DE102005036945B4 - Automatic control of the additive addition in Feinstzerkleinerungsprozessen - Google Patents

Abstract

method for automatic control of additive addition in Feinstzerkleinerungsprozessen, characterized in that the with increasing viscosity changing Back pressure in the grinding container is measured and depending to a predetermined pressure value, the control of the additive addition takes place.

Description

The The invention relates to an automatic control of the additive addition in Feinstzerkleinerungsprozessen.

In the case of comminution processes with products in the range of particle size smaller than 1 μm, particle-particle interactions in many cases lead to agglomeration phenomena. Despite stress and energy input into the mill, the agglomeration can not be prevented but is accompanied by the increase in the measured product fineness. This phenomenon can be avoided by the targeted adjustment of the surface charge or by the adsorption of suitable molecules on the surface of the product particles. To implement this product stabilization, therefore, the addition of additives is required. An overdose of these additives can lead to spontaneous agglomeration phenomena or to increased wear in the mill. The addition of the additives takes place in practice as far as possible empirically gained experience, such. B. in the DE 44 11 105 C1 described.

The The object of the invention is the agglomeration of particles to prevent the crushing process by increasing the viscosity of the monitored processing products in stirred mills and adjusted.

Is solved This object is achieved by the features of claim 1. Further developments The invention will become apparent from the dependent claims of the invention.

According to one preferred execution method is the back pressure in the grinding container measured, depending on to a predetermined pressure value, the control of the additive addition takes place.

Corresponding Further advantageous embodiments of the method is the Addition of additive continuously or discontinuously or in the storage container.

The amount of additive that must be added continuously or discontinuously is through the control unit 20 regulated. Since the amount added depends in particular on the Mahlgutviscosity, the pressure associated therewith in the grinding container at the Mahlbehältereinlaß is measured as back pressure. The pressure value is then passed as an electrical / electronic signal to the reservoir, which adds the additive to the Mahlbehältereinlaß. The treated regrind passes through a separator 22 who is the product spill 24 connects, from the agitator mill.

The operation of the agitator mill can, as in 3 shown, take place in circulation operation with a reservoir or with another agitator mill or else in Einpassagenbetrieb. To increase the size reduction grinding media Mahlkörper are provided in the grinding, the diameter of which depends on the desired product fineness.

For the example of the real comminution of Al ₂ O ₃ particles with electrostatic stabilization are in 1 the pH value, the ζ potential and the median value of the particle size distribution over the specified specific energy. The pH was controlled to a constant value in each series of experiments. Show this 1 the influence of the pH on the ζ potential and the reduction progress (ζ potentials and x _50.3 : DT 1200 measurements).

In spite of very different pH values of the product suspension were almost identical courses of the ζ potential determined. Cause for it is that for the regulation of lower constant pH values requires a larger amount of acid, the stronger increasing conductivity and the stronger ones that follow Compression of the electrochemical double layer.

It can be seen that, apart from comminution without stabilization and comminution at pH 9, the pH of the product suspension up to a specific energy of about 100,000 kJ · kg ^{-1 has} no influence on the comminution result or the agglomeration state, ie, for example, to produce a product particle size of 80 nm, stabilization at pH 8 is sufficient. At specific energy inputs greater than 100,000 kJ · kg ^-1 , however, the measured comminution progress stagnates at pH 8, while at smaller pH values a further decrease in the comminution particle size is detectable.

In another series of experiments, the pH was first adjusted to pH 8 and only after a specific energy input of 30,000 kJ · kg ^-1 down to a specific energy input of 150,000 kJ · kg ^{-1 down} to pH 5. There is no change in the ζ potential curve. However, re-agglomeration phenomena in the range of specific energy inputs of around 500,000 kJ · kg ^{-1 can} be avoided (cf. 1 , variable).

Depending on the pH of the millbase suspension, investigations at the Institute of Mechanical Process Engineering of the TU Braunschweig and at the Chair of Solid and Interfacial Process Engineering of the Technical University of Munich also showed a stagnation of the reduction progress at specific energy inputs greater than 100,000 kJ · kg ^-1 . Was the pH at the end of the crushing experiment, z. B. adjusted from pH 8 to pH 5, identical median values of the particle size distribution were again determined at the same energy inputs. These results show that the pH of the millbase suspension only influences the agglomeration state of the suspension and that the stagnation of the comminution progress frequently measured in industrial practice is due to reagglomeration phenomena.

In 2 the shear stress is plotted against the shear rate for various suspensions which were subjected to different pH values for 8 hours each with otherwise identical operating parameters. As the pH increases, the viscosity of the suspension increases. At a pH of 5, the lowest and at a pH of 10 is the highest viscosity.

In the 3 illustrated device combination consists of a stirred mill 2 whose stirrer shaft 4 with a drive 6 communicates. On the stirrer shaft 4 are disc-shaped grinding elements 6 arranged. The stirring shaft 4 is horizontal in a grinding container 8th Arranged with a lining 10 is provided. The enema 12 to the agitator mill is via lines with a supply tank 14 connected. In the supply tank is a mixer 16 provided that mixes additives to the millbase. The additive passes through a reservoir 18 in the supply tank. The additive serves to stabilize the agglomeration state. For this purpose, two different additives for an electrostatic and other steric additives can be used. By electrostatic additives are meant acids, bases such. As citric acid, acetic acid, nitric acid or sodium hydroxide solution. By steric additives are meant long-chain, usually organic molecules, polymers and surface-active substances, such as polyacrylic acid and polycarboxylic acid. Equally possible is the use of combinations of both types of additive.

Claims (8)

Method for the automatic control of additive addition in Feinstzerkleinerungsprozessen, characterized in that the increasing viscosity with increasing viscosity is measured in the grinding container and in dependence on a predetermined pressure value, the control of the additive addition takes place. Method according to claim 1, characterized in that that the Additive addition takes place continuously. Method according to claim 1, characterized in that that the Addition of additive is discontinuous. Method according to one of claims 1 to 3, characterized that the Additive in the reservoir he follows. Method according to one of claims 1 to 3, characterized that the Additive addition in the inlet area the agitator mill is done. Method according to one of claims 1 to 3, characterized that the Add additive directly into the grinding chamber through one or more additions he follows. Method according to one of claims 1 to 6, characterized that the Addition of additive takes place with decreasing particle diameter of the millbase. Method according to one of claims 1 to 5, characterized that the Additive depending on From Mahlkörperverschleiß done.