DD285335B5 - METHOD AND DEVICE FOR PREPARING MOISTURE FINE-COATED SMOKE GAS - Google Patents

Description

For this 2 pages drawings

Field of application of the invention

The present invention relates to the treatment of fine-grained moist accumulating or subsequently moistened synthetic gypsum, as obtained mainly in the flue gas desulfurization, but also in the production of hydrofluoric acid and other chemical processes.

There are also applications in other areas wherever the task is to transfer fine-grained substances into a coarse-grained good.

Characteristic of the known technical solutions

With the increasing requirements for keeping the air clean, the desulphurization of flue gases from the combustion of fossil fuels gains importance. The methods used today produce considerable quantities of gypsum, which must be reused. In some applications, it has been possible to design processes such that flue gas gypsum replaces natural gypsum. Thus, flue gas gypsum is converted into calcium sulfate hemihydrate by autoclaving and used for the production of molded bodies (DE 3711367). Also gypsum fiber boards are produced from flue gas gypsum with fibrous aggregates, which solidify after shaping by a pressure and temperature treatment (DE 3419559).

'There are proposals to produce building materials from mixtures in which flue gas gypsum has a significant proportion (DE 3639841, DE 3529823, DE 3205147). They are primarily intended for heavy-duty, low-strength applications.

A large part of the flue gas gypsum is not used for technical purposes and must be landfilled.

At the same time, natural gypsum is mined on a large scale for industrial purposes. The cause is partly the poor handling of the bunkers and chutes strongly prone to bridging flue gas gypsum. The substitution of natural gypsum by flue gas gypsum as setting regulator has hitherto only been carried out to a limited extent in cement (for example DE 201667), because prior to use in the existing cement plants a treatment is required whose costs, however, generally exceed the recovery costs for natural gypsum.

It is known to reduce the moisture by admixing a dry fine-pored material, preferably fly ash, whereby the lower moisture results from the simple mixing rule (DE 3620778). However, such a preparation is insufficient for many applications. It comes then, for example, in plants on which otherwise Anhydritschotter is processed, to permanent disturbances in the flow of material.

For briquetting without additives, the previous drying to <1 wt .-% moisture is necessary (DE 3201853). Due to the high fineness, the drying process is not mechanically possible. Therefore, an energy-intensive thermal process with high operational complexity is required.

The briquetting εη takes place with high electrical drive power of the machines at high wear.

This also applies to another method in which the material is processed with a Koller extruder.

The problem is the guarantee of a high dimensional stability of flue gas gypsum briquettes, especially under subsequent exposure to moisture. Described is the increase in shelf life, abrasion resistance and compressive strength of briquettes by mixing with a binder before briquetting, especially with the known hydraulically abi indenden building materials cement or REA gypsum building materials gypsum phases α- and ß-hemihydrate and anhydrite II with 3 to 40t iw .-% (DE 3501 238).

The use of binders incurs additional costs for expensive briquette production.

Also very expensive is a method in which the briquetting of the flue gas gypsum is partially calcined by being dried at relatively high temperatures, ie exhaust gas temperatures of 120 ⁰ C to 150 ⁰ C (DE 3626912).

From other fields of technology apparatuses are known, with which moist fine-grained materials are granulated. Thus, there are various rotor granulators in which a drum provided with holes, welcho receives the estate and pressure rollers or mats are mutually offset in rotating relative motion, whereby the material is pressed through the holes (DD 243170, DE 3615677). Similarly, a device for passing, in particular granulation and / or sieving a good, consisting of a vertical rotationally symmetric container with a conical bottom, in which the conical surface is formed by a sieve and a circulating in the container Streichwendel the good through the sieve pushes (DE 3617175).

These solutions have in common that the material is pressed by mechanical pressure through the openings.

Depending on the applied pressure, a relatively high energy consumption, wear and maintenance costs arise. Gypsum agglomerates made with these apparatus would have a low dimensional stability because of the residual moisture and they could not be transported away from the place of shaping without a large part of the flue gas gypsum being present again as a shapeless mass.

Aim of the egg

The aim of the invention is the treatment of moist fine-grained flue gas gypsum at low cost, to allow the economic use of large quantities of flue gas gypsum, especially in the building materials industry, as a secondary raw material.

Explanation of the essence of the invention

The invention has for its object to transfer wet and fine-grained flue gas plaster cost in a coarse-grained material to make it manageable on existing industrial equipment for such material the task.

According to the invention, the smoke garment to be treated is divided into individual bodies, which are enveloped with a crust of a, preferably hydraulically, hardening binder. By bypassing the process steps of drying and pressing and containing the gypsum bodies in the interior flue gas gypsum in the initial state, an energetic advantage over methods is achieved in which the entire amount of substance is subjected to a conversion. It eliminates the use of heat energy and the high drive power for press tools.

For the production of gypsum bodies, the thixotropic properties of the moist flue gas gypsum can be used.

After passing from a delivery stream into the area above an apertured dividing surface, its fluidity is increased by induced vibration so that it passes through the openings and the tearing strands subsequently form the nodular gypsum bodies. As soon as the gypsum comes out of the field of action of the vibration, the water is partially withdrawn from the near-surface areas of the tubers, as the capillary structure disturbed during the vibration absorbs the water again. At the same time this improves the conditions for the subsequent encrustation in connection with the binder.

In particular, at low initial moisture of the flue gas gypsum another variant of the division in individual plaster body wemen applied by thrust means mechanically circulate the flue gas gypsum on the dividing surface, so that the bridge formation is prevented through the openings, according to the invention, the flow achieved without pressure application

Because of the low strengths, the Gius tubers must be gently collected. This is carried along below the dividing surface with a conveyor, which causes a gentle circulation of the bed during the conveying process, at the same time the all-round encrustation of the plaster body is ensured with binder. The fatigue strength of the encrustation is established only after the end of the solidification reaction of the binder.

In order to support the use of binders or solidification, the binder may be premixed at least with a substance which is present as a solid in granulations of preferably <10 mm and / or enters into the strength-promoting chemical reaction with the binder.

The invention was also the technical problem of proposing a device for carrying out the method.

According to the invention, the object is achieved by means of a dividing surface disposed below a feeding hopper, coupled with a conveying screw known per se. In the division surface there are openings for the split material passage due to gravity. To prevent bridge formation, the division surface operates in vibration or in an alternating movement. The auger below the dividing surface exercises in one of the functions feeding the binder, gentle collection of the gypsum in the binder bed and circulation of gypsum bodies in the binder. To avoid bridge formation, the dividing surface of the device can also be designed as a trough, in which the thrust members rotate in the form of a helix or of revolving plates.

embodiments

example 1

From a flue gas gypsum with a moisture content of 30% stored for several months, nodular bodies were produced according to the described method with a volume of 5 to 10 cm ³ . Hüttenzement ZZ 1/25 was used as binder. The cement input was 10% by weight to the total.

The substances are characterized by the following analytical values:

Part / characteristic Share in% by weight ZZ1 / 25 Flue gas gypsum Loss of ignition at 0.16 1000 ⁰ C 23.9 24.13 SiO ₂ 1.1 7.14 Al ₂ O ₃ 0.4 1.61 Fe ₂ O ₃ 0.5 53.77 CaO 33.2 4.98 MgO 0.9 3.68 SO ₃ 43.3 0.89 K ₂ O 0.04 0.30 Na ₂ O 0.01 2.1 > 90pm 0 6.7 > 63μσι 0.7 21.7 > 4C in the 3.0

After a storage period of one month, the test material was in coarse-grained form without fines.

Example 2

FIG. 1; FIG. 2

The device shown in Figures 1 and 2 consists of a flat dividing surface 2 with circular holes on the.

a hopper 1 is permanently mounted. To create the vibration, the division surface is equipped with external vibrators (f = 2625min ~ ').

From the binder feed point 4, a screw conveyor 5 leads below the dividing surface 2 along to the discharge 6.

The device can be arranged both stationary and on a chassis of a vehicle.

Example 3

FIG. 3; Figure 4; FIG. 5

The device shown has, in contrast to the aforementioned embodiment 2, a trough-shaped dividing surface 2, which consists of a basket formed of welded round steel. In this basket, a spiral screw 7 (Fig. 4) or rotating Umwälzbleche 8 (Fig. 5) are arranged.

Claims (5)

A process for the treatment of wet fine-grained flue gas gypsum with the addition of a hardening binder to obtain a coarse-grained lump, characterized in that flue gas gypsum is divided from a flow by passing an apertured division surface (2) without external pressure application due to gravity, according to which the falling gypsum strands are trapped in a bed of self-hardening or hydraulic binding agent, which is guided by a conveyor underneath the Tt Jungflage, and the gypsum bodies are coated on all sides with binding agent during the joint expulsion with gentle circulation. 2. The method according to claim 1, characterized in that the passage of the Rauchgasgipyes by the Te'lungsfläche (2) is supported by vibration and / or circulation on the division surface. 3. The method according to claim 1, characterized by the premixing of the binder with at least one substance which promotes the hardening of the crusts by the binder by being present as solids in grain sizes of preferably <10mm and / or in the strength-promoting chemical reaction with the binder occurs. 4. An apparatus for the preparation of wet fine-grained flue gas gypsum, characterized by a division surface (2) in which openings for the divided material passage are due to gravity and which operates in vibration or an alternating movement and bofindet under a hopper (1) , coupled with a below the dividing surface (2) along, known per se screw conveyor (5), which here in one of the functions supplying the binder, gently collecting the gypsum in the binder bed and circulation of the gypsum body in the binder exerts. 5. The device according to claim 4, characterized in that the dividing surface (2) is formed as a trough in which rotate about an axis a screw helix (7) or Umwälzbleche (8) as thrust members, which circulate the goods on the division surface (2) , wherein the openings are present in such a large number and such geometry that everything passes without solidification through the openings and the thrust members are formed so that no material pressures occur in the material to be treated.