Of all techniques practised by mankind, drying is most likely the oldest method. The growth and reproduction of microorganisms which cause decay and deterioration reactions can be prevented by removal of moisture during drying. The process of drying leads to a reduction in weight and volume which means a reduction in packing, storage and transportation costs. This also allows the product to be stored easily under ambient temperatures. The most important purpose of a drier is to provide heated air beyond room temperature and in doing so it evaporates moisture in maize. As the heated air passes through maize, it carries moisture with it causing its humidity to rise as it passes through the grain. The most important variables in drying are temperature, the velocity of the air stream and humidity.
The use of solar dryers is best in areas where there is abundant solar energy. Of all the cereal crops grown in Zimbabwe, maize or corn is one of the most important. The hardships of transportation and rate of deterioration become less as the moisture content in maize lessens. The majority of Zimbabwean communal farmers lose a lot of grain during post-harvest and storage. Maize that is harvested with high moisture is most likely to deteriorate faster due to fungi infestation and rot. Most farmers resort to drying their produce by spreading their maize using natural unforced air flow on wooden platforms and infield. The natural drying of maize is ineffective due to drying rate, hygiene and quality of drying. This causes the need for better drying techniques that provide clean, quality, storage conditions to ensure the safe storage of grain throughout the season. 1.1 Background Maize is a cereal food crop used for food by both human being and animals.
During harvest, maize mostly has a high moisture content of about 20%-25% which is a good environment for the growth of fungi and insects that usually cause maize damage. In order to avoid this, drying of maize must be done to reduce the moisture content to about 11.8%-13% for safe year-round storage. Most communal farmers in Zimbabwe harvest their maize in April and store them in wooden platforms to dry. Some farmers prefer to leave maize in the fields to dry and harvest their maize in May. These two methods of drying take long to dry and affect the quality of maize. Issues of farmers being turned down to deliver their maize to Grain Marketing Board (GMB) are now the rise. GMB only accepts maize with a maximum of 12.5% moisture content. Most communal farmers are forced to sun-dry their maize at the GMB gates as they won’t be having reliable transport (mostly scot-cart) to ferry their maize back home to dry.
This has been observed to reduce the profits of communal farmers as the maize is also stolen at the GMB gates. The rate of dependency on weather has greatly affected the present maize drying process in Zimbabwe. At times rain and humid air cause the deterioration of the maize which compromises the grade of maize. Harvesting losses too have been observed to be a problem by the present maize drying process in communal lands as windy conditions blew away maize from the sun drying platforms. 1.2 Problem Statement The current natural maize drying methods are tedious, time-wasting, and wastage, in terms of production and consequently have a very low hygienic level. Technological methods which have been developed over the years use electricity which is not readily available in most Zimbabwean communal lands.
Moreover, electricity consumption is not economic when there can an alternative renewable energy source like solar energy to harness. The need to save time, reduce labour, improve quality of dried maize with the better hygienic method as well as the use of renewable solar energy has resulted in the idea of having a solar maize dryer. A parameter control system is also needed to automatically control the response of the maize dryer when unfavourable conditions are present like humid air and low-temperature air flow. 1.3 Aim The aim of the project is to design and simulate a small-scale solar maize dryer with automated dryer control for use in rural communities where electricity and other sources of power are not available. 1.4 Objectives i. To design a solar collector that absorbs solar radiation for heating air to the recommended maize drying limit. ii. To design a drying chamber with maize agitating system to homogenously mix grain.
To design the maize transfer and air ducting systems. iv. To design and automate optimum design parameters for a small-scale maize dryer v. To fabricate a prototype of a small-scale solar maize dryer. 1.5 Scope The project is confined to the drying of maize using solar energy as well as the parameter control aspect of the dryer. The two main components of this project are a heating solar energy collector and a heating chamber. The solar energy will be harvested by means of air-heating solar energy collector which consists of a cover plate, absorber plate, an insulator. Temperature and humidity control systems will be designed as well for the best performance of the dryer. This project will design maize handling and air ducting systems. 1.6 Justification The tonnage of maize losses due to poor drying are growing high and high every day. Zimbabwe is facing a rapid maize production growth. The need for artificial maize drying systems is rising day by day.
The need also to use renewable energy source for drying is also environmentally friendly as compared to using rarely accessible electricity. The automated solar dryer will solve all these rising problems and also possess several other advantages. The advantages of this solar dryer include an increase in quality of harvested grain by reducing crop exposure to weather, reduces harvesting losses, including head, shattering and cracked kernel, reduces dependency on weather conditions for harvest, allows use of straight combining for small grains, reduces size and/or number of combines and other harvest-related equipment and labour required due to extending harvest time and allows more time for post-harvest field work.
