Hello

I compute natural gas dew point in "ASPEN HYSYS", natural gas contains different hydrocarbons constituents. some correlations also exist that i get help for computing dew point. for your problem HYSYS probably could help to you. 

Regards,

Reza

sorry but I want to calculate just by hand. therefore need right theoretical understanding to begin. do you have anything like notes etc.

i don't know such model but you could find it . i searched the google and find this website take a look: http://www.thersites.nl/completemodel.aspx

thanks a lot but this is only for temperature my aim is to calculate at different dilution as well.

You can analyse your tar sample using GC-MS and obtain the concentration of each tar compound (aromatics and/or oxygenated). Once you have this information the general tar dewpoint can be calculated by the sum of the partial pressure of each compound considering the concentration of each one. I will try to find useful equations and send it to you but initially you need to know the influence of each compound in your tar, this mean the concentration. Normally tar can be analysed using GC-MS or GC-FID instruments.

If you want to know the influence of the temperature you also need the dewpoint for each compound, then you can predict if it will be in gaseous or liquid form.

Hope this will be useful...I dealt with the same problem. You can also use some of the online tools. For example in the Energy Research Centre (ECN) of Netherlands, webpage there is a tool to calculate this, I will also look for the link to send it to you :)

many thanks for your reply, I can arrange SPA of the gas sample so the concentration are there. I would appreciate if you will help me in solving for say 2-4 compounds of tar to learn.

Yeah sure no probs I will send you theequations I used a while ago (just need to look for them). in the meantime please check out this website where you can calculate a general dewpoint based on concentrations of major tar compounds:

http://www.thersites.nl/simplemodel.aspx

yes indeed I wil

Hi Mohit

Actually the problem that you are trying to solve is quite complicated. In order to be able to calculate the dew point of tar compounds, you first need to be able to calculate their saturation vapour pressure at different temperatures. Then by knowing their partial pressure in the mixture you can calculate their relative saturation. A good correlation for vapour pressure saturation calculation for pure compounds can be found in the following paper.

Kh. Mejbri, A. Bellagi, Corresponding states correlation for the saturated vapor pressure of pure fluids, Thermochimica Acta 01/2005; DOI: 10.1016/j.tca.2005.06.040

This correlation makes use of the corresponding states method in which the critical temperature and pressure of the compounds must be known. Those you can find in chemical compound data banks but you might not be able to find those for some compex compounds found in tar mixtures (e.g guaiacol). A good book that will help you calculate all the necessary properties by using the group contribution theory is the following:

The Properties of Gases and Liquids, by Bruce Polling, John Prausnitz and John O'Conell. (fantastic book)

You will find everything you need in there. The theory described in that book will enable you to also include fugacity effects in your calculations. I hope this helps.

thanks a lot, I will try to get book first. I will certainly need your guidance thereafter, I will contact you later please.