11 replies to this topic

[steamreformer]

Dear all,

I am looking for nitrogen psychometric chart,i search it on google but i couldnt able to find it .i shall be highly thankful to all of u if somebody has .actually i want to calculate the amount of moisture in nitrogen leaving the absorber from the top,and i think that this is teh most applicable way.
regards

[breizh]

Hi,
To me , if you have only water and nitogen , you need to know the total pressure on top of your absorber , the temperature of the gaz and then PT = PN2 +Pwater .I guess you can get access to Pwater versus temperature .

Hope it helps .
Breizh

[bernath]

Dear breizh and talha,

I'm not completely understand the explanation. So, I'm gonna put my own words to describe it. Please let me know if it's wrong.

In order to calculate the amount of moisture content in nitrogen, first we need to know the total pressure and temperature of the gas. Then look up the steam tables, find the corresponding vapor pressure. Afterward we convert it to mass, then finally we get the moisture content.

I have one question regarding this method. If we use steam tables to determine the vapor pressure, then we have to assume that the water or water vapor is in its saturated condition(i.e. RH = 100%). Is that true?

Btw, I'm currently having the same problem with 'steamreformer'. I need to know the moisture content of syngas at the outlet of my venturi scrubber. My syngas initially contains 2 - 3% of H2O in the inlet. This moisture content problem is arise as I perform mass and heat balance calculation on the scrubber. Those calculations are unlikely to be solved without knowing the moisture content of scrubber outlet.

I'd be very grateful for any response here.

thank you

[djack77494]

I have one question regarding this method. If we use steam tables to determine the vapor pressure, then we have to assume that the water or water vapor is in its saturated condition(i.e. RH = 100%). Is that true?

Yes, that is true. Using the steam tables is valid only if you have equilibrium conditions where the gas moisture content is in equilibrium with liquid water.

[S.AHMAD]

Dear kanankiri

Your words are correct. We have not much choice, except to assume saturated conditions.

regards

[steamreformer]

Dear all,

I agree with all of you now with yr suggestions. But the problem is that I am not able to find out the vapour pressure of nitrogen at diffrent temperatures. Can any one help me? For air it's available easily on net.

[MrShorty]

NIST has N2 in their database (webbook.nist.gov), Cheresources.com also has a few downloads and links to physical property information/databases, if you're limited to internet resources. The Properties of Liquids and Gases, DIPPR, and Perry's all have N2 vapor pressures, if you have access to any of these resources.

One other thing to add. Where you're talking about both water and N2 vapor pressures at the same time, I would mention that it's hard to talk about "vapor pressure" of pure N2 above its critical point of 126 K, as pure liquid N2 can't exist above this temperature. You haven't mentioned what temperature range you are interested in, but, unless you are talking about cryogenic temperatures, that may be part of why you can't find vapor pressure data.

[djack77494]

But the problem is that I am not able to find out the vapour pressure of nitrogen at diffrent temperatures. Can any one help me? For air it's available easily on net.

steam,
You are worrying me here. You don't need the "vapor pressure" of nitrogen. Nitrogen in this context is a gas and will have an incredibly high vapor pressure - well beyond its partial pressure. I'm afraid you're missing some basic concepts. You need to determine the partial pressure of water/moisture, but you do not need to calculate the partial pressure of nitrogen or any other gas. The nitrogen partial pressure will be the total pressure - water partial pressure. There is no nitrogen vapor-liquid equilibrium going on here.

[Art Montemayor]

Steam:

Everything that our members has recommended to you is applicable to your problem.

One part of your problem that I sense is the REAL problem is that you don't know the basics of what you should be applying: John Dalton's famous Law of Partial Pressures. In fact, this subject or Law has not even been mentioned in this thread up to now. Our members undoubtedly know it - and probably know it well - but it hasn't been mentioned explicitedly. That, more than anything is why I suspect you are going around in circles, groping for Nitrogen vapor pressures when this is out of the realm of your problem - just as Shorty infers.

Your gaseous system pressure at the top of the absorber is known. That is the System Pressure. It is made up of partial pressures - that is Dalton's Law. If this nitrogen gas is saturated with water vapor, then the water vapor pressure (at the saturated temperature) is the water's partial pressure. The vapor pressure of nitrogen has nothing to add to the solution.

As all our members agree, the System Pressure - the vapor pressure of water (actually, the partial pressure) = the partial pressure of nitrogen. This is true, of course, only if the System is made up of only nitrogen gas and water vapor. There are practical problems in this type of industrial problem:

1. Usually, there are other gases (or vapors) involved;
2. Dalton's Law is theoretically valid only at atmospheric conditions (pressure); at higher pressures, you start to realize deviations from the law due to mutual atomic attractions in the system. Therefore, you have to apply correction factors - which I understand are applied in all simulation programs that are used to resolve this type of problem.

I hope this summary explanation helps. I believe you simply have to go back to basics.

[bernath]

One other thing to add. Where you're talking about both water and N2 vapor pressures at the same time, I would mention that it's hard to talk about "vapor pressure" of pure N2 above its critical point of 126 K, as pure liquid N2 can't exist above this temperature. You haven't mentioned what temperature range you are interested in, but, unless you are talking about cryogenic temperatures, that may be part of why you can't find vapor pressure data.

I think have a few questions to ask related to above nitrogen vapor pressure.

Shorty said that it's hard to talk about the vapor pressure anymore above it's critical point. The nitrogen will not be present as a liquid anymore. Thus, it's all gas from here, not vapor. My question is can we calculate the the partial pressure of nitrogen in the gas in a similar way that we calculate the vapor pressure of nitrogen, e.g. using Antoine equation. Can we treat that gas like we treat the vapor pressure.

I looked across the table searched for the (Antoine) constants, but was very upset knowing that my operating temperature is way too far from the range temperature. Later, I was found that similar condition also occur to Oxygen, Hydrogen, Carbon Dioxide and Carbon Monoxide.

This problem is arise as I calculated the dew point (or temperature) of the syngas. As far as I know, we have to calculate the vapor pressure of each gas, then using trial and error method to determine the dew point(Himmelblau's book). I'm using Antoine equation to determine all the vapor pressures, but was unable to proceed forward as I wasn't able to determine the vapor pressures of above mentioned gases.

Plz help with the explanation, frenz.

Thank you,
best regards,
btjajadi

[Art Montemayor]

kanankiri:

As dJack has said about Steamreformer, I think you also are missing the basics here.

Your topic may be similar to Steamreformer's but now that he has gone off somewhere, you are persisting in your problem. Although you haven't specified your dilemma in detail, I can guess what you are having trouble with. I think you are trying to find the dewpoint (the point at which the water vapor content in a saturated gas starts to condense - or form the first drop of "dew") of a gas because you need to find the water content in that gas stream. Is that correct? If so, please state the facts and give us all the details. By beating around the bush, we are all getting very confused in trying to help you resolve your problem.

If you are using Himmelblau's excellent book, then make a DETAILED reference to it. You should know by now that Himmelblau's book has been through many editions - and all of them are different. Tell us the title, the author, the edition, the page, the ISBN number and publisher. That way, we know exactly what you are referring to.

Await your reply. If your topic is not as I described, then please start a new, independent thread on that specific topic and furnish ALL the basic data.