How To Determine Which Storage Silo Is Best For YouSeptember 20, 2018
Answer these questions to avoid surprises with your bulk storage
Let’s face it, selecting a silo for your storage needs isn’t like picking out a pair of socks. It’s a big decision. There are a lot of variables and plenty at stake, not the least of which is the safety of your colleagues and the success of your business. It can make the decision overwhelming. As a storage silo manufacturer, I’ve fielded every kind of question you can imagine. Whether it’s a request for simple additional storage or designing a silo suitable for storing unique materials – from coal dust to plastic additives – I’ve heard it all. And I always say the same thing: There is a solution for everyone.
The trick is to ask yourself a series of questions before you move forward. I will list them out here. These are all variables that need to be addressed before a silo can be bid, designed, built or shipped. But the process doesn’t have to be confusing. In fact, it can be rewarding. Just take it one question at a time.
What Will You Be Storing?
Create a list of your application’s specific requirements before you engage a silo vendor. Tell your vendor the characteristics of the material you’re storing, including particle size (such as fine powder or granular), abrasiveness, and density. Think about how you intend to feed and discharge material from the silo. This will help determine the most cost-effective option. And consider whether your material’s composition is such that your silo will require flow-aid devices such as bin activators, vibrators, aeration, or mechanical agitation. Also consider how much of this material you’ll need to meet your supply chain needs. No matter what chemicals you are storing, your silo will likely require components such as dust collector flanges, manways, nozzles, flow control, stairways, and peripheral conveyor supports. Familiarize yourself with these terms in advance. For specific information on structural steel construction, you might review such reference books as Structural Engineering Handbook and Manual Of Street Construction.
Understand that most silos are pneumatically fed, some are gravity fed, and others have mechanical feeding systems. The feed and discharge systems are separate entities from the silo weldment and vary from customer to customer depending on what they are storing, what they are used to using, and how they want (or need) to handle the product. This part of the system is the responsibility of the company doing the material handling on behalf of the end customer.
How Much Construction Time Is Required?
The construction of the silo can and should be a straightforward process. You want to avoid last-minute changes. Changes can happen for a number of reasons and be costly. Common changes include a sudden requirement to add capacity, which could involve a height change, diameter change or even additional silos. If the design of the handling system is changed, it can affect the silo design. This can include changes to silo connections, discharge clearances and overall dimensions. Changes in product bulk density can also have a significant impact. I’ve seen a 40 pounds per cubic feet (PCF) design go to a 45 PCF design, which on a 5,000 CF silo amounts to an added dead load of 25,000 pounds.
Give careful thought to your timeline and budget and expectations at the planning stage. You don’t want to rush anything. Build in plenty of time to adjust for conditions. Your timeline will be influenced by the type of site you are building on. A greenfield site is new construction; a brownfield site is adding to an existing facility. When installing a silo next to existing equipment on a brownfield site, you can’t afford down time. Make sure you talk to your site contractor about all the variables, from using a crane to setting up scaffolding. Do as much up-front planning as possible to ensure your construction runs smoothly and on time.
To give you a sense of the duration of a project, give three or four weeks for an engineering timeline, during which you consider and approve drawings, and eight to 10 weeks for fabrication following the customer’s final project approval. Of course, lead times go up and down according to the size and complexity of a project. But that should give you a good sense.
How Would You Like Your Silo To Look?
Paint systems can range from no coating at all to sophisticated multi-coat paint systems. Some coatings require inspection in order to satisfy federal, state, and city regulations. With such a wide variety of paints, your vendor needs to be a specialist in the field who can guide you through the decision-making. It’s not just a matter of picking blue because you like blue. The paint coatings not only provide your appearance to the public but serve as protection from corrosion and other damage. Make it a decision that will work for you on aesthetic and pragmatic levels. And understand that coatings are essential. They provide corrosion and abrasion resistance. The higher quality means more protection during the life of the silo. Take into account the impact weather will have on it. Rain can cause inadequate coatings to delaminate from the surface. The heat and cold cycles can cause the metal to expand and contract, which could cause the coatings to separate. The pounding from the sun’s ultraviolet rays can accelerate coating deterioration and chalking. Consider all these factors. The right coating can make all the difference. The good news is a quality vendor will be experienced in planning for all these scenarios.
The most common coatings tend to be epoxy primer with polyurethane topcoats. Custom coatings, which are usually customer specified, can range from primer only to high-end zinc prime/epoxy mid-coat/polyurethane topcoat. Custom color match is usually available and coating life usually can last up to 20 years with proper maintenance.
Where Will the Silo Be Located?
It’s the old real estate maxim: location, location, location. Consider the size of the area where the silo will be located. This will help determine the silo type and construction method. Then ask yourself how the silo will get there. Make sure your vendor is capable of transporting and installing the silo in the area. Ask detailed questions about the logistics of the transport. Inquire about specialized trailers, which allow for maneuverability and can be lowered or raised in the air depending on site circumstances. Silos generally can be manufactured up to 16 feet in diameter and shipped in one piece up to 90 feet long with a 90,000 pound weight. Construction, size and weight are defined by the structural requirements more so than the size requirements.
In geographic terms, the location of your silo can be affected by local building codes and other safety regulations that apply to the project. This affects the design, construction and installation of your silo and needs to be considered upfront. Some locations may require a permit, too. Vendors follow the current IBC standard building codes for the specific job site location in question. There are no specific design codes for dry bulk silos so a combination of API, ASME and AWWI are used at certain times to calculate allowable stresses and other design factors.
How Will The Silo Be Maintained?
You need to consider what you’ll need to do to maintain high performance at minimal cost throughout the life of the silo. Make sure your silo has easy access to internal components for routine maintenance. Periodic inspection by customer maintenance people is required to keep up with paint touch-up and other minor issues. As your silo ages, look to your manufacturer to provide inspection services to ensure its safe and lasting operation. Eventually, many years down the road, these inspections can help you assess whether to repair or replace your silo.
There are more things that go into the decision, such as the customer’s budget for the storage part of the system, the customer’s expectations to have the new system in place before needing additional storage or material handling equipment, and what the customer’s needs will be five years from now, but these are the biggies.
If you get through these questions you will put yourself in a great position to have a storage silo that is quality-built and pleasing to the eye, which will serve your company effectively for many years.
Tom Nomady is General Sales Manager at Imperial Industries Inc. in Wausau, WI. He has a bachelor’s degree in industrial engineering/product development and additional training in welding and painting. He has worked for a worldwide food company, specializing in custom machine design and facilities planning, and a large sanitary stainless company as a sales engineer for custom-designed and fabricated food processing equipment. He has been with Imperial Industries since 1993.
The full version of this article can be seen in the August 2018 issue of Chemical Engineering.