text: In view of its performance, the process seemed a suitable basis for the development of more efficient variants. Around 1940, the Japanese built several small reduction furnaces operating at lower temperatures: one at Tsukiji (1.8 m × 60 m), two at Hachinohe (2 furnaces of 2.8 m × 50 m), and three at Takasago (2 furnaces of 1.83 m × 27 m and 1 furnace of 1.25 m × 17 m). However, since they do not produce Luppen, they cannot be equated with the Krupp-Renn process.
  Although direct reduction in a rotary furnace has been the subject of numerous developments, the logical descendant of the Krupp-Renn process is the "Krupp-CODIR process". Developed in the 1970s, it is based on the general principles of the Krupp-Renn process with a lower temperature reduction, typically between 950 and 1,050 °C, which saves fuel but is insufficient to achieve partial melting of the charge. The addition of basic corrective additives (generally limestone or dolomite) mixed with the ore allows the removal of sulfur from the coal, although the thermolysis of these additives is highly endothermic. This process has been adopted by three plants: Dunswart Iron & Steel Works in South Africa in 1973, Sunflag Iron and Steel in 1989, and Goldstar Steel & Alloy in India in 1993. Although the industrial application is now well established, the process has not had the impact of its predecessor.
  Finally, there are many post-Krupp-Renn direct reduction processes based on a tubular rotary furnace. At the beginning of the 21st century, their combined output represented between 1% and 2% of world steel production. In 1935 and 1960, the output of the Krupp-Renn process (1 and 2 million tons respectively) represented just under 1% of world steel production.