Expander in a cryogenic air separation plant - Essay Example

Expander in a Cryogenic Air Separation Plant Expander in a Cryogenic Air Separation Plant The separation of gases or gases liquefaction is a major characteristic of a cryogenic plant (Finley 2013). The liquefaction of gases may happen at elevated temperatures, but it usually occurs at very low temperatures. Quite a large number of industrial cryogenic processes occur at temperatures ranging from –165°C to –195°C, which is their coldest end. However, some processes even operate at temperatures as low as–269°C.

The expander is one of the features of a typical cryogenic plant and it ensures refrigeration for the cryogenic process (Bloch 2006; Jumonville 2010; Mokhatab & Poe 2012). Ameen argues that “expanders are used to expand various gases efficiently from high to low pressures to obtain refrigeration” (Ameen 2006 p. 142). Jumonville asserts that in spite of variations in specific processes, “almost all turboexpanders are used to remove energy from a gas stream, thereby producing power and cooling the gas” (Jumonville 2010 p. 148). In the process of expanding high pressure gas across the turbine, the extraction of most of the gas’s energy potential occurs (Gopalakrishnan & Hardeveld n.

d; Mokhatab & Poe 2012). The energy extracted is then transmitted to the shaft and the compressor (Bloch 2006). Consequently, an enormous reduction of pressure in the gas occurs. This consequential fall in pressure together with efficient energy extraction creates refrigeration, which is essential for cryogenic processing of gas (Sapali 2009). Therefore, the use of expanders in a cryogenic plant is to expand high pressure gas thereby leading to temperature fall. This decline in temperature results into refrigeration, which is essential for liquefaction of gases in a cryogenic plant (Finley 2013; Mokhatab & Poe 2012).

Jumonville (2010) argues that “in most applications, the turboexpander normally runs faster and operates with colder temperatures than any other equipment in the plant” (Jumonville 2010 p.147). The turbine Expanders converts the cryogenic fluid stream hydraulic energy into electric energy (Habets & Kimmel 1999). The expander used in a cryogenic plant is usually associated with numerous benefits. The use expanders in cryogenic plants ensures optimum efficiency, reduces operation cost and also offer reliable and strength augmentation (Kerry 2010).

The cryogenic turbine expanders’ efficiency (thermodynamic efficiency) can be observed by obtaining the difference in enthalpy at the inlet and the exit. For an upward flow expander, the pressure of the fluid is reduced continuously from the inlet to outlet, which makes the density of the fluid to be highest at the inlet and lowest at the outlet of the expander. The fluid buoyant forces are in the aligned with the direction of the flow of the expander, which greatly improves efficiency. Upward flow expanders also ensure a reduction in the essential force for balancing the axial thrust, which is hydraulically induced (Finley 2013).

The installation of two-phase expanders also boosts the process efficiency and reduces costs. Two-phase expanders also simplify the process liquefaction under normal operation (Finley 2013). In spite of the differences in the expander designs, most plants use similar process flow (Mokhatab & Poe 2012). The energy extracted from high pressure gas can be utilized in other places in the process, for example booster compressor. Turboexpander-Compressor is intrinsically efficient making it the first choice for petrochemical industry as well as other industrial process that utilize refrigeration for liquefaction (Bloch & Soares 2001).

Therefore, expanders are crucial features of any cryogenic plant and their absence is likely to jeopardise the plant’s process. BibliographyAmeen, A 2006, “Refrigeration and air conditioning,” Prentice-Hall of India, New Delhi.Bloch, HP 2006, “Compressors and Modern Process Applications,” John Wiley & Sons, Hoboken.Bloch, HP & Soares, C 2001, “Turboexpanders and process applications,” Gulf Professional Pub., Boston.Finley, C 2013, “Expansive Thinking, Two-Phase Liquefied Gas Expanders for improving LNG Liquefaction Plant Efficiency.

” Viewed on March 2, 2014 http://www.ebaraintl.com/news/expansive-thinking-two-phase-liquified-gas-expanders-for-improving-lng-liquefaction-plant-efficiency/Gopalakrishnan, S & Hardeveld, W n.d, “AN ADVANCED CRYOGENIC EXPANDER FOR NATURAL GAS LIQUEFACTION PLANTS.” Viewed on March 2, 2014 Habets, G & Kimmel, H 1999, “ECONOMICS OF CRYOGENIC TURBINE EXPANDERS”, The International Journal of Hydrocarbon Engineering. Viewed on March 2, 2014 Jumonville, J 2010, “TUTORIAL ON CRYOGENIC TURBOEXPANDERS.

” Viewed on March 2, 2014 Kerry, FG 2010, “Industrial Gas Handbook: Gas Separation and Purification,” CRC Press, Boca Raton.Mokhatab, S & Poe, WA 2012, “Handbook of natural gas transmission and processing”, Gulf Professional, Oxford.Sapali, SN 2009, “Refrigeration and air conditioning,” PHI Learning Private Ltd., New Delhi.