Particle Technology - Chapter 1 PDF

CHAPTER ONE  PART- I Introduction to Mechanical Unit Operations  INTRODUCTION Chemical Engineering is the branch of engineering which is concerned with the design and operation of industrial chemical plants. A chemical or process plant is required to carry ou...

CHAPTER ONE  PART- I Introduction to Mechanical Unit Operations  INTRODUCTION Chemical Engineering is the branch of engineering which is concerned with the design and operation of industrial chemical plants. A chemical or process plant is required to carry out transformation of raw materials into desired products efficiently, economically and safely. A chemical engineer is the one who develops, designs, constructs, operates and controls any physical and/or chemical or biochemical changing process.  Chemical Engineering is branch of engineering which deals with the production of bulk materials from basic raw materials in a most economical way by chemical means. Chemical engineer role  Also engaged in the processing of  The operations carried out in the chemical process industry involving physical changes in the materials handled/in the system under consideration are regarded as unit operations.  Features of unit operations : (i) They are physical in nature. (A physical change results in a change in property of matter and it requires some sort of driving force.) (ii) They are common to all types of diverse industries (with no change in concept, merely change in conditions). (iii) Individual operations have common techniques and are based on the same scientific principles irrespective of/regardless of the materials being processed. (iv) Practical methods of carrying them out/conducting them may be more or less different in different industries. (v) They are independent of industries in which they are carried out  Broadly, unit operations are : (i) Mechanical operations e.g., size reduction, conveying, sieving, etc. (ii) Fluid flow operations in which the pressure difference acts as a driving force, filitration, solid fluidization (iii) Heat transfer (operations) in which the temperature difference acts as a driving force e.g., evaporation and heat exchange (iv) Mass transfer operations in which the Mechanical operations involving particulate solids are : (1) Size reduction-crushing and grinding. (2) Mixing-solid-solid and liquid-liquid, etc. (3) Classification-screening, froth flotation, magnetic separation, jigging, tabling and electrostatic separation (classification - it comprises of techniques of classifying a solid mixture into fractions, which differ from each other in some property) and wet classification. (4) Solid-fluid separations - filtration, sedimentation and centrifugal separation. (5) Gas-solid separations - dust collection, bag filtration, electrostatic precipitation. (6) Solid handling - storage, feeding and conveying. MECHANICAL SEPARATIONS These separation techniques are applicable to heterogeneous mixtures and grouped into five headings as: (i) separation of solids from solids, (ii) separation of solids from solids in liquids, (iii) separation of solids from liquids, (iv) separation of solids or liquid drops from gases and  Solids are separated in the dry state by screening, electrostatic separation and magnetic separation. Solids are separated from gases by gravity settling, centrifugal separation/settling filtration and electrostatic precipitation. Solids are separated from liquids by filtration and sedimentation. Various methods that are used for the separation of solids from solids in liquids include jigging, flotation, classification and tabling. Immiscible liquids are separated from one another by using either a gravity decanter or a centrifugal decanter.  Examples physical process which are considered unit operation Chemical Engineers work in four main segments of the chemical process industries - research and development design, production and sales. BUSINESS DEVELOPMENT: SALT PRODUCTION CANDLE PRODUCTION WAX PRODUCTION AJAX PRODUCTION LIQUID SOAP PRODUCTION FUEL ALCHOL PRODUCTION  PART- II PARTICLE TECHNOLOGY Particle size measurement Particle size measuring methods e a n alysis Imag qu e 1. Microscopic techniques: techni are based on direct observation (used as a reference method) Light microscopy (>0.5m) (Scanning) electron microscopy (>5nm) 2. Sieving  Sieve analysis is performed using a stack of sieves where each lower sieve has a smaller aperture size than that of the sieve above it. Dry sieving (50 m – 10cm) Wet sieving (>20 m)  Aperture size : the dimension of the opening.  Mesh number : the number of openings per inch. E.g. 200 mesh = 200 openings/inch = 74 m/opening  The particle size of the material remaining between the two sieves is mostly accepted to be halve of the sum of the two sieve openings.  The results of the sieve analysis can be represented by: Histogram Differential Distribution Cumulative distribution Sieve standards: Mesh size vs. aperture size 3. Sedimentation  It depend on the fact that the terminal velocity of a particle in a fluid increase with size.  s   f gd sph 2 Based on stokes’s law:  18 18 x d sph    s   f g t  Stokes's diameter (dst) is defined as the diameter of the sphere that would settle at the same rate as the particle.  Particle size range 50 m – 0.5 m Detection techniques: Photo, X-ray, Gravimetric, Densitometric, Pipette-sedimentometry Sedimentation in a centrifugal field is applicable (1 m – 1nm) 4. Electrical sensing zone (coulter counter)  Instrument measures particle volume which can be expressed as dv : the diameter of a sphere that has the same volume as the particle.  The number and size of particles suspended in an electrolyte is determined by causing them to pass through an orifice an either side of which is immersed an electrode. The changes in electric resistance as particles pass through the orifice generate voltage pulses whose amplitude are proportional to the volumes of the particles. Size range (400 m – 0.5 m) Electrical sensing zone (coulter counter) Helps to count the particles Based on the resistance b/n the electrodes Particle size measurement Light scattering techniques  Particles pass through a laser beam and the light scattered by them is collected over a range of angles in the forward direction.  The angles of diffraction are, in the simplest case inversely related to the particle size.  Distribution of scattered intensity is analysed by computer to yield the particle size distribution. Light scattering techniques Light scattering techniques Size Distribution Analysis  PART- III SCREENING TECHNOLOGY END