Side-wall discharge system

A thin-walled deep grain storage tank with improved sidewall discharge system involving a plurality of successive flat plates periodically mounted to the inside of a pair of vertical, parallel I-beam and/or Z-bar sidewall support members with openings for grain flow between successive plates, and a sidewall discharge means at the base of the tank. In this manner an internal chute is formed capable of staged discharge from successive top strata of stored grain. Such a system is useful in alleviating the problems associated with the build up of excess eccentric sidewall pressure during grain discharge without significantly altering the design and construction parameters and their associated economics.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus for discharging particulate material 
from a storage tank. More specifically, it relates to a sidewall discharge 
system for tall thin-walled grain storage tanks. 
2. Description of the Prior Art 
In designing, engineering and constructing contemporary large, deep storage 
tanks a major economic incentive is placed on the efficient use of 
materials to maximize capacity within acceptable structural limits. Thus, 
the contemporary storage tank intended for storing granular free-flowing 
material frequently is a thin-walled structure with the roof supported 
directly on the foundation by use of vertical members. In such tanks, the 
load associated with the stored granular mass is intended to be 
distributed evenly downward toward the base and foundation of the tank. 
It is known that when discharging grain or the like from a tall storage 
tank that a considerable amount of grain is set in motion. As long as the 
discharge is from the center of the tank the pattern of this movement is 
concentric with the tank. However, it is further recognized in the art 
that if grain is discharged from the side of the tank the pattern of 
movement becomes eccentric with the tank. The depth of the grain directly 
above the opening becomes significantly less than on the opposite wall of 
the tank creating a difference in sidewall pressure around the perimeter 
of the tank. This results in an eccentric distortion of the tank that 
conceivably could become severe enough to cause permanent distortion or 
even structural failure of the tank. 
Up to the present time, when faced with such a problem the usual solution 
is to design sufficient hoop strength and rigidity into the tank to 
account for the development of the eccentric forces during discharge. It 
has also been proposed that a series of baffles and wear plates (generally 
of a frusto/rectangular/pyramidal shape) be periodically attached to the 
inside of the wall directly above the sidewall opening or that a vertical 
flume with periodically spaced openings and internal baffles be mounted on 
the interior of the wall directly above the opening. In this manner the 
upper portion of the tank will discharge in successive layers, thus 
alleviating the distortion problem. However, each of these proposals 
involves additional expense in material, fabrication, and construction and 
the cumulative economic effect is significant. 
Various other methods and apparatus for discharging granular material from 
storage tanks have been suggested. For example, U.S. Pat. No. 3,341,090 
proposes the use of concentric walls forming an annular space between the 
wall, with perforations in the inner wall and with both the annulus and 
the inner silo having concentric central outlets with a sloped bottom. The 
purpose of such a structure is to mix the granular material from different 
strata as the silo discharges. An apparatus of similar purpose but 
different structure was disclosed in U.S. Pat. No. 2,907,501 wherein 
proportional blending of particulate material from a stratified storage 
vessel was achieved during discharge by use of a centrally located chute 
with a plurality of entrances at various depths with each entrance being 
equipped with an outwardly extending deflecting means. In contrast to the 
above patents, U.S. Pat. No. 4,030,633 discloses a sloped bottom hopper 
equipped with a plurality of material discharge spouts distributed such 
that laminar mass flow is achieved during discharge. In other words, the 
objective of the device is to have substantially first in-first out 
storage. 
In U.S. Pat. No. 4,109,827 a centrally located discharge column, with a 
series of discharge openings is mounted within a hopper in order to create 
a choked flow discharge path for the express purpose of minimizing 
vibration and impact, while in U.S. Pat. No. 4,138,021 a centrally located 
vertical structure is disclosed which is useful in both loading and 
unloading of the storage receptacle resulting in uniform sidewall forces. 
SUMMARY OF THE INVENTION 
In view of the problems associated with eccentric sidewall loading during 
discharge of granular material from a storage tank employing a sidewall 
discharge or the so-called side draw-off system (SDOS) we have discovered 
an improved SDOS that is economically attractive from the structural 
design, capital investment, and installation viewpoints. Thus, the present 
invention provides, in a storage tank for particulate material having 
exterior sidewalls attached to the interior vertical structural members 
that directly support the roof, the specific improvement comprising: 
(a) at least two of the support members being adjacent and essentially 
parallel from the foundation to the top of the storage tank; 
(b) a sidewall discharge means located between the adjacent support members 
through which stored particulate material is withdrawn; and 
(c) a plurality of essentially vertical flat surfaces periodically mounted 
along the inside of the pair of adjacent vertical support members leaving 
openings between successive surfaces thereby forming an interior chute 
with a plurality of openings in communication with the discharge means 
that allows selective flow of the stored particulate material during 
discharge, from successive top strata. 
In one specific embodiment, the present invention provides that the 
adjacent vertical support members are about two feet apart and about six 
inches wide and the essentially flat vertical surfaces are about three 
feet long with from about six to twelve inch openings between successive 
surfaces. It is further provided in a preferred embodiment that the lower 
portion of the adjacent vertical structural members are I-beams up to an 
intermediate level within the tank and are Z-bar beams of slightly smaller 
dimension from the intermediate level to the top of the tank. 
It is an object of the present invention to provide a sidewall discharge 
system for granular or particulate material storage, that alleviates the 
problems associated with eccentric sidewall pressure build-up during 
discharge. It is an associated object that the SDOS be economical, 
particularly that its presence does not alter the basic design, 
engineering and construction parameters of the tank. Fulfillment of these 
objects and the presence and fulfillment of other objects will be apparent 
upon the reading of the complete specification and claims taken in 
conjunction with the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The sidewall discharge system of the present invention, how it functions, 
and how it is incorporated into a contemporary thin-wall tall storage tank 
can perhaps be best explained and understood by reference to the drawings. 
FIG. 1 illustrates a cross-sectional view of such a storage tank 10 
equipped with the sidewall discharge apparatus of the present invention 
generally designated by the numeral 12. Discharge port 14 is located at a 
customer specified location of storage tank 10 between two vertical 
support members 16 and 18. The vertical support members 16 and 18 extend 
upward from the foundation of storage tank 10 essentially parallel, 
terminating at the top of the tank 10. Attached to the interior of the 
vertical support members 16 and 18 are a series of flat surfaces 20, each 
sequentially spaced relative to the next flat surface 20 such as to create 
an opening 22 between each flat surface. In this manner a vertical chute 
or conduit is created involving the exterior surface 24 of tank 10, the 
two essentially vertical parallel support members 16 and 18, and the 
series of flat surfaces 20. 
FIG. 2 is a close-up view of the discharge apparatus 12 of FIG. 1 showing a 
portion of the exterior wall 24, the two vertical support members 16 and 
18 and a series of three consecutive flat surfaces 20 separated by 
openings 22. FIG. 3 illustrates a top cross-sectional view of the lower 
portion of the discharge apparatus 12 of FIG. 1 wherein the vertical 
support members 16 and 18 have an I-beam cross-section. As illustrated, 
the chute is made up on two sides by I-beam members 16 and 18 and by flat 
surfaces 20 and exterior wall 24 on the other two sides, thus producing an 
interior conduit 28 capable of delivering stored particulate material such 
as grain or the like, from the top of the storage tank downward to the 
discharge port 14. Similarly FIG. 4 illustrates a top cross-sectional view 
of the upper portion of the discharge apparatus 12 of FIG. 1 wherein the 
vertical support members 16 and 18 have a modified Z-bar structure. FIG. 5 
illustrates the transition from the lower I-beam cross-sectioned vertical 
support members to the Z-bar cross-sectioned vertical support members 
occurring part way up tank 12. As illustrated, the point of transition 
involves a horizontal plate 30 to account for any reduction in size of the 
upper Z-bar vertical support member relative to the lower I-beam vertical 
support member. 
In operation, the discharging particulate material will selectively enter 
the uppermost opening 20 falling vertically downward through the chute to 
the discharge port 14. As such, at any given time, the angle of 
inclination of the stored particulate material; i.e., the slope of the top 
of the stored grain, will tend to remain flat, minimizing the difference 
in height across the storage tank 12. Consequently the pressure difference 
experienced at the sidewall will also be minimized resulting in 
essentially no induced eccentricity of the tank 12. 
Having thus described the preferred embodiments for the invention with a 
certain degree of particularity, it is manifest that many changes can be 
made in the details in the construction and the arrangement of the 
components without departing from the spirit and scope of this disclosure. 
Therefore, it is to be understood that the invention is not limited to the 
embodiment set forth herein for purposes of exemplification, but is to be 
limited only by the scope of the attached claims including a full range of 
the equivalents to which each element thereof is entitled.