Steam reformer, simulation

Figure 6.2.32 Evolution of methane conversion ( Ht). mean radial process gas temperature and external and internal tube skin temperatures (Tprocessi and Tint), and total pressure in a tube of a steam reformer simulations by a one-dimensional reactor model (Section 4.10.7.3), internal/external tube diameter 10.2/13.2cm, heated tube length 11.1m, ring-shaped catalyst (height 1 cm, diameters 0.8 and 1.7cm), molar steam to methane ratio 3.4, average flue gas temperature 1100°C [data from Xu and Froment (1989a, b) Plehiers and Froment (1989)].

A fired tube reactor was configured to match the dimensions and catalyst loading of an existing oxo-alcohol synthesis gas steam reformer. Simulation results at observed conditions (feed gas composition, outlet temperature, steam to earbon ratio, ete.) agree very well with observed results. Catalyst activity is first determined by matching key effluent eomposition. 

Yokota, O. et al., Steam reforming of methane by using a solar simulator controlled by H20/ CH4 = 1/1, Appl. Organomet. Chem., 14,867,2000. 

This study was carried out to simulate the 3D temperature field in and around the large steam reforming catalyst particles at the wall of a reformer tube, under various conditions (Dixon et al., 2003). We wanted to use this study with spherical catalyst particles to find an approach to incorporate thermal effects into the pellets, within reasonable constraints of computational effort and realism. This was our first look at the problem of bringing together CFD and heterogeneously catalyzed reactions. To have included species transport in the particles would have required a 3D diffusion-reaction model for each particle to be included in the flow simulation. The computational burden of this approach would have been very large. For the purposes of this first study, therefore, species transport was not incorporated in the model, and diffusion and mass transfer limitations were not directly represented. 

The simulation of the thermal effects of the steam reforming reaction was based on a published reaction model (Hou and Hughes, 2001) for methane... 

Our initial work on reaction thermal effects involved CFD simulations of fluid flow and heat transfer with temperature-dependent heat sinks inside spherical particles. These mimicked the heat effects caused by the endothermic steam reforming reaction. The steep activity profiles in the catalyst particles were approximated by a step change from full to zero activity at a point 5% of the sphere radius into the pellet. 

Some Computed Simulation Results for Steam Reformers... 

In this section we collect some computed results when simulating industrial steam reformers. We compare the actual plant outputs with those obtained by simulation using the three models that we have developed earlier. We investigate both the close to thermodynamic equilibrium case and the far from thermodynamic equilibrium case. 

However, a simple comparison of the stated simulation results does not favor any particular model. To differentiate the models, we propose run comparison tests of the three models for a steam reformer, called Plant (3), that runs far from its thermodynamic equilibrium. 

Create a MATLAB program to simulate steam reformers and methanators of... 

A rigorous dusty gas model and two simplified models have been used to simulate industrial steam reformers and methanators. The basic principles for the solution of both the nonadiabatic steam reformer and the adiabatic methanator are given. The details of developing solution algorithms from the models are left to the reader as a serious and extensive project. 

S. Elnashaie, A. Adris, M.A. Soliman, A.S. Al-Ubaid, Digital simulation of industrial steam reformers, Canadian Journal Chemical Engineering, 70, 786-793, 1992... 

The major units of the Aspen-HYSYS simulation for natural gas steam reforming based fuel cell system are presented in Figure 3. 

Several operating conditions have been found which satisfy the requirements for no coke formation. The optimum S/C ratio at 3.5 appears to fulfill the requirements for temperatures around 800°C for steam reforming process. The optimum O/C and S/C ratios are found 0.45 and 1.5 respectively for ATR reactor simulations at the inlet temperature of 700°C. 

TeGrotenhuis et al. [58] performed a 1 000 h stability test in a micro structured reactor for the steam reforming reaction with a catalyst not specified. A mixture of 74% isooctane, 20% xylene and 5% methylcyclohexane as simulated gasoline was fed to the reactor at a S/C ratio of three and a 650 °C reaction temperature. A regeneration step was performed after 500 h and finally the catalyst converted 97% of the feed. 

Ndm3 (min gcal) Tests were performed for both low- and high-temperature water-gas shift. The feed was composed of simulated high-temperature shift product for low-temperature shift (3% CO, 14% C02, 25% HzO and 55% H2) and of a simulated steam reforming product for high-temperature water-gas shift (9% CO, 8% C02, 34% H20 and 49% H2). 

A reformate flow rate of 25-175 Ndm3 min-1, simulating methanol steam reformer product gases, and 2.5-17.5 Ndm3 min-1 air were fed to the reactors. The simulated reformate was composed of 68.9% H2, 0.6% CO, 22.4% C02, 6.9% H20 and 0.4% CH3OH, the last to simulate incomplete conversion. The carbon monoxide output of the single reactors and of both switched in series is shown in Figure 2.72. The CO output of the two reactors switched in series was <10 ppm and the optimum air volume split between the first and second reactors was determined as 70/30. 

For reformate flow rates up to 400 Ndm3 min-1, the CO output was determined as < 12 ppm for simulated methanol. The reactors were operated at full load (20 kW equivalent power output) for -100 h without deactivation. In connection with the 20 kW methanol reformer, the CO output of the two final reactors was < 10 ppm for more than 2 h at a feed concentration of 1.6% carbon monoxide. Because the reformer was realized as a combination of steam reformer and catalytic burner in the plate and fin design as well, this may be regarded as an impressive demonstration of the capabilities of the integrated heat exchanger design for fuel processors in the kilowatt range. 

A simulative comparison of dense and microporous membrane reactors for the steam reforming of methane,... 

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