(61d) Thermal Fluids: The Key to Overall Site Integration

Thermal
Fluids: the Key to Overall Site Integration

G.T.Polley, M.Picon Nunez & E.Tamakloe

Dept. of Chemical Engineering, University of Guanajuato, Mexico

Structure of
Presentation

·        
Need for efficient transfer of energy
across separate geographical zone

·        
Overall Factory Sites

·        
Improvement of CDU Fired Heater
Efficiency

Transfer of Energy Across
Geographical Zones

A recent study of the energy
efficiency of an FCC plant revealed a number of distillation column re-boilers
positioned well below the heat recovery pinch but being driven by steam.

Examination of the plant
structure (Figure 1) revealed the probable cause of this inefficiency, the
piping costs associated with the use of direct integration would be very high
and not justified by the energy saving achieved.

Figure 1.  Plant
Structure

Design of New Plant
Using Process Decomposition Analysis

Full Problem:                          36    MW      
6.04 M$/annum

Column Region:                      3.2                 2.46

Gas Area:                                74.1                7.53

Summation:                             77.3 MW       9.99 M$/annum

Failure to transfer energy between the two zones results in
over 100 % increase in energy consumption.

Inter-Zonal Transfers: Comparison of Grand Composite Curves

Analysis of inter-zonal transfers
involves comparison of pinch locations in each of the zones and the Grand
Composite Curves for each of the zones.

Column Region:

Gas Processing Area:

The temperature differences allow for indirect integration.
This is a preferred option for it allows the plant zones to be independently
operated and minimises that transport of process fluid across the plant.

Transfer limited by formation of second pinch.

By using oil operating between 245 and 120 C it is possible
to transfer 39 MW between the two zones. The decomposition analysis is:

Full Problem:                          36    MW      
6.04 M$/annum      DT = 10 C

Column Region:                       4.9                2.10                                     24 C

Gas Area:                               35.13              4.97                                      10 C

Summation:                            40.03  MW   
7.07  M$/annum

The transfer has resulted in a net energy saving of 37.3 MW.
The process uses 4.03 MW more than the prediction for the overall problem.

A document providing full design solution is available from
the authors.

Overall Factory
Sites

?Site Composites? are built up by extracting the ?supply?
and ?demand? elements of the Grand Composite Curves for the Individual Plants.

Capital costs dominated by piping costs.

The capital cost of piping varies with diameter raised to a
power 3.

Size of pipe required to transport a liquid very much
smaller than that required to transfer steam.

Use thermal fluid. DO NOT TRANSPORT STEAM.

Improvement of CDU
Fired Heater Efficiency

Fouling rates in convective section of a fired
heater are affected by the flow conditions on the crude side

If crude enters as a single phase liquid
fouling rates are high