Segmented Pin Jet Mill for Precise Particle Size Control
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Solution Overview
Problem
Existing jet mills face inefficiencies in energy utilization, particle collision likelihood, and inability to produce precise particle size distributions due to limitations in gas jet velocity and classification systems, leading to wasted kinetic energy and broad particle size spectra.
Innovation Solution
A jet mill design with a milling chamber featuring pins arranged in alternating planes and segments, which forces particles to collide with pins, accelerates jets, and allows for selective milling, optimizing impact forces and number of collisions to achieve precise particle size distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed gas jets are used to accelerate particles in opposed jet mills, then particle velocity increases, but the factual jet speeds inside the mill are much lower than the nozzle exit speeds due to energy dissipation
Solution Approach 1:
The milling chamber is divided into multiple pin segments arranged in alternating planes, creating a segmented structure that forces particles to collide with pins at each segment rather than allowing continuous jet flow. This segmentation maintains collision effectiveness while reducing overall energy dissipation.
Solution Approach 2:
Pins are introduced as intermediary objects between the gas jet and particles. The pins force particles to collide with them, ensuring that kinetic energy is transferred to particles through direct impact rather than relying on high-speed gas jet propagation, thereby reducing energy loss in the gas phase.
2Speed
If particles are accelerated at the outer circumference of the jet, then some particles gain velocity, but the load of solids of the inner part of the jet is very low and most particles do not manage to enter into the inner jet
Solution Approach 1:
Pins serve as intermediaries that force particles from the outer jet circumference to collide with them, ensuring that even particles that would not naturally enter the inner jet region are still accelerated and milled effectively. This eliminates the need for particles to penetrate deep into the jet core.
Solution Approach 2:
Instead of relying on particles to naturally penetrate into the inner jet region, the invention inverts the approach by placing pins throughout the jet path that force particles to collide with them at various positions, including the outer circumference where particle density is higher.
3Quantity of substance
If jets are allowed to spread to the side when they collide in the middle of the milling chamber, then particle distribution increases, but fine particles can follow the spreading jet more easily thus avoiding a frontal impact with each other
Solution Approach 1:
Pins are positioned to intercept particles before the jets can spread laterally. By forcing particles to collide with pins, the system ensures frontal impacts occur at controlled locations rather than allowing particles to follow the spreading jet flow and miss each other.
Solution Approach 2:
The pins are positioned in advance along the jet path to force particle collisions before the jets have a chance to spread significantly. This preliminary action ensures that particles undergo frontal impacts while the jet is still relatively concentrated, maximizing impact force.
4Power
If opposed jet mill configuration is used, then particles are accelerated by gas jets, but the kinetic energy transfer between particles is rather low and supplied energy transfer per stressing event is low
Solution Approach 1:
Pins act as intermediaries that force direct particle-to-pin collisions, ensuring that the kinetic energy of the gas jet is efficiently transferred to particles through mechanical impact rather than relying on weak particle-to-particle energy transfer in the opposed jet configuration.
Solution Approach 2:
The invention replaces the purely fluid-mechanical opposed jet system with a hybrid system incorporating solid pins. This substitution introduces direct mechanical impact, which is far more efficient at transferring kinetic energy to particles than the weak particle-particle interactions in the original opposed jet mill.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design significantly increases kinetic energy utilization by 60 times, enables precise particle size control, and produces narrower particle size distributions with higher throughput, reducing energy waste and improving milling efficiency.
Implementation Method 1
A jet mill mills material by using a high-speed jet of compressed air, gas or steam to generate impacts between particles
Implementation Method 2
The maximum jet speed for air as milling gas is around 330 m/s which is the sonic speed of the gas. Using Laval nozzles, even supersonic speed can be achieved at the exit of the nozzles
Implementation Method 3
The particles are crushed by the energy introduced by the milling gas... the accelerated particles hit each other and are thereby milled to smaller particles
Implementation Method 4
The air classifier separates the fine particles from the coarse particles. Particles that are too coarse are rejected by the classifier and fall back down into the fluidized bed
Data Source
AI summary
The invention relates to a jet mill comprising a milling chamber with a longitudinal axis, an inlet at one end of the axis and an outlet at the opposite end of the axis, the milling chamber comprising a multitude of pins arranged in the free flow cross-section of the milling chamber, wherein the pins are arranged in at least two planes perpendicular to the longitudinal axis, the planes being distant to each other in the longitudinal direction, and the pins of one plane being laterally offset to the pins of the subsequent plane, wherein the milling chamber is divided into alternate pin segments and acceleration segments, the pin segments each having at least two planes of pins, and the acceleration segments having no pins.