Silo cleaning process

A silo which is impeded by a mass of cohering particles is cleaned by extending at least one flexible tube connected to a mace into the silo to near the coherent mass and flowing gas through the tube and mace at a rate and pressure causing swinging and writhing movements by the mace and tube.

BACKGROUND OF THE INVENTION 
This invention relates to cleaning silos for storing particulate materials 
where the storing and delivering capacity of the silo is impeded by 
cohesive masses of the particles within the silo. 
In general, silos are typified by coalsilos and coal silos are described in 
the publication AF-791 "Coal Preparation for Combustion and Conversion" 
(prepared for Electric Power Research Company, May 1978) as follows: 
"Coal storage silos are constructed of either steel or concrete although, 
in the large sizes, steel structures have not proven as economical as 
concrete. Small concrete silos are built up of precast staves banded 
together with wire hoops; large silos are constructed of continuously 
poured concrete using the slipform technique. 
The dimensions of concrete silos have responded to demands for larger 
capacities and to developments in the state of the art in construction 
techniques. Silo heights of two to three times the silo diameter are 
generally found most economical. Capacity of a 70 ft silo, depending on 
its height, is 10,000 to 15,000 tons. Its installed cost ranges from $100 
to $200/ton of storage capacity. Early designs of concrete silos provided 
rather simple coal drawdown methods. A system of seven gates works well 
enough with most clean coals, except for occasional rat-holing, i.e., a 
narrow withdrawal funnel down through the center line of each gate. At 
other times, coals may bridge over the gate openings, causing flow to 
become erratic or to halt completely. Preferred designs incorporate the 
mass or plug flow principle through the use of multiple hoppes having 
sides sloping upwards at up to 70 degrees, with inlet openings up to 18 ft 
in diameter and outlet openings as large as practical or rectangular." 
SUMMARY OF THE INVENTION 
The present invention relates to cleaning a silo in which particulate 
solids have formed cohesive masses. At least one flexible hose is 
connected to a mace. The mace body is arranged to have a density exceeding 
that of the material in the silo. The peripheral surfaces of the mace are 
preferably composed of spark-resistant material where the solid particles 
or dust in the silo may be or become explosive. The hose connected to the 
mace is extended downward from an upper portion of the silo so that the 
mace is supported by the hose at a depth at least near that of a cohesive 
mass of the silo contents. A gas which is relatively inert to the material 
in the silo is pumped through the hose at a pressure and rate such that 
the mace is pneumatically driven into a swinging and writhing motion that 
moves it into and out of contact with cohesive masses encountered along a 
segment of the interior of the silo. At least one such mace is disposed 
and operated in positions such that substantially all of the cohesive 
masses within the silo are disrupted into masses of relatively 
free-flowing particles.

DESCRIPTION OF THE INVENTION 
Applications discovered that a process of cleaning a silo with a gas 
powered mace can be highly effective if--but only if--the components and 
functions of the mace and the powering of it are tailored to the 
properites of the materials being treated. Maces, mace supporting hoses 
and mace powering gas flows, of different sizes and configurations have 
been tested in the cleaning of coal silos. In the cleaning of a 13,000-ton 
coal silo containing a typical accumulation of cohesive meases of coal 
which impeded its operation, the application of a series of pneumatically 
powered "robots" (of proprietary design, which was kept secret) cleaned 
(i.e., freed-up and removed coal at a rate of 16 tons in 24 hours (or 
about 0.67 tons per hour). In contrast, in cleaning a similarly impeded 
silo with two gas powered maces of the present invention, the coal was 
cleaned at a rate of 1800 tons in 20 hours (or about 90 tons per hour). 
FIG. 1 shows a coal silo 1 having a coal buildup 2 comprising a relatively 
cohesive mass of coal particles. A gas supply hose 3, such as a 1-inch 
heavy duty air hose, is connected between a mace 4 and a source of highly 
pressurized inert gas such as air compressor 5. 
The hose 3 is extended downward from an upper portion of the silo and 
temporarily fastened near the top at a location such as point 6, so that 
the hose supports the mace at a depth at least near the coal buildup 2. A 
safety chain or cable 3a is preferably attached between the hose and mace, 
in case the hose coupling should fail. 
FIG. 2 illustrates the details of a particularly preferred embodiment of 
the present type of mace, which weighs about 5.5 pounds. A gas hose 
connection 7, such as a 1-inch Chicago Pneumatic UM-75-M or equal 
Gladihand type air hose connection with safety pin is provided at the top 
of a tubular body. The hose connection 7 is attached, preferably by welds 
and threads, to a bushing 8 such as a 11/2-inch by 1-inch National 
Pipethread bushing. The bushing 8 is similarly connected to a coupling 9, 
such as a 11/2-inch National Pipethread coupling. The coupling 9 is 
similarly connected to a pipe nipple 10, such as a 11/2-inch by 6-inch 
National Pipethread nipple. The pipe nipple 10 is similarly connected to a 
pipe cap 11, such as a 11/2-inch National Pipethread cap. 
Preferably, a single laterally disposed gas discharge port 12 is provided 
in the side of the pipe cap 11. The port or ports are preferably sized and 
arranged to provide a total flow equivalent to a flow of air through a 
7/16-inch hole in a direction substantially perpendicular to the axis of 
the hose and mace. 
The projections 13 of the mace 4 preferably comprise three triangular flat 
plates which are equally spaced with their longest sides aligned axially 
along the pipe nipple 10, such as 11/4.times.4.times.21/2-inch AR grade 
iron plate, welded to the nipple 10. Each of the most exposed peripheral 
surfaces of the mace 4 are at least coated with a spark-resistant facing 
14, such as a brass facing. The mace can be constructed entirely of brass, 
bronze or other spark-resistant material. 
As will be apparent to those skilled in the art, different configurations 
of the mace and its projections (and, for treating coal or other 
potentially explosive materials, spark-resistant outer surfaces) can 
suitably be employed. The density of the mace with its interior filled 
with gas preferably exceeds the density of the material in the silo to be 
cleaned to an extent such that the mace tends to sink within at least a 
non-coherent mass of particles of that material. To further this, the 
projections on the mace should have outer surfaces which are preferably 
generally rounded to enhance such a penetration. 
In general, the mace preferably comprises an elongated body containing a 
central gas conduit and a gas exhaust port directed perpendicular to its 
long axis. At least two projections on the mace are preferably oriented so 
that the lateral force of gas exhausting through the port or ports is 
directed generally perpendicular to the planes of those protections. 
Preferably, this is accomplished by employing at least three substantially 
equally spaced projections with a single exhaust port between a pair of 
projections, so that substantailly any lateral thrust of the mace body 
moves it generally perpendicular to the planes of at least two 
projections. 
The following outlines a particularly preferred procedure for cleaning a 
coal silo in accordance with the present invention: 
1. Rig up three high volume air compressors with 150 psi capability. Run 
three individual lines (high strength) to the top of the silo and down to 
the point of the highest material buildup near the edge of the silo. 
2. Connect the mace on the end of each air line and hook up a safety catch 
bridal and duct tape the air connection. 
3. Fasten the air hose to the silo railing to suspend the mace. 
4. Turn on a conveyor system for removing material from the silo and start 
the air compressors. 
5. Whenever one of the air lines stops jumping or the air escape becomes 
steady the mace is stuck or covred with coal. Pick up on the hose until it 
again starts to jump then lower back down. 
6. When the mace starts hitting the concrete silo wall or steel liner lower 
the air hose. Move each of the units around the silo to the extent 
required to get fairly even removal of coal buildup. 
7. Monitor the material being removed from the silo, for example, by means 
of a belt scale. This also gives an indication as to when a mace may need 
to be lowered or moved. 
8. After a significant amount of material has been removed, an inspection 
door can be opened to give a better indication of where each mace should 
be placed. Use the inspection door to determine when all buildup has been 
removed. 
Tests have indicated that such a procedure can be done on a 70 ft. silo 
with over 2000 tons of buildup in less than 20 hours without the use of 
water; and no mess or extra cleanup is generated. 
TESTED ALTERNATIVES 
The effectiveness of the following arrangements were compared with the 
above-described preferred embodiment of the present invention for cleaning 
a coal silo. 
Similarly shaped maces made with longer bodies, or made of thicker pipes, 
or having weights about one-half to two times greater than 5.5 pounds, 
were found to be much less efficient. A spinning arrangement of flail-like 
chains on a bearing-mounted body tended to stop spinning and cleaning 
about as soon as it contacted a coherent mass of coal. Operating a mace 
with about the above shape and weight, but with a pipe nipple connected 
above the mace resulted in relatively quickly breaking the pipe nipple. 
SUITABLE COMPOSITIONS AND PROCEDURES 
In general, the present invention is applicable to cleaning substantially 
any silo which contains a particulate material having a tendency to form 
cohesive masses impeding the performance of the silo. Examples of such 
silos include those for storing mined out oil shale, sulfur, uranium ore, 
trona, etc. 
The density and size of the mace should be correlated relative to the 
density of the material in the silo to be cleaned and the strength of the 
cohesion with which such particles are bound into a cohesive mass. 
Basically, the mace should be capable of readily penetrating into a 
non-cohesive mass of such particles. 
The mace-supporting flexible hose and the pressure and rate of flow of gas 
through the hose should be correlated with the weight of the mace so that 
when the mace is immersed within a noncohesive mass of particles, the gas 
flow tends to be driven upward and out of the mass of particles and into 
swinging and writhing and jumping movements within the silo. A preferred 
arrangement for use in coal silos comprises a combination of a flexible 
air hose having an inner diameter of about 1 to 1.25 inches with air 
flowed through the hose at a pressure of about 90 to 120 psi, where the 
hose length is at least about 50 feet and the air is exhausted through an 
outlet opening of about 1/4th to 5/8ths-inch in diameter and a mace of the 
type shown in the drawing weighing about 3 to 8 pounds.