Reactors thermal balance

Normally when a small change is made in the condition of a reactor, only a comparatively small change in the response occurs. Such a system is uniquely stable. In some cases, a small positive perturbation can result in an abrupt change to one steady state, and a small negative perturbation to a different steady condition. Such multiplicities occur most commonly in variable temperature CSTRs. Also, there are cases where a process occurring in a porous catalyst may have more than one effectiveness at the same Thiele number and thermal balance. Some isothermal systems likewise can have multiplicities, for instance, CSTRs with rate equations that have a maximum, as in Example (d) following. 

The utihty stream gets started at operating temperature and flow rate. In the following experiments, the utihty stream is heated so as to initiate the reaction. The main and secondary process tines are fed with water at room temperature and with the same flow rate as one of the experiments. Once steady state is reached, operating parameters are recorded. Process tines are then fed with the reactants, hydrogen peroxide and sodium thiosulfate. At steady state, operating parameters are recorded, and a sample of a known mass of reactor products is introduced in the Dewar vessel. Temperature in the Dewar vessel is recorded until equilibrium is reached, that is, until the reaction ends. This calorimetric method is aimed at calculating the conversion rate at the product outlet and thus the conversion rate in the reactor. The latter is also determined by thermal balances between process inlet and outlet of the reactor. Finally, the reactor is rinsed with water. This procedure is repeated for each experiment... 

Two methods have been used to calculate the conversion rate in the reactor. They are based on thermal balances first between inlet and outlet of process and utility streams in the reactor and then between sampling and thermal equilibrium in the Dewar vessel. The former leads to the conversion rate obtained in the reactor, x and the latter gives the conversion rate downstream from the reactor outlet, 1 - X-... 

In a third reactor (R3, thermal support unit), the solid obtained in R2 is fully oxidized to hematite with air. This third zone is aimed at closing the thermal balance of the process the heat released is used to carry out the endothermic step. In practice, this would correspond to the burning of a part of the hydrogen produced, to supply the heat for this step. This third unit can be avoided if the endothermicity of the process is accepted, and the reoxidation with water is completed in R2, so maximizing the amount of H2 produced per unit weight of catalyst. 

Thermal balance calculations show that the reactor could have been relieved via gas flow, that is, one phase flow, through the rupture disk and safety valve up to 250 °C and 65 bar. When the accident happened, the mass... 

Low-dimensional models for loop, recycle, and tank reactors could similarly be derived starting from the coupled mass and thermal balances. Here, we present the reduced models and refer to a previous publication (Chakraborty and Balakotaiah, 2004) for the derivation of these models. 

Coupled mass and thermal energy balances are required to analyze the nonisother-mal response of a well-mixed continuous-stirred tank reactor. These balances can be obtained by employing a macroscopic control volume that includes the entire contents of the CSTR, or by integrating plug-flow balances for a differential reactor under the assumption that temperature and concentrations are not a function of spatial coordinates in the macroscopic CSTR. The macroscopic approach is used for the mass balance, and the differential approach is employed for the thermal energy balance. At high-mass-transfer Peclet numbers, the steady-state macroscopic mass balance on reactant A with axial convection and one chemical reaction, and units of moles per time, is... 

If our semi-batch process is exothermic and we lose flow of heat transfer fluid to the reactor jacket, the ensuing event is unlikely to become a runaway with regard to temperature if we block flow of LR into the process. Upon losing cooling to the process, the thermal balance for our semi-batch reactor becomes... 

The design of plug flow reactors (tubular and tower devices) does not assume mixing in the direction of flow (axial turbulence), therefore the chemical processes within a blend of reactants occurs in laminar flow conditions. A combination of the displacement and plug flow reactors, with consideration of their material and thermal balances, makes it possible to calculate the optimal design of a device for any chemical process. 

Power self-limitation of the "hot" reactor at the balance of the reactor thermal power and the emergency heat removal channels" capacity in beyond design accidents ... 

Hydrogen may be efficientiy produced in the system illustrated earlier in Fig. 3.12, where nuclear heat is transferred from the primary side coolant in the IHX and then transported in a closed heat transport loop to the thermal hydrogen production plant (Yan et al., 2005). The process parameters in Fig. 3.15 indicates that the IHX transfers 170 MWth of the total 600 MW reactor thermal power to the hydrogen process. The balance of the reactor thermal power is used by the gas turbine to generate 203 MWg electricity. 

Reactor thermal hydraulic performance is challenging due to the low operating pressure (2-3 MPa), the properties of the helium-xenon gas mixture and the need to maintain a low reactor core pressure drop to maximize system performance. The maximum fuel element surface temperature is approximately 1300 K during normal full power operation. Sensitivity studies were performed for the range of fuel element sizes, flow configurations, and reactor materials to balance heat transfer and pressure drop through the core. 

In DHRUVA, on-line computation of important physics and process parameters has been achieved. The parameters selected are reactor thermal power, reactivity load due to Xenon, core reactivity balance, heavy water system inventory and performance monitoring of shut-off rods control valve and dump valves. Also off-line application for fuel management, failed fuel detection and location, and stores inventory management have been implemented. 

Reactor thermal power is calculated using standard heat balance equation [9] P = mC Ar (2)... 

The rate of heat production in a tank reactor is generally determined by the thermal balance of the system. Experience has shown that, when drawing up a thermal balance for the reactor itself and its cooling jacket, both the stirrer power... 

A number of sensitivity studies were performed to determine the effect of parameter variations on the plant s overall heat balance and other parameters of interest. Of particular interest was the effect of parameter variation on required reactor thermal output, required radiator area, and reactor inlet temperature. The overall mass of the SNPP is minimized when reactor thermal output and required radiator area are near minimum values as the mass of the reactor, the reactor radiation shield, and the heat rejection segment dominate the overall SNPP mass. Minimizing the required thermal output of the reactor has many benefits as the mass of the fuel load, reactor structure, and reactor radiation... 

Numerical simulations allowed the reproduction of the reactor s dynamic behavior, mainly the thermal balance. Despite the differences between the models, both models reproduced almost in the same way in terms of the reactor and coolant fluid temperature dynamic profiles. Regarding the use of a specific model, the authors advise to take into account some points if the internal heat and mass-transfer coefficients of the catalyst particles are significant. Dynamic Model I is more suitable to represent the reactor dynamic behavior in case of difficulties in the measurement of such parameters. Dynamic Model II must be chosen. For design and simulation studies, where computational time and numeric difficulties for model solution are not limiting factors. Dynamic Model I is the most reliable however, if the same factors are limiting. Dynamic Model II should be the best alternative. 

Steady state models of the automobile catalytic converter have been reported in the literature 138), but only a dynamic model can do justice to the demands of an urban car. The central importance of the transient thermal behavior of the reactor was pointed out by Vardi and Biller, who made a model of the pellet bed without chemical reactions as a onedimensional continuum 139). The gas and the solid are assumed to have different temperatures, with heat transfer between the phases. The equations of heat balance are ... 

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