Materials reactor operating window

Biomass materials (powdered, microcrystalline cellulose and ground corn cob material) have been successfully gasified in a windowed chemical reactor operating at the focus of the Odeillo 1 Mw-th s°la-r furnace. The quartz window survived radiant flux levels in excess of 1000 w/cm2 however impurities carried by the steam flow into the reactor ultimately clouded the window. Some devitrification may also have occured. Future experiments should be designed... 

The reactor assembly was heated by electric heaters. The maximum operating temperature Is determined by the window construction. Sapphire windows (from EIMAC), brazed into Kovar sleeves, were used the sleeves were then welded directly into the stainless steel reactor housing. We found that the cell so constructed was capable of trouble-free, continuous operation at 450°C operations at somewhat higher temperatures are probably still possible but were not explored. Sapphire was chosen as a window material because it is insensitive to water vapor and is transparent in tljie wave number range of our interest (about 2400 cm to 2000 cm in these experiments). Moreover, the thermal expansion characteristics of the reactor were found to match well with those of the window fixture. 

What are the maximum and minimum operating temperatures and pressures A cell that is to be operated at atmospheric pressure at 473 K can be far simpler in design than one operated at 50 bar and 1000 K. These parameters place constraints on the window materials (e.g., Kapton vs. beryllium), the sealing mechanism of the cell (e.g., can O-rings be tolerated, will water cooling of the seals be necessary ), and the thicknesses of the reactor walls and windows. 

S.J. Zinkle, and N.M. Ghoniem, Operating Temperature Windows for Fusion Reactor Structural Materials, Fuusion Eng, Des., 51-52, 55-71 (2000). 

One critical issue especially related to methanol steam reforming is the narrow operating temperature window required for the reactors, which is related to the catalyst technology applied. Both reactor design and reactor material may help to achieve this goal. Highly heat conductive reactor material such as aluminum or... 

Outside the inner region (D2O) a subcritical assembly of fissile material in the form of a melt of fluorides (LiF/BeF2 containing UF4 or fluorides of other fissile nuclides at a temperature of 500/700° C inlet/outlet) is circulated producing the thermal energy required to drive the turbines. The operation of the core in a subcritical state (k = 0.97) increases the safety of the reactor. As it has been shown before (see Sect. 57.3.6), the reactivity window for safe operation of a critical reactor is given by 1 + (where fl is the fraction of delayed neutrons). 

The kinetics of the reaction and the properties of the catalyst, especially the thermal stability, will further narrow the range of possible reaction conditions and define a "window" of possible operating parameters. Process optimization, energy efficiency, and safety aspects will then determine at what conditions within the "window" the reactor should operate to give the optimum result. And then mathematical models are used to determine how big the reactor must be to obtain the performance (conversion and pressure drop) determined by the process optimization. Instrumentation is then considered, proper materials of construction are selected, catalyst loading and unloading is considered, possible transport limitations are determined, workshop manufacture is considered, and at last the design of the reactor is completed. The procedure is, of course, iterative since the reactor cost is one of the parameters in the economical optimization, but, as mentioned above, often a factor of minor importance for the overall result. 

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