“Reduction of nanoparticle emissions by the optimization of residual combustion gases filtering processes“
Nanometric particles represented a subject of high interest in the last two decades of scientific research. The world is increasingly pressing problem highlights the damaging effect of nanopowders and liquid acids or dioxins and furans (< 100 nm).
These, once inhaled, get very quickly into the blood stream and cannot be eliminated because they cannot be identified by the macrophage cells. Recent research has shown that if the raw material is not hazardous, it can become toxic if it is in the form of nanoparticles. Besides the particle composition, their size is very important, too, from the public health point of view. Inhaled nanoparticles can because free radicals can damage DNA and alter gene, increasing the probability of producing cancer and increased incidence of teratogenic and mutagenic events. The industrial emissions (waste incineration, metallurgical industries, cement factories, thermo centrals, etc.) and the emissions of internal combustion engine are main responsibility in terms of nanoparticles pollution.
Results in the form of smoke gases from combustion processes contain, in addition to carbon dioxide and water, at least traces of finely divided carbon (VOC), carbon monoxide, oxides of nitrogen, phosphorus and sulfur, halogen acids, metal oxides, that heavy metal vapor. The de novo synthesis, VOCs and carbon monoxide in the presence of halogenated acids pass into the halogen derivatives of dioxins and furans, which are included as such in the form of nanoparticles or adsorbed on finely divided carbon evacuated through the flue gas stream, along with the other components mentioned. All chemical compounds contained in exhaust gases from combustion processes have adverse effect on the atmosphere, biodiversity and human body. Spreading both in the form of nanoparticles and adsorbed on finely divided carbon determined to maintain long as very fine suspension in the atmosphere and also the most direct way of assimilation pulmonary, blood and cells establishment of these emissions.
The pollutant emitting sources are generally equipped with various filters for particles, but they work only on micrometric particles, while the nanometric particles almost entirely escape in the environment. Although the mass of the nanometric particles is small in comparison to the mass of the micrometric particles, the first exceed in number almost 4 magnitude orders the rest of the particles
Romania adopted a large part of the community legislation in the environmental protection domain. The adopted legislation (HG 541/2003; MAPM Order 462/1993) limits the powder emissions to 30-50 mg/m3 for the large burning installations, and 50 mg/m3 for other industrial sectors, but there are no efficient solutions regarding the filtration of nanoparticles.
The project proposes to make a study on the limitation of emissions of nanoparticles in the atmosphere by optimizing the conditions for filtering waste gas.
The classical methods used in manipulating (retaining and separation) of micrometric particles have been tried mostly unsuccessful in the case of nanometric particles in the last years [5-9]. In traditional installations capture only a small fraction of nanoparticles emitted are collected, and that only when attached to larger particles. The mechanical devices (cyclones, sack filters, sedimentation rooms) are not effective, due to the small weight of the nanoparticles, and the chemical effects are slow and can alter the nanoparticles composition during the procedure. The classical electrostatic filters (based on Corona effect) have a high efficiency in retaining micrometric particles (93-99%), but the nanometric particles escape almost totally in the air.
The most promising methods used lately in manipulating the nanoparticles are the ones based on dielectrophoresis (DEP). This method consists in the movement of polarizable matter placed in non-uniform electric field, without being previously electrically charged. The dielectric particles move in non-uniform electric fields because of the interaction between the induced dipolar momentum within the particle and the applied electric field. The dielectrophoretic force depends on the size of the particles, their conductivity, the dielectric constant of the particles and of the medium, and on the gradient of the square of the applied field intensity. Because it does not depend on the direction of the field, DEP can also be generated by alternating fields, hence making the dielectrophoretic force very selective, due to the dependence of the dielectric constant on the frequency. In fluid mediums, dielectrophoretic force and the hydrodynamic forces of nature (viscosity) determine the trajectory of a particle, weight, Archimedes, thermal, Brownian, and quantum forces due to the small dimensions of the particles. All these forces give a resultant dependence on the particle physical properties, fluid medium and the applied field (frequency, intensity), which causes deviation and finally retention in predefined areas, resulting in reducing the concentration of nanoparticles or even removed from the fluid environment . Because there is no unitary model to describe the electrohydrodynamic of the nanoparticles up to the present, the projects intends to study the movement of the particles with nanometric dimensions subjected to the forces enumerated above. After the numerical implementation, the model will provide information on the dynamics of the nanoparticles, in order to achieve the knowledge needed in building some devices for manipulating the nanoparticles. The numerical simulation is one of the most efficient, most economical and most rapid tools in investigating the behavior of complex systems. The use of this method involves at least two steps: building a mathematical model realistic enough to describe correctly the studied system (in our case – nanometric suspension of particles in a fluid medium subjected to electric fields), and elaborating a numerical code to solve the mathematical problem, with the desired precision in an acceptable computing time. The final goal of numerical simulation will be to find a set of parameters for which the problem of retention of nanoparticles in fluid medium (wastes gases) takes place with maximum efficiency, following research that experimental stage of the project, the device can be designed taking into account simulation results. Moreover, based on the experimental results, a feedback can be performed, leading to the improvement of the mathematical model used. The mathematical computations will be performed using a specialized computer program, ANSYS Multiphysics, which uses the finite element method. This software has programs dedicated to fluid mechanics problems, to electric analysis at low and high frequencies, in two and three dimensions and will be purchased from the project budget.
On the other hand, the project aims to estimate the extent of the pollution with nanoparticles in the city of Timişoara and identify operators whose production processes leading to emission of nanoparticles. In parallel, we will carry out activities to inform the population about the risks of nanoparticles emission, as well as visits to the undertakings responsible for emissions, in order to estimate their intention to invest in equipment with nanometric particulate filters.