Integration Of Heat Pumps

A schematic of a simple vapor compression heat pump is shown in Fig. 6.37. A heat pump is a device that absorbs heat at a low 

Thus the appropriate placement of heat pumps is that they should be placed across the pinch. Note that the principle needs careful interpretation if there are utility pinches. In such circumstances, heat pump replacement above the process pinch or below it can be economic, providing that the heat pump is placed across a utility pinch. Such considerations are outside the scope of the present text. 

For any given type of heat pump, a higher COPhp leads to better economics. Having a better COPhp and hence better economics means working across a small temperature lift with the heat pump. The 

Energy Targets for Heat Exchanger Network and Utilities 205 

Using the grand composite curve, the loads and temperatures of 

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Figure 6.38 Integration of heat pumps with the process.

Figure 16.37 Integration of heat pump 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. 

Cost reduction of the NGL plant by integrating different heat pump systems... 

To choose one of these three columns for integrating by heat pump systems, we consider the approach of exergy destruction for each column. Table 2 shows that the exergy destruction through the de-propanizer column is greater than the other columns so this column has more potential for retrofitting by heat pump systems. 

Aspen Plus simulator has been used for integrating three types of heat pump systems into the de-propanizer column and eliminating the condenser and reboiler completely, as a result. 

Reairai ement of Equipment. There are certain guidelines that should be followed when the sequence of equipment is considered. Some are obvious. For example, one should try to pump a liquid rather than compress a gas thus, it will always be better to place a pump before a vaporizer rather than a compressor after it. However, other topological changes are somewhat more subtle. The most common examples of equipment rearrangement are associated with the separation section of a process and the integration of heat transfer equipment. In this section the sequencing of separation equipment is the focus, and heat integration is covered in Chapter 15. The separation sequence for the DME process is considered in... 

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. 

This paper describes work on equipment and instrumentation aimed at a computer-assisted lab-scale resin prep, facility. The approach has been to focus on hardware modules which could be developed and used incrementally on route to system integration. Thus, a primary split of process parameters was made into heat transfer and temperature control, and mass transfer and agitation. In the first of these the paper reports work on a range of temperature measurement, indicators and control units. On the mass transfer side most attention has been on liquid delivery systems with a little work on stirrer drives. Following a general analysis of different pump types the paper describes a programmable micro-computer multi-pump unit and gives results of its use. 

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). 

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