The dataset ranks 100 companies, but ownership is fragmented rather than concentrated: the leading assignee holds 722 of the 57,055 records in scope, and the top 5 combined account for only 3.8% of all records. That means no single company's claim portfolio dominates the field, and a freedom-to-operate review needs to look well beyond the top few names. The ranked leaders include established heavy-industry and power-plant equipment makers alongside Chinese research universities, reflecting both commercial and academic filing activity in this space.

Filings rose steadily through the late 2010s, peaked at 947 in 2020, and have since settled into a plateau — 871 in 2021 down to 839 in 2024, a 4% change across that span. That is not a sign of a declining field; it looks more like a technology area that has moved from rapid growth to steady, established filing volume. Figures for 2025 and 2026 will continue to rise as publications catch up with filings, since publication typically lags filing by around 18 months.

F22B (steam generation & boilers) is the densest class, covering 8.5% of all 57,055 records, followed by F01K (steam & thermal power plants) at 4.9%. Separation processes, flue and combustion-residue handling, and furnace accessories each sit in the 3.6–3.8% range, while gas-turbine plants trail at 2.0%. Because a single record can carry multiple IPC classes, these percentages overlap and do not sum to 100%, but they do show where claim density is heaviest and where it thins out.

China is the largest receiving office by a clear margin, with 6,438 filings, ahead of the United States at 3,405 and the European Patent Office at 2,218. The United Kingdom follows at 1,930 and WIPO's PCT route accounts for 1,487, with Canada at 1,001. Any filing or freedom-to-operate strategy for this technology needs to account for the Chinese office as the largest single jurisdiction in scope, not just the US and Europe.

US9057023B2, assigned to ThyssenKrupp Uhde GmbH and dated 2015-06-16, covers a specific method and apparatus for keeping coke oven chambers hot using externally heated burners while the associated waste heat boiler is shut down for maintenance. It blocks that particular maintenance-continuity approach — combining a coke oven chamber bench, flue gas collection line, chimney, waste heat boiler and waste gas collection line in the claimed configuration — rather than waste heat boiler technology broadly. Someone designing a different way to maintain oven temperature during a boiler outage, without the claimed burner-and-flue-gas arrangement, would likely sit outside its claims.