While the dew point identifies the condition at which vapor first begins to condense to liquid, it provides no information about the quantity of condensation resulting from a small degree of cooling. If there are small quantities of higher molecular weight material present, it is preferable to use a direct measurement. Since dew point can be calculated from composition, direct determination of dew point for a liquefied petroleum gas sample is a measure of composition. Once the composition of a mixture has been determined it is possible to calculate various properties such as specific gravity, vapor pressure, calorific value, and dew point. gr.) ( Chapter 8: Gas cleaning processes). The natural gas after appropriate treatment for acid gas reduction, odorization, and hydrocarbon and moisture dew point adjustment would then be sold within prescribed limits of pressure, calorific value, and possibly Wobbe Index (cv/(sp. Similarly, the water dew point is reduced to a level sufficient to preclude formation of C 1 to C 4 hydrates in the system. Thus if the hydrocarbon dew point is reduced to such a level that retrograde condensation, i.e., condensation resulting from pressure drop, cannot occur under the worst conditions likely to be experienced in the gas transmission system. It is, of course, of more direct practical value and if there are small quantities of higher molecular weight material present, it is preferable to use a direct measurement. Since dew point can be calculated from composition, direct determination of dew point for a particular liquefied petroleum gas sample is a measure of composition. No two hydrocarbon dew point curves are alike due to differing gas compositions. A hydrocarbon dew point curve is a reference chart that determines the specific pressure and temperature at which condensation occurs. The hydrocarbon dew point is a function of gas composition and pressure. When phase change occurs, certain components of the gas stream drop out and form liquids thereby making an accurate gas sample impossible to obtain. In the simplest terms, hydrocarbon dew point is the point at which the gas components begin to change phase from gas to liquid. The hydrocarbon dew point is often considered to be the most important factor when performing any type of gas sampling. The formed liquid (condensate) exists as a liquid below the dew point temperature but above the dew point the liquid is a gaseous component of the gas. The dew point or dew point temperature of a gas is the temperature at which the water vapor or low-boiling hydrocarbon derivatives contained in the gas is transformed into the liquid state. Speight Ph.D., D.Sc., in Natural Gas (Second Edition), 2019 4.4.5 Dew point The accuracy of the sensor can be better than ☒.5☏. The balance between wetter lower resistance and heater higher resistance provides the signal for the dew-point. This lowering resistance increases the heater output which lowers the resistance. The lithium chloride is hygroscopic and attracts moisture lowering the grid resistance. Newer versions use lithium chloride solution on a grid with an integral heater. It is also sensitive to contamination and requires periodic maintenance and calibrations, and is relatively expensive. This type of sensor is very accurate, very slow to respond, but inaccurate at low humidity levels. When steady state is reached, the temperature of the solution is indicative of the dew-point of the air. One type of dew-point sensor uses a saturated salt solution (usually lithium chloride) in contact with the air whose humidity is to be measured. Eng., in Fundamentals of HVAC Control Systems, 2008 Lithium Chloride Dew-point Sensorsĭew-point sensors are the most accurate type of humidity sensor, but they are also the most expensive.
The reading text for this course was originally written by.
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