Presentation on theme: "PARTICLES Authors: Dr. Bajnóczy Gábor Kiss Bernadett Tonkó Csilla BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL."— Presentation transcript:
PARTICLES Authors: Dr. Bajnóczy Gábor Kiss Bernadett Tonkó Csilla BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING
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Particles Properties: solid and/or liquid state small size varied composition can cause significant environmental damage Aerosol: solid and/or liquid particles, dispersed in gas Smoke: solid particles, dispersed in gas Fog: liquid drops dispersed in gas Classification: Alive or lifeless material alive: bacterium, fungi, spores lifeless: soot/smut, dust, sea salt, etc. (deal with them) particles origin: Primary: direct in the course of some process, e.g. condensation, erosion Secondary: from gaseous material
Harmful effects of particles Particles penetrate deeply into the respiratory system: Bigger than molecule, but not in settling size range Get deeper than molecule (slow Brownian motion) Increase the effect of toxic gaseous air pollutants: SO 2, NO 2 etc. absorb at the particles surface - get deeper Increasing turbidity of atmosphere Visibility decreasing Warming effect of solar radiation is restricted Gaseous material → solid particles. NH 3 + SO 2 → ammonium sulfate
Primary emission (the particles get direct into the atmosphere) Secondary emission (the particles formed from gaseous state in the atmosphere) (1.) The maximum quantity is natural origin from seawater seawater surface → bubble → burst → → wind → salt crystals after evaporation background aerosol. Bubble burst → salt crystals Natural source of particles
(2) Volcanic eruption: variable quantity – sometimes significant amount is emitted into the atmosphere Volcanic ash: due to small size, long residence time in the atmosphere (3) Natural source of hydrogen sulphide → sulfuric acid and ammonium → ammonium sulphate particles (4) soil erosion dust (5) forest fire. wind
Particles from human activities Different industr ial processes (stone crushers, grinding, metallurgy, cement and lime production, etc.) and the result of energy generation from coal. Less, but not negligible : waste and agricultural burning and transportation.
Size of particles Size range: 0,0002 – 5000 μm Atmosphere pollution: 0,001 – 100 μm. Size depends on source: >10 μm: usually from mechanical processes (grinding, breaking, erosion etc.) 10 – 0,1 μm: result of burning process In atmosphere: two main group μm ≥ particles PM ,5 μm ≥ particles PM 2,5 Another classification: 1. Huge particles: diameter > 1 μm 2. Large particles: 0,1 = = 1 μm 3. Aitken particles: diameter < 0,1 μm
Dangerous range for the lungs Particle size in micrometer
Formation of particles Soot Carbon-rich (55-80 %), agglomerate of nm particles Size: may be higher than 10 μm Compound: carbon, hydrocarbon, S and N content compounds, microelement Carbon content compound → soot
Simplified process of soot formation Initial process is similar to PAH formation, thus the soot always contains carcinogenic PAH substances. Soot in flame Soot-C + O → CO Soot-C + OH* → CO + H Soot-C + NO → CO + N Soot-C + H 2 O → CO + H 2
Formation of particles Ash Origin: coal and biomass firing The fuel does not contain ash. It forms from the ash forming compounds during the combustion. Coal firing: a./ acidic ash forming: SiO 2, Al 2 O 3 b./ basic ash forming: CaO, Fe 2 O 3, MgO Biomass firing The ash forming materials mainly SiO 2 and KCl The ash forming materials may imbedded in the solid fuel or may be individual, separated particles.
Behavior of ash forming particles Individual inorganic particles quickly melt and evaporate and will condensate in amorf or crystal form on the cooler part of the boiler (heat exchanger) Similar, but delayed process takes place with the imbedded inorganic particles. Metal evaporation from the carbon containing fuel, due to the metal oxide reduction by carbon at high temperature. The metal steam is oxidized by the oxygen content of flue gas forming metal oxide particles mainly in PM 2.5 range The non volatile inorganic matters form PM 10 particles. potassium chloride crust in heat exchanger – frequent by burning of herbaceous plants
FATE OF PARTICLES FROM THE ATMOSPHERE All particles deposit on the soil surface. Differences are only in the residence time in the atmosphere The residence time depends on the particle size Two possibilities to deposit on the soil surface Dry deposition Wet precipitation
Dry sedimentation particle size μm Sedimentation velocity cm/sec < 0.1negligible 0,18 x ,08 x , FATE OF PARTICLES FROM THE ATMOSPHERE DRY DEPOSITION larger particles will have the opportunity to reach the soil by dry sedimentation upward air currents counteract the deposition 20 % of the atmospheric particles leave the atmosphere by dry deposition
FATE OF PARTICLES FROM THE ATMOSPHERE WET PRECIPITATION RAIN OUT WASH OUT Falling rain or snow collects particles from the atmosphere and carries them to the earth‘s surface Particles serve as site (nuclei) on which water condenses or ice form Particle size > 0.1 μm Particle size < 0.1 μm These small particles, Aitken particles are so small that due to the impact pressure in front of the falling raindrop, the Aitken particles bypass the drop. RAIN DROP
EFFECT OF PARTICLES ON PLANTS Reduction of photosynthesis: particles on the leaf surface reduce the irradiation. This effect was significant in the vicinity of former cement factories. The dust settled on the surface of leaves or fruits may contain toxic matters. The consumption of these plants by humans or animals might be unhealthy
HEALTH EFFECT OF PARTICLES Particles, which penetrate the human body: themselves toxic content adsorbed toxic material Harmful effect – size-dependent Most of them fix in nose or deposit on upper trachea Cilia movement → deposited particles travels up → pharynx particle size > 7-10 μm
HEALTH EFFECT OF PARTICLES particle size in range 0,1- (7-10) μm Most dangerous particle size range: Gets down into the alveoli Settles on the gas exchange surface decreasing the oxygen – carbon dioxide exchange There is no cleaning mechanism in the alveoli mining disease: silicosis particle size < 0.1 μm There is no sedimentation during inhalation and exhalation.
Particle elimination techniques Taking into account 1. Gas flow parameters: limited opportunities at high temperature and pressure than for atmospheric pressure and below 200 °C 2. Particle parameters: size and material quality BASED ON EXTERNAL FORCE BASED ON BARRIERS cyclonwet dust separator electrostatic precipitator decreasing particle size bag filter gravitational settling chamber filter-bed with granulates
Efficiency of particle separators Efficiency of elimination < 1μm1-3 μm3-10 μm> 10 μm Electrostatic precipitator ,5 Bag dust filter~100 Venturi-washer>7099>99 Multi cyclone
Gravitational settling chamber The simplest, but least effective effective removal: particle size >50 μm used in water purification
CYCLONE ~15-30 m/sec gas velocity centrifugal force is applied several g/m 3 particle content can be decreased under 0,1 g/m 3 Advantage: Wide temperature range, even T >1000 °C. High efficiency (η=95%) and cheap Disadvantage: particle size < 10 μm, efficiency decreases drastically Better efficiency: more cyclone serial or parallel connection (multi cyclone) particles purified gas dusty gas
ELECTROSTATIC PRECIPITATOR Flue gas cleaning method of plants using solid fossil fuels. Advantage: simple structure without moving parts good efficiency low electric energy demand efficiency: 0,2-0,5 μm particles : 97-98% particles size >2 μm : >98% removal efficiency is influenced by temperature (preferred interval: 120 – 200 °C) and the specific resistance of particle
Theory of electrostatic precipitator Ionization voltage < voltage gradient < breakdown voltage
ELECTROSTATIC PRECIPITATOR specific electric resistance [ohm*cm] no charge up excess of CaO, MgO, SiO 2, Al 2 O 3 quick charge loss excess of Fe 2 O 3, Na 2 O, H 2 O BEST RANGE
Bag dust filter The best efficiency dust separator (> 1μm particles: ~99%) Application: 120°C – 200°C Filter cake thickening results in better efficiency Advantage: Efficiency of elimination doesn’t depend on the electrical properties of particles. Due to the adsorption on filter cake elimination of gaseous pollutants: e.g. dioxins. Disadvantage: Filter cake thickening → filter resistance increases → batch filtration technology elimination of filter cake with shake or back pressure