0 m3/1000 ACM. The selection of any gas-cleaning device is based on the performance of the system. In view of this, empirical and semi-empirical correlations are put forward for the prediction of the performance of the scrubber in terms of different pertinent variables of the system for water as well as alkali scrubbing. Experimental results fit extremely well with the correlations. The removal efficiency achievable in the present tapered bubble column scrubber has been found to be higher than that of a single-stage standard bubble column with some modification. The present tapered bubble column is, therefore, hydrodynamically, energetically, and efficiency-wise much better than a standard bubble column.

Investigation on multiple benefits of wet ESP for emission control in an Indian coal fired thermal power plant

In this article, the operation of wet electrostatic precipitators (WESP) as air pollution control device in an Indian coal fired thermal power plant has been investigated in respect of its efficacy in removing particulate laden gaseous emissions. The WESP was installed for reducing the particulate matter (PM) emission to meet the Indian stack emission standard of PM. Interestingly, the study reveals that the WESP reduced the SO2 and CO2 emissions potentially. The system, therefore, functions also simultaneously as a CO2 capture system. Since CO2 is a green house gas (GHG), operating a WESP for cleaning flue gas of a coal fired thermal power plant can be considered as a GHG emission mitigation option as well. The level of NOx emission could not be conclusively analyzed perhaps might be due to air dilution of the flue gas. It is finally suggested that the plant operators would like to operate the plant using dilute alkaline reagent replacing the water as the scrubbing medium so as to obtain multiple benefits of cleaning all acidic gases by the WESP followed by better ash management.

Velocity-selective resonance dips in the probe absorption spectra of Rb D2 transitions induced by a pump laser

We report experimental observation of velocity-selective resonances in the Doppler-broadened probe absorption spectra of 85Rb and 87Rb D2 transitions in the presence of a strong copropagating pump laser locked to a frequency within the Doppler profile of the transition. The set of three dips having the separation of allowed hyperfine transitions can be moved along the Doppler profile by tuning the pump laser frequency indicating a resonance between the pump laser frequency and the velocity shifted probe laser frequency.

Observation of electromagnetically induced transparency in six-level Rb atoms and theoretical simulation of the observed spectra

We report the observation of electromagnetically induced transparency (EIT) in a six-level Λ-type system in atomic Rb vapor containing both 87Rb and 85Rb. The experimental observation includes five velocity selective optically pumped (VSOP) absorption dips for both 87Rb and 85Rb. The EIT signal appears on the background of one such VSOP absorption dips. The measured EIT linewidth () shows sub-natural ( ) values for both lower and higher values of pump Rabi-frequencies. The density matrix based theoretical model for the six-level system is developed and solved numerically by taking into account the Doppler broadening. A complete analytical solution (non perturbative) for a three level Λ-type system has been obtained and compared with the experimentally observed sub-natural EIT linewidth. The simulated spectra are in good agreement with the experimental findings.

Analysis of Bio-Sorption of Cr(VI) onto Raw Rice Husk by a Hybrid Theoretical Model Using Results of Batch Experiments

In this study, batch adsorption experiments are conducted for removing Cr(VI) from its aqueous solution using raw rice husk after its characterization by scanning electron microscopy, BET and Fourier transform infrared spectroscopy analyses. The effects of different operating parameters are investigated and optimized. The maximum percentage of removal observed was 99% under optimal operating conditions. Experimental results follow the Langmuir adsorption isotherm reasonably well. A hybrid mathematical model that takes into account the shrinking core approach coupled with the well-known progressive conversion model has been proposed to simulate the dynamic behaviour of the present system using the results obtained from the batch adsorption experiments. The proposed model can also be potentially applicable to any similar other solid–liquid adsorption–diffusion system. Based on the experimental findings and theoretical analyses carried out in this study, several recommendations are holistically put forward for developing the understanding of the adsorptive removal of heavy metals including Cr(VI) and other pollutants.

Revisiting the four-level inverted-Y system under both Doppler-free and Doppler-broadened conditions: an analytical approach

We report the occurrence of electromagnetically induced transparency (EIT) in the simulated probe response signal for a four-level inverted-Y type system that is being acted upon by a weak coherent probe field, a strong coherent pump field and a coherent repump field. There are two ground energy levels, one intermediate energy level and one uppermost energy level. The weak probe field couples the lowest ground level to the intermediate level whereas the repump field connects the other ground level with the intermediate level. The strong control field couples the intermediate level with the uppermost energy level, thereby forming an inverted-Y type system. The density matrix based theoretical model has been developed and solved analytically for this four-level system and the probe response signal has been simulated at different values of the control and repump Rabi frequencies, control and repump frequency detunings and under both Doppler-free and Doppler-broadened conditions using the parameters of 87Rb D2 transition. Extremely low line width (few tens of kHz) for the EIT signal has been noticed under thermal averaging for copropagating probe, control and repump field configuration. The EIT signal is found to be immune to the variation in the control Rabi frequency.

Selecting Particulate and Gaseous Pollution Control Device

Industrialization tends to be accompanied by growing population and increasing awareness on environmental problems, making the use of pollution control equipment imperative. However, the air pollution is a complex phenomenon, as the pollutants distributed in the air are molecularly more random than in other media (soil and water). The control of air pollution, therefore, often becomes a more energy intensive process, leading to increased CO2 emissions. Further, air pollution comprises particulate and gaseous pollutions requiring different control philosophies. When the control of both particulate and gaseous pollutants is required in a single step, the selection of equipment is further complicated. This article outlines how such complications could be avoided by developing an understanding on the criteria of selecting air pollution control devices. The advantages and disadvantages of all generic control devices are critically appraised for the better understanding by both the designers and users. Emission trading, bubble policy, and the recommendations of the World Bank Guidelines for controlling particulates, SO2, and NOX pollution are highlighted. The recent research on the development of air pollution control devices are appraised critically. Finally, the criteria on selecting equipment for controlling particulate-laden-gaseous pollution in a single step are critically elucidated with few case studies.

Characterising the performance of a tapered scrubber for controlling particulate emission

The performance of a modified tapered scrubber using water is presented in this article. The column is fabricated with internals so as to improve the performance of a simple tapered bubble scrubber. Experimentation indicates that the system developed can obtain almost 100% particulate (fly ash) removal efficiency under certain hydrodynamical conditions and the removal efficiency has been found to be higher than the existing similar systems. An empirical correlation is put forward for the prediction of removal efficiency as a function of relevant variables of the system. Experimental results agree very well with the correlation.

Abatement of particulate-laden SO2 in tapered bubble column with internals

The performance of particulate-laden SO2 scrubbing in a modified tapered bubble column with internals is reported in this article. The presence of particles improved the particulate-laden SO2 removal efficiency to about 15% that was elucidated by the facilitated adsorptive mass transport. Experimentation revealed that nearly 100% removal efficiency of particulate-laden SO2 was achievable without any additives or pretreatment under certain operating condition of the scrubber. An empirical correlation was developed to predict the performance of the modified tapered scrubber. Experimental values fitted excellently well with the predicted values through the correlation (within ±5% deviation). The performance of the modified tapered bubble scrubber with column internals has been found to be better than a tapered bubble column without any internals.

Insights of the Removal Mechanisms of Pharmaceutical and Personal Care Products in Constructed Wetlands

Purpose of ReviewPharmaceutical and personal care products (PPCPs) are chemicals employed in human healthcare, veterinary, medical diagnosis, and cosmetics, which have increasingly polluted water sources. Extensive research has demonstrated constructed wetlands (CWs) technology as a low-cost but efficient approach for PPCPs removal. There has been a growing interest to better understand the degradation mechanisms of PPCPs in wetland cells. Data corroborated in this review show that these degradation mechanisms include photolytic degradation, adsorption, phytodegradation, and microbial degradation. Each of these degradation mechanisms performs differently in wetland cells. This review also highlights the lack of research works to quantify the contribution of these degradation mechanisms to the overall efficiency of CWs to remove PPCPs as a major bottleneck for further application of this technology. The ultimate goal is to apply and prioritize a suitable degradation mechanism for successfully eliminating corresponding PPCPs. This review, therefore, provides further insights to (i) elucidate the importance of these removal mechanisms, and (ii) quantify their contribution in overall PPCPs removal processes. This review aims to understand the importance and contribution of degradation mechanisms of PPCPs removal in constructed wetlands.Recent FindingsThe degradation mechanisms of PPCPs in constructed wetlands depended on various conditions; yet, which factors are preferred? Furthermore, the number of research works, related to quantifying the contribution of degradation mechanisms, is limited.SummaryThe hydrophobic/hydrophilic character, reflecting as log Kow (or log Dow), is the most commonly used. The photolytic degradation is appropriate with low and moderate hydrophobic values (log Dow from − 2.3 to 3). The role of adsorption is moderate, while it is more efficient with the higher hydrophobic compounds. The media is important for plant growth and micro-organism community development. The plant uptake is better for PPCPs with higher hydrophobicity (log Kow from 1 to 4). However, it is difficult to quantify their contribution and the number of related studies is limited.