FR2464239A1 - METHOD FOR MANUFACTURING LIGHTWEIGHT AGGREGATE PELLETS FROM INDUSTRIAL RESIDUES - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR MANUFACTURING LIGHT AGGREGATE PELLETS FROM INDUSTRIAL RESIDUES. GREEN PASTILLES ARE SHAPED BEFORE SRITING IN A ROTARY OVEN BY BRINGING IN CONTACT WITH THE BASE MATERIAL A BINDER SATURATED WITH WATER, WHICH IS SPRAYED IN THE FORM OF SLUDGE OR LIQUID ON THIS BASE MATERIAL. THE INVENTION APPLIES TO THE PREPARATION OF AGGREGATES FOR THE MANUFACTURE OF CONCRETE.

Description

The present invention relates to a method for producing pellets

  light aggregates from finely divided industrial residues, such as fly ash, residues from enrichment and flotation operations and dust, as a base material, in which a binder is brought into contact with

  the base material for forming green pellets

  and we sinter these green pellets into a

  rotary kiln to get the final pellets.

  In the field of concrete construction work, in certain cases, a material whose properties can not be obtained by the use of concrete types based on a conventional aggregate is required. These special cases may correspond, for example, to poor grinding conditions, to the desire to obtain high load-bearing capacities, given the inherent weight of the construction, or to the need for better thermal insulation capacity than materials. based on conventional concrete. These conditions may occasionally be technically satisfied with normal-composition concrete, but the solutions

  become heavier to support economically.

  Thus, in the construction industry, there is a general tendency to build buildings

  of lower weight concrete and higher porosity

  without giving up the favorable properties that had previously been attained. One such method is to replace the aggregate made of natural stone with an aggregate whose material has been artificially produced and has a lower weight and higher porosity, so-called light aggregate. Concrete made from such an aggregate is called by analogy

"light concrete".

  The manufacture of light aggregates from

  clay, shale, perlite and other

  natural raw materials, as a material for

  on the other hand, is known in its general features. Similarly, it is known to use as starting materials

  industrial residues such as ashes

  coal-fired plants, residues from enrichment operations and

  flotation, residues from coal mines

good, slag, etc ...

  The known methods assume that we work

  the starting material together with additives, with water, to obtain a soft mixture. This mixture is, by means of machines designed for this purpose, in the form of granules, so-called green pellets, which are then sintered. In the sintering process, the organic compounds are burned by burning, so that pore remains in the pellets. At the same time, water and other volatile substances escape in gaseous form, leading to expansion and volume increase in some materials. The final result is in the form of porous pellets whose density is considerably lower than the density

natural rock.

  According to a known method of manufacturing light aggregates from industrial residues, a suitably moist mixture of

  considered residues, for example voluminous ashes

  and water, possibly adding

  very additives; after premixing and homogenization in an activator, the mixture is passed through an inclined granulator rotary plate. During the projection of water in appropriate quantities, green pellets of spherical shape are formed on the plate. After these green pellets have received a desired size, they are taken off the tray and transported to a sintering plant.

  The difficulties of manufacturing an

  However, the acceptable light weight of finely divided residues is still large. The following are the greatest difficulties known to date, which are encountered in the implementation of the processes: (1) The green pellets can not be given the mechanical strength required for the transport

  subsequent treatment and heat treatment.

  (2) Due to the poor resistance of green pellets, it is necessary to choose

  sintering in which the green pellets remain

  rest during the sintering process. Generally known and most commonly used installations are so-called sintering deck installations. In these, the green pellets rest in the form of a bed with a thickness of about 20 to 30 cm on an endless apron passing

  slowly through the sintering furnace.

  In the thick still bed, all

  potting green pellets becomes impossible, at the same time that the pellets are sintered with each other. This results in a sintered mixture in mass more or less strongly, which must be ground and which will give aggregates pellets corners

  angular. The processes do not differ from each other

  with regard to operations aimed at

  reduce this sintering mass. At the same time,

  during, processes using the fritta-

  Ge require that after sintering the sintered mixture is ground.

  The pellets obtained in this way produce a heavy type aggregate. Pellets have sharp edges and open pores, and when mixed to form concrete, more water (prehydration) must be added than natural rock aggregate. The water to cement ratio of the concrete becomes higher and,

  therefore, resistance becomes correlative

lower.

  (3) In most industrial residues,

  there is no expansion during the pro-

  sintering process. We do not have a volum-

  less of the aggregate than by the effect of the pores and cavities produced in the pellets

  when combustible and volatile elements (or-

  sometimes coal powder and water) escape. It even happens that the pores of these pellets are open, resulting in unsatisfactory cement-to-cement ratio in the manufacture

concrete.

  (4) Many industrial residues have such a high sintering temperature, or sinter in such a narrow temperature range, that control of the sintering process becomes costly

  and difficult to obtain, if not totally impossible.

  For example, if fly ash from coal-fired power plants is used, it is necessary to choose the fraction or

  fractions having the physical and chemical properties

  most favorable, among the ashes

  picked on the electro-filters of the power stations. The remaining ashes can not be used for this purpose

  (5) The chemical and mineralogical composition

  that industrial residues vary to a large extent. In unfavorable cases, sintering may

2464Z39

  at completely unacceptable temperatures.

tables.

  If, for example, iron is present in the ferri (trivalent iron) form and the atmosphere of the sintering furnace is oxidizing, the sintering has

  rather than at a high temperature, which is

  favorable from the economic point of view. The heart of the pellets which is in a reducing medium because of the carbon particles which remain,

  on the contrary sintered, dilated, swelled and

  comes a rigid mass resembling lava. Sintering in a reducing atmosphere can not be Justified economically for materials if

cheap.

  Thus, the requirement of a light aggregate acceptable

  economically and from the point of view of

  of the construction technique, manufactured in

  shooting of industrial residues, assumes the following:

  - green pellets must be

  in such a way that they withstand the

  canic involved in the most favorable sintering process;

  - the sintering must take place in a rotary oven

  to allow and facilitate free expansion of the pellets and to reduce bulk sintering; - it is necessary to stimulate the expansion of the pellets

  during sintering, by means of suitable additives

  for this purpose; - it is necessary to choose the additives and the methods that are used to introduce them, in such a way

  that we can monitor and control the processes

  sus as much green pellet formation as sintering; - a sintering of the surface layer must take place in an early stage of the process of

  sintering to form an impermeable film

  ble preventing escape of gases that cause expansion; the composition of the surface layer of the pellets must be such that under the prevailing conditions, the sintering begins in this layer

  before sintering of the material of the heart begins.

  It is necessary that a film be produced around the heart

  an elastic element which, because of its density and elasticity, allows a homogeneous expansion of the core without uncontrolled escape of gas. The pellets thus obtain a form substantially

  spherical and especially a closed pore structure.

  These pellets do not absorb water in the manner of the light sintered aggregate on apron, which, in

  same time as the spherical shape, has a favorable effect

  the water requirement of concrete with a predetermined consistency. According to the invention, green pellets of chemical and physical compositions are obtained such that the nodules can be transported, without being broken, in the oven, which may be in the

  present case a rotary kiln, and undergo the combustion

  expansion. This expansion can be controlled by controlling the properties of the sludge used for pellet formation

  on the one hand, and by adjusting the

  busttion and temperature in the oven, on the other hand.

  The granules of light aggregates, which we obtain

  by means of generally known methods,

  do not meet the conditions imposed.

  The object of the invention is to eliminate the incon-

  venents involved in processes previously

  known to manufacture lightweight aggregates.

  The process according to the invention is mainly characterized in that: the binder is a binder saturated with water; - The binder is sprayed as a slurry or a liquid on the base material, during the formation of green pellets. According to the invention, it is possible to

  the finely divided, non-moistened material (cen-

  flying dusts, flotation residues, etc ...) on an inclined granulation plate, or the material is sprayed with sludge consisting of clay and / or high molecular weight organic substances,

  playing the role of "primer" (eg

  sulphite residue, cellulose derivatives

  various materials and equivalent materials).

  The purpose of this mud is to give the feet

  greenhouses the mechanical strength necessary for the subsequent mechanical treatment, on the one hand, and to give the green pellets a chemical and mineralogical composition such that the sintering is

  easier and starts in the superficial layer-

  green pellets before the gas begins to be produced inside the pellets, on the other hand. It is also possible to use for this purpose non-expandable raw materials by using, in the green pellets production phase, expandable clay and / or additives

of the type mentioned above.

  By controlling the quantity and type of sludge used in the formation phase of the green pellets, it is possible to modify the properties of the raw material in a direction favorable to the

  sintering process, which is of great importance

  lift, for example when pellets of fly ash of different kinds are formed. By means of the organic material, an oxidation of the iron compounds in the surface layer is prevented

  oxidation which would cause a delay in frying

  the surface layer, with respect to the interior of the pellets, and cracking

and a deformation of the pellets.

  The sintering which is preferably carried out in a rotary kiln with multiple compartments for

  better monitor and control the process of

  chage and sintering and the process of expansion,

  leads to a dense surface layer that

  fishing gases formed inside the pellets to escape. This gives a light aggregate with closed pores, these being, from the point of view of

  concrete technology, to be preferred to pores or-

  green. By properly choosing the temperature

  of combustion and time, it is possible to pre-

  to use, from the same starting material,

  aggregates with dimensions, weight and

desired resistance. -

  It is important that the clay sludge used in the formation process of green pellets is saturated with water, ie the clay does not absorb water taken at the same time. clay mud after the beginning of the process. This can happen if dried clay is used without a sufficiently long period of saturation

at the water.

  The thermal economy can also be improved in comparison with the known processes, because of the

  additives that have been discussed in

  reactions that produce ex-

  can be maneuvered even at relatively low temperatures. By performing sintering tests in a rotary kiln, it has been established that the best pellets are obtained by dividing the process into several phases of heat treatment, namely: (a) heating, removal of humidity; (b) surface sintering, expansion in one or more steps; and

(c) cooling.

  For the possibility of surveillance and

  of the order, these phases will be carried out in

  it has separate compartments of the furnace, the rotation of which may be varied independently of one another. The following will be indicated, in the form of examples, the properties of pellets obtained by the process

  according to the invention, by comparing them with the

  h corresponding properties of prepared lozenges

according to the prior art.

Example 1

  Resistance of green pellets Green pellets were prepared on a single granulation plate, by a known method, from fly ash only, and by projecting only water, on the one hand, and, depending on the invention, starting from the same ashes

  flying and projecting clay mud

  killed of clay saturated with water, and water, the proportion

  invariable clay content being 6 percent by weight of the green pellet, on the other hand. In both cases, the moisture content was 25 percent

in weight.

  The pellets were dropped in a

  1 meter high on a floor of

  concrete and the number of falls

  appearance of the first visible crack.

  The following mean values were obtained: Fly ash + water alone: 20 falls

  Fly ash + clay mud: 39 falls.

  All the green pellets were spherical and of the same diameter.

Example 2

  With the method described, it is possible to ob-

  hold pellets of light aggregates of different degrees of expansion. Table 1 presents some results obtained by burning in a muffle furnace.

Table 1

  Expansion of nodules with combustion of 10 minutes

in a muffle furnace.-

Example 3

  A number of 4 cm × 4 cm × 16 cm mold bunches = 256 cm 3 of equal volumes of sintered pellets of the type

  In commerce, on the one hand, and in

  according to the invention, on the other hand. In the increase of raw material +% by weight volume of binder in the material 100% total dry OA O00 A Fly ash + 6% 12020C 12140C of clay B Fly ash + 15% of clay 11800C 12030C C Fly ash + 57 % clay 11610C 11740C D Fly ash + 5% sulphite waste liquor 11960C 12100C E Floating residues I + 18% clay 11520C 11640C vibrating, the molds were filled with a single cement paste , with a water cement ratio of 0.33. It was removed from the mold after one day and tested at the press after three days. The diameter of the pellets was 10 to 12 mm. The following results were obtained:

Table 2

  Properties of light aggregates A to E: types of light aggregates prepared according to the invention.

  F and G: types of light commercial aggregates.

  Compressive strength was measured on aggregates of 10 to 12 mm in a cement mortar. The pellets prepared according to the invention

  D3 were heavier but their resistance

  Material Weight Porosity Porosity Resistance

  water light the compres-

  ue 5mm 1 hr 2 (_ _ / 1g),% (%) _ (MN / m). TI i

A 1538 | 1.3 1.4 43.2 35.2

B 1350 1.5 1.9 49.6 31.5

C 1577 0.6 0.9 39.3 32.2

D 1633 1.8 3.8 45.4 35.0

E 2000 0.6 0.9 32.8 34.1

F (to

it is

gile) 600 24 26 12.8

G (at

ashes

volan-

  1530 12 15 41.9 21.1 I., _ _ _ _ _. _ _ _ _ _ _, _ _ _ _ _ i _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _?

  advantageous from the point of view of the economy of

your.

Claims (7)

  1. A process for producing lightweight aggregate pellets from finely divided industrial residues, such as fly ash, enrichment and flotation process residues and dusts, as a base material, in which at least one binder is contacted with the base material of which   green pellets, and in which the   green bales in a rotary kiln to obtain the finished pellets, characterized in that a binder saturated with water is used as binder and the binder is sprayed in the form of sludge or liquid on the base material, for the formation of the lozenges green.   2. A process according to claim 1, characterized in that one pulverizes or projects the   binding by means of nozzles or similar means.   3. A process according to claim 1, characterized in that the spraying is carried out intermittently.   4. A process according to claim 1, characterized in that the spraying is carried out continuously.   5. A process according to claim 1, characterized in that the binder used is clay saturated with water.   6. A process according to claim 1, characterized in that as binder organic materials having a molecular weight are used.   such as sulphite waste liquor that or similar materials.   7. A process according to claim 5, wherein the industrial residue consists of fly ash, characterized in that clay is taken in a proportion of 5 percent by weight   to 15 percent by weight of the total dry matter.