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Drying

Drying
26
Aug

Reporting

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

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Drying test

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.  

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Evaluation of grain dryers

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. 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Troubleshooting

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.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/examples-ofdryers/troubleshooting
26
Aug

Conclusions for Economic Feasibility Studies

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.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Cost of drying

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.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Weight loss in drying

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. 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Potential Economic Benefits from Drying

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

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Economic aspects of drying

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.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Two stage drying

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. 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Centralized drying

1. Economics of scale in drying can often only be reached through centralized dryers in a strategic location where enough paddy can be collected to be dried in a machine with sufficient capacity. 

2. Centralized drying can be done by farmers’ cooperatives or small contract operators at village level, at local rice mills or at collection points in the trading system. 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

De-centralized On-farm drying

1.Ideally the paddy needs to be dried on farm level immediately after harvest, which is mostly done through sun-drying.

2. For the production of better quality rice and the prevention of the weather risk farm level dryers can offer solutions, if the following criteria are taken care of: 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Drying strategies

1.  Paddy should be dried as quickly as possible but other considerations regarding the rice postproduction system and economic criteria have to be taken into account when developing a drying strategy. 

2. Options include de-centralized on-farm drying, centralized drying at collection points and two-stage drying also referred to as combination drying.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Dust collection system

1. Grain handling will create dust, making 

working around a grain drying hazardous.

2.  Efficient dust collection systems should be installed around the dryer to remove dust in and around the dryer.  

3. The conventional system for dust collection of grain is the cyclone.  

4. As with other accessories, fan and cyclone need to be properly sized depending on the dryer specifications.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Conveyors and Elevators

1. Using conveyors and elevators for horizontal

and vertical transport of grains to load, circulate or discharge grains will improve the efficiency of the drying operation and reduce labour cost. 

2. Elevators should be properly sized so that they match the capacity of the dryer.

3. A properly designed bucket elevator for a re-circulating batch dryer can easily reach capacities of 10 t/h.

 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Moisture meter

1. Keeping track of grain moisture content during

drying is crucial to properly dry grain; that is, to avoid over drying or incomplete drying.

2. Over drying leads to monetary loss when selling the grain and reduced milling yields due to cracking of the brittle dry grains.

3. Incomplete drying causes qualitative and quantitative losses due to fungal growth, insect activity and respiration.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Paddy Pre-cleaner

1. Paddy Pre-cleaner: Fines in rice create dust

during the loading and drying process and reduce airflow through the rice grain.

2.  Pre-cleaners are indispensable in many drying systems. 

3. Pre-cleaners usually consist of a scalper that lets through the grain but retains straw and a smaller second screen that removes small stones and other impurities.

4. An air aspirator will suck out dust and light empty grains.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Safety considerations for Solar drying

For safe operation of the burner, the dryer needs to be equipped with: 

1. A flame control to turn off fuel supply in case of ignition failure (automatic burners in re-circulating batch dryers).

2. In gravity-fed pot-type burners a safety device that turns off fuel supply when there is a power failure that shuts of the fan.

3. High temperature limits switch or temperature control to prevent overheating.

4. Proper electrical wiring of all electric components.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/safety
26
Aug

Solar Drying

The use of solar energy as a heat source (solar drying, solar assisted drying) has been evaluated intensively by many projects and institutions. While some solutions were proven to be technically feasible none was successfully commercialized for paddy drying because of the following reasons: 

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
26
Aug

Direct and Indirect Heating

1. In direct heating the combustion products

are mixed with the drying air meaning that they come in contact with the paddy. 

2. In western countries this is only allowed for products used to feed animals.

3. In SE Asia direct fired heaters are not considered as problem because the flue gases will only pollute the rice hull, which is not considered a problem since the hull is removed during the milling process.

File Courtesy: 
http://www.riceindia.net/RKBank/Training_Manual_Paddy_Drying.pdf
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