Practical Process Integration Retrofit Part 3. Path Analysis

Practical Process Integration Retrofit

Part 3. Path Analysis

G.T.Polley

The concept of transferring heat along paths was first suggested by Dhole [1]. It was subsequently investigated by Adiarso [2] and Van Reisen [3,4]. It forms the basis of a technique known as Network Pinch introduced by Zhu & Asante [5].

When using path analysis the engineer concentrates on minimising the number of changes that are made to the existing network structure for such changes generally involve quite large capital investment.

The identification of existing heat recovery paths and possible new paths is usually quite straight forward and does not require the use of special software.

The technique should not be used in isolation. It is worth undertaking a cross-pinch analysis to establish if structural change is justified. For instance when software employing the network pinch analysis was applied to a large problem Al Riyami et al [6], it failed to identify simple energy saving opportunities associated with re-boilers positioned well below the pinch [7].

Procedure

Example: Increased Heat Recovery in Pre-Heat Train

Features to be Observed in Path Analysis

Bridges

Blocks

Fixed Loads

References

[1]  V.R.Dhole, Private Communication, UMIST, 1990

[2]  Adiarso, Application of Problem Decomposition in Process Integration Retrofit, M.Sc. Dissertation, UMIST, 1993

[3] Van Reisen J.L.B., Grievink J., Polley G.T. & Verheijen P.J.T.The placement of two-stream and multi-stream heat-exchangers in an existing network through path analysis, Comp.& Chem. Engng., 1995, 19,S143-S148

[4] Van Reisen J.L.B., Polley G.T. & Verheijen P.J.T. Structural Targeting for Heat Integration Retrofit, Appl. Thermal Engng. 1998, 18(5), 283-294

[5] Asante N.D.K. & Zhu X.X. An automated approach for heat exchanger network retrofit featuring minimal topology modifications, Comp.& Chem. Engng., 1996, 20,S7-S12

[6] Al Riyami B.A., Klemes J. & Perry S., Heat integration retrofit analysis of a heat exchanger network of a fluid catalytic cracking plant, Appl.Thermal Engng. 2001, 21, 1449-1487

[7] Polley G.T. & Kumana J.D. Energy Saving Retrofit of FCC Plant,       NPRA  Annual Meeting, March 2007, San Antonio, Texas