System for controlling separating gravity in dense-media cyclone

This invention is directed to a method of beneficiating a material, such as coal, by subjecting the coal to be treated to the action of a dense-media cyclone, where the dense-media thereof is a slurry of magnetite in water. More particularly, the present invention relates to a method to control the separating gravity of said cyclone within predetermined limits by (1) measuring the flow rate and percent magnetite in the flow discharging from the cyclone, and (2) based on pre-calibrated data, adjusting the feed flow and content, i.e. magnetite and/or water, into said cyclone, thereby controlling said separating gravity within predetermined limits.

BACKGROUND OF THE INVENTION 
The present invention is directed to a method of beneficiating material, 
such as coal, by the sink-and-float process utilizing a dense-media 
cyclone. More particularly this invention relates to such method in which 
the separating gravity of the dense-media cyclone is controlled to insure 
the optimum beneficiation of the treated material. 
The use of dense-media separators for segregating material according to its 
specific gravity is well known in the material separating art, such as the 
processing of coal. In these separators, a dense-media formed of a finely 
divided high gravity solid, such as magnetite, suspended in water, is 
maintained within a vessel, i.e. cyclone. The material or coal to be 
separated is introduced into the dense-media, and the material or coal 
which has a specific gravity less than the specific gravity of the 
suspension reports to the cyclone overflow. For convenience, the coal may 
be termed the overflow. Material or refuse which has a specific gravity 
greater than the suspension reports to the cyclone underflow. Thus, the 
sink material may be termed the underflow. 
By the very nature of this beneficiating process, the coal and refuse, 
overflow and underflow respectively, entrain a certain quantity of the 
magnetite which must be removed from the coal if the coal is to be 
thoroughly cleaned for commercial use. Further, recovery of the magnetite, 
which may be re-used in the process, is necessary for an efficient and 
economical process. While the present invention relates solely to the 
primary separation of the coal from the refuse, the magnetite recovery 
step suggests a further feature of the process, and that is the need to 
replenish the dense-media suspension. In replenishing the suspension care 
must be taken to insure a suitable specific gravity within predetermined 
limits in the cyclone to achieve the primary separation. 
A conventional method of controlling the specific gravity of the separating 
vessel has been for the operator to check the specific gravity of samples 
of the dense-media at regular intervals and manually make adjustments 
based on such checks. Another method involves measuring the specific 
gravity of the media continuously as it enters the vessel and adding water 
or magnetitie when necessary. Such methods, even when automated, had 
disadvantages. 
U.S. Pat. Nos. 3,246,750 and 3,247,961 (Chase et al), each entitled, 
"Method and Apparatus for Controlling Specific Gravity in a Heavy Medium 
Process," teach a system for separating mineral particles, such as coal, 
which system in part includes "measuring a specific gravity representative 
of the suspension in the vessel." Based on this measuring, adjustments are 
made to bring the vessel's specific gravity within predetermined limits. 
Controls for the systems described in the above patents rely upon the need 
to maintain a constancy within the cyclone to obtain an optimum 
classification of products therefrom. 
The present invention represents a unique approach to obtaining a precise 
separating gravity in a dense-media cyclone using magnetite-water as the 
slurry therein. Specifically, this invention resulted from the recognition 
in the processing of coal that there is a correlation between the quantity 
of magnetite in the cyclone overflow and the separating gravity of the 
cyclone. The manner by which such recognition has been incorporated into 
the system of this invention will be described in the following 
specifications. 
SUMMARY OF THE INVENTION 
This invention relates to a method of beneficiating a material, such as 
coal, by subjecting the coal to be treated to the action of a dense-media 
cyclone, where the dense-media thereof is a slurry of magnetite in water. 
Since, as discovered herein, the separating gravity in a dense-media 
cyclone is a function of the distribution of the magnetite between the 
overflow and underflow discharging from the cyclone, the present method 
controls the separating gravity of the cyclone within predetermined limits 
by (1) measuring the flow rate and percent magnetite in the overflow, for 
example, discharging from the cyclone, and (2) based on pre-calibrated 
data, adjusting the feed flow and content of additional magnetite and/or 
water, into the cyclone, thereby reestablishing said separating gravity to 
within predetermined limits.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
This invention is directed to a method of beneficiating material, such as 
coal, by the gravimetric process. It should be understood that such 
process is merely one of several steps in the beneficiation of material. 
That is, the overall process may include (1) particle sizing, (2) cyclone 
separation, and (3) washing and screening, prior to obtaining usable 
material. While each step involves specific technologies, the present 
invention is directed only to the intermediate step noted above. 
Turning now to such intermediate step with particular reference to FIG. 1, 
typically raw coal (feed) is directed into a dense-media separator or 
cyclone 10 which utilizes the specific gravity of the media to separate 
refuse from the coal. In the case of coal, a slurry of coal, magnetite and 
water, is fed into cyclone 10. Make-up magnetite valve 12 and make-up 
water valve 14 are continuousy adjusted, in a manner to be described 
hereinafter to provide a feed density greater than 1.00. Such feed density 
is monitored by meter 26 while the flow rate and percent magnetite of the 
feed are monitored by meters 22 and 24, respectively. 
In operation, controlled amounts of magnetite and water are added to the 
cyclone 10 to achieve a separating gravity within prescribed limits, 
typically 1.30 to 2.00. Separating gravity as used herein means the 
specific gravity at which a particle has an equal chance of reporting to 
overflow or underflow, or where 50% of the particles that have a specific 
gravity equal to the separating gravity report to the overflow and 50% to 
the underflow. 
The present invention is based on the discovery that the separating gravity 
in a dense-medium cyclone, in which water and magnetite are mixed to form 
the slurry feed to the cyclone, is a function of the distribution of the 
magnetite between the overflow and underflow. That is, by measuring the 
flow rate and percent magnetite in one or each of these streams, the 
percent reporting to either the overflow or underflow can be determined. 
FIG. 2, for example, is a graph showing the relationship of the separating 
gravity in the cyclone versus the percent magnetite in the overflow. Thus, 
by monitoring the respective streams from the cyclone changes in the 
percent magnetite may be readily observed and appropriate changes made to 
the feed of water and magnetite to the cyclone. 
The monitoring of the change in magnetite and the appropriate changes to 
the feed make-up can be accomplished automatically. Referring again to 
FIG. 1, after the overflow, i.e. clean coal, and the underflow, i.e. 
refuse, leave the cyclone 10 a flow meter 16 and a coil 18 measure the 
flow rate of slurry in GPM and percent magnetite in each respective 
stream. These measurements are transmitted to a micro-processor 20 which 
calculates the percent magnetite and compares it to a pre-calibrated curve 
to determine the separating gravity. If corrections are required the 
microprocessor 20 transmits a signal to the appropriate valve 12,14 to add 
magnetite or water, whichever is required to change the separating 
gravity. Simultaneously, a flow meter 22 and coil 24 on the feed measure 
the GPM of slurry and percent magnetite. These measurements are 
transmitted to the micro-processor 20 for comparison with the previously 
calculated values. Finally, a density gauge 26 may be incorporated into 
the system to monitor the feed density and to control the amount of 
non-magnetic material, i.e. water, being circulated. 
As reported earlier in describing the general operation of a dense media 
cyclone, recovery of the magnetite from the overflow and underflow is 
vital to an economic operation. By recovering the magnetite it is possible 
to reuse same in the system. Accordingly, recirculating means 28 are 
provided for supplying or delivering the recovered magnetite for reuse in 
the system of this invention. Thus, the input or material feed to the 
cyclone is derived from several sources. The non-magnetites, i.e. raw coal 
to be cleaned has been designated "Feed" in FIG. 1. Recirculated 
magnetite, and water, since the magnetite is not in a dry state, are fed 
to the cyclone by means 28. Finally, since magnetite recovery from the 
cleaned coal and refuse is not 100%, make-up magnetite and water are 
introduced into the cyclone by valves 12 and 14. 
The method of this invention may be illustrated best by way of a specific 
example. 
EXAMPLE 
Equipment 
a. Cyclone 10-ten (10) inch diameter; the capacity is estimated to be 
fifteen (15) TPH feed solids operating at an inlet or feed pressure of 20 
psi. 
b. Micro-processor 20-Hewlett-Packard model HP85, manufactured by 
Hewlett-Packard Co. 
c. Flow meters 16,22-magnetic flowmeter model 10D1416F, manufactured by 
Fischer and Porter Co. 
d. Coil 18,24-Ramsey Coil model 30-21, manufactured by Ramsey Engineering 
Co. 
e. Density gauge 26-Texas Nuclear model SGH, manufactured by Texas Nuclear 
Co. 
Operation 
The input or material feed to the cycone 10 can be expressed TPH (tons per 
hour) or GPM (gallons per minute). For such 10" diameter cyclone, the 
material feed from the several sources comprises: 
water--46 TPH, (185 GPM) 
non-magnetics--15 TPH, (45 GPM) 
magnetite--25 TPH, (20 GPM) 
Based on such breakdown of the material feed, a typical separating gravity 
for the cyclone is 1.40. However, during processing of the coal such 
separating gravity may change affecting the separation of the coal from 
the refuse. By the method of this invention, the separating gravity may be 
readily restored to the desired level. 
For the 10" diameter cyclone of this Example, and from the operation data 
presented above, the feed input is 250 GPM. Consequently, the output 
between the overflow (clean coal) and underflow (refuse) totals 250 GPM. 
If the feed input includes 25 TPH of magnetite, then 25 TPH of magnetite 
will exit the cyclone in the overflow and underflow streams. The present 
invention is based on the recognition of a correlation between the 
magnetite in the overflow (or underflow) and the separating gravity of the 
cyclone. If the coil 18 shows, for example, that 20% or 5 TPH of magnetite 
is present in the overflow stream, a review of FIG. 2 will show that at 
20% magnetite reporting to cyclone overflow the separating gravity of the 
cyclone will have increased slightly to about 1.41. The percent magnetite 
passing through coil 18 is continuously monitored and the appropriate data 
transmitted to microprocessor 20. If the separating gravity of the cyclone 
increases or decreases to an unacceptable level, microprocessor 20 will 
transmit a signal to the make-up valves 12 or 14 and a change in the feed 
will be made to reestablish the separating gravity to an acceptable level. 
For example, most of the magnetite fed to the cyclone will be of 
recirculated magnetite. Of the 25 TPH needed, approximately 24 TPH will 
enter the system through means 28. As a consequence, additional make-up 
magnetite and/or water must be added. However, the relative proportions of 
the additions may be changed to bring the separating gravity into line 
with the desired values. 
Thus, by monitoring the percent magnetite in the overflow, for example, it 
is possible to automatically adjust the input feed to the cyclone to 
restore the separating gravity of the cyclone to the desired level to 
insure optimum separating conditions between the coal and refuse.