Particle Size Distribution and Cyclone Efficiency Distribution Essay

In this experiment take upion cogency of a cycl matchless has been obdurate for two types of constituents Fly ash and MgO in an air stream. much(prenominal) a corpse is commonly found in in sploshries victimisation coal and refractories. speck surface of it dissemination of ambient air as tumesce as cycl ace baffle has also been footprintd using Electrical Low wring Impactor (ELPI). The collection efficiency of the cyclones was in 85 -95% range for Fly Ash patter and approximately 96% for MgO dust under experimental conditions.The pinpoint coat diffusion in the ambient air as wellspring as in the cyclone exhaust was showed a log normal dispersion and each of these scatterings was composed of more(prenominal) than one sizing of it of it scatterings. A. Introduction In modern industrial era we have to live with dust and powders on continuous basis. There atomic build 18 numerous industrial processes that expenditure earthy sensibles in powder form l ike powder metallurgy, sintering plants in coordinated steel plants, cement industry, polymer engineering etc. to name a few.It is not unreasonable to expect that the industries that use powders as raw material, throws lot of particulate matter matter into the atmosphere around it. Even in the cases, when the raw material in not a powder, the emissions contains lot of particulate matter. approximately examples ar emissions from pillory furnaces, coal fired plants etc. to name a few. vehicular pollution is one of the major quotations of suspended particulate matter (spm) in the atmosphere in the urban atomic number 18as. Therefore, the knowledge of instalment size diffusion is required and very(prenominal) useful in many cases. Some examples be the following Estimation of dust hazard to the personal handling powders in industries Designing an equipment for removing dust from a gas stream like exhaust gas of blast furnace and other furnaces Selection of a suitable dust cleaning system for a given environment Estimation of the efficiency of filters and other dust collection systems Identifying the source of the dust particles Estimation of properties of an aerosol tramp etc. Therefore, it is useful to understand the method and practices of amount and describing particle size dispersal and also the various methods and instruments that are employ to clean dust from a gas stream.This experiment is concerned with sizing distribution of atmospherical dust and the efficiency of a dust collection system go out be determined. The following section described different distributions of particle size in a dust take. A. 1 Description of particle size distributions Dust particle or airborne particles are not of a given size rather there are particles of different sizes in a dust warning. This size range can be very large in the range of tens of nanometers to hundreds of micron. The exact size distribution depends upon the source of the particulate matter.For example size distribution in a blast furnace exhaust will be different from that in a wheel emission and so on. A particle size distribution can be described by the following mathematical expression Here, d is the diameter of the dust particle and dN is number of the dust particle in the diameter range d to d+dd. a, b, ? and ? are the constants. Depending on the value of these constants there are two kinds of particle size distributions. unity is Nukiyama Tanasawa distribution and the other is rosin-Rammler distribution. For Nukiyam Tanasawa distribution, ?= 2 and ? = 1 and the expression is Rosin Rammler distribution is described by the following expression The Rosin Rammlerdistribution was developed to represent size distribution of coal particles, that was received by sieving of coal particles. Here di is a particular screen door size or the minimum size of a particle retained by that select R is the pitch of the coal particles retained by all the sieves wi th size d > di and was expressed as percentage of the total coal weight b and n are constants. To evaluate these constants in these size distributions, one needs to do curve fitting.Therefore, it is easier to go for simpler statistical distributions based on normal distribution. For any distribution, there is a basal and a banner excursus. For a sample these can be calculated by using the following formulae Sample Mean Sample Standard Deviation From these sample statistics one can calculate tribe parameters like true besotted or population mean, ? and old-hat distribution ? with certain degree of accuracy. However, if the sample can be considered to be true representative of the true population then one can take sample statistics (mean and step deviation) as population parameters ? and ?.While the mean is a measure of the central tendency, standard deviation gives distribution of particle size around the mean. If standard deviation is large then the distribution is wide and vice versa. If two more parameters skew and kurtosis that measure symmetry and peakedness respectively are also used in conjugation with mean and standard deviation, then can only describe a size distribution. For a normal distribution, skew and kurtosis are zero and the distribution is mono-modal with peak at the mean and is symmetric most the mean. Such a distribution is applicable for simple distributions with m/s > 2. 5.If this ratio is littler then the distribution, generally shows large positive skew. To rein in such a problem one goes for log-normal distribution, which is a normal distribution of the logarithm of the particle size. Most of the natural size distributions are surpass described by log-normal distribution. As mass distribution is more becharm and used frequently, therefore, one can deduce mass distribution from size distribution. To do this one needs to calculate mean and standard distribution of the mass of the particles and this is done by dividing indi vidual size measurements by trance calculating the mean and the standard deviation.For most of the pollution control applications log-normal distribution is used. Probability distribution function (pdf) for such a distribution with mean ? and standard deviation ? is given by the following expression Such a distribution is shown in figure 1, below. In this case, the peak shifts in left direction with increasing standard deviation, ?. Fig. 1 Shift of the hazard distribution peak in left direction with increasing standard deviation of the sample There is another very important cyclorama of particle size distribution.Generally a dust sample amass from certain location does not consist of a single distribution instead it consists of many size distributions. It is easier to identify and separate these distributions when the peaks are well separated. However, many times the peaks are so close that these distributions mingle up as a single composite size distribution and one needs to ex tract individual distributions out of this composite distribution by carefully deconvoluting the composite size distribution. Before describing a size distribution, one needs to first measure the size distribution.There are many instruments that help in measurement of particle size and the size distribution. Some important proficiencys are described in the following section. A. 2 measurement of Particle Size and Size-Distribution Sieving This is the most conventional and easiest method for particle size-distribution measurement. In this case a representative sample of the particulate matter is taken by suitable have method like divided cone method. In divided cone method, the particulate matter is made as a cone and one quarter of the cone is taken.This process is repeat hill the final sample size is taken. This sample is then sieved by using a series of sieves of different sizes in a back-to-back order. The particle that remains above the sieve of a particle number (size) is given that size and in this manner the size-distribution of the entire sample is measured. test size is given by a number. That number represents number of aperture in a linear inch. Thus a sieve of size 75 means, there are 75 apertures in one inch of that sieve and so on. Therefore, a larger sieve number corresponds to a smaller sieve size.This method is very easy and suitable for coarse particles of size greater than 50 ? m. However, for finer sized particles, this technique becomes very unreliable. visual Microscopy Optical microscope is also very useful method to measure size distribution of particulate matter. This method can be used to measure size distribution of particulate matter from any source. Different sampling methods can be used to collect the sample for size distribution measurement. Some of these are (i) Filtration Membrane filters are generally used to collect samples that have different color or refractive index than the filter.(ii) depository on a glass slide is another useful technique, oddly for large particles. However, for getting a representative sample one should be careful. (iii) Thermal precipitation is another useful technique however, care should be taken to avoid segregation of sizes. (iv) Electrostatic precipitation on a glass slide or electron microscope grid is another technique that is commonly employed. However, optical microscopy is limited to 1 ? m sized particles as maximum magnification is 1000 only. This is because, motiveless is the probing signal and its wavelength is of that order.For measuring the size distribution if still finer particles one needs to use scanning electron microscope (SEM) and transmission electron microscope (TEM). In case of SEM a rivet electron beam is scanned in a raster and the image is make by collecting the different type of electron signals like inessential electron or back scattered electron. In case of TEM, the focused electron beam is transmitted through the particle and an imag e of the particle is formed at higher magnification 100,000. Cyclones Cyclones are used in general as dust removing system however, these are also used for separating particles into different size groups.One example is use of cyclone in personal dust sampler to separate the powder into two fractions one which is respirable and another which is not. cascade down impactors In this system, particles are pile up in different size groups in different typifys according to the aerodynamic impaction onto a substrate. Each stage can be analyzed chemically, measured using a microscope or can be even weighed electronically. These are used for sampling of particulate matter in atmosphere or in chimney or furnace exhaust gas. These are capable of sizing the particulate matter in 0.05 to 10 mm range. These systems have evolved considerably and modern systems are supply with quartz crystal microbalance for detecting mass number of the dust particle and even electrical detection of the parti cles, which has been charged before classifying into different sizes. One such system is Electrical Low Pressure Impactor (ELPI). This equipment will be described in somewhat detail in the next subsection. public exposure Battery In this system particles are classified based on their ability to diffuse through a series of mesh screens. smaller particles diffuse faster and vice versa. Finer particles are thus collected easily than the coarser particles. This system can be used for particles smaller than 1 ? m. Electrical Mobility Analyzers In this system, the particles are charged prior to separation. The charged particles are separated by applying electric field. Smaller particles have higher mobility collectable to smaller mass than the larger particles. Therefore, electric field removes the particles in selective manner at different stages according to their sizes.This system can do sizing of particles in the size range 1 ? m to 1 mm. Light Scattering Devices These are based on scattering of write down by the dust particle in the suspension. It can use ironical as well as wet suspension. The angle of scattering of light is related to its size. Normally a highly collimated laser light is used. though the minimum size is limited by the wavelength of the light and is 0. 3 mm newer systems have been designed that can measure particles in nm size range as well. However, these are costly equipments.