ABSTRACT

In Argentina, an important grain producer in the world ranking, canola (rapeseed) has been successful in recent years. This culture represents a new choice of early harvest that is included in the rotation plan of winter crops. The early agricultural-practice requires employing methods to appoint the grains to good conditions for the safe storage in order to reduce loss of quality. The fresh grains of canola must be dried before and during store. To realize a process of this characteristics can be more expensive for small farmers due to important need of infrastructure and high operative costs of hot dry.

As reply to this problem, in this work is presented the study of drying in-bin of canola (rapeseed) with near-ambient air. This process offers profits compared with conventional hot drying since it requires low cost of infrastructure and causes the minimum effects on the final quality of grains. The variables of process are studied to know the characteristics of drying and seed deterioration. Simulation models are applied to estimate the times of drying and in-bin cooling. During the drying/cooling process it was observed that: a) grain and bed density increase, while bed porosity decreases following an approximately linear variation in time; b) bed height decreases in time, mainly during the first 27 hours of drying; c) equivalent diameter of grain practically was not experience changes, showing scarcely a linear decreasing tends in time (neither it was observed damages on grain surface); d) was not observed appreciable changes on the quality parameters refraction index, performance of oil extraction, acidity index and germination power; e) the drying time can be predicted through the programmable simulator designed to drying in-bin of shelled corn and other grains (Agric. Engng. Information Series, 1980) with an error lesser than 2.2%; f) the in-bin cooling time for canola (17 hours) was comparable with data of literature extrapolated from Christensen model (1982), which predicts 14 hours for cooling time.

INTRODUCTION

In Argentina, canola culture has been successful in recent years and it is included between the rotation plan of winter crops as new choice of early harvest. Canola grains are frequently reaped fresh and the wet seeds must be then dried. If not, when grains are harvested with high moisture content, greater losses of quality during storage can occur due to growth of molds, insect infestation and increasing of free fatty acid level. Then, drying processes are applied to reduce the deterioration risk. The present trend is to employ in-bin drying with unheated or near-ambient air, because this technique is an adequate non-aggressive method to preserve the technological properties of the grains resembling the initial stage. On the other hand, this procedure results very accessible to small farmers due to the minimum capital cost that involves compared with conventional hot drying.

From literature, many studies of drying of grains with near-ambient air realized in different zones of Canada, Europe and USA, have been reported (Bloome and Shove, 1971; Fraser and Muir, 1981; Jayas et al., 1988; Kanujoso et al., 1995; Lang et al., 1993; Lasseran and Fleurat–Lessard, 1990; Muir and Sinha, 1986; Muir et al., 1991; Sanderson et al., 1988; Sanderson et al., 1998; Sanderson et al., 1989; Sokhansanj et al., 1986; Morey and Cloud, 1998). However, is not available information about this topic in other countries. As reply to this problem, this work presents the study of drying in-bin of canola (rapeseed) with near-ambient air with the objective of develop tentative guidelines to conduce this process in the most important agricultural area of Argentina. The variables of process are studied to know the characteristics of drying and seed deterioration. Simulation models are applied to estimate the times of drying and in-bin cooling.

MATERIALS AND METHODS

Experimental equipment

The equipment employed was designed for previous studies (Pagano and Crozza, 1999; Pagano et al., 1995, 1996, 1998, 1999) and is showed schematically in Fig. 1. The main components are:

• Metallic column of grain storage (1.20 m height, 0.36 m diameter, with perforated floor, airflow straightener inside the chamber, 4 rings of pressure taps 0.3048 m apart)
• Systems of heating and supply of air (electric resistor, centrifugal fan, duct, chamber)
• Instruments for airflow and pressure-drop measure (orifice plate, analogical meters of differential pressure, thermometers)
• Hardware and software for monitoring and data-acquisition of grain/air temperature.

Figure: Schematic of the experimental equipment.

Sample preparation

A sample of about 59.150 kg of clean canola (rapeseed) with 11% moisture content (d.b.), 3.96% foreign material and 94% of germination power, obtained from a local plant of grain conditioning was used.

Design of the experience

The full time of the continuous process (128 hours) was divided in different steps: one of them (the first) was to drying operation and other corresponded for in-bin cooling. An airflow rate of 0.2 m³/s-m² was selected and kept constant. The monitoring of the drying/cooling process was realized by the following of:

• Physical variables: temperature of grains at 0.3048, 0.6096, and 0.9144 m bed depth, moisture content of grains at 0.9144 m bed depth, temperature and relative humidity of air at the duct, chamber, and outlet of the silo, grain and bulk densities, bed porosity, bed depth and bed level decline, equivalent diameter of grains.
• Chemical variables: moisture content, refraction index, performance of oil extraction, acidity index.
• Biological variables: power of germination.

Moisture content, refraction index and oil extraction

During the process, the moisture content was determined by triplicate using a sample of about 10 g in a air oven during 3 hours at 130°C (AOCS, 1997). The samples were extracted with an auger sampler from the top of the silo.

The refraction index was measured at time zero and at the end of the process using an ABBE refractometer at 26.5-26.8°C (related to water refraction index = 1.333). Too, for these two samples, the oil extraction was realized with solvent in a Butt equip.

RESULTS AND DISCUSSION

From the obtained results it can be drawn that:

• Grain and bulk densities increase (Fig. 3).
• Bed porosity decreases following an approximately linear variation in time (Fig. 4).
• Bed depth decreases (Fig. 5) and bed level decline increases (Fig. 6) in time, mainly during the first 27 hours of drying.
• Equivalent diameter of grain practically was not experience changes (Fig. 7), showing scarcely a linear decreasing tends in time (neither it was observed damages on grain surface).
• It was not observed appreciable changes neither on the chemical and biological parameters of quality (Table 1).

Table 1: Chemical and biological variables.

Time of process, t (hours)	Moisture Content, X (% d.b.)	Refraction Index, IR	Performance of oil extraction, η (%)	Acidity index, IA	Power of germination, PG (%)
0	11.07	1.4710	43.06	5.50	94
128	6.47	1.4708	42.46	5.19	94

Simulation models were applied to estimate the times of drying and in-bin cooling of canola.

For the prediction of drying time, a programmable simulator designed to drying in-bin of shelled corn and other grains (Agric. Engng. Information Series, 1980) was used. The obtained result was 38.2 hours for the drying time. The measured time for dry the grain from 11.07 to 6.07% moisture content (d.b.) was 39 hours, then it can be observed that the mentioned program can be predict the drying time for canola with an error lesser than 2.2%.

For the prediction of cooling time, an extrapolation of Christensen model (1982) for a airflow rate of 0.2 m³/s-m² was applied, and the estimated time result of 14 hours, comparable value with the experimental cooling time wich was 17 hours.

Figure 1: Moisture content.

Figure 2: Bulk and grain densities.

Figure 3: Bed porosity.

Figure 4: Bed depth.

Figure 5: Bed level decline.

Figure 6: Equivalent diameter.

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