Heat pump integration

Figure 6.38 Integration of heat pumps with the process.

Unfortunately, the overall design problem is even more complex in practice. Spare driving forces in the process could be exploited equally well to allow the use of moderate utilities or the integration of heat engines, heat pumps, etc. in preference to distillation integration. 

Heat Pumps. Because of added capital and complexity, heat pumps are rarely economical, although they were formerly commonly used in ethylene/ethane and propylene/propane spHtters. Generally, the former spHtters are integrated into the refrigeration system the latter are driven by low level waste heat, cascading to cooling water. 

The use of the pinch technology method in the design of heat exchanger networks has been outlined in Sections 3.17.1 to 3.17.6. The method can also be applied to the integration of other process units such as, separation column, reactors, compressors and expanders, boilers and heat pumps. The wider applications of pinch technology are discussed in the Institution of Chemical Engineers Guide, IChemE (1994) and by Linnhoff et al. (1983), and Townsend and Linnhoff (1982), (1983), (1993). 

The New Energy and Industrial Technology Development Organization (NEDO), 1993. Final Report for the Project of Super-Heat Pump and Energy Integrated System, September 1993 (in Japanese). 

There are two fundamental ways in which a heat pump can be integrated with the process across and not across the pinch14. Integration not across (above) the pinch is illustrated in Figure 16.37a. This arrangement imports W... 

Figure 16.37 Integration of heat pump with the process.

Figure 16.38 shows a heat pump appropriately integrated against a process. Figure 16.38a shows the overall balance. Figure 16.38b illustrates how the grand composite curve can be used to size the heat pump. How the heat pump performs determines its coefficient of performance. The coefficient of performance for a heat pump can generally be defined as the useful energy delivered to the process divided by the power expended to produce this useful energy. From Figure 16.38a ...

Using the grand composite curve, the loads and temperatures of the cooling and heating duties and hence the COPhp of integrated heat pumps can be readily assessed. 

For heat pumping to be economic on a stand-alone basis, it must operate across a small temperature difference, which for distillation means close boiling mixtures. In addition, the use of the scheme is only going to make sense if the column is constrained to operate either on a stand-alone basis or at a pressure that would mean it would be across the pinch. Otherwise, heat integration with the process might be a much better option. Vapor recompression schemes for distillation therefore only make sense for the distillation of close boiling mixtures in constrained situations3. 

In addition to the development of new products with previously unavailable property combinations, the task of making the process more efficient is important, particularly in this day and age. The cost factor energy can still be reduced if, for example, the heat of polymerization can be better utilized. It has been suggested that heat pumps be used for this purpose and the energy recovered be employed for the devolatilization step (38). In the same paper the author also suggests the integration in one factory of the monomer/polymer and end product fabrication, the latter since the polymer is already available in the molten state. 

P. Mizsey and Z. Fonyo. Energy integrated distillation system design enhanced by heat pumping distillation and absorption. Inst. Chem,. Eng., pages B69-B75, 1992. 

Technology development of a 5 kW PEM, integrated with a reversible heat pump and photovoltaic field. 

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