Optimum feed temperature

Observe how the conversion profile changes as the entering temperature is decreased from 600 K, 

When there are no phase changes, the heat of reaction at temperature T is related to the heal of reaction at the standard reference temperature by 

For adiabatic operation (g = 0) of a PFR, PBR, CSTR, or batch reactor, and neglecting we solve Equation (SI 1-4) for the adiabatic conversion-temperature relationship is  

Solving Equation (SI 1-5) for the adiabatic temperature-conversion relationship  

Example 11-3 Polymath Adiabatic Isomerization of Normal Butane 

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It is important to notice that the optimum feed temperature Tfa decreases sharply as Fc increases. This is due to the fact that increased quantities of heat are removed from the regenerator as the catalyst circulation rate increases. 

The amount of catalyst needed depends on the feed temperature and the conversion if is fixed, it can be shown that there is an optimum feed temperature. If the feed temperature is so high that is reached only when T Tgq [line (a) in Fig. 3.17], the final rate is almost zero, and a very large mass of catalyst would be needed. Changing the feed temperature to Tp also requires a large amount of catalyst, since every part of the catalyst is... 

For a multistage reactor, there is an optimum feed temperature for each stage, but the intermediate conversions are also variables to be optimized. For a three-stage converter with a fixed total conversion, there are three feed temperatures and two intermediate conversions to be optimized to get the minimum amount of catalyst. 

Further calculations led to the plot of 1 jr vs. x in Figure 3.20a. The value of WjF, the area under the curve, is 0.196. Calculations for other feed temperatures were used to prepare a plot of W/Fji versus Tp, shown in Figure 3.20b. The optimum feed temperature is 412°C, which makes the final temperature 622°C, only 4°C below T. ... 

Figure 3.20 Determining optimum feed temperature for an SO2 converter (a) Getting W/F for Tp = 410°C. (b) W/Fa for different feed temperatures.

The optimum feed temperature to a deaerator is the boiling point of water at the deaerator pressure. Typically, 230°F to 240°F. However, in many of the plants, BFW to the deaerator is heated to 160°F to 180°F by heat exchange with process pumparound or product streams. 

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