Material or article handling – Apparatus for moving material between zones having different... – Including screw conveyor
Patent
1981-04-13
1983-07-05
Sheridan, Robert G.
Material or article handling
Apparatus for moving material between zones having different...
Including screw conveyor
198661, 406 61, B65G 5348
Patent
active
043915612
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the feeding of particulate matter into a high pressure zone, and in particular to a screw feed apparatus frequently known as a solids pump.
There are occasions such as introducing pulverized coal into a high pressure air stream where it is necessary to pump the coal to this high pressure level. This has been done with screw pumps where a helical member having flights is rotated within a cylinder, and the coal is supplied to the upstream end of this cylinder. These pumps operate at high speed (over 900 rpm).
In some cases a reducing pitch is used so that the coal is compacted as it travels through the cylinder, becoming sufficiently compacted that the high pressure air cannot leak back through the coal. In other cases a reducing nozzle is located at the outlet end so that the coal is compacted as it pushes through the nozzle thereby forming a seal at that location.
Those pumps we have been able to find which are capable of sealing against a reasonable back pressure have suffered from the disadvantage of high power consumption.
SUMMARY OF THE INVENTION
Accordingly, it is an object of our invention to pump particulate or granular solids into a high pressure zone without back leakage of gases and with a relatively low power consumption.
An apparatus for feeding a granular material into a pressurized zone has a stationary hollow cylinder with a frustoconical reducing nozzle located at the discharge end. Means for feeding the granular material into the cylinder is located at the upstream end. A rotary feed screw is located within the cylinder and has helical flights which have a decreasing pitch towards the discharge end. This feed screw is rotated at high speed within the cylinder. At the discharge end the outside diameter of the flights have a taper which is preferably equal to but possibly greater than the taper of the nozzle. The helical feed screw is located in a position slightly withdrawn from the discharge end so that the radial clearance between the tapered flights and the nozzle is significantly greater than the radial clearance between the uniform OD flights and the bore of the cylinder. The tapered flights extend into but not completely through the nozzle. A columnal plug preferably cylindrical is centrally located within the nozzle and attached to the end of the feed screw.
The optimum length of the tapered portion of the flights appears to be between 40 and 60 percent of the inside diameter of the cylinder. Successful operation has been experienced with the radial clearance between the flights and the nozzle being greater than twice the clearance between the uniform OD flights and the bore, while even better performance has been experienced when this ratio exceeds four. The cylindrical plug is located within the nozzle by making it an extension of the feed screw shaft. It is believed that best operation is obtained if the taper of the flights equals that of the nozzle and that furthermore the clearance between the tapered flights and the nozzle should exceed three times the largest particle size of the material being pumped.
The knowledge of superior performance of our invention flows from test results. The theory underlying the superior performance is based on speculation. Tests were being run to determine an optimum coal plug thickness. The screw shaft was once withdrawn as a shortcut method for obtaining a thicker plug, and the superior results were first noticed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general arrangement of the pump assembly; and
FIG. 2 is a detail at the discharge end of the pump.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An inlet hopper 10 is arranged to supply a granular material such as pulverized coal to the upstream side of a stationary cylinder 12. A rotary feed screw 14 is concentrically and rotatably mounted within the cylinder. The screw is cantilevered from radial bearing 16 and thrust bearing 18 with an adjustable length joint 20 located between the bearings. Drive motor 22 rotates the screw at a h
REFERENCES:
patent: 3093419 (1963-06-01), Bowers
Pote Bruce M.
Smith Donald A.
Combustion Engineering Inc.
Kochey Jr. Edward L.
Sheridan Robert G.
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