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Hydrocarbon dew point is an essential quality parameter for natural gas. It refers to the temperature at which the first hydrocarbons, usually the heaviest ones, begin to condense out of the gas phase into the liquid phase.
Factors Influencing Hydrocarbon Dew Point
Understanding the Hydrocarbon Dew Point involves considering two primary factors:
The composition of the gas
The pressure applied.
The percentage of heavier hydrocarbons in the gas directly correlates with a higher dew point. The pressure, on the other hand, exhibits a unique behavior.
Examining a typical natural gas phase diagram, represented by the blue line known as the "phase envelope," reveals crucial insights. The right-hand side of this line marks the phase boundary between the vapor and liquid phases, essentially indicating different hydrocarbon dew points at varying pressures. The "cricondentherm" signifies the maximum dew point achievable at any pressure, typically ranging from 25-35 bar for pipeline quality gas.
Pressure's Role in the Dew Point
The impact of pressure on the dew point is intriguing. Lowering the pressure decreases the dew point for a given gas mix, as long as the pressure is below the cricondentherm pressure. At pressures higher than the cricondentherm pressure, increasing the pressure lowers the dew point as well. This area of the phase diagram is known as the retrograde region. The retrograde behavior is unique to gas mixtures such as natural gas.
Looking Ahead: Importance of Dew Point Measurements
In future posts, we will discuss why measurement of hydrocarbon dew point (as well as water dew point) is important for natural gas refiners, pipelines, storage facilities, and gas-based power plants. Remember, you can visit Tutorial and Videos or the Technical Resources pages for much more in depth discussions.
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