Dear Sir,

We are an engineering company manufacturing the Gas Conditioning Skids for the new up coming Power projects. At one project we require to check the dew point of the available Natural gas CH4 is 94.01 % at the pressure of 26.5 barg.


The power generation capacity is 467 MW CCPP.

Kindly let us know the procedure for calculating the dew point of the gas.

If there is any particular software the from where we can get the same?

If you can confirm the dew point of the gas & any further information is required the same can be provided to you.

Best regards,

Naveen Kumar

The issue of 'dew point of natural gas' is a complex one that is often misunderstood. Thorough discussion of this topic would take many pages so I must be overly brief.
The 'dew point' of the natural gas is the temperature at which a component of the gas mixture begins to condense. The condensing component could be either water or a heavy hydrocarbon.
Dew point is a complex function of both the precise gas mixture (C1 through C15+, water, etc.) and pressure.

Dew Point Temperature = F( [c1],...,[c15],[N2],[CO2],[H2O],etc.}

The Gas Research Institute, and others, have determined a relationship between the CONCENTRATION of water and the 'water dew point' down to a temperature of -40 for a single 'ideal' natural gas composition (the relationship below -40 can only be an educated guess). All 'water dew point' measuring instruments use this, or similar, data to create their 'dew point' calibration curves. Since 'dew point' is a function of the gas matrix (not simply concentration & pressure) a sensor calibrated on nitrogen suffer from addition error if used in natural gas and the magnitude of the error will change with gas composition.
 
So now what do you do?  

Focus on the key issues: 1) too high a hydrocarbon dew point will clog fuel injectors, change the combustion profile (temperature, rpms, pollution), and possible cause damage to the turbine;  2) a high water dew point causes hydrate formation in the gas supply pipeline and absorbs BTUs.
Gas turbine operators will rarely experience a problem due to water dew point - this problem is a biggie for gas transmission companies. If you must know, the best choice would an instrument that measures concentration as concentration is independent of both composition and pressure.
The Hydrocarbon Dew Point should be the key question for all natural gas fired turbines as it is the direct cause of several operational problems. The incidence of 'hot' gas has increased drastically in the past two years as fewer gas processing facilities are removing the C3+ components of the natural gas due to the low market price for those components.
Your best choice is to go with a direct measurement of hydrocarbon dew point. I specifically say direct measurement to guide you away from a GC. GC's can estimate the HC dew point only if they accurately measure every component in the natural gas. Since most GC's cannot individually measure C5 through C15 their estimations of dew point can have huge errors. In addition to being able to predict an impending operational problem (if gas has high HC dew point expect a problem) you will also know whether or not you need to preheat the incoming gas and by how much. A simple control loop based upon the measurement can save lots of money in unneeded pre-heat energy.

Hydrocarbon (HC) and moisture dew point depends upon gas composition and pressure.
The hydrocarbon as well as water dew point of the gas can be easily calculated from standard softwares like ASPEN or HYSIS. However, standard analysis (upto C6) should not be used for dew point determination as Small quantities of heavy HC increase DP considerably. Only Extended Gas Analysis (upto C14)should be used for this purpose.
Also remember that most of the CTG suppliers require a minimum degree of superheat above the DP, at the CTG inlet. So a heating may be required depending upon the supply temperature.

Could you please tell me if you could have found a table or a graph showing the Natural Gas dew point versus the pressure (with any coorection factor if any)

thanks in advance

Murat Bilgin KOC

does anyone know the dew point for nitric acid, i am trying to find literature when oxidizing no2 to n205, and then forming nitric acid from the n205

thanks

regarding dewpoint for natural gas
where can one find dewpoint curves in electronic format for natural gas at various pressures and temperatures.
i am looking for most accurate data on pressures in the 3500 to 5000 psi and down to (-40 f ),,or is there a calculation or program that is available ?

hopmail

Please start a separate thread, and consider for, your own sake, to post your question in "Chemical Process Engineering" rather than Power Gen.