Membrane steam reformer

A. Nijmeijer, Flydrogen-selective silica membranes for use in membrane steam reforming, PhD dissertation, University of Twente, the Netherlands, 1999. 

In chapter 2, some basic ideas about steam reforming in conventional and membrane reactors are worked out. In this chapter the operation of conventional steam-reformers is compared with possible membrane steam-reformers. In this chapter also a techno-economic evaluation of a membrane reactor compared with the conventional process is provided. The boundary conditions imposed by process technology and the techno-economic evaluation result in the formulation of requirements for the development of the membranes, i.e. selectivity, flux, tube length, operating pressure, etc. 

The hydrogen content in the gas influences the coke formation rate [7] as well. In a recent article Hou et al. [19] showed the influence of the removal of hydrogen on coking rates in a membrane steam reformer using palladium membranes. The need of a minimum concentration of hydrogen is of special importance when operating a membrane steam reformer, because it limits the process conditions at which such a reactor can be operated. 

Of course, this reactive adsorption is favoured by removal of hydrogen from the reaction zone. When 80% of the hydrogen is removed in the membrane reactor, the H2S tolerance of the catalyst is about halve the tolerance when no hydrogen is removed from the reaction zone. A higher degree of sulphur removal from the feed stream should be accomplished when operating a membrane steam reformer. 

In this paragraph two of the most appropriate concepts for steam reforming employing a membrane will be discussed, namely Membrane Steam Reforming (MSR) and Gas Heated Reforming (GHR) with enriched air. The cases are described below, and are based on a Techno-Economic Evaluation prepared by KEMA, SINTEF and Norsk Hydro [21],... 

The high-pressure gas (retentate) stream leaves the membrane steam reformer at 625°C and 30 bar, while the H2-rich permeate stream leaves the membrane steam reformer at 555°C and 1.5 bar. Pure nitrogen from an air separation plant is supplied as a sweep gas on the permeate side of the membrane. 

Figure 3 Process layout of a membrane steam reformer [21],...

Another possible concept for membrane steam reforming is Gas Heated Reforming (GHR). A flowsheet of this process is provided in Figure 4. 

The mixed feed stream is given a final preheating to 430°C, and fed to the gas-heated reformer, where the feedstock is partially converted to synthesis gas by conventional membrane steam reforming (paragraph 5.1). The partially reformed gas leaves the gas-heated reformer and is fed to the secondary reformer together with enriched air and hence partially combusted. 

The location of the catalyst. A membrane steam reformer contains two types of tubes, the reformer tubes and the membrane tubes. The membrane tubes are placed inside the reformer tubes. There are two possibilities for both the location of the separative layer on the membrane tube and the location of the catalyst. The separating layer can be located at the inside or at the outside of the support tube. Membrane tubes with their separative layer inside are less sensitive towards operational and handling damage. 

Figure 5 Cross-section of a reformer tube in a membrane steam reformer. The separative layer is located at...

Sintef Applied Chemistry, Simulation and Cost Estimation of Membrane Steam Reformers , Microsoft Excel spreadsheet (1996). 

Somewhat surprisingly, however, only a very limited amount of literature is available on hydrothermal stability of even the most commonly applied mesoporous membrane type, namely y-alumina membranes on OC-AI2O3 supports. These mesoporous y-alumina membranes are the common supports for the microporous silica membranes to be used in membrane steam reformers. In the investigations that finally led to the present study, delamination of the y-alumina membrane from the OC-AI2O3 supports in hot steam was found to be a major compli-... 

The results obtained for microporous silica membranes in the membrane steam-reforming project, described in this thesis, provide favourable perspectives to realise a Th-permselective membrane reactor for the dehydrogenation of H2S. Realisation of such a reactor, however, imposes significant scientific and technical challenges. 

A Techno Economic Evaluation revealed the main factors influencing the costs and thereby the cost-effectiveness of a membrane steam-reformer compared to conventional processes (chapter 2). The evaluation showed that membrane steam reforming can be cost-effective. 

When suitable membranes are available real process technology and catalysis-oriented research can be performed. Important fields of research for membrane steam-reformers may include (see also chapter 2) ... 

Hydrogen-selective Silica Membranes for Use in Membrane Steam Reforming... 

Hydrogen-Selective Silica Membranes for Use in Membrane Steam Reforming Thesis University of Twente, Enschede - With ref. - With summary in Dutch ISBN 90-36513863... 

Figure 2.45. Schematic cross-section of membrane steam reformer for automotive uses (Lin and Rei, 2000 Itoh et al., 2002).

De Falco M, Nardella P, Marrelli L, Di Paola L, Basile A, Gallucci F (2008) The effect of heat flux profile and of other geometric and operating variables in designing industrial membrane steam reformers. Chem Eng J 138 442-451... 

The milder condition makes it possible to locate membrane assisted reformer downstream of a gas turbine with a consequent reduction in energy saving. An interesting application of membrane steam reforming reactor to co-generative systems was reported by laquaniello et The process layout is shown in... 

De Falco, M. (2008). Pd-based membrane steam reformers a simulation study of reactor performance. International Journal of Hydrogen Energy, 33, 3036—3040. 

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