Steel and Ferroalloys

Steel and ferroalloy making involve many processes that generate dust, which include the sintering process (pre-treatment of iron ore), the blast furnace operation, coal and coke transportation and finally, the processing of slag powder. The Temperature of the gases and the abrasiveness of the dust condition the gas solid separation technologies for each process.

Coal discharge dedusting
Coal – used for coke production - tends to generate significant amounts of dust during discharge from trucks after transportation. This dust needs to be captured with specifically designed hoods and a final collection system, such as bag filters and cyclones. Regular cyclones and multicyclones have many operation advantages but typically fail to meet the current emission standards due to the fineness of the particles.
 
Coal dedusting also present serious challenges for bag filters. Coal dust is composed of fine particles that tend to accumulate and adhere to filter media surfaces. Over time, this accumulation can lead to filter clogging. Coal dust is also highly combustible and can create fire and explosion hazards if not properly controlled. A proper filter selection and dust explosion prevention measures are mandatory to minimize risks.
 
Plant maintenance and environmental departments handling the coal discharge need an efficient final dedusting system that is robust and safe enough to operate for several years without significant maintenance or operating costs and at a reasonable cost.
 
ACS solutions include high efficiency cyclones (HR to RE cyclone families) which are a real alternative to other more maintenance demanding or costly dedusters, reaching emissions as low as 50mg/Nm³

“Hot Car” dedusting while transporting coke
Coke is typically produced at a coke plant and then transported to the steel manufacturing plant where it is used in the iron and steel production in blast furnaces. Transportation is ensured by so called “hot cars” - designed to maintain the high temperature of the coke and to prevent spills or other accidents that could be dangerous to workers or damage equipment. During the transportation process, cyclones or wet scrubbers prevent the release of dust and other particulates into the air, reducing the health hazard and minimizing environmental impact. Plant maintenance and environmental departments in charge of the coke transportation in Hot Cars need an efficient final dedusting system (typically with emissions below 50mg/Nm³ that is robust to operate for several years without significant maintenance or operating costs and operating on a dry basis, without generating secondary pollution.

ACS solutions include cost efficient cyclone systems (AT to HR cyclone families) which are a real alternative to wet scrubbers, reaching emissions as low as 50mg/Nm³.

Sinter dedusting in recirculation lines
Sinter is used in the steelmaking industry as a feed material for blast furnaces that use heat and oxygen to reduce iron ore into molten iron. Sinter is a good feed material for blast furnaces because it is porous and allows the oxygen to flow through it easily. This helps to improve the efficiency of the blast furnace and the quality of the molten iron.
 
A sinter strand is a continuous bed of iron ore fines, fluxes, and recycled materials. The bed is heated to a high temperature, causing the materials to fuse together and form a porous mass called sinter. The sinter is then crushed, cooled, and screened to remove dust.

There is a main air intake to supply oxygen to the combustion process and an Electrostatic Precipitator (ESP) is typically used as the deduster before the stack. 
 
The recirculation line in a sinter strand can also help to reduce dust emissions. It allows the hot off-gas to be recycled back to the sinter strand, which helps to cool down the sinter and prevent dust from being produced. Another benefit of using a recirculation line is that it can help to reduce NOx emissions. By recirculating hot off-gas, the amount of oxygen in the combustion process is reduced, which helps to reduce NOx emissions.
 
It also mandatory to have dedusting before the recirculation fan to avoid its rapid wear due to the abrasiveness of the sharp and angular particles (Mohs hardness of ~7). The dust particles can cause the fan blades to wear out quickly, which can lead to downtime and increased maintenance costs. However, this particle separation process is by itself demanding for any particulate trap. ESPs can be used but have a very high Capex and cyclones can rapidly wear out if not properly designed and engineered.  
 
ACS solutions include cyclones with low pressure drop and specifically designed to remove particles above 20 microns, particularly damaging for recirculation fans (SD cyclone families), assuring a very long life and being an alternative to ESPs. Slag Powder Processing
Slag is a waste product that is produced during the steel making process. It is a mixture of molten oxides, silicates, and other materials. It can be processed into powder by a variety of methods, including air granulation, water granulation and ball milling. Slag, and especially white slag, can be used for concrete aggregate, soil amendment, landfill cover and for road construction.
 
Slag powder is a fine powder that can easily become airborne both after conveying and discharge and needs to be dedusted and separated. However, slag powder has a Mohs hardness of ~7, harder than steel, and is composed of sharp, angular particles that can easily steel plates. It can also tear or puncture bag filters. Cyclones can be used before bag filters to protect them or even replacing bag filters in certain circumstances.   
 
ACS solutions for slag powder capture include inner lined cyclones, specifically designed to protect bag filters (AT to HR cyclone families), ensuring a very long lifetime and very high efficiency cyclones with low abrasion (RE to EX cyclone families) to exempt the use of bag filters.