Deaeration system and internal storage-cooling drying
Typical high-speed drying process drastically reduces the grain moisture content using heated air on to the transfer to storage, grain is cooled quickly in the dryer. The deaeration process developed at Purdue University in the late 1960-ies. High-speed drying process was changed by transferring hot grain in the cooling container, eliminating moisture dry cooling.
Internal storage cooling is an alternative to consider dry. Transfer the heated grain is in storage and not in special for cooling the hopper, as in deaeration. In this case, the process eliminates an additional processing step, than can not boast of deaeration. Although deaeration and has the advantage over internal storage cooling (energy saving, increase capacity, grain quality), the presence of the additional processing step makes the cooling storage a viable alternative. And deaeration, cooling and storage are studied in detail in this publication.
The grain comes from heated high-speed dryer into the hopper, the fix of which passes without the air stream order 4-6 hours, and then cooled. Due to this high-speed dryer capacity increases because it is not used for cooling. For continuous-flow production, the burner of the dryer may be added to the cooling section that is able to convert a sequence of dry.
Immediately after drying at high speed in the inner part of the machine kernels of grain wetter than on the outer tracks. When there is slow cooling after quenching, it is lost from 2-3% moisture. Conversely, a small percentage of water is lost during rapid cooling in the dryer. Due to the fact that the grain contains heat, which is sufficient to remove the water in the cooling process, the deaeration, uses less fuel. High power high-speed dryers can effectively remove the water.
Due to the rapid drying and cooling deaeration of the grain kernel get the final stage of processing. This improved the quality of the kernel is less sensitivity and resistance to damage in case of subsequent loading and unloading operations.
When a high-speed dryer is used for deaeration, the temperature may be increased. It is possible in connection with the harvesting of grain in the dryer with a higher moisture content in less time. Increase the temperature of the drying air increases the power of the machine and increases fuel economy at high speed. When drying air temperature increased, and the quality increases (weight determination and testing of the cracking of the grain under stress). It gives a guarantee of satisfactory quality culture.
The result of deaeration is as follows:
- 20-40% energy savings;
- increase the capacity of the dryer varies from 50 to 70%.
Actual energy saving in the first place, depends on initial humidity of grain. Weather conditions and the temperature of the culture also affect consumption of energy and power.
After cooling at the completion of the grain with deaeration cell is transferred to storage. In the process of hardening the condensate may accumulate in the grain near the bin wall, which can lead to its damage. In this case, the grain that has passed the quenching bunker de-aeration, should not be stored there. If the bunker de-aeration will be used for the last of the dried grain, you should follow all the recommendations on this storage.
Separate hopper refrigeration (or bins) required for the process of deaeration. The location of the dryer and the cooling bins allow for easy transfer of chilled grain storage. Each of the bins have a high capacity which allows to carry out drying during the day. The heated grain is delivered into the hopper throughout the day. After which it is cooled with fans off. After the first heating, the grain is placed in the hopper for 4-6 hours, turn on the cooling fan. Typically, such cooling fans are run in the evening, if the grain was loaded in the morning. The next day the dryer goes to the second bunker. Then the cooled grain is transferred to the storage. The deaeration process is alternated from day to day.
Large hopper capacity can contain grain for more than one day before sending it to storage. To get the maximum effect deaeration, cooling fan operation should be adjusted to ensure 4-6 hours hardening of the heated grain. If deaeration is used only one tank, its capacity must be adequate to allow several days of drying. Next, the grain is transported to the bunker for hardening, after which the content is delivered to the base cooling. Each day the bins are filling grain, and work to ensure maximum benefit from the cooling fans in the deaeration process is repeated. These actions always require initial testing and experimentation over the speed of the cooling fan in the system hopper. The operation of the cooling fan can be monitored 24-hours or percentage timer. It is the latter option allows the operator to adjust the working time of the fan based on the percentage of the period.
When using only one tank, apply a particular method of cooling and transferring grain:
- dryer can be closed, and cooling is completed. The completion of cooling and transfer of grain takes considerable time, which reduces the overall throughput of the drying system;
- the dryer can be used in the normal cooling mode, and the grain is directed directly to the storage location, and deaeration when the grain enters the cooling tank. Chilled corn should not be placed above the heated grain in the cooling bin, since moisture from the heated moist air will condense on the cooled grain. Grain from the dryer can be delivered to the cooling tank, after which it needs to be uploaded (the final stage);
in some cases, the heated grain from the dryer put in a chilled storage tank. This should be avoided. Such a delivery is considered normal if the heated grain is delivered at a slower speed than unloaded from the refrigerated bin. It is typical for dryers with a continuous flow of delivery in the container cooling with high capacity of shipment. Aeration in the hopper will cool the grain, it is possible with large-capacity dryers.
For complete unloading of the hopper with a flat bottom can be made if staying there the grain will be stored in a cool, dry and good condition. However, the cooling bins should be cleaned completely before you fill them past the party store.
Air flow and equipment needs
The success of the deaeration system depends on the proper design and selection of equipment, in particular:
-high flow capacity, cooling air delivery systems;
-correct selection of cooling fans and ventilation delivery systems;
-coordinated management system with adequate capacity.
Bunkers for cooling must be of such dimensions as to withstand the maximum filling speed of the dryer for 24 hours. Remember, in the case of using deaeration, power dryers will be greatly increased (from 50-75%). Also, if the bins are left in the grain after unloading in connection with gravity, it should be removed from the hopper. The amount of grain in the hopper, which remains after unloading due to gravity can be calculated by multiplying the cubic meters of the bunker on the diameter of 0,11. Thus, the 24-foot hopper with a flat bottom will have about 1520 bushels of grain remaining after the gravitational unloading (0,11*243 or 0,11*24*24*24).
If you have other needs, they should look in the settings of the system deaeration hopper. For the bunker today require a 4-row harvester, and further can be used 6-or 8-row machine. Bunkers have extra capacity because they can be used for storage.ф
Grain bins can be equipped with a wide range of air flow (ft3/min/bushel) used depending on the purpose. In silos that support the aeration, the air flow rate in the range from 1/5 to 1/20 ft3/min/bushel. This possibility is enough to change the temperature of stored grain in the offseason and to maintain uniform temperature in the whole warehouse. The drying bins are fully perforated floors and fans with large air flow (corresponding to half of ft3/min/bushel range). This is enough air for drying grain.
In most cases, ventilated storage bins and drying provide cooling during de-aeration. It depends on the speed of the air flow in the capacity and speed of delivery of the heated grain dryers.
Container de-aeration movement of air is upward, so that the first loaded grain is cooled in the first place. At the time of the deferral of start of the fan (at least 4 hours). Then the fan comes into action, and dryers provide the hopper with grain. Heated cereal to the top of the hopper should not be chilled before it will not work temper (heating time 4-6 hours).
When the vessel is filled, and the drying process is complete, should take at least 4 hours to cool the grain. In connection with this operation, the fan must deliver enough air to match the work of drying. If the cooling fan is perfectly matched with the capacity of drying and starts working after 6 hours from the start of drying (cooling after drying), cooling will take place after 6 hours from the completion of drying.
Selection of the fan
The minimum flow rate of the air flow in 12 ft3/min per bushel per hour drying capacity, ensures the cooling of the grain. The fan should be chosen so as to distribute the flow of air during filling of the tank. As a rule, it is impossible to combine the speed of cooling and speed drying. At small depths the cooling proceeds faster than on large, because of the increased airflow. From experience, you can make various adjustments: to make starting and operating the fan corresponds to the minimal period of tempering the grain before cooling (4 hours).
Air consumption depends on the capacity of the dryer, not bin size. The minimum air flow rate is 4800 ft3/min, which corresponds to the volume of the heated grain at 400 bushels per hour supplied for cooling in the hopper. Within 24 hours this dryer fill hopper cooling 9,600 bushels (400 bushels per hour x 24 hours). The cooling fan provides airflow at 4800 ft3/min, when the vessel is filled. Whereby the flow rate of air equal to 1/2 cubic meters per minute at full load of the hopper. On the other hand, if you want to skip the dryer is 19,200 bushels, you will need 48 hours to fill the hopper and use the same synchrony with the drying 4800 ft3/min. In this case, the fan delivers 1/4 ft3/min/bushel for the complete filling of the container.
Despite the fact that the perforated floor of the drying hoppers is preferable for cooling, you can use partial decks with the duct system. Important external perforated surface and the size of the pipe, as the air velocity should be sufficiently low to prevent excessive increase of static impact load, and, as a result, reducing the fan performance.
The air velocity entering the grain through the perforated area in square feet should not exceed 25-30 feet/minute and maintained at this level. In the duct system or partial decking, the flow rate of air in any location is moving through the opening, passage or canal, not exceeding 1500-2000 ft/min. Any restrictions are not desirable. They increase speed and create sediments with an additional static pressure.
Additional processing of the granules in case of need
Additional processing of grain in the deaeration process can sometimes lead to difficulties. In the deaeration distinguish 3 main grain operations overload:
-unloading of wet grain;
-the movement of heated grain from the dryer to the tank deaeration;
-the movement of the cooled grain with the hopper de-aeration storage.
There is another operation that can occur. It happens that this unnecessary operation is a repeating operation mode three basic steps in a shorter period of time. For example, remove one or more operations in the process of transferring the cooled grain with the hopper for storage. Avoid long periods of downtime when performing other operations, high speeds are necessary. In other cases, it may be added for additional handling equipment (e.g., second), enabling continuous transmission with a slower pace. Additional transfers of grain can be particularly important in the process of using a single hopper cooling: it is important to quickly clean container to continue the drying. Each installation is individual, but you should consider the transfer of grain in the system deaeration. I note that some components of handling equipment such as augers, decreases (when moving over wet and warm grains). Such grain may not pass through the pipe output at an angle of 45° C. It is able eventually to narrow the passage moving from the dryer into a cooling hopper of grain.
The inner de-aeration system is similar with one exception - slow cooling, where the quenching and soaking grains is not recommended. With storage, heated grain delivered into the hopper with sufficient air flow for cooling. Storage occurs there. If the heated grain is put into a container, and cooling is delayed, as in de-aeration, condensation can accumulate on the walls of the vessel and, in consequence, to get to the product. Ate there will be accumulation of condensate, the wetter the grain, retained within the vessel wall, will deteriorate. The severity of the problem depends on the temperature outside. Cold weather will increase the amount of condensation that leads to large losses when the walls of the bunker will heat up.
For internal storage systems-cooling, fans must submit a greater amount of air to meet the high drying rate. This means that the airflow of the cooling fan or fans is focused on the maximum capacity of the dryer is the capacity of the hopper. The capacity of the dryer increases by 20-40% when in storage there is a cooling. Sufficient airflow is basically the same as for deaeration of 12 ft3/min/ bushel.
For existing silos, equipped with a ventilation system, the volume of the heated grain, corresponding to the capacity of delivery in container for one hour, determines the airflow rate of the fan during aeration. The standard tank provides aeration air flow about 1/10 ft3/min/ bushel filled to capacity. Thus, the cell capacity for storing 12,000 bushels should be purged of air not less than 1200 ft3/min in the case of filling. In the end, heated the grain should be delivered to the container at a rate of 100 bushels/hour (12 ft3/min x 100 bushels/hour = 1200 ft3/min). For the full period of 24 hours it will be 2,400 bushels, and the hopper will be filled within 5 or 6 days. If the container is filled faster than stated, additional airflow for cooling must correspond to the rate of drying. In the case of snap bins aeration duct system for storage and cooling, it is recommended to supply high quality grain in the first tank to protect the problem area between the ducts. For success you need to read the thermometers.
Internal storage-cooling involves the fan start as soon as hot grain enters the bin. The unit must continue its work until the exhaust heated the grain in the upper part of the hopper. As soon as the temperature in the hopper will coincide with the external degree, you can use a fan for aeration. Degree it is advisable to reduce to 35° F in late fall and early winter.
The direction of air flow
For grain storage aeration systems are recommended to provide the movement of air down the bunker and output through the fan. However, for deaeration and chilled storage it is necessary that the air is forcibly circulated up the hopper and withdrawn therefrom. In most cases, the cooling fans operate during the drying and feeding the heated grain in the hopper. When using the upward flow of air to the grain at the bottom of the container is not exposed to heat. When this moisture is removed in the upper parts of the structure, it condenses on the walls and the roof, which is especially noticeable in cold weather. If deaeration is not likely to cause any problems with grain storage, as when moving the cooled mass along the walls of the hopper, the mixing of the grain. Lateral condensation is not terrible if the fans move enough air volume and are run simultaneously with the supply of heated grain in the hopper.
Proper management requires accurate checking of grain moisture before and after cooling, determine the temperature of the heated culture when unloading from the dryer and cooled in the bunker. For monitoring the cooling system using special probe. For this purpose, define the temperature of the cable in the bins, with a volume of 20,000 to 25,000 bushels or more. Indoor and outdoor thermometer consisting of a single Orb, located in the suction air of the upper part of the hopper is a useful device in the control system for cooling. However, low reading on the thermometer does not necessarily indicate the correctness of using the capacity. The grain that is in the upper and Central part of the hopper, will cool last, thus you should check with a special probe. Fan operation may not be suspended until a container filled with heated grain.
Care should be taken when inspecting bins during cooling of hot grain. Hot and humid air coming off the grain can impede proper breathing and eventually lead to excessive dehydration leading to heat stroke. No one needs to infiltrate the bunker under such temperature conditions. Caution should be exercised even standing in front of the door to the bunker, because the metal surface can be slippery and the visibility is low.
To gain experience in the management or control deaeration the cooling system in the vault, you need to check the temperature of the grain immediately after high-speed drying, in the process of getting into the hopper and after cooling. The best way to check the temperature of the grain after high-speed drying is to place the sample in the flask, insert the thermometer and read the information, once the degree is done. The heated grain must be left in the thermos before taking the next sample. This thermos will keep warm for the next sample.
Electrical testers humidity General purpose does not give reliable results regarding the moisture content of hot grain after its diversion from high-speed dryers. To this end, experiments were conducted to determine the level of reliability of the results from moisture meters.
One of the experiments showed that in order to quickly cool the sample heated grains, it is necessary to submit air to the grain with a small fan. Regulation of the level of moisture should occur because a certain part is removed in the process of rapid cooling. The measurement of electrical testers give inaccurate readings on only dried and cooled grain. The correction is carried out on the basis of thorough mixing, duplicate samples: one cooled rapidly and check other well-sealed and put in an airtight container, then cooled for 24 hours, and only then check. A test sample may also be subjected to drying in an oven or subject to Duvel-test (during oil refining).
Check the moisture content of hot grain coming from a dryer, is required to manage the deaeration or in the vault of the cooling system. However, you should also place the grain sample in the container after cooling, to verify that the desired humidity level is reached.
Conversion high-speed dryers
Batch dryers, both automatic and manual mode is suitable for deaeration. In this regard, just missing the cooling cycle and discharge directly after drying. In some staged batch drying, the proportion of heating and cooling in final phase can be adjusted. In these dryers the final stage is the observance of a thermal mode.
Continuous-flow dryers, as a rule, it is very difficult to adjust to the deaeration. Probably the best way of restructuring the majority of continuous-flow dryers is the addition of the block of the burner to the cooling section. This will allow you to use the dryer in the proper order. Internal dryers for cooling, things are different: you need to deactivate the burner in the cooling section. Some continuous-flow dryers can only use one fan for delivering air to heating and cooling. In these dryers the burner may be added to the air flow in the cooling section. Sometimes the removal of partitions between sections of heating and cooling and redistribution of the diverter on the system provide the ability to transform for de-aeration.
In some continuous-flow dryers with 2 fans, especially with high air flow rate (ft3∙min/bushel), positive transformation can be achieved by eliminating the cooling fan and removing the divider between sections of heating and cooling. In the case of poorly vented dryers significantly reduced the rate ft3∙min/bushel. Furthermore, since the airflow of the fan for drying will be increased, the burner output may not be consistent.
In all situations the transformation of continuous-flow dryers for de-aeration must be carried out only by the manufacturer or by agreement with the manufacturer. The manufacturer is obliged to provide you with recommendations on the dryer, its performance and security in operation after conversion under deaeration.
The problems of condensation
In the case of a deaeration and cooling the heated storage the grain should move auger out of the pipe high-speed drying. Condensation can occur in this equipment, especially in cold weather. The condensate in the line to the Elevator can drain down the tank and freezing. The equipment must be constantly monitored to serious accumulations of condensate. Periodic cleaning of the pallet Elevator, hopper and other equipment will help minimize these problems.
When heated grain is fed through the pipe, the warm moist air moves up and condenses. This condensate may back down and get into the bunker. If condensation occurs in the beginning of the Elevator, she is able to get into the other containers through the feed tube of grain. Manual or controlled valve on the end of the pipe near the hopper can prevent the movement of air up the pipe, and means to resolve the issue with kondensirovannye.
The problems of condensation in the pipe can be eliminated by installing exhaust fans in the roof of the bunker. They will move from 25 to 50% more air (1/8 to 1/4 inch of water at a static pressure) than the cooling fans. Drawing in the upper part of the hopper, will operate under slight negative pressure (1/8 to 1/4 inch of water) and to provide slight suction warm moist air moving up the pipe.
Another solution may be to keep the pressure in the pipe, using a small fan that has an impact on a stream of air, sending her down to the bunker.
Note: corn is dangerous!
Never enter the hopper with grain or other storage when it is loaded.
The movement of the grain occurs with such speed that the asleep man of medium height in just a few seconds and leads to suffocation.