Loop reactor experiments, results

The measured temperature- and concentration profiles are plotted in Fig. 7 versus the length of the catalyst bed. The points are experimentally determined whereas the thick-line curves have been calculated using the kinetic constants obtained in the loop reactor experiments. A close agreement between the experimental results of the pilot reactor and the calculated values is apparent. Only the calculated CO and CC2 concentrations are a little high, causing also a higher temperature maximum. 

Prior to the kinetic experiments, possible deactivation phenomena of the catalytic system were checked by recycling experiments with prenal and citral as substrates. These results provide not only important hints on the form of the rate equation, but also on which reaction is convenient for long-term investigations in the loop reactor. After the reaction, the aqueous and organic phases were separated and the catalyst phase was reused without further purification. Results on the hydrogenation of prenal are shown in Fig. 7. The reaction rate clearly decreases if the catalyst phase is reused. According to GC analysis and H-NMR studies, this can be attributed to the fact that the product of the reaction, prenol, is highly soluble in water. Consequently, a simple phase... 

Since the overall reaction rate in the loop reactor is limited by mass transport at the phase boundary, one would expect that the Ru concentration has a weaker influence on the rate of reaction than in the batch reactor. We have carried out experiments at a Ru concentration of 0.005 M as well as at 0.01 M and observed nearly a doubling of the overall reaction rate, giving rise to a reaction order of 0.96 with regard to Ru. The result is somehow surprising, since it can be explained only in terms of a kinetic control of the reaction, like in the batch reactor. On the other hand, previous experiments clearly indicate a mass transport limitation at the L/L-interphase. So the question which arises is how it can be possible that a multiphase reaction system is limited by both mass transport and kinetics ... 

Experiments with laboratory monoliths of small cross-section area can lead to biased results due to an uneven flow distribution in the channels, especially close to the reactor wall. The wash-coat of the outer broken chaimels should be scraped away, and the void between the reactor wall and the monolith should be carefully plugged. To minimize wall effects, the diameter of the monolith should be ten tunes the chaimel diameter at least. Plug flow must prevail in a packed bed of crushed catalyst. The bed length and radius should be more than 50 and 10 particle diameters respectively, the flow resistance of the bed support must be unifonn throughout its cross-section, and the particle size distribution must be as narrow as possible. Otherwise, there can be oy-passes or dead vohunes. These hydrodynamic problems are overcome in a recycle loop reactor because the same physical and chemical conditions prevail everywhere. 

Oxidizing nature of the fission process. The fission of a mole of UF.1 would yield more equivalents of cation than of anion if the noble gas isotopes of half-life greater than 10 min were lost and if all other elements formed fluorides of their lowe.st reported valence state. If this were the case the system would, presumably, retain cation-anion equivalence by reduction of fluorides of the most noble fission products to metal and perhaps by reduction of some U + to U +. If, however, all the elements of uncertain valence state listed in Article 12-6.2 deposit as metals, the balance would be in the opposite direction. Only about 3.2 equivalents of coml)iiicd cations result, and since the number of active anion equivalents is a minimum of 4 (from the four fluorines of UF4), the deficiency must 1)0 alleviated by oxidation of the container. The evidence from the Aircraft Reactor Experiment, the in-pile loops, and the in-pile capsules has not shown the fission process to cause serious oxidation of the container it is possible that these experiments burned too little uranium to yield significant results. If fission of UF4 is shown to be oxidizing, the detrimental effect could be overcome by deliberate and occasional addition of a reducing agent to create a small and stable concentration of soluble UF3 in the fuel mixture. 

About 80% pyritic sulfur removal has been achieved by microbial desulfurization of Illinois 6 and Indiana 3 coals using T. ferrooxidans in laboratory shake-flask experiments and in a two-inch pipeline loop. The 10 to 25 wt% coal/water slurry was recirculated at 6-7 ft/sec for 7 to 12 days at 70-90°F. Results also show that the rates of bacterial desulfurization are higher in the pipeline loop under turbulent flow conditions for particle sizes, 43 to 200/m as compared to the shake-flask experiments. It is visualized that the proposed coal slurry pipelines could be used as biological plug flow reactors under aerobic conditions. The laboratory corrosion studies show that use of a corrosion inhibitor will limit the pipeline corrosion rates to acceptable levels. 

If an absorption phenomenon is occurring, changing the materials of construction of the wetted surfaces could impact the results. The best reactor results (in which the reactor volume based on the tracer analysis most closely matches the geometrically calculated reactor volume) were attained with stainless steel materials of constmction. The injector loops, tubing from the injectors to the mixing tee, and the reactor were all changed to stainless steel materials of construction of equivalent volumes. The flat top experiments were repeated for this configuration Fig. 13.10 shows the results. 

Next, we replaced the injector loops, tubing from the injectors to the mixing tee, and reactor with Teflon tubing of equivalent volumes. The flat top experiment was then repeated, with the results from this experiment plotted in Fig. 13.11. 

Some authors have claimed that KOH-NH3 primary coolant chemistry as applied in the WER reactors leads to lower radiation dose rates on the primary system. In the course of their work at the DIDO Water Loop, Large and Wood-wark (1989) investigated this type of primary coolant chemistry under conditions which were comparable to those applied in the experiments with LiOH chemistry. Their results showed comparatively low corrosion product concentrations in the coolant, suspended solids as well as dissolved species the radioactivity buildup on the loop surfaces, however, was on the same order as that experienced with coordinated Li/B chemistry. From these findings the authors concluded that the comparatively low radiation dose rates which are reported from VVER plants are not due to the type of coolant chemistry employed, but to the absence of Stellite and Inconel in the primary circuit, i. e. to low cobalt and nickel inventories of the materials in contact with the primary coolant. 

The philosophy of Dounreay fast reactor (DFR), (full power 60 MWth/15MWe, sodium-potassium coolant) was to have the experimental part of the system only inside the reactor vessel, and in the outside zone every effort was to be made to minimize the risk of breakdown of the cooling system. This explains the unusual feature of 24 coolant loops, which results in a size of pumps and heat exchanger where experience had been accumulated in previous experimental work. 

The thermal output of the reactor is 1,600 MW, with three main cooling loops, to ensure investment costs and core characteristics similar to those of future large cores. The main steam conditions are 495X and 169 atg, to attain higher thermal efficiency based on past experience and the results of recent R D on steam generator (SG) design and materials. 

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