what is a drum dryer?
A drum dryer is a rotating cylinder that uses steam or hot air to heat feedstock and reduce the moisture content during a manufacturing process. The configuration may include one or more drums. A drum dryer may use atmospheric pressure or function under a vacuum. Drum dryers have many applications in the food industry because they are very efficient for drying pastes or gelatinous materials.
In the simplest configuration, a single drum dryer is supported on a frame so it can rotate on its axis. Steam is forced through the inside. A thin layer of feedstock is then applied to the outside of the drum. As the temperature rises, the moisture in the feedstock reaches boiling point, begins to evaporate, and leaves the feedstock. The dried layer of feedstock is removed from the drum with a scraper.
Depending upon the products it will be processing, a drum dryer is typically made from cast iron or stainless steel. The length of time the feedstock remains on the drum depends on the original moisture content and the desired ending moisture content. The range is usually between a few seconds and half a minute. Feedstock may be applied to the drum dryer by rollers, dipping the lower edge of the drum into a tray of feedstock, or spraying it on to the drum surface.
A double drum dryer consists of two drums mounted side by side and rotating toward each other. The layer of feedstock is controlled by the distance between the two drums. Feedstock is applied to the two drums from above. This configuration can increase production capacity.
If the feedstock is subject to damage from excess heat, a vacuum drum dryer may be used. The entire drum is encased in a vacuum chamber where air can be evacuated; this reduces the boiling point, and the drying can be accomplished at a lower temperature. Vacuum systems are more expensive to operate and are more commonly used for higher value products such as pharmaceuticals.
Another type of rotary drum dryer is a double or triple pass system. In this configuration, the drums are nested one inside the other. The feedstock is introduced to the innermost hottest drum and is moved along with channeling flights mounted to the drum interior and with hot air. After the feedstock loses a certain amount of moisture, the air flow carries it to the next drum, which is cooler, where it continues to lose moisture. If there is a third drum, it is even cooler with slower air flow, thus continuing the drying process while protecting the feedstock from heat damage.
rotary dryer design & working principle
For evaporating moisture from concentrates or other products from plant operations, Rotary Dryers are designed and constructed for high efficiency and economy in fuel consumption.Whenever possible to apply heat direct to the material to be dried, Rotary Dryers of the Direct Heating Design are used. If it is not possible to apply heat direct to the material to be dried, Rotary Dryers of the Indirect Heating Design can be furnished so that the heated gases will not come in direct contact with the material.
Rotary Dryer is a simple, inexpensive unit for reducing the moisture content of flotation concentrates, as well as chemical and industrial products. Frequently the saving of shipping weight so effected will pay for the dryer in a few months. Difficulties from freezing while in transit are also eliminated. Many industrial projects are now using Dryers for control and production purposes on many materials.
Three main types of Rotary Dryers can be supplied. The direct heat unit is used when it is permissible for the drying gases to come in direct contact with the material being dried. Partition plates increase the heating surface. Drying may be by hot air or exhaust gases from other operations. If this drying gas has a deleterious effect on the product, then an indirect type of dryer can be supplied. A further derivation is the Tedrow Steam Dryer.
Of the different types of dryers that there are the most common is the ROTARY DRUM DRYER/Kiln, This type of drier is common not only in the mining industry but you will find them in fertilizer plants, Cement plants, and peat hogs to name but a few.
The theories behind these machines are very simple, heat an air space up, and then tumble the material to be dried through this space until it is dried. All though it sounds simple there are problems that have to be solved before the required results are met. But first, so you know what we are talking about lets go through the design of a drier.
First is the KILN, this provides the heat, The BURNER is inside this portion. The fuel for the burner is usually diesel although heavy crude oil could be used in some cases. To be able to generate enough heat to dry the concentrate air must be added by way of a BLOWER.
In front of the kiln is the point that the wet concentrate enters the drier. It is put into the revolving SHELL. The shell is on a slight incline. As the Concentrate is tumbled through the hot air mass of the drier it travels down this incline to the exit of the drier.
At this exit point the concentrate is either deposited straight into a storage area or taken to the storage area by a conveyor. It is also at this point that there is an EXHAUST HOOD. This provides a controlled escape passage for the fumes and water vapor that is generated by the concentrate drying. This is a very important function and the operator will have to be sure that it is open at all times. If it should become blocked the water vapor will not be able to escape. The concentrate will become wet and sticky which will result in the discharge plugging. The wet sticky concentrate will also lower efficiency level of the drier for an extended period of time.
This happens because inside the drier shell are what are termed FLIGHTS these are flat pieces of metal that are bolted onto the shell.
They are there to lift the concentrate up to the top of the shells rotation and drop the concentrate through the hot air. If the water vapor isnt taken away, the concentrate becomes sticky from reabsorbing the water.
This sticky concentrate will fill the spaces between the flights.
The concentrate will not be lifted and dropped through the hot air. This results in a long term condition of poor performance even after the initial problem has been cured. These flights will remain buried in concentrate.
This removal of the water vapor is one of the functions of the blower. It assists the natural process of air movement as the hot air mass expands.
To prevent the buildup of concentrate on the flights there are often CHAINS attached to them. As the drier revolves the chains slap the flights preventing concentrate from building up on dryers walls.
The drier shell is rotated separately from the stationary kiln section. To achieve the rotation a BULL GEAR is attached around the shell section. There are also two flat rings attached to the shell. These provide surfaces for support rollers to roll on. There is another problem that the inclined shell has, the incline causes the shell to want to slide in the direction of the incline. To prevent this additional rollers are attached to the last set of rollers.
rotary drum dryer drying system, working principle and details
Rotary dryer or rotary drum dryer is widely used to dry humidity granularity materials in the industries of mineral dressing, building material, metallurgy and chemical, coal mining, etc. Wide supply scope and simple operation are itsmain features, materials should be dried to 3-10% water content tomeet the demands forbriquetting.
The material is fed in the rotary drum dryer by the conveyor, and whenits coming through the cylinder, the hot air will flow from it and makes it dried,. The dried material will be collected at the output.
In this drying process, the material will move as the cylinder rotation. With the gravity, the material will fall from high-end to low-end. There are also copy boards in the dryer to raise the material, so that the material and hot airs contact surface area increases, which helps to increase the drying rate and let the material forward.
1. At the input area, the hot air is much higher than the raw material which leads a rapid heat exchange between the hot air and the raw material,moisture becomes easy to evaporate. This heat way is suitable for high moisture materials.
2. For the viscous materials, when it feeds into the dryer, as the rapid waterevaporates, the moisture down and helps to reduce the bonding rate, the easier-move material increase the drying efficiency.
rotary dryer: operating principle, classifications, uses, advanta
The rotary dryer also known as tumbling dryer is an equipment employed to minimize the moisture content of feed materials by bringing it in direct contact with a heated gas. It consists of an inclined long drum or cylindrical shell often fitted with internal flights or lifters; rotated slowly upon bearings through which the material to be dried flow with a tumbling/cascading action in concurrent (for heat-sensitive materials) or counter-current flow with the heating air or gases.
The movement of the material is due to the combined effect of inclination of the shell to the horizontal and the internal tumbling action or mechanical turn over thus the name tumbling dryer. The nature of the feed determines the directions of gas flow through the cylinder and it is relative to the solid. This drying equipment can also perform batch or continuous processing of the wet feed.
A rotary dryer is said to be of the direct type if, by virtue of its design, heat is added to or removed from the solids by direct exchange between the gas and solids. The direct heat dryers are the simplest and the most economical class. They are used when direct contact with the hot gas or air is not detrimental to the fed.
When high temperature is required for the drying process in a direct-heated rotary dryer, a combustion chamber is used and when low temperature is required on the other hand, for thermolabile materials, steam coil is used.
Although there is an infinite variation of rotary dryers, which present characteristics suitable for drying, chemical reactions, mixing, solvent recovery, thermal decompositions, sintering and agglomeration of solids, the main types of rotary dryers include;
1. Excessive entrainment losses in the exist gas stream is possible especially if the material contains extremely fine particles due to the large gas volumes and high gas velocities that are usually required.