2 replies to this topic

[wkit]

Currently i am helping the process engineers in the refinery to perform a mass balance checking of Naphtha Hydrotreating Unit by using spreadsheet to do the calculation. From plant data given, i do a overall mass balance, from my calculation, the deviation in the last whole year (total output/total input * 100% ) is within 1% hence it is acceptable, however starting from tis yr Jan till now, the deviation is up to 5% already.

Besides the instruments problem, May i know is there any other troubleshooting methods for tis case ?

Thanks alot

Edited by wkit, 24 June 2011 - 08:32 PM.

[kkala]

Yes, an instrument problem looks the most probable cause from the 5% deviation. Having worked in Fertlizers, we faced a similar problem for months, due to wrong measurement of liquid ammonia coming into the plant.
Nevertheless, the main streams entering naphtha hydro treating unit have come out of other refinery units, so their flow rates can be also measured there. Similarly, exit streams from naphtha hydro treating unit come into other refinery units or tanks, so they can be also measured there. A check according to it could help.
At first look I would try to compare deviations of the same months in 2010 & 2011 (e.g. Jan to May)to see whether these are seasonal. Then I would try to detect any change of operating conditions in the HDT unit (ingoing naphtha spec, outgoing naphtha spec, change in temperatures, often depressuring, shut downs & similar disturbances, etc) or in existing instrumentation, in order to trace the cause of deviation.
Operators of the unit have to be questioned about the latter.
Probably some additional instruments should be placed; Supervisors of the unit may be the most appropriate persons for advice to solve this problem.

[Technical Bard]

Another thing to watch out for, particularly in gas phase streams, is the laboratory analysis - if your analysis is bad, or your are using old analysis data to calculate mass flows from volumetric flows, this can create significant error.