In the choice of the best dryer for your company you must consider not only the quantity of product you need to dry, but also how you want the water evaporation process to take place. In fact, the desiccant body is the most important part of the plant as it carries out the drying process and therefore the removal of moisture from the grain.
Depending on how the loading and unloading points of the desiccant body are structured, a distinction is made between continuous or discontinuous plants. In this article, Mecmar explains how a continuous flow grain dryer works and why it represents a valid choice for farms that need to dry large quantities of product without interruptions in production.
What is a continuous dryer?
In the family of grain dryers, the continuous flow dryer is a system in which the drying process of the grain proceeds uninterrupted. In fact, the green product is introduced from one end of the dryer and comes out dried and cooled at another end.
The possibility of continuous drying makes the product more popular in drying plants as it fully satisfies the need for production that is active around the clock. In addition, the high efficiency and low consumption are integrated with technologies designed to recover the heat and energy required by the product to be treated, both in terms of heat supplied by the same and in volumes of hot air that it requires for drying.
On the market, there are both horizontal continuous grain dryers and vertical continuous dryers.
Depending on how the grain moves inside the dryer, continuous dryers are divided into tower dryers, in which the grain descends vertically thanks to gravity; and belt dryers, in which the grain is arranged horizontally and mechanically stirred and pushed towards the discharge.
Vertical dryers can be tower dryers or cross-flow dryers:
- Tower dryers: they use gravity alone without diverting the flow of the grain: this is crossed by a flow of hot air which, passing through the grain, will transport the humidity to the outside.
- Cross-flow dryers: in this case the grain moves in a zig-zag manner but through a staggered series of horizontal channels through which the hot air passes. (fig.1)
Continuous vertical tower dryers
Thanks to the vertical structure, tower dryers are the most popular choice for companies that want a reliable product with reduced risks of mechanical problems with limited plant dimensions. In fact, by exploiting gravity alone, the only elements that move inside the machine are the extractor and the fan, two only mechanisms which, in addition to ensuring longevity and less maintenance, make the drying process homogeneous and delicate.
The hot blown air in the upper part of the dryer it reduces the humidity of the cereal, while in the lower part there is the cooling and discharge of the cereals ready for storage. Thanks to its characteristics, it is possible to choose the continuous flow dryer according to your drying needs.
Its configuration is similar to that of discontinuous flow dryers, but the continuous flow one has a divided pressure chamber: hot air is pushed into the upper chamber, while unheated air is pushed into the lower chamber for cooling the cereals (fig. 2). Unlike those with discontinuous flow, continuous flow dryers use high temperatures and air flow rates, vary in column width and dimensions, and have a sensor that controls the unloading speed and therefore the humidity of the dried grain.
A fundamental aspect that differentiates the column dryer from the horizontal one is its ability to exploit the humidity of the grain to regulate the rate of fall of the grain downwards: consequently the product will not be discharged until it has reached the degree desired drying.
Continuous vertical cross-flow dryers
In cross-flow dryers, the grains descend by gravity through a series of staggered lozenges that produce a zig-zag motion and continuous mixing of the grain. The geometry of the lozenges guarantees a uniform descent over the entire section of the column, to avoid the formation of preferential currents.
In the first drying area, the product is hit by hot air: in this way, each grain is deprived of most of the moisture it contains.
Otherwise, in the highest part of the dryer (called tempering trance) the product is not affected by any air flow (there are no lozenges, but only sheet metal boxes). In this area, the innermost moisture of the grain tends to move towards the outside, facilitating subsequent evaporation and improving the homogeneity of drying.
Finally, during the subsequent drying phase, the residual moisture is removed up to the final desired value.
Continuous horizontal belt dryers
Finally, we have the continuous horizontal belt dryers (fig.3): their operating principle is based on the volumetric distribution of the product over a mobile belt. The drying process carried out with these machines consists of a first forward phase, during which the drying begins, and a subsequent return phase, in which the drying phase ends. Before the product is unloaded, there is a final cooling phase of the grains. Vacuum cooling increases the drying energy efficiency by 25% to 30%, which is a significant advantage (especially in the cold northern territories).
Since 1999 Mecmar has been studying and manufacturing innovative tower drying systems that always respond to the new demands of its customers, both in terms of hourly production and maintenance and installation of the systems.
In Mecmar's tower dryers the drying process is divided into four distinct phases, which correspond to a single working configuration of the machine: loading, drying, cooling and unloading. For this reason, the Mecmar tower dryers are also characterized by the simplicity of transport and assembly, as in the case of the RT series in which the dryer can be delivered to the customer already assembled and ready for deployment.
If you too want a customized configuration for your company and an efficient and highly productive system, do not hesitate to contact us. The Mecmar team will be at your disposal to guide you in choosing the best continuous flow dryer for your needs.