Click for Site Map and Index

HOMETen Types of Home Problems

Homogeneous Examples

 

Type 9 Home Problem -- PART I of the Solution
Problems that promote discussion.

First, the group analyzes the problem by sizing the reactors graphically on the plot of the inverse reaction rate (1/-rA) versus the conversion (X).

They see how it operated before the damage to the CSTR:

 

and after the damage to the CSTR:

 

From this, the group gathers that the reaction rate (-rA) in the CSTR dropped significantly. The group then starts to brain-storm on the possible malfunctions that could cause this change in reaction rate.

 

Jane: "Maybe the dent has caused dead-zones (areas where there is incomplete mixing) within the reactor, so that the CSTR is no longer well-mixed. We could take samples from various locations in the CSTR and check the concentration."

Steve: "Maybe there was just an error in measuring the conversion. We should check the lab equipment."

You: "Maybe the flow to or from the CSTR is no longer optimized. If the flow to the CSTR is too low, then we will not get enough product. If the flow increases, then the conversion drops. We know this from the mole balance on a CSTR. With a constant volume, an increase in FAo would cause a slide to lower conversion."

"We should check the flow meters and the pump between the heat exchanger and the CSTR to make sure they are operating properly."

Bill: "The feed temperature could be too low. This would decrease our rate constant (k) and our reaction rate (-rA), if the reaction is endothermic. If the temperature is too high and the reaction is exothermic, that would also decrease our reaction rate. We need to check and make sure that the heat exchanger and temperature sensors are working properly."

Steve: "The dent may have decreased the volume of the CSTR enough to cause a slide to the left along the graph. We should empty the tank and fix the dent."

Jane: "The feed concentration may be too low. That could cause a decrease in the reaction rate and a slide to the left in conversion. We should check the concentration of our feed."

You: "Well maybe the agitator in the CSTR is broken. That could be why the reactor makes a different noise. If the fluid in the CSTR were not properly mixed, the reaction rate would decrease."

 

Following this discussion, you go to Dr. Pakbed and tell him your theories. He also believes it is the agitator that is broken, so he orders an inspection of the agitator.

After a careful inspection, it turns out that the agitator is indeed the culprit. Unfortunately, Dr. Pakbed cannot shut down the line to have the agitator fixed. He needs the CSTR and PFR to convert 70% of the butalene (A) to tirene (B). He wants you to propose a solution that can be implemented without shutting the line down for a day to fix the agitator.

 

On to PART II of the Solution

 

Back to Homogeneous Example 9

 


CRE Thoughts Ten Types Homogeneous Example 9