One assignee leads the ranked field with 158 of the 382 records in scope, a wide margin over the next four ranked companies, who together bring the top 5 combined to 317 records, or 83.0% of everything in the dataset. Fifth place sits at only 13 records, showing how sharply filing activity drops off after the leader. This concentration means most of the process-level claim space in this exact search scope is already occupied by a handful of companies rather than spread across the 41 ranked assignees.

No — filings peaked in 2020 at 50 and had fallen to 10 by 2024, down from 29 in 2021, a 66% decline over that three-year span. 2024 is the most recent year the trend can treat as complete; 2025 and 2026 figures will keep rising as publications catch up, since publication typically lags filing by around 18 months. Read the recent slowdown as real but not final — it reflects a cooling wave of filing activity after the 2020 peak, not a dead field.

The scope combines blast furnace top gas handling — reducing gas injection, shaft tuyere injection, gas recirculation loops, oxygen blast furnace operation — with the carbon capture and gas cleaning side: pressure swing adsorption, carbon dioxide removal and top gas cleaning. IPC data shows 89.8% of the 382 records classify under C21B iron production, with F27B and F27D furnace-hardware classes each covering roughly a quarter of records and B01D separation processes at 9.2%. It is primarily a process-claims field with a secondary hardware layer.

The IPC composition points to lighter claim density outside the C21B core: B01D separation processes cover only 9.2% of records, and specific sub-steps like desorbed-gas liquefaction to liquid CO2, light-hydrocarbon conversion of coke oven gas, and multi-stream gas blending control appear less consolidated than the main furnace-process claims. These are the branches worth a targeted prior-art search before assuming the space is closed, particularly since the leading assignees' portfolios concentrate on furnace-level process control rather than this downstream gas-handling detail.

EP4696788A1, filed by CISDI Engineering Co., Ltd and published 2026-02-18, discloses a near-zero-carbon co-production process combining pressure swing adsorption decarbonization of blast furnace gas, liquefaction and rectification of the desorbed stream into liquid CO2, and a split decarbonized-gas stream — part returned to the furnace, part blended with purified converter and coke oven gas ahead of low-temperature methanol wash and temperature swing adsorption. Because it is so close to the 2026 data cut-off, its prosecution status and eventual claim scope are still unsettled, so anyone designing a similar multi-stream gas-blending or PSA-to-liquefaction route should track its file history rather than treat it as settled art yet.