Build my Feedmill: Grain drying
by John Bowes, International Sales Director, Sukup Manufacturing Co
On March 13th at VIV Asia in Bangkok, Milling and Grain, in conjunction with VIV Asia, held the Build my Feedmill Conference for feed industry professionals, academics and businesspersons to discover more about the inner workings of a feed mill.
For two-hours, our 12 speakers gave presentations about their own unique products that assist with the inner workings of the feed mill, and carried us through the entire milling process, from intake and conveying to weighing, grinding, pelleting, drying and cooling, through to automation.
This article is the second in the series that will allow our readers to discover more about the inner workings of a feed mill, directly from our Build my Feedmill Conference speakers.
Crops store best if they are cool, dry, and clean. Mould growth is dependent on both temperature and crop moisture content. Crops that contain considerable foreign material or broken kernels will be more susceptible to mould and insects, so it is important that crops are cleaned to reduce this hazard or dried to between one andtwo percent lower moisture content than clean crops.
All stored grain needs to be checked on a regular basis. Check stored grain bi-weekly during critical fall and spring months when outside air temperatures are changing rapidly. Check at least once a month during winter, but more often if there are problems.
Search for small changes that are indicators of potential problems, such as crusting or condensation on your bin roof. It may also be necessary to check the moisture of grain with a moisture meter. Any increase in temperature indicates a problem, unless outdoor temperatures are warmer than the crop.
Check and record temperatures at several points in your grain bin. Testing the weight of your crops is another evaluation to ensure it is at its best quality and in peak condition.
Filling and coring the bin
Best storage results are obtained when cropsare level in the bin (See Figure One). Lowering the centre core of stored crops improve airflow and make checking the crop easier. Levelling can be done with a grain spreader or by withdrawing grain from the centre after filling.
In most bins, normal grain discharge flow creates a centre core that flows directly down to the unload conveyor or unload spout. This creates an inverted cone in the surface grain that gradually increases in diameter. As unload continues, grain funnels down the centre core and to the conveyor or unload spout.
A bin filled to the peak will not have uniform airflow. Peaked grain is hard to manage and is especially risky when grain is stored above its safe moisture content. Part of the peak in all bins should be removed by coring the bin. It is important to core bins filled with moist grain, especially if the bin does not have a powered grain spreader that levels the surface and spreads fines and trash.
Coring bin will remove the majority of fines and foreign material because most fines tend to accumulate in centre of bin. This is important since fines are more susceptible to spoilage and will restrict airflow. This practice obviously improves airflow through grain, which reduces chance of spoilage and helps aeration fans work more efficiently.
Crops are normally placed in storage at temperatures much warmer than winter temperatures. Since crops are good insulators, grain in the centre of the bin will be the same temperature as at harvest, even after outside temperatures have dropped well below freezing. This temperature differential causes moisture migration.
Air near bin wall cools and sinks to bottom of bin, pushing air up in the centre. When grain near the surface cools the warm air, moisture in the air condenses. Cool air cannot hold as much moisture as warm air. As this circulation continues, moisture begins to accumulate near top centre of the bin.
Crusting is an indication of moisture accumulation and mould growth. An aeration system cools grain uniformly, limiting moisture migration. In spring and summer months when outside air gets warmer, moisture migration can occur the opposite way and moisture will accumulate at bottom of bin.
Sukup Manufacturing recommends the following items for proper grain storage:
- Transitions can cause pressure loss and air loss if improperly installed. The outlet area of transition must be adequate for airflow produced by fans. The shape should provide a smooth airflow route without any abrupt direction changes. If any bin stiffeners need to be cut to install transitions, suitable alternative support must be provided to prevent bin wall collapse. Transition must be properly sealed at both ends to prevent air loss
- Temperature sensors accurately trace progress of aeration cooling or heating cycles. They help identify hot spots in grain. They also indicate overall heating and approximate average grain temperature. Check with your bin manufacturer to be sure cables, supports, and the roof can withstand the drag from grain filling and unloading. Breakaway anchors should be used at bottom of the cables to assure alignment but allow for a sweep auger. Cables suspended from the roof should be properly supported and secured to floor by a professional. Absolutely no weights or plates should be attached to the bottom of temperature cables
- Temperatures may change only 0.5°-1 °C per week, so read and record them accurately. A continual increase in temperature is a warning that must be heeded, especially if one spot in the bin is heating faster than grain as a whole. Experience indicates that once heating starts, it continues to escalate at an increasing rate until cooling is applied
- Cleaning grain before storing improves storage. Fines, foreign material and broken kernels are grain-handling problems. Kernels break during harvesting and handling. Select a grain cleaner that collects and conveys screenings away. The most common locations are at receiving, after dryer just before delivery to storage, and at load-out. Cleaning is easier at low flow rates. Coring bin also will remove a major portion of fines and foreign material
- Roof vents ensure proper airflow and prevent snow or rain from entering the bin. Roof vents also increase efficiency of aeration system and should always be used in drying. Without adequate open area to let air and moisture out of bin, the aeration or drying system will not work sufficiently. There should be a 1ft2 (.093 m2) opening for every 1500 CFM (2550 m3/hr) the fan will produce. Have at least a 11⁄2' (38.1 mm) eave opening. Keep centre cap and manhole open during cooling and drying but closed during storage. Also, roof vents need to be cleaned of dust and debris after each season in order to prevent roof damage
- Grain Spreaders are available for bins up to 60' in diameter and provide a more level grain surface in the bin. Peaked grain results in increased airflow resistance in the peak portion of the bin. Furthermore, fines and foreign material in grain tend to gather in the centre of bins. These fines result in increased airflow resistance. Properly adjusted and operated grain spreaders will leave top surface of grain level, with fines and foreign material more evenly distributed throughout grain mass. The level surface and more evenly distributed fine material results in uniform airflow resistance throughout the entire bin.