FI77435B - FOERFARANDE FOER FRAMSTAELLNING AV SVAVELDIOXID. - Google Patents

Description

1 77435

Method for producing sulfur dioxide

The invention relates to a process for the production of sulfur dioxide by thermal decomposition of metal sulphates and simultaneous roasting of sulphide ores.

Thermal decomposition of metal sulfates and sulfuric acid is a strongly endothermic process. Therefore, coal, fuel oil or fuel gas, or preferably sulfur or sulfide ores, preferably pyrite, are often burned in the same reaction space to provide the required heat of reaction. In this case, thermal decomposition is performed using fuel oil or gas as well as sulfur, often in kilns.

The modern thermal decomposition process in fluidized bed reactors requires the permanent presence of a fluidized bed, in which case iron oxide in particular is suitable as a bed material. Sulfur pyrite, which is also a relatively valuable source of energy, acts as a compensator for the losses caused by wear.

A problem with this process is the feeding of sulfur pyrite, especially in the form of finely divided flotation pyrite, and sulphates, which are often sulfuric acid and hygroscopic, to fluidized bed reactors in such a way that they are distributed in the bed so that energy consumption and energy release are well balanced; 25 often in fairly large reactors in all areas. Only .. then the best possible decomposition efficiency can be achieved • without metal oxides leaving the reactor or sinter layers forming as a result of local overheating.

It is an object of the invention to improve the supply of both sulphide ores and metal sulphates to fluidized bed reactors, but also to other suitable reactors, such as bed or rotary kilns, in order to achieve optimal mixing of energy consuming and releasing raw materials.

2,77435 This is accomplished by granulating metal sulfates and sulfide ores, hereinafter referred to as kies, together, possibly in combination with other energy sources, and feeding them as granules to reactors.

The present invention thus relates to a process for the production of sulfur dioxide by thermal decomposition of metal sulphates and simultaneous roasting of sulphide ores in suitable reactors, in which process the metal sulphates are co-granulated with the metal sulphides and then fed to the reactors as granules.

Although the solids alone are difficult to granulate and provide weak granules unsuitable for mechanical conveying and kiln feeding, it was surprisingly found that the metal sulfates and the solids together are well granulated and provide stable granules that meet the mechanical requirements for reactor feed operation.

The granules obtained consist of an inner core consisting of metal sulphates and a jacket which is kitty. Sulfuric acid-containing metal sulfates, such as those obtained by concentrating the dilute acid or pickling solutions formed during the preparation of TiCl 2, can be granulated without problems when "dry", i. not as a pasty, but as a crumbling filter cake.

Thus, particularly suitable metal sulphates in the context of the present invention are filter cakes containing infectious acid. Their adhesive acid content can be reduced prior to granulation by mechanical post-moisture removal, for example by strip compression filters, thereby improving the friability of the filter cakes.

Granulation can be done in different devices. Granulation plates are quite well suited, in which case the granulation takes place in one or more stages.

However, due to the hygroscopic properties of the oxygen-containing salts, the granules quickly become moist and sticky. According to the invention, relatively strong are obtained

II

77435 can be easily poured by coating the above-mentioned granules in another granulation plate or on the outer ring of the same plate with a kitten. The granules thus formed adsorb only a small amount of moisture when standing for a long time in air 5 and remain very pourable.

The process according to the invention is characterized in that the metal sulphates are pre-granulated with sulfuric acid and / or granulation auxiliaries and then coated with metal sulphides.

10 Dry »pourable metal sulphates can be pre-granulated by the addition of sulfuric acid, oil or known granulating aids such as molasses, fish glue, bentonite or sulphite waste liquor, and then covered with kitty.

Kitten crushes with a particle size of up to 5 mm can be used as kittens. However, the invention offers particular advantages when using flotation strips with a particle size of mainly less than 0.1 mm. The granules obtained with it are quite pourable and storage-resistant. In addition, the great difficulties encountered in feeding flotation solids to fluidized bed reactors are avoided.

The ratio between strip and metal sulphates can be varied within wide limits depending on the requirements for the use of the raw material supply. By adding known granulation auxiliaries, the durability of this tuft can be improved, especially when the tuft / metal sulphate ratio is high, which is not normally necessary.

It proves advantageous to grind the granules of metal sulphates and metal sulphides with dry, non-stick substances. Such non-stick materials include coal dust, crushed coal, sulfur and / or combustion wastes. This flour further improves the pourability of the granules.

The use of the granules prepared according to the invention makes it possible to operate the reactors more evenly and to have better decomposition efficiency, especially in the case of fluidized-bed reactors.

4,77435

The advantages of the invention will become apparent from the following examples, which do not limit the scope of the invention.

Example 1 (comparative example)

Crumbly metal sulphates (mainly Fe sulphate-5, including Mg, Al, Mn and other sulphates) containing about 30% by weight of sticky acid (65% as unsalted acid) (= filter salt I) were granulated on a granulation plate. After 1-2 minutes, fine particles had formed granules with a diameter of 10 3-10 mm. As it was further rotated on the plate, the surface of the granules became moist glossy and the granules began to adhere to each other after 4-5 minutes.

When the granules were ground with lignite dust after being on a granulation plate for 2-4 min, they remained pourable.

Some of the granules were left to stand in an open mcilja interior. The granules were clearly adhered after 48 h. The weight gain due to adsorption of air moisture is 13.6%.

20 Example 2 (comparative example)

Attempts were made to granulate sulfur pyrite A (foam fiber, 70% of which had a particle size of less than 0.04 mm) on a granulation plate. This resulted in the formation of few ages with a diameter of 3-20 mm, which were easy to press in 25 hands and were unsuitable for normal transport and dosing equipment.

Example 3

To the granulation plate (d = 0.8 mm) was simultaneously added filter salt I obtained by post-removing 30 moisture from the suction filter cake with a belt press filter and breaking the plate-like cake with a hammer mill, and sulfur pyrite A in a ratio of 1: 1. After 5 min, dry, opaque, well-pourable granules were obtained. The sieve analysis is shown in Table 1.

Il 77435

Example 4

2 kg of filter salt I was placed on a granulation plate. After 3 min, 2 kg of sulfur pyrite A was added to the wet glossy granules over 30 s.

The granules were strong enough to meet the normal requirements for transport, storage and dosing. After 3 weeks in an open-air laboratory, they were still well pourable. The weight gain due to moisture adsorption was 3.2%.

Example 5

According to Example 4, filter salt 15 i and sulfur pyrite B (crushed pyrite with an average particle size of 1.3 mm) were granulated. The granules formed were glossy and also very pourable.

Example 6

The granules were prepared according to Example 4 and then floured with 100 g of lignite dust. Both immediately after preparation and kept for 3 weeks in an open dish, the pourability was clearly better than that of the unmilled granules of Example 4.

Example 7 According to Example 4, filter salt I and sulfur pyrite A were granulated in a ratio of 2: 1 (7a) and 1: 2 (7b). In both cases, sufficiently strong, well-pourable granules were obtained.

; Example 8 Filter salt II (suction filter cake containing 42% 65% sulfuric acid as adhesive moisture) was pre-granulated according to Example 4 and post-granulated with an equal amount of sulfur pyrite A. The granules (sieve analysis in Table 1) were highly pourable, but clearly weaker in pressure resistance than the granules according to pre-kernels 3-7.

77435

Example 9

A granulation plate with a diameter of 1 m and a depth of 0.2 m was provided with an inner cylindrical ring with a diameter of 0.6 m and a depth of 0.15 m. 100 kg / h of filter salt I was metered into this area. The steady-state granules formed by the filter salt I rotated in the outer region and 50 kg / h of sulfur pyrite A were added thereto.

Example 10

The pourable ferrous sulfate monohydrate prepared by removing water from ferrous sulfate heptahydrate was granulated in the inner region of the granulation plate by spraying with a molasses solution. Sulfur ore A was added to the rotating granules of the plate in a weight ratio of 1: 1. Highly pourable granules with a grain size and strength similar to the granules prepared according to Example 9 spun out of the outer region.

Il 77435

table 1

Screening analysis of different granulation products 5 Eg <2 mm 2-6 mm 6 - 10 nm> 10 mm No._Weight% _Weight%% wt% Wt% 3 32 38 23 7 4 7 66 22 5 10 5 11 57 24 8 7 a 12 59 25 4 7 b 10 62 23 5 15 8 37 47 '11 5 9 2 83 14 1

Claims (6)

8 77435 A process for the production of sulfur dioxide by thermal decomposition of metal sulphates and simultaneous roasting of sulphide ores in suitable reactors, wherein the metal sulphates are co-granulated with metal sulphides and then fed to reactors, characterized in that the metal sulphates are then pre-granulated with sulfuric acid and / or Process according to Claim 1, characterized in that the metal sulphates are filter cakes containing infectious acid. Method according to Claim 1 or 2, characterized in that the adhesive acid content of the filter cakes is reduced by a subsequent mechanical dehumidification before granulation. Process according to one of Claims 1 to 3, characterized in that the granules consisting of metal sulphates 20 and metal sulphides are ground with dry, non-adhesive substances. Method according to Claim 4, characterized in that the dry, non-adhesive substances are coal dust, crushed coal, sulfur and / or combustion waste. Method according to one of Claims 1 to 5, characterized in that the granulation is carried out on granulation plates in one or more stages. Il