Tubular reactors cooled or heated from the wall

7 Tubular Reactors Cooled or Heated from the Wall 

In this section we shall be concerned with more realistic models of tubular reactors. The isothermal reactor is obviously the simplest type, but it implies that either there are no large heat effects or that they can be completely dominated by temperature control. The reactor with an optimal temperature profile is clearly the most desirable, but this means that the rate of heat exchange can be regulated precisely at each point. Between these two extremes there is a range of designs about which something should be said. We shall not always solve the equations in detail but we shall try to show the important features of the behavior of the reactor by means of examples. 

It will be convenient to divide this section more formally than the others, according to the following scheme. Under Sec. 9.7.1 we discuss the genera form of the equations when the wall temperature is constant and illustrate this by considering an endothermic cracking reaction. Under Sec. 9,7.2 we shall consider cocurrent and countercurrent cooled reactors and use the ammonia synthesis reactor as an illustration. These correspond to the two subcases of the third type of design problem mentioned in Sec. 9.5. 

We have chosen the signs in the basic equations of Sec, 9.5 so that the terms are positive when the reaction is exothermic and the reactor is being cooled. Even though the reaction may be endothermic (i.e., / 0) and the temperature 7 much higher than that of the reactants, 7, we shall retain the 

In these equations, Ar is the cross-sectional area of the reactor and Oc the perimeter of the heat interchange area in any section. The ratio Arjac has the dimensions of length and is known as the hydraulic radius it will be denoted by p in this section. The dimensionless quantity 

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Sec. 9.7 Tubular Reactors Cooled or Heated from the Wall... 

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