Membrane reformers methane reforming

Steam methane reforming with membrane reformer/WGS reactor for hydrogen production. 

The product gas leaves the secondary reformer at a temperature of 885°C and is heat-exchanged in the primary membrane reformer. After that, the product gas leaving the gas-heated reformer is utilised for preheating of the natural gas feed, heating of circulating water in the saturator loop and generation of LP steam at 3 bar. Finally, after a temperature decrease to 265°C the gas is fed to a shift converter, after which again methanation takes place and removal of CO2 and traces of water. 

In the case of recirculation-type membrane reformer, efficiency of reactor heat utilisation = 60%, yield of hydrogen from methane = 95%... 

In the conceptual design, the nuclear plant is a type of SFR, mixed oxide fuel, sodium cooled with power output of 240 MWt for producing 200 000 Nm /h. The schematic diagram of nuclear-heated recirculation-type membrane reformer is shown in Figure 15. The hydrogen production cost of this process is assessed to be competitive with those of the conventional, natural gas burning, steam methane reformer plants. 

The application of membrane reactors to methane reforming has also been evaluated in two recent studies. A technical and economic evaluation of the use of dense Pd-membrane in methane steam reforming has been presented by Aasberg-Petersen et aL [6.10]. They assumed a thin (2 Lim thick) Pd membrane, which exhibited perfect separation and, as a result, the pure hydrogen product was taken from the permeate side of the membrane. No sweep gas was used on the permeate side of the reactor. This necessitated compression of the low pressure hydrogen product. The authors concluded that membrane-based reforming using a dense film membrane became attractive only in the cases where electrical costs were low. 

Membrane reformers take advantage of a useful feature of hydrogen, namely its ability to selectively permeate through Pd or Pd alloy membranes. As has been shown on a laboratory scale, the hydrogen is relatively clean and its continuous removal increases the methane conversion level [21]. 

The hydrothermal stability of the materials is more important as far as the use of membranes in methane reforming reactor is concerned. In general, improving the hydrothermal stability of membranes is difficult owing to the metastable nature of porous, particularly microporous structures and their tendency to change in the way of surface area reduction. Yet, recent reports [33, 34] show that improvements have been made in the hydrothermal stability of membranes based on silica, a material... 

P. Ferreira-Aparicio, M. Benito, K. Koua-chi, S. Menad, Catalysis in membrane reformers A high-performance catalytic system for hydrogen production from methane,/. Catal. 2005, 231, 331-343. 

Simakov DSA and Sheintuch M. Experimental optimization of an autonomous scaled-down methane membrane reformer for hydrogen generation. Ind. Eng. Chem. Res. 2010 49 1123-1129. 

Shu J, Grandjean BPA, Kaliaguine S (1995) Asymmetric Pd-Ag/stainless steel catalytic membranes for methane steam reforming. Catal Today 25 327-332... 

Chen Z, Yan Y, Elnashaie SSEH (2003) Novel dreulating fast Iluidized-bed membrane reformer for efficient production of hydrogen fiom steam tefOTming of methane. Chem Eng Sci 58 4335-4349... 

Y. Chen, Y. Wang, H. Xu and G. Xiong, Hydrogen production capacity of membrane reformer for methane steam reforming near practical working conditions, J. Membr. Sci., 2008, 322, 453 59. 

Chen, Z., Yan, Y. and Elnashaie, S.S.E.H. (2003) Novel circulating fast fluidized bed membrane reformer for efficient production of hydrogen from steam reforming of methane. Chemical Engineering and Science, 58 (19), 4335-4349. 

A third option is to consider an autothermal membrane reformer, where oxygen from an ASU is mixed with the methane feed and heat for reforming is provided by direct in situ oxidation of the feed, with no need of heat transfer surfaces (Fig. 10.13c). In this case, the flow of O2 to the membrane reformer can be cahbrated so that heat of endothermic and exothermic reactions exactly balance each other, and the reformed gas exits at the desired temperature. 

Key words membrane reformer, hydrogen production, steam methane... 

A membrane reformer equipped with palladium membrane modules for in situ hydrogen separation is a compact, simple and highly efficient hydrogen production system, and an improvement in these respects on the conventional steam methane reformer. In addition, CO2 in the off-gas of a membrane reformer can be easily separated and captured by direct liquefaction, owing to the high concentration of COj. 

The 40 Nm /h-class membrane reformer has a structure in which multi-reactor tubes are packed in the rectangular vessel. TGC made a few modifications to the first membrane reformer, which attained an efficiency level of 76.2%. The second membrane reformer increased the number of membrane modules from 224 to 256, in order to operate the system for higher methane... 

An energy efficiency rating of 76% had already been achieved in the production of hydrogen with the first 40 Nm /h-class membrane reformer system the second system was designed to improve on this. For this purpose, the 40 NmVh-class membrane reformer was operated at a higher methane conversion rate and reduced natural gas input, steam-to-carbon ratio, auxiliary power consumption and heat losses. These improvements were expected to increase the efficiency up to 80% on the system design basis. 

Basile, A., Campanari, S., Manzolini, G., lulianelli. A., Longo, T., Liguori, S., et al. (2011). Methane steam reforming in a Pd-Ag membrane reformer an experimental study on the reaction pressure influence at middle temperature. International Journal of Hydrogen Energy, 36, 1531—1539. 

Simakov, D. S. A., Sheintuch, M. (2011). Model-hased optimization of hydrogen generation by methane steam reforming in autothermal packed-bed membrane reformer. AIChE Journal, 57, 525-541. 

Mundschau et al. [122] presented a catalytic membrane reformer for diesel fuel, which was composed of yttria-stabilized zirconia for distributed air introduction into fuel feed reaching into the catalytic fixed bed. The latter contained either iron or cobalt perovskite catalysts (Lao sSro sCoOs. or Lao.5Sro.5Fe03 a). However, the catalyst produced significant amounts of methane impairing the hydrogen yield. 

Marigliano et al. compared the performance of two different types of tubular methane steam reforming membrane reactors by numerical simulations [413]. In the first, the catalyst was packed into the palladium/silver membrane tube, and in the second it was positioned in the annular region surrounding the membrane tube. Both configurations were heated from the outside. Owing to the indirect heat transfer to the catalyst bed inside the membrane tube, methane conversion was lower in this instance, and under certain conditions it was even inferior to a conventional fixed bed... 

Figure 5.37 Effect of reaction pressureon methane conversion for methane steam reforming in membrane reactors with different types of membranes reaction temperature 500°C S/C ratio 3 A, thermodynamic equilibrium , conversion in a membrane reactor with porous ceramic membrane 0, methane conversion in a membrane reactor with dense palladium membrane [406].

In particular, vdth methane steam reforming the application of membranes allows the equilibrium of the reaction (see Section 3.1) to shift in favourable directions. Thus, the membrane reformer could be operated at a lower temperature. 

Besides methane, methanol is the fuel most frequently investigated for membrane reformers. 

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