Title of Invention

A CLOSED CIRCUIT PNEUMATIC DISC CLASSIFIER

Abstract

The present invention relates to a pneumatic disc classifier in closed circuit characterized it comprises that a circular disc in vertical orientation; two slant walls modifying the bottom profile of the disc to converge to a square cross section at the bottom; a recycle channel split subsequently to a vertical channel and a semicircular channel ; a vertical uptake a quarter circular channel and a horizontal tangential entry channel completing the closed loop for the system; a pneumatic feeder with nozzleventuri and an auxiliary nozzle with nozzle-venturi ; a central outlet for the product and a classifier nozzle hosed in a nozzle carrier which is located inside the classifier and positioned for introducing two channels on both sides of the nozzle, connecting the circular profile of the classifier to the recycle channel.

Full Text

This invention relates to a closed circuit pneumatic disc classifier Classification, the process of separating particle streams into different size fractions, is one of the most important mechanical operation, next only to comminution, associated with mineral industries or for that matter any industry in the field of material processing and handling. As the field of powder or particle technology is growing so also the demand firom such industries for innovative methods, be it for the production of ultra-fine powders or for maintaining the size consistency of the material. The importance of the latter for better quality control, forced the pace of research and development in the field of classification and to come out with various classifiers capable of separating materials into pre-defined size grades. Based on the mode of operation, dry or wet process, and based on the operating principles different classification mechanisms have been identified to suit the needs of a particular industry. From the basics, the systematic movement of a particle in a flow, described by its trajectory, is governed by its stationery settling rate in the gravity field. The most important forces controlling the movement are the drag force, gravity, dynamic lift, inertia, centrifugal force and electrical forces. Different classifiers are identified based on the main forces used for classification. Mechanical air classifier is one of such system generally employed for the classification of very fine powders. Even when it can serve the purpose, it has got its own limitations, especially in the field of food, drugs and pharmaceutical industries, where contamination of the products is a prime criterion. It is in this context, a disc centrifijge pneumatic classifier was developed to operate based on pneumatic principles alone. The closed circuit pneumatic disc classifier according to the invention essentially consists of a circular disc chamber in vertical orientation, modified to suit the classification process. The bottom periphery of the disc is opened out and altered to form two slant walls. These slant walls are kept at a specific angle from the horizontal so as to ensure instant sliding of the classified fractions out of the circular profile of the classifier. Length of these walls were fixed in such a way that they converge to provide a square cross section for the recycle path at the bottom of the classifier. The recycle line is split into a vertical channel and a semi-circular channel. While the classified fraction is collected at the bottom of the vertical channel, the semi-circular channel, along with an uptake channel is used to complete the closed loop for the classifier. An outlet is provided at the centre of the disc chamber, the dimension of which depends on the specific requirements. The powder to be classified is fed tangentially to the chamber using a pneumatic feeder, with a nozzle-venturi arrangement. Suction due to the expansion of compressed air through the feeder nozzle drags the powder along with a substantial amount of air into the chamber. Classification is based on the centrifugal force imparted to the particles by rotation and the drag force. Since the outlet for the finer fraction is at the centre of the disc, the lowest radius of rotation, the particles have to undergo before leaving the classifier as product is the radius of the central outlet itself (Since this radius of the outlet, compared to the chamber diameter is much lower, such classifier can classify powders in finer size ranges. Towards providing the freedom to control the fineness of the product or the cut-size of the product, a classifier nozzle was introduced, with the nozzle carrier carrying the nozzle located at a specific location without any hindrance to the circular profile of the classifier. The shape and position of the nozzle carrier introduces two square channels on both sides of the nozzle, connecting the classifier profile to the recycle path. Expansion of air through this classifier nozzle creates suction in these two channels. This suction supplements the centrifugal force for finer classification. Higher the pressure maintained at this nozzle, larger will be the suction and finer will be the product. In other words, the classifier nozzle pressure can be adjusted to achieve any fineness required for the product. The scope of this closed circuit pneumatic disc classifier operating in close circuit can be made more versatile for achieving multiple size fractions in finer size ranges simultaneously. Towards this end, such classifiers are connected in series with the air-product mixture coming out of the central outlet of the first classifier taken to the tangential inlet channel of the second classifier and so on. The pneumatic feeder of the second classifier is replaced by a flow control nozzle with nozzle-venturi arrangement. The pressure at this flow control nozzle can be adjusted to maintain the same flow conditions inside the first classifier, while it was working as a single classifier unit. Depending on the number of size fractions required the number of classifiers to be connected in series can be fixed. The closed circuit pneumatic disc classifier according to this invention comprises of a circular disc in vertical orientation, modified by altering the bottom profile of the disc using two slant walls to converge to a square cross section at the bottom, a recycle channel split into two channels one vertical and the other semicircular, a vertical uptake a quarter circular channel and a horizontal tangential entry channel together completing the closed loop for the system, a pneumatic feeder with nozzle-venturi and an auxiliary nozzle with nozzle-venturi, a central outlet for the product and a classifier nozzle housed in a nozzle carrier located at a specific location inside the classifier, with the shape and location of the classifier nozzle carrier introducing two channels on both sides of the nozzle. This closed circuit pneumatic disc classifier can be operated as a battery of classifiers by connecting a number of classifiers in series, by replacing the pneumatic feeder of the second classifier onwards by flow control nozzles with nozzle-venturi which connects the product outlet of the first classifier to the tangential inlet channel of the next and so on. The closed circuit pneumatic disc classifier according to this invention will now be described with reference to the accompanying drawings. Figure 1 illustrate a preferred embodiment of the closed circuit pneumatic disc classifier according to this invention. Figure 2 illustrate a cascade connection of a plurality of closed circuit pneumatic disc classifiers according to the invention It comprises of a modified circular disc chamber (A) in vertical orientation. The disc is modified by altering the bottom periphery to two slant walls (B) which converge to form a square cross section for the recycle channel (C) at the bottom of the classifier. The angle of convergence (D) is maintained at a specific value to ensure instant sliding of the classified fi"action out of the circular profile (E) of the classifier to the said recycle channel. Towards converting the classification process into a closed circuit operation, the said recycle channel is split into a vertical channel (F) and a semi circular channel (G). The classified material or the coarser fraction from the classifier is collected at the bottom of the said vertical channel (F). The said semicircular channel leads to a vertical uptake channel (H), a quarter circular channel (I) and finally to the horizontal tangential entry channel (J) to complete the closed loop for the classification system. This closed loop helps to minimise the overlapping between the classified stream and the product stream, by maintaining a stream of circulating air carrying the fraction of material closer to the cut point size for repeated classification. The material to be classified is fed to the classifier using a pneumatic feeder (K) with a nozzle-venturi arrangement. Preferably an auxiliary nozzle (L) is used to supplement the total air requirements inside the system, depending on the classification needs of a given material. From the said feeder the air material mixture enters the classifier tangentially along with the circulating air-material mixture through the said tangential channel (J), which extends into the classifier itself The finer stream or the air-product mixture is taken out of the classifier through the central outlet (M), provided at the centre of the circular profile of the classifier and subsequently to a cyclone separator-fitter bag assembly for product separation. Towards controlling the fineness of the product coming out of the central outlet, a classifier nozzle (N) is introduced in the classifier. The location and shape of the nozzle carrier (O), carrying the said classifier nozzle introduces two channels (P) of square cross section on both sides of the nozzle. The air inlet (Q) for the said classifier nozzle comes from the rear of the classifier Expansion of air through the said classifier nozzle creates suction in the said channels and this suction compliments the centrifugal force imparted to the particles by rotation. Higher the pressure at this nozzle larger the suction and finer the product carrying out of the said central outlet. In other words, the desired cut size for the product can be achieved by varying the pressure maintained at the said classifier nozzle (N). Three closed circuit pneumatic disc classifier according to this invention are connected in series in the embodiment shown in figure 2. The air-product mixture from the central outlet of the first classifier cell (R) is connected to the tangential inlet of the second classifier cell (S) through a flow control nozzle with nozzle-venturi (U). Now, the air-product mixture from the central outlet of the second classifier (S) is connected to the tangential inlet of the third classifier (T) through another flow control nozzle with nozzle-venturi (U). These flow control nozzles helps to maintain the required flow conditions inside each of the classifier. In this embodiment the coarsest fraction of the powder is the first fraction collected below the recycle channel of the first classifier and the finest fraction is that collected from the central outlet of the third classifier. WE CLAIM : 1. A closed circuit pneumatic disc classifier characterized it comprises that a circular disc (A) in vertical orientation; two slant walls (B) modifying the bottom profile of the disc to converge to a square cross section at the bottom; a recycle channel (C) split subsequently to a vertical channel (F) and a semicircular channel (G); a vertical uptake channel (H), a quarter circular channel (I) and a horizontal tangential entry channel (J) completing the closed loop for the system; a pneumatic feeder (K) with nozzle-venturi and an auxiliary venturi nozzle (L) with nozzle-venturi; a central outlet (M) for the product and a classifier nozzle (N) hosed in a nozzle carrier (O) which is located inside the classifier and positioned for introducing two channels on both sides of the nozzle, connecting the circular profile of the classifier to the recycle channel. 2. A closed circuit pneumatic disc classifier as claimed in claim 1, wherein the auxiliary venturi nozzle (L) is provided to the semi-circular channel (G) for supplementing air circulation in the classifier.

Documents:

0183-mas-1999 abstract-duplicate.pdf

0183-mas-1999 abstract.jpg

0183-mas-1999 abstract.pdf

0183-mas-1999 claims-duplicate.pdf

0183-mas-1999 claims.pdf

0183-mas-1999 correspondence-others.pdf

0183-mas-1999 correspondence-po.pdf

0183-mas-1999 description (complete)-duplicate.pdf

0183-mas-1999 description (complete).pdf

0183-mas-1999 drawings.pdf

0183-mas-1999 form-1.pdf

0183-mas-1999 form-19.pdf

0183-mas-1999 form-26.pdf

0183-mas-1999 form-3.pdf