SU1736930A1 - Method of processing bauxite pulp - Google Patents

Abstract

Usage: the invention relates to the field of alumina production. Essence: bauxite pulp is heated in pulp-pulp heat exchangers, and then with steam. In this case, heating with steam is carried out first in an autoclave with a heat exchange surface, and then in a direct contact autoclave. Heated pulp is leached in autoclaves and cooled in pulp-pulp heat exchangers in the temperature range exceeding no more than 1.5 times the heating interval of the pulp in an autoclave with a heat-exchange surface. 1 il.

Description

The invention relates to alumina production and can be used for autoclave leaching of bauxite.

A known method for leaching bauxite is to pump pulp through an autoclave unit when heated to 270-300 ° C. The installation is a long pipe through which bauxite pulp is transported by means of a piston pump. Around this pipe there are several separate tubular sections, which are preheaters and pipe-type autoclaves in the pipe. In the tube section of the first along the heater pulp, steam of self-evaporation of boiled pulp from the self-evaporators is fed, and in the tube core of the last heater, the pulp is boiled directly (i.e., pulp-pulp heat exchange takes place). This is the regenerative heating of the raw pulp. The final heating of the pulp is carried out in autoclaves by supplying in their annular part of the hot steam under a pressure of 70–80 atm or organic heat transfer medium, the number of which is determined by the possibility of reaching the maximum temperature of the pulp.

The disadvantage of this method is that the heating of the pulp with live steam is carried out through the heat exchange surface, and not through the direct contact of the pulp with steam. Direct contact heating of the pulp allows leaching at a higher temperature than when heated through a heat transfer surface. An increase in pulp temperature is due to the free dilution energy and a much higher heat transfer coefficient.

There is also known a method for leaching bauxite, which involves pumping pulp with a piston pump through pulp-pulp heaters, a mixture preheater, autoclaves, and a self-evaporator.

s

Och

you

renal pulp and agitator. At the same time, the boiled pulp is cooled in a self-evaporator to 183-185 ° C, which corresponds to a vapor pressure of 7 self-evaporation (13-15 ° C, taking into account the depression), equal to the pressure of the heating steam on the evaporation coming from the CHP plant, since self-evaporation steam is transferred to residue.

The disadvantage of this method is the increased consumption of 30 atm of steam, which determines the power of the CHP plant. This saves 7 steam at steam, but it is not compensated for by increased consumption of 30 steam at steam, and 7 steam does not determine the capacity of the CHP, as it is a product of throttling 30 steam of steam in the turbines of the CHP.

The aim of the invention is to reduce the heat consumption of heating steam during autoclave leaching of bauxite.

The drawing shows a schematic diagram of the proposed method.

The scheme includes pulp-condensate and pulp-pulp heaters 1 and 2, heating autoclaves 3 and 4 with a heat-exchange surface (dummy heating) and contact type, respectively, a battery

5 reaction autoclaves, self-evaporator

6 cooked (leached) pulp; contact heater 7 of recycled water; and tank 8 of hot water used for washing sludge.

The method is carried out as follows.

Cheese pulp with a temperature of 90-95 ° C is fed from the agitator by a piston pump (not shown) to the pipe part of heaters 1, to the annular part of which the condensate from autoclave 3 is fed in countercurrently. Then the slurry, heated to about 110-115 ° C, enters the pipe part of pulp and pulp heaters 2. The pulp is heated to 175-180 ° C. This completes the regenerative heating. Next, the pulp enters the first heating autoclave 3 along its course, into the heat exchange pipes of which the steam is supplied. As an autoclave 3, an apparatus of known construction can be used. The pulp is heated in it to 200–205 ° C and goes into a contact-type autoclave 4, where it is heated to the maximum possible temperature of 235–240 ° C (taking into account depression) at a pressure of superheated steam of 25–30 MPa (temperature 340–345 ° C ). Next, the heated pulp is pumped through the battery 5 of the reaction autoclaves and then supplied with a temperature of 230-235 ° C to the pulp-pulp heaters 2 (to the tube side), and from them to the self-evaporator 6, already cooled in the preheaters 2 to t85-190 ° C. Of

self-evaporator 6; boiled pulp cooled to 120-125 ° C; enters the dilution tank (not shown), and steam from self-evaporator 6 goes to the contact heater 7 to heat the circulating water. In the dilution tank (agitator), the pulp is still evaporated, and steam is also used. Instead of pulp-condensate preheaters 1, steam-condensate can be used

powered by steam from self-evaporator 6 (both can be used, this is not essential for the proposed method),

The proposed autoclave leaching scheme for bauxite makes it possible to more efficiently use the heat of boiled pulp for the preliminary (regenerative) heating of raw pulp. With the indicated parameters of live steam, the increase in the temperature of regenerative heating compared to, for example, the method of the prototype is approximately 25-30 ° C. With pulp-pulp heat transfer, the degree of self-evaporation of boiled pulp decreases, i.e. less water is removed from it, which is essential for the further course of the technology. Therefore, in the scheme, along with the autoclave of the contact heating of the pulp, a blind heating autoclave is used in which the pulp does not dilute. As a result, it is necessary to have less, Tea, the value of the steam used in this autoclave, to evaporate the boiled pulp. This will keep the amount of water used for flushing the sludge unchanged, since the concentration

boiled pulp before dilution remains in the same range as in the basic method.

 Example. The pulp is heated in a blind heat autoclave in the range equal to Atic 30 ° C {205-175), and cooling at At2 45 ° C (235-190).

In this case, the consumption of heating steam in the CHP (30 ati) will be

 95 1550 0.75 (238-175) 4 O4273-16.2 t / h,

where 95 is the consumption (on average) of raw pulp through batteries, m / h;

1550 - the proportion of raw pulp, kg / m3;

0.75 - the heat capacity of the raw pulp, kcal / kg ° C;

238 — reaction temperature (outlet temperature 235 ° C) of the final heating of the pulp, ° C;

175 — final temperature of regenerative heating of raw pulp in pulp-pulp preheaters, ° C;

427.9 - the difference of etalpies of heating steam and condensate at 30 ata, kcal / kg.

The consumption of heating steam prototype:

D1-1550 0.75 (238-150) 10

-3

--22.7 t / h

427.9

where 150 is the temperature of the regenerative heating of raw pulp, ° C.

If translated into heat, in the first case:

Q- 6957.5 kcal / h, in the second -Q 9718.5 kcal / h.

Claims (1)

Invention Formula A method of processing bauxite pulp, including its heating in pulp-bullets heat exchangers, and then steam, leaching in autoclaves and cooling in pulp-pulp heat exchangers, characterized in that, in order to reduce heat consumption, steam heating is first carried out in an autoclave with a heat-exchange surface and then in an autoclave of direct contact, while cooling of the pulp is carried out in a temperature range exceeding no more than 1.5 times the heating interval of the pulp in an autoclave with a heat-exchange surface. .one