Gas fraction

Liquefied gas fractions (propane, propylene, butanes, butenes) that will be able to provide feedstocks to units of MTBE, ETBE, alkylation, dimerization, polymerization after sweetening and/or selective hydrogenation. 

In this section gas processing will be described in the context of site needs and evacuation, i.e. how gas may be processed for disposal or prior to transportation by pipeline to a downstream gas plant. Gas fractionation and liquefaction will be described in Section 10.1.4 Downstream Gas Processing . 

Gas fractionation plants require considerable investment and in many situations would not be economic. However, less complete NGL recovery methods may still prove cost effective. 

Ethylene Stripping. The acetylene absorber bottom product is routed to the ethylene stripper, which operates at low pressure. In the bottom part of this tower the loaded solvent is stripped by heat input according to the purity specifications of the acetylene product. A lean DMF fraction is routed to the top of the upper part for selective absorption of acetylene. This feature reduces the acetylene content in the recycle gas to its minimum (typically 1%). The overhead gas fraction is recycled to the cracked gas compression of the olefin plant for the recovery of the ethylene. 

Carbonyl sulfide occurs as a by-product ia the manufacture of carbon disulfide and is an impurity ia some natural gases, ia many manufactured fuel gases and refinery gases, and ia combustion products of sulfur-containing fuels (25). It tends to be concentrated ia the propane fraction ia gas fractionation an amine sweetening process is needed to remove it. 

Absorption recovers valuable light components such as propane/propylene and butane/ butylene as vapors from fractionating columns. These vapors are bubbled through an absorption fluid, such as kerosene or heavy naphtha, in a fractionating-like column to dissolve in the oil while gases, such as hydrogen, methane, ethane, and ethylene, pass through. Absorption is effectively performed at 100 to 150 psi with absorber heated and distilled. The gas fraction is condensed as liquefied petroleum gas (LPG). The liquid fraction is reused in the absorption tower. 

MF = total acid-gas fraction in inlet gas, moles acid gas/mole inlet gas... 

In the Texaco process, there are two steps, an initial liquefaction step followed by treatment in an entrained bed gasifier. The liquefaction step involves heating the plastic scrap in such a way that partial depolymerisation occurs, generating a heavy oil and some gas fractions. Some of the gas is recycled as fuel for the process. 

Although the total content of carbohydrate fractions of the three components is similar, as reported by Williams et al., 1990, it was found that protein-rich fractions have a significantly lower glucuronic acid content. Circular dichroism studies conducted on different GA fractions showed that only the AGP and GP components have a secondary structure (Renard et al., 2006). The AGP fraction was isolated by gel filtration chromatography and subjected to deglycosylation with hydrofluoric acid (HF) to separate the protein (Qi et al., 1991). About 400 amino acids were contained by the AGP protein fraction ( 33% are... 

Texaco gasification is based on a combination of two process steps, a liquefaction step and an entrained bed gasifier. In the liquefaction step the plastic waste is cracked under relatively mild thermal conditions. This depolymerisation results in a synthetic heavy oil and a gas fraction, which in part is condensable. The noncondensable fraction is used as a fuel in the process. The process is very comparable to the cracking of vacuum residues that originate from oil recycling processes. 

FIGURE 13.14 ASF plot for Fe-LTFT with required manipulations indicated (decrease in gas fraction and increase in liquid and wax fractions). 

Fig. 10. Normalized drag force at arbitrary Reynolds numbers and gas fractions. The symbols represent the simulation data, the solid line the Ergun correlation Eq. (18), the dashed line the Wen-Yu correlation Eq. (46) for e = 0.8, and the grey line the correlation by Hill et al. (2001a,b) Eq. (47) and the long-dashed line Eq. (19), both for e = 0.5.

According to Eq. (8.6), the primary abundances should increase as the logarithm of the gas fraction, the proportionality coefficient giving another estimate of the yield. For example, from the data in Table 7.9, assuming solar oxygen abundance in the local ISM, the effective yield is between 0.5 and 0.7 Z . Other gas-rich systems in which one may try to test this relationship (which obviously does not apply,... 

Fig. 8.12. Relation between oxygen abundance of H II regions in irregular (open squares) and spiral galaxies (filled circles, taking abundances at 0.4 of the de Vaucouleurs isophotal radius R25) plotted against the gas fraction, after Pilyugin, Vilchez and Contini (2004). The heavy curve shows expectation from the Simple model with an oxygen yield of 0.0027 (or about 0.5 Z ) and the broken curves show the same with the yield 1.5 x higher or lower, whereas the dotted curve shows a yield 4 x lower. The effective yield, defined as Zo/(— ln/z), increases systematically with luminosity, and the gas fraction decreases.

The distribution function for field stars in the halo is reasonably well fitted by the Simple model equation (8.20) with a small remaining gas fraction, but with a very low effective yield p 10-11Z for oxygen (see earlier comments on dwarf galaxies). This was first noted (actually for globular clusters) by Hartwick (1976), who pointed out that it could be readily explained by continuous loss of gas from the halo in the form of a homogeneous wind with a mass loss rate from the system proportional to the rate of star formation. In this case,... 

Show that in Hartwick s continuous outflow model, the relation between gas-phase abundance and gas fraction is... 

Again, p — 1/3 gives a fair fit to Fig. 11.17. The mass-metallicity relation is associated with the decrease in gas fraction concomitant with the increasing mass, and the G-dwarf problem is neatly solved models of hierarchical structure formation make use of this and several other factors leading to rather similar effects to those of inflow discussed in Chapter 8 (Nagashima Okamoto 2006). 

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