Environmental Science and Pollution Research - In order to investigate the spatial and temporal variations of aerosols and its soluble chemical compositions of the data gap zone in the central... 相似文献
To reveal the formation mechanism of a pulse-jet airflow’s cleaning effect in a filter bag, a theoretical model is built by using the theory of the gas jet and unitary adiabatic flow according to given specifications and dimensions of the bags and resistance characteristics of the cloth and dust layer. It is about the relationship between cleaning system structure and operating parameters. The model follows the principle that the flow and kinetic energy of jet flow injected into a filter bag should be consistent with the flow of cleaning airflow in the bag and the pressure drop flowing through the filter cloth and dust layer. The purpose of the model is to achieve the peak pressure of cleaning airflow, which dominates the effect of the pulse-jet cleaning process. The cleaning system structure includes air pressure in the nozzle, structure and size of nozzle, exit velocity of nozzle, jet distance, and diameter of jet cross section. Based on the condition of the cleaning system structure and operating parameters established by using the theoretical model, Fluent software is applied to carry out a numerical simulation of the jet airflow field at the nozzle’s outlet, jet airflow field between nozzle and bag top, and cleaning airflow field in the filter bag. Experimental results are used to verify the reliability of the theoretical model. They are obtained in a pilot-scale test filter with a single bag, with length 2 m and in general full-scale dimensions of the cleaning system. The results show that when any rectification measure is not installed at the bag opening, the cross-sectional area covered by the jet gas is hardly sufficient to cover the entire area of the bag opening. A large portion of the gases injected into the filter bag will overflow reversely upward from the edge due to pressure differences between the upper area and lower area inside the bag opening. This led to a serious shortage of the cleaning airflow and ar limited increase in static pressure. When a venturi-type rectifier tube is installed at the bag opening, the jet flow is converted to funnel flow for which the cross-section velocity distribution is more uniform at the throat of the rectifier tube due to the guided effects of the upper tapered pipe. Then it is transited to stressful flow below the bag opening via rectified effects of the lower dilated pipe. The results show that the gap between the static pressure of gas in the bag and the expected value is significantly reduced. The theoretical value of the nozzle diameter is enlarged to compensate for two aspects of adverse effects of cleaning airflow and energy. This is because the flow is not a purely free-form jet from the nozzle to the entrance of the rectifier tube and because the gas suffers from local resistance while flowing through the rectifier tube. The numerical simulation and experiment show that the peak pressure of cleaning airflow in the filter bag is able to reach the expected value. The results confirm that the mechanism of the pulse-jet cleaning airflow and the calculation method of the pulse-jet cleaning system structure and operating parameters offered in this study are correct. The study results provide a scientific basis for designing the system of pulse-jet fabric filters.
Implications: Pulse-jet cleaned fabric filters are commonly used for air pollution control in many industries. Pulse-jet cleaning is widely used for this purpose as it enables frequent cleaning while the filter is operating. However, the theoretical system of the forming mechanism of the pulse-jet cleaning has not formed so far. This indicates the theoretical model plays an important role in designing effective pulse-jet cleaned fabric filters. 相似文献
Assessments of past environmental policies—termed accountability studies—contribute important information to the decision-making process used to review the efficacy of past policies, and subsequently aid in the development of effective new policies. These studies have used a variety of methods that have achieved varying levels of success at linking improvements in air quality and/or health to regulations. The Health Effects Institute defines the air pollution accountability framework as a chain of events that includes the regulation of interest, air quality, exposure/dose, and health outcomes, and suggests that accountability research should address impacts for each of these linkages. Early accountability studies investigated short-term, local regulatory actions (for example, coal use banned city-wide on a specific date or traffic pattern changes made for Olympic Games). Recent studies assessed regulations implemented over longer time and larger spatial scales. Studies on broader scales require accountability research methods that account for effects of confounding factors that increase over time and space. Improved estimates of appropriate baseline levels (sometimes termed “counterfactual”—the expected state in a scenario without an intervention) that account for confounders and uncertainties at each link in the accountability chain will help estimate causality with greater certainty. In the direct accountability framework, researchers link outcomes with regulations using statistical methods that bypass the link-by-link approach of classical accountability. Direct accountability results and methods complement the classical approach. New studies should take advantage of advanced planning for accountability studies, new data sources (such as satellite measurements), and new statistical methods. Evaluation of new methods and data sources is necessary to improve investigations of long-term regulations, and associated uncertainty should be accounted for at each link to provide a confidence estimate of air quality regulation effectiveness. The final step in any accountability is the comparison of results with the proposed benefits of an air quality policy.
Implications: The field of air pollution accountability continues to grow in importance to a number of stakeholders. Two frameworks, the classical accountability chain and direct accountability, have been used to estimate impacts of regulatory actions, and both require careful attention to confounders and uncertainties. Researchers should continue to develop and evaluate both methods as they investigate current and future air pollution regulations. 相似文献