Isothermal reactors

Chattopadhyay, S., Veser, G., Detailed simulations of catalytic ond non-catalytic ignition during H2-oxidation in a micro-channel reactor isothermal case, in Proceedings of the ChemConn-2001, pp. 1-6 (December 2001), Chennai,... 

Try to operate the reactor isothermally with the PID-control as programmed to control the heat input rate. 

Investigate the batch reactor for the case of an equilibrium reaction. Reset the equilibrium constant to the original value in the program. Run first the batch reactor isothermally in the range of 300 to 400 R and determine the equilibrium conversion. Use the Parameter Plot tool for this to obtain the values at each temperature. At low temperatures make sure the STOPTIME is always sufficiently long to reach equilibrium. Using the same temperatures as in Exercise 1, find the reaction times to achieve fraction conversions XA of 90, 95 und 99%. 

Figure 5.2 Graphical representation of the performance equations for batch reactors, isothermal or nonisothermal.

Simple examination of A Hr of a reaction immediately tells us how much heat will be absorbed or hberated in the reaction. This is the amount of heat Q that must be added or extracted to maintain the reactor isothermal. (This heat is exactly the enthalpy change in any flow reactor or in a batch reactor at constant pressure, and it is close to this for other conditions.)... 

HEAT REMOVAL OR ADDITION TO MAINTAIN A REACTOR ISOTHERMAL... 

Example 5-1 Consider the reaction A B, r = kCA, 300 = min, AHr = -20 kcal/mole in a 10 liter reactor with C o = 2 moles/liter and To =300 K- At what rate must heat be removed to maintain the reactor isothermal at 300 K for (a) a batch reactor at 90% conversion ... 

Heat Removal or Addition to Maintain a Reactor Isothermal 217... 

This mode is seldom used except for extremely slow processes such as fermentation or for very small reactors where the surface area for heat transfer is large enough to maintain the reactor thermostatted at the temperature of the surroundings. In fact, we seldom want to operate a reactor isothermally, because we want to optimize the temperature and temperature profile in the reactor to optimize the rate and selectivity, and this is most efficiently achieved... 

Well-mixed reactor, isothermality could be maintained. 

Determine Che plug-flow reactor volume necessary to produce 300 millioa pounds of ethylene a year from cracking a feed stream of pure ethane, The reaction is irreversible and follows an elementary rate law. We want to achieve 80% conversion of ethane, operating the reactor isothermally at 1100 K at a pressiu e of 6 atm. 

The kinetic measurements were carried out in a 15 mm id. differential fixed bed reactor. Isothermality was ensured by inmersion of the differential reactor in an external fluidized bed at the desired reaction temperature. The temperature of the fluidized bed was controlled with a PlD controller. The experiments were performed under differential reactor conditions, at atmospheric pressure and at temperatures between 130 and 170 C. 

Since the temperature must be the same in all parts of this type of reactor, isothermal operation is always achieved as long as steady-state conditions prevail. However, the reactor temperature may be different from that of the feed stream, because of either the heat of reaction or the energy exchange with the surroundings. Hence the treatment in this chapter is restricted to cases where the feed and reactor temperatures are the same. The more general case will be considered in Chap. 5, along with nonisor thermal behavior. 

The experimental rig consisted of a stainless tubular preheater and reactor in series, 17 mm ID and 250 mm long with 5.5 mm axial thermowell. Electric tapes controlled by Eurotherm heated the reactor and preheater. 1-4 g of catalyst (extrudates 1.5 mm in diameter and 2-3 mm length) diluted with 4-8 g of inert SiC pellets to keep the reactor isothermal, was located between two layers of SiC particles of 3-4 mm in diameter. The preheater, operated at 300°C was filled with SiC. 

Below, we describe tbe design formulation of isothermal batch reactors with multiple reactions for various types of chemical reactions (reversible, series, parallel, etc.). In most cases, we solve the equations numerically by applying a numerical technique such as the Runge-Kutta method, but, in some simple cases, analytical solutions are obtained. Note that, for isothermal operations, we do not have to consider the effect of temperature variation, and we use the energy balance equation to determine tbe dimensionless heat-transfer number, HTN, required to maintain the reactor isothermal. 

Heat which must be removed to keep reactor isothermal is... 

The reactor isothermicity is assured by (i) the very low adiabatic temperature raise (< 3°C) and (ii) the use of a micro-reactor with annular cross section (higher external surface per unit volume) heated by a three zone electrical furnace. Moreover, an uniform temperature profile has been revealed by the internal thermocouple placed along the reactor axis. 

BOG conditions and about +3 x 10" / C for EOC conditions over the normal operating temperature range. In the calculation of the total reactor isothermal temperature coefficient of reactivity, the fuel and moderator temperatures up to about 1700 C (3092 F) have been varied isothermally. The inner and outer reflector temperatures on which the reflector contributions to the temperature coefficient calculations are based, are assumed to be in equilibrium with the respective fuel temperatures as discussed later. Table 4.2-12 lists the assumed temperature conditions used to determine the temperature coefficients of reactivity that have been plotted as a function of the active core temperature in Figures 4.2-6 to 4.2-8. A nine neutron group radial diffusion calculational model with cross sections based on the temperatures indicated in Table 4.2-12, was utilized to determine the temperature coefficients of reactivity. 

For long-term transient events such as conduction cooldown, the inner reflector temperature rise lags behind the core temperature rise by typically 3 to 4 hr and only catches up to the active core temperature rise after 50 or more hours at which time the total reactor isothermal temperature coefficient is extremely negative (approximately -10 x 10 V C) i.e. Curve C of Figures... 

Figure 4.2-6 shows the calculated temperature coefficient of reactivity for the BOC-IC condition. Curve A is the fuel prompt doppler coefficient due to heatup of the fuel compact matrix as a function of the assumed fuel temperature. Curve B is the active core isothermal temperature coefficient and is the Siam of the doppler coefficient and the moderator temperature coefficient of reactivity which is also strongly negative, due in large measure to the presence of LBP in the BOC condition. The moderator coefficient, not shown in Figure 4.2-6, would be the difference between Curve B and Curve A and would be -4.0 x 10" / C at 800 C (1472 F), for example. Curve C is the total reactor isothermal coefficient and includes the positive contribution of the reflector heatup to the estimated inner and outer reflector temperatures that would result when the fuel reaches the indicated temperature. 

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