Introduction to Industrial Automation

Example 4.11:  Chemical Process Automation in a Reactor

Consider the chemical reactor shown in Figure 4.31, where two different liquids are mixed in order 

for a new product to be produced under concrete stirring and temperature conditions. The mix-

ing process starts only if the “Operation Cycle On” condition is true and is realized by a simple 

ON-OFF switch. If during the mixing process the condition is confuted, the mixing process con-

tinues until the end of operation cycle, and then the reactor stops to operate. The mixing process 

must follow the next seven steps:    

 

1.  The valve V

1

 closes

  2.  With precondition that the valve V

1

 has been closed, the refrigerator (RFG) starts to operate 

and simultaneously the valve V

2

 opens. The valve V

2

 remains open until the liquid A level 

inside the reactor reaches the height L

2

 and is detected by a corresponding sensor.

  3. With step 2 completed, the stirring impeller (STR) starts to operate. The stirring impeller 

and the refrigerator stop to operate at the end of the mixing cycle.

  4.  With the precondition that the stirring impeller operates, the valve V

3

 opens and remains 

open, until the liquid B level reaches the height L

3 

detected by a second corresponding 

sensor.

  5.  With Step 4 completed, a time interval of 40 min follows for the mixing and the chemical 

reaction of the two liquids.

  6.  At the end of this reaction period, the valve V

1

 opens and the reactor starts to empty.

 

7.  When the level of the produced liquid drops to height L

1

, then the valve V

1

 closes and a new 

operation cycle begins if the corresponding condition exists.

The required state diagram is shown in Figure 4.32, containing six states and three auxiliary vari-

ables, where the signal “HS” corresponds to the “Operation Cycle On” condition, which is realized 

by a hand-operated switch of SPST type.

 

 

 

V

1

V

2

V

3

RFG

STR

L

1

L

2

L

3

Liquid A

Liquid B