Fluid energy mills are used to reduce the particle size of a variety of materials such as pigments, agricultural chemicals, carbon black, ceramics, minerals and metals, pharmaceuticals, cosmetics, precious metals, propellants, resins, toner and titanium dioxide. The particle size reduction typically occurs as a result of particle-to-particle collisions because generally, a fluid energy mill contains no moving parts.
The fluid energy mill typically comprises a hollow interior that acts as a grinding chamber where the particle collisions occur. Within the grinding chamber, a vortex is formed via the introduction of a compressed gas or grinding fluid through fluid nozzles fluid energy mill positioned in an annular configuration around the periphery of the grinding chamber. The compressed gas (e.g., air, steam, nitrogen, etc.), when introduced into the grinding chamber, forms a high-speed vortex as it travels within the grinding chamber. The gas circles within the grinding chamber at a decreased radii until released from the grinding chamber through a gas outlet. The particles to be ground are deposited within the grinding chamber and swept up into the high-speed vortex, thereby resulting in high speed particle-to-particle collisions as well as collisions with the interior portion of the grinding chamber walls.
Typically, heavier particles have longer residence time within the vortex. Lighter particles (i.e., those sufficiently reduced particles) move with the vortex of gas until the outlet is reached. Typically, fluid energy mills are capable of producing fine (less than 10 microns) and ultra fine (less than 5 microns) particles.
Typical nozzles that have been used include DeLaval nozzles (converging-diverging nozzles) through which the grinding fluid (also known as compression gas) is injected into the grinding chamber. In such nozzles, the grinding occurs at the boundary between the particles and the high-velocity grinding fluid, also referred to as the shear zone. However, such nozzles are disadvantageous because the pattern of the gas exiting the nozzle results in a substantial core of the gas-stream flow that is unavailable for grinding as the particles cannot penetrate the core of the fluid flow. Therefore, a greater amount of energy is necessary and a greater volume of compression gas is required to grind the particulate matter to the desired particle size.
Another disadvantage, with respect to fluid energy mills typically found within the art, is that they consume a significant amount of resources including energy and grinding gas due to the particular nozzles used therein.
Thus, there is a need within the industry for a mechanism for reducing energy and compression gas consumption as well as increasing the surface area of the fluid boundary useable for grinding particulate matter.
The present invention proposes placing ring jets in an annular configuration around the fluid energy mill. These ring jets have a spiked nozzle with a ‘C’ shaped compression orifice and opening. The spiked nozzle is shaped such that its surface is flush with the inside wall of the fluid energy mill. Grinding fluid emanating from the ring jets attrites the larger particles that are found closer to the wall of the fluid energy mill. Once the larger particles are ground to finer particles of desired size, such smaller particles leave the chamber through an outlet.