SK40997A3 - Method for the continuous production of precipitated calcium carbonate - Google Patents

Abstract

A process for continuous pptd. calcium carbonate prodn. comprises carrying out carbonation in series-connected cells, the supply of gas and slurry and their dispersion being effected by providing each cell with a gas and slurry feeder (2) with an integrated stirrer (RW).

Description

Process for the continuous production of precipitated calcium carbonate

Technical field

The invention relates to the continuous production of white pigment (calcium carbonate) using calcium hydroxide and carbon dioxide gas according to the equation

Ca (OH) + CO, <-> CaCO, + HO

2 3 2

BACKGROUND OF THE INVENTION. The prior art is limited to grinding natural calcium carbonate (marble, chalk) or inventions for the production of precipitated calcium carbonate by series processes.

Another method produces step-precipitated calcium carbonate by injecting a low-concentrated, white calcium hydroxide slurry into a CO ₂ gas stream, which is inside a downstream spray tower.

SUMMARY OF THE INVENTION

The technical task to be solved by the invention for continuous production is characterized by a process of gradual carbonization in serially connected cells until the calcium carbonate is reached, whereby the gas supply and slurry as well as their dispersion (Fig. 1) are carried out such that each cell has a gas supply device 2 and a slurry supply device 1 with an integrated stirrer 4.

For the broad industrial use of precipitated calcium carbonate (PCC), besides stability, achieving the desired grain size and distribution as well as the production of certain crystal forms is very important.

The method allows for crystal forms that are predominantly desired by users of calcite - rhombohedral and scalenohedral aragonite acicular

Calcite requires, as is known in the literature, reaction temperatures below 30 ° C, with scalenohedral calcite occurring at temperatures of 25 to 28 ° C and rhombohedral calcite only occurring at very low temperatures. Aragonite needs higher temperatures, preferably 30 to 36 ° C.

Acceleration of the starting times is achieved by filling the first cell with 2/3 of the carbonate having the desired crystal shape and immediately introducing the flue gas together with the start of the hydroxide flow.

Carbonation is achieved at a CO ₂ concentration in the flue gas of 10%. The duty block performance is proportional to the CO ₂ concentration. The grain size is affected by the hydroxide suspension, the flow rate and the excess flue gas.

An example of an embodiment of the invention

The invention claimed herein, shown in FIG. 1, it is composed of one to several blocks with square cells with a minimum content of 340 liters per cell, depending on the required power.

Each cell J has a special stirrer 4 for dispersing the hydroxide slurry with the flue gas.

For this purpose, a combined gas supply and slurry tube 2 is connected by a flange via a stirrer shaft 4 centric on the engine.

The stirrer 4 produces a certain negative pressure which permits both the introduction of gas at a minimum pressure and, on the other hand, enhances circulation within the cell.

This combination provides a dispersion that allows the reaction between the hydroxide and the gas at the lowest power of the stirrer 4 (1.5 kW). Hydroxide enters from one cell J through the glass tube 1 without pressure into a tube 2 combined for the gas supply and the suspension of the nearest cell 2. Carbonation is controlled by the amount of flue gas or flow rate as well as the adjusted hydroxide concentration.

Claims (5)

Method for the continuous production of precipitated calcium carbonate, characterized in that the carbonization is carried out in serially connected cells, the gas and suspension being supplied as well as dispersing them (Fig. 1) so that each cell is equipped with a device 1 for gas inlet and slurry inlet device 2 with integrated stirrer (RW). Method according to claim 1, characterized in that cells whose plan is square and the height is at least 1,000 mm are used. Method according to claims 1 and 2, characterized in that the arrangement of duties is block, the number of targets and blocks being given by the capacity of the device. Method according to claims 1 to 3, characterized in that scalenohedral calcite is produced at temperatures below 28 ° C, rhombohedral calcite at temperatures below 15 ° C, and acular aragonite at temperatures above 30 ° C. 5. The method of claims l to 4, characterized in that it is in a high percentage can be produced a grain size _of less than 2 microns.