Batch Sedimentation Lab Manual PDF

## DEPARTMENT OF CHEMICAL ENGINEERING Motilal Nehru National Institute of Technology Allahabad Prayagraj - 211004, UP (India) ### FMMO LAB MANUAL ### Exp. Title: BATCH SEDIMENTATION ### Exp. No. 1 ### AIM: To study the performance of sedimentation process. ### APPARATUS REQUIRED: - Measuring cylin...

## DEPARTMENT OF CHEMICAL ENGINEERING Motilal Nehru National Institute of Technology Allahabad Prayagraj - 211004, UP (India) ### FMMO LAB MANUAL ### Exp. Title: BATCH SEDIMENTATION ### Exp. No. 1 ### AIM: To study the performance of sedimentation process. ### APPARATUS REQUIRED: - Measuring cylindrical flask - Lime stone powder - Stop watch - Glass rod ### APPARATUS DESCRIPTION: Sedimentation is a process used widely in the clarification of water and waste water. Particles settled from suspension in different ways, depending on the concentration of the suspension and the characteristics of the particle. The simplest type sedimentation is the settling of dilute suspension of particles which have little or no tendency to flocculate, in these circumstances, the prediction of clarification and their scale up to plant design is relatively straightforward. For higher concentration where inter particle effects become significant and agglomeration may take place, different regimes of settling rates occur, known as zone settling. Information from batch tests for such systems forms a vital part of the search for optimum design and operation of industrial sedimentation tanks. The sedimentation apparatus allows demonstration of these different characteristic for any chosen sediment/water system. Five equal sized glass cylinders are mounted vertically on a backboard incorporating measuring scale. Each of cylinders may be removed from the board of washing, filing, and mixing of solid particles. Solution containing different amount of suspension can be placed in the cylinders and the difference in sedimentation rates observed by measuring the changes in height of the various solid/liquid interfaces with respect to time. The equipment includes the following accessories necessary for a self-contained facility: stop clock, three plastic beakers of 2 litre capacities, specific gravity bottle. An accurate balance is required for weighing the solids. The whole apparatus is bench-mounted and provided with back lighting. ### THEORY: The principle of particle mechanics that under the separation described here. If a particle started at rest with respect to the fluid in which is immersed and is then moved through the fluid by an external force, its motion can be divided into two stages. The first stage is the short period of acceleration, during which the velocity increases from zero to terminal velocity. The second stage is the period during which the particle is at terminal velocity. The particle heavier than the suspending fluid may be removed from a gas or liquid in a large settling box or setting tank in which the fluid velocity is low and the particle have ample time to settle out. Simple device of this kind, however have limited usefulness because of the incompleteness of a separation and never required to remove the settled solid from the floor of the vessel. The industrial separators nearly or provide for the continuous removal of settled solid. The separation will may be partial or very nearly complete. A settler that removes virtually all the particles from a liquid is known as a clarifier, where as a device that separates the solids into two fractions is called classifier. #### Gravity Classifiers Most classifiers in chemical processing separate particles on the basis of size, in situation in which the density of the particles is the same as that of the larger ones. By adjusting the upward velocity of the liquid so that it is smaller than the terminal settling velocity of acceptably large crystals, this device carries unwanted fine crystals back to the crystallizing zone for further growth. The image depicts the experimental setup, with the five cylinders mounted vertically. The cylinders are marked with 100 ml to illustrate the volume of liquid used in the experiment. The five cylinders show the four distinct zones of sedimentation: Clarified zone, Discrete particle settling, Hindered settling, Transition zone, and Compression. The image is also labeled with the corresponding heights of each zone, for example, h_oo. ### BATCH SEDIMENTATION: These are several stages in the settling of flocculated suspension, and different zones are formed as sedimentation proceeds usually. The concentration of solids is high enough that sedimentation of individual particles or flocs is hindered by other solids to such an extends that all solids at a given level settled at a common velocity. At first, the solid is uniformly distributed in the liquid. The total depth of suspension is Z. After a short time, the solids have settled to give a zone of clear liquid, zone A and zone B of settled solid. Above zone B is a transition layer, zone C in which the solid contain varies from that in the original pump there in zone B In zone B, the concentration is uniform and equal to the original concentration, since the settling rate is same through this zone. The boundary between zone D and C and between C and B may not be distinct, but the boundary zones A and B are usually sharp. As settling continues the depth of the zone B and A increases. The depth of zone C remains nearly constant and that of zone B decreases. Eventually zone b disappears, and all the solids are in zones C and D. Meanwhile, the gradual accumulation of the solid puts stress on the material at the bottom which compresses solids in layer D. Compression breaks down the structure of floor or aggregates and the liquid is expelled into the upper zones. Sometime the liquid in the flocs spurts out of zone B as small as layer decompresses. Finally, when weight of solid is balanced by the compressive strength of the flocs, the settling process stops. The entire process is called sedimentation. The image shows the sedimentation curve, with the height of interface on the y-axis and the time on the x-axis. The sedimentation curve shows the zones of sedimentation and the rate of sedimentation over time. For example, the curve shows the top interface liquid/solid, and the sediment layer thickness, at different time intervals. ### RATE OF SEDIMENTATION: A typical plot of interface height (the boundary between zones A and B) is shown in figure. During the every stages of settling the velocity is constant, as shown by the curve. When zone D disappears, the rate of settling starts to decrease and steadily drops until the ultimate height is reached. For the example shown, the interface height was still decreasing at 20 h, and the ultimate height was only estimated. Slurries vary greatly in their settling rates and in the relative height of various zones during settling. The initial rate is a function of the feed concentration, but in the late stages, the settling rate also depends on the initial height Zo, since compression effects are more important with the thicker sludge layer. Experimental studies of the settling rate for different initial heights and concentration are needed for the design of a thickener. The image shows a conceptual graph of height versus settling time. The image shows the different zones and how the height of each zone changes over time. The settling time is on the x-axis and the height of visual interface, % of initial height, is on the y-axis. ### OBSERVATION TABLE: | Sl. No. | Height of clean liquid interface, Z(cm) | Settling time, t (hr) | |---|---|---| | 1. | | | | 2. | | | | 3. | | | ### Note: 1. Plot the graph Z (clean liquid interface height), cm Vs settling time, t hr. 2. Find the rate of sedimentation with the help of graph plotted; dz/dt i.e. slope of graph. ### Specifications 1. No. of cylinders = 5 2. Material of cylinder = Glass 3. Size of cylinder = 1 m height, 50 mm diameter ### Utilities Required - Electronic top Pan balance - Capacity: 3000 g - Sensitivity: 0.1 g ### Service Required - Electric supply: 220-240 V/ 50 Hz ### PRECAUTION: - Rinse the measuring cylinder flask properly so that no dust particle remains in it. - Don't disturb the apparatus during experiment. - Take readings carefully. - Plot the graph carefully. ### RESULT: Plot the graph Z (clean liquid interface height), cm Versus Settling Time, t (hr)