Cooled Reactor System

2 Results for Adiabatic Reactors with Cold-Shot Cooling 

For the expensive catalyst, the optimum economic steady-state design has a vessel with seven beds. The TAC is 2.03 x 106 per year, which is about half that of the single adiabatic reactor system. The recycle flowrate is 0.66kmol/s, which is more than that of the interstage-cooled system because of the use for cold feed to provide cooling. The total catalyst in all the beds is 33,800 kg. The optimum bed inlet temperatures range from Ti = 475 K to 7V = 486.9 K. The optimum yRA/ymi ratio is 0.994. 

This process has four design degrees of freedom. The four design optimization variables used are the diameter of the tubes Aube, the length of the tubes L,ube, the flowrate of the process gas fed into one tube TUlbe. and the v A/yWB ratio. 

The diameter of the reactor tubes is a design optimization variable, but a maximum limit of 0.12 m is used to avoid mechanical and heat transfer difficulties. The cross-sectional area of the reactor vessel is assumed to be twice the total cross-sectional area of all the reactor tubes, that is, the volume in the shell outside the tubes is equal to the total tube volume. 

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For both the expensive and inexpensive catalysts, the cooled reactor system has the lowest total annual cost among all the alternative systems. This occurs for two reasons ... 

In the closedloop tests, all controllers are on automatic. The disturbances in the adiabatic reactor systems are setpoint changes in the inlet temperature and changes in recycle flow-rate, FR. The cooled reactor system has the same disturbances with an additional disturbance... 

TABLE 6.7 Controller Tuning for Cooled Reactor System ... 

Decreasing recycle flow has the opposite effects. Temperatures increase, pressure decreases, and the heat transfer coefficients decrease. Thus the cooled reactor system has some inherent self-regulatory properties that make it openloop-stable, at least for the set of kinetic and design parameters used in this example. Later in this chapter, a hot reaction system will be discussed that has a higher activation energy and larger specific reaction rate. As we will see, this new system is openloop-unstable. 

Closedloop Response Figure 6.23 shows the response of the cooled reactor system to ramped increases and decreases of 10 K in the setpoint of the inlet temperature controller Tin. Raising the inlet temperature produces a decrease in reactor exit temperature of --2.5 K. The production rate increases by only 3%, which indicates that inlet temperature is a poor manipulated variable for production rate changes in this system. 

Figure 6.25 shows the responses to ramped changes of +10.4 K and —12.1 K in the setpoint of the peak temperature controller 7peak. Production rate is changed by 25%, which indicates that the peak temperature provides an effective production rate handle in the cooled reactor system. 

The impact of reaction kinetics on the steady-state design and dynamic controllability of the cooled reactor system is studied in this section. All the results presented in previous sections used a moderate activation energy (69,710 kJ/kmol) and a moderate specific reaction rate. Now the activation energy is doubled (E = 139,420 kJ/kmol). In addition, the reaction rate at 500 K is increased by a factor of 4 (the preexponential factor a = 1.46 x 107kmols 1 bar 2 kg-cat 1). These changes in reaction kinetics make the system highly nonlinear and very sensitive to changes in temperature. 

The openloop response of the suboptimal cooled reactor system (with smaller tubes) is shown in Figure 6.28. The much larger heat-transfer area makes this system openloop stable for a 20% increase or a 20% decrease in recycle flow. Note that the decrease produces an oscillatory response that eventually dies out. Remember that the system is openloop, so the oscillations are not due to the action of any controller. 

Nuclear Energy Research Advisory Committee and Generation IV International Forum, Generation IV Roadmap - R D Scope Report for Water-Cooled Reactor Systems , GIF -003-00, (December 2002). 

There are reports on the use of solid state displacement reactions, too. The joints were made from Tic and Si powder processed at 1400 C, and their shear strength at room temperature reached 50 MPa Nevertheless, these joints were weak compared to SiC/SiC composites, so strength improvement is required for their applications to gas/liquid cooled reactor systems. Additionally, irradiation behavior of these joints will also require to be studied... 

The Chernobyl accident, as well as that at Three Mile Island, therefore suggests that the circumstances under which a rapid rise in cladding temperature can occur should receive special study, both experimentally and analytically, for water-cooled reactor systems. 

W. D. Fowler, C. L. Rickard, and H. B. Stewart, Progress and economics in High Temperature Gas-Cooled Reactor systems. General Atomic Rept. GA-7407, September 1, 1966. 

The Initial brief for the study was that It should consider only civil engineering aspects of nuclear power plants based on gas cooled reactor systems. The brief, however, was extended to Include an assessment of the civil engineering aspects of decommissioning light water cooled reactor systems, particularly the pressurised water reactor. 

In so far as gas cooled reactor systems are concerned, detailed recommendations in respect of further work are as follows ... 

Gas cooled nuclear generating plants In commercial operation In the U.K. at the present time are based either on the magnox reactor system or the advanced gas cooled reactor system. The magnox reactor systems utilise single cavity pressure vessels, the earlier ones being of steel construction, the later ones of prestressed concrete. The advanced gas cooled reactor systems utilise either single cavity or multicavity pressure vessels of prestressed concrete construction. 

POSSIBLE FEATURES TO AID DECOMMISSIONING OF GAS COOLED REACTOR SYSTEMS... 

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