Solid material comminution or disintegration – Apparatus – Including means applying fluid to material
Reexamination Certificate
2000-02-25
2004-11-23
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Apparatus
Including means applying fluid to material
C241S079100, C241S080000, C241S119000, C241S186300
Reexamination Certificate
active
06820829
ABSTRACT:
FIELD OF THE INVENTION
The invention is in the field of physical separation of particulate matter. Specifically, the invention relates to the operation of a comminution device as a size reducing device, as concentrator, and as a separator of less friable particles liberated from the feed matrix in the grinding operation. More specifically, the invention is in the field of physical separation of particles removed from the comminution device to recover desirable particles from return to the comminution device.
BACKGROUND OF THE INVENTION
Comminutors are employed to reduce the size of particles to a range which is desirable and to liberate impurities so that they can be removed downstream of comminution. The feed particles may range in size up to several inches while the product particles may range from inches down to microns in size. More comminution energy is required to bring a mixture of particles of widely ranging friabilities to the desired size consist than when the friable components alone are present. The invention relates to reducing comminution energy consumption and increasing the throughput of comminutors while improving the quality of the product of comminution by separating the friable and less friable components as they are liberated from the feed matrix within the grinding operation and before the hard component is overground. Specifically, the invention relates to modification and operation of comminuting devices and their classifiers, if they are used, so as to separate two streams from the comminution device. One is concentrated in the hard and less friable components liberated from the feed in the grinding operation. This may be either an impurity or a valuable component of the feed. The other is concentrated in the friable component of the feed. More specifically, the invention relates to combining the operation of a comminution device and a separation device so as to separate the hard components of the feed as they are liberated inside the comminutor but before they are overground. Separation methods based on gravity, size classification, dry magnetic separation, and triboelectric means are used to separate hard material [form] from friable material found in a mill concentrated steam taken from the comminution device. Particulate matter of differing chemical and physical makeup can have different magnetic properties and may be electrically charged by contact and friction, tribocharging. By including triboelectric separation means, modified dry magnetic separators can be effective in recovering friable material of a great range of types from the mill concentrated fraction taken from the mill. By this combined pulverizer-separator operation, the MagMill™ can produce high quality comminution products without significant loss of the desired component. The MagMill™ is the name given to the above described combination of mill and separator. The friable material so separated is returned to the grinding zone for grinding to product fineness while the hard component is collected separately and not returned to the mill. By this means, both the quality and the recovery of the separated components are improved when compared to that of the state-of-the-art technology in which everything is reduced to the same size consist and then separated downstream of the comminution device.
The invention is distinguished from the state-of-the-art by processing a significant amount of the particles circulating inside the comminution device. In current technology, tramp iron exits are employed to separate very small amounts of hard and abrasive material before it destroys the inside of the grinding device. The rate of withdrawal of this undesirable material is typically less than 1/10% of the rate of feed to the comminutor. The desired goal is protection of the grinding device, not improvement of the quality of the product or increasing throughput and decreasing power draw. By contrast, the present invention preferentially extracts material from the inside of the comminutor which is concentrated in hard components of the feed. Indeed, if it is desired to improve the quality of the product, then the amount of material to be separated from the inside of the comminutor must be sufficient to have an effect. One tenth of one percent, generally, is not enough. The required amount is dependent upon the concentration of hard components in the withdrawn material and the recovery of more friable material from this stream which is subsequently returned to the comminutor for grinding to size specification. The present invention is unique in showing how and where to withdraw this material from the comminutor and in employing unique and powerful methods for recovery of the friable component inadvertently withdrawn from the internally circulating stream inside the comminutor.
Indeed, it has been discovered that particles of quality the same as or worse than that withdrawn from the tramp metal chutes can be withdrawn from the inside of a coal pulverizer at locations several feet above the throat area where air enters and tramp metal exits. This has been observed in grinding a blend of raw coals from North Central Pennsylvania in an ABB C. E. Raymond 633 bowl mill. For this mill, coal was withdrawn from the pyrite trap at the rate of 67 pounds per hour. This is small compared to the nominal 12-15 TPH fed to the pulverizer. The coal withdrawn from the pyrite traps had an ash level of 69.1 Wt. % and a sulfur level of 23.4 Wt. %. In the experimental tests, coal was withdrawn at the rate of 8.2 Lb/Hr from a sampling port located several feet above the top of the grinding bowl in the region which is open for air flow upward. While the particle size was smaller than that withdrawn from the pyrite traps, it had an ash level of 58.1 Wt. % and a sulfur level 33.6 Wt. %. This illustrates the potential for separation of refuse quality material from the flow of particles inside the pulverizer.
By way of example, coal is dry-milled to 200 mesh (74 micron) topsize at pulverized-coal fired power plants to promote good combustion characteristics. [See, for example,
Steam, Its Generation and Use,
Chapter 9, “Preparation and Utilization of Pulverized Coal,” Babcock & Wilcox, New York, N.Y., 1978, and
Combustion Fossil Power Systems, A Reference Book on Fuel Burning and Steam Generation,
Ed., Joseph G. Singer, Chapter 12, “Pulverizers and Pulverized-Coal Systems,” Combustion Engineering, Inc., Windsor, Conn. 1981, incorporated by reference herein]. The fine coal generated in the pulverizer is air-conveyed out of the mill directly to the burner. Coincidentally, grinding to 200 mesh is also effective in liberating fine minerals encased in the feed-coal particles even after the coal has been cleaned using conventional wet processing technology. However, other than tramp iron chutes called pyrite traps for removing small amounts of pyrites and other coarse debris, no means are employed in the coal pulverizers now used to separate minerals which are liberated there. Separation of hard minerals at the pulverizer would improve operation of the power plant by increasing the pulverizer throughput and reducing the power draw, by reducing abrasive wear, by reducing slagging, fouling, and water wall wastage in the furnace, by reducing emissions of sulfur and other hazardous air pollutants such as trace metals associated with minerals in the coal, including mercury, and arsenic which is deleterious to the operation of catalytic scrubbers used in post combustion separation of sulfur and nitrogen oxides.
The bulk of the hydrocarbon structure of bituminous coals is much softer than the minerals commonly found in coal. Consequently, hard minerals require more passes through the mill's grinding zone to reach product size specification (70% to 80% finer than 74 microns particle diameter) than does the soft coal. Because of this, the concentration of hard minerals is greater in the stream of oversize particles circulating inside the pulverizer (internal circulation) than it is in the feed coal. Iron pyrite, on
Jamison Russell E.
Oder Robin R.
EXPORTech Company, Inc.
Rosenbaum Mark
Schwartz Ansel M.
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