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[fff]

Hi.

How do I determine the number of tubes and its size for a packed bed reactor?
Also, how do I know the outer shell length and diameter?

Thanks for any help.

[Art Montemayor]

fff:

Very good, basic question for a Chemical Engineering student.

However, I sincerely hope that you have already taken (and passed) Chemical Reaction Kinetics – or, at the very least, presently taking this important course – usually given in the last years of your university curriculum. If you haven’t taken (or presently taking) this course – or if you slept through it – then you are in very deep water and it is best to let this sleeping bear alone. Since you raised the query and haven’t given us any background information and data, or scope of work, I have to assume that you are a whiz at Reaction Kinetics and are aware of the following:

In flow systems, other conditions being constant, the fractional conversion is determined by the time during which the reactants are in contact with the fixed catalyst. This time contact is not directly measureable, but it depends upon the rate of flow and the quantity of the catalyst. It is usually treated in reactor design and operational practice in terms of “SPACE VELOCITY”. Spacie velocity is defined as the volume of gas (@ standard temperature and pressure) or liquid passing through a fixed volume of catalyst space, v_C, in unit time divided by the latter. The mathematical expression is:

Space Velocity = V/v_C

Where,

V = volumetric flow of reactant, volume / time unit;

v_C = volume of fixed bed catalyst exposed to reactant, volumetric unit.

It may be referred to any principal constituent of the reacting mixture.

Additionally, if you go to:

http://en.wikipedia.org/wiki/Space_velocity_(chemistry)

You will find the following:

“In chemical engineering and reactor engineering, space velocity refers to the quotient of the entering volumetric flow rate of the reactants divided by the reactor volume (or the catalyst bed volume) which indicates how many reactor volumes of feed can be treated in a unit time (for instance, a reactor with a space velocity of 7 hr⁻¹ is able to process feed equivalent to seven times the reactor volume each hour). It is commonly regarded as the reciprocal of the reactor space time. In industry, space velocity can be further defined by the phase of the reactants at given conditions. Special values for this measurement exist for liquids and gases, and for systems that use solid catalysts.”

I hope you now see the logical path and necessary calculations required to identify the the number of tubes, their size, and the outer reactor shell length and diameter for a packed bed reactor.

It is one of the simplest problems to resolve in Chemical Engineering – once you identify the Space Velocity for the reaction in question.