Conveyors: fluid current – With diverse power-driven conveyor – Rotary
Reexamination Certificate
2002-07-15
2003-09-09
Dillon, Joseph A. (Department: 3651)
Conveyors: fluid current
With diverse power-driven conveyor
Rotary
C406S181000
Reexamination Certificate
active
06616384
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
In the processing of comminuted cellulosic fibrous material, for example, wood chips, to produce cellulose pulp, one of the somewhat essential devices used to introduce a pressurized slurry of material to a treatment vessel is what is known in the art as the High Pressure Feeder (“HPF”). The HPF is a rotary valve-type device that, with the aid of a high-pressure pump, transfers a slurry of material and liquid at one pressure for example, between about 0 to 2 bar gauge, to a second higher pressure, for example, between about 5-15 bar gauge, at which treatment of the material is most desired. One advantageous function of this device is the capability to act as an pressure isolation device. Should a disruption in the operation of the digester or the feed system occur, the HPF prevents the high-pressure medium from escaping to the low-pressure medium or to the surrounding environment.
Since the early development of the continuous cooking process by the late Johan Richter and others (as documented in Mr. Richter's
The History of Continuous Cooking [
1981]), the HPF has been an essential feature of the feed system of the continuous digester. In this 1981 publication Mr. Richter documented the early development of the HPF, in particular some early designs are shown in FIGS. 17, 18, 21, and 22 of this publication. Rydholm also documents one early “balanced rotor” HPF design in FIG. 1.1 of the 1970 publication
Continuous Pulping Processes
. The development of HPF design is also documented in U.S. Pat. Nos. 2,459,180; 2,688,416; 2,870,009; 2,901,149; 2,914,223; 3,041,232; 4,033,811; 4,338,049; 4,430,029; 4,508,473; and 4,516,887. Not until the recent development of the slurry-type pumping of the material by Prough, et al., as described in U.S. Pat. Nos. 5,476,572; 5,622,598; 5,635,025; 5,736,006; 5,753,075; 5,766,418; and 5,795,438 and marketed under the name LO-LEVEL® Feed System by Ahistrom Machinery Inc. of Glens Falls, N.Y., has the elimination of the HPF and pumping directly to the treatment vessel been technically feasible.
However, the present design of the HPF, as exemplified by the designs shown in U.S. Pat. Nos. 5,236,285 and 5,236,286, has not progressed significantly since the earlier designs developed by Richter, et al. The recent development of digester feed system technology, as exemplified by the work performed in the development of the LO-LEVEL® Feed System, and documented in U.S. Pat. No. 5,476,572 and the other patents listed above, has resulted in new insights into the limitations of existing HPF designs and how these limitations can be overcome by improving the HPF as a result of these insights. The present invention is an example of such an improvement.
As shown in FIGS. 3, 4 and 5 of U.S. Pat. No. 5,236,285, the HPF comprises or consists of a stationary housing with a pocketed cylindrical rotor mounted for rotation in the housing. The housing includes four ports: a high-pressure inlet port; a high-pressure outlet port; a low-pressure inlet port and a low-pressure outlet port. The low-pressure inlet is opposite the low-pressure outlet and the high-pressure inlet is opposite the high-pressure outlet. As the pocketed rotor (driven by a variable speed motor and gear reducer) rotates in the housing, the through-going pockets of the rotor sequentially communicate with the four ports of the housing. Typically, the rotor contains two or more through-going pockets such that different pockets communicate with different high and low-pressure ports as the rotor rotates. The unique, hydraulically-balanced design of the HPF permits the rotor pockets to be exposed to high and low pressure fluids simultaneously without causing a load imbalance and excessive wear of the rotor or its lining.
Typically, the top port of the feeder housing of the HPF is the low-pressure inlet port into which a slurry of chips and liquid is introduced to the feeder. This historically has been true for over thirty years since the slurry of chips and liquor have been introduced to the HPF by gravity from a conduit, known in the art as the Chip Chute, mounted above the HPF. However, due to the pump-feeding which characterizes the LO-LEVEL Feed System marketed by Ahlstrom Machinery Inc., the pressurized slurry flow from the slurry pump may be introduced to a low-pressure inlet of the HPF which is oriented wherever necessitated by the installation. The pump-fed slurry can be introduced to a port located physically on top, on either side, on the bottom of the HPF, or even to a port oriented at an oblique angle, that is, at any angle of orientation desired. However, for the sake of illustration, the low-pressure inlet of the HPF of the present invention will be assumed to be located on top of the feeder, for example, as shown in FIGS. 3-5 of U.S. Pat. No. 5,236,285. The rotor typically rotates at a speed of between about 5 to 15 rpm, preferably, between about 7 to 10 rpm, depending upon the capacity of the HPF and the production rate of the pulping system it is used to feed.
As the low-pressure slurry is introduced to the low-pressure inlet of the HPF, one or more of the through-going pockets of the rotating rotor receive the slurry. As noted above, the low-pressure outlet of the HPF is located opposite the low-pressure inlet. Therefore, as the slurry is introduced to the low-pressure inlet and the first end of one of the through-going pockets, the slurry flows into the pocket and toward the second end of the pocket, in this case, toward the lower end of the pocket, and toward the low-pressure outlet. The low-pressure outlet port of the HPF is typically provided with a screen element, for example, a cast horizontal bar type screen element (see for example the screen element 29 in U.S. Pat. No. 5,443,162). This screen element retains the chips in the slurry within the feeder and allows some of the liquid in the slurry to pass out of the second end of the pocket and through the screen. This liquid typically is recirculated back to a location upstream of the HPF. The chips that are introduced to the rotor pocket, including those chips retained by the screen element, are transported by the rotation of the rotor. After a typical one-quarter revolution of the rotor, the first end of the pocket that was once in communication with the low-pressure inlet is placed in communication with the high pressure outlet. The high-pressure outlet typically communicates with the inlet of a digester, either a continuous or batch digester, via one or more conduits. At the same time, the rotation of the rotor also places the second end of the through-going pocket, which was just in communication with the low-pressure outlet, in communication with the high-pressure inlet. The high pressure inlet typically receives a flow of high-pressure liquid from a high-pressure hydraulic pump. The pressure of this liquid typically ranges from about 5 to 15 bar gauge, and is typically about 7-10 bar gauge. This high-pressure liquid displaces the slurry of chips and liquid from the through-going pocket and out of the high-pressure outlet and ultimately to the inlet of the digester.
As the rotor continues to rotate, the second end of the pocket which received the high-pressure fluid then is placed in communication with the low-pressure inlet and receives another supply of slurry from the conduit connected to the low-pressure inlet. Similarly, the first end of the pocket is rotated into communication with the low-pressure outlet of the housing, having the screen element. The process described above then repeats itself such that during one complete revolution of the rotor each through-going pocket receives and discharges two charges of chips and liquid. The rotor typically contains at least two, typically four, through-going pockets such that the rotor is repeatedly receiving slurry from the low-pressure inlet and discharging slurry out the high-pressure outlet. The ends of the these pockets act as both an inlet for slurry and an outlet depending upon the orientation of the rotor.
Over the year
Andritz Inc.
Dillon Joseph A.
Nixon & Vanderhye P.C.
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