Reactor reformer/burner heat-exchanger

Table 5.6 Specifications of the microstructured reformer/burner heat-exchanger reactors of 100 Wei and 5 kWei power equivalent as assumed by Delsman et al. for their calculations [386].

An example of a larger scale fixed-bed reactor is the heat-exchange reformer developed by Haldor Topsoe [476]. It was used for fuel cell applications in the power range of from 50 to 250kW. As shown in Figure 7.1, it is composed of a central homogeneous burner for natural gas fuel and anode off-gas and two annular... 

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. 

Figure 2.74 (Left) reformer/burner and (right) PrOx reactor/heat exchanger of the 100W fuel processor [ISMol 4] (source IMM).

The heat integration system consists of a catalytic burner reactor (BUR) and three heat exchangers (HXl, HX2, HX3). In the catalytic burner reactor, the unconverted hydrogen is combusted at 370 °C to deliver the heat necessary for the vaporizer and the reformer. The whole FP-FC system operates autothermally. 

Figure 15.3b shows the performance of all process units in terms of rational efficiency. The rational efficiency is defined as the ratio between the desired output of a process unit and the necessary input to this unit [ 11 ]. The performance expressed in terms of rational efficiency only shows the relative efficiency of individual system units and is sensitive to the definition of the input and output streams. In Figure 15.3a, the performance of the system is shown as the absolute exergy losses of these units. Figure 15.3b shows that the reformer and mixer perform very well in terms of relative efficiency, followed by the heat exchangers HXl, HX2 and HX3, whereas the performance of the FC, burner, vaporizer and COS reactor is lower. 

The mixture composition was chosen as H2O C = 1.9 and O2 C = 0.47 to achieve complete conversion and to avoid carbon deposition. The WGS reaction was performed in two adiabatic reactor stages with inlet temperatures of 673 and 573 K. An intermediate heat exchanger was not required as cold water was injected into the system. The catalytic burner and reformer were both required for water evaporation and superheating to cover the complete heat demand and to guarantee the inlet temperature for the first WGS reactor stage. When the operation temperature of... 

Seo ct al. reported on the development and operation of a 100-kW natural gas fuel processor, tvhich tvas developed for a molten carbonate fuel cell [609]. The molten carbonate fuel cell does not require any carbon monoxide clean-up (see Section 2.3.2), and thus the system consisted merely of a burner to supply the steam reformer, a compressor, heat-exchangers, the desulfurisation stage and the reformer itself. The reformer was built by relying on conventional technology with tubular reactors top-fired externally from the natural gas burner. The 16 steam reformer tubes shown in Figure 9.33 were operated at a S/C ratio of 2.6 and 3-bar pressure, while the design operating temperature was 700 °C. Seo et al. reported that the efficiency of their system was still too low. Therefore, an improved version of the fuel processor is under development. 

Figure 9.37 Design concepts of IdaTech steam reformers left, tubular fixed bed steam reformer reactors are placed around a central burner right, heat-exchange reformer the pre-reformer is placed in the outer area ofthe device while the reformer is more in the centre the combustion gases ofthe homogeneous burner pass through several annular gaps between the annular catalyst beds for heating [105].

Other recent significant developments in PAFC technology are improvements in gas diffusion electrode construction and tests on materials that offer better carbon corrosion protection. Of course, many improvements can be made in the system design, with better BOP components such as the reformer, shift reactors, heat exchangers, and burners. Much of this is covered in the chapters that follow. For example. Figure 8.4 shows a schematic arrangement of the essential components in a PAFC system. The actual fuel cell stack is a small part of the total system. 

Fuel reforming system that requires a fuel reformer, chemical reactors, heat exchangers, fans/blowers, burner, etc. Fuel flow rate to the fuel cell could use an ejector system to eliminate the fan for the fuel flow to the stack. 

The reformer takes an input flow rate of methane and computes the hydrogen output. The reformer module balances energy by combusting the reformate stream with air and exchanging the heat released to the catalyst reactor. Parameters on the reformer are the steam-to-carbon ratio and the outlet temperature of the exhaust products from the internal burner. The temperature at which the equilibrium reforming occurs depends on these parameters. Figure 1 shows the variation in thermal efficiency of the reformer with temperature and steam-to-carbon ratio. The minimum steam-to-carbon ratio is 2 however, reformers are often operated with excess steam to improve the efficiency and prevent coking problems. 

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