E-MAK dryers provide the most efficient aggregate drying and heating due to the special design blades within the dryer which creates optimum heat transfer surface and guarantees minimum fuel consumption.
In asphalt plants, the aggregate must be heated to a temperature of approximately 160°C to ensure a good and homogeneous mixture.
E-MAK dryers are made of materials resistant to deformation and wear. The body and drive rings are held together with using bolts only (no welding) which helps to avoid the defects due to high and sudden temperature changes. Dryer rings and rollers are made of special, long-lasting forged steel. Insulated with rock wool and made of stainless steel, outer body consists of non-welded compensation springs that are easy to replace. With the help of these compensation springs the body load is distributed evenly and the body becomes flexible enough to meet the thermal expansions.
The special design inside the dryer is composed of easily changeable blade structure with different alignments and angles available. Since the burner flame travels longer inside the dryer, aggregate can contact with hot air and hot surface longer. Thus, it can effectively heat up and dry. There is a pre-combustion chamber that protects the inner surface of the dryer, preventing direct contact with the burner flame.
The exhaust gas emission values can be checked thanks to the vacuum control system and special wing structure. Soft starter or inverter in the driving system can restart the mechanism even if the plant is loaded. Burner options with different fuel alternatives can be adjusted automatically depending on the moisture of the aggregate and the amount entering the dryer.
There are two basic types of dryers. They are given names considering the reciprocal flow directions of the aggregate and the air inside the dryer. The drying principles of both dryers are the same. In parallel (co-current) flow dryers, aggregate flow and air flow are in the same direction. The flame and the cold aggregate enter the dryer through the same nozzle, and the materials are directed towards the exit direction.
In counter-current dryers flame and aggregate are given from different nozzles. The aggregate moves against the air stream and leaves the dryer. Counter-current dryers are mostly used in batch type plants while parallel flow dryers are used in continuous type plants. When compared, counter-current dryers perform better heat exchange than parallel flow dryers.
The drying process is the costliest stage in hot-mix production as the consumption of the fuel is the greatest. The dryer capacity is specified for a certain amount of moisture (generally 5% ). If the moisture content of the aggregate is above the given value, it is necessary to reduce the amount of the aggregate directed to the dryer for a better drying and heating. Moreover, the temperature and the type of the mixture to be produced affect the performance. The two most important factors affecting the performance of the asphalt plant are the drying and heating processes.
Whether the determined capacity is suitable for the production or not is determined by humidity controls. These controls are carried out rapidly to avoid delays in the production. There are two methods to do that. One is to check whether there is moisture in the aggregate taken from the dryer outlet in vapor form. The second is to move a dry and reflective object at a certain height over the aggregate pile and see if there is any condensation on it. If there is condensation on it, it means that the aggregate is not completely free of moisture.
For the dryer to operate effectively, the air and the fuel directed to the burner must be proportional. Combustion problems are rarely encountered in dryers operating with natural gas or liquid petroleum. The first unit that determines the performance of an asphalt plant is the dryer. The basic functions of the dryer, getting the aggregate to the desired temperature and dehumidification, are the two basic processes that must be strictly controlled for an error-free production in an asphalt plant.
Adjusting the temperature of the aggregate and that of the mixture is closely related. Bituminous binder added to the aggregate takes heat from the aggregate. Overheated aggregate leads to a decrease in the quality of the mixture due to the fluidization of the bituminous binder. On the other hand, mixing the aggregate that is not heated enough with the binder will result in a mixture with low processability. In continuous type plants, there is one thermometer inside the dryer to control the aggregate temperature whereas in batch type plants there are two of them, one at the exit of the dryer the other in the hot bunkers. In continuous type plants, the thermometer inside the dryer is also affected by the hot air inside the dryer, so the measurement may not be accurate. For this reason, measurement in batch type plants generally gives sharper results.