AU540431B2

AU540431B2 - Apparatus for throttling a dry pulverized solid material pump

Info

Publication number: AU540431B2
Application number: AU60000/80A
Authority: AU
Inventors: John Henry Bonin; Arnold Dewey Daniel Jr.; John William Meyer
Original assignee: Lockheed Missiles and Space Co Inc
Current assignee: Lockheed Martin Corp
Priority date: 1979-05-07
Filing date: 1980-04-10
Publication date: 1984-11-15
Anticipated expiration: 2000-04-10
Also published as: AU6000080A

Description

APPARATUS FOR THROTTLING A DRY PULVERIZED SOLID MATERIAL PUMP

Technical Field

This invention relates to a kinetic extruder for feeding pulverized coal from an atmospheric pressure hopper to an elevated pressure reactor vessel for gasification of the coal. It relates more particularly to a kinetic extruder capable of controlling and adjusting the amount of feedstock by means of a rotor having throttleable control orifices.

Background Art

As noted in co-pending patent application No. entitled "The Kinetic Extruder: A Dry Pulverized Solid Material Pump", and co-pending patent application No. entitled "A System for Throttling and Compensation for Variable Feedstock Properties", there are a number of industrial processes which require the feeding of solid material from a lower atmospheric pressure environment to the elevated pressure environment within the working vessel. As is noted in these co-pending patent applications, one such process is coal gasification. Coal gasification processes generate combustible gases by pyrolyzing pulverized or powdered coal at elevated temperatures.

In the prior art arrangement, a liquid-solid mixture is umped into the pressure vessel. This prior art arrangement is referred to as the slurry feed method and suffers the disadvantage that the liquid has to be separated from the solid prior to it being utilized in the process. Another arrangement is to load the solid material into a pressurized hopper type device, pressurize the hopper with inert gas, and then dump the material, along with the inert gas, into the pressure vessel. This method is commonly referred to as the Lockhopper feed method. It does allow for varying the amount of material to be fed to the process.

The co-pending patent application entitled "The Kinetic Extruder: A Dry Pulverized Solid Material Pump", discloses a method and apparatus that overcomes the shortcomings of other prior art devices. This is achieved by utilizing a rotor enclosed within a pressurized container. The material is fed to the rotor from an atmospheric feed hopper through a stationary feed pipe and then is forced from the rotor into the high pressure vessel.

Although the kinetic extruder shown in that patent application solves many problems that exist in the prior art devices, it suffers a disadvantage of not being able to vary the feed rate of the material in an efficient manner. The patent application entitled "A System for Throttling and Compensation for Variable Feedstock Properties" allows for a degree of flexibility in the feed rate of the material but still is not as flexible in this area as desired.

Disclosure of Invention

The present invention provides a method and apparatus capable of controlling and adjusting the amount of material fed from a low pressure container into a pressurized container. This result is achieved by using a rotor that includes among other things, controllable orifices. The rotor is provided with a plurality of generally radial-extending sprues through which the pulverized or powdered material passes. Material flow from the sprues is limited by throttleable control orifices. The rate of flow of the material is controlled by controlling the pressure at a point between the sprues and the control orifice.

The rotor includes a hub which Is connected to a drive means. A material supply means extends into the hub for feeding pulverized material thereto.

Brief Description of Drawings

Figure 1 is a vertical sectional view, with portions shown diagrammatically, of the variable material feeder embodying the pressure control system of this invention; Figure 2 is an enlarged sectional view of the prior art control orifice;

Figure 3 is an enlarged sectional view of the throttleable control orifice of the present invention] and

Figure 4 is a plot of the throttling ratio as a function of the control pressure at the control orifice.

Best Mode of Carrying Out the Invention

The present invention shows a means to directly influence the pressure difference across the control orifice and thereby control the discharge rate of the orifice. This in turn changes the flow rate through the sprues and thereby the flow rate through the feeder.

Referring now to Figure 1, there is shown, a rotor 2 that is rotatably mounted in the horizontal axis within the pressure vessel 4. It is understood that, although the rotor is shown and described as being mounted by a horizontal axis, it could be mounted on a vertical or other axis as well. The rotor includes hub portions 6 and mounting clamps 9 and 10. The rotor is rotatably supported by bearings 12. Seals 14 are provided on either side of the bearings to seal the lubricant and to prevent dust from damaging the bearings.

Extending from portion 6 of the rotor 2 is a drive shaft 8. A motor (not shown) is attached to the drive shaft by any well known means to drive the rotor at the desired speed. A stationary T-shaped feed tube 18 is mounted co-axially within the rotor and cooperates with spin-up zone 20 to feed pulverized coal to the plurality of sprues 16.

The feed tube 18 is positioned within the rotor 2 by a bearing 17 and the bearing 17 is protected by the seal 19.

Sprues, as shown, may be made in two sections. First section 22, viewed sectionally, has a transition from a rectangular cross-sectional shape to a circular crosssectional shape, provides a large reduction in area. The second section 24 defines an aperture which is circular in cross-sectional area and which has a relatively small area reduction in the radial direction. The coal egresses from the second section 24 through a plenum 26 into control orifices 28.

The sprues and control orifices are designed to be easily replaceable.

The rotor hub portion defines a central gas plenum 30. A gas feed line 32 connects the contral gas plenum 30 to the control orifice plenums 26. The central gas plenum 30 is connected through gas feed line 34 through a rotating seal 5 to a plenum pressure regulator and control system, shown generally as 36.

In operation, coal is fed to the rotor through T-shape feed tube 18 and into the spin-up zone 20. Coal is then fed into first section sprue from the spin-up zone. Centrifugal force feeds the coal through the sprue and through the second section sprue and out to the control orifice into pressure vessel 4.

During this operation, the velocity of the solid material in the sprues should be properly selected to avoid gas leakage from the high pressure region. If the material velocity is too slow, there will be excess gas leakage into the spin-up zone, making it difficult to maintain flow through the T-shape feed tube. If the material velocity is too fast, the gas pressure gradient in the sprue is raised to a high value, choking the sprue. This choking can be overcome by requiring a high rotor speed, which, in turn, will increase the centrifugal force to keep the material flowing, or by changing the pressure gradient by means of gas injection.

As described in co-pending patent application No. entitled "The Kinetic Extruder: A Dry Pulverized Solid Material Pump", the coal flow through the kinetic extruder sprues is stabilized by an isobaric control orifice which fixes the solids throughput independent of the delivery pressure. This control orifice configuration is shown in Figure 2. It should be noted that due to the presence of the pressure equalization ports 37, the pressure difference across this control orifice is zero. A gas pressure gradient exists only in the sprue portion of the flow channel. The solids flow rate through the control orifice is a function only of the outlet diameter and the local centrifugal force level, as given by the equation: m = Cd^5/2G^1/2 where d = hole diameter G = (G-force) w = rotational rotor speed r = rotor radius C = empirical constant (C = 0.32 lbs/sec/in^5/2

(0.14 Kg/sec/cm^5/2) for conical orifice shapes) In the new throttleable control orifice configuration of the present invention, shown in Figure 3, there are no pressure equalization ports and gas is supplied to the upper portion of the control orifice hopper by means of a plenum in the rotor. This plenum is in turn fed gas from an external supply. The gas pressure in the control orifice hopper may thus be controlled independently of the delivery pressure. The control orifice throughput is then given by

where

/ = gas pressure gradient near the outlet of the control orifice. The magnitude and sign of is controllable by the overall pressure difference across the control orifice. The pressure gradient adds to the body force and m will be higher than the isobaric orifice value, if P₂ > P₃. Similarly if subtracts for the G-force and the solids flow rate will be reduced.

Due to the convergent shape of the control orifice, in comparison to the sprue, relatively significant outlet pressure gradients can be induced with quite modest control orifice pressure differences (e.g., 10 - 50 psi or 0.7 - 3.4 atm.). The effective delivery pressure for the sprue channel is therefore not changed significantly in throttling the control orifices.

Test data for a kinetic extruder rotor equipped with this throttling system is presented in Figure 4. There is plotted the throttling ratio as a function of the control orifice pressure difference (P₂ - P₃). Here the throttling ratio is defined as the rotor solids throughput divided by the throughput that is achieved when the control orifice is isobaric (P₂ = P₃). The feedstock was a 70% passing 200 mesh coal grind. The rotor speed was approximately 3000 RPM and was not varied significantly in the tests.

The Figure 4 data clearly demonstrates the effectiveness of the throttling system. An overall range of 3:1 in feed rate was achieved over a control pressure difference range of -10 to +20 psi or -.7 to 1.4 atm. Furthermore the data verified that the throttling effect is sensitive only to the control orifice pressure difference and not sensitive to the absolute value of the delivery pressure.

Claims

1. Apparatus for control of the continuous feeding of pulverized matter into a pressurized container, which apparatus includes a rotatably driven rotor for centrifugally feeding the pulverized matter which rotor includes a plurality of sprues through which the pulverized matter is fed and a plurality of controllable orifices cooperatively connected to said plurality of sprues, the improvement comprising, means for controlling the pressure at the junction of said sprues and said controllable orifices for controlling the feed rate of said pulverized matter.

2. An apparatus of the type defined in claim 1 wherein, said means for controlling the pressure at the junction of said sprue and controllable orifice includes an orifice plenum at said junction and means for controlling the gas pressure at said junction.

3. An apparatus of the type defined in claim 2 wherein, said means for controlling the gas pressure includes a central gas plenum defined by the hub of said rotor and conduct means connecting said central gas plenum to said orifice plenums.

4. Apparatus for feeding and controlling the feed rate of pulverized matter into a pressurized container comprising, a rotatably driven rotor that includes at least a radial sprue and a radial orifice, said sprue and said orifice defining a passage for feeding the pulverized matter to the pressurized container, and pressure control means connected to the junction of said sprue and said orifice for controlling the pressure at said junction thereby controlling the flow of pulverized matter through the said passage to the pressurized container.

5. The apparatus for feeding and controlling the feed rate of pulverized matter as defined in claim 4 wherein said pressure control means includes a source of gas pressure, a central gas plenum, and a gas passage means wherein said gas pressure control means is connected to said central gas plenum, and said gas passage means is connected between the central gas plenum means and the junction of said sprue and said orifice.