FI92151B - Method for smelting waste plaster and ferrous material for managing sparingly soluble slag and sulphur - Google Patents

Description

92151

METHOD FOR MELTING WASTE PLASTER AND FERROUS MATERIAL FOR THE RECOVERY OF LOW SOLUBLE SLAG AND SULFUR

This invention relates to a process for melting waste gypsum and ferrous material in a single flame melting furnace to produce a sparingly soluble slag suitable for further use or storage, and sulfur dioxide, the concentration of which can be optimized to recover sulfur as either elemental sulfur, liquid sulfur dioxide or sulfur dioxide.

The utilization of waste gypsum has now been extensively studied in order to get rid of the ever-increasing amount of waste gypsum. The production of phosphoric acid generates waste gypsum, which is problematic because it does not cure, and thus the heavy metals bound to it may dissolve to a small extent. Gypsum generated as desulphurisation waste from power plant flue gas cleaning does not fully harden, but must be stabilized before landfilling or use in earthworks, and after drying, gypsum waste can cause dust problems. Thus, waste gypsum causes problems both without stabilization and when stabilized. If flue gas desulphurisation is carried out on a large scale using lime addition methods, it is estimated that in 2000 more than one million tonnes of desulphurisation waste and ash will be generated in Finland alone.

According to the present invention, a process has now been developed in which waste gypsum is smelted together with an ferrous material such as roasting waste, ferrous sulphate or pyrite in a flame smelting furnace using coal, coke, hydrocarbons (gases, oil) and / or sulphide material, e.g. pyrite concentrate. released energy. Either oxygen or oxygen-enriched air is used as the process gas. In the shaft of a flame melting furnace, gypsum calcium sulphate (CaSO 4) decomposes into calcium oxide by sulfur as sulfur dioxide in the gas phase. The calcium oxide, together with the iron oxides and any silicate material fed to the process, forms molten, low-sulfur (less than 1 wt% S), calcium ferrite or olivine slag in the bottom furnace of the flame melting furnace. Ko. the slag is discharged from the bottom furnace and either cast into a solid ingot or granulated. Since the impurities (heavy metals, etc.) contained in the gypsum and the ferrous material fed to the process are in a sparingly soluble form in the slag, the slag can be used, for example, as a soil filler or stored without causing environmental damage. The essential features of the invention appear from the claims.

Depending on the material to be fed, it is either oxidized or reduced in the reaction shaft. When feeding ferrous material in which iron is oxide or in which iron is formed as oxide, the reduction potential of the process is adjusted by the oxygen factor of the fuel so that the ratio of iron oxides (Fe2 + / Fe ^ +) in the resulting slag is such that the slag is in the molten temperature . The ferrous material requiring reduction can be, for example, roasting waste from the production of sulfuric acid or ferrous sulphate from the production of titanium oxide, which is calcined (FeSO417H2O> FeSO441H2O + 6 H2O) before smelting.

The feed ratios of gypsum and ferrous material are chosen so that the CaO content of the resulting slag is 10 to 45% by weight.

Il 3 92151

By feeding sulphide-containing ferrous material, most of the energy required by the process is obtained. as heat released from the combustion of the material. Such an iron-containing material may be, for example, a pyrite concentrate. In this case, the oxygen potential of the process is adjusted by the amount of process oxygen so that the ratio of iron oxides (Fe2 + / Fe3 +) in the resulting slag is such that the slag is molten in the desired range. A suitable temperature range has been found to be 1150-1400 ° C. Depending on the process temperature and the CaO content of the slag, a suitable Fe2 + / Fe3 + ratio in the slag is 0.4 to 3.0.

If desired, silicate materials, for example sand, can also be fed to the process as a slag former. In this case, the feed ratios of the above-mentioned materials are adjusted so that the composition of the slag is as desired, e.g. oliviinikuona. The sulfur content of the resulting gas can be adjusted e.g. by feeding a sulfide material so that it is optimal for recovering sulfur as either sulfuric acid, liquid sulfur dioxide, or elemental sulfur. If necessary, process gases can be diluted with air.

Impurities contained in gypsum and ferrous materials, such as heavy metals, are partially enriched in process dust generated in the process, which can be easily treated separately, e.g. to recover any valuable metals. 1

The invention is further illustrated by the following examples.

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Example 1 226 kg of dried waste gypsum (22.5% S, 33% Ca, <0.15% Fe) was melted together with 553 kg of ferrous sulphate (FeSO 2, F, 18.9% S, 0.4% Ca, 31.6% Fe) in a miniature flame melting furnace at about 11 during the hour, when the average solids feed rates were 20.6 kg / h gypsum and 50.3 kg / h ferrous sulfate. The reaction shaft of the small flame melting furnace was 2430 mm in height and 300 to 400 mm in diameter. An average of 12.5 kg / h of butane and 25.9 Nm / h of oxygen were used for smelting. The average temperature of the reaction shaft was 1397 ° C.

An average of 2.8 kg / h of butane and 6.2 Nm ^ / h of oxygen were fed to the bottom furnace of the small flame melting furnace to cover heat losses. At the end of the test period, the molten slag accumulated in the reactor sub-furnace was discharged from the furnace. The analysis of the slag was 0.04% S, 45.5% Fe and 25.9% CaO. The Fe 2+ / Fe 2+ ratio in the slag was 1.90 according to the Satmagan magnetite assay. The gas analysis for the test period was as follows: 0.7% H 2, 1.1% O 2 + Ar, 16.9% N 2, 0.8% CO, 49.0% CO 2 and 31.4% SO 2.

Example 2

Based on Example 1, material balances have been calculated in Table 1 for processes in which a) ferrous sulphate, b) pyrite roast and c) pyrite concentrate are fed together with gypsum as a solid. The total solids supply is 28,000 kg / h. Slag and gas temperatures are assumed to be 1400 ° C. The heat losses in the calculations are assumed to be 22,000 MJ / h. Possible leakage air volumes have not been taken into account in the calculations. In each case, the sulfur content of the slag produced is of the order of 0.04%, but the process conditions can, if desired, be adjusted so that the sulfur content of 921 51 5 is lower. In each case, the sulfur dioxide content of the gas produced is such that sulfur dioxide can be recovered from it, possibly by diluting the gas using known methods for the production of sulfuric acid, liquid sulfur dioxide or elemental sulfur.

Table 1.

I IN PLASTER kg / h 8 1451 12 885 | 10 480 I

I I% S | 22.5 | 22.5 I 22.5 I

I I% Fe 0.15 | 0.15 I 0.15 I

I I% Ca | 33.3 | 33.3 | 33.3 | | | ------------------ | --------- | --------- | --------- | I I I ferro-Ipyrite-Ipyrite-1 I I | sulphateIpasute | concentrate |

II I I I I

I I kg / h 19 855 | 15 115 | 17 520 |

II I I I I

I I% S | 18.9 I 0.4 | 48.3 I

I I% Fe 31.6 | 65.7 | 46.1 I I% Ca I 0.4 | 0.4 I 0.1 | | | ------------------ | --------- | --------- | --------- |

I SOLID- I I I I

I I FEED kg / h 28 000 28 000 28,000 I

I I ------------------ I --------- I --------- I ......— I

I IBUTANE kg / h 3 710 | 3 370 I 175 I

I IHAPPI Nm3 / h 7 463 | 6 800 | 7 470 I

I ......... I ------------------ I --------- I --------- I ......... I

PRODUCTS ICE kg / h 12 370 I 19 780 16 618 I

II I I I I

I I% S | 0.04 I 0.04 I 0.04 I

I I% Fe 52.8 | 50.2 I 48.6 I

I I% CaO 29.6 | 29.8 I 30.4 I

I I Fe2VFe3 * | 2.71 | 2.00 I 1.67

I I ------------------ I --------- I --------- I --------- I

I IKAASU Nm3 / h 19 772 I 14 052 8 332 I

II I I I I

I I% HjO | 50.1 | 47.7 | 5.7 |

I I * COj I 28.3 I 36.5 I 3.3 I

I I% S02 I 19.7 | 14.0 90.9 I

| --------------------------------................. ........ |

Example 3 234 kg of waste gypsum (23.0% S, 33.4% Ca, 0.12% Fe) were melted together with 365.7 kg of pyrite roast (Fe 2 O 3 (0.42% S, 0.42% Ca, 65.7% Fe) in a miniature flame melting furnace over a period of about 9.5 hours, with an average solids feed rate of 24.9 kg / h 6 92151 gypsum and 38.9 kg / h pyrite roasting.The size of the miniature flame kiln was the same as in Example 1. h of butane and 25.9 Nm1 / h of oxygen The average temperature of the reaction shaft was 1386 ° C.

Em. An average of 2.8 kg / h of butane and 6.2 Nm1 / h of oxygen were fed to the PiLSU lower furnace to cover heat losses. At the end of the test period, the molten slag accumulated in the reactor sub-furnace was discharged from the furnace. The analysis of the slag was <0.1% S, 53.4% Fe, 14.2% CaO. The Fe2 + / Fe3 + ratio in the slag was 2.8 according to the magnetite assay by the Satmagan method. The gas analysis averaged 3.5% H 2, 0.5% O 2 + Ar, 18.5% N 2, 7.1% CO, 57.4% CO 2 and 14.8% SO 2.

Claims (3)

92151 A method for melting waste gypsum and ferrous material at a temperature of 1150 to 1400 ° C, characterized in that waste gypsum and ferrous material such as roasting waste, ferrous sulphate or pyrite are fed to a flame melting furnace to melt them in such a way that the resulting slag has a CaO content of 10 to 45 p % using carbon, coke, hydrocarbons and / or energy released from the combustion of sulphide ferrous material and using either oxygen or oxygen-enriched air as the process gas, decomposing the gypsum calcium sulphate to calcium oxide by sulfur dioxide as sulfur dioxide to the gas phase, the calcium oxide, together with the iron oxides, forms a molten slag containing less than 1% of sulfur in the bottom furnace of the flame melting furnace, with an iron oxide ratio (Fe2 + / Fe3 +) of 0.4 to 3.0. Method according to Claim 1, characterized in that a silicate material is fed to the flame melting furnace as a slag former. Process according to Claim 1, characterized in that the sulfur is recovered from the gas generated in the flame melting furnace either as sulfuric acid, liquid sulfur dioxide or elemental sulfur. 92151