REACTORS: IDEALIZED CHEMICAL REACTORS - Biomass as a Sustainable Energy Source for the Future - page 180

z z + dz

+dV

+

DS dc A
dL

DS dc A
dL

0= φ n , A − φ n , A +d φ n , A − −− R ð Þ) −

DS d 2 c A
dL

: :

d φ n , A − + R ð Þ − S dL = 0 ð Eq 6 48 Þ

Dividing by S dL and knowing that d φ n , A = Su dc A lead to

D d 2 c A

u dc A

dL − dL 2 +

R ð Þ − =0 ð Eq : 6 : 49 Þ

To solve the molar balance, the term ( R A ) must be substituted by the kinetic

expression, e.g., kc A , and then a numerical method must be applied to obtain the
concentration as a function of the axial position in the reactor.

−

CHAPTER SUMMARY AND STUDY GUIDE

This chapter provides the basics of chemical reactor engineering. It describes the three
most common ideal chemical reactors: the BR, the CSTR, and the PFR (Figure 6.8).
The analysis focuses on the mass and energy balances for single reactions, leaving
aside complex kinetic laws and multiple reactions.
The concept of RTD is introduced as a way of quantifying the non-idealities of the
flow. It is shown how to determine the RTD curve and its meaning.

Time 1 Time 2 Time 3

Batch

r , V r , V r , V

φ n,A0

φ n,A φ n,A0 φ n,A φ n,A0

φ n,A

Steady
CSTR

r , V r , V r , V

Steady
plug
low

φ n,A0

φ n,A0 φ n,A φ n,A φ n,A0 φ n,A

r ( x,z ) r ( x,z ) r ( x,z )

FIGURE 6.8 Scheme of the three types of ideal reactors covered in this chapter.