Screws for a carbonizing machine

Abstract

Screws for a carbonizing machine for carbonizing organic material into useful char product.

Claims

1. A screw for a carbonizing machine, said screw comprised of a linear shaft comprised of a predetermined length and number of multiple sections, wherein each section in a system has a distinct configuration and orientation, each said section comprises: a helical advancing screw configuration of a higher open volume than a standard helical screw to provide for additional venting capacity of said system at a lower gas velocity thereby increasing said system throughput rates while reducing solid carry over in any vents; a helical screw configuration with a pitch that gradually reduces to form a change in volume to a lesser degree than said helical advancing screw configuration to minimize material backflow into said venting and increase said system capacity for throughput; a standard helical screw; a tight pitch single lead screw for initial compression of any material in the system; a screw having radially abutting paddles that are progressively axially angularly out of phase with said screw linear shaft, and a screw having a reverse hand, wherein the multiple sections are maintained in a predetermined order.

2. In combination a screw as claimed in claim 1 wherein a first feed section is an open volume longer lead screw with a square face and reinforced back flight to increase the volumetric feed capacity of said system while being able to absorb high mechanical loading from new uncompressed raw material entering the screw.

3. In combination, two screws as claimed in claim 1 and a carbonizing machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a prior art carbonizing machine.

(2) FIG. 2 is a top view of the prior art carbonizing machine.

(3) FIG. 3 is a cross-sectional view of a carbonizing machine showing the deposition problem of the prior art.

(4) FIG. 4 is an end view showing the football shape of the typical twin lead (bi-lobe) twin screw cross sectional geometry.

(5) FIG. 5 is a cross section isometric of a standard bi-lobe twin screw twin lead geometry.

(6) FIG. 6 is a full side view of a portion of a bi-lobe twin screw.

(7) FIG. 7 is a full side view of a portion of FIG. 18 (check this against new Figures) showing a half single flight push screw for the feed port area.

(8) FIG. 8 is a full end view in perspective of a half single flight push screw.

(9) FIG. 9A is a full end view of a single square to standard twin lead transition of a screw of this invention.

(10) FIG. 9B is an isometric of one lead of twin lead squared flight RH lead.

(11) FIG. 10 is an isometric cross-section view of a portion of a screw which shows a bi-lobe twin screw.

(12) FIG. 11 shows twin half single flight push screw.

(13) FIG. 12 is a schematic of a prior art machine known as the Loomans screw design based on the Loomans patents described Supra

(14) FIG. 13 is a partial assembly of the screw assembly at the discharge end showing the standard single flight discharge screws.

(15) FIG. 14 is a partial assembly of 12 inch screws from the feed end, showing a full transition from square single flight to standard twin lead geometry.

(16) FIG. 15A is a view of the transition screw pair with 0.75 D of lead over 0.75 D of length rotating 360 degrees.

(17) FIG. 15B is a view of a transition screw pair with 1.5 D of lead over 0.75 D of length rotating 180 degrees.

(18) FIG. 15C is a view of a transition screw pair with 2.0 D of lead over 2.0 lead of length rotating 360 degrees.

(19) FIG. 16 is a partial assembly of a pair of transition screws.

(20) FIG. 17 is a side view of a single square to standard twin lead transition.

(21) FIG. 18 is a full view assembly of the twin screws embodying this invention and a schematic of the inventive screws set forth herein, in a housing.

DETAILED DESCRIPTION OF THE DRAWINGS

(22) Details of the construction of a machine useful with the screws of this invention are disclosed in U.S. patent application Ser. No. 12/589,373, filed on Oct. 22, 2009 naming the inventors Fred L. Jones and James G. Kowalczyk, all of which is incorporated herein by reference to teach such machines and how they are constructed and operated.

(23) Turning now to the invention herein, there are two conditions that promote the carry over and build up of particular solids in the feeding and venting areas. One of them is the velocity of the gas flow out of the barrel openings (which if too high carries solids out with the gas phase) and the second is the restriction of forward flow of solid material down the barrel from the vents, by abrupt changes in the screw geometry, where the material transitions from a relaxed state to a compressed state (causing solid material to back up into the vent areas).

(24) The inventive screw geometry transition sections described in this application dramatically reduce the carryover of particulate solids and solve the problem of high velocity carry over of particulate solids into the vent openings and from the feed opening.

(25) Looking at the typical cross section of a bi lobed twin screw mixer screw profile (FIG. 4), there is shown that the cross section is typically a football shape wherein one of the co-rotating twin screw bi-lobe geometries is described by the mating screw as they are conjugal as described in an earlier U.S. Pat. No. 3,195,868, B. Loomans et al and U.S. Pat. No. 3,198,491, B. Loomans et al, FIGS. 4, 5 and 6.

(26) By modifying this screw geometry, which includes removing one lobe of the foot ball shape and creating a flat face on the forwarding edge of the other lobe (as shown in FIGS. 7 and 8 of this application), one can significantly reduce the volume in the barrel that is normally consumed by the missing metal of the screw. This greatly opens up the free volume in that area of the machine. In the extreme, the one lobe that remains can have metal removed from its trailing face increasing the open volume even further (as shown in FIG. 9). Additionally a typical twin lead feed screw (as shown in FIG. 10) has a lead equal to its diameter. That is the linear displacement of the spiral wrap of the individual screw flight to traverse 360 degrees of rotation is equal to the diameter of the screw. If one increases the lead of the screw, one increases the volumetric through put. This gives the screw more conveying capacity. Increasing the lead, however, diminishes the ability of the screw to overcome pressure drop, so there is a compromise in any process for the optimum screw lead. In this case, because of the interest in simple conveying, with no extrusion of the product in the feed or vent areas, the lead between 1.5 and 3 diameters would be optimized. The following equation shows the general values of the “A” term for a standard 2″ diameter screw. V.sub.d=½(2P−1)F.sub.dH.sub.maxWv.sub.bz. The “A” term is the downstream volumetric conveying capacity of the screw. As the lead is increased the downstream conveying capacity (cubic inches per revolution) is increased also. However, beyond 45 degrees of helix angle (approximately a 3/1 lead) the “A” term begins to decrease due to back flow in the channel. Therefore against no back pressure the optimal lead would be 3 to 1. This is an increase in volumetric flow rate of 1.7 times over the standard 1 diameter lead. As one can observe, by modifying the screw flight to that as shown in FIG. 11 (example #3 (what's this)?) and using the increased lead of 3 to 1, the open volume screw can forward 2.2 times the volume of the standard feed screw.

(27) Combined with a rectangular opening in the barrel (an opening wherein the length is proportionately longer than the width) rather than the original round openings described in the original patent, the velocity of the gas escaping from the vent is reduced dramatically, while the conveying capacity of the screw is increased dramatically.

(28) Calculation sheet #1 shows the effect of both the open volume screw and the larger rectangular vents on a typical 2 inch twin screw machine. Graph #1 shows the reduction in velocity from the vent ports due to the larger open volume of the screw and the effect of the rectangular ports. This reduction in velocity greatly reduces the particulate solids that are carried out of the machine through the ports. These features also greatly increase the capacity of the system regardless of the throughput rates. The calculations are based on ports that are typically the width and length of the figure eight, essentially square ports. In the case for optimization, these ports will typically be the width of the figure eight bores and between 2 and 2.5 length to diameter ratios long.

(29) Additionally to aid in retaining particulate solids in the machine while they are passing under the vent ports, as well as to aid initial feeding in the feed hopper area of the machine, the barrel and liner has a relief on the down swing side of the screw rotation to suck material into the machine and keep material from transgressing out the port openings.

(30) One problem with the current system described in U.S. Pat. No. 5,017,269 to Loomans et al (as shown in FIG. 12), is the transition from the free flowing geometries to those that create the compression and work energy that goes into the materials. These transitions are abrupt and create dams in the continuous processor that typically obstruct the forward flow of material and materially contribute to the back flow of particulate solids back into the venting area. Changing the screw geometries to produce greater open volume under the feed and vent ports then going directly into the compression and energy dissipating screws of the original screw exacerbates the problem to an even greater extent.

(31) The instant invention deals with new and unique screws that create smooth transitions from the greater volume screws to the more traditional compression and energy creating screws in the processor. These transition screws eliminate the obstructions that typically plague the prior art screws with significant back flow of material and carry over of solids into the vents. These screw geometries create a smooth transition from the single lead half flight screws to the normal twin lead screws in a smooth and uniform transition, always forwarding the material during the transition phase, so that only the gas phase of the product is directed back to the vent openings, and not the particulate solids. The transition screws start out with the geometry of the open volume on one end and end up with the standard twin lead configuration on the other. This transition could easily be replicated from an open volume screw to a standard single lead screw (as shown in FIG. 13). However, there is no requirement for that type of transition in the current screw assembly. FIGS. 14 and 15, show the free flowing transition from the one face squared off single flight to the standard twin lead feed screw geometry and FIGS. 16 and 17 show the free flowing transition from the high volume total squared flight single flight to the standard twin lead feed screw respectively. The transition screws are approx. 0.75 diameters long but can be made in different length to diameter ratios if necessary, typically from 0.75 D to approx. 3 D long The lead is adjusted so that the transition will line up at 90 or 180 degree intervals to perfectly match the screw geometries of the mating screws at each end. For the application of carbonizing particulate solids, the practical limits of geometry for the transition screws can vary from 0.5 diameters to 2 diameters in length, and can vary in lead from 0.5 diameters to 2 diameters while changing configuration from the open to the more closed volume as shown in the attached Figures. An optimum length and lead is 0.75 long with a lead of 1.5 diameters. Thus the screw land will make 180 degrees of revolution in 0.75 diameters of length.

(32) A typical volume change of the reactor due to the decrease in open area as the screw transitions is shown in FIG. 14A, for example. This example depicts a change of volume from the open single land to the compressing twin land in a screw with 360 degrees of revolution (0.75 D lead) over a length of 0.75 D. Likewise FIG. 14B depicts the same transition in a 0.75 D long screw, but with 180 degrees of revolution or a lead of 1.5 D. FIG. 14C depicts the same transition but over 2 diameters of length and at 360 degrees of rotation or a lead of 2 diameters. One can readily see that it is possible to change the severity of the transition by varying the parameters as outlined in this description of the invention.

(33) Due to the fact that the feed port of the machine will accept material that is very low bulk density and has to compact it as well as forward the material, this screw section of the assembly contains a single flight with only one squared off face. This gives the screw extra strength for compacting the material as well as sustaining the screw integrity if, for instance, a hard object of foreign matter is accidentally fed into the system. The gas relief vents downstream utilize the more open volume screw with both sides of the single flight squared off, as they are only conveying material through the port area and require maximum open volume to let gas escape up the vents.

(34) The complete assembly of the screw geometry with the unique sections designed for this process as described in this invention are shown in FIG. 18