Better Heat Exchanger Designs

Disc- and doughnut-type heat exchangers for gases have lesser pressure drops and do not have idle gas pockets (which may occur in conventional shell- and tube-type heat exchangers with segmental baffles), and the orientations of inlet and exit nozzles for the process streams can he made to suit the ducts (routes of gas duct can also be shortened which is helpful to reduce the pressure drops) without generally affecting plant performance. 

These features increase energy efficiency of the plant since air blower needs less power, and gas-to-gas heat exchange is improved. 

Plate heat exchangers can recover heat from hot sulphuric acid as hot water earlier designs of trombone-type acid coolers wasted all the heat). The hot water can be obtained at a temperature within three to five degrees of the temperature of the incoming hot acid stream and hence can be used elsewhere in the premises. 

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Shoot, B. E., Better Method to Find Pressure Drop, Heat Exchanger Design Handbook, Gulf Publishing Company, (1968) p. 20. 

At the first level of detail, it is not necessary to know the internal parameters for all the units, since what is desired is just the overall performance. For example, in a heat exchanger design, it suffices to know the heat duty, the total area, and the temperatures of the output streams the details such as the percentage baffle cut, tube layout, or baffle spacing can be specified later when the details of the proposed plant are better defined. It is important to realize the level of detail modeled by a commercial computer program. For example, a chemical reactor could be modeled as an equilibrium reactor, in which the input stream is brought to a new temperature and pressure and the... 

Shell and tube heat exchanger design or rating it is better to use a computer software, such as HTRl. 

Heat transfer operations. Heat transfer fluids other than steam and cooling water utilities are sometimes introduced into the design of the heat exchange system. These heat transfer media are sometimes liquid hydrocarbons used at high pressure. When possible, higher boiling liquids should be used. Better still, the flammable material should be substituted with a nonflammable medium such as water or molten salt. 

Economic analysis of designs at lower natural hypochlorite strengths equally show potential investment benefits. They are, however, much less significant than the batch and high concentration cases described above. While an economic case can be made for retrofitting an in-loop reactor to a system that already has an end-of-pipe treatment system based on payback, it is not always clear that this is a better option than an end-of-pipe hybrid system as described earlier in the chapter. For a particular system the optimum solution is often as much a function of the required expenditure on the heat exchangers as it is the relative cost of the reactor options. 

Some newer heating system technologies involve modifications to conventional heat exchangers or the burn design. These changes provide steady-state efficiencies approaching 90%, with seasonal efficiencies to 85%. This is about 10% better than the steady-state efficiencies of 78 to 80% for the most efficient conventional designs. 

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