Expansion, gas

For the flow of gases, expansion factor Y, which allows for the change in gas density as it expands adiabaticaUy from pi to po, is given by... 

Use the kinetic-molecular theory to explain the following properties of gases expansion, fluidity, low density, compressibility, and diffusion. 

The relationship required is the gas expansion factor (E), and is defined for a given quantity (mass or number of moles) of gas as... 

In gas reservoir engineering, the gas expansion factor, E, is commonly used. However, in oil reservoir engineering it is often more convenient to refer to the gas formation volume factor which is the reciprocal E, and is expressed in units of scf/stb (using field units). The reason for this will become apparent in Section 8. 

Gas reservoirs are produced by expansion of the gas contained in the reservoir. The high compressibility of the gas relative to the water in the reservoir (either connate water or underlying aquifer) make the gas expansion the dominant drive mechanism. Relative to oil reservoirs, the material balance calculation for gas reservoirs is rather simple. A major challenge in gas field development is to ensure a long sustainable plateau (typically 10 years) to attain a good sales price for the gas the customer usually requires a reliable supply of gas at an agreed rate over many years. The recovery factor for gas reservoirs depends upon how low the abandonment pressure can be reduced, which is why compression facilities are often provided on surface. Typical recovery factors are In the range 50 to 80 percent. 

Condensable hydrocarbon components are usually removed from gas to avoid liquid drop out in pipelines, or to recover valuable natural gas liquids where there is no facility for gas export. Cooling to ambient conditions can be achieved by air or water heat exchange, or to sub zero temperatures by gas expansion or refrigeration. Many other processes such as compression and absorption also work more efficiently at low temperatures. 

The thermal efficiency of the process (QE) should be compared with a thermodynamically ideal Carnot cycle, which can be done by comparing the respective indicator diagrams. These show the variation of temperamre, volume and pressure in the combustion chamber during the operating cycle. In the Carnot cycle one mole of gas is subjected to alternate isothermal and adiabatic compression or expansion at two temperatures. By die first law of thermodynamics the isothermal work done on (compression) or by the gas (expansion) is accompanied by the absorption or evolution of heat (Figure 2.2). 

Figure 1-9. Two-stage process gas expansion turbine for a terephtalic acid plant. (Source GHH-Borsig.)...

Gas expansion turbines may embody different designs depending on the proeess media and assoeiated systems. Speeial requirements may pertain to duties sueh as sealing off toxie, flaimuable, eaustie, eoiTosive, erosive, and high-temperature media. These requirements may lead to sealing geometries tliat are eommon to mrbines and turboeompressors. 

Earlier ehapters explained tliat air separation expanders are mrbines that expand gases in two steps, using primary and seeondary gas expansion deviees. Inlet guide vanes (or inlet nozzles) are the primary expansion deviee. Their funetion is to eonvert almost half of... 

The power input in bubble column, on the other hand, is evaluated from isothermal gas expansion as (Jones, 1985)... 

Roslovskii, A. 1. And Zakaznov, V. F. 1971. Effect of Gas Expansion During Combustion on the Possibility of Using Flame Arresters. Combustion and Elame, 17, 215-221. 

Overpressure effects due to the vessel failure appear to be determined by gas expansion, not by flash vaporization. 

Due to gas expansion from external fire, the API code [10] provides for calculation of the pressure relief valve orifice area for a gas containing vessel exposed to external fire on die unwetted surface ... 

Expansion turbines are related in many design features to the centrifugal compressor. The key exception being that the turbine receives a high pressure gas for expansion and power recovery to a lower pressure and is usually accompanied by the recovery of the energy from the expansion. For example, applications can be (1) air separation plants (2) natural gas expansion and liquefaction (for gas let-down in pipeline transmission to replace throttle valves where no... 

Figure 3.1 Comparison of reversible isothermal and adiabatic (C =jR) ideal gas expansions.

The first analytical estimation of the value of the Markstein number in the presence of realistic gas expansion was given by Clavin and Williams [8]. In the approximation of a one-step Arrhenius reaction with a high activation energy P, they found fhe following expression for Ma ... 

TT( is nondimensionalized by the flame transit hme T( = 3/Sl. Here, 7 is the normalized gas expansion ratio. Because of the difference in density between the fresh and burnt gas, gravity will also influence the d5mamics of the flame front. The effect of gravity has been included through a Froude number, Fr = Sl/ Sg), positive for a flame propagating downward. Similar expressions have been derived by Matalon and Matkowski [13], and by Frankel and Sivashinsky [14]. 

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