08.04.2026
A Master’s thesis demonstrates that Filtrabit’s technology provides both environmental benefits and direct profitability for Outokumpu’s Tornio stainless steel plant.
A Master’s thesis from the University of Oulu demonstrates that Filtrabit’s modular dust extraction technology provides both environmental benefits and direct profitability for Outokumpu’s Tornio stainless steel plant.
The study included technical analysis of particle size fractions and chemical compositions of the dust collected, as well as detailed economic calculations on the value of the collected raw material and reduced waste management fees.
Ilari Juntti
University of Oulu, Degree Programme of Mechanical engineering
Master’s thesis, 2026
Original publication in Finnish language:
https://oulurepo.oulu.fi/bitstream/handle/10024/61355/nbnfioulu-202603182223.pdf
This Master’s thesis evaluates the technical, economic and environmental benefits of the Filtrabit DC401 modular dust collection unit in a stainless-steel production environment. The study was conducted at Outokumpu’s Tornio stainless-steel melting shop, where a Filtrabit DC401 dust collection unit was installed in the alloy handling system. The pilot operation was limited to the recovery of ferrochrome dust.
The research was based on a literature review, industrial pilot operation, operational measurement data, laboratory analyses and economic evaluation. The collected dust was weighed and analyzed according to particle size and chemical composition. The economic analysis quantified the value of the recovered dust based on its chromium content and assessed the associated savings in waste management.
The results show that the modular dust collection system enables efficient recovery of metal-containing dust directly from its source. The system separated the dust into two distinct fractions, one of which contained a significant proportion of chromium. This enables the material to be returned to the melting process. The solution is economically justified in situations where dust recovery also leads to savings in waste treatment.
The system improved dust control within the alloy handling system and reduced diffuse emissions in the process area. The results indicate that targeted dust collection is a technically functional and economically justified solution for dust control in the steel industry. The solution supports material efficiency and circular economy objectives.
Keywords: Cleantech, Dust control, Ferrochrome
The research was conducted at Outokumpu’s Tornio stainless steel smelting plant on the alloy conveyor of Production Line 1, which serves the Electric Arc Furnace (EAF), Chrome Converter, Argon Oxygen Decarburization unit (AOD) and the Ladle Station. All alloying agents that are not added during the EAF basket charging phase with recycled steel pass through the alloy conveyor. The alloy conveyor consists of a loading hopper, a vibrating feeder located beneath it, and an ascending conveyor system several dozen meters long that transfers the material to the subsequent stages of the process.
Dust is generated particularly at the vibrating feeder of the alloy hall’s loading hopper, where the material flow crumbles the alloying agents and creates fines to be transported by the airflow. A primary source of dust emissions for the alloy conveyor is located at this point, to which the new dust extraction unit investigated in this study is also connected. The process environment is a typical material handling area of a stainless steel smelter. Dust is formed as a result of large material flows and their handling, which causes significant local dust emissions, especially at the conveyor’s feed and discharge points.
Prior to the new dust extraction system, dust management at the vibrating feeder was handled by a baghouse filtration system, which also serves as the general ventilation for the alloy hall. The suction power of the device is distributed across dozens of suction points throughout the alloy hall, resulting in limited local extraction efficiency.
The new equipment was installed to improve targeted dust capture alongside the previous dust filtration system as part of the existing suction ductwork. The dust collected by the old baghouse system consisted of various dust fractions from alloying agents and raw materials. The most significant main components were burnt lime (CaO), dolomitic lime (CaO-MgO), and ferrochrome-based dust. Because the system operates as a wide-ranging general system, dust accumulated from several different sources, resulting in a heterogeneous composition of collected dust containing both metallic and non-metallic components.
The system evaluated in the study, the Filtrabit DC401, is a flow-dynamics-based dust extraction unit designed to remove fine process dust directly from its point of origin. The system’s separation process consists of two stages: pre-separation of the coarse fraction via cyclones and separation of the fine fraction based on a patented flow-dynamic separation core.
The first separation stage of the system is based on cyclonic separation. Larger and denser particles move toward the wall and descend into the collection hopper, from which they are removed into a separate collection vessel. The cyclone stage reduces the particle load directed toward the subsequent separation. In the second stage, the airflow is directed into four patented separation cores.
In the separation cores, the flow is guided into geometrically shaped channels where tangential and radial acceleration components are generated. Particles with sufficient inertia deviate from the main flow and move into a side stream, where they are collected.
According to the manufacturer’s specifications, separation efficiency exceeds 99% for particles with a diameter greater than 2.5𝜇𝑚 (PM > 2.5𝜇𝑚) and approximately 96% for smaller particles (PM < 2.5𝜇𝑚).
The separated dust is directed into a dust collection hopper and further into collection bags. At the Tornio unit, the cleaned air can be directed either back to the alloy conveyor or to the smelter’s original dust collection system via an adjustable valve ratio. The device operates as a standalone unit or as part of a larger filtration system. The system is modular and allows for the parallel installation of multiple units to increase capacity.
Three separate test runs were similarly conducted for ferrochrome before moving to continuous full-scale operation. During the full-scale phase, a total of 2556.34 tons of ferrochrome was processed during the trial period, and the system collected a total of 6347.6 kg of dust. The dust collected during full-scale operation includes both coarse and fine fractions and is utilized to evaluate separation efficiency and dust accumulation on a production scale.
The results show that the Filtrabit system collects dust from both investigated main alloying agent flows, and the collected ferrochrome dust (HC52) is mainly distributed into the coarse fraction (93.57%) and to a lesser extent into the fine fraction (6.43%).
| Alloy | Loading frequency | Processed amount [tons] | Total dust collected [kg] | Dust ratio [%] | Coarse fraction [kg] | Coarse [%] | Fine fraction [kg] | Fine [%] |
| ADOL | Test runs (n=6) | 26.70 | 363.80 | 1.36% | 318.60 | 87.58 | 45.20 | 12.42 |
| HC52 | Test runs (n=3) | 62.50 | 142.40 | 0.23% | 127.00 | 89.19 | 15.40 | 10.80 |
| HC52 | Full-scale phase 71 days | 2556.34 | 6347.60 | 0.25% | 5939.20 | 93.57 | 408.40 | 6.43 |
During the trial run, the system collected an average of 2.48 kg of dust per ton of crushed ferrochrome and 13.63 kg of dust per ton of processed dolomitic lime. The amount of dust collected by the system is directly linked to the number of loadings in the alloy system and the characteristics of the processed alloying agent.
The dust collection potential of ferrochrome was examined on a monthly and annual scale by utilizing historical alloy consumption from 2022–2025 and the average dust collection ratio per processed alloy ton determined in the trial.
Based on extrapolation, the system can collect approximately 8.2 tons per month and 98.45 tons of ferrochrome dust per year in continuous production use. This demonstrates that dust recovery constitutes a quantitatively significant side stream compared to a situation where dust remains uncontrolled in process areas or is directed to centralized filtration systems.
For comparison, the collection volumes of the old centralized filtration system averaged 11.79 tons per month (2025), which is noted to remain at a normal utilization rate alongside the new system.
Based on the trial run, the share of collected dust was an average of 0.25% of the total mass of the collected alloying agent (ferrochrome), or 0.32 kg per ton of steel produced. Based on the results, Filtrabit system dust collection forms a recurring and predictable material flow in continuous production. Its magnitude can be reliably estimated based on the measurement results obtained during the trial run.
| Year | Estimated dust collected (tons / year) |
| 2025 | 142,96 |
| 2024 | 79,84 |
| 2023 | 65,68 |
| 2022 | 105,33 |
| On average | 98,45 |
The economic value of the collected dust was determined based on the chromium contained in the material. According to the technical results presented earlier, the estimated average annual accumulation of ferrochrome dust is approximately 98.45 tons, of which 6.43% is the fine fraction, which was excluded from the assessment due to unsuitability for being returned to the process. There are approximately 92.12 tons of usable dust per year.
The chromium content of the usable dust was determined to be an average of 32% based on X-ray Fluorescence Spectrometry (XRF) analysis conducted at Outokumpu’s laboratory, which corresponds to approximately 29.5 tons of pure chromium annually.
The material replacement value was determined based on the general market prices for ferrochrome presented in the literature review, with the price of ferrochrome containing 50% chromium typically ranging between €1,500–2,000/t. This price range was used as a reference value, which was then scaled based on the chromium content of the collected dust.
Using this calculation method, the calculated replacement value of the chromium contained in the collected dust is in the magnitude of approximately 88,000–118,000 euros per year, depending on the price level used. The value should be viewed as indicative and does not represent a realized sales price, but rather the potential replacement value of the material in the smelting process.
The economic significance of the collected dust consists of the material replacement value as well as changes in the dust handling chain. When dust is collected in a targeted manner and directed as a usable material flow into the smelting processes, costs related to waste management are directly reduced.
Dusts generated at the steel smelter are divided into several fractions. Some of the dust accumulated in field areas and eventually became vacuum waste, some is transported with flue gas dust for further processing, and some ended up in the old alloy system and finally as landfill waste. These waste streams involve various handling and transportation stages, which are a direct cost item.
With its recyclable coarse fraction, the Filtrabit system creates an opportunity to reduce waste management costs. The collected dust is removed from some waste fraction handling chain, the costs of which can be several hundred euros per ton. It is impossible to determine a final exact price.
Based on the test period, energy costs are estimated at approximately 120 €/month.
Net Present Value (NPV) analysis shows that the profitability of the investment is realized in situations where the collected fraction can be utilized in the process or another material circulation solution and external dust handling costs are realized as savings.
In the Life Cycle Cost (LCC) analysis, the system’s cost structure is easily predictable because it consists mainly of a fixed monthly leasing fee and energy consumption. The share of variable costs in the total cost is relatively small, which reduces economic uncertainty.
In field work at the steel smelter, particularly in the vicinity of alloy systems, workers may be exposed to metal-containing dusts if personal protective equipment fails. Especially regarding chromium-containing dusts, the occupational safety perspective is central, as the dust may contain compounds harmful to health, such as Hexavalent Chromium (Cr VI).
Targeted dust collection in the alloy system directly affects the presence of dust in the work environment and reduces the amount of chromium-containing dust in the immediate vicinity of the process. This effect is not quantified on a mass basis in this work.
The results of the work show that a modular dust filtration system can influence the management of dust generated in the alloy system from both technical and functional perspectives. The separation efficiencies achieved in the trial use of the Filtrabit DC401 system and the collected dust volumes support the view that Filtrabit technology is suitable for local and targeted dust collection in managing fugitive emissions related to alloying agents.
Overall, the results support the research premise that a modular dust extraction solution can serve as a technically and functionally justified part of modern steel industry dust management. Based on the trial run, the Filtrabit DC401 system is an economically justified investment.
Significant differences were observed between the collected fractions in both chemical composition and grain size. This proves the manufacturer’s promise regarding the Filtrabit system’s ability to separate distinct fractions using the patented separation core. The ability to mechanically separate dust fractions in this way creates many new opportunities for the beneficial use of the device. The technical separation capability of the device differs strongly from solutions traditionally compared in literature.
The significance of the study for the material economy of dusty fractions is not limited only to the ferrochrome dust used in the study. The results provide basic information on the behavior of metal-containing, yet lime-containing, dust fractions in the Filtrabit dust separation system. This information is applicable in planned follow-up experiments for other metal-containing dusts, such as flue gas dusts. The results of the study serve as a starting point for subsequent experiments promoting the circular economy.
Profitability consists primarily of two factors: avoided recycling and handling costs and the recycling value of the recovered material. Without material utilization, the system’s net cash flow does not become positive based on operating costs alone. The recycling potential turns the net cash flow positive. The economic justification of the system is linked to the metal content of the collected material and its replacement value as an alloying agent returned to the process.
Detailed cost or value data are not presented in the examination, as they contain confidential information related to production. Furthermore, HSEQ benefits, such as management of dust concentration in the work environment, process cleanliness, and risk management, were not quantified in monetary terms. However, these factors can have a significant impact on the total benefit, especially in the long term.
Based on interviews, dustiness in the alloy system area has been observed to decrease during the trial run, but simultaneously, other measures have also been implemented to improve the work environment, which is why the system’s impact cannot be quantitatively isolated.
Hexavalent chromium, discussed in the literature review, is carcinogenic and, in small particle sizes, particularly sensitive to respiratory exposure. In this study, the annual amount of captured pure chromium is in the magnitude of approximately 30 tons, which is a significant amount captured directly from the point of origin. The Filtrabit DC401 system also collects small-particle-size chromium dusts away from process areas, thereby reducing the risk of exposure. Although the Cr(VI) concentration was not quantified in this work, dust recovery at the source breaks the potential exposure path before the dust spreads into work areas.
Alloy loading is a dust-intensive phase where fugitive dust management relying solely on a centralized system is not a fully effective means. A modular solution enables better fugitive dust management at the key source by supporting broader general ventilation.
Based on the trial run, the Filtrabit DC401 is technically suitable for dust management in the alloy system and integrates into the existing process without production interference. The system separates dust into two fractions, the coarser of which contains significant chromium content and forms a potential material flow to be returned to the process. The technical performance meets the requirements of the application.
From an environmental perspective, the system targets one significant chromium dust formation point. In 2024, the steel smelter’s particulate emissions were 13 tons, of which chromium’s share was 291 kg. Targeted dust collection reduces the amount of metal-containing dust generated in the alloy system from ending up as fugitive emissions and waste streams. The solution supports the plant’s readiness to manage chromium-containing particulate emissions and meet tightening BAT (Best Available Techniques) level requirements by collecting 30 tons of chromium dust annually, of which — based on literature — 42–180 kg is carcinogenic hexavalent chromium. The measured reduction in fugitive dust emissions supports the fulfillment of environmental permit requirements and strengthens emission control in the alloy system.
