The assignee ranking covers 32 companies drawn from the 107 records in scope, and it is a full ranking rather than a top-50 or top-100 cut. The leader holds 19 records, with the fifth-placed company at 9 and the tenth at 4, showing a steep drop-off after the first handful of names. The top 5 companies combined account for 59.8% of all 107 records, and the top 10 combined account for 85.0%, so filing activity is heavily concentrated among a small group rather than spread evenly across the 32 ranked entities.

Filings peaked in 2017 at 15 records and the trend since has been uneven rather than steadily rising. Looking at the most recent span that can be treated as complete, 2021 to 2024, filings held flat at 5 records in both years — a 0% change over that three-year window. Years after 2024 in the underlying data are still incomplete because patent publication typically lags filing by around 18 months, so any apparent drop in the most recent one or two years reflects that lag rather than an actual slowdown.

C21B, the class for iron production including blast furnace and shaft furnace reduction, covers 85.0% of the 107 records in scope and is clearly the core class for this technology. C22B (metal extraction and refining) is next at 29.0%, followed by furnace and kiln hardware classes F27B and F27D at 22.4% each, and steelmaking follow-on claims under C21C at 19.6%. Smaller classes covering gas purification, material conveying and alloying each account for under 10% of records, marking them as thinner, less-claimed branches of the same technology area.

US9546409B2, assigned to HYL Technologies with a 2017-01-17 date, claims a process for producing direct reduced iron using a fossil-fuel-derived reducing gas that carries sulfur compounds and BTX contaminants. The gas is heated, then passed through a bed of DRI particles or iron oxide outside the main reduction reactor, where that bed adsorbs the sulfur and destroys the BTX before the cleaned gas is recombined with the reactor's main reducing-gas stream. It sits within the same HYL/Midrex family lineage that produced two of the most-cited coal-gas DRI documents in this dataset, so it is a useful reference point for anyone designing a gas-conditioning step around a shaft-furnace reduction process.

Based on IPC class shares across the 107 records, the thinnest branches are fuel-gas purification at 5.6%, material conveying and handling at 3.7%, and alloying at 3.7% — all well below the 22-29% density of the furnace-hardware and metal-extraction classes. Co-assignee collaboration is also sparse, with only 3 recorded co-filing pairs across the dataset, suggesting joint-development filings in this space are uncommon. Together these signals point toward gas-purification integration and conveying/logistics claims as areas with comparatively open claim space, though 'less-crowded' does not guarantee a claim will grant — a proper novelty search against the specific documents is still required.