|
 Main subject - mar/apr 2007
Seed Processing Units
Leopoldo Baudet
lmbaudet@ufpel.edu.br
Francisco A. Villela
francisco.villela@ufpel.edu.br
In a box fight the winner of the golden belt will be the best fit and that also performs best. In seed production, the lots that had the best physical training or preparation will certainly be holding the trophy for quality, since they will fall within the standards set to consider them as seeds that can be traded and will satisfy the farmer's demands.
The quality of a seed lot is set after it has been processed, since it has undergone all the stages required for seeds to be ready for planting. Seed lots processing takes place at the Seed Processing Unit or SPU.
The SPU starts to show its importance right after harvesting, and its planning should follow adequate norms and procedures that ensure that the seed producer will get the product at the right time, in the right quantity and with the desired quality. Many times the SPU is chosen by the seed producers as a venue for business, so that he invites buyers to come and visit, turning the SPU into the showcase of the seed company. Thus, the SPU should be the pride of the seed producer, reflecting the investment undertaken and should always stay clean, functional, efficient, safe and economically feasible.
To plan the setting of a SPU it is necessary to have preliminary basic information that will help the process, such as assessment of the unit's site (transportation, workforce, climate, electricity), conditions for processing (species, cultivars, planting dates and harvest dates) and conditions for storage (type and period of storage, packing).
Seed harvest and drying
As a rule of thumb, harvest should take place as close as possible to the stage of physiological maturity of seeds, and when the degree of seed moisture (regarding mechanic shedding) and the local weather conditions are appropriate. It is a normal condition that seeds which have been recently harvested show high moisture content, which is incompatible with its handling and storage, thus, they need to be artificially dried. This fact should be interpreted as a real risk for seeds that remain on the field, which deteriorate if drying is delayed for more than 24 hours.
In the state of Rio Grande do Sul-Brazil , a minimum of 60% of the soybean seed harvest is artificially dried; seeds are harvested with approximately 18% moisture. In the state of Mato Grosso-Brazil, where the rainy season coincides with the harvest of soybean, 100% of seeds undergo drying. In regions with a dryer climate, where harvest dates occur in days with dry weather and low air humidity, the need to dry seeds is extremely low since they are harvested with low moisture content.
The planning of the SPU should consider, when drying, not only the type of dryer to acquire but the best suitable drying system. The drying system comprises the reception hoppers, elevators, a pre-cleaning machine, bucket elevators, moist product storage bins, elevator, dryer, dry product storage bins or flux regulators as well as a heating system composed by an oven, gas heater, electric resistance, etc.
The ideal drying capacity of a SPU should be that capable of dealing with the day's harvest, exception made when there are moist product storage bins or silos that have ventilation devices.
The heaters that are recommended for seeds are those intermittent (or continuous dryers adapted to the intermittent mode), which are capable of drying up to four seed batches per day, entering the system with 18% moisture and exiting with 13% moisture.
Care in the selection of the drying system is warranted through its role in the process: efficient dryers are good allies to seed producers since they provide standard and uniform drying conditions which will efficiently remove water from the seed (from 0.8 to 1.5 percentage points per hour, if the are intermittent dryers), without reducing their physiological quality; however, care should be exercised in that temperature of the seed mass doesn't exceed 40°C.
Stationary dryers with perforated floors or perforated central tubes show a lower drying capacity per day, being able to remove 0,3 to 0,5 percentage points of moisture per hour. They can be used as storage bins if there's no movement of seeds during the process, thus minimizing possible mechanical damage.
An example of aspects concerned with the planning of a SPU follows: A company wishes to produce 2,000 tons of soybean seeds (50,000/40kg-bags), for which it will have to crop a minimum of 900ha. This area takes into consideration a minimum loss of 50% (25% field losses and 25% discarded material during cleaning and drying), harvest takes between 30 to 45 days to collect 2,500 t (e.g. 900ha x 2.8t.ha-1), all of which determines that reception at the SPU will last for approximately 40 days at a rate of 62.5 t per day, so that the same volume should be dried on a daily basis.
An intermittent dryer, with a static capacity of 8 t and able to dry three batches per day, will dry 24t every 24h so that to cope with the 63t.day-1 reaching the SPU, a total of three drying bins with 8t of static capacity need to be considered.
Should the seed producer choose a stationary dryer system, six wooden drying bins with radial distribution of air and 8 t capacity would yield a total drying capacity of 72 t per day, when considering 1,5 batches per dryer per day.
The same scheme can be applied for a company that plans to manage a larger volume of seeds.
Seed cleaning
When considering seed processing, the different physical features among the seeds and the undesirable components of the lot are the main factors to choose the machinery that will separate them. For the vast majority of the seed lots, more than one type of machine is necessary to ensure that the quality standard for the seed lot is met.
The planning of a SPU involves many factors to warrant success, so that seed be received, pre-cleaned, dried, cleaned and graded, treated, bagged, stored and distributed.
The equipment needed for transport, drying, cleaning and grading should be distributed in such a way that seed be processed in a continuum, from reception to the loading site from where it will exit the SPU for distribution. The sequence should be flexible enough so that any unnecessary equipment for that specific seed batch can be easily avoided without interference on the flux or end quality of the batch.
page 2 ->> Seed Processing Units
|
|
............
|
