STD & NTP conditions
STD & NTP conditions
(OP)
Hello,
I have a query on STP and NTP conditions.In process calculation, we use Standard operating conditions (STP) and sometimes normal operating conditions, why?. In real life the actual condition exists in the plant, still why we use STP and NTP?
I Really would appreciate your reply.
Thanks
I have a query on STP and NTP conditions.In process calculation, we use Standard operating conditions (STP) and sometimes normal operating conditions, why?. In real life the actual condition exists in the plant, still why we use STP and NTP?
I Really would appreciate your reply.
Thanks





RE: STD & NTP conditions
Some times the aparatus that measures physical properties, like density, or viscosity, or analyzers operate at a much more milder conditions than the actual plant conditions. That's when we use "normal" or " standard" conditions" so that every one knows at what conditions those parameters and properties were measured.
I hope this helps..
RE: STD & NTP conditions
The biggest limitation of either volume flow rate at standard conditions or mass flow rate is that these parameters don't allow direct calculation of velocity. With volume flow rate at "actual" conditions, the bulk velocity is directly calculated from the pipe area. That is often a useful thing to know. If you have a volume flow rate at STP and divide by the pipe area you'll get a number that means absolutely nothing. I see people do that all the time and they're always wrong.
I don't know what your NTP is. Often metric flows are stated in nm3/hr meaning "cubic meters per hour at normal standard conditions". (why they chose and "n" instead of an "s" seems to be plain mean spiritedness to make sure that they're not confused with U.S. measurements). Is that what you mean?
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: STD & NTP conditions
There is no universally accepted "Standard temperature and pressure" or "Normal temperature and pressure" for gases. There are at least a dozen or more different sets of reference temperature and pressure that are referred to as "standard" or "normal". Read this article in the online Citizendium article:
Click here ==> Reference conditions of gas temperature and pressure
Instead of simply referring to set of reference temperature and pressure as "standard" or "normal", it is much better to always clearly state the reference temperature and pressure.
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: STD & NTP conditions
Best regards
Morten
RE: STD & NTP conditions
Mark Hutton
RE: STD & NTP conditions
The only reason is to make flowrates under widely differing conditions comparable. What we pay for is the amount of mass or matter that is transferred, rather than the volume. Converting to standard or normal conditions is just a convoluted way of converting volumetric quantities into mass (or molar) based quantities. I have been kicking against this convention and trying to get people to just work in mass flows directly for the last 30 years. And I have been spectacularly unsuccessful at it. Its a convention that is not going to go away, so you and I will just have to learn to live with it.
Just think of STP or NTP as being another way of expressing mass. And, as David has pointed out, don't forget to convert to actual conditions when you want to calculate velocities or pressure drops.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: STD & NTP conditions
Am mentioning about Std Temp & Pre (STP) and Normal Temp & Pre (NTP).
In plant while measuring the units in DCS, we look in which conditions, STP,NTP or actual conditions.
We measure and supply some chemicals to customer that will be in actual conditions, isn't it?
Thanks
Pons
RE: STD & NTP conditions
David
RE: STD & NTP conditions
RE: STD & NTP conditions
Have few queries...The value displayed in DCS will be in actual condition or in STP/NTP conditions?
Monitoring the flow based from DCS is based on actual conditions?
Thanks
Pons
RE: STD & NTP conditions
David
RE: STD & NTP conditions
You may have pressure and temperature available. You may also have multivariable transmitters. In such cases one could apply the ideal gas laws or even use the process data to provide something like "mass flow" information.
Pressure and temperature compensated flow data does not happen automatically. Someone must decide that they want corrected flow rates and pay for the effort to make it happen. I did this when I worked for an operating company building and operating cryogenic natural gas plants. Not everyone wants the corrected flows. Few would pay for the additional calculations. The company paid me whether I was working in my office or playing in the plants. I had fun with such requests.
RE: STD & NTP conditions
Best regards
Morten
RE: STD & NTP conditions
I got your points. Thanks a lot for your valuable replies.
Regards
Pons