Alkaline absorbents for SO2 and SO3 removal: A comprehensive review.

Injection of an alkaline absorbent into the flue gas can significantly reduce SO2 and SO3 emissions. The article presents alkaline absorbents employed in industrial processes to remove SO2 and SO3 from flue gases, detailing their characteristics and applications across various process conditions. It summarizes the mechanisms and influencing factors behind SO2 and SO3 removal, outlines the impact of multi-component gases, particularly SO2, on SO3 removal in actual flue gases, and elucidates this competitive phenomenon from a theoretical standpoint. The article compares the application scenarios and efficiencies of alkaline absorbents across different processes, identifies the optimal combinations of various absorbents and processes, and proposes a synergistic approach for the removal of SO2 and SO3. The findings demonstrate that by injecting calcium- or sodium-based absorbents into dry processes, SO2 and SO3 can be removed efficiently and cost-effectively, with process optimization and absorbent modifications further enhancing the SOx removal efficiency. In the future, by blending two or more absorbents and applying them to dry processes, a synergistic removal of SO2 and SO3 can be achieved.

Experimental investigation on the use of COVID-19 waste in bituminous concrete.

The COVID-19 pandemic has resulted in unprecedented growth in the production and disposal of PPEs, face masks, gloves, face shields, and disinfectants. Daily consumption of masks and PPE has increased the plastic load on the municipality and very few plastics are taken to the recycling during the complete shut down during Covid-19. Plastic pollution is already a matter of concern that is increasing due to the negligence of humans. COVID-19 health crisis puts extra pressure on the regular waste management systems as increased daily consumption of single-use plastics around the world. It leads to the inappropriate management of waste; including mobile incineration, direct land-filling, and local burning of the waste. As the PPE kits and gowns are made of polypropylene plastic, they are non-biodegradable like any other plastics. Incineration and land-filling of plastics do not help them to degrade, even if it increases the number of pollutants in the form of microparticles. In this paper, we discussed the research procedures to utilize the waste plastic specifically Covid-19 waste which is received from the health care clinics in Bituminous concrete for the construction of flexible roads. The main objective of the study was to investigate the effectiveness of the bituminous mix modified with Polypropylene gowns waste and to compare it with the conventional bituminous mix. This research concentrated on the Maximum Stability and Flow Value of the asphalt mixture with the waste. The measurements of the Plastic of 10%, 12.5%, 15%, 17.5 %, and 20% were utilized as substitutions for the bitumen binder in the mix. From the experimental investigation, it is concluded that the optimum bitumen content is found at 10% Plastic waste with 6.5 bitumen content. Bitumen properties also increase with the addition of PPE waste.

Nitrogen oxide reduction through absorbent solutions containing nitric acid and hydrogen peroxide in hollow fiber membrane modules.

Emissions of nitrogen oxides such as NO and NO2, which are commonly known as NOx, are threats to human existence and cause environmental problems. Mainly, two techniques have been developed to drastically reduce these emissions, which are dry and wet processes. The wet process has several advantages, major identifiable advantages are the adaptability to the flue gas, low operating temperatures and no poisoning and inactivation catalyst. Also, a mixture of hydrogen peroxide and nitric acid are used as absorbents solution for NOx reduction in the wet process. The advantages of using this mixture include the ability to reduce the negative effect of NOx and does not contaminate the scrubbing solution. In addition, nitric acid has an economical advantage in the process considering the fact that it is produced in the process. Finally, it can be conducted at ambient temperature. This study furthermore used a mixture of hydrogen peroxide and nitric acid solutions as an absorbent to reduce NOx in hollow fiber membrane modules. The hydrogen peroxide oxidized HNO2 to nitric acid, while enhances the oxidation through an autocatalytic reaction. The effects of the feed gas flow rate, hydrogen peroxide concentrations and number of fibers on the NOx reduction, absorbed NOx and flux were varied to study. The experimental results showed that the increase in the feed gas flow rate from 100 to 200 mL/min decreased NOx reduction from about 98 to 94% but increased the absorbed NOx and flux from about 0.13 to 0.255 mmol/h and 0.85-1.63 mmol/m2.h, respectively The increase in proportion of NOx in the feed gas effect was dominant than the increase in absorbed NOx. An increase in hydrogen peroxide concentration from 0.5 to 10 wt.% in the absorbent solutions increased NOx reduction, absorbed NOx and flux from about 94 to 98%, 0.257-0.267 mmol/h and 1.09-1.13 mmol/m2.h, respectively. Additionally, the H2O2 plays an important role in enhancing HNO2 oxidation to HNO3. Furthermore, an increase in the number of fibers from 50 to 150 in the membrane module increased NOx reduction and absorbed NOx from 86 to 97% and 0.23-0.27 mmol/h. Flux decreased from 2.98 to 1.13 mmol/m2.h due to increment in the gas-liquid contact surface area.