FR2490719A1 - PROCESS FOR PNEUMATIC BACKFILLING USING ALPHA-SULFATE-SEMI-HYDRATE AND / OR BETA-SULFATE-SEMI-HYDRATE - Google Patents

Abstract

THE PNEUMATIC BACKFILLING PROCESS USES ALPHA-SULFATE-SEMI-HYDRATE AND OR BETA-SULFATE-SEMI-HYDRATE, OBTAINED IN PARTICULAR FROM THE RESIDUES OF THERMAL POWER PLANTS HEATED WITH COAL. NATURAL ANHYDRITE AND OR COARSE CRUSHED LIME STONE ARE ADDED TO THE ABOVE SULPHATE (S). USE IN PARTICULAR FOR UNDERGROUND APPLICATIONS.

Description

The invention relates to a pneumatic backfill method

  only by means of alpha-sulphate hemihydrate and / or beta

  sulphate hemihydrate obtained in particular from the

  coal-fired power plants and for

  underground cations. The residues that come into play here, coming from coal-fired power stations, are formed by scrubbing the off-gases. The washing is used for desulfurization by absorption on stone

  lime (CaCO3) or lime in the form of oxide (CaO) or hydro-

  xyde (Ca (OH) 2). The residues that form contain SO 2 separated essentially as calcium sulfite (CaSO 3 .XH 2 O). Sulphite is obtained as a suspension and possibly also contains dust if lime, in particular lime was used in

  wet separators that serve simultaneously to separate

  dust and S02. However, calcium sulphite can also be obtained relatively dust-free if electro-filters are installed before washing with a liquid. The residues described are obtained in

  relatively large quantities. Residues are however

  Since they are difficult to handle because of their consistency and their chemical properties, their storage in particular presents serious difficulties. The residues are therefore

  processed into either alpha-sulphate-hemihydrate or beta-sulphate

  sulfate-hemihydrate. In detail we start from an aqueous solution that has formed in the washing of flue gases and which

  has absorbed the sulfur dioxide contained in the flue gases.

  By the use of lime in the wet wash CaSO3 is formed. 2H2O (sulfite-dihydrate). The residues resulting from the lime wash are oxidized in a container

  by air. The treated residues reach a thick

  sisseur. In this thickener is formed lime sludge CaSO4.2H20 (sulfate-dihydrate). If the raw plaster slurry thus formed is introduced into a dryer, it is formed by

  calcination beta-sulfate-hemihydrate.

  For the preparation of alpha-sulfate-hemihydrate plaster

  crude is added with water in a mixer. The plaster mud

  The crude product which is formed is pumped continuously in an autoclave and recrystallized under defined conditions (temperature below 150 ° C) in alpha-sulfate-hemihydrate. Additives to adjust the pH value and to modify the crystallization mode of the alphasulphate-hemihydrate can be added in the autoclave and allow to obtain alpha-sulfate-hemihydrate of various properties. as the final product. This alpha-sulfate-hemihydrate is withdrawn continuously in aqueous suspension from the autoclave and separated from the aqueous phase in a centrifuge. By drying, by

  example in a continuous drier, it forms the alpha-

  powdered sulphate-hemihydrate (CaSO4.1 / 2H2O). Both alpha-sulphate-hemihydrate and beta-sulphate-hemihydrate are suitable for underground substructure work because of their strength and strength. Because of its lower strength, beta-sulfate-hemihydrate has only limited uses, especially in filling technique. Especially for the alpha-sulphate-hemihydrate used as a construction material it is necessary to take into account, when

  is pure, of relatively high hardness and fragility.

  These properties allow only limited use of the alphasulphate-hemihydrate for underground work, but it has been found that an addition of fly ash from coal-fired furnaces confers on the alpha-sulphate-hemihydrate the desired deformability and thus opens the way for its

  use as a construction material for

Underground retaining walls.

  Both the use of alpha-sulphate-hemihydrate and / or beta-sulphatesemihydrate as a construction material for underground work, both in pure form and as a mixture with fly ash, as well as The use of these materials for daytime work is done by blowing, if possible. In the backfill blowing, the powder material

  is conveyed pneumatically from a silo to the place of use

  sation and blown with considerable addition of water.

  Blow-back of alpha-sulphate-hemihydrate

  pure or beta-sulphate-hemihydrate occurs boucha-

  if pneumatic backfilling is carried out on large courses. This danger is eliminated to a large extent

  whether alpha-sulphate-hemihydrate and / or beta-sulphate

  hydrate is mixed with fly ash, that is, if a mixture of alpha-sulfate-hemihydrate and / or beta-sulphate-hemihydrate and fly ash is used. Despite the additioi of fly ash there are sometimes incidents of

  which result from the passage of an irregular mixture

  link. At generally regular intervals, voluminous ashes

  they come out in increasing proportions. According to the invention, this is reduced to a particular behavior of the dust particles in the sulphate-hemihydrate dust stream which

  appears in a form not visible externally but uni-

  in a different concentration of the masses and

seems to a standing wave.

  The object of the invention is to avoid alpha blockages.

  sulphate-semi-hydrate and / or pure beta-sulphate-hemihydrate as well as operational incidents during blowing

  of these materials added with fly ash. According to the

  This goal is achieved by the addition of natural anhydrite

  rel and / or coarse-grained limestone. The alpha-

  sulphate-semi-hydrate, or beta-sulphate-hemihydrate are not

  therefore more used in pure form but with an addition of anhy-

  natural stone or stone, or, in the case of

  use of semi-hydrate sulphate and ash -

  flying, also with an addition of natural anhydrite or

limestone.

  The addition according to the invention of natural anhydrite or limestone does not react to blowing with water that has been added. Water is bound by alpha-sulfate-hemihydrate

  and / or beta-sulfate-hemihydrate before the anhydrite

  turel and limestone can not react. This is also

  the case when natural anhydrite is added

  reaction accelerators. Coarse grains of the additive

  In accordance with the invention, the mass behavior which, compared with the pneumatic transport of pure alpha-sulfate-hemihydrate and / or beta-sulphate-hemihydrate, enables substantially greater transport distances and ensures a uniform regular distribution of fly ash in

  alpha-sulfate-hemihydrate and / or beta-sulfate-hemihydrate.

  For backfill, the addition of natural anhydrite and / or limestone will be limited to 8 - 22% of the total mix. Additions that exceed these values decrease the resistance undesirably. The amounts of additives that are below the limit given by the invention

  on the other hand do not have a sufficient effect in the sense of

vention.

  The mixture used according to the invention of alpha-sulfate-semis

  hydrates with fly ash and natural anhydrite or

  limestone may, for example, present the composition

  60% alpha-hemihydrate, 30% ash

lantes and 10% natural anhydrite.

  Natural anhydrite (natural gypsum) and limestone are obtained in day or underground quarries. The

  stone is broken up by blasting and is presented

  continued in the form of large blocks. These blocks are first rough crushed, then crushed to a medium grain size and crushed again finely in the facilities

  use. For the first rough crushing of

  drums, jaw crushers or crushers

  Roller mills with sieving and return circuit are indicated, for medium milling use impact mills or roller mills. The coarse grains required by the invention dispense with fine crushing because

  granules of 7 to 13 mm should be used. The addition

  According to the invention, anhydrite or lime will preferably be used before the construction material is introduced into the silos at the point of use. In order to avoid separation of the mixture during transport to the

  place of use or the filling of silos or containers

  backfill piers, natural anhydrite and limestone

  are wet with water before being mixed with the alpha-

  sulphate-hemihydrate and / or beta-sulphate-hemihydrate and

  fly ash and then sprinkled with sulphate

  hydrate. By wetting with water and the subsequent dusting

  you get big grains with a fluffy outer surface

  whose stuffed animal is made of sulphate

  hemihydrate. Coarse grains sprinkled this way

  have good conservation power in all

  langes so that a separation is excluded.

E 4 9 0 7 1 9

- 6-

Claims (4)

  1. Pneumatic backfilling method using alpha-   sulphate-hemihydrate and / or beta-sulphate-hemihydrate,   in particular from coal-fired thermal power plant residues, for underground applications, characterized in that natural anhydrite and / or coarsely crushed limestone are added to the above mentioned sulphate (s) ( s). 2. Method according to claim 1, characterized in that the proportion of limestone and / or added anhydrite is between 8 and 22% of the total amount of the mixture used. 3. Method according to claim 2, characterized in that the grains of natural anhydrite and / or limestone,   added have a particle size of between 7 and 13 mm.   4. Method according to any one of claims 1   a 3, characterized in that the coarse natural anhydrite and / or the limestone are wetted with water before addition   and sprinkled with alpha-sulfate-hemihydrate and / or beta- sulfate-hemihydrate.