Control of solids discharge from pressurized vessel

Control of discharge of particulate solids from a pressurized vessel is attained through a downwardly directed conduit with or without the use of valves. The lower end of the conduit has a greater cross-sectional area than the upper end of the conduit. The lower end of the conduit may extend into a fluidized bed. Discharge of solids from the vessel may be controlled by controlling the height and degree of aeration of the fluidized bed.

BACKGROUND 
There are numerous applications in the field of fluid bed reactors 
operating under pressure where it is desired to withdraw solids 
continuously to a lower pressure. Heretofore, control of such withdrawal 
has been by way of valved lock hoppers, riser pipes, etc. For example, see 
U.S. Pat. No. 4,106,210 which discloses discharge of solids through an 
upwardly directed riser pipe described as being of a tapered design to 
maintain uniform rates of flow. 
One of the features of the present invention is the use of a downwardly 
directed conduit or standpipe of non-uniform cross-section. Per se, such a 
conduit is known from U.S. Pat. No. 2,943,994 for quenching the 
temperature of a gas and from U.S. Pat. No. 3,661,799 wherein the conduit 
is a petroleum cracking reactor. 
SUMMARY OF THE INVENTION 
The discharge of solids under pressure in a vessel is accomplished by way 
of a conduit communicating at one end with the lower end of the vessel and 
extending downwardly therefrom. The conduit is of non-uniform inner 
diameter with the cross-sectional area at the lower end of the conduit 
being greater than the cross-sectional area thereabove. The lower end of 
the conduit is associated with a control means for controlling the rate of 
discharge from said conduit. The control means preferably includes a 
fluidized bed wherein the height and degree of aeration of the bed is 
selectively variable. The fluidized bed has an outlet for discharge of 
solids introduced into the fluidized bed from said conduit. 
It is an object of the present invention to provide for control of solids 
discharged from a pressurized vessel in a manner which is continuous, 
valveless, and controllable over a range such as 1 to over 1,000 tons per 
hour. 
It is another object of the present invention to control solids discharge 
from a pressurized vessel by way of a downwardly extending conduit 
constructed so that the cross-sectional area of the conduit progressively 
increases to facilitate expansion and consequent reduction of pressure of 
interstitial gas while the solids are subjected to gravity and pressure 
from within the vessel. 
Other objects will appear hereinafter.

Referring to the drawings in detail, wherein like numerals indicate like 
elements, there is shown in FIG. 1 a vessel designated generally as 10. 
The vessel 10 at its upper end has a charge port to facilitate introducing 
solids 20 such as a catalyst or solid reactant into the chamber 18. The 
chamber 18 above the level of solids 20 in housing 36 may be pressurized 
by way of conduit 16 containing a pressure regulator valve 14. 
The vessel 10 has a bottom portion 22 tapered at an angle corresponding 
generally to the angle of repose of the solids 20. The typical angle for 
the tapered portion 22 is about 70.degree.. The tapered bottom portion 22 
is in direct communication with the upper end of a discharge conduit 
designated generally as 23. The inner diameter of conduit 23 progressively 
increases in a downwardly direction. One inexpensive way of constructing 
such a conduit is to utilize a plurality of conduit portions 24, 26, 28, 
30 and 32 having progressively larger inner diameters. The overlapped end 
portions of the respective conduit portions are welded to one another. In 
place of conduit 23, there is shown an alternative conduit designated 23' 
in FIG. 2. Conduit 23' is uniformly tapered so that the inner diameter 
progressively and continuously increases in a downward direction away from 
the vessel 10. It is understood that chamber 18 may represent in practice 
a vessel in which a process reaction is carried out under pressure. 
Examples of such would include fluidized iron ore reduction reactors, 
pressurized fluidized bed coal combustors, pressurized gas phase olefin 
polymerization reactors, etc. 
The preferred embodiment of the present invention is to provide means for 
controlling the discharge of solids 20 from the lower end of conduit 23 or 
23' without using a valve. One such means is shown in FIG. 1 wherein a 
fluidized bed 34 of solids 20 is provided within a housing 36. Housing 36 
has an inner transverse dimension which is approximately four times the 
diameter of conduit portion 32. Bed 34 is fluidized by air or other gas 
which enters housing 36 by way of conduit 39 and the down shot grid 38. A 
down shot grid discharges the fluidized gas in a direction away from the 
surface of the fluidized bed 34. Housing 36 has an outlet 40 for discharge 
of solids 20 introduced into the bed 34 from the conduit 23. Suitable 
pressure gauges 42 may be provided where desired, such as the locations 
illustrated in FIG. 1. 
The solids 20 may be intermittently or continuously and controllably 
discharged over a wide range of flow rates to over 1,000 tons per hour or 
more depending upon the size of the discharge conduit 23. The solids 
within the conduit 23 are subjected to gravity, to the force of the 
pressure within chamber 18 above the solids 20, and to the resulting 
condition wherein the interstitial air or other gas expands and loses 
pressure as such solids and interstitial air or other gas move downwardly 
through the conduit 23. The expansion of the interstitial gas has a 
cooling effect on the solids 20. 
When the discharge from the lower end of the conduit 23 is controlled by a 
fluidized bed, the surface of the bed 34 should be above the lower end of 
the conduit 23 as illustrated in FIG. 1. If the height of the bed 34 and 
the degree of fluidization is kept constant, the rate of discharge from 
vessel 10 by way of the conduit 23 will likewise be constant. By varying 
the height of the bed 34 and the degree of aeration, the rate of discharge 
from the vessel 10 by way of the conduit 23 may be selectively varied over 
a wide range with reliable control. The present invention is capable of 
being used with a variety of different granular materials as the solids 
20. Thus, the present invention may be used where the solids 20 have a 
mean particle size of 60 microns, a bulk density of 40 pounds per cubic 
foot, and a particle density of 80 pounds per cubic foot. These 
characteristics are by way of illustration and not by way of limitation. 
The preferred embodiment of the conduit 23 or 23' requires that the 
cross-sectional area progressively increase in a downward direction away 
from the pressure vessel 10. The cross-sectional area may progressively 
increase in a continuous or step-wise manner. Any conventional discharge 
contrl means including a mechanical valve may be used. Even if the 
fluidized bed is used as the control means, the interstitial gas need not 
be completely depressurized. 
In the drawing, the vessel 10 is only shown diagrammatically. Vessel 10 may 
include various paraphernalia, control devices, heating and/or cooling 
structure, etc. The upper end of the housing 36 may be open or closed as 
desired. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.