Hazardous area sizing 1

[wdudi]

I'm trying to find dimendions of hazardous area for vent stack according to IGE/SR/25. Vent stack has 300 mm diameter and is attached to natural gas transmission pipeline ID=1400 mm (conditions inside are: pressure p= 84 bar, temperature T=293 °K). Based on formula in 5.2.3.2 of IGE/SR/25 calculated mass flowrate through stack is ca. 1100 kg/s. Dimensions of hazardous area in IGE/SR/25 are presented in tabular form only for maximum mass flowrate = 500 kg/s. What should I do to resolve my problem? How to calculate hazardous area radii and haigh for mass flowrate grater than 500 kg/s (or is it a maximum practicaly allowable value?).

 

[MortenA]

Could you tell me what IGE/SR/25 - just for my curiosity? What countries does it apply for?

Best regards

Morten

 

[wdudi]

IGE/SR/25 is a technical document (safety recommendations) prepared by english Institution of Gas Engineers and Managers called "Hazardous area classification of Natural Gas installations". I'm from Poland, but I think this document is worldwide known (specially in british commonwealth) and could be usefull for oil&gas industry in my country too.

 

[tickle]

IP15 is the institute of petroleum haz area classification. It states that "specific dispersion modelling of actual process fluids and venting conditions is used...' It gives standard areas up to 1.5 kg/s.

API 520 (or 521) gives a graphical method of calculating the extent of haz area for high velocity venting. It gives rise to a haz area a little smaller than dispersion modelling (in my experience)

In all of the haz area classifications I have done for significant vents (pipeline blowdown, plant ESD's) I have always used a third party to model the dispersion using Phast. The key is to give them the correct information.

One item that is important for dispersion is the wind speed and the terrain. Things that are not mentioned in your post.

You also need to consider; J-T cooling of the gas, dispersion at low velocities and lots more

 

[wdudi]

tickle,
thank you for your support. In my opinion you've described two possible ways to size up a hazardous area:
first based on API RP is design by formulae and graphical method, second (let me say smarter) is a design by analysis (e.g. using Phast software). That two methods should give us similar results and here I have also a problem. Perheaps in methods based on formulae (like in API RP521 or IGE/SR/25) are safety coefficients included?? Why I suppose that? Because I made also calculations in Phast Professional 6.51 for cases when calculated mass flowrates through stack where less then 500kg/s. The maximum dimension in a plan view of LFL contour was indifferently ca. 40% smaller then result of analytical calculations. It'll be most good for me to calibrate my models in phast, but for other designers in my office to use a "traditional" methods is faster and more comfortable. I try to help them, but my way is difficult.