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Temperature compensation in Plant Incoming Feed and on product out linHelpful Member! 

10815L (Chemical) (OP)
3 Oct 11 11:37
Hi alls,
I have one question about temperature compensation in plant incoming feed flow lines and product out going lines theses include, Liquid hydrocarbons and gas lines.
My question is why temperature compensation were not used for inside plant flow transmeters for material balance arround the distillation columns and reactors (separators)?
What the reason and why no temperature compensation used in, inside flow transmeters.
rmw (Mechanical)
3 Oct 11 20:48
Well.... temperature compensation is used on flowmeters in critical service and that would include product feeds and outflows since billing is done based on those flowmeter readings.  If you have flowmeters in the plant that aren't temp. compensated, someone decided that the extra cost didn't justify the benefit.

10815L (Chemical) (OP)
3 Oct 11 23:59
One thermocouple how much can cost infront of easy material  balance calcullations arround the columns, separators.
Could you elaborate this philospy please!!!
Helpful Member!  sshep (Chemical)
7 Oct 11 10:54
At an added loop cost of 10k per point, considering: thermowell, thermocouple, loop diagrams, JB and IO point usage, DCS configuration, it can add up. Meter error for internal metering will exist already at maybe 2%, so you are only making the meter slightly more accurate by compensation. If you have the temperature anyway, it can be included in the reconcilliation without configuring the compensation in the DCS.

The more complicated you make the controls, the greater the chance of failure- i.e. consider the impact of failure of the temperature measurement resulting in wacky readings. It is usually just more trouble than it is worth. Your meters will already consider the flowing density at an assumed process temperature which is usually good enough.

If you have engineering units of mass being displayed already, consider yourself lucky. The greater problem usually is finding the flowing density (and standard density if using standard volumetric flow) already being used so as to convert volumetric units to mass.

In many cases for plant data reconcilliation purposes, just free the large stream to make a square case. For example: sum your distillate and product flow (and compositions) to calculate the feed flow to a tower- it will be off a bit from the plant measure but your job will be considerably easier. If off alot there is a bad meter anyway. By making this simplifying assumption, the overall and component balances will match exactly for column simulation etc.

best wishes,
10815L (Chemical) (OP)
7 Oct 11 13:23
sshep-thanks a lot for detailed answer, now I understand the philospy of temperature compensation.
jmw (Industrial)
7 Oct 11 14:04
But, what type of flow meters?
What were the calibration conditions?
Is the temperature relatively stable?

If temperature doesn't vary significantly, you may not need to have continuous monitoring.

If the process temperatures are relatively stable and known, then it may be that the meters were calibrated for that condition.
Maybe they are calibrated to give the volume at the process temperature or maybe they are calibrated to give the volume at the reference temperature.

So the first thing to check would be the meter specifications to see what the reality is and then to see if the current conditions match the original calibration conditions.




10815L (Chemical) (OP)
8 Oct 11 6:43
I will check all conditions and will back soon here.
10815L (Chemical) (OP)
18 Oct 11 12:32
Flow transmeter is DP type, and no reference temperature was used.
Damping factor is used 0.48 and TF is used 0.07 line temperature is used that is the real time time temperature.
Hope you will explain further based on this input.

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