CS210876B1 - Method for drying of grain material - Google Patents

Description

The invention relates to a method for drying granular material in a system in which heat and mass (moisture) transfer between the granular material in a fluidized or crushed layer and a preheated drying gaseous medium is effected and wherein the gaseous medium passes through the path after leaving the granular material layer. where the dust particles of the granular material are separated off and in which heat is transferred from the gaseous medium to the surroundings of the system.

Fluid drying is very often used to dry granular materials, possibly slurries, or to evaporate solutions. It is usually arranged in such a way that the drying medium sucked in by the fan is preheated in a heat exchanger or mixed with the flue gas and is then contacted with the material to be dried or the agitated mechanical finer in a drying chamber which flows downwards. The flow rate of the drying medium is usually at a multiple of the threshold fluidization rate, sometimes - for example, with larger particle size distribution of the granular material - working near the fluidization threshold.

In some cases, the pressure loss is lower than the fluidization threshold, with partial fluidization and partial fining of the material. The periodic or continuous drying arrangement is chosen according to the nature of the whole technological set. During periodic drying, the practically constant temperature of the drying medium exiting the material layer stabilizes first, - the period of decreasing drying rate - its temperature increases. The outgoing gas is practically saturated with water vapor in the first phase.

When drying the granular materials, the drying medium exiting the material layer carries with it dust particles which are separated from it by the drying system, usually in cyclones. Therefore, it is not possible to evacuate the gaseous medium from the drying system 210876 immediately after the layer of material and this medium passes through a relatively long route before leaving the system. Sometimes the length of this route is influenced by the design parameters of the whole technological set.

If the gaseous medium exiting from the material layer is practically saturated with water vapor, water vapor may condense along this path and the run-off condensate will cause clogging of the cyclone and an extension of the first phase of periodic drying, respectively. extending the necessary residence time of the material in continuously operating drying systems. This disadvantage is overcome by thermal insulation of the route and cyclones. Despite this, however, especially during periodic drying, water vapor condensation and thus the drying process is adversely affected.

This lack of drying of the granular materials eliminates the method of drying the granular materials of the present invention. This method consists in discharging the condensate produced by the condensation of water vapor from the gaseous medium as it passes through the path between the surface of the granular material layer and the outlet of the drying system. In this case, the water condensate is separated above the drying chamber and / or above the cyclone according to the arrangement of the drying system.

The process according to the invention completely prevents condensate from being returned to the dried material layer in the drying chamber and cyclones. The means described so far can only be achieved by selecting suitable process conditions in which the gaseous medium exiting the layer of granular material has a low moisture content. However, such a solution is inefficient since it assumes a low layer of granular material β a high flow rate of the preheated drying medium. The process according to the invention reduces the drying time, in some cases by up to half or more. The process can be used for both periodic and continuous drying, especially when working with a higher layer of granular material around the fluidization threshold.

An example of nucleate with a rake having an inside diameter of 1.6 m and a height of 0.8 m, provided with a perforated bottom coated with a sieve, is placed 550 kg of wet pearl styrendivinylbenzene copolymers and dried with an air flow of 105 ° C and constant flow under the sieve. mixing the copolymers with a scraper. Air and drift pass through a 300 mm diameter steel duct to a cyclone located 15 m above the nucleate, and air from the cyclone exits through a 10 m diameter duct that forms the exit of the drying system. The pipe is insulated with a 50 mm layer of glass wool and a 10 mm layer of concrete screed.

At the beginning of drying, the air temperature is stabilized at 35 to 40 ° C over a layer of copolymers (measured 0.3 m above the nucleate), after which time the temperature begins to rise. Condensate collectors are placed on the pipeline from the suction to the cyclone at a height of 1.0 m above the nucleage and the cyclone from the system at a height of 0.6 m above the cyclone, from which the condensate is discharged outside the pipeline).

The duration of the constant drying rate period is:

(a) in the case of no condensate drain

b) in the case of condensate drain

Claims (1)

SUBJECT OF THE INVENTION A method of drying granular materials in a system wherein heat and mass transfer between the granular material in a fluidized or thinned layer and a preheated drying gaseous medium such as air, air / flue gas mixture, nitrogen or other inert gas occurs, and wherein the gaseous medium upon exit The layer of granular material passes through a path where dust particles of the granular material are separated and where heat is transferred from the gaseous medium to the surroundings of the system, characterized in that the condensate formed by condensation of water vapor from the gaseous medium layer of granular material and the outlet of the drying system is discharged off this route.