A typical reforming section in a large-scale Haber-Bosch process (Figure 1) comprises two reactors. A mixture of methane (CH4) and steam (H2O) is fed into a primary reformer to produce syngas via steam reforming (SMR). The gas product is then fed into a secondary reformer where it is mixed with air before going through a second steam reforming process. The air introduced into the secondary reformer (ATR) provides not only a suitable amount of nitrogen for ammonia synthesis but also some oxygen to exothermally oxidize part of the feed stream, thus decreasing the energy requirements of the steam reforming section of this reformer.
An alternative reforming process is proposed in Figure 2. Unlike the conventional approach, the first reactor is used to catalytically oxidize the methane feedstock at low temperatures using a sub-stoichiometric amount of air (CPOX) and consuming 100% of the oxygen. In the secondary reformer, a steam reforming process is performed to increase the amount of H2 produced.
Based on thermodynamic grounds, these two processes are expected to produce the same reformate; however, the use of low-temperature catalytic partial oxidation in the first reformer may lead to smaller reactor sizes as well as the reduction of potential fire hazards as flammable mixtures will not be exposed to high temperatures.
Is there any other foreseeable advantage of the alternative reforming approach?
In steam reforming heat must be supplied to the process for the reaction to proceed. i.e., endothermic reaction. Methane reacts with steam under the pressure about 2-3 bar in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic—that is, heat must be supplied to the process for the reaction to proceed. If give steam in secondary reformer then heat is not sufficient by self-generation, not possible as per your approach 2.Size and design of Secondary reformer must be changed according to Figure-2.Because the steam is feed to Sec. Ref .
Dear Prem Baboo , Thank you for your comment. For the sake of simplicity, the pressure and temperature in both approaches were set to 1 atm and 800C. Thermodynamics dictates that the overall heat duty must be the same in both approaches and the calculations shown in the diagram indicate so. In addition, steam methane reforming is a thermodynamically driven process whereas catalytic partial oxidation is a fast reaction driven by kinetics. In reality, the primary reformer in the conventional approach must operate with a steam-to-carbon ratio of ~4 to minimize catalyst deactivation due to coke formation, which requires a significant amount of heat.
Dear oscar marin, your thought is good, but practically not possible steam reaction is complicated phenomena and possible occur in tubular reactor like primary reformer tube( sufficient length and heat transfer area).and also different type of catalyst. according to KBR and HATS. Both Primary and secondary reformer design is different.
Dear Prem Baboo , I agree with you. Catalytic processes carry inherent complexity. However, key processes like methane steam reforming have been extensively investigated and all of this research has led to improved reactor designs and catalytic materials. For instance, microchannel reactor technology coupled with induction heating has been successfully tested as an alternative reactor design to minimize mass/heat transfer limitations while reducing greenhouse emissions. The goal of the question is to figure out if we can produce a suitable reformate for ammonia synthesis without using cryogenic separation or air separation units in the process like other alternative technologies do.
Ok, I salute your thinking keep it up with good ideas, The great work because the primary reformer is the main contributor of GHG.
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