Pinch Analysis Exercise [PDF]

Citation preview

Pinch Analysis Question and Answers



Questioned by – Dr.Narayana (Chemical & Process Engineering, University of Moratuwa, Sri Lanka)



Answered by – Eng. Prasanna Welahetti(Chemical & Process Engineering, University of Moratuwa, Sri Lanka)



EXERCISE 1 A heat recovery problem consists of two streams given in the Table. Stream



Type



1 2



Hot Cold



Supply temperature (0C) 100 10



Target temperature (0C) 40 150



Enthalpy change (kW) 12 7



1 For a minimum permissible temperature difference (dTmin) of 100C,calculate the minimum hot and cold utility requirements. 2. What are the hot and cold stream pinch temperatures? 3. If the (dTmin) is increased to 200C, what will happen to the utility requirements? EXERCISE 2 The stream data for a process are given in the Table. No



Steam type



1 2 3 4 5



Hot Hot Hot Cold Cold



Supply temperature (0C) 160 150 140 60 60



Target temperature (0C) 40 50 110 160 150



Enthalpy change (kW) 3.6 5.0 1.5 5.0 1.8



1. Sketch the composite curves for dTmin= 100C. 2. From the composite curves, determine the target for hot and cold utility for dT min= 200C.



Answers EXERCISE 1 1.



Stream



Type



1 2



Hot Cold



Supply temperature (0C) 100 10



Hot Steam Enthalpy (kW) Temperature(C') 0 40 12 100



Target temperature (0C) 40 150



Enthalpy change (kW)



CP Values (KW/0C)



12 7



0.2 0.05



Cold Stream Enthalpy (kW) Temperature(C') 8 10 15 150



Heat Recovery



= (𝐶𝑝)𝑐 ( 𝛥𝑇) = 0.05 × 90 − 10 =4kW



Minimum Hot Utility



=7 − 4 =3kW



Minimum Hot Utility



=12 − 4 =8kW



2. Hot Pinch Utility



= 100℃



Cold Pinch Utility



= 90℃



3. When, 𝑇𝑚𝑖𝑛 = 20℃ Cold Stream curve is shifted to right side, New Cold Stream Enthalpy (kW) Temperature(C') 8.5 10 12 80 15.5 150



New heat duty



= 0.05 × (150 − 80) =3.5𝑘𝑊



New Cold duty



=12 − 7 − 3.5 =8.5 𝑘𝑊



EXERCISE 2 1.



No



Steam type



1 2 3 4 5



Hot Hot Hot Cold Cold



Supply temperature (0C) 160 150 140 60 60



Target temperature (0C) 40 50 110 160 150



Enthalpy change (kW)



CP Values (KW/0C)



3.6 5.0 1.5 5.0 1.8



0.03 0.05 0.05 0.05 0.02



Composite Heat Values



T (C˚) Range



Hot Composite(kW) Cold Composite(kW)



160-150 150-140 140-110 110-60 60-50 50-40



0.3 0.8 3.9 4.0 0.8 0.3



0.5 0.7 2.1 3.5 0 0



Hot Composite Stream Enthalpy(kW) Temperature(C˚) 0 40 0.3 50 1.1 60 5.1 110 9 140 9.8 150 10.1 160



Cold Composite Stream Enthalpy(kW) Temperature(C˚) 4.2 60 7.7 110 9.8 140 10.5 150 11 160



2.



Hot Composite Stream Temperature(C˚) Enthalpy(kW) 0 40 0.3 50 1.1 60 5.1 110 9 140 9.8 150 10.1 160



New Cold Composite Stream Temperature(C˚) Enthalpy(kW) 4.9 60 8.4 110 10.5 140 11.2 150 11.7 160



Cool duty



= 4.9 𝑘𝑊(from the graph)



Heat Duty



= 11.7 − 10.1(from the graph) =1.6kW