35 replies to this topic

[rkvizag04]

Hi ,
anyone can advice me how to calculate the blowdown valve sizing, with examples.
and it is necessary to install RO plate at downstream.

[daryon]

Hi ,
anyone can advice me how to calculate the blowdown valve sizing, with examples.
and it is necessary to install RO plate at downstream.

The BDV is typically full bore actuated ball valve with a RO downstream of it. It is the bore diameter of the RO that controls the rate of the depressurisation. There are quite a few threads on this forum that discuss RO sizing and what you need to be thinking about when trying to limit the rate of depressurisation of your system. Just try searching for blowdown or RO sizing. As you question is posted in the simulation forum i assume you wish to size an RO using HYSYS or some other simulation software, is that right?

HYSYS has a dynamic depressurisation utility which performs RO bore diameter sizing calculations. You input the volume of the system to be depressurised, the starting pressure, the required end pressure or the blowdown time, and the gas properties at starting conditions (as well as some other system parameters). Then the utility will determine the required RO bore diatmeter to achieve the blowdown, the peak mass flowrate through the RO, upstream of RO fluid and metal temperatures, and downstream of RO fluid temperature. It is a very useful tool and if used correctly impoves the accuracy of blowdown calculations.

I'll stop there because i'm not sure your're even asking about HYSYS, Let me know if you need more info

Edited by daryon, 06 October 2009 - 09:54 PM.

[fallah]

HYSYS has a dynamic depressurisation utility which performs RO bore diameter sizing calculations.

As far as i know,dynamic depressurisation utility in HYSYS hasn't capability of sizing RO downstream of BDV,and this action left to perform by one of the RO sizing softwares.

[daryon]

Hi Fallah,

HYSYS depressursing utility will calculate a RO bore area required for depressuisation of a speficied volume within a given time, or to a given pressure. I have used this facility to determine required RO bore areas on numerous occasions, from the area you can easily work out the RO bore diameter for an RO datasheet. As for the RO plate thickness calculation this is best done by the RO supplier, HYSYS won't do this. The supplier determines the plate thickness given the RO bore diameter, upstream pressure, gas flowrate and properties.

Edited by daryon, 07 October 2009 - 07:23 PM.

[fallah]

The supplier determines the plate thickness given the RO bore diameter, upstream pressure, gas flowrate and properties.

Gas flowrate to be determined by RO supplier?!! Please clarify.

Would you please send (attached to your reply) the output of HYSYS (as PDF file) in which the RO bore diameter being shown.

Edited by fallah, 08 October 2009 - 02:32 AM.

[daryon]

Hi Fallah,

You have mis-read what I said. The RO supplier calculates the RO plate thickness only... based on the RO bore diamter, upstream pressure, gas flowrate and properties that are specified on the RO datsheet.

But, thinking about a little longer... all you need to calculate RO plate thickness is line size and schedule, RO bore diameter, inlet pressure, and pressure drop. You don't really need the gas properties or flowrate. Sorry for the confusion.

I have attached the print out from the HYSYS depressurisation utility. The bore Area is shown - 81.18 mm² which gives a bore diameter of 10.6 mm. I sepcifed I wanted to blowdown the system (8 m³) from 99 barg to 6.9 barg in 900 secs (15 mins) and HYSYS calculated the RO bore area.

Best Regards
Daryon

Attached Files

•  HYSYS Depressurisation Example.pdf   24.29KB   1526 downloads

Edited by daryon, 08 October 2009 - 05:26 AM.

[fallah]

Hi Fallah,

You have mis-read what I said. The RO supplier calculates the RO plate thickness only... based on the RO bore diamter, upstream pressure, gas flowrate and properties that are specified on the RO datsheet.

But, thinking about a little longer... all you need to calculate RO plate thickness is line size and schedule, RO bore diameter, inlet pressure, and pressure drop. You don't really need the gas properties or flowrate. Sorry for the confusion.

I have attached the print out from the HYSYS depressurisation utility. The bore Area is shown - 81.18 mm² which gives a bore diameter of 10.6 mm. I sepcifed I wanted to blowdown the system (8 m³) from 99 barg to 6.9 barg in 900 secs (15 mins) and HYSYS calculated the RO bore area.

Best Regards
Daryon

In the first part of your statement you are right and i accept i had mis-read what you said.
But looking at the attached PDF file you can see 81.18 mm2 is area of the valve (not RO) and to be specified by user (as indicated in bottom of the first page of the PDF file).I am not sure about the qualification/application of this value but as i previously said the RO sizing normally would be done by RO software utilizing "peak vapor flow through valve" (HYSYS output),calculated line size based on this peak flow ,initial upstream pressure and fixed back pressure.

[daryon]

Hi Fallah,

Yes the area is reported under valve parameters but this is just the way HYSYS reports it. It's not the valve area, its the RO area based on the discharge coefficient specified by the user. Valves are not talked about in terms of area, Cv and percentage opening yes but not area.

For the blowdown calculation I was using the supersonic flow equation, and i sepcifed the discharge coefficent and also the area intially. There is a star next the reported figure of area which is making you think it is user specified right? But I only specified a starting value (50mm²) and then HYSYS adjusted this until depressurisation to 6.9 barg was achieved in 900 secs.

I think your approach is fine, why not use other software to get the RO bore diameter using the peak gas flow. All i'm saying is that you don't necessarily need to do use RO sizing software to get bore diameter as HYSYS gives you the RO area through which the peak flow rate is calculated. Why don't check your RO sizing software based on the peak flowrate in the PDF I attached and see if it matchs the 10.6 mm bore diamter HYSYS calculates?

Edited by daryon, 08 October 2009 - 08:10 PM.

[fallah]

Hi Fallah,

Yes the area is reported under valve parameters but this is just the way HYSYS reports it. It's not the valve area, its the RO area based on the discharge coefficient specified by the user. Valves are not talked about in terms of area, Cv and percentage opening yes but not area.

For the blowdown calculation I was using the supersonic flow equation, and i sepcifed the discharge coefficent and also the area intially. There is a star next the reported figure of area which is making you think it is user specified right? But I only specified a starting value (50mm²) and then HYSYS adjusted this until depressurisation to 6.9 barg was achieved in 900 secs.

I think your approach is fine, why not use other software to get the RO bore diameter using the peak gas flow. All i'm saying is that you don't necessarily need to do use RO sizing software to get bore diameter as HYSYS gives you the RO area through which the peak flow rate is calculated. Why don't check your RO sizing software based on the peak flowrate in the PDF I attached and see if it matchs the 10.6 mm bore diamter HYSYS calculates?

daryon,

Thanks for consuming your time to submit above explanation.I will follow the matter as checking the RO size by comparing HYSYS output with RO sizing software's output.I will let you know the result.

Edited by fallah, 09 October 2009 - 05:59 AM.

[kandan]

Hi Fallah, Yes the area is reported under valve parameters but this is just the way HYSYS reports it. It's not the valve area, its the RO area based on the discharge coefficient specified by the user. Valves are not talked about in terms of area, Cv and percentage opening yes but not area. For the blowdown calculation I was using the supersonic flow equation, and i sepcifed the discharge coefficent and also the area intially. There is a star next the reported figure of area which is making you think it is user specified right? But I only specified a starting value (50mm²) and then HYSYS adjusted this until depressurisation to 6.9 barg was achieved in 900 secs. I think your approach is fine, why not use other software to get the RO bore diameter using the peak gas flow. All i'm saying is that you don't necessarily need to do use RO sizing software to get bore diameter as HYSYS gives you the RO area through which the peak flow rate is calculated. Why don't check your RO sizing software based on the peak flowrate in the PDF I attached and see if it matchs the 10.6 mm bore diamter HYSYS calculates?

daryon, Thanks for consuming your time to submit above explanation.I will follow the matter as checking the RO size by comparing HYSYS output with RO sizing software's output.I will let you know the result.

Though HYSYS gives RO size.. it is better to leave it to the RO vendor. Inputs will be the flow through RO, u/s and d/s pressure and gas characteristics to vendor..

[dtmgo1]

Hi fallah, I was following this thread, did you get a chance to compare results?

[PaoloPemi]

generally in blowdown a direct integration procedure is required only when evaporating a liquid phase (and you need to take in account the changes in properties),
with gas at high pressure there are closed forms (see for example Rasouli and Williams) or you may consider a simple model based on critical+transonic flow,
transonic flow may be modeled with a single parameter (a straight line in flow-pressure),
you can put this in Excel with the advantage that you can easily modify the different parameters as for example the flow correlation for Ro

[Musab Ammad]

regarding to fallah querry about comparison of bore dia with hysys, vendor software and in-house made excel sheet . with my little knowledge, i tried to calculate bore dia via above stated tools.
i used daryon attached pdf data for calculation of bore dia. Compressibility factor, heat capacity ratio and molecular weight is assumed due to unavailabilty of data.

• hysys bore dia = sqrt(4*81.18)/pi = 10.1 mm
• Vendor software = 12.5 mm
• Excel sheet = 12.6 mm

it seems that hysys provide pretty close results. the diffrence is due to the assumption i made for calculation.  Orifice Cal. Sheet.pdf   70.45KB   502 downloads  Bore dia Calc.bmp   868.38KB   280 downloads

[PaoloPemi]

am i missing something ?
The original question (from rkvizag04) was
"anyone can advice me how to calculate the blowdown valve sizing, with examples. and it is necessary to install RO plate at downstream."
it seems he is asking for the procedure...
By the way I do these calc's in Excel (see above post),
you need a few formulas plus fluid properties (I use Prode Properties but other software should give similar results),
you may expect errors (discharging time) in the range 10-20%.

[Musab Ammad]

thanks paolopemi for indicating the error of discharging time.

regarding to the original question of blowdown valve sizing via hysys, attached pdf might help.  Depressuring-a-Practical-Guide.pdf   286.6KB   550 downloads

[kkala]

Some probably useful notes on the topic:
1. Another option of (emergency) depressurization uses only a special valve without restriction orifice downstream. This has been applied in a local refinery. More on http://www.cheresour...-pcv-on-spheres '> http://www.cheresour...-pcv-on-spheres (start reading from the end of the thread).
2. Besides (emergency) depressurization, blowdown valves are used elsewhere. A blowdown valve to reject water from steam boiler drum does not have a downstream orifice (in all boilers seen).

[sima-f]

hi

could any one explain for me in fire case depressurizing heat loss shall be considered or not?

[fallah]

hi

could any one explain for me in fire case depressurizing heat loss shall be considered or not?

 

Hi,

 

Heat loss from where? Please clarify...

[sima-f]

hi

in heat flux tab of depressuring with hysys, heat loss parameter & model shall be selected, i think this means heat loss from pipe or vessel with ambient, but when i choose "none" for this section, hysys calculated large no. for Cv and if i choose detailed and complete information i received lower cv.

so i dont know which one is true?

thanks for your help

[fallah]

Hi,

 

When you are dealing with heat flux tab, you would select which "operating mode"?

 

I think if you select "Fire" mode the heat loss model options wouldn't affect so on Cv value.. Please recheck and inform of the result...

[sima-f]

hi

i check it again in other case, but cv is changed when heat loss mode is actived.in detailed heat loss case cv is lower that other case.and i am so confused about it.

thanks

[fallah]

Hi,

 

You didn't response to my question about "operating mode". Did you select "Fire"? Please specify...

[PaoloPemi]

if the question is general (not related to specific features in your simulator)

coudn't you consider a simplified model coded for example in Excel ?

see for example

 

http://www.air-dispe...m/feature2.html

 

(other methods have been presented and for addtional accuracy you may utilize a direct integration tecnique)

you can simulate a blowdown for a single phase (gas) fluid with a relatively simple effort and good accuracy.

[sima-f]

hi

yes

[sima-f]

 dear paollopemi

hi

thatnks for your attention.

but i need it for my calculation in compressor station project. and client approved that this clculation shall be accomplished with hysys v.8.