pt lec.pptx particle technology ppt engr
- 1. Characterization of Particulate solid Properties UNIT OPERATIONS OF CHEMICAL ENGINEERING, 7TH EDITION, MCCABE, SMITH, HARRIOTT CHAPTER. 28
- 2. Particle Technology (An introduction) Particle technology is a term used to refer to the science and technology related to the handling and processing of particles and powders. It is also often described as power technology, particle science, powder science.
- 3. Particle Technology (An introduction) A knowledge of particle technology may be used in the oil industry to design the catalytic cracking reactor which produces gasoline from oil. Ignorance of particle technology may result in lost production, poor product quality, risk to health, dust explosion or storage silo collapse.
- 4. What is a Particle? a minute part of matter a very small speck of solid matter Unit of matter of indeterminate dimensions and volume
- 5. Why? Where? Most chemical engineers will find themselves working with particles at some point in their professional life Chemical engineers meet particulate solids in carrying out many unit operations Crushing Drying Filtering Crystallization Solid fluid reacting Dust collecting and many more
- 6. Objectives The objective of this course is to introduce the subject of particle technology to students in disciplines requiring knowledge of the processing and handling of particles and powders. Characterize particles and particulate systems Identify and design important traditional unit operations.
- 7. Introduction In addition to Chemical Composition, the behavior of particulate materials is often dominated by the Physical Properties of Constituent particles. From manufacturing and development perspective, some of the most important physical properties to measure are, Particle Size Particle Shape Surface Properties Mechanical Properties Charge Properties Microstructure
- 8. Importance…??? Reactivity dependence on Particle Size Solubility dependence on Particle Size
- 9. Particle Shape & Size
- 10. Particle Shape Regular shape particles can accurately be described by giving its shape and number of dimension. For an irregular shape particle, individual particles are conveniently expressed in term of their Sphericity. Sphericity is independent of the particle size. Dp = equivalent/nominal diameter Vp = volume of one particle Sp = surface area of particle
- 11. Sphere A sphere is a perfectly round geometrical object in three dimensional space that is the surface on a completely round ball.
- 12. For a perfectly spherical diameter, the value for Sphericity equals to 1. In case of Irregular shape particles, nominal value of equivalent diameter is taken. Nominal Size: Size used for the general identification of the actual size of the particle. Nominal size gives us a domain within which actual size lies with little bit tolerance. It will approximately be equal to actual size, but need not to be exactly the same as particle size. E.g: 100 ± 0.05 m rod is available.
- 14. Equivalent Spherical Diameter: Diameter of an irregular shape object is the diameter of a sphere of equivalent volume. Bulk Properties: An intensive property is a bulk property, meaning that it is the physical property of the system that does not depends upon the size or the amount of material in the system. E.g: temperature, density, hardness of the object etc. Intensive Properties: Properties that does not depend upon the size or the amount of material in the system, e.g: temperature, density, hardness of the object etc. Extensive Properties: Properties that depend upon the size or the amount of material in the system, e.g: mass, volume etc.
- 16. Particle Size
- 18. PARTICLE SIZE In general, diameter is specified for equidimensional particles. Most of the particles are not equidimensional, therefore they can not be specified by a single dimension “diameter”. Therefore the concept of equivalent sphere has been introduced.
- 19. Equivalent spheres in comparison with Particle dimensions: Based upon the measurement techniques, the particles are related to equivalent sphere diameters by, a. The sphere of the same volume of the particle. b. The sphere of the same surface area as the particle. c. The sphere of the same surface area per unit volume. d. The sphere of the same area when projected on a plane normal to the direction of motion. e. The sphere of the same projected area as viewed from above when lying in a position of maximum stability (as with a microscope). f. The sphere which will just pass through the same size of square aperture as the particle (as on a screen). g. The sphere with the same settling velocity as the particle in a specified fluid.
- 20. Mixed Particles and SIZE ANALYSIS If we have a sample of uniform particles of diameter = Dp, The total volume of the particles will be = m/ρp, (representing mass and density of the particles), Since the volume of one particle = Vp, Total volume ‘V’ of N particles = V = Vp.N The total number of particles in sample = N = m/ ρpVp Total surface area of the particles is given by,
- 21. Mixed particle size and size analysis Both these equations are applied to mixtures having various sizes and densities. The mixture is sorted into fractions, each of constant density and approximately constant size. Each fraction is then weighed, or the individual particle can be counted or measured by number of methods. Information from such a particle size analysis is tabulated to show the mass or number fractions in each size increment as a function of average particle size in the increment. An analysis tabulated in this way is called a differential analysis. The results are often presented in histogram as shown in the figure.
- 22. Description of populations of particles Particle population is described in terms of Particle size distributions. Cumulative Size Distribution. Frequency Size Distribution.
- 23. Specific surface area of mixture If the particle density ρp and Sphericity Φs are known, the surface area of particles in each fraction can be calculated and added to give the specific surface, Aw (The total surface area of the unit mass of particles): For deriving this equation, it has been assumed that Sphericity and density of the mixture is constant. Where xi = mass fraction in a given increment, Dpi = average diameter (taken as arithmetic average of the smallest and largest particle diameters in increment).
- 24. Average particle size The average particle size for a mixture of particles is defined in several different ways. Volume surface mean diameter Ds: If number of particle Ni in each fraction is known, instead of mass fraction xi, then:
- 25. Arithmetic mean diameter: NT = number of particles in the entire sample Mass mean diameter: Volume mean diameter: Total volume of the sample Divided by number of particles For sample consisting of uniform particles these average diameters are, of course, all the same. For mixture containing particle of various sizes, however, the several average diameters may differ widely from one another.
- 26. Number of particles in mixture The volume of any particle is proportional to its "diameter" cubed. a = volume shape factor For sphere the value of a is 0.5236 and for short cylinder it is 0.785. Assuming that a is independent of size, then:
- 27. Methods of particle size measurement UNIT OPERATIONS OF CHEMICAL ENGINEERING, 7TH EDITION, MCCABE, SMITH, HARRIOTT CHAPTER. 28
- 28. Screen analysis •Testing sieves are made of woven wire screens. •Openings are square. •Screens are identified by Mesh No. •Mesh No. is the numbers of opening per linear inch. •Area of opening in any screen = 2 x Area of opening in next smaller screen. •Mesh dimension of any screen = 1.41 x Mesh dimension of next smaller screen.
- 29. Sieving
- 30. Sieving Screens or sieve analysis is used to measure the size (and size distribution) of particles in size range of 0.0015 and 3 inch. Woven wire screens, Silk, Plastic cloth, perforated or punched plate. Openings are in the form of squares. Each screen is identified in meshes per inch. A stack of screens is arranged with the smallest mesh at the bottom and the largest one at the top. Vibratory motion is produced to cause better separation of particles. Particles retained on each screen are then removed and weighed to draw the Cumulative and Frequency distribution curves.
- 31. The results of screen analysis are tabulated to show the mass fraction of each screen increment as a function of the mesh size range of the increment. The notation 14/20 means “through 14 mesh and on 20 mesh”. Typical screen analysis is given in next slide. First column: mesh size, second column: width of opening of screen, third column: mass fraction of total sample that is retained on that screen xi (where i is the number starting from the bottom of the stack), fourth column: averaged particle size Dpi (since the particle on any screen are passed immediately by the screen ahead of it, the averaged of these two screen are needed to specify the averaged size in that increment). Fifth column: cumulative fraction smaller than Dpi. Sieving
- 33. Description of populations of particles Particle population is described in terms of Particle size distributions. Cumulative Size Distribution. Frequency Size Distribution.