Best Viewed in Mozilla Firefox, Google Chrome

Production Know How

Production Know How
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
26
Aug

Fixed-Bed Batch Dryers

1. Fixed bed batch dryers usually have rectangular

bins with plenum chamber underneath or circular bins with central duct.

2. The most common fixed bed dryers are flat bed dryers which have a very simple design. Grains are laid out on a perforated screen, and dried by forcing air from below. 

3. The air fan that provides the drying air is usually a simple axial flow fan, powered by a diesel engine or by an electric motor. 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-drying-methods/heated-air-drying
26
Aug

Low-temperature drying

1.In low-temperature drying the objective of the dryer management is to keep the RH of the drying air at the equilibrium relative humidity (ERH) corresponding to the desired final moisture content of the grain, or the equilibrium moisture content (EMC). 

2. The effect of the temperature is minimal compared to the RH. For example a final MC of 14% is desired one should target an RH of the drying air of around 75%. 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/heatedair-and-low-temperature-drying
26
Aug

Heated-air fixed-bed batch dryers

1. In heated-air fixed-bed batch dryers, the hot drying air enters the grain bulk at the inlet, moves through the grain while absorbing water and exits the grain bulk at the outlet. 

2. The grain at the inlet dries faster because of the drying air has the highest water absorbing capacity. Because of the shallow bed and relatively high airflow rates, drying occurs fastest in all layers of the grain bulk at the inlet and slowest at the outlet. As a result a moisture gradient develops, which is still present at the end of drying.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/heated-air-and-low-temperature-drying
26
Aug

Additional factors affecting the drying rate

Besides layer depth and mixing interval the drying rate of sun drying depends on other factors which are usually out of control of the operator:

1.Temperature and humidity of ambient air: The rate at which rice dried is affected significantly by the temperature and humidity of the air which move over or through the grain. 

2. For this reason, in most Tropical and Humid climates, Sun drying is only successful during a few hours in the mid-day. Initial moisture content of grain: Wet grains dry more rapidly than comparatively dry grains.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-drying-methods/sun-drying
26
Aug

Protection during Sun Drying

1. During hot days the grain temperature may rise above 50-60ºC. If that is the case cover the grain at mid-day to prevent over-heating;

2.Cover the grain immediately if it starts raining. Re-wetting of grain causes fissured grains and high grain breakage during milling;

3.Prevent contamination of grain with other materials and keep animals off the grain; and

monitor grain moisture content and grain temperature.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/Index.php/paddy-drying-methods/sun-drying
26
Aug

Mixing while Sun Drying

1. During good weather conditions mixing or turning the grain is the most important activity for maintaining good quality.

2. Turn or stir the grain at least once per hour, better every 30 minutes to achieve uniform moisture content. 

3. Variation in moisture content within the grain causes re-wetting and subsequent grain cracking of dried kernels.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/paddy-drying-method s/sun-drying
26
Aug

Layer thickness while Sun drying

1. Rice millers invariably use concrete floors for drying. Such drying results in sun-cracks and contamination on quality of rice is little realised as much of the milling is in hullers which by themselves contribute to breakage.

2. In case of sun drying the produce is spread on hard floor or threshing yard around 10-cm thickness, and is allowed to dry by heat from the Sun.

3. Spread the grains in thin layers, ideally 2-4 cm.

File Courtesy: 
http://www.ikisan.com/CropSpecific/Eng/links/ap_riceDrying.shtml
Syndicate content
Copy rights | Disclaimer | RKMP Policies