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Show Unmixed Combustion for Efficient Heat and American Flame Research Committee Mass Transfer in Chemical Processing Systems 1997 Fall International Symposium Moving again one step to the right we see that the solid phase of the reactor is now a mixture of nickel oxide with calcium oxide. At this point methane is added to the reactor. The methane reacts with the nickel oxide in a slightly exothermic reaction, reducing it to metallic nickel, but the temperature is too high for effective removal of carbon dioxide by the calcium oxide. The gaseous effluent from the reactor at this point is therefore a mixture of water vapor and carbon dioxide. This n o w returns the reactor back to its original state ready to resume reforming of steam and methane into hydrogen. Figure 8 indicates the gaseous composition of the reforming reaction products toward the end of a typical test conducted in EER's pilot plant test facility. This corresponds to a hydrogen concentration, on a dry basis, of about 92 percent by volume. In actual practice, the product composition is not constant; it starts out low and increases rapidly during the first one-fourth to one-third of the reforming step, stabilizing toward the end, with a typical average concentration somewhat closer to about 85 percent. Figure 9 shows actual measurements of hydrogen concentration obtained during a single reforming cycle in which diesel was used as the fuel. In this example the hydrogen concentration started out at about 63 percent but rose to a final concentration of 88.5 percent, with a cycle average of 81.4 percent. What is the upshot of all of this? A thermodynamically efficient reforming process at small scales that delivers a product gas with a substantially higher hydrogen concentration than even large scale hydrogen manufacture. This means that additional shift reactors are not necessarily needed, and that the process of final hydrogen purification is much simpler, and therefore less expensive. Also, since Unmixed Combustion is used to produce heat, there are effectively no oxides of nitrogen produced, and virtually all hydrocarbons are oxidized (typically to less than one ppm). Levels of carbon monoxide are typically less than 10 ppm. Therefore, relative to conventional reforming, and compared with most alternative hydrogen production processes, the Unmixed Combustion based reforming process is extremely pollution free. SUMMARY Unmixed Combustion shows promise as an alternative to fire for cleanly generating heat in a number of applications. It has been demonstrated as effective for destruction of hazardous waste surrogates and is being pursued for the commercial development of small scale steam reformers for on-site hydrogen production and fuel-cell based distributed power production. The process is not without limitations, however. The maximum temperatures developed by Unmixed Combustion will be limited by material properties. The Unmixed Combustion catalyst m a y also be subject to poisoning, as are conventional heterogeneous catalysts. Still, as w e enter the 21st Century with concerns about pollution, depleted energy reserves, and global warming innovative energy technologies including Unmixed Combustion will increasingly find a role in our future. Fairmont Hotel Chicago, Illinois September 21 -241997 Page 10 |