Absorption of heavy hydrocarbons

Operating problems Solution degradation, foaming, corrosion Column instability, erosion, corrosion Absorption of heavy hydrocarbons... 

Multistage Concurrent Absorption of Heavy Hydrocarbons 645 Table 20.3 Initial composition of the gas and the absorbent (molar fraction %). 

In addition. Figure 2 presents a comparison between the voliune of heavy hydrocarbon molecules (neutral and ionized) measured by light absorption 14, 15) and the volume of soot particles measured by molecular beam sampling and electron microscopy (7, 11). These data show that enough heavy molecules exist to account for soot formation, thereby supporting the view that these molecules are probably intermediates of soot. 

Bubble absorbers (of the plate type), surface absorbers (film and column), and also spray absorbers (nozzle and high-velocity direct-flow absorbers) are widely used in plants for complex preparation of gas to perform absorption dehydration, or absorption extraction of heavy hydrocarbons from the gas. 

Absorption Extraction of Heavy Hydrocarbons and Water Vapor from Natural Gas... 

In the process of extraction of heavy hydrocarbons, a Uquid saturated with heavy hydrocarbons can be taken as the absorbent, for example, petroleum, solar or transformer oil, weathered condensate etc. For the absorption dehydration of gas, glycols are used diethylene glycol (DEG) or triethylene glycol (TEG). 

I 20 Absorption Extraction of Heavy Hydrocarbons and Water Vapor from Natural Gas Table 20.1 The initial composition of the gas-liquid mixture. 

The calculation results for a single-stage absorption are shown in Fig. 20.6. It is worth to note that at certain values of pressure and temperature, some components are desorbed from the liquid to the gaseous phase (this corresponds to negative values of me ). Thus, for condensate weathered at Tb = 20 °C and ps = 0.1 MPa, desorption is observed at T > 15 °C and p < 1.2 MPa. A reduction of Tb and an increase of ps results in desorption of heavy hydrocarbons at higher values of p and lower values of T. 

Consider now the absorption extraction of heavy hydrocarbons under the conditions of counter-current flow in a column absorber presented schematically in Fig. 20.7. Gas of a given composition yo = (yoi, yo2, , yon), where yoi is the molar fraction of i-th component, with the flow rate Qgo enters the bottom part of the column. At the same time, an absorbent with composition xo = (xoi 5 02, , on) and flow rate qo enters the top part of the column. The number of contact stages is equal to N. Each stage is equipped with a perforated plate operating in the ablation regime. This means that the liquid is not collected on the plate, but exists in a dispersed state in the inter-plate space. Each contact stage contains a separation device, for example, a mesh droplet catcher, in which the exhausted absorbent is separated from the gas and directed toward the next plate. 

Dehydration can be performed by a number of methods cooling, absorption and adsorption. Water removal by cooling is simply a condensation process at lower temperatures the gas can hold less water vapour. This method of dehydration is often used when gas has to be cooled to recover heavy hydrocarbons. Inhibitors such as glycol may have to be injected upstream of the chillers to prevent hydrate formation. 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

Figure 6 illustrates another highly developed application of our FTIR facility. Trace (A) shows the complete absorbance spectrum, 600-3600 cm-1, of a CVS bag sample of a typical auto exhaust. While dominated by water vapor and CO2 absorption, several interesting features are visible. For instance, the carbon monoxide band is readily apparent, as is absorption due to heavy hydrocarbon (indicated by the broad unresolved C-H stretch band). In Trace (B) absorption due to CH4, NO2, formaldehyde and as well, water and heavy hydrocarbon can clearly be seen. In Trace (C),... 

---