Saturated water content chart

It is essential to estimate correctly the saturated water content in the incoming natural gas (generally expressed in mg/Sm ). This can be estimated by using simulation software or it can be calculated using equation of states. The most commonly used method to estimate the saturated water content is to use a saturated water content chart developed by McKetta and Wehe as presented in Figure 5.6 [3]. 

Relative humidity is usually considered only in connection with atmospheric air, but since it is unconcerned with the nature of any other components or the total mixture pressure, the term is applicable to vapor content in any problem. The saturated water vapor pressure at a given temperature is always known from steam tables or charts. It is the existing partial vapor pressure which is desired and therefore calculable when the relative humidity is stated. 

The quantity of water in saturated natural gas at various pressures can be estimated from Figure 11-1, which is based on the correlation of McKetta and Wehe (1958). This chart provides essentially the same data as the frequently used correlation of McCarthy et al. (1950), but has the advantage of including corrections for gas specific gravity and water salinity. The corrections are used as simple multipliers for water content values shown on the main chart. For example, if the gas has a molecular weight of 26 and is in equilibrium with an aqueous phase containing 3% salt, the correction factors would be Cq = 0.98 and C = 0.93. For this case, and conditions of I50°F and 3.000 psia, the gas would have a water content of (0.93)(0.98KI04) = 95 Ih/MMscf. 

For the case shown in Figure 11-32, it is assumed that a natural gas stream is saturated with water at SOO psia and 90°F and that it is desired to dehydrate this gas to a water content of 10 Ib/MMscf (dew point 28°F). With triethylene glycol a concentration of 98.5% can readily be attained with simple atmospheric pressure regeneration. The dew-point chart. Figure 11-15, shows an equilibrium dew point of about I5°F for this glycol concentration, equivalent to a 13°F approach at the top of the column. 

The psychrometric chart (oT humidity chart) conlam values of a number of process variables for air-water vapor systems at 1 atm. The values listed on the chart include dry-bulb temperature (the temperature measured by common temperature-measurement instruments), moisture content or absolute humidity (mass ratio of water vapor to dry air), relative humidity, humid volume (volume per mass of dry air), wet-bulb temperature (the temperature reading on a thermometer with a water-saturated wick around the bulb immersed in a flowing stream of humid air), and enthalpy per mass of dry air. If you know the values of any two of these variables for humid air at or near 1 atm, you can use the chart to determine the values of the other four, which can greatly simplify material and energy balance calculations. 

The adiabatic cooling lines are lines of almost constant enthalpy for the entering air-water mixture, and you can use them as such without much error (1 or 2%). However, if you want to correct a saturated enthalpy value for the deviation which exists for a less-than-saturated air-water vapor mixture, you can employ the enthalpy deviation lines which appear on the chart and which can be used as illustrated in the examples below. Any process that is not a wet-bulb process or an adiabatic process with recirculated water can be treated by the usual material and energy balances, taking the basic data for the calculation from the humidity charts. If there is any increase or decrease in the moisture content of the air in a psychrometric process, the small enthalpy effect of the moisture added to the air or lost by the air may be included in the energy balance for the process to make it more exact as illustrated in Examples 4.47 and 4.49. 

The dry bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. The wet-bulb temperature (0w) is the temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel. In other words, wet bulb temperature is the temperature reached by water surface if the air is passed over it. Wet bulb temperature is a function of dry bulb temperature and humidity. The chart shows dry bulb temperature on the x-axis and moisture content on the y-axis. Any point below the saturation line represents air that is unsaturated, therefore, the chart has relative humidity cxirves going up to 100% relative humidity. Wet bulb temperature lines are constant enthalpy or adiabatic cooling lines. The change in composition of... 

If an acceptable chart showing the variation of water-vapor content with saturation or water dew-point... 

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