Reactor/heat exchanger systems temperature maximum

A reliable control of the reaction course can be obtained by isothermal operation. Nevertheless, to maintain a constant reaction medium temperature, the heat exchange system must be able to remove even the maximum heat release rate of the reaction. Strictly isothermal behavior is difficult to achieve due to the thermal inertia of the reactor. However, in actual practice, the reaction temperature (Tr) can be controlled within 2°C, by using a cascade temperature controller (see Section 9.2.3). Isothermal conditions may also be achieved by using reflux cooling (see Section 9.2.3.3), provided the boiling point of the reaction mass does not change with composition. 

Analysis Part (b) Counter Current Exchange We note that near the entrance to the reactor, the coolant temperature is above the reactant entrance temperature. However, as we move down the reactor the reacdon generates heat" and the reactor temperature rises above the coolant temperature. We note that reaches a minimum (corresponding to (he reactor temperature maximum) near the oitrance to the reactor and then increases as the reactor temperature decreases. A higher maximum temperature in the reactor, along with a hitter exit cont ersion. X. and equilibrium conversion. X, are achieved in the counter current heat exchange system than fw the co-current system. 

A reaction A—>P is to be performed in a batch reactor. The reaction follows first-order kinetics and at 50 °C, the conversion reaches 99% in 60 seconds (the rate constant is k = 0.077 s 1. The charge will be 5 m3 in a reactor with a heat exchange area of 15 m2 and an overall heat transfer coefficient of 500 Wm 2 K 1. The maximum temperature difference with the cooling system is 50 K. 

H. Sato (JAEA) presented a paper discussing detection methods and system behaviour assessments for a tube rupture of the intermediate heat exchanger (IHX) for a sulphur-iodine based nuclear hydrogen plant. A rupture could be detected by monitoring the secondary helium gas supply using a control system that monitors the differential pressure between the primary and secondary helium gas supply. Isolation valves would be used to reduce the helium flow between the primary and secondary cooling systems. The study showed that the maximum temperature of the reactor core does not exceed its initial value and that system behaviour did not exceed acceptance criteria. 

The trend followed in newer plants is to increase conversion per pass with the result of higher ammonia outlet concentrations and lower outlet temperatures from the last bed. However, as optimum energy efficiency of the whole ammonia plant requires maximum high-pressure steam generation, part of the heat must be recovered before the reaction is completed in the reactor system. This can be accomplished [900], [901], [930], [931] by using three catalyst beds in separate pressure vessels with boilers after the second and the third vessel and an inlet - outlet heat exchanger for the first catalyst bed. 

Six-control rod subassemblies made of 90% enriched B4C were used in JOYO MK-II and were located symmetrically in the third row. In 1994, one control rod was moved to the fifth row to provide a position for irradiation test assemblies with on-line instrumentation. Since then, the control rod subassemblies have been loaded asymmetrically. The JOYO cooling system has two primary sodium loops, two secondary loops and an auxiliary cooling system. The cooling system uses approximately 200 tons of sodium. In the MK-II core, sodium enters the core at 370°C at a flow rate of 1 100 tons/h/loop and exits the reactor vessel at 500°C. The maximum outlet temperature of a fuel subassembly is about 570 C. An intermediate heat exchanger (IHX) separates radioactive sodium in the primary system from non-radioactive... 

For shdl and tube heat exchange Numerous related topics including evaporation Section 4.1, distillation. Section 4.2, crystallization Section 4.6, freeze concentration Section 4.3, melt crystallization. Section 4.4, PFTR reactors Sections 6.5-6.12. Approach temperature 5 to 8°C use 0.4 THTU/pass design so that the total pressure drop on the liquid side is about 70 kPa. Allow 4 velocity heads pressure drop for each pass in a multipass system. Put inside the tubes the more corrosive, higher pressure, dirtier, hotter and more viscous fluids. Recommended liquid velocities 1 to 1.5 m/s with maximum velocity increasing as more exotic alloys used. Use triangular pitch for all fixed tube sheet and for steam condensing on the shell side. Try U = 0.5 kW/m °C for water/liquid U = 0.3 kW/m °C for hydrocarbon/hydrocarbon U = 0.03 kW/m °C for gas/ liquid and 0.03 kW/m °C for gas/gas. 

In terms of passive decay heat removal systems, a major difference is noted between the liquid cooled AHTR and gas cooled reactors. The AHTR can be built in very large sizes (>2400 MW(th)), while the maximum size of a gas cooled reactor with passive decay heat removal systems is limited to -600 MW(th). The controlling factor in decay heat removal is the ability to transport this heat from the center of the reactor core to the vessel wall or to a heat exchanger in the reactor vessel. The AHTR uses a liquid coolant, where natural circulation can move very large quantities of decay heat from the hottest fuel to the vessel wall with a small coolant temperature difference ( 50°C). Unfortunately, under accident conditions when a gas cooled reactor is depressurized, the natural circulation of gases is not efficient in transporting heat from the fuel in the center of the reactor to the reactor vessel. The heat must be conducted through the reactor fuel to the vessel wall. This inefficient heat transport process limits the size of the reactor to -600 MW(th) to ensure that the fuel in the hottest location in the reactor core does not overheat and fail under accident conditions. 

The reference MSFR is a 3-GWth reactor with a total fuel salt volume of 18 operated at a maximum fuel salt temperature of 750°C (Mathieu et al., 2009 Merle-Lucotte et al., 2012). The system includes three circuits the fuel circuit, the intermediate circuit, and the power conversion circuit. The fuel circuit, defined as the circuit containing the fuel salt during power generation, includes the core cavity, the inlet and outlet pipes, a gas injection system, salt-bubble separators, pumps, and fuel heat exchangers. 

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