Method and apparatus for controlling the discharge of particulate solids from an expanded bed of such solids

An apparatus for controlling the discharge of particulate solids through a discharge opening from a zone containing an expanded bed of particulate solids, the apparatus comprising a plurality of vertical doors positioned to open and close the discharge opening with the doors being adapted to open and close by rotation about a vertical axis; a mounting means to support the doors in position; and a controller adapted to control the opening and closing of the doors.

This invention relates to an apparatus for controlling the discharge of 
particulate solids from an expanded bed. 
This invention further relates to an improvement in methods for drying 
particulate solids in an expanded bed whereby solids are removed from the 
expanded bed by the use of vertical doors. 
In many industrial applications, particulate solids are dried in expanded 
beds. Expanded bed as used herein refers to ebullated beds, fluidized 
beds, semi-fluidized beds, and the like. Such beds generally comprise 
solids which are agitated by the flow of gas upwardly through the solids 
so that the apparent volume of the bed of solids is substantially greater 
than the volume of the solids with no gas flowing upwardly through the 
solids. The use of such expanded beds is well known to those skilled in 
the art and, as indicated, such expanded beds are used in many instances 
for drying particulate solids. 
In many instances, coal, as mined, contains undesirably high quantities of 
water for transportation and use as a fuel. This problem is common to all 
coals, although in higher grade coal such as anthracite and bituminous 
coal, the problem is less severe because the water content of the coal is 
normally lower and the heating value of coal is higher. The situation is 
different with respect to lower grade coals such as subbituminous, 
lignite, and brown coals. Such coals, as produced, typically contain from 
about 25 to about 65 weight percent water. While many such coals are 
desirable as fuels because of their relatively low mining cost, and since 
many such coals have a relatively low sulfur content, the use of such 
lower grade coals as a fuel has been greatly inhibited by the fact that, 
as produced, they typically contain a relatively high percentage of water. 
The drying required with such low rank coals is a deep drying process for 
the removal of surface water plus the large quantities of interstitial 
water present in such low rank coals. When higher grade coals are dried, 
the drying is commonly for the purpose of drying the surface water from 
the coal particle surfaces but not interstitial water, since the 
interstitial water content of the higher rank coal is relatively low. 
In either instance, a commonly used method comprises the use of a coal 
drying zone in which the particulate coal is supported above a grate such 
as a slotted grate, moving grate, or the like, in an expanded bed with a 
heated gas flowing upwardly through the expanded bed to dry the coal 
solids. 
In the drying of coal solids as discussed above, as well as in the drying 
of other particulate solids, a continuing problem is the regulation of the 
flow of particulate solids across the grate so that the solids are 
uniformly discharged from the discharge side of the vessel at a desired 
rate. Desirably, the flow across the grate is as nearly "plug" flow as 
possible. In other words, any given particle moves across the grate at the 
same rate and is exposed to the same conditions as any other solid 
particle. This is an idealized situation, but desirably, it is closely 
approximated for optimum dryer operation. 
In prior art attempts to control the flow of particulate solids from 
expanded beds wherein the solids were dried, horizontal doors have been 
used to regulate the discharge of the solids. Normally, the door is 
subjected to a predetermined torque to open the door a desired distance to 
accomplish the removal of a desired quantity of solids. Such approaches 
have resulted in the removal of particulate solids at a desired rate, but 
not uniformly across the depth of the expanded bed. 
Accordingly, an improved method for controlling the discharge of 
particulate solids from expanded beds has been sought. It has now been 
found that solids are uniformly discharged from all depths of an expanded 
bed by the use of an apparatus which comprises: 
(a) a plurality of vertical door means pivotally mounted to open and close 
the discharge opening with the doors being adapted to open and close by 
rotation about a vertical axis; 
(b) a mounting means to support the doors in position to open and close the 
discharge opening; and 
(c) a controller means adapted to control the opening and closing of the 
doors. 
Such an apparatus is useful in processes for the drying of coal as 
discussed above, as well as in processes for drying other particulate 
solids in expanded beds.

In the description of the Figures, the same numbers will be used throughout 
to refer to the same or similar components. 
In FIG. 1, a dryer 10 is shown. Dryer 10 comprises a vessel 12 including a 
grate 14 above which particulate solids 20 are positioned in an expanded 
bed. Coal is charged to vessel 12 through an inlet 16 which may be any 
suitable solids handling system such as a vibrating table or other type of 
solids feeder. Air is injected into vessel 12 through a line 18 and, in 
many embodiments, is heated air. In some instances, fuel may also be 
injected beneath grate 14 with the combustion gases forming the hot gas 
which passes upwardly through grate 14 and solids 20. The exhaust gases 
from the drying process are recovered through a line 22 and passed to fine 
solids removal, recycling, clean-up, or the like, as known to those 
skilled in the art. Such drying processes, in general, are considered to 
be known to those skilled in the art. Vessel 12 as shown in FIG. 1 
includes a coal discharge chute 24 which comprises a casing 32 through 
which particulate solids are recovered from vessel 12. The flow of solids 
from vessel 12 is regulated by a horizontal gate 26. Gate 26 is pivotally 
mounted at a horizontal connection 28. In the operation of gate 26, torque 
as shown by arrow 30 is applied as required to maintain gate 26 in a 
desired position. It will be clear upon a review of FIG. 1 that solids at 
the top of the expanded bed in vessel 12 have a much smaller area through 
which they may escape from vessel 12 than do solids at the bottom of the 
expanded bed above grate 14. In general, the solids at the top of the 
expanded bed are those lighter solids which either are smaller in size or 
have already been dried to a substantial degree. The heavier solids at the 
bottom of the expanded bed are normally the larger particles or those 
particles that have not yet been dried to the same degree as those 
particles at the top of the expanded bed. As a result, the particles, both 
the larger particles and the wetter particles, are to be expected nearer 
the bottom of the expanded bed and, in the use of the apparatus shown in 
FIG. 1, will be those particles which are most likely to escape vessel 12 
in a short time interval. Accordingly, the use of gate 26, while it is 
effective in establishing a desired flow rate, is not effective in 
achieving plug flow across the expanded bed in vessel 12 or in removing 
solids uniformly across the depth of the expanded bed. 
In FIG. 2, an embodiment of the apparatus of the present invention is 
shown. An upper mounting member 33 and a lower mounting member 35 are 
positioned above and below the discharge from the expanded bed in vessel 
12. A vertical door 36 is positioned to open and close to regulate the 
flow of particulate solids from the expanded bed in vessel 12. In the 
operation of the apparatus shown in FIG. 2, a plurality of doors 36, only 
one of which is shown, are positioned to open and close to thereby open 
and close the discharge opening for particulate solids from vessel 12. 
When doors 36 are opened, flow is unimpeded from the top, middle, or 
bottom of the expanded bed. Solids 20, in any portion of the expanded bed, 
can freely flow through the discharge opening. When it is desired to stop 
flow, doors 36 are closed. Desirably, flow is regulated by fully opening 
or fully closing doors 36 so that flow from the expanded bed is unimpeded 
when solids are to be discharged. It is readily seen that the use of the 
apparatus shown in FIG. 2 closely simulates plug flow through the 
ebullated bed present in vessel 12 and results in the uniform removal of 
particulate solids from all levels of the expanded bed. 
In FIG. 3, the mounting members and doors 36 are shown in greater detail. A 
frame 34 is conveniently used to mount the apparatus of the present 
invention in place over the discharge opening from an expanded bed zone. 
Frame 34 includes upper mounting member 33 and lower mounting member 35. 
Doors 36 are supported on vertical support members 48 which are rotatably 
supported in upper mounting member 33 and lower mounting member 35. As 
shown in FIG. 3, support members 48 are rods which are supported by a 
suitable support means such as thrust bearings (not shown) and journal 
bearings (not shown) in lower mounting member 35 and by journal bearings 
(not shown) in upper mounting member 33. Doors 36 are desirably rigidly 
mounted on support members 48 so that rotation of support members 48 
results in rotation of doors 36. Support members 48 desirably extend a 
distance above upper mounting member 33. Control rods 46 are positioned on 
each of support members 48 and join support members 48 to a push rod 44 
which is used to open and close doors 36. Push rod 44 is desirably 
rotatably attached to control rods 46, so that when push rod 44 is moved, 
doors 36 are opened or closed. Control means (not shown) such as a 
variable time or the like can be used to open and close doors 36 at any 
selected interval or frequency to achieve the removal of particulate 
solids from the expanded bed at a desired rate. It is clear, upon 
observation of FIG. 3, that when doors 36 are opened, the flow of solids 
from the expanded bed is unimpeded and solids can be recovered with equal 
freedom from the upper, middle, or lower portions of the expanded bed. 
Similarly, when it is desired to close doors 36, since expanded beds tend 
to behave as fluids rather than solids, doors 36 are readily closed to 
stop flow until it is desired to remove additional quantities of solids. 
While the apparatus of the present invention is useful in many 
applications, one application in which it is considered to be particularly 
suitable is in conjunction with methods for drying particulate solids such 
as coal with hot gases. Such processes are well known to those skilled in 
the art, however, the apparatus used to regulate the flow from such 
vessels heretofore has not provided the uniform solids recovery across the 
full width of the expanded bed provided by Applicant's claimed apparatus. 
A plurality of doors are desirably used. The doors can be of substantially 
any size although it is preferred that the doors be at least five times, 
and preferably ten times, the diameter of the largest particulate solids 
in width. Preferably, the doors are even wider. Similarly, support members 
48 could be joined to doors 36 in the middle or at positions other than at 
one edge, although it is greatly preferred that support members be joined 
to an edge of doors 36. The apparatus can be constructed of materials 
known to those skilled in the art for use in such applications. Similarly, 
a variety of means for opening and closing doors 36 could be used, 
although the apparatus set forth is considered to be a preferred 
embodiment. 
Having thus described the invention by reference to its preferred 
embodiments, it is pointed out that the embodiments described are 
illustrative rather than limiting in nature, and that many variations and 
modifications are possible within the scope of the present invention. Many 
such variations and modifications may be considered obvious and desirable 
by those skilled in the art based upon a review of the foregoing 
description of preferred embodiments.