Environmental and economic issues concerning the use of wet scrubbers coupled to bagasse-fired boilers: a case study in the Brazilian sugarcane industry

For decades, wet scrubbers have been used to control particulate matter (PM) emitted by bagasse-fired boilers in the sugarcane industry. This choice was justified by their acceptable performance in meeting environmental standards, the abundance of water resources, and the fact that their operation was simpler and less expensive than other dry cleaning operations. However, the progressive tightening of PM emission limits, as well as the need for more rational water and wastewater management in these applications, has changed this aspect of the industry. Despite the extensive technical literature on wet scrubbers, the lack of up-to-date indicators of their performance in sugarcane industries has prevented the optimization of wet scrubbing processes. This paper clearly shows that the use of wet scrubbers can result in significant water and heat losses, as well as high operating costs for wastewater treatment stations (WTSs). Mass and energy balances were determined for a typical ethanol-sugar plant operating in Brazil, which is the world's largest sugarcane producer. The key boiler and scrubber performance indicators were evaluated experimentally over the course of a crop season and were compared to the legal particulate emission and water quality requirements in Brazil. The boiler processed an average of 114.8 t/h of bagasse containing 46.8% moisture and generated 4.75 t of gas and 28.2 kg of PM for each ton of dry burned bagasse. Of the total PM (ash and soot), 68% was collected as dry material in the grate, heat exchangers, and multicyclone; 25% was collected in the wet scrubber; and 7% was emitted to the atmosphere, in compliance with the Brazilian standards. The operation of the WTS linked to the gas cleaning system was inefficient, using 70% of the water to convey the dry PM retained in the boiler, heat exchangers, and multicyclone and only 30% to operate the wet scrubber. Evaporation caused the loss of 10.5% of the scrubbing water to the atmosphere. The transportation of moist cake (7.9 t/h, 78% wb) for disposal in fields resulted in significant fuel costs and water losses. The operation of the WTS accounted for 62% of the total capital expenditure of the cleaning system, while the wet scrubber accounted for only 38%. This work provides updated performance indicators and alternatives for optimizing a gas cleaning system to promote more rational water and wastewater management and savings for the sugarcane sector. Graphic abstract Required collection efficiency for bagasse boilers based on the inlet PM concentration and emission limits imposed in Brazil, China, and most countries

Miniaturizing wet scrubbers for aerosolized droplet capture

Particles dispersed and transmitted through the air (e.g., particulate matter pollution, bioaerosols) are ubiquitous and one of the leading causes of adverse health effects and disease transmission. A variety of sampling methods (e.g., filters, cyclones, impactors) have been developed to assess personal exposures. However, a gap still remains in the accessibility and ease-of-use of these technologies for people without experience or training in collecting airborne samples. Additionally, wet scrubbers (large non-portable industrial systems) utilize liquid sprays to remove particles from the air; the goal is to "scrub" (i.e., clean) the exhaust of industrial smoke stacks, not collect the particles for analysis. Inspired by wet scrubbers, we developed a device fundamentally different from existing portable air samplers by using aerosolized microdroplets to capture airborne particles in personal spaces (e.g., homes, offices, schools). Our aerosol-sampling device is the size of a pint of ice cream (0.5 L), can be operated without specialized training, and features a winding flow path in a supersaturated relative humidity environment enabling droplet growth. The integrated open mesofluidic channels shuttle coalesced droplets to a collection chamber for subsequent sample analysis. Here, we present the experimental demonstration of aerosol capture into water droplets. Iterative study optimized the non-linear flow manipulating baffles and enabled us to retain 83% of the aerosolized microdroplets in the confined volume of our device. As a proof-of-concept for bioaerosol capture into the liquid medium, 0.5-3 μm model particles were used to evaluate aerosol capture efficiency.

Experimental study of the dust-removal performance of a wet scrubber

A variety of dust control methods are often applied in coal mines, among which the application of wet scrubbers has proven to be an efficient technology for the removal of dust in airstreams, rather than diluting or confining the dust. In this paper, a wet scrubber design was developed. Based on a self-designed experimental test platform, the total dust concentration, respirable dust concentration, air volume, and average pressure drops of wet scrubbers with 12, 16, 20, and 24 blades were measured under different water intake conditions. The results show that the different water intake levels have only minimal effects on the air volume of the wet scrubbers. However, increased water intake had improved the dust removal efficiency of the wet scrubbers with the same number of blades. The wet scrubber with 16 blades was found to have the best dust removal efficiency at a water intake level of 1.35 m3/h. Its total dust and respirable dust removal efficiency reached 96.81% and 95.59%, respectively. The air volume was 200.4 m3/min, and the average pressure drop was determined to be 169.4 Pa. In addition, when the wet scrubber with 16 blades was applied in a coal preparation plant in China’s Shanxi Province, it was observed that the total dust concentration had fallen below 8.1 mg/m3, and the respirable dust concentration had fallen below 5.9 mg/m3. Therefore, the results obtained in this research investigation provide important references for the use of wet scrubbers to improve coal production environmental conditions.

Air Quality Management for Electroplating Industry for Mumbai Metropolitan Region, Maharashtra—Air Quality Management for Electroplating Industry

Electroplating is considered to be a major polluting industry because it discharges toxic materials and heavy metals through effluent like wastewater, air emissions and solid wastes. There are many registered electroplating units in Mumbai Metropolitan Region (MMR). The quantities of gaseous wastes generated from these industries were estimated and the existing control and treatment techniques for these gaseous wastes were evaluated. Further, Air Quality Modeling (AQM) study was also carried out to predict the concentration of acid mist with the help of emission, characteristics of stack and meteorology. A Gaussian plume model based SCREEN View software was used to predict concentrations for two industries which showed that the acid mist emissions from stack were under the consented limits. Further, health impact survey was performed at 1km radius of the industry to study the effects of air pollution on human health. It showed that 47%, 40% and 57% workers near the electroplating industries are suffering from chest pain, eye irritation and breathlessness respectively. Clustering of electroplating industries in the MMR will improve the waste management in the region. Installation of efficient air pollution control equipment like wet scrubbers can eliminate the hazards caused due to acid mist emissions from electroplating industries.

Performance Evaluation of Cyclone Particulate Controller and Wet Scrubber Unit in Paper Mill 7/8 PT. Pura Nusapersada Kudus

The need is increasing in line with the high market demand for a product. One product that is widely used is paper. One of the recycled paper industries is PT. Pura Nusapersada Unit Paper Mill 7/8, where the production process uses water vapor from a coal-fired boiler. This process can produce ash that can pollute the air so that air pollutant control devices such as cyclones and wet scrubbers are needed. It is necessary to evaluate the efficiency of the cyclone and wet scrubber by knowing the specifications and working principles of the tool, the emissions produced, the effectiveness of the equipment, the factors that influence, problems, operation, and maintenance. The method used is direct observation, interviews, data in the form of documents, references, and routine reports. The cyclone used is a multi-cyclone type, and the wet scrubber is a venturi scrubber type. From the calculations that have been done, the efficiency of the Hitachi Boiler is 94.195%, and the Hamada II Boiler is 96.844%. The boiler produces emissions that meet quality standards for the Minister of Environment Regulation No. 07/2007. The efficiency calculation should be done once a year so that the quality of the equipment is monitored and does not pollute the surrounding air quality.