Buying a new silo - faults and design features to look for

Author: Philip Burrill | Date: 18 Jul 2017

Department of Agriculture and Fisheries, Qld

Take home messages

  1. Grain silos have a typical working life of 25 – 30 years plus. It is worth investing time to consider the type of silo and its features so it is an asset to the business, not a liability.
  2. Have a mix of silo sizes / capacities that allow for grain quality segregations when required
  3. Ensure the new silo meets the sealable standard AS2628 so fumigations are effective
  4. Silos should be easy to clean – hygiene, fitted with aeration cooling and sealable when fumigation is required
  5. A safe ladder and work area at the top of the silo is required for both grain inspections and maintenance to rubber seals on lids and vents

Fumigation

A good starting point is to look for a manufacturer that can guarantee their silos will meet the Australian Standard AS2628. The GRDC extension team, researchers and industry has worked for many years to establish this silo sealing standard. It aims to enable growers to quickly and confidently identify new silos that are designed and built to a quality standard to ensure effective fumigations are achieved when required.

This is absolutely crucial, as it allows growers to store grain for long periods, confident that when storage pests are detected, grain can be effectively fumigated.  Australia now only has fumigant (gas) products for controlling live insect pests in stored grain.

When fumigation products like phosphine, sulfuryl fluoride (Profume®), or controlled atmospheres, such as carbon dioxide and nitrogen are used to kill pests, the storage being treated must be able to hold a given concentration of the product in the gas phase for a specified length of time (C X T).  In unsealed structures the fumigation gas is lost rapidly, resulting in poor pest control.

What to look for:

  • The silo was originally ‘designed’ and built as a sealable silo;
  • Good quality structural strength in the silo’s steel frame and sheeting to ensure it can still be made gas-tight for fumigations, after years of use, with only minor maintenance;
  • Good quality rubber is used on seals around all silo openings;
  • A system that will apply firm, even pressure right around the rubber seals on openings;
  • Design & location of silo roof vents for aeration are easy to seal effectively and maintain;
  • The bottom silo outlet will seal properly against the weight of grain when silo is full;
  • Bottom outlet can be ‘resealed’ gas-tight after some grain has been out-loaded;
  • Fumigation recirculation plumbing is fitted to larger silo > 150 tonnes capacity; and
  • Good quality pressure relief valve, UV light resistant, large capacity.

Aeration

Aeration cooling of grain in storage is one of the most valuable, non-chemical tools we have in Australia for reducing pest problems and maintaining grain quality attributes.

While the low air flows (2 to 4 L/s/t) for aeration cooling won’t reduce grain moisture significantly, it will provide uniform moisture conditions throughout the silo, prevent moisture migration and lower grain temperatures.

The cool, uniform grain conditions that are achieved with effective aeration, slow or stop the insect pest life cycle, reduce mould growth and maintain grain quality. Aeration fans can also be used for ventilation after fumigation, thereby reducing the required ventilation periods to meet residue standards.

Prior to buying silos, it can be helpful to seek independent advice on the appropriate aeration fan size, fan type and the auto controller used to run fans. Not all silo manufacturers or silo suppliers have staff trained in the area of aeration equipment.

What to look for with aeration:

  • Fan size & specifications  - advice on fans suited the size of silo and grain types you will store;
  • Aeration ducting - suited to grain types stored and ease of cleaning when silo is empty;
  • Roof vents or ‘Chinaman’ hat vents – correct design with no back-pressure on fans and easy to access to undertake maintenance; and
  • Automatic aeration fan controller - good quality unit with reliable service back up if required.

Hygiene

Look for a silo that is easy to clean when it is empty. Look at the internal design, such walls, aeration ducting and perforated flooring.   Is it going to trap grain residues in areas that are hard to clean? Insect pests will live and breed in residues left in silos. This allows newly harvested, clean grain to be rapidly infested.

What to look for with hygiene:

  • Silo internal walls that do not hold grain residues;
  • Aeration ducting – that is easy to clean when silo is empty;
  • Full floor, perforated flooring in base of flat bottom silos – if possible, avoid this design. With Australian conditions insects will live under flooring in grain residues that build up over time; and
  • Silo base structural design –  silo base that does not pool water under silo if washing out.

Ease of filling and out-loading grain

How easy will it be to fill or outload from your silos?  The overall storage facility site layout for truck movement, plus matching auger reach heights to silos are the more obvious considerations.

In some cases requesting an additional 20 to 30 cm in the silo base leg height to raise the outlet, can assist with moving auger hoppers into place, or allow for a conveyor belt under a row of silos in the future.

For the silo top fill point, the top lid rotation position and design needs to be considered to ensure augers can be moved into position without damaging lids, roof ladder rails or vents.

What to look for with filling and out-loading:

  • Height of silo base outlet suits your equipment and future out-load requirements;
  • Top fill point design provides easy auger access and low risk of damage to top lid; and
  • Any ground operated top lid opening / closing system is well designed for simple operation.

Selecting the mix of silo sizes & types

Spend time considering your long term future needs of grain types grown and the quality segregation requirements for these grains. Should you purchase four large capacity flat bottom silos, or buy two large capacity silos and a number of medium size cone based silos?

Growers are well aware of the importance of testing for various grain quality attributes at harvest time including the usual - grain moisture content, protein, screening, weather damage grain etc.  A mix of storage sizes can allow for grain segregations to achieve optimum dollar return for various grain markets.  It may also provide the option to blend where appropriate.

Summary

There are many benefits to on-farm grain storage, but buying a cheap, poorly designed, inferior silo is going to cause more problems than it is worth over the long term.

Storing grain on farm gives you marketing flexibility and benefits with harvest time logistics, but it only works if every effort is made to ensure grain quality in storage is maintained. The first step is to investing in a quality silo that is an asset to your business.

Further reading

Acknowledgements

The author wishes to acknowledge the significant contributions of Grain growers partnership in on-farm research, silo manufactures, storage equipment suppliers and DAF Qld’s Postharvest research team. The author would also like to thank GRDC, and GRDC’s national grain storage extension team for their continued support.

Contact details

Philip Burrill
Department of Agriculture & Fisheries, AgriScience Qld.
Hermitage research facility, 604 Yangan Rd, Warwick Qld. 4370
Phone: 0427 696 500   or  1800 WEEVIL
Email: philip.burrill@daf.qld.gov.au

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