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Storage Silo
Selection – Dry Bulk Applications
By Bill Neighbors –
President Tank Connection
The process of silo selection starts
with a series of questions that require answers before proceeding.
This is one of the main problems witnessed in today’s dry bulk
storage market. Tank and silo selection many times is based on a
preferred “construction type” in lieu of “stored material”
performance requirements. Silo manufacturers tend to process
customer information relative to their standard storage products and
design parameters, which leaves the client responsible for the
outcome. This is an archaic approach which is safe for the vendor,
but many times misses the mark in achieving a functional and
efficient storage system that performs per your requirements.
The “top 10” list below includes
basic considerations that should be addressed on every storage
application. If the application under review is routine and no
problem areas exist with the stored material or the discharge
stream, a standard tank quote can be generated. If any of items
listed are a concern, a specialist in integrated storage
applications can advise you on the correct approach.
Considerations
1. How much material will be
stored….tons / cubic feet?
2. Are there any unique
characteristics of the stored material to consider?
3. What materials of construction
should be used?
4. What product density should be
used for volume and design calculation?
5. Is material degradation a
concern?
6. Is material segregation a
concern?
7. What type of material discharge
pattern is preferred or required for the application? (i.e., funnel
flow, mass
flow, expanded flow, etc.)
8. Is a hopper flow aid device
required for reliable discharge?
9. Should my material be tested by a
“flow specialist”?
10. Do I need a reliable performance
guarantee from the silo supplier?
You don’t need to have all the
answers, but you do need to know a reliable storage specialist in
dry bulk applications that can advise you in these areas. With the
basics covered, the selection process can be now be narrowed for
customer review and preference.
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 Example 1:
We need to store 5000 cubic feet of
hydrated lime. Based on the capacity requirements as detailed
below, a bolted or shop-welded tank is correct for the application.
Based on experience with the
material and an extensive number of applications in the field, a
flow aid device is required. A bin activator sized at half the tank
diameter will provide reliable material discharge. A bin activator
provides a “funnel flow” material discharge pattern. The material
does not need to be tested. Material degradation should not be a
concern. |
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Example 2:
 Storage application requires 25,000
cubic feet of a granular product. It is desired to minimize material
segregation during discharge. First we will note that size
selection exceeds a shop-welded tank. This eliminates the shop-weld
tank, unless we break the capacity requirements into a two tank
package. The correct storage selection is a bolted smoothwall
tank. The correct flow discharge selected is mass flow. This
does not mean we specify a silo designed for
“mass flow” design loads. The
correct request is to specify a silo designed for “functional mass
flow” discharge. In order
to provide reliable “functional mass flow” (FIFO) discharge, the
material will need to be tested.
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Tank & Silo Selection
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Shop-Weld Construction
Applications: Plastic resins, food
products, dry chemicals,
minerals, wood waste & misc. dry
other
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Hopper capacities under
10,000 cubic feet
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Shop-controlled quality
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One piece tank
construction
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Factory applied coating
systems
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Increased freight cost
to the jobsite
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Less field installation
requirements
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Bolted Smoothwall Flat Panel (FP) Construction
Applications: Cement, fly ash, coal,
limestone, lime, aggregates,
minerals, chemicals, plastics, select
foods, wood waste & misc. dry other
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Hopper capacities from
1000 – 100,000 cubic feet
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Shop-controlled quality
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Modular construction
requires bolted field assembly
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Decreased field
installation timeframe
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Factory applied powder
coating systems |
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Field-Weld Construction
Applications: Minerals, aggregates,
dry chemicals & misc. dry other
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Hopper capacities from
20,000 – 250,000 cubic feet
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Shop-controlled quality
– minimize large piece count
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Modular construction
requires field welded assembly
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Increased field
installation timeframe
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Field applied coating
systems
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Slip &
Jump-form Concrete Construction
Applications: Minerals, grains, wood
waste & misc. dry other
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Hopper capacities from
20,000 – 300,000 cubic feet
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Slip-form quality –
high - continuous pour, monolith design
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Jump-form construction
- cold joint construction
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Increased field
installation timeframe
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Increased foundation
requirements
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Hybrid Silo Construction
(combines the best qualities of bolted FP,
field-weld & concrete construction)
Applications: Cement, fly ash, coal,
limestone, lime, aggregates,
minerals, chemicals & misc. dry other
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Hopper capacities from
20,000 – 150,000 cubic feet
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Shop-controlled quality
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Modular construction
requires field assembly
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Decreased field
installation timeframe
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Factory applied powder
coating systems
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In general, dry bulk applications that require a storage volume of
less than 10,000 cubic feet will utilize a shop-welded or smoothwall
bolted silo. Both products are used interchangeably in the
industry. Shop-weld and bolted construction maintain advantages as
listed above. Under review, the total installed costs (material +
freight + field installation) are comparable between both products.
Bolted FP (flat panel), field-weld,
concrete and hybrid silos are typically utilized in large volume
storage applications. All four designs are routinely specified in
the power industry. In the industrial market, bolted FP and hybrid
construction are the most cost efficient silo designs. Field-weld
and concrete construction require extended field installation
timeframes, which equates to higher installed cost.
Relative to steel and alloy
“materials of construction” selection, bolted, shop-weld and
field-weld silos are available in coated carbon steel, stainless
steel and aluminum construction. All tanks/silos are customized for
the application and are available with full skirt support, leg
supports, structure supports or lug supports. Typical silo
accessories include a filter flange connection for dust control,
level control nozzles, manway access into silo deck and hopper
areas, maintenance access platforms, caged ladders, spiral
stairways, perimeter guardrails, pressure vacuum relief devices and
custom requirements for system integration.
In summary, if the basics are covered
in storage silo selection, years of trouble free containment and
reliable discharge can be expected. In today’s industrial market, a
storage specialist should advise or confirm your selection. In all
cases, a reliable integrated storage system starts with a properly
designed and configured silo. Guesswork has been removed from the
equation.
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