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Zawartość zarchiwizowana w dniu 2022-11-21

Odoriferous nuisances in steel industry: emissions at the blast-furnace slag granulation

Cel

The objective of this study was to carry out research into techniques or methods of reducing hydrogen sulphide and sulphur dioxide emissions in blast-furnace slag granulation.
A study of reduction methods and control techniques was therefore necessary.
As far as granulation itself is concerned, the technique adopted is that of controlling the temperature of the quenching water. Similarly, maintaining the right ratio between slag rate and water rate also helps reduce emissions. Slag temperature (extrapolated from the molten iron temperature) also has an effect, but is less easy to control.

However, although these methods do make a significant contribution towards reducing emissions of sulphur compounds, they constitute only a partial solution.

End-of-line reduction techniques were therefore envisaged. Owing to the high flow-rates involved and the presence of dusts and soluble sulphur compounds, scrubbing techniques were selected. These require chemical additives in order to obtain optimum pH conditions and neutralise the captured compounds, transforming them into less problematic products.

The feasibility of scrubbing was first of all analysed in a packed column. The dust content of emissions led to the design of a jet contactor (venturi scrubber) and a cable bundle contactor (Amazon contactor). These techniques turned out to be promising.

The qualities of the venturi scrubber were demonstrated in terms of control of the sulphur compounds in question. The flow-rates to be treated by INBA would appear to be too high for the use of this type of equipment. Any reduction in flow-rate is likely to alter workstation environment quality by increasing H2S concentrations.

Amazon contractors were also found to be suitable, offering the possibility of a satisfactory compromise between efficiency, pressure loss, water flow-rate and consumption of reagents. A scrubbing solution of soda/hypochlorite was found to be effective, and the most environmentally friendly as regards the quality of the waste water.

In terms of investment cost, and although the study was not continued up the project stage, the reduction techniques using scrubbing can be expected to be significantly less costly than adapting a 'clean' system of water cooling.

Summing up, a method of reducing emissions was selected (control of quenching water temperature), and the feasibility of control techniques using scrubbing was demonstrated. Project studies remain to be carried out in order to validate these options, or a combination thereof, from the economic point of view.

The influence of the rate of direct injection of coal into the blast-furnace was also studied, but fluctuations in the various production parameters (casting temperature, etc.) meant that its impact on emissions could not be clearly established.
Sulphur dioxide emissions constitute a problem affecting workstations all along the casting line, whereas hydrogen sulphide emissions are particularly associated with granulation.

The first step was to characterise these emissions.
In the casting floor area SO2 emissions are the most critical, and a number of values exceeding the recommended TLV were observed in the course of the study. However, these should be regarded in context, as they relate to the concentrations detected without taking account of exposure duration, which would appear to be significantly shorter than that for which the limit applies. H2S emissions are less of a concern in connection with the casting floor. H2S levels fall sharply with the use of a concentrated granulation technique such as INBA, where the smokestack design ensures sufficient updraught to prevent H2S emissions affecting the casting floor and workstations.
By contrast, from the point of view of environmental regulations, H2S levels are well above recommendations such as the German TA-Luft (concentrations are higher than 5 mg/Nm{3}).

The problem of odour emissions into the environment is significant and relatively difficult to solve simply by increasing the height of the smokestack, which would have to be unrealistically high.

The odour nuisance at workstations is no less important, with concentrations of 200 o.u./Nm{3} being the order of the day.

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Koordynator

Société Belge de Filtration
Wkład UE
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Adres
Voie Minckelers 1
1348 Louvain-la-Neuve
Belgia

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