Chapter 6 Design for Single Reaction In this chapter we deal with single reaction.These are reactions whose progress can be described and followed adequately by using one and only one rate expression coupled with the necessary stoichiometric and equilibrium expressions. For such reactions product distribution is fixed; hence,the important factor in comparing design is the reactor size
1 Chapter 6 Design for Single Reaction In this chapter we deal with single reaction. These are reactions whose progress can be described and followed adequately by using one and only one rate expression coupled with the necessary stoichiometric and equilibrium expressions. For such reactions product distribution is fixed; hence, the important factor in comparing design is the reactor size
6.1 Size Comparison of Single Reactors ·Batch reactor Batch reactor has the advantage of small instrumentation cost and flexibility of operation.It has the disadvantage of high labor and handling cost,often considerable shutdown time to empty,clean out,and refill,and poorer quality control of the product. 2
2 6.1 Size Comparison of Single Reactors • Batch reactor • Batch reactor has the advantage of small instrumentation cost and flexibility of operation. It has the disadvantage of high labor and handling cost, often considerable shutdown time to empty, clean out, and refill, and poorer quality control of the product
Regarding reactor size,for a given duty and a constant volume system,an element of fluid reacts for the same length of time in the batch and in the plug flow reactor.Thus, the same volume of these reactors is needed to do a given job. On a long-term production basis we must correct the size requirement estimate to account for the shutdown time between batches. 3
3 • Regarding reactor size, for a given duty and a constant volume system, an element of fluid reacts for the same length of time in the batch and in the plug flow reactor. Thus, the same volume of these reactors is needed to do a given job. • On a long-term production basis we must correct the size requirement estimate to account for the shutdown time between batches
Mixed versus plug flow reactor,first-and second-order reaction Make a comparison for large class of reactions approximated by the simple nth- order rate law: w-张-c where n varies anywhere from zero to three.For mixed flow Eq.5.11 gives Tm CAOY CAoXA=1 XA(1+EAXA) FA0m-TA kCAo(1-XA)” whereas for plug flow Eq.5.17 gives 4
4 • Mixed versus plug flow reactor, first- and second-order reaction • Make a comparison for large class of reactions approximated by the simple nthorder rate law:
Dividing we find that (TCAO)m .[x+l (1) (TCAO)p 。ix With constant density,or s =0,this expression integrates to XA (TCAO)m n卡1 (rCX)p 可 or (2) n=1 (TCAO )p -In(1-XA)p 5
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