cascade system by Hadeel Rahem Jasim.pptx

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1. Cascade system 1 By Ph.D. Hadeel Raheem Jasim

2. Cascade system By meaning is : sequential operations. By mechanical and chemical engineering : cascade refrigeration and cryogenic cycles is a multi-stage thermodynamic cycle. Two phase presentation 2

3. Cascade system We will explain the cascade system in refrigeration systems and the importance of its use. Cryogenic 3

4. Cascade system 4 In a cascade refrigeration system, two or more vapor-compression cycles with individual refrigerant cycles are used . The evaporation-condensation temperatures of each cycle are sequentially lower with some overlap to cover the total temperature drop desired. With refrigerants selected to work efficiently in the temperature range they cover.

5. Cascade cycle 2021 Two phase presentation 5

6. Coefficient of performance (COP) 6

7. Advantages 7 The performance of cascade system can be enhanced by….   Reducing the temperature difference for heat transfer in evaporator, condenser and cascade condenser. Reduce compression power conception comparing with larger compressors. It avoids the problem of sub-atomic pressure which will occur in the evaporation if a single fluid is used in both the stages Better efficiency compared to conventional refrigeration systems.

8. Using 8 This types of systems used for The refrigerant used low temperature application cycle depends on what refrigerant in used for ( medical storage purposes i.e. storage of blood, vaccines, bone banks) Liquefaction of gases such as (CH4, N2, CO2 , C2H4,….).

9. Cascade liquefaction 2021 cryogenic 9

10. Introduction 10 The cascade system is an extension of the precooled system, in which the precooled system is precooled by other refrigeration systems . The cascade system was the first liquefaction system used to produce liquid air.

11. ternary cycle 11 Cascade refrigerating plant is used in the liquefaction of natural gas, which consists principally of hydrocarbons of the paraffin series, of which methane has the lowest boiling point at atmospheric pressure. Refrigeration down to that temperature can be provided by a ternary cycle using propane C 3 H 8 , ethane C 2 H 6 and methane CH 4 , whose boiling points at standard atmospheric pressure. Boiling point (K) Gases No. 231.1 Propane (C 3 H 8 ) 1 184.5 Ethane (C 2 H 6 ) 2 111.5 Methane (CH 4 ) 3

12. Ternary cycle 2021 12 For further thermodynamic advantage , the methane circuit, the compressed methane vapour would first be cooled by heat exchange with the propane in the propane evaporator before being condensed by heat exchange with the ethane in the ethane evaporator, so reducing the degree of irreversibility involved in the cooling and condensation of the methane .

13. ternary cycle 13 In a plant for liquefying natural gas ethylene , C2H4 with a boiling point of 169.4 Κ at standard atmospheric pressure, replaces ethane as the second-stage refrigerant, and the liquefied gas is finally cooled by the flashing process . in this way, what little nitrogen there is in the gas can be separated out, since the temperature is not low enough to cause it to liquefy. In large-scale plant of this type, the compressors themselves would be rotary turbo-machines instead of the reciprocating type shown diagrammatically in the figure.

14. cascade system 14 A cascade system suggested by Keesom (1933) is shown in Fig .. This system uses ammonia to liquefy ethylene at 1925 kPa ( 19 atm ), which is used in turn to liquefy methane at 2530 kPa (25 atm ). The methane is used finally to liquefy nitrogen gas at 1885 kPa (18.6 atm ). Boiling point (C) Boiling point (K) Gases No. -33.2 239.8 Ammonia (NH3) 1 -103.6 169.4 Ethylene (C2H4) 2 -161.5 111.5 Methane (CH4) 3 -195.64 77.36 Nitrogen (N2) 4

15. Cascade cycle 15 Advantages of cascading are the reasonably small pressure range of the refrigerant in any one cycle and the ability to choose refrigerants that have the most suitable properties within each of the comparatively narrow temperature ranges.

16. Keesom cascade cycle 16 NH3 C2H4 CH4 N2

17. 17

18. Illustrates a still more sophisticated plant for the liquefaction of natural gas. This is described as a mixed-refrigerant cascade plant. The mixed refrigerant is composed of four hydrocarbons of progressively lower boiling-point temperature; these pass round a complex cycle which, in effect, comprises four vapour -compression refrigeration processes in cascade , each with its own condensing , throttle and evaporating stages but without separation of the refrigerants from each other, the mixed refrigerant vapour being compressed in a single compressor. Complex Cascade plant

19. Cascade cycle. 19

20. Multiple cascade plant for the production of solid carb o n dioxide A three-stage process which bears some resemblance to the cascade plant Each gas has its own phase change liquefaction scheme

21. The entire process can be followed on the temperature entropy diagram. Since carbon dioxide provides the working fluid throughout, interstage flash tanks can be used in place of surface heat exchangers, solid carb o n dioxide

22. It will be seen from this diagram that the triple-point pressure of C02 is above normal atmospheric p ressure , so that C02 never occurs in the liquid phase at atmospheric pressure; hence the name " dry ice" for solid C02 , for at atmospheric pressure it sublimates directly into C02 vapour without passing through the liquid phase

23. The maximum pressure in the C02 circuit must be such that the saturation temperature at this pressure will be above the temperature of the cooling water used to condense the C02 vapour in the condenser between G and H ( this necessitates a pressure of some 70 atm ) .

24. 24 solving problem The specific reversible work of compression in steady flow is equal to ∫vdp consequence of the reduction in specific volume of the vapour in the intercooling process reduction in the required work input results from multi-stage compression with intercooling between stages This cooling of the vapour after compression in a stage takes place by direct contact between the superheated vapour and liquid at the same pressure, as the vapour is bubbled through the liquid in an inter-stage flash tank. This method solves the problem of intercooling at sub-atmospheric temperatures.

25. However, when the liquid from L passes through the first-stage throttle into the "snow" chamber, it flashes into a solid-vapour mixture at state M , since the pressure in the chamber is below the triple-point pressure.

26. 26 The solid C0 2 at state Ν i s collected from the snow chamber and the vapour at state Β is drawn into the suction of the first stage compressor, together with make up vapour precooled by passing it through a coil in the snow chamber.

27. 27 Using the flow quantities thus calculated , the total work input to the compressors per unit mass of dry ice formed may be calculated and the rational efficiency thence determined

28. References 30 Haywood , R.W., Analysis of engineering cycles: thermodynamics and fluid mechanics series. 2013: Elsevier . Yoon , J.-I., et al., Characteristics of cryogenic cascade refrigeration cycle for liquefaction of natural gas with the pressure drop of heat exchanger. 2012. 36(6): p. 756-761 . 3 . Barron , R.F. and G.F. Nellis , Cryogenic heat transfer. 2017: CRC press.

29. THANK YOU Hadeel R. Jasim h [email protected] 31