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 which can control the feed rate and compensate for variations in feedstock properties.

Background Art

As set forth in co-pending application No. entitled "The Kinetic Extruder: A Dry Pulverized Solid Material Pump", there are a number of industrial processes which require vessels that operate at elevated pressures; and as a part of their operation, it is necessary to feed solid material to them from a lower atmospheric pressure environment. One such process is coal gasification, which utilizes pulverized or powdered coal to generate combus¬ tible gases. Such processes require the feeding of pulverized or powdered coal from an atmospheric pressure hopper to an elevated pressure reactor vessel.

The co-pending patent application discloses a method and apparatus for the continuous feeding of pulverized or powdered material to the pressurized container without the need for a carrier fluid, while eliminating blow-back of gas through the material or the material feeding means. This result is achieved by the use of a rotor within a pressurized container to which the material is applied. The material Is fed from an atmospheric feed hopper through a stationary feed pipe, then through a stationary inner hub and then to a spin-up zone between the stationary inner hub and the rotatably-driven rotor, where the material is forced into the rotor.

Although this kinetic extruder solves many problems

existing in the prior art, it cannot compensate for variations in the permeability-of the feed material, nor can the feed rate of the material be varied over an exte range.

In a continuous process, it is desirable to vary the rate of feed of the pulverized material to compensate fo changes in other parameters within the coal gasification ^' process. Also, the permeability of the pulverized coal will vary as coals f om different coal fields are used a sometimes, for coals within a single field. Since the rate of feed of pulverized coal through the -kinetic extr is dependent upon the permeability, it is desirable to compensate for undesirable variations in the permeability of the coal being fed and to be able to adjust the feed rate to the reactor demand.

Disclosure of Invention

The present invention provides a method and apparatus for adjusting and controlling the feed rate of feed mater such as pulverized coal,- into a pressurized container and to compensate for variations in feed stc-ck properties at a fixed feed rate. This is achieved by a rotor mounted within the pressurized container that Includes staged sprues. The rotor includes a hub which iβ connected to a drive means. A material supply means extends through the wall of the container to the hub. A line for controlling the gas pressure connects to a plenum in the rotor and fr there to points along the sprues for the purpose of controlling the gas pressure at these injection points. The gas pressure control line is connected to a gas suppl and control system.

The present invention provides a method to overcome the limitations imposed by the co-pending patent applica¬ tion when the requirement to be able to handle various feed stock of different properties and the requirement to be able to vary the feed rate at reasonable power levels

are superimposed to the normal pressurization requirement.

When higher feed rates -are required or materials having lower permeability are being used, the pressure gradient within the sprues is increased, reducing the net centri¬ fugal forces acting on the material and thus the flow rate. By injecting high pressure gases into the sprue, a favorable pressure gradient can be assured and a more beneficial force balance re-established.

The capability of the device described in the co- pending patent application is greatly degraded if higher feed rates are required or if a feed stock having lower permeability is used. In these instances, the pressure gradient within the sprues is increased; this reduces or even stops the feed rate if a constant rotor speed is maintained. It requires a very large increase in drive power if the rotor speed is increased to overcome the pressure gradient. The present invention reduces the pressure gradient by injecting a high pressure gas into the sprue and thereby makes it possible to feed lower permeability feed stock or feed at higher rates without substantially increasing the rotor speed and the correspond¬ ing driving power.

Brief Description of Drawings

Figure 1 is a plan view for a gas injection example,

Figure 2 is a plot of the area of the gas injection example of Figure 1 versus distance along the gas injection example,

Figures 3 -and are plots of pressure and pressure gradient distributions without gas injection,

.Figure 5 is a plot of pressure..gradient distributions for a different permeability material without gas injection,

Figure 6 is a plot of pressure gradient distributions for the same material plotted in-Figure 5, but with the addition of gas injection,

Figure is a plot of sprue pressure gradient distribu-

tions for high and.low permeability material with a passive gas injection,

Figure 8 is a plot of sprue pressure gradient distributions for high and low permeability material wit active gas injection,

Figure 9 is a vertical sectional view, with portions shown diagrammatically, of the variable material feeder embodying this invention for feeding pulverized or powde material to a pressurized container,

Figure 10 is an enlarged sectional view of the porti of the rotor of Figure 1.

Best Mode of Carrying Out the Invention

Referring now to Figure 9_ _» there is shown a rotor 2 that is rotatably mounted in the horizontal axis within t pressure vessel 4. It is understood that, although the rotor is shown and described as being mounted by a horizo tal axis, it could be mounted on a vertical or other axis as well. The rotor includes hub portions 6 and mountijig 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 bearing 17 and the bearing 17 is protected by the seal 1

Sprues, as shown, are made in two ^' sections. First section 22, viewed sectionally, has a transition from a rectangular cross-sectional shape to a circular cross- sectional shape, which 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. A plenum 25j as shown in Figure 10, is located around the second section of the sprue. The coal discharge is from second section 24 into control orifice 28, which are held onto the rotor 2 by two screws (not shown). The function of the control orifice is to meter and stabilize the coal flow through the sprue.

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 central gas plenum *30 to the sprue plenums 25 _* The central gas plenum 3° s 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 the 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 higher 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 into the sprue.

The present invention is directed to a means to directly influence the pressure distribution in the sprues.

Computations are presented here illustrating.the beneficial effects of gas injection for a particular spr configuration example. The calculations are made using computer analysis of the porous bed flow in the sprue channel. The analysis has been validated by comparison with data obtained in tests with the kinetic _. extruder.

The sprue configuration chosen for the example is shown schematically in Figure 1. Solid's motion is from right to left. The sprue inlet pressure is 1 atm and th sprue outlet or delivery pressure is 28 atm. The origin (z = 0) is fixed at the outlet or high pressure end of t sprue. Control gas injection points are assumed to be a normalized positions of z = 0.1, 0.2, 0.3, and 0.4. The exact area profile of the example sprue is illustrated i Figure 2. Other data used for the example calculations are as follows:

Sprue Length = 0.70 ft (0.21 m)

Sprue Outlet Area = 5.24 x 10 ^""3 ft

(4.87 x lO ^*" __ ^~ )

Solids Bed Permeability = 2.8 x _.0 ^~~~ or 4.2 x ^' lO ^"*1

(2.6 x 10 ^"13 or 3.9 x 10~

Solids Bulk Density = 42 lb/ft ³ (675 Kg/m ³ )

Solids Bed Porosity = 0.533

Gas Viscosity = 1.2 x 10 ⁵ lb/ft - sec. ( lO ^"" - ⁵ Kg m - sec.)

The solids bed data is characteristic of a TQ _\ passin 200 mesh coal grind.

Figures 3 an 4 show the results of a calculation for bed permeability value k = 4.2 x 1 ^"~~ ft ² (3.9 x 10~ ¹³ m and no gas injection. Sprue gas pressure distributions a given in Figure 3 for a range of solids throughputs corre ponding to sprue outlet mass velocities from 0 to 220 lbs sec/ft ² (1073 Kg/sec/m ). Pressure gradients -, for the same case, are presented in Figure 4.

The pressure gradient is a key parameter which effect

( O

the operation of the kinetic extruder since the rotor speed must be high enough for the centrifugal body force to exceed the opposing pressure gradient in magnitude throughout the sprue for the solids throughput to be maintained, i.e.:

2

P™ > dz

where ^ = bed density r = distance from rotational axis w = rotor angular velocity -■■■■2- = pressure gradient in compatible units As can be seen in the Figure 3 and 4 results, the pressure gradient is sensitive to solids throughput. High throughputs tend to concentrate the pressure drop near the outlet end of the sprue, thus increasing (in absolute value) the pressure ^' gradient in that area.

The pressure gradient distributions are also sensitive to solids bed properties, particularly permeability, in a similar fashion. Figure 5 shows calculated results for the same data except that the bed permeability is reduced from

4.2 x 10~ ¹² ft ² (3.9 x 10~ ¹³ m ² ) to 2.8 x 10 ¹² ft ²

— ^" i ^*" **- ^* , p (2.6 x 10 ). It may ,be noted that the range of sprue outlet pressure gradients, for the same range in throughputs, increases from -32 78 to -32 - -ll8 when the permeability is reduced. rotor speed, required to success u y pump e ow permea lity ma eria .

Power requirements increase rapidly with rotor speed, thus high speed represents a significant penalty.

The beneficial effects of gas injection may now be discussed. A large number of gas injection patterns are possible. There may be any number of gas injection points along the sprue. Gas may be injected through either a small orifice or a porous section in the sprue wall. The flow resistance (e.g., orifice area) at the injection points may

be different or the same for all injection points. Gas bleeds may all originate from ^' the same plenum in the roto or there may be two or more plenums maintained at differe pressures. The gas injection may be "active", that is, t plenum pressure is adjusted according to changes in throu put or feed stock properties (i.e., permeability), or it may be "passive" plenum pressure kept constant regardles

Herein one "active" injection case and one "passive" injection case are analyzed as examples. The gas injectio points are shown in Figure 1 and are the same in both case

In the "active" case:

All injection point orifice areas = 2 x 10 -6 ft2

(1.9 10 ^"*7 m ² ) Control gas plenum pressure = 29-6 atm or

35-7 atm

In the "passive" case:

All injection point orifice areas = 5 x 10 -6 ft2

(4.5 x lCf ⁷ m ² )

Control gas plenum pressure* = 29.6 atm

All other data is common to the previous example without gas injection.

Figure 6 shows the calculated sprue pressure -gradient distributions for the "passive" case gas injection and for k = 2.8 x 10~ ¹² ft ² (2.6 x 10~ ¹³ m ² ). This is to be compa with ^" the distributions without gas injection shown in

Figure 5. As can be clearly seen, the gas injection has a effect similar to increasing the permeability of the feed stock. ^" Without gas injection, the dg = 118 at a throughput of 220 lbs/sec/ft ² (1073 κ| sec?m )• with gas injection this was reduced to I dpi = 77- This would reduce the rotor speed requiremeδτ ^m f'or operation.

The benefits of "passive" gas injection are further illustrated in Figure 7» This shows a comparison of the sprue pressure gradients with and- without gas injection fo the high and low permeabilities examples. The results sho that the dg_ curves have less sensitivity to changes in dz

permeability when gas injection is used. Minimum rotational body force curves for the cases with gas injection, labeled 3' and 4 ¹ in Figure 7, are much closer together than those with no gas injection, I ¹ and 2'.

If "active" gas injection is used, even more precise tailoring of the pressure gradient is possible. Figure 8 shows a comparison of pressure gradients for the high and low permeability cases similar to Figure 7. Curves 1 and 2 are high and low permeabilities without gas injection as before. Curve 3 is for gas injection with injection orifice areas of 2 x 10 —6 ft2 (1.9 x 10—7' ^* m2), a plenum pressure of

29.6 atm, and k = 4.2 x 10 ^*"12 ft ² (3.9 10~ ¹³ m ² ). Curve 4 is for k = 2.8 x 10~ ¹² ft ² (2.6 x 10~ ¹³ m ² ) and a plenum pressure of 35.7 atm, which increases the injection flows.

Comparing the disparities between 3 and 4 vs. 1 and 2 shows that the effects of the changes in feedstock permeability have been almost perfectly compensated for by the "active" gas injection.