Published March 2014
PEP has studied a variety of processes concerning synthesis gas (syngas) over the years, most recently PEP Report 148B [PEP148B] in 2013, which covered syngas from natural gas reforming. That report updated and improved the designs and evaluations of natural gas processes from PEP Report 148A [PEP148A], published in 1995, which in turn updated the 1983 PEP Report 148, published in two parts [PEP148-1, PEP148-2]. Meanwhile, Midrex Technologies, Inc. gave presentations on their technology at the Third Annual GTL North America Conference in Houston in early 2013 [201401001, 201401002], which was developed around iron reduction for steel production. The Midrex technology was similar to the natural gas reforming processes, but was outside the scope of PEP Report 148B, so this review was added to consider their concept.
The natural gas version of the Midrex iron reduction concept uses a natural gas reformer to generate syngas, which feeds a shaft furnace full of solid iron particles. The shaft furnace depletes the oxygen content in the particles . The interesting part for PEP was the recycle of carbon dioxide to the reformer to produce the syngas. Since Midrex has licensed a number of plants around the world for direct reduced iron (DRI), it looked like it might provide an economical means of turning carbon dioxide back to syngas. That turns out to be incorrect for the standard natural gas reformer-based DRI process though, because the syngas is mostly converted to carbon dioxide and water while reducing the iron, so there remains a net purge of carbon dioxide. Plus the DRI process does nothing with the carbon dioxide from the furnace side of the reformer .
Midrex, however, after licensing dozens of DRI processes around the world, is now attempting to adapt their SynRG™ reformer to enter the syngas-for-chemicals market, and includes carbon dioxide recycle, tail gas recycle, and flue gas carbon dioxide capture as sources for the carbon dioxide. While not specifically intended as a carbon capture or emissions reduction strategy, such a process could be useful if it proves to be economical.
The literature for the Midrex technology emphasizes a molar ratio (H2:CO) of 1.5-1.8 for iron reduction applications, but can be adjusted to a much wider range. The practical lower limit is around 1 to avoid carbon formation, and can be expanded to higher ratios, although the higher the ratio, the more it becomes a more typical steam methane reformer (SMR). We assume a molar ratio of around 2 for chemical applications, such as gas-to-liquids (GTL) or methanol, and a capacity set by the maximum size of the current single line MIDREX® SynRG™ reformer for chemical applications (225 kNm3/hr) .
While the process is labeled as being attributed to Midrex, it is actually our own independent interpretation of Midrex patents, literature, and discussions with representatives, so the design may not reflect, in whole or in part, the actual Midrex plant configuration. However, we do believe that it is sufficiently representative of the process to estimate the plant economics, within the range of accuracy for economic evaluations of conceptual process designs.