Maize drying methods. Ukrainian elevators experience
Corn is the main crop for many Ukrainian grain elevators. And though granaries have been working with it for decades, the questions of drying are still of current interest. How to dry corn to achieve the desired moisture content, while maintaining the quality of the grain and saving energy resources? Everyone’s approach in this case is different. Experts from three agroholdings share their experience today.
Sergey Shcherban, head of the technical department of AGROTRADE Group, says:
When you feed corn to the dryer we immediately raise the temperature of the heating agent to 110, 120 C. This is especially true if the corn has a moisture content of 25% or higher.
There is a theory that it bakes the top layer. But, in our opinion, it’s not how you initially take the grain into the dryer and start drying that matters, but how you go into the cooling process. It is when the corn is cooled that it can start to crack. That’s why you have to lower the temperature gradually and not abruptly.
American NECO and MC dryers help us in this process. We installed them on several elevators. In our opinion, such dryers are the most optimal for drying corn. In them the drying temperature can be adjusted seasonally. Let’s say that in the upper zone the temperature is 110 C, then we move to a zone with 90 C, and then to 40-45 C, and then it is direct cooling.
Last year as an experiment we added a ventilated tank made by PETKUS to our NECO dryer.
An operative tank of PETKUS production has a peorized surface, but it does not let water in from outside. Inside the tank there is a perforated tube, in which air is blown, which blows the grain mass. So the corn comes out of the dryer still warm, but in this tank we cool it gently.
Of course, if we do cooling in such a way injured grain will be, there will also be dust, but the amount of breakage is leveled by the large volume of grain, which we have time to dry using this technology.
Vasiliy Kret says about the elevator director of the company Kusto Agro JV Zhmerynka:
In order to get good quality corn after drying Kusto Agro companies follow the technology of forming batches according to humidity.
We have two grain dryers, shall we say, two mowing lines. We send corn with moisture higher than 25% on one line and less than 25% on the other one. That way we minimise over or under drying. This method is used at all the enterprises in Ukraine and in the world.
Our dryers are automated. Ideally, of course, the final moisture content should be set automatically, and the dryer should stop when the set point is reached. But in practice, it often happens that we have several clients with grain of different moisture at one time. If we throw it all into the dryer, no machine will work.
My advice is, if you take in grain with different moisture content, you better regulate the dryer manually rather than trust the automation. The operator will see when to reduce the temperature of the drying agent. But in this case you should have a very qualified drier. A lot will depend on his knowledge and experience. Therefore, we need to select personnel, especially dryers, very responsibly.
After drying the corn should have the humidity of 14,5%. It is bad if you over-dry it up to 13,2 % and bad if you under-dry it stopping on 15 % moisture content. Moisture of 14,5% is optimal. If you guessed it, you’ll be on top. But this humidity isn’t always achievable. A lot depends on dryers and their operators.
Corn can be dried on any dryer. But profitable is the one that has the lowest energy costs at high productivity.
says Alexander Popov, chief engineer of Volyn. grain product:
We dry corn in two stages. The first stage takes most of the moisture on the shaft dryer. Humidity of corn at the input 28-40%, at the output 23-24%. In this case the husk comes off the grain.
Between the first and the second stage the corn stays frozen for several days. It can lie in hoppers or in floor storage. During this period, the kernel gives moisture to the outer shell, and the grain dries more easily.
The second stage of laying aside corn we finish drying on the American grain dryer Sukup modular type drying grid in grid. The dryer can be any manufacturer. The bottom line is that if the facility has two dryers and one of them is net-to-mesh, then the corn first goes into the shaft dryer, and then into the net-to-mesh dryer. If you work with a dryer, take into account the fact that they have cells for rape, t.е. 0.8-1 mm, so the husks are not clogged. There are the same Sukup for corn, where the mesh is 4 mm, and there are no problems with the output of husks.
Our American corn comes in with moisture no higher than 24%, it doesn’t clog up the dryer and gives out moisture intensively.
If this moisture content is the initial corn, it can be dried in one step.
This technology was not invented by us, it was written in the textbooks of the 50s.
No matter how many grain dryers you have in your elevator, two or one, they have to work in flux. We don’t waste time loading and unloading. The dryer must not stop. Otherwise its work is not effective.
We dry our corn at a heat agent temperature of no more than 95 C. If in the beginning of my career dryers raised the temperature even to 150 C, the modern hybrids at this temperature will turn into dust.
Last year we had a difficult corn harvest season in our region. One week it rained, one week there was a break. When the weather was clear, the combine harvesters gave out the maximum. So to dry the whole corn stream we switched on both dryers and knocked down the first moisture. We dried and laid the corn to rest. When it rained, we returned to the second stage, that is, we brought the grain to the right condition. Floor storages are ideal for this layout.
We also work with metal storage tanks in two stages. We put the corn after the first drying into the operative tank. It warms up there for a few days. When the temperature gauge shows 40 C, we turn on the fan. Temperature goes with humidity. So we remove 3-4% moisture.
Drying grain on farms in Brazil
The minimum crop currently being harvested in the country. is 150 million tons/year of grain. Most of this grain is dried with equipment produced by Brazil’s leading manufacturer of grain dryers. Kepler Weber, whose main shareholder is the state. Most surprising is that almost all dryers in Brazil are wood-fired and do not have a built-in heat exchanger. It so happens that the country has almost no natural gas and oil, and so the eucalyptus, which is quite common here, became the main energy source during the drying of grain.
Wood-fired dryers have been constantly improved and increased in power, but in our opinion this has not spared their attractive simplicity in design and operation. To assess their benefits and reliability truly can be only after several years of operation of equipment. Grain drying in Brazil is really put on an industrial basis. The maximum thermal capacity of Brazilian dryers reaches 12 MW, soybeans are sometimes dried with the productivity up to 200 t/h (at 5% moisture content reduction), and rice. Up to 400 t/h.
As we can see, the heat generator has no air heat exchanger, but at the same time, the grain during drying does not absorb the characteristic smell of combustion products. This is because the dryer is designed so that only 20 % of the air heated to around 100 °C from a heat generator is supplied into the drying zone. Another 40% of heated air from the cooling zone of grain in the lower part of the dryer in the recirculation mode and 40% of ambient air. There is a limited possibility to regulate the ambient air inflow, which means. and air temperatures in the drying zone. As a rule, the temperature regulation is performed by controlling the amount of firewood (otherwise, if the ambient air supply is blocked considerably, the risk of sparks getting into the grain increases).Fig. 1 schematic representation of the heat generator model, which is most often used in grain dryers.
The heat generator consists of:
secondary gas afterburning chamber. third section;
vortex chamber to separate sparks and solid impurities;
If you look in the “agricultural encyclopedia” published in 1955, you can see there grain dryers running on coal or wood, which have almost the same design of heat generator as the modern Brazilian.
Obviously, cheap liquid fuel and later gas pushed biofuel dryers out of our market. Even the design of the dryer shaft was not of the lidded elements like most modern gas-fired shaft dryers. In a louvered shaft, the grain moves with each individual louvered column from top to bottom in a straight line, but in a roofed shaft, the grain moves with the louvered column from top to bottom in a straight line. zigzagging. In the second variant the grain fills practically all the volume of the shaft, and in the shaft of the first type of dryer the grain will be 40% less, and the specific energy consumption for drying will increase by about 20%. However, a shaft with louvre elements has its significant advantage. it is a fire hazard because it is the grain that is cleaned better and there is no significant accumulation of flammable straw waste and other impurities that can cause a fire.
Obviously, this advantage has led to the widespread use of this type of mine in Brazil. When using a cheap source of energy, namely wood, the question of saving is not so critical. over, even the simplest dryers of this type have the possibility to recirculate the air from the cooling zone of the corn or soybeans and therefore during the drying of corn or soybeans with a heat carrier temperature of 100° and above, the possibility of recovering that 10-15% of the energy is realistic.
How to make a drum type dryer with their own hands?
For small farms will be profitable to assemble a grain dryer with their own hands. First of all you must decide if you will process one or several crops.
Then you have to decide if you want to move the grain vertically or horizontally. Vertical dryers are the most economical, because the grain moves under the action of its own gravity. So you will save on additional equipment and electricity. In the horizontal type of mechanisms requires an additional device (agitator or a conveyor to mix the grain evenly).
Alvan Blanch Continuous Double Flow Grain Dryer. Animation
Well-proven for the manufacture at home dryers drum type. But they consume relatively large amounts of energy.
Also decide how you will load grain. batchwise or continuously. At home it is better to do it in portions, as the drying mode can be adjusted for different quality grains. Continuous drying requires an additional auger device, which will feed the grain. And the drying mode will be set only by the speed of feed and movement of grain material.
Also important is the direction of air flow. There are devices with four directions:
- one-way air current;
- counterflow (grain moves from top to bottom, air moves from bottom to top);
- mixed flow (the highest drying performance, but difficult to manufacture);
- Cross-flow (the air moves horizontally, minus high electricity consumption).
Grain Drying Small Scale Pallet Bin Dry Down Experiment
Drawing of a grain dryer
The bad news is that, unfortunately, you won’t find blueprints on the Internet that are sufficient for the construction of a grain dryer. And this is understandable. all the manufacturers keep them secret.
Therefore, you have to draw and produce a grain dryer completely by yourself. And in this we can not help you.
However, if you have hands and a head, this is the least of your problems. It is much more important to choose the right type of dryer and the right working equipment (fans, burners, unloading system, etc.).п.)
Picture.General drawing of a Ravaro dryer in AutoCAD.
Dryers: classification and types
Dryers, where grain is heated by burning fuel, are the most common in agriculture and industry. Such dryers can be stationary, t.е. with fixed equipment in special buildings, as well as mobile.
The design is simple. All of them have a heating furnace (furnace) and a drying chamber for drying grain. The fireboxes of our dryers are usually powered by solid fuel. wood, coal, etc. Chambers for dried grain, depending on the design and capacity of dryers have different shape and volume. Grain in the chamber at the moment of drying can be in a stationary state (in batch dryers) or in a continuous slow motion (in continuous dryers).
In all modern dryers, heat energy is transferred from the combustion chamber to the grain to be dried, mainly through convective heat transfer. Convection is the transfer of heat by moving layers of gaseous or liquid matter.
Heat transfer by convection from the furnace to the grain is performed either by heated air currents, or by a mixture of air and flue gases.
In the first case, the air is heated by contact with the hot surface of the furnace or with the metal pipes through which the gaseous products of combustion pass. The heat resulting from the combustion of fuel is transferred to the air only through the furnace or special pipe walls, and the flue gases produced are discharged to the outside, which results in the loss of a large amount of thermal energy.
Such heating devices are called calorifiers. Caloriferous furnaces have a low coefficient of performance and therefore require higher fuel consumption.
Much more efficient and economical are devices, which heat the grain with a mixture of combustion gases and air. In this case the efficiency of the furnace is increased, and the fuel consumption is drastically reduced. Such heating devices are called direct action furnaces.
the most widely used grain dryers that run on a mixture of flue gases and air.
When operating dryers with direct-acting furnaces, it is necessary to prevent the possibility of sparks from the furnace entering the drying chamber, as well as to carefully control and monitor the drying mode to avoid feeding excessively hot gas-air mixture into the grain.
The main requirement that all dryers must meet is that the grain in the drying process is heated evenly, without burning or local overheating. The maximum temperature for heating the grains to avoid deterioration should not exceed the established regulatory values: 40-45 °. when drying seed grain and 50-55 °. when drying food and feed grain. The temperature of the coolant in this case can be much higher.
Drying plants are divided into two main groups according to their complexity and design features: the simplest and mechanized
How to create a grain dryer with your own hands: the possibilities and type of equipment
If you do not need a large dryer, your own hands to make it quite possible. The drum models are distinguished by the simplest operation mechanism. In their action involves the rotation of a cylindrical container (drum) with the corn in a vertical plane, through which the product is dried.
This structure of the drum dryers is fairly easy to repeat. A galvanized tube of large diameter can be used as a drum. Inside it, you can place longitudinal slats, which will help the grain to be poured over more gently. The drum must be equipped with a rotation mechanism. It is also convenient to install a generator to supply warm air inside the dryer, which will speed up the processing of the product.
Construction of fire driers
How can I save on the cost of drying grain?
Fire or artificial drying can be done in several ways. Thus, in the southern regions smoke drying is the most common method. The essence of it consists in letting the hot air together with the smoke through the layer of fruit spread in the box. The coolant is fed directly from the furnace, and the duration of the process itself stretches for quite a long time. from 4 to 7 days. The end product is of low quality and, moreover, concentrates a caustic “fragrance” of smoke. Therefore, this kind of drying cannot be recommended as an optimal variant.
Good drying results are achieved with hot air alone. This kind of drying can be done in a normal Russian oven by loading it with trays of berries, vegetables or fruits after removing the coals and baking the baking sheet. Before installing the trays prepared with wet fruits, you need to make sure that the optimal temperature is achieved. When heated too high the product can be irreparably damaged: it will either burn or look “fishy” because the skin will burst and the juice will run out. To test the thermal conditions, it is sufficient to use a simple piece of white paper. If the product yellowing or, worse, charring occurs when placing it in the oven, do not dry it. After 15-20 minutes of natural cooling, check again that the temperature is acceptable.
Place the trays on a special trivet made of flat bricks. Then loosely cover the choke of the furnace, for which purpose the damper is placed at an angle on two bricks or planks. The inclination is required to allow the exhaust air to escape through the side slits. The chimney must be half-covered in order to allow unobstructed ventilation. As the product dries, the ventilation is reduced, reducing the slit more and more. At the end of drying it is necessary to remove the damper from its stands and lean it against the oven’s forehead, leaving only small slits on the sides. It is very convenient for drying in a Russian oven to use a special screen with slits made at the top and bottom (figure 1).
|fig. 1. Drying in Russian oven:1. chimney; 2. damper; 3. shutter with slits; 4. strainer (basket) for dryingThe arrows show: a. inlet air; b. outlet of used humid air|
If an oven is used to dry fruit, the door must not be closed too tightly to avoid steaming. At the beginning of the drying process the slits between the oven and the door should be as wide as possible: gradually reduce them as the process goes on. To install the sieves use bricks or side ribs, available in any oven. If the stove suddenly cools down faster than the product is dried, it is better to interrupt the process and move it to the next day. Do not dry fruits when the stove is heated. After all, if the oven overheats above 100 degrees, the chance of spoiling the long-awaited harvest is too great.
It is very convenient, practical and rational to carry out the process in drying cabinets installed above the stove: in this case it is possible to use the heat of the stove for cooking advantageously.
An over-the-hob dryer (figure 2) is a cupboard without a bottom, with or without a door that can be opened over the entire height and width of the front wall. It is placed over any hot surface on several bricks, which are stacked flat with the necessary clearances of 3-5 cm for the air intake. From below to the walls of the cabinet at a distance of 5-8 centimeters with the help of wire attached iron sheet. It serves as a kind of fuse, since it protects the lower sieve from overheating.
The hot air entering through the gaps flows freely through the row of screens and already, enriched with moisture, leaves the room through the exhaust pipe. The latter is installed on the four-slope roof of the cabinet and is necessarily equipped with a damper to regulate ventilation.
The sieves themselves are placed 12-15 cm one above the other on special runners-bars, which are fastened to the sides of the cabinet at a slight angle to the back wall.
|Picture 2. Plate dryer:1. heating surface (plate); 2. cupboard dryer; 3. sieves for fruit; 4. bricks; 5. gaps between the bricks, which ensure the flow of air; 6. extractor pipe; 7. tank for collecting drops (condensate); 8. chimney|
A special spacing plan is used to allow the hot air to flow not only through but also over the sieves, thus increasing the efficiency of the drying process. The stepwise installation of the sieve system in the over-tile cabinet is achieved through their size (they are only slightly shorter than the box) and the attachment of special slats-slats for the odd elements of the fire dryer‘s structure. The first sieve is fixed so that it is close to the door, but it does not reach the back wall by ten centimeters. The second sieve, on the contrary, is attached to the back wall, ten centimeters from the door. All the sieves are placed in the same manner.
Cabinets of this design are made from improvised materials. This can be both thin unpainted planks and the usual sheets of plywood. The walls are made double with a distance between the sheets of 2 to 3 centimeters. The average size of the cabinet is one meter in height and 0.7 meter in width. Then, according to these dimensions are prepared and installed about 6-7 screens. Frame knocked down from the usual wooden slats of thickness 10-15 mm and a height of 30 to 45 millimeters. It is fastened with metal angles, and the bottom of it is made at choice:
In the case of complete absence of these materials, you can do with a high-strength cloth, which is stretched over the bottom of the frame.
Small dryers, which require only two sheets of roofing iron, are very suitable for installation over a gas or wood stove. Figure 3 shows a diagram of its cutting.
|Figure 3. Diagram of the overhead dryer (all dimensions in millimetres)|
The dimensions of the base of such a 400?400 mm, and a total height of 660 mm. It can hold 7 screens, weighing about 1 square metre. The roof A is removable; in some cases it is not necessary to use it. The B sieves are fixed on B shelves, made of roof iron and fixed to the walls of the dryer by means of two screws. The shelves are attached to the narrow wooden slats D, which are located on the two outer sides of the dryer.
The floor E is also made of roofing iron. It is constructed with eight Ø100 openings for the hot air?50 mm each. If necessary, they are covered with two slats G, which are attached to the bottom side of the dryer floor.
Openings are made at the bottom for free access of fresh air. On the inside of the dryer, under the upper and lower shelves, a U-shaped hole in the bulb is attached to the rear wall. 8-10 mm holes are made in the side wall of the cartridge to insert the thermometer. If a thermometer is not used, the slots are plugged with cork or wooden plugs.
When the thermometer is placed on the bottom side, the temperature set in the recipe is monitored. And the upper thermometer should not go below forty degrees. If you notice that the product moistens on the highest sieves, you must modify the drying parameters a little. For this purpose, either the product layer is reduced, which, because of its thickness, simply has no time to dehydrate, or a smaller number of sieves. from six to four. is carried out for final drying. Sometimes an iron chimney is attached to the lid to improve the draft. But in this case we should not forget about condensation. To collect water droplets formed as a result of natural cooling, on the underside of the lid under the pipe at a distance of 2-2.5 cm should be hung a tray or any other container.
For fire protection purposes, if the dryer is installed over a gas stove, a metal ring is placed on the burner to be heated by the released heat. If there is no such additional heating element, the floor of the dryer may be damaged by the flame of the burner: at best, the product will catch fire and, at worst, there will be a fire because of the fire of the sieve.
Closet dryer with special heating in its structure practically does not differ from the above-mentioned above-slab dryer. The difference lies only in the overall dimensions and some design features. This unit consists of the heating system and the drying oven itself (Figure 4). The heating system is located in the hog compartment. Its components are:
Structurally, the heater can be either moved out from under the dryer or placed under it. often than others, wood-fired heaters are used.
|Figure 4. Closet dryer with wood heating:1. sieves (mesh pallets); 2. exhaust pipe; 3. chimney; 4. furnace; 5. openings serving for inflow of cold air|
Large diameter hogs are made by zigzagging from the kiln to the chimney under two drying closets. This structure of fire dryers makes it possible to use the heat of exhaust fumes in the most effective way. The brick walls of the hog house serve as a base (frame) for installation of drying cabinets. Its external dimensions are the same as the size and quantity of the drying sections. A flap must be installed in the chimney to regulate combustion. On the outside wall at the base of the fire chamber, there are openings for the cold air, which can be adjusted with doors or simple shutters.
The number of drying closets depends only on the drying volume. They are made of bricks, boards or other (unpainted) improvised materials. If two pieces of equipment are installed, partitions are placed between them. The iron sheet serves as the bottom of the cupboard, which separates the headbox and the sieves, and does not reach the back wall 20-30 cm in order to keep the hot air in. A hood is placed on the top, which is a four-slope iron lid with an exhaust pipe and the obligatory damper for regulating the ventilation. A tightly closing door serves as the front wall. Inside the cabinet on special rails (in the form of iron angles or wooden slats) at a slight angle to the back wall sieves with fruit are installed. All sieve trays are staggered in a similar way as the fire dryers.
Figure 5 shows another view of the cabinet dryer, heated kerosene. In the lower part of the unit an iron plate is suspended above the kerosene kettle. From the heat of its heating, the air will rise up, passing through the loaded sieves and flowing around them.
The dimensions of such a cabinet are 50 cm wide and 75 cm deep. The distance from the ceiling to the top sieve must be 15 cm, and the distance between the rows of screens is 10 cm. A large opening in the ceiling of the cupboard allows the warm air and water vapour to escape.
The use of any fire dryer presupposes strict compliance with fire safety regulations.
In my dryer, sliced fruit is placed on cell trays. The grid is made of metal, with the size of meshes 8×8 mm. In this “engineering marvel”, six pallets can be installed on rails attached to the side frames.
The gables are made of three strips of thin sheet metal. I made longitudinal bends at the bottom of each strip: this prevents sudden rain from getting inside the dryer. The roof is made of two sheets of honeycomb polycarbonate.
How corn is dried on an industrial scale
Maize is most often dried on an industrial scale on the cob. A chamber dryer is used for this. The process takes place at a temperature of 35 to 50°C.
It takes about 8.5 MJ of thermal energy to remove 1 kg of moisture. Chamber dryers have an efficiency of about 35% and mine dryers have an efficiency of 60%.
In the first phase, they start with preheating of the raw material. They use elevated temperatures to do this, t. к. The germ heats up more slowly. Scientific experiments have shown that heating at 50°C shortens the drying time by 7 hours and increases the moisture yield by nearly 11. The result is a yield increase of 22% compared to conventional drying.
The corn is first dried on the cob, t. к. Moist grains are hard to separate without damage. Cobs are dried to 18-20% moisture content, after which the grain is milled. Then it is sent to the final drying.
There is a differential mode. It makes it possible to increase the productivity of the units by 20-30%. The principle is the gradual increase in temperature.
Technical characteristics and dimensions of the dryer
In recent years shaft dryers are used more often. Technical specifications of the units are given in the table.
|Characteristics||Minimal index||Maximal index|
|Moisture removal from corn from 25% to 15%, t/h||2,5||22|
|Natural gas consumption per ton, m³||1,1||1,1|