Grain & Seed Cleaning Solutions

Processing of seeds is a maer of experience and in-depth knowledge of various products and parcular processes ideally suited to the specific processing task. Gentle handling, strict and genuine separaon of different lots, as well as highly accurate final purity and uniformity, are the main supporng pillars of seed cleaning.

All over the world, the seed industry is moving towards an increased level of industrial producon with high capacity plants for cleaning and grading the seed. This development increases the demand for high capacity, high quality and cost-effecve seed www.africaagricultureinsight.com processing soluons.

With modern high-quality harvesters, grain is oen received fairly well cleaned if the sengs were correct and if capacity was not pushed to the limit and if grain was dry and if there were not too many dirty patches and if no heat damage took place and if conveyors did not damage the kernels etc.

Lots of Ifs. So, if in doubt, therefore, it is recommended that fines and broken kernels in the case of maize especially, at least be removed prior to storage.

Pre-Cleaning grain prior to intake into a silo system is one of the most important ways in which to add value to the crop and to assist in the process to secure a long life for the grain during storage.

Keep in mind, the grain quality will start to deteriorate immediately once it has been harvested. The deterioraon process must be delayed as far as possible to ensure the end user sll has a quality product to work with.

Pockets of foreign material in silos, especially fines, which tend to group together during conveyance, can cause hot spots and will negavely affect aeraon. Those pockets would have a higher density than the rest of the grain and during aeraon, air would by-pass those dense pocket, causing it to retain more moisture, as moisture is captured there and not allowed to move away and out of the grain with the air that is forced through the grain.

The dockage furthermore takes up valuable storage space - even up to 5% or more may be taken up with a lowvalue product that can furthermore contain poisonous seeds that can be spread throughout the silo and can be cause for downgrading the product.

If a large parcel of grain is rejected by the buyer or the central co-op, the cost of cleaning and resubming the grain to the negave buyer can be well in excess of the cost of a good cleaner

Even if the grain is only cleaned before selling, the owner has control over the dockage and can use it as feed for livestock or sell the dockage while under his control but have no claim over the dockage once sold. He may just face deducons in the selling price.

Precleaning and final cleaning:

Pre-cleaning refers to grain that has undergone cleaning where either over or under or overs and unders have been removed from the grain to an acceptable level. This may be up to 97 or 98 or 99%, depending on sales terms. We would recommend pre-cleaning grain to as high a level as possible and usually to around 98 or 99%.

All cleaners are more effecve at lower capacies, so if a pre-cleaner benchmarked at 40 tons per hour top capacity is used at full capacity, it would inevitably have a lower cleaning efficiency than if ulized at 30 tons per hour. The operator has control over this and should find an opmal level at which to operate the system.

Final cleaning refers to the process which grain undergoes before it enters a processing facility such as a mill. Capacies are usually lower and are geared towards the capacity of the processing facility ie. a 5 ton per hour maize mill would usually work well with a 10 ton per hour final cleaning system but does not require 40 tons per hour final cleaning system which would simply not be cost effecve.

Final cleaning usually also includes an aspiraon system whereby dust not removed through grading alone, as well as light parcles, the same size as the grain kernel and therefore not removed through grading, is included.

What cleaner should be selected?

Other than own storage, the cleaning of grain represents the most logical step for the Grainman to add value to his product. Annual seasonal changes require different approaches to cleaning. In some years heavy rains may have caused a lot of roen and undersized kernels in the crop. This causes large tonnages to be downgraded and aer a thorough cleaning by the buyers, the grain is again blended into first grade. The mills are also baling to deal with grain received at farm gate that has not been thoroughly precleaned since it places too much stress on their own final cleaners causing bolenecks and poorly cleaned grain to enter the mill which can be disastrous.

Cleaning normally includes the following elements:

1. Grading for size: This is usually the least expensive equipment and can consist of the following main types of cleaners:

1. Rotary drum cleaners: It usually has a relavely large capacity between 20 and 60 tons per hour and should isolate over- as well as undersized parcles.

2. Vibraon cleaners: Usually smaller capacity final cleaners (5-15 tons per hour) but with a high-quality end product.

3. Eccentric cleaners: Smaller (2-8 ton per hour).

4. Oscillang cleaners with large capacies of 80 - 240 tons per hour per cleaner

5. Gravity cleaners: Only isolate throughs and cannot isolate overs as well. Large capacies of more than 200 tons per hour are achievable. (Do not confuse this with gravity cleaners that separate parcles on the basis of specific weight)

2. Aspiraon: This refers to a sucon process with a fan, cyclone, ducng and rotary valve and is used in combinaon with graders for size as the light foreign parcles of the same size as the kernel is isolated. This equipment is likewise not excessively priced.

3. De-stoners and grading according to the kernel's specific weight. Stones that passed through a size grader can be isolated here while roen kernels not light enough to be aspirated off can also be isolated. Wheat with falling number problems can, on good separators also be isolated. This is usually more expensive equipment.

4. Colour sorters can isolate speckled kernels or deviaons based on colour. These machines are normally used in high-value items such as seed material, coffee, beans, nuts etc. for human consumpon and are also used in packing plants and food processing plants. While the cost of these sorters has come down recently, entry-level machines would start at around R500,000 at 2-3 tons per hour. Lazer sorters form the new generaon.

5. Other special cleaning equipment includes sorters and other indented cylinders grading by the length of the kernel for instance as well as magnets (oen used in conjuncon with basic graders also), centrifugal cleaners etc.