Question

Hi there! I can not find solution of Octave Levenspiel Chapter 26. I need it immediately. Can you please help me!Thank you.

A solid feed consisting of

20 wt% of 1-mm particles and smaller

30 wt% of 2-mm particles

50 wt% of 4-mm particles

passes through a rotating tubular reactor somewhat like a cement kiln where it reacts with gas to give a hard nonfriable solid product (SCMI reaction control, T = 4 h for 4-mm particles).

26.3. Find the residence time needed for 100% conversion of solids.

26.4. Find the mean conversion of the solids for a residence time of 15 min.

26.5. Particles of uniform size are 60% converted on the average (shrinking core model with reaction controlling) when flowing through a single fluidized bed. If the reactor is made twice as large but contains the same amount of solids and with the same gas environment what would be the conversion of solids?

26.6. Solids of unchanging size, R = 0.3 mm, are reacted with gas in a steady flow bench scale fluidized reactor with the following result. F, = 10 gmlsec, W = 1000 gm, X, = 0.75 Also, the conversion is strongly temperature-sensitive suggesting that the reaction step is rate-controlling. Design a commercial sized fluidized bed reactor (find W) to treat 4 metric tonslhr of solid feed of size R = 0.3 mm to 98% conversion.

26.7. Solve Example 26.3 with the following modification: the kinetics of the reaction is ash diffusion controlled with T(R = 100 ~m=) 1 0 min.

26.8. Repeat Example 26.4 if twice the stoichiometric ratio of gas to solid, still at C,,, is fed to the reactor.

26.9. Repeat Example 26.4 if the gas is assumed to pass in plug flow through the reactor.

Answer 1

26.3) For plug flow SCMI reaction model, we have (residence time) directly proportional to R (radius of particle

.........(1)

We have been given that for 4 mm particle (r =2 mm), residence time is 4 hrs. So using this info. and eq1:

For 2 mm particle:

Similarly For 1 mm particle:

The mean conversion can be found using formula:

Here tp is residence time given in a reactor. And is the residence time for 100% conversion of that particle and xi is the fraction of that praticle.

For 2 mm particle: x1 = 0.3 and = 120 min

For 4 mm particle: x2 = 0.5 and ​​​ = 240 min

For 1 mm particle: x3 = 0.2 and = 60 min

We want XB = 1

On solving this:

We get tp = 105.7 min = 1.76 hrs

26.4)

The mean conversion can be found using formula:

Here tp is residence time given in a reactor. And is the residence time for 100% conversion of that particle and xi is the fraction of that praticle.

For 2 mm particle: x1 = 0.3 and = 120 min

For 4 mm particle: x2 = 0.5 and ​​​ = 240 min

For 1 mm particle: x3 = 0.2 and = 60 min

1 - XB = 0.697

XB = 0.30

26.5)

We are given that, weight of solid is same. Also the gas envirnment is same ie the initial concentration, molar flow can be assumed to be same.

In case of fluidized bed, the residence time depends on the weight of catalyst and not on the size of the reactor. So there will be no change in the residence time of the reactor after doubling its size.

The conversion is only function of the residence time.

So the conversion will also not change by changing the size of reactor.