Removal, reactors

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Figure 2.4. Area of spill showing removed reactor.

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

Fig. 2. CO removal reactor integrated with microchannel plate 2.2. Experimental set-up...

For the practical use of this CO removal reactor, the microchannel reactor should be operated carefully to maintain operating temperature ranges because the reaction temperature is critical for the microchannel reactor performance such as CO conversion, selectivity and methanation as disclosed in the above results. It also seems that the present microchannel reactor is promising as a compact and high efficient CO remover for PEMFC systems. 

A microchannel reactor for CO preferential oxidation was developed. The reactor was consisted of microchannel patterned stainless steel plates which were coated by R11/AI2O3 catalyst. The reactor completely removed 1% CO contained in the Ha-rich reformed gas and controlled CO outlet concentration less than Ippm at 130 200°C and 50,000h. However, CH4 was produced from 180"C and CO selectivity was about 50%. For high performance of present PrOx reactor, reaction temperature should be carefully and uniformly controlled to reach high CO conversion and selectivity, and low CH4 production. It seems that the present microchaimel reactor is promising as a CO removal reactor for PEMFC systems. 

Safety aspects of drum storage, pellet screening, dust removal, reactor loading and unloading, and activation of process catalysts are discussed [1], and reprocessing aspects are considered, with disposal as a last resort [2], Hydrogenation catalysts introduce their own problems [3],... 

Figure 20. Fuel cell performance demonstration for the Battelle methanol processor and the carbon monoxide removal reactor.

Current efforts are focusing on optimizing the carbon monoxide removal reactor and developing a system prototype using commercially available pumps, blowers, fuel cells, valves, and controllers.In addition, durability testing along with thermal cycling needs to be done. 

Fuel reprocessing has three objectives (a) to recover U or Pu from the spent fuel for reuse as a nuclear reactor fuel or to render the waste less hazardous, (b) to remove fission products from the actinides to lessen short-term radioactivity problems and in the case of recycle of the actinides, to remove reactor poisons, and (c) to convert the radioactive waste into a safe form for storage. Fuel reprocessing was/is important in the production of plutonium for weapons use. 

The effluent water from the hardness removal reactor is basic and tends to deposit scales in distribution pipes. For this reason, this water should be stabilized. Stabilization is normally done using carbon dioxide, a process called recarbonation. Stabilization using carbon dioxide affects the concentration of the bicarbonate ion in the treated water. The concentrations of the SO4, Cl and NO3 ions are not affected, however, because they do not react with carbon dioxide. Their concentrations remain the same as when they were in the influent to the treatment plant. The original cation Na from the influent raw water is also not affected for the same reason that it does not react with carbon dioxide. Na is, however, introduced with the soda ash. 

Renninger, N., McMahon, K. D., Rnopp, R., Nitsche. H.. Clark, D. S., and Keasling, J. D. (2001). Uranyl precipitation by biomass from an enhanced biological phosphorus removal reactor. Biodegradation 12, 401-410. 

Similarly, a second run using a reactor of different L/D ratio should produce data that overlays the original data in the reaction phase plane if no boundary layer diffusion effects are present. As in the conventional PFR, a change of reactor is required from run to run. However, since the preferred configuration of a TS-PFR involves an oven containing a removable reactor, it is easy to place reactors of various configurations in the oven. (See Chapter 13.)... 

When the main heat transfer system can not work normally, the ERHRS will automatically put into operation in ten minutes to remove reactor residual heat to ultimate heat sink (atmosphere). 

Coordinated research programmes on heat transfer and decay heat removal, reactor physics and validation of predictive methods for fuel behaviour are being conducted under the auspices of the IAEA. Actinide waste and plutonium burning gives another possible application for HTGRs and worldwide attention is being given to this possibility. 

Decay heat removal Reactor Cavity Cooling System Passive - See design basis accidents... 

Heat removal Reactor pool Air coolers Passive (B) Passive (B) Conum on the vessel bottom is cooled bv the water of the reactor pool... 

Volume specific catalyst loading Mass specific activity of catalyst Heat of reaction and heat transport/transfer Catalyst and reactor costs Mass transport/transfer Homogeneous distribution of catalyst Thermal expansion Adhesion (stationary / transient operation) Chemical compatibiUty Development effort Deactivation rate versus regeneration / removal Reactor joining method Stacking schemes and modular approaches Migration effects Reactor size implications T/ p>-requirements... 

The reactor core consists of 265 fuel assemblies installed in the plates of the removable reactor screen at points of a regular hexagonal lattice, with a 72 mm pitch. The core height is 1100 mm the core equivalent diameter is 1230.7 mm. Each fuel assembly is composed of two main parts the upper part is a suspension and the lower part is a cassette consisting of a tight fuel element bundle, burnable absorber rods and the displacers of a plate type. Fig. 11-12. 

Natural circulation of coolant to remove reactor heat during normal operation ... 

The concept of a continuous crystallizer is abstracted by the MSMPR, mixed suspension, and mixed product removal reactor (Figure 9.7). 

Balance of Plant - The BOP costs may be less if lower cost materials can be used in the recuperators. In addition, the stack temperatures will be closer to typical reformer and sulfur removal reactor operating temperatures this further reduces the load on the thermal management system. However, it must be remembered that the main factor driving the heat duty of the thermal management system is the amount of cooling air required for stable stack operation, which in turn depends on the internal reforming capability of the stack and on the acceptable temperature rise across the stack. 

Removing CO by virtue of a catalyst outside the CL [92] or fuel cell itself, for example, adopting a CO oxidation reactor, to remove CO is practical and may bring good result [93,94]. He et al. [95] studied the possibility of integrating a CO removal reactor into a fuel cell stack, for which six typical catalysts were screened under fuel cell operation conditions. Nearly 100% CO conversion was achieved with an Ir/CoO,-Al203/carbon catalyst with good selective oxidation (O2/CO = 1.5) at 76°C and 100% relative humidity. 

Heat removal systems 1) Gas-turbine system is used for normal core heat removal and transient deeay heat removal. 2) Cavity cooling system is the only safety-related system it removes reactor heat through reactor pressure vessel passively, by naturally circulating atmospheric air. 3) Auxiliary cooling system is a non-safety grade system used to shorten eooling time imder normal and accident transient conditions. 

Engineering and Ventilation Controls All gases are maintained in ventilated storage cabinets. The laboratory contains area monitors for toxic and flammable gases. Immediately evacuate upon alarm. Scrubbers are used to remove reactor effluent containing residual toxic gases. 

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