Evaluating the performance of a turbulent wet scrubber for scrubbing particulate matter.

UNLABELLED: A turbulent wet scrubber was designed and developed to scrub particulate matter (PM) at micrometer and submicrometer levels from the effluent gas stream of an industrial coal furnace. Experiments were conducted to estimate the particle removal efficiency of the turbulent scrubber with different gas flow rates and liquid heads above the nozzle. Particles larger than 1 microm were removed very efficiently, at nearly 100%, depending upon the flow rate, the concentration of the dust-laden air stream, and the water level in the reservoir Particles smaller than 1 microm were also removed to a greater extent at higher gas flow rates and for greater liquid heads. Pressure-drop studies were also carried out to estimate the energy consumed by the scrubber for the entire range of particle sizes distributed in the carrier gas. A maximum pressure drop of 217 mm H2O was observed for a liquid head of 36 cm and a gas flow rate of 7 m3/min. The number of transfer units (NTU) analysis for the efficiencies achieved by the turbulent scrubber over the range of particles also reveals that the contacting power achieved by the scrubber is better except for smaller particles. The turbulent scrubber is more competent for scrubbing particulate matter, in particular PM2.5, than other higher energy or conventional scrubbers, and is comparable to other wet scrubbers of its kind for the amount of energy spent. IMPLICATIONS: The evaluation of the turbulent scrubber is done to add a novel scrubber in the list of wet scrubbers for industrial applications, yet simple in design, easy to operate, with better compactness, and with high efficiencies at lower energy consumption. Hence the turbulent scrubber can be used to combat particulate from industrial gaseous effluents and also has a scope to absorb gaseous pollutants if the gases are soluble in the medium used for particles capture.

Dynamics of PM2.5 concentrations in Kathmandu Valley, Nepal.

This study analyzed daily patterns and dynamics of PM(2.5) concentrations in the Kathmandu Valley during three winters. The PM(2.5) data showed a daily repetitive cycle which represents influence of local air flow and dispersion and accumulation of air pollutants in the valley. Two concentration peaks were observed in the morning and in the evening periods, and they fell down during the daytime and the nighttime periods. This indicates local emission sources as major contributors in the valley. The more pronounced morning peak compared to the evening peak showed that the upslope wind in the morning helped to move the polluted inversion layer downward, subsequently adding to freshly emitted pollutants and causing a sharp pollutant concentration rise in the morning. Katabatic wind and rise of temperature in the basin during the day helped the pollutant upflow and dilution, resulting in a sharp PM(2.5) concentration decline. Through the afternoon, the decrease in air temperature followed by decrease in wind speed caused to lower PM(2.5) peaks in the evening. Also, higher morning peaks of PM(2.5) concentrations compared to the evening indicated pollution from the previous day is added to the fresh emission. The valley had increased PM(2.5) from the beginning of October which continued till the first week of February. The increase in PM(2.5) peak fit the logistic equation y=[k/(1+exp (p-qx)]+asin(bx) where k, p, q, a, and b are constants.