Title of Invention

FLUID ENERGY MILL WITH A CLOSED CIRCUIT PNEUMATIC CLASSIFIER

Abstract

The invention relates to a fluid energy mill with a closed circuit pneumatic classifier comprising a semi-circular tubular grinding chamber providing the grinding zone; at least two grinding nozzle through which compressed air is fed to a grinding zone in a direction tangential to the inner periphery of the grinding chamber; pneumatic feeder having a nozzle-venturi for continuous feeding of the material to be ground; a vertical channel attached to a channel through a tubular channel for connecting the grinding chamber to a disc centrifuge pneumatic classifier the said channel extending into the said classifier, enabling tangential entry of the mixture of the ground material and air from grinding chamber to the classifier; and a recycle channel for recycling the remains after separating the ground product of required fineness to the grinding chamber.

Full Text

This invention relates to an ultra-fine fluid energy mill with a closed circuit pneumatic classifier. Responding to the growing demands of the processing industries for finer and high quality powder products, a novel idea for comminution was developed by powder technologists in which the material to be ground is accelerated in a high velocity fluid stream and allowed to undergo size reduction by mutual collision of particles. Being referred to as Jet milling or fluid energy grinding, this mode of size reduction is expected to consume more energy compared to conventional means like media milling. Still, such mills started finding industrial applications, as many of their advantages far outweighed their drawbacks, especially for industries related to drugs, pharmaceuticals, food processing, paint and pigment industries and for grinding heat sensitive and explosive materials. In the case of all these industries apart from their need for ultra-fine powders, they are very much particular to avoid any chances for contamination of their product and also to eliminate the effect of heat generated during media milling, on the physical and chemical properties of the material being ground. More investigations and researches in this field of fine comminution and various types of jet mills developed subsequently were primarily targeted to reduce the energy consumption or to ensure better utilisation of the input energy, while maintaining all the undisputed advantages of the mill or even trying to improve upon it. Based on the design concepts of various research groups the jet mills now in applications can broadly be classified into Jet-o-Hlzer and Microniser. The main design variation between the two is that in the former the grinding and classification take place in separate sections of the mill, while in the latter both the processes occur in the same chamber. Based on the design directions and conoepts followed during the development of the elliptical fluid energy mill and subsequently the circular tubular fluid energy mill and circular disc shaped fluid energy mill and based on the feed back from experimentation, a more energy efficient fluid energy mill, capable of achieving ultra-fine poweder products, is developed. The orientation of the ultra-fine fluid energy mill with a closed circuit pneumatic classifer Is vertical, with a semi-circular tubular shaped chamber fitted with optimised nozale locations for the grinding nozzles, constituting the grinding chamber. The leading end of this chamber is connected to a modified pneumatic disc-centrifuge classifier with the help of an uptake and a perfectly circular bend and the recycle channel of the classifier connected to the lagging end of the chamber. This closed circuit milling system is capable of controlling the fineness of the product on-line with the help of a classifer nozzle introduced at a specific location inside the classifier. Thus the invention provides an ultra-fine fluid energy mill with a closed circuit pneumatic classifier comprising a semicircular tubular grinding chamber providing a grinding zone; at least two grinding nozzles, through which compressed air is fed to the grinding zone in a direction tangential to the inner periphery of the grinding chamber; a pneumatic feeder having a nozzle-venturi for continuous feeding of the material to be ground; a vertical channel attached to a channel through a quarter circular tubular channel for connecting' the grinding ohamber to a disc centrifuge pneumatic classifier enabling tangential entry of the mixture of the ground material and air from grinding chamber to the classifier and a recycle channel for recycling the remains after separating the ground product of required fineness back to the grinding chamber. The grinding nozzles are aligned with respect to the grinding chamber in such a way that the axis of the nozzle jets are tangential to the inner wall of the semicircular tubular grinding chamber. Since the tendency of the circulating load of air inside the system is always to deflect the nozzle jets towards the outer periphery, the said direction of the nozzle axis will reduce the erosion of the outer wall of the grinding chamber. A pneumatic feeder using a nozzle-venturi for feeding the material continuously to the chamber, an uptake channel with a quarter circular tubular channel to connect the grindidng chamber to a pneumatic classifier in closed circuit. While the product leaves the system through the central outlet of the classifier, the classified material gets recycled to the grinding zone through a recycle channel connected to the lagging end of the grinding chamber. Fineness of the product from the classifier is controlled on-line by introducing a classifier nozzle at a specific location, without obstructing in any way the circular profile of the air stream. Expansion of air through this nozzle creates suction in the channels on both sides of the nozzle carrier in which the nozzle is mounted. This suction compliments the centrifugal force imparted to the particles. Higher the pressure maintained in this nozzle, better will be the fineness of the product. The fluid energy mill aocording to the invention will now be described with reference to the accompanying drawing: Figure 1 illustrate a preferred embodiment of the ultra-fine fluid energy mill according to the invention. It comprises a semi-circular tubular grinding chamber (A) which provides the grinding zone for the mill. Two or more grinding nozzles (B) are provided through which compressed air is sent into to the grinding zone. These are positioned for sending the oompressed air in a direction (C) tangential to the inner periphery of the semicircular tubular grinding chamber (A). The nozzles used are either sonic or supersonic depending on the requirements decided by the use of the mill. By positioning the j the grinding nozzles (B) to send'compressed air in a direction (C) tangential to the inner periphery of the grinding chamber (A) the erosion of the outer wall of the grinding chamber in use is found to reduce. A pneumatic feeder (D) with a nozzle-venturi is provided for feeding the material to be ground to the grinding chamber (A), Expansion of compressed air fed through the nozzle- venturi provides suction for dragging the feed material into the grinding chamber (A). A vertical channel (E) with a quarter circular tubular channel a disc centrifuge classifier (I) for separating the ground material of required fineness and recycle the remaining to the grinding chamber (A) for further grinding through a recycle channel (0) connecting the classifier (I) to the grinding chamber (A), Preferably an auxiliary pneumatic nozzle-venturi (G) is provided to the quarter circular tubular channel (F) for providing extra air to enhance the material flow from the grinding chamber to the classifier (I). The disc centrifuge classifier (I) comprises a central outlet (J) through which the ground product of required fineness is taken out along with air and the product is seperated using a cyclone separator filter bag assembly. A classifier noz2le (M) is located inside the classifier and held by a carrier (K). The shape of the carrier (K) introduces two channels (L) of uniform cross-section on either side of the classifier nozzle (M). The classifier nozzle (M) is provided with an air inlet (N) from the rear. The ultra-fine fluid energy mill according to the inventiion is suitable for fine grinding of material with minimum contamination during grinding. It is more efficient than the fluid energy mills already known. I CLAIM: 1. An ultra-fine fluid energy mill with a closed circuit pneumatic classifier comprising a semi-circular tubular grinding chamber (A) providing the grinding zone; at least two grinding nozzle (B) through which compressed air is fed to a grinding zone in a direction (C) tangential to the inner periphery of the grinding chamber (A); pneumatic feeder (D) having a nozzle™ venturi for continuous feeding of the material to be ground; a vertioal channel (E) attached to a channel (H) through a quarter circular tubular channel (F) for connecting the grinding chamber (A) to a disc centrifuge pneumatic classifier (I) the said channel (H) extending into the said classifier (I), enabling tangential entry of the mixture of the ground material and air from grinding chamber (A) to the classifier (I); and a recycle channel (0) for recycling the remains after separating the ground product of required fineness to the grinding chamber (A). 2. The fluid energy mill as claimed in claim 1, wherein the disc centrifuge pneumatic classifer (I), comprises a central out let (J) for collecting the ground material of desired fineness, a classifier nozzle (M) for controlling the fineness of the ground material provided with two channels (L) of uniform cross-section and held by a carrier (K) and an air inlet (N) attached to the classifier from rear. 3. The fluid energy mill as claimd in claim 1 wherein an auxiliary nozzle (8) with venturi is provided to the quarter circular tubular channel (F). 4. An ultra-fine fluid energy mill with a closed - oirouit pneumatic classifier substantially as herein described with reference to the accompanying drawing.

Documents:

157-mas-1999-abstract.pdf

157-mas-1999-claims filed.pdf

157-mas-1999-claims granted.pdf

157-mas-1999-correspondnece-others.pdf

157-mas-1999-correspondnece-po.pdf

157-mas-1999-description(complete)filed.pdf

157-mas-1999-description(complete)granted.pdf

157-mas-1999-drawings.pdf

157-mas-1999-form 1.pdf

157-mas-1999-form 19.pdf

157-mas-1999-form 26.pdf

abs-157-mas-1999.jpg