Hydrocarbon Dewpointing

It is fundamental to the design and operation of fractionation columns, and its study forms part of the first and second years of degree courses in Chemical Engineering.

The dewpoint in a multicomponent hydrocarbon system is the temperature and pressure at which liquid of the heaviest component begins to form from the vapour phase. The separation produces two streams:

• A liquid, which is rich in the heavier components and lean in the lighter ones, and
• A vapour, which is lean in the heavy components and rich in the lighter ones.

Repeating the separation a number of times, which may be carried out within a packed column, a sieve-tray column, a bubble-cap column or a centrifuge, produces streams of different quality at the outlets.

In a great sci-fi book, 'Radio Planet' the author put it well: "What comes off first is the best"

Answering this question might require more than a few pages but one that hasnt been covered yet is gas pipelines.

The hydrocarbon dewpoint of a gas is the temperature (at a specified pressure) at which the first drop of hydrocarbon liquid is seen. For gas transport this gives a temperature above which the gas must be kept to avoid any liquid condensation in the pipeline. If gases are maintained above their dewpoint then no liquids are formed in thepipeline so they do not need to be pigged / sphered; do not need liquid handling facilities, slugcatchers etc at the receiving end and you dont get two phase flow in the line all of which would cost large amounts of cash.

This terminology is used for vapor pressure of highest molecular weight solvent and is less than 10 percent of the highest molecular weight solvent in organic mix during distillation process.

This is used for separation of different organic components using distillation process and determine degree of purity of solvents, polymer and others

If you have a mixture of gasses and you want to determine the mix ratio, you can use dewpointing. Dewpointing is simply placing a temperature controlled mirror surface into the gas mixture and determining the temperature that gas first condenses on the mirror surface at a particular pressure. The determination can be made visually or with optical instruments. This temperature is the dewpoint temperature. Knowing this temperature and pressure, allows you to go into a set of tables and determine the concentration of the condensed gas. The measurement is relevant in many industries. Water vapor can condense out of gas streams at low temperature and clog nozzles, cause corrosion, and many other problems. Knowing and controlling water concentration in gas is important in many engineering disciplines.

it's also important when you've to select material and assess the likelihood to have corrosion. If your gase is dry then you'll not have any corrosion. In oil&gas usually a gas is considered as "dry" when the operating temp is at least 10 °C above the water dew point.

this is taken from Norsok M001, material selection

"A gas is considered dry when the water dew point at the actual pressure is at least 10 °C lower than the actual operation temperature for the system"

rust & corrosion prevention

Thanks guys, very rich contents, much appreciate