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Frequently Asked Questions

Below is the list of questions that we usually receive. Please note that IRRI does not endorse manufacturers or brands of equipment. 

For further questions, please send an email to postharvest@irri.org. 
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2101 Combine harvester Can you tell me the technical specifications for a combine harvester in terms of drum speed and machine speed? That depends completely on the design of the machine. A good starting point is the operators manual. We can't give you blanket information. For example, the threshing drum speed depends on the crop threshed, the diameter of the drum, the type of threshing elements used etc. Forward speed depends on the capacity of the machine and, the cutting height, straw grain ratio of the crop and the crop density / yield.  
2100 Combine harvester Could you please help me in getting some information on Rice Combine harvester developed by IRRI? Where can I buy it? The rice mini combine harvester was not developed by IRRI but by Briggs&Stratton in collaboration with the Philippine Rice Research Institute (PhilRice). The design was then transferred to several manufacturers in Vietnam and the Philippines. The machine is based on a Chinese design but the quality is much improved. IRRI is working with Nong Lang University in Ho Chi Minh City in Vietnam and several national research institutions on introducing mechanized harvesting in Cambodia, Laos, and Myanmar. The mini combine turned out a viable solution for demonstrating the principle of combine harvesting, so we imported one machine from Vietnam to Cambodia and helped AfricaRice to also import a machine to Africa. The machine was then used for field days and promotion of mechanized harvesting. We observed that in Vietnam and Cambodia the mini combine gets quickly replaced by small rice combines with 2-2.5m cutting width. We don’t know of any manufacturer anymore in Southeast Asia who makes mini combines. IRRI itself is a research and training institute. While we might produce prototypes of new machines every now and then, we don’t produce commercial machines and we also don’t trade with them. If we know a good supplier delivering good quality products and services we might refer inquiries to them. Disclaimer: Please note that while we are providing you with the information about manufacturers, IRRI is not endorsing any specific manufacturer nor do we warrant the quality or fitness for use of any product or service provided by the manufacturer. There might be alternative sources who produce similar equipment with similar specifications and quality.  
3109 Drying, general I am from Africa and would like to buy a dryer. Can I buy from IRRI? We are getting lots of similar requests from Africa from different countries. The key components of a dryer are the blower and the rice husk furnace. The bin can be easily made locally. The blower could be made locally but we would have to train a manufacturer and do some quality control. Therefore we usually suggest to import those component for the first dryer units, to ensure they work according to the specs. There are three options. 1.) We can ask a partner, like Nong Lam University in Ho Chi Minh City, to send a team to Africa for installing the first unit and provide training of users. This guarantees that the unit works and is less costly than sending IRRI staff, but it is still the most expensive option. 2.) We can provide addresses of manufacturers of good blowers so that they can import one unit. We can then also provide the drawings of the bin and a simple furnace. This is the cheapest version with some sort of quality control for the fan, but likelihood of failure is quite high. 3.) We work with a local manufacturer and transfer the fan technology and do some training on fan testing. This would be ideal, because then in the future he could also provide fans to other investors. This would need a project though for doing the technology transfer activities.  
3005 Drying, general I would like to have information on commercially available dryers for village level. There are many types of mechanical dryers. For some specific examples and contacts see the Rice Knowledge Bank. RKB page 
3001 Drying, general Since solar energy is free, would it not be great to have a solar rice dryer? While the idea of using the free energy from the sun for drying is very exciting, most solar dryers for rice have failed. One exception is the Solar Bubble Dryer (SBD) (->link), which is a recent development and was commercialized as Version 1 in September 2014. It is very promising with respect to replacing sun drying (-> link) and eliminating the losses cause by spreading the grains on the ground and exposing them to the elements. Solar energy can be used for two purposes: 1.) To generate heat in order to increase the temperature of the drying air for reduction of the relative humidity of the air to enable / speed up the drying process. 2.) To generate electrical energy to move the drying air through the grain bulk or over the grains and to transport the evaporated water away from the grains. The SBD uses the overflow drying principle that requires only a small blower with little power requirement and used relatively low drying air temperatures. The drying tunnel itself, which also contains the grains, serves as the solar collector that generates heat and the SBD therefore does not require much additional area for solar panels for generating heat. Attempts to use solar collectors for heated air drying (-> Link to Definition) have mostly failed though due to the relatively low solar energy from the sun per square meter and the high air flow rates required in heated air dryers. Heated air dryers also need strong blowers to force the drying air through the grain bulk. Using solar collectors to generate heat for rice drying in heated air dryers is not economically feasible and there are technical constraints. An example, flat bed dryer with 1t capacity. 1.) Heating the drying air • Assuming an average solar radiation of 500W/m³ and 70% collector efficiency, one square meter of solar panel can generate 1, 260 kJ/h or roughly 15, 000 kJ/day. • The desired drying rate in heated air dryers for optimum dryer use, grain quality and economic operation is 1% moisture content per hour. To achieve this air with a temperature of 43°C needs to be moved through the grains. In the tropics average ambient air temperatures are somewhere between 25-35 degrees so on average a temperature rise of 10 K is needed, which would require around 50 kJ/h energy for heating the air. For one ton batch capacity this would require more than 40 m2 collector area for the solar collector. 2.) Generating electricity for the blower • For each ton dryer capacity this requires 0.7-1 kW motor power for the blower to force the drying air through the grain bulk at around 0.2m/s air velocity. Powering the motor with photovoltaic is not economically feasible. Advantages of solar energy • Solar energy is freely available during the day and is environmentally friendly. • A solar dryer can be completely independent from other energy sources and can be used anywhere. Disadvantages of solar energy • Most heat for drying is needed when it rains or at night when solar radiation is low. • High investment cost and space requirement for solar collectors for heated air drying, the solar collector area needed is around 10 times the area of the drying bin. • Temperature control is a major problem. Conclusion The Solar Bubble Dryer is a promising concept for using solar energy for drying since it uses overflow drying and low temperatures. For heated air drying solar collectors are not economically feasible since the specific investment cost (cost per ton installed capacity) and the space requirement remains major constraints to using solar power for heating the drying air.  RKB Link 
3004 Drying, general The drying time of my flat bed dryer is too long, what could be the reason?  Link do extended document with answer 
3003 Drying, general There is a lot of fly ash or black sooth in my paddy which reduces its market value. How can I reduce it? Most paddy dryers are direct fired, which means they don't use a heat exchanger and the flue gas of the furnace is mixed with ambient air and then blown into the dryer. If the furnace - fan combination is not designed properly the fan can suck ash from the furnace and blow it into the air distribution system of the dryer. If the air velocity is high enough the ash or sooth even gets carried into the grain bulk. Most furnaces have a fly ash separation device, e.g. by using a set of baffles that forces the air to turn sharply and separates the ash trough centrifugal force. Other furnaces use a circular air flow like in a cyclone for ash separation. If you find too much fly ash in the drying air check the following: 1.) Is the as separation device designed according to the specifications? 2.) Has fly ash accumulated in the as separation device? If so, clean it. 3.) Is the air velocity according to the specification? Too high air flow can suck excess ash from the furnace. Link to formatted answer 
3002 Drying, general What is the ideal fuel for heating the air in a dryer?  Kerosene is a common, but expensive fuel, dryers using kerosene are therefore often not used. Rice hull is an alternative and most of the recent dryer installations in Asia therefore use rice hull. In terms of temperature control LPG would have an advantage but we have not seen a single dryer with a LPG burner yet, mainly because of higher cost compared to kerosene. We cannot recommend electricity as the source for heat because of the prohibitive cost. Solar collectors are one option (see Solar Bubble Dryer) but the heat generated by them is only available at daytime and is dependent on the solar radiation.  
3102 Flat bed dryer Do I need to mix / stir the grains in a flat bed dryer to avoid uneven drying at the bottom and the top of the grain bulk?  If the dryer is designed properly and the right airflow rates (creating 0.2m/s air velocity through the grain bulk) and drying air temperature (less than 43 degree Celsius) are applied, mixing is not necessary. Lower air flow rates lead to uneven drying. So do higher drying air temperatures. Reversing the air flow after some time will lead to even more even drying - see Reversible air flow flat bed dryer.  
3100 Flat bed dryer How many tons of paddy is the batch load in flat bed dryer? The original UPLB/IRRI flat bed dryers designed in the 1970s had 1 and 2 tons capacity. Due to economics of scale and high operating cost for the kerosene furnace for heating the drying air they were not successfully introduced anywhere. These dryers were modified in Vietnam for a capacity of 4 tons and equipped with a rice husk furnace to reduce energy cost. These dryers were scaled out in Vietnam in the 1990s and transferred to Cambodia, Indonesia, Myanmar and Lao PDR starting from 2006 and commercialized there. Since then flat bed dryers with up to 20t capacity were installed in Vietnam and Cambodia. The larger the size the more uneconomical the loading and unloading operations gets, which are still mostly done using manual labor. Once capacity of a flat bed dryer gets beyond 4-6t it usually makes sense to consider a more advanced dryer, like a re-circulating batch dryer, in which all operations can be automated.  
3107 Flat bed dryer I want to construct my own batch dryer (Flat Bed Dryer or Reversible Airflow Flat Bed Dryer). What are the key considerations? Any heated air dryer consists of four components, a drying bin, a blower for generating airflow for moving air through the grains, an air distribution system to distribute the air as evenly as possible through the grain bulk, and a heater for pre-heating the ambient air. The key component of any dryer is the blower. If the blower not specified properly or is manufactured poorly, it will reduce the airflow and the whole dryer will not work. We therefore usually recommend to purchase the first blower from a manufacturer that can make good quality one. Often, local manufacturers produce blowers that perform poorly (one blower bought from a manufacturer in the Philippines produced only 50% of the required air delivery when put on a blower test rig). The second important component is the air heater. It should have clean combustion, even feed rate for even temperature over time, minimized fly ash in the drying air, should be easy to operate, and don’t pose any safety hazard. The drying bin is relatively simple, it can easily be made locally. The false floor needs to withstand the load of the grains, and the air distribution system needs to provide even airflow across the ground section of the drying bin.  
3108 Flat bed dryer I would love to have a detailed design and dimensions of a successful flat bed dryer installation to facilitate installation here in my site. Giving recommendations for the Installation of a flat bed dryer requires a lot of site specific information. A dryer is not something you just buy off the shelf or according to specifications. You need to consider the following: 1.) Capacity needs to be matched with the incoming crop. 2.) Available type of fuel for heating the drying air. 3.) Available materials and prices of those for constructing the drying bin (metal, bricks, concrete). 4.) Availability of components (blower, furnace..), and labor situation for the drying operation. Very general specifications for a flat bed dryer are: Capacity between 4-10t/batch, drying air temperature of not more than 43 degrees Celsius, air velocity through the grain bulk at least 0.2m/s at each location of the cross section of the bulk, layer depth of the paddy inside the bin 30cm for best grain quality, maximum 40 cm.  
3106 Flat bed dryer What does the ideal space look like for setting-up a flat bed dryer? The dryer should be protected from rain, so a roof is a must. On the other hand the dryer produces a lot of heat, which makes the working conditions for the laborers difficult. The ideal space is therefore just a roof on stilts to protect the dryer from rain. This facilitates sufficient air exchange and is also a cheap option.   
3104 Flat bed dryer Where can I obtain drawings of small capacity flatbed dryer with less than 4 tons capacity. We have drawings for a 2t flat bed dryer with a drying bin made from metal. However, they date back to the 1980s. Except in a few cases this size has not been commercialized successfully. Due to "economics of scale" factors most dryers have at least 4t capacity. Also now most drying bins are made from concrete or brickwork, which safes cost. We still send the drawings to people interested but usually they are only used for demo units, and for introducing the concept of mechanical drying. So on principle we can send you drawings if you confirm that we informed you about the fact that it is an outdated design in terms of economically feasible capacity.  
3105 Flat bed dryer Why do I have uneven drying in Flat Bed Dryer? The heated air enters the fixed grain bed on the bottom and leaves the bed partly saturated on the top. During it’s way through the grain bed the air increasingly adsorbs water, which means that the drying potential of the air decreases the more it moves up in the grain bulk. The result is a moisture gradient can easily reach 5% and more. In practice at the end of the drying process the grain at the bottom will have around 10-12% MC while the one at the top will still have around 16%. When unloading the dryer these grains with different MC are mixed and thus an average MC of say 14% is achieved. However, the dryer grains will adsorb moisture from the wetter grains, a process during which fissuring occurs. This leads to breakage of the fissured grains during the milling process. The moisture gradient can be minimized by either : - reducing drying air temperature - mixing of after 3-4 hours - reducing the grain depth or with a combination of the above but these all increases drying cost and decreases capacity.  
3101 Flat Bed Dryer How long does it take to dry the batch dryer load from drying start to unloading?  A good flat bed dryer has a drying rate of 1-1.5% moisture content per hour. So the drying time depends on how much moisture has t be removed. Example: At a drying rate of 1%/h and an initial moisture content of 24% it would take 10 hours to dry to 14% final moisture content.  
3103 Flat Bed Dryer What is the air temp exiting the blower and what is the air temp in the plenum chamber of the flat bed dryer? The temperature exiting the blower should be 43 degrees Celsius or less (Air velocity through the grain bulk should be 0.2m/s). There is usually no significant heat loss in the air distribution system so the air temperature in the plenum chamber should be roughly the same, 43 degrees Celsius or less. If the air temperature at the outlet of the air heater is higher than 43 degrees Celsius it has to be mixed with ambient air to achieve the desired air temperature.   
3300 Harvesting, general What are the currently available Solar Bubble Dryers in the market and how much do they cost? Currently, GrainPro, Inc. is producing Solar Bubble Dryers with 1 MT and 0.5 MT capacity. A larger version with several tons capacity is under development. Refer to GrainPro, Inc. website for the price. www.grainpro.com  
4101 Hermetic storage Can I store coffee in hermetic storage? Info on hermetic storage of coffee is also available at: http://www.mesoamerican.org/solutions_storage_systems.htm They have also some info on solar coffee drying systems  
4104 Hermetic storage Can I use any plastic bag instead of the Super bag? No. Plastic films that plastic bags are made of are very thin and usually have high oxygen permeability. Normal plastic bags, e.g. polyethylene bags (PE bags, polybags), which can be bought for various purposes, let too much oxygen pass through the material. They are therefore not hermetic in the sense of hermetic storage. The IRRI Super bag is made from a special plastic composition that minimizes the oxygen permeability. The figure below shows a comparison of normal plastic bags, in this case made from polyethylene (PE) with the IRRI Super bag. It is obvious that the oxygen that is depleted inside the PE bag is replaced by oxygen that moves through the plastic from the air outside the bag. Page with graph  
4102 Hermetic storage Do rats or mice attach hermetic Cocoons? Usually we don't have problems with rats when the Cocoons are set-up properly. If there is rat damage it is usually from the empty cocoons thrown in a corner and left there instead of putting them inside the storage bag that comes with the cocoon. For the Super bags, in most countries we don't have problems with rats. Myanmar is an exception, around 8% of all bags got damaged by rats in a recent trial. We could not trace that back to a management error, they might have a very aggressive species there.  
4103 Hermetic storage What crops can I store in Super bags? The Super bags have also been found suitable for dried maize, coffee, cocoa, beans, rice bran and several other crops.  
4100 Hermetic storage Where can I buy Superbags and how much do they cost? The IRRI Super bag was jointly developed by IRRI and GrainPro, Inc., which is located in Subic, Pampanga, Philippines. As of 2016 the IRRI Super bags are equivalent with the GrainPro® SuperGrainbag® Farm™. GrainPro has distributors in many rice growing countries. Kindly refer to the GrainPro website for more details (www.grainpro.com). Please note that IRRI does not endorse or recommend specific manufacturers, if several manufacturers are producing similar products with similar quality. There are other supposedly hermetic storage bags in different markets but we have not tested them and some bags we tested had too high oxygen permeability to be hermetic. To our knowledge GrainPro is therefore currently the only manufacturer who makes hermetic storage bags according to the hermetic specifications and with the manufacturing quality required by our projects. Formatted text 
9200 IRRI moisture meter Where can I buy IRRI Moisture meter and how much does it cost? We were not able to raise the funds needed to commercialize the IRRI Moisture meter and have it produced in signifiant numbers to get an acceptable low price. We are out of stock and do not sell IRRI Moisture Meter anymore. If you are a company interested in producing it, a sample unit of Mark II and Mark III moisture meter and a manufacturers manual is available at IRRI.   
9101 IRRI Quality kit Are there alternative suppliers of the IRRI grain quality kit? No. But we are planning to outsource the production of the quality kit. If you are interested to produce it please inquire for details at postharvest@irri.org.  
9100 IRRI Quality kit Where can I buy IRRI Grain Quality kit and how much does it cost? One unit of IRRI Grain Quality Kit costs USD 305 with a digital moisture meter. And USD 145 without the moisture meter. The grain quality kit is intended for use in our training courses and extension activities with our collaborators, thus, we have limited stocks. Some tools were partly manufactured like the indented sheet grader, moisture meter, milling chart, and leaf color chart. Other tools are sourced in the market like the infrared thermometer, mini scale, caliper, graduated cylinder and magnifier.   
NEW Others Can you tell me about who to improve the rice postharvest industry in Senegal? (any west African state) thank you very much for your inquiry. IRRI has an office in Burundi and activities in East Africa (Mozambique, Tanzania). West Africa is taken care of by AfricaRice. We have supported, and are continuing to do so, AfricaRice and other partners in Africa in particular with mechanization and postharvest technologies options since this has not been the major priority of AfricaRice, and there are are a lot of learnings in Asia, which can be useful for Africa. For example, we have facilitated the shipping of postharvest technologies like threshers, combine harvesters, quality toolkits etc to African partners and we also have helped several companies in Africa to improve their rice processing by facilitating links to consultants who either provided advise or installed and commissioned postharvest equipment. We have also suggested consultants to GIZ and other donors and implementing agencies e.g. for mechanization studies. But despite these activities our knowledge about rice in Africa and in particular about the rice industry is quite limited. AfricaRice has a research station in Senegal, so I would suggest that you visit them and see how they could help you. I would suggest to contact John Manful at AfricaRice. (j.manful@cgiar.org). He is in charge with postharvest and rice quality at AfricaRice. One way to learn about different postharvest options for farmers and the industry is to participate in our 2 week Postproduction to Market training course. It is a hands-on training and exposes the participants to all the different technology options available for harvesting, drying, storage, milling and has modules on grain and seed quality, markets, business models and project planning. We just finished this year's course and a second one is ongoing this week. The next one will be in April 2017. And then we obviously also can create custom training either formal or a study tours following our full cost recovery guidelines.  
9300 Others I am doing my PhD study on postharvest losses. Can you send me protocols to measure losses? We usually design protocols for loss assessments based on the objective and the technology we are looking at. We don't have standardized protocols. I would have led you to the Rice Knowledge Bank, but you found that already. The training materials usually contain information about how to measure losses. Another source are the RNAM publications on technologies and performance testing, they should be available in the internet. National systems also have standards for performance and loss assessments, for example AMTEC in the Philippines and other agricultural testing centers of other countries. I don't have the time to compile literature for other people so you need to do the literature study yourself. What I could offer is have a look at our protocol once you have designed it and give you some comments on it.  
9001 Others Which manufacturers of agricultural machinery does IRRI recommend? Please note that while we are providing you with the information about manufacturers, IRRI is not endorsing any specific manufacturer nor do we warrant the quality or fitness for use of any product or service provided by the manufacturer. There might be alternative sources who produce similar equipment with similar specifications and quality.  
3200 Reversible air flow flat bed dryer Where can I get drawings of reversible airflow flatbed dryer (RAFBD) The RAFBD was developed by Nong Lam University (NLU) in Ho Chi Minh CIty, Vietnam. It is based on the design of the ordinary flat bed dryer (FBD). You can request for some information about the Vietnamese RAFBD from Dr. Nguyen Thanh Nghi from NLU (ntnghi78@yahoo.com.vn). In partnership with NLU and with national research partners,IRRI helped to transfer drying technologies to other countries. So far the RAFBD was transferred to the Philippines by NLU and PhilRice with some assistance from IRRI.In the Philippines, you may contact PhilRice (Evangeline Sibayan, Rice Engineering and Mechanization Division Philippine Rice Research Institute Science City of Muñoz, Nueva Ecija, ebsibayan@philrice.gov.ph)  
3501 Rice husk furnace Can I use the downdraft rice husk furnace for drying other things than rice? Can you tell me the ideal operating conditions? The current furnace is designed to burn around 25kg of rice husk per hour, which creates a temperature increase of around 10-15 degree Celsius above ambient air temperature at a drying air flow rate of 4 m^3 / second. If you have lower airflow rates the temperature raise could be higher. If you have higher airflow rates the similarly the temperature raise would be lower. The bottom line is, if you are using the furnace for a non standard application (flat bed dryer for drying rice with with 4t capacity, ambient air temperature around 30 degrees Celsius, drying air temperature around 43 degrees Celsius) you need some significant adaptive R&D. If you have somebody who can do that it is fine, if not failure is quite likely, as many examples of failed modifications suggest.  
3503 Rice husk furnace Can I use the IRRI rice husk furnace for fluidized bed drying?  Fluidised bed dryer is often applied for the first stage-drying in a big-scale system with a high capacity and needs high temperature from 80 to 100 degC. This dryer should need a high capacity furnace to provide enough heat for drying. Our IRRI-downdraft rice husk furnace (dRHF) is a semi-automatic furnace with high efficiency, but the design so far just provide maximum about 250 MJ/h. It is used for a flatbed dryer having a capacity of 4-6 ton paddy/batch/(8-10h).  
3502 Rice husk furnace I would like to attend training on how to build the Downdraft Rice Husk Furnace (dRHF). Where can I sign up? We are currently not conducting any trainings on dRHF anymore. However, we can refer you to trained manufacturer to whom you can order furnace. In case you are a manufacturer and would like to produce the furnace, we can also provide you with drawings and technical information about it after we have discussed licensing arrangements with you.  
3302 Solar bubble dryer Can I use a starter battery (car battery) for the Solar Bubble Dryer You can but the starter battery will deteriorate very quickly since it is designed for another purpose - providing extremely high current for a very short time. When you use it with the Solar Bubble Dryer it will loose its capacity within a year. It will still appear to function properly when you measure the voltage at the end of charging but the usage time will be drastically reduced. See the IRRI fact sheet “Deep Cycle Battery for the solar bubble dryer” Fact Sheet, Solar Battery 
3301 Solar bubble dryer  I am very much interested in exploring the possibility of using the Solar Bubble Dryer. Can you please provide more information about this new technology? The dryer was developed through a cooperation between IRRI, GrainPro, Inc. (manufacturer of hermetic storage systems), and Hohenheim University in Germany. It consists of of an inflatable drying tunnel, one or two small electrical blowers, and a solar system with photovoltaic panels to generate electricity from the sunlight and a battery to store power for operation of the blowers at night or during rain with low sunshine. It is independent from any conventional form of energy and therefore cheap in operation. It protects the grains from the elements and improves the sundryring. Link to formatted text 
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