CS271372B1 - Method of inset fluidization drier control for sodium carbonate's higher hydrates drying - Google Patents

Abstract

The rate of airflow through the drier, the temperature of the solid phase in the drier and temperature differences between the temperature of granular phase in the layer and the temperature of drying air are measured. The temperature of the incoming drying air is regulated on the basis of the required speed of drying, respectively on the basis of the required product of the temperature difference and airflow. The maximum allowable temperature in the fluid layer is defined. The end of the drying is indicated by the abrupt change of the temperature difference under the defined limit and the created dry substance contains the maximum dihydrate of sodium carbonate.

Description

The invention relates to a process for controlling a fluidized bed dryer for drying higher sodium carbonate hydrates NagCOyxHgO, wherein x is a number of 5 to 10 to active sodium carbonate. This product is a suitable means for desulphurization of flue gases or other fumes containing sulfur oxides.

Drying is a diffusion operation. The drying rate is proportional to the driving force and the drying air flow. From an economic point of view, it is advantageous for the drying rate to be maximized as operating costs are reduced. However, from a physical point of view, the drying rate is limited by the particle size and the melting point of the crystals. There are conditions where drying is energy and therefore economically acceptable. Obviously, in increasing the flow rate above the minimum flow rate, the heat consumption required to heat it increases. Most of the wet granular material when dried in a fluidized bed apparatus behaves in such a way that the layer initially channels and forms irregular geysers until the surface water dries and the material stops sticking. This condition is undesirable because it negatively affects the speed of the process and can be countered, for example, by mechanical agitation or a special grate arrangement. An example of such a grate is a wound grate according to the art. A.O. No. 126,062. This type of grate is particularly advantageous for drying granular and crystalline materials that are very wet and adhere.

When drying crystals of higher sodium carbonate hydrates, the moisture content and hence the specific weight change. The consequence is that the fluid characteristics of the material vary. It is also problematic to finish drying, especially in cases where the required humidity is to be achieved.

Currently, crystalline, respectively. the granular materials dry so that at a constant flow rate and temperature of the drying air, respectively. air / flue gas mixture, the material remains in the apparatus for a given period of time,

In some cases, the drying is controlled so that the temperature of the fluidized bed is constant, respectively. changed according to the prescribed algorithm. This must then be determined empirically independently. The disadvantage of this method is that changing the initial moisture content of the material affects the drying time, and this must be respected by the algorithm. This results in energy losses and operating times.

It has now been found that by measuring the air flow temperature difference between the temperature of the fluidized bed and the temperature of the drying gas, it is possible to optimally control the batch fluidized bed dryer for drying higher sodium carbonate hydrates. both. Air flow measurements can be made using conventional commercial sensors. Temperature measurement, resp. the temperature difference must be made with a sensor whose time constant is not more than 5 seconds.

• The actual control of the dryer is carried out by adjusting the air flow rate to two to three times the threshold rate of sodium carbonate decahydrate fluldation after the material is metered in, and adjusting the temperature difference by heating the drying air. The drying time varies from two to four hours depending on the drying speed and the drying speed. on the product of air flow and temperature difference.

For the use of sodium carbonate as the active sorbent sulfur oxides from waste gases need _м that the water content in a molar ratio of at most 2, based on sodium carbonate.

It has been found that under these conditions the drying rate decreases sharply and on this basis it can be considered as terminated in terms of the technological operation.

The advantage of the process according to the invention is the high intensity of drying of the water of crystallization from sodium carbonate hydrates and a reliable indication of the end of the operation regardless of the input moisture of the material.

The following example illustrates the process of the invention.

Example

Sodium carbonate decahydrate having a particle size of 0.2 to 0.5 mm containing two moles of surface water. was dried in a 0.15 m oven equipped with a mechanical stirrer at a flow rate of 40 ΝπΡ / h. The temperature difference was measured by two resistance thermometers, whose time constant was 3.3 s. The temperature difference was maintained at 35 ° C by controlling the drying air temperature. After 140 minutes, the drying air temperature reached the permissible limit of 100 ° C and the temperature difference began to drop sharply. This signaled the completion of the operation and the resulting active sodium carbonate was discharged from the oven.

It was then subjected to a standard sulfur sorption sorption activity test and the solid phase conversion was found to be 94.2 wt%.

Claims (2)

A method for controlling a batch fluidized bed dryer for drying higher sodium carbonate hydrates, wherein the air flow through the dryer is measured, the solid phase temperature in the dryer and the temperature difference between the granular phase temperature in the bed and the drying air temperature, characterized in based on the desired drying rate, respectively. the desired product of the temperature difference and the air flow, the maximum allowable temperature in the fluidized bed being determined. 2. 6. The method of claim 1, wherein the end of the pounding is indicated by a rapid change in temperature difference below a predetermined limit, and the resulting dry matter comprises at most sodium carbonate dihydrate.