The invention relates to a drying plant for the drying of organic products, particularly agricultural products, and of the kind disclosed in the preamble to claim 1.

It is well-known to use drying plants for the drying of various agricultural products, e.g. grain and vegetables. Such drying plants are very energy- demanding, which naturally applies especially to plants arranged for the drying of green crops with very high water content. Therefore, the very high energy prices make it attractive to produce a drying plant with less energy comsumption per evaporated ton of water, while at the same time avoiding some of the

-inconveniences involved with the known kinds of drying plants. The inconveniences arise in connection with the varying water content of the harvested crops and the varying discharge amounts resulting herefrom. At low rates of discharge, the variations in the discharge amounts result in the binding of dust particles in the discharge system, which gives rise either to reduced plant capacity or stoppage for cleaning of the discharge system.

It is a commonly known technique to use a rotating drying drum which is fed at the one end with heated air and the product which is to be dried, and where at the discharge end there is provided a drop-vessel for the separation of the material by means of a ventilator for the removal of drying air with particles. Usually, the particles are separated from the drying air with a cyclone.

It is also known to control the amount of drying air to the drying drum with automatic or manual dampers.

However, the disadvantage is a small range of regulation when it is desired to avoid condensation in the discharge channel. There are quite narrow limits for how low the discharge rate can be to avoid the build up of coatings and stoppage when the discharge air is wet and filled with dust.

It is therefore common practice to operate with maximum air speed and maximum temperature, regardless of the moisture content of the product to be dried, and regardless of the amounts which are to be dried. Frequent stoppages for cleaning of the discharge system are hereby avoided, but the resulting energy economy is very poor.

From German patent publication no. 2,650,919 is known a drying drum plant for highly water-containing pro¬ ducts where a part of the dried product can be recirculated, hereby obtaining an end-product with certain characteristics. The plant comprises one or more presses from which the oilcakes are led to a drying drum, from where the discharge air is led to a cyclone battery comprising a number of cyclones connected in parallel. There is no doubt that one can hereby obtain a desired end-product with certain particle size and degree of moisture, but this is achieved with a relatively high energy consumption, in that parts of the product are recirculated in order to control the drying process as desired.

The object of the invention is to provide a drying plant of the kind disclosed in the preamble to claim 1, which both reduces the consumption of energy and the number of stoppages for cleaning of the discharge system, and where the plant obtained can be adjusted for the drying of widely different crops. This is achieved by configuring the plant according to the

invention as characterized in claim 1.

By coupling that number of discharge pipes with each their dust separation element, corresponding to that amount of water which is to be dried off, a sufficient air speed is always achieved so that condensation is completely avoided and the desired drying is achieved. The plant can be adjusted either for grain, which is normally dried down to 3-10%, or for vegetable crops which are to be dried down to 70- 90%. The plant never uses more energy than that which is precisely necessary to remove the water in the product to be dried. Consequently, a good energy economy is achieved, regardless of which product is treated by the plant, and it is not necessary to recirculate parts of the dried product to control the drying process.

Moreover, the capacity of the plant becomes adjustable, which is a great practical advantage, even though the greatest advantage is probably that the plant can be used for any kind of comminuted organic product which is required to be dried down.

By configuring the plant according to the invention as disclosed and characterized in claim 2, it is ensured that the discharge air is constantly under full control, also after the dust or particle separation element. This is particularly important by the drying of crops with a very high dust content where there will still be a small amount of dust left, also in the discharge air after the dust separation element.

The discharge air from the dust separation elements can be fed to their individual discharge pipes, but is preferably fed to a common discharge pipe as

disclosed and characterized in claim 3. This simpli¬ fies a possible final cleaning of the discharge air, e.g. of motes of dust, in that a chimney filter can be used or dust-burning can be effected.

The plant according to the invention can be configured as disclosed and characterized in claim 4. This results in a very efficient cleaning of the discharge air. A cyclofan is a cyclone with its own ventilator and ejection device for the collected mass of particles.

Finally, the plant according to the invention can be configured as disclosed and characterized in claim 5, whereby it is a simple matter to ensure constant flow rates in each discharge pipe, all the way from the drop chamber to the chimney. The individual discharge pipes do not, however, need to have the same capacity or cross-sectional area in order to achieve the desired effect. For example, it is quite possible to have a discharge pipe of 50m ³ air/minute together with two discharge pipes of 100m ³ air/minute each and a discharge pipe of 200m ³ air/minute, thus providing the possibility of a suitable number of combinations between 50m ³ air/minute and 450m ³ air/minute. It is naturally also possible to have a number of completely identical discharge pipes, which simpli¬ fies the production of the plant and minimizes the number of spare parts.

The invention will now be described in more detail with reference to the drawing, which shows a functional diagram of a plant according to the invention with four discharge pipes, each with its own cyclofan.

In the drawing, the reference figure 1 indicates a

heating apparatus, e.g. an oil burner or a gas burner, in connection with a stationary oven 2 which supplies hot air to a drum drier 3 with inlet pipe 9 for the product to be dried. The product to be dried can be grain, vegetable crops or any other crushed or comminuted product with a certain water content which is desired to be dried off, either partly or completely.

The discharge end of the drum drier 3 leads into a discharge housing 4, from the bottom of which the dried products are removed by means of a conveyor 5, and from the top of which the discharge air is removed.

The drawing shows schematically that from the top of the discharge housing there are provided four discharge pipes 11 leading to their individual cyclofans 6, and that each cyclofan has a disharge pipe 10 leading to a common chimney 7.

In the upper left-hand side of the drawing, it is also shown schematically that it is also possible for the discharge pipes 10 to extend from each cyclofan 6 to individual chimney pipes 8.

Each discharge pipe comprising discharge pipe 11, cyclofan 6 and discharge pipe 10 or 10 , is arranged in such a manner that the velocity of the discharge air and the separation of the particles can be maintained without condensation of the discharge air, which would bind the particles to the walls of the pipes.

The number of cyclones in operation is adjusted to suit the production and the amount of water in the material which is desired to be dried off. The

ventilator and conveyor systems with dust or particle separation elements can be operated individually and regulated separately, e.g. by start-stop regulation and also by cascade regulation.

There is hereby obtained a plant which can be used for the drying of various crops with widely varying moisture content, and the energy savings achieved in comparison with known kinds of plant will usually be greater than 10%.