|Production Know How
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Calculate the following data to characterize the performance of the dryer:
1. Average and standard deviation of the moisture content before and after drying.
2. Total weight loss of paddy
3. Drying rate (%/h)
4. Increase in broken grain (i.e. percentage of broken grains before drying minus percentage of broken grains after drying)
5. Increase in cracked grain (i.e. percentage of cracked grains before drying minus percentage of cracked grains after drying)
6. Electric power consumption/Fuel consumption
1.Paddy of a known source should be selected with grain moisture content that is typical for grain harvested in the area.
2. The paddy should be cleaned to remove very few impurities (straws, etc).
2. Before loading the materials, mix the paddy and take at least 10 samples of the paddy of 10g each to determine variance in moisture content.
3. In addition, sample of 500g of wet paddy is taken for laboratory analysis. If possible, take the entire weight of the paddy before loading.
4. Load the paddy and start the dryer. Measure the time taken to load the dryer and dry the paddy down to 14% moisture content.
5. If possible, measure power consumption with a watt meter and measure fuel consumption with a flow meter. Alternatively, fuel consumption can be estimated by taking the initial weight or volume of the fuel and the final fuel weight after drying is completed.
6. During the drying process, measure drying air temperature with a thermometer at different locations in the dryer. After drying is completed, take the weight of the entire batch of dried grain.
1. After purchase or instalment of a grain dryer it is important to evaluate its performance.
2. This is usually done by conducting a drying test.
3. Drying tests are important because actual performance data are often different from rated performance that is provided by the manufacturer.
1. A drying system can only maintain quality but it cannot improve the quality of paddy.
2. When a dryer produces poor quality paddy it is therefore important to compare the paddy from the dryer with a reference sample from the same batch that was dried under controlled conditions, e.g. in an air-conditioned room, or in the shade by spreading a thin layer and frequently mixing.
3. Otherwise it is difficult to tell whether the low quality is caused by quality reduction that occurred before drying, e.g. during field drying, or in the drying system.
Considering the issues in the last two sections the following recommendations for economic analyses of mechanical drying can be made:
1. Investing in a dryer for saving the crop.
2. The problem is that in this case the fixed cost component of the drying cost (depreciation) per batch is very high because the dryer is only used in emergency, meaning a few times a year.
3. A dryer used only in emergency cannot be used economically.
4. Realistic data should be used for the annual dryer utilization considering alternatives like the option to Sun dry during good weather.
5. The price difference for wet and dry paddy needs to be sufficient to compensate for: the cost of drying; for the weight loss that occurs during drying; and to provide some profit for the operation.
1. Case studies in Asian countries indicate that mechanical dryers with cost higher than 5% of the paddy value cannot be introduced successfully.
2. There is no point in listing cost numbers for different drying systems here since drying cost depends on many site specific factors and a “business plan” including a cost-benefit calculation is needed for each individual drying system considering the conditions of the locality.
3.Drying costs are composed of fixed cost consisting depreciation, cost of interest, repair cost, and opportunity cost, and variable costs mainly of fuel, labour, and electricity costs.
4. Depending on the purpose of the drying cost calculation, drying cost can either be stated as annual cost or as cost per unit of weight.
5. If the assessment is done to compare the dryer with other drying systems, e.g. with Sun drying, the cost per unit of weight is more appropriate, if the drying system is evaluated as part of the whole postharvest system annual cost figures might be more feasible.
6. In the following, the cost is referred to one metric ton of dried paddy.
Total drying costs are composed of two components, fixed cost and variable cost.
Total drying cost = Fixed cost + Variable cost
1.During the drying process water is removed from the grains .
2. That means that after drying, paddy weight is lost and the dried paddy is to be sold since in most markets paddy is traded on a weight basis.
3. In markets, where paddy is still traded on a volume basis there is a similar effect since paddy shrinks in volume during drying also.
Depending on the prevailing frame conditions and the postharvest system the use of mechanical dryers might provide the following economic benefits
Economic benefit Pre-condition constraints:
1. Increased market value of the (higher quality) paddy
2. Existing and significant price differentiation for different quality levels must compensate for drying cost plus weight reduction occurring during drying
3. Market access: Little differentiation of quality in the market. Little implementation of standards.
4. Quality markets still limited. a) Small batches of different varieties. b) Secured income from minimizing weather risk and c) Significant discount for spoilt or wet paddy, need to sell after harvest
5.Possibility of buying additional wet paddy. Discount would not cover drying cost Increased income from being able to process more grain in a given time
6.Limited working capital
1. The use of mechanical drying systems offers so many advantages over sun drying like maintenance of paddy quality, safe drying during rain and at night, increased capacity, easy control of drying parameters and the potential for saving on labour cost.
2. Reasons for failure of introduction of numerous drying systems have been attributed.
3. The constraints can be grouped under headers related to technology, know-how, post-production system, management and economics.
4. Technology can be developed for know-how and management related issues can be addressed through capacity building measures, and post harvest system related problems by choosing the right technology options.
5. However, with respect to economics of drying, faces a problem, which is unique for post-production operations, namely the availability of sun drying as a simple and very inexpensive alternative.
6. In most cases pure economics therefore become the limiting factor for the introduction of mechanical drying systems.
The requirements for quick drying immediately after harvest to moisture content that is safe for temporary storage, the two-stage drying system or combination drying system was developed.
1. A typical first stage dryer takes advantage of the fact that surface moisture can be removed rapidly from very wet paddy without causing any damage to the grains by using very high temperature for a short period of time.
2. Drying air temperature in first stage dryers can reach over 100ºC in fluidized bed dryers where the grain is exposed to the drying air only for a few minutes.
3. After this rapid pre-drying to a moisture content of 18%, the grain is considered safe for up to two weeks of storage.
4.The grain is then transferred to a storage bin with aeration facilities where it is slowly dried to the desired moisture content of 14% or lower with only slightly pre-heated air or even ambient air if the climatic
5. Although two-stage drying has many advantages. Two different drying principles well suited to the different drying phases of paddy grains at different moisture content ranges.
6. The introduction of two-stage drying in South East-Asia has so far failed.
7. This strategy is used only in Thailand by the commercial sector.