6 replies to this topic

[mrbabu]

to simulate a blowdown with Prode Properties (in case the standard procedure is not applicable)

is it better to adopt V-H or V-P flash specifications ?
the Volume-Enthalpy specification should allow a more accurate solution of energy balance, is it true ?
I have a vessel with liquid vaporizing (fire case) and I wish to define my own models for RO and piping,

does that make sense from a practical point of view ?

[marchem]

the V-H flash solves directly for temperature and pressure given volume and enthalpy,

you can obtain a somewhat equivalent result by dividing dP in several steps and

solving a series of V-P flash operations, from that point of view it is preferable to solve

a series of V-H flash operations.

However I would caution that many values (an example, heat from fire)

are usually estimated (with maybe large errors) and any procedure *can't be* very accurate...

For the same reasons it doesn't make much sense (in my opinion)  

the claims of superiority of a procedure against another,
a critical review of calculated values in most cases is required....

see also the comments in previous threads discussing blowdown...

[serra]

"the Volume-Enthalpy specification should allow a more accurate solution of energy balance, is it true ?"

 

I agree with marchem, in some cases you may find a equivalent numerical solution with different flash operations,

of course in Excel it is easier to call a simgle macro in Prode Properties which does all the work

instead to have many lines of code running slow...

[mrbabu]

thanks marchem & serra,

to estimate the heat absorbed in fire I adopt the API correlation,

do you consider that procedure accurate ?

[marchem]

it's a standard, difficult to say how reliable are the values predicted,

anyway most engineers do use those values...

for a detailed discussion about the models see the M.A. Wong thesis "Development of a mathematical model for blowdown of vessels containing multi-component hydrocarbon mixtures",

if you plan to write your own procedure that may help you a lot.

[mrbabu]

thanks,

it seems they did specific tests for estimating  the heat absorbed in fire,

instead  to adopt the methods proposed in standards (for example, API).

[marchem]

right,

the main advantage of adopting a standard is that you are not required to provide a proof that results are correct :-)

 

Really, simulating a blowdown is a complex matter, 

most engineers do utilize some software but with little control over the many different parameters ,

as result it is difficult to guess how accurate the results are...