COLD VENT STACK - HELP

[stefano santoro]

Hi everyone,
I am writing from Italy and I'd like to have your opinion on a particular aspect of the Trans Adriatic Pipeline (TAP) that will transport gas via Greece and Albania and acrossthe Adriatic Sea to Italy’s southern Puglia Region and further to Western Europe. Crossing the Adriatic Sea from Central-Western Albania, the offshore pipeline gets onshore in South-East Italy and ties in to the Italian gas network South of Lecce.
The Pipeline Receiving Terminal will transport yearly 10 Bln Cubic meters of Gas in a first phase and lately it will double to 20 Bln. My doubts are, given the size and volumes involved, about the depressurization technology that will be used.
The depressurization of the station piping/equipment, both in emergency and in maintenance
condition, will happen through two dedicated vent stacks, to be installed within the
TAP Terminal. The cold vent stacks are designed to blow down the terminal piping and
equipment.
The vent stacks (10 m hight)are designed to blow down the entire volume between the
inlet- and outlet ESD valves from design pressure (145 barg) to 6.9 barg within approximately 15
min. The hold-up of the terminal is 48.6 Tons of Natural Gas (and will double when the Terminal will process 20 bln cubic meters of gas), that they say will be released ie for emergency or maintenance in the Air in 15 minutes. The Pipeline reciving terminal is respectively 800 meters and 1175 meters away from 2 towns with 7000 inhabitants each.
Does it make sense? I know already that few engineers have expresses profound doubts on this procedure.
what do you think?
Many thanks for your opinions in advance
Stefano

PS if that could help I could provide a comprehensive document via mail on request.Many Thanks

 

[georgeverghese]

Presume this receiving terminal is at the Lecce end in SE Italy.

10m height for a cold vent stack seems awfully short for a large receiving terminal, if you are looking for knee jerk response. It may be a vent stack, but consideration of accidental ignition of the vent stream and the consequent flare radiation loads on plant operators and facilities cannot be ruled out in most cases.

Also, venting of these hydrocarbon streams is usually frowned upon these days due to the much higher greenhouse gas effects from methane as compared to the combusted gas stream.

 

[EmmanuelTop]

API 521 provides guidance on flare stack height calculation (I would follow similar approach for cold vents, especially if the facility is manned).

Look for identification of real risks and scenarios under which you would have to activate the depressurization system and see if the consequence justifies the cause. If there is no emergency scenario, you can probably end up with almost any stack height, given that it is placed in an appropriate location.

Dejan IVANOVIC
Process Engineer, MSChE

 

[stefano santoro]

Dear all,
many thanks for your answers; the real questions here that could give me a lot of help are:
1) is it a normal practice to declare that in emergency and maintenance the Terminal will cold venting 48 Tons of Natural Gas in the air at 25 Bar pressure (this is what they declare) at 700- 1000 meters from 14.000 people... consider that the Tons will double when they'll reach the 20 bln cubic meter per year. The question is what about the real risk of accident given that those cold vent stack are within the plant..at 200 meteres from the control center of the plant? What about the real risk is in relation to Unconfined Vapor Cloud Explosion ...well known and studied and very dangerous expecially if again the terminal is respectively 800 meters and 1175 meters away from 2 towns with 7000 inhabitants each.

2)How many Pipeline Receiving Terminal from your experience do you know that are built so close to the population and adopting this tecnology for depressurization. (ie in Italy none...they are 4-5 Km away....ie an LNG terminal delivering 3,5 bln cubic meters per year is 12 miles from the land) ..the real risk is in relation to Unconfined Vapor Cloud Explosions)

With GAS, the emergency situations, like many other activities, are impossible to predict but the potential scale is Huge. Engineering studies should tell the "what if" scenario consequences...and from many angles it looks like the combination Here of Distances and Technology (Cold Vents) it's an announced potential disaster...worst than in the case if it was in a safer and more distant scenario. Many thanks for your answers...

PS yes George...it is the plant in the province of Lecce...that is causing an incredible amount of complaint and protests from people and engineers experts because of technology and distance for towns...they managed to put the plant site in one of the most populated and concetrated area of the province of Lecce within 3 km you have more 20.000 people, instead of putting it in other industrialised areas available.

PS2 Emmanuel...the question is....can such a big PRT be considered properly placed given the distances above mentioned from the people? From my researches in Italy ther's nothing similar ...and ie in France the Dunkerque Gas terminal is 4 km away from people.Many Thanks

 

[EmmanuelTop]

I don't think you can answer all those questions properly without a documented (and quantified) risk assessment. And the townspeople won't quit their protests unless they hear good arguments from your/operator side. You don't seem to be an expert in technical safety, so hire a consultant to do this job for you.



Dejan IVANOVIC
Process Engineer, MSChE

 

[stefano santoro]

Infact I am not an expert at all on this field...and I am simply writing here as a private, not business/PRT related person. I am just curious to ask your general and umbiased opinion on the issues raised by the engineers/techical people that I have met and listened to in relation to this project. My parents live close to the place where they think to build the PRT.
It looks like that SIZE (10-20 Bln cubic meters of Nat Gas per year), TECHNOLOGY USED (Cold Vents) and DISTANCE from people, makes the project a bit Scary and unusual to say the least.

Many Thanks again for your ideas/opinions

 

[stefano santoro]

PS..the problem here is that the consultants are not normally umbiased as they get millions in fees from the Oil and Gas Industry...SAD BUT TRUE

 

[georgeverghese]

To address these concerns, one should get a copy of the facility relief and depressurisation study report, probably authored by a contract oil - gas engineering company, one of the editions of which should be approved by the plant owner's project lead process or process safety engineer ( which would appear to be someone in BP and or SOCAR in this case, from what I see on the net). In it, there should this sub study on the facility emergency depressurisation, which should address the following:

a) A detailed gas dispersion analysis, done at various wind speeds and wind stability classes relevant to this location, which should show that gas concentration levels at all locations of interest within and outside the plant are acceptable. For locations external to the plant, ground level concentrations at all inhabited locations whould also have to meet the local / international / WHO standards). This study should also address ground level concentrations for any contaminants such as H2S and other nasty compounds such as benzene, ethylbenzene)

b)For the case when the vent stream has accidentally ignited, thermal radiation loads at relevant locations of interest should also meet API / plant owners company standards.

Obviously, the study should address both configurations of the vent stack ( 1 stack for now and 2 for later ) for all these cases.

There may also be other vent streams appearing at this vent, which may be safety relief streams, or even some continous vent streams. All these cases should be studied.

Noise levels, both for short term depressurisation scenarios and safety relief streams, and long term noise levels resulting from any continous vent streams should all be covered.

A safety sterile area around the vent stacks is also typically mapped out - no facilities, temporary or permanent should be built within this sterile area, and plant operator access into this sterile area will require Plant Owners approval. This sterile area is to be kept within the plant boundary limits.

The role of the Plant Owner's lead process safety and process engineer in this study is critical, given that these engineers (and their managers) will be held responsible by BP / Socar for the accuracy of the numbers presented, the scenarios identified, the methods and tools used for the study, and for the conclusions derived.

It is customary in my experience, that the Plant Owner present this approved study report to the local government HSE departments and get their written acceptance and approval of the study findings also on behalf of the people they represent. The local Govt officials may appoint their own independant consultant to vet this study if they choose to. Without this approval, no plant design gets the green light to proceed with construction of this facility from the local and or federal Govt., in my experience. For a large company like BP, would imagine BP themselves would not proceed with the construction of this facility without Govt acceptance of this study's conclusions.

 

[georgeverghese]

Also take a look at the Environmental Impact Assessment Report (EIA report) that would be produced by the Plant Owner for submission to the local Govt for acceptance - this report would address all liquid and gaseous emissions from the plant and would take many of its conclusions from the plant relief and depressurisation study report. The EIA report should also take into account the potential impact of any explosions that may occur within the plant.

 

[georgeverghese]

Yes, can see the people around Melendugno are all up in arms about this PRT on youtube. The facility here does not appear to be a compressor booster station like the one at the departing end at Fier in Albania.