Reid Vapour Pressure Methods in HYSYS

Reid Vapour Pressure Methods in HYSYS Yesterday Yes terday I was asked to explain why the Reid VP at 37.8 C in the Standard HYSYS properties was different from that same property in the Cold Property tility. !n"e !n"e I fond the explanation I did #a$ely remem%er that this has indeed "han$ed at some point in time& so this explanation is only #alid for more re"ent #ersions of HYSYS& I'd say that ())*.+ and hi$her shold %e like this. ,oth #ales are "al"lated sin$ the -S/ 03(317327& ,4& ,4& the RVP in Standard property is "al"lated on a dry %asis5 he RVP in the "old properties tility is "al"lated sin$ the ori$inal -S/ 03(317327 whi"h ses the flid as is 6in"ldin$ any water present. !9 that the Cold Properties pa$e in the ,oilin$ Point Cr#e 4tility also shows the RVP "al"lated on a dry %asis5 ,elow is a fll des"ription of the #arios methods a#aila%le a#aila%le in HYSYS:

TVP The TVP is the bubble-point pressure of the stream (i.e. when the liquid is saturated – vapour fraction = 0). This is calculated b flashin! the stream at the reference temperature and with a vapour fraction of 0.

HYSYS RVP Method The "VP calculation in the #$%$% %tandard stream correlation and &oilin! Point 'urves utilities is defined as the pressure at 00* at which the vapour volume will be + times as much as the liquid volume (i.e. the pressure at wh ich ,0 of the stream b volume is vapour at 00*). This is the same as the %T/ 121-31435 method6 but as mentionned above the #$%$% "VP "VP method is alwas done on a dr dr  basis (i.e. an water content of the stream is i!nored)6 and alwas uses the #$%7/ *lash. (i.e. the flash method that is used if #$%7/ *lash is selected on the Stab Test tab tab of the *luid Pac8a!e6 within the %imulation &asis 9nvironment.)

API 5B1.1 (Naphtha) This method is useful for !asolines and finished petroleum products but not crudes or o:!enated blends. TVP is correlated a!ainst "V "VP6 P6 Te Temperature mperature and the slope of %T/ ,; distillation curve at the 0 point. This e:tension solves the corrected version of the P7 databoo8 equation of the correlation6 for the "VP. "VP.  reco!ni
This method is the default in other simulation tools and is at the other end of the "VP spectrum from the #$%$% +> method (0 vapour evolution vs. ,0 vapour evolution). This is wh default "VP methods cannot be compared across process simulators.

API 5B1.2 (rude) ?enerall used for condensate and crude oil sstems6 (tpicall wide boilin! pre-processed hdrocarbons). TVP is correlated a!ainst "VP and Temperature. This e:tension solves the P7 databoo8 equation of the correlation for "VP. The correlation is based on ver old data from 5@5 but is popular with 9n!ineers for quic8 and dirt calculations.

ASTM !"2"#$2 This is the standard and accepted procedure for "VP lab measurement. Aiquid hdrocarbon is saturated with air at 11* and  atm pressure. %ince the lab procedure does not specif that the test chamber is dr6 the air used to saturate the hdrocarbon is assumed to be saturated with water. This air-saturated hdrocarbon is then mi:ed with dr air in a +> volume ratio6 and flashed at the "VP reference temperature such that the total volume is constant (since the e:perimental  procedure uses a sealed bomb). The !au!e pressure of the resultin! mi:ture is then reported as the "VP.

ASTM !"2"#%"&%' Btherwise 8nown as P121. The pressure is adCusted at the "VP reference temperature until the vapour>liquid ratio is +> b volume.This method is essentiall the same as the default #$%$% method6 e:cept it is not on a dr basis and the flash method used is the same as for the rest of the flowsheet.

ASTM !'5"#'1 This method was developed for o:!enated !asolines. 7t is the same as 121-,2 method e:cept that everthin! is on a completel dr basis – i.e. the air is not saturated with wa ter.

ASTM !51'1#'1

This was developed for !asolines and !asoline-o:!enate blends as an alternative to the +5@15 method. 7n the e:perimental procedure6 the hdrocarbon is saturated with dr air then placed in an evacuated bomb with five times its volume. The total pressure is then converted to a dr vapour pressure equivalent (VP9) and then reported as the "VP. 7n this e:tension the method used is to mi: near vacuum air at 0.0 psia and 00* with hdrocarbon at  atm and 11* in the ratio +>.This is then flashed at constant volume at the "VP reference temperature. The pressure is then converted to the VP9 and reported as the "VP.