Cascade cycle

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Fig. 8. (a) Pressure—enthalpy diagram and (b) system schematic for a cascade cycle. 

FIG. 11-114 Three- and nine-level cascade cycle cooling curve for natural gas. 

The mixed refrigerant cwcle was developed to meet the need for hq-uefying large quantities of natural gas to minimize transportation costs of this fuel. This cycle resembles the classic cascade cycle in principle and may best be understood by referring to that cycle. In the latter, the natural gas stream after purification is cooled successively by vaporization of propane, ethylene, and methane. Each refrigerant may be vaporized at two or three pressure levels to increase the natural gas coohng efficiency, but at a cost of considerable increased process complexity. 

The mixed refrigerant cycle is a variation of the cascade cycle and involves the circulation of a single multicoiTmonent refrigerant stream. The simplification of the compression and heat exchange services in such a cycle can offer potential for reduced capital expenditure over the conventional cascade cycle. 

Published analyses of cascade cycles by means of energy balances under conditions comparable to those used in analyzing expander cycles are very scarce. Longwell and Kruse tabulated computer-calculated compressor and expander powers for a C3Hg-C2Fl4-CF[4 cascade. For a feed of 1,566 Ib-moles/hr at 515 psia and 60°F, 490 lb-moles of LNG and two gaseous products were produced. 

Meunier, F., Second law analysis of a solid adsorption heat pump operating on reversible cascade cycles application to the zeolite-water pair. Heat Recovery Systems, 1985, 5, 133 141. 

In mechanical refrigeration, a multicomponent refrigerant consisting of nitrogen, methane, ethane, and propane is used through a cascade cycle. When these liquids evaporate, the heat required is obtained from... 

Complex refrigeration cycles can be built up in different ways. Figure 24.29 shows a cascade cycle with multistage compression and expansion of the high-temperature cycle. 

If the refrigeration system involves a cascade cycle, the partition temperature is an important additional degree of freedom to be optimized. 

Kinard GE and Gaumer LS (1973) Mixed Refrigerant Cascade Cycles for LNG, Chem Eng Prog, 69 56. 

There are situations where it is desirable to combine several cycles in series in order to take advantage of a very wide temperature range or to utilize what would otherwise be waste heat to improve efficiency. Such a cycle is called a cascaded cycle. A cascaded cycle made of three Rankine cycles in series is shown schematically in Fig. 5.1. The cascaded cycle is made of three subcycles. Subcycle A, 1-2-3-4-1, is the topping cycle subcycle B, 5-6-7-8-S, is the middle cycle and subcycle C, 9-10-11-12-9, is the bottom cycle. The waste heat of the upstream cycle is the heat input of the downstream cycle. Since the net work output is equal to the sum of the three outputs and the heat input is that of the topping cycle alone, a substantial efficiency increase is possible. 

There are applications when the temperature difference between the heat source and the heat sink is quite large. A single power cycle usually cannot be used to utilize the full range of the available temperature difference. A cascade cycle must be used to gain maximum possible efficiency from the... 

Figure 5.11 Cascade cycle energy flow diagram.

The overall efficiency of the cascaded cycle is the total output... 

The cascaded cycle efficiency may, therefore, be substantially greater than the cycle efficiency of any of its components operating alone. 

Build a cascaded cycle in series with = 5 using CyclePad. 

Build a cascaded cycle in parallel with = 5 using CyclePad. The topping cycle is an open gas turbine cycle. 

There are several variations of the basic vapor refrigeration cycle. A cascade cycle is used when the temperature difference between the evaporator and the condenser is quite large. The multistaged cycle is used to reduce the required compressor power input. 

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