Natural Gas Cavitation

[neroverdi41]

Hello everyone.

Natural gas will pass through the control valve I designed at 50 C temperature and 55 bar pressure. In this case, I want to calculate whether there will be any cavitation in the valve. I know that natural gas will remain as gas under these conditions. I also know that cavitation is due to the transition from liquid to gas. But I don't know how to interpret it. Can you help me?

 

[SPDL310]

If your process modeling shows that your natural gas is 100% gas at the inlet conditions then there can be no cavitation. You are already in the gas region of your bubble-point curve additional pressure drops will not cause cavitation. You are more likely for generate droplets from condensed vapors than cavitation.

For liquid flows you can use the cavitation index method shown below to determine the likelihood of cavitation.

https://trimteck.com/understanding-and-predicting-cavitation-in-control-valves/

 

[neroverdi41]

If your process modeling shows that your natural gas is 100% gas at the inlet conditions then there can be no cavitation. You are already in the gas region of your bubble-point curve additional pressure drops will not cause cavitation. You are more likely for generate droplets from condensed vapors than cavitation.

For liquid flows you can use the cavitation index method shown below to determine the likelihood of cavitation.

https://trimteck.com/understanding-and-predicting-cavitation-in-control-valves/

thank you for your answer but how can I take precautions against this? if it always stays in gas then how can it be a flashing problem? How can I calculate the vapor pressure of a natural gas fluid at 50 C temperature and 55 bar pressure? Because this is how I can decide whether there is a flashing problem or not. At 50 degrees, natural gas has no vapor pressure. According to this, should I take the value under normal conditions?

 

[GBTorpenhow]

Cavitation and flashing are only possible when the fluid entering the valve is a liquid. Your inlet fluid is not a liquid, so flashing and cavitation are not a concern.

 

[Snickster]

See attached Pressure-Enthalpy graph. Natural gas is clearly a gas at stated conditions.

 

[Taicho567]

It's not a concern here. It's in gas state so cavitation won't occur. Your gas temperature need to be really low at a certain pressure to change it to liquid, which is not going to happen in your case. No liquid, formation of bubble is not going to happen.

Cavitation occurs when the liquid pressure inside the valve is low enough (below liquid vapor pressure) to allow the formation of bubbles and when subjected to high pressure (above the liquid vapor pressure), the bubble would implode.

 

[neroverdi41]

Thank you all, friends.

“Our production efficiency is higher from droplets of condensed vapors rather than cavitation.”

There is a comment above that it can only be condensed vapor droplets. That's why I was worried.

 

[neroverdi41]

Ekli Basınç-Entalpi grafiğine bakınız. Doğal gaz belirtilen koşullarda açıkça bir gazdır.

Which book did you quote? Can you share it with me? I don't fully understand this graph. the graph looks complicated. how can I interpret the enthalpy?

 

[Snickster]

It is a typical pressure-enthalpy diagram. The enthalpy is a measure of the energy contained in a gas. You need to understand thermodynamics to understand, If you were a mechanical engineer you would take college courses in thermodynamics. It cannot be explained here.

“Our production efficiency is higher from droplets of condensed vapors rather than cavitation.”

What exactly is your problem. Can you provide complete details?

 

[SPDL310]

Please see the following on natural gas behavior.

https://petrowiki.spe.org/Natural_gas_properties

To fully asses the risks to the valve you should consult with your valve supplier, and process engineer do determine the valve requirements. As others have stated in general you are starting off in a fully gas region. You have not stated how large of a pressure drop you will be taking the expected flow rate of the gas or the recovery factor of the control valve that you are considering. We can only give you general advice.

With your inlet conditions the two things you would need to consider are J-T cooling and possible droplet condensation.

 

[neroverdi41]

Tipik bir basınç-entalpi diyagramıdır. Entalpi, bir gazda bulunan enerjinin bir ölçüsüdür. Anlamak için termodinamiği anlamanız gerekir. Eğer bir makine mühendisi olsaydınız, termodinamik üzerine üniversite dersleri alırdınız. Burada açıklanamaz.

“Yoğuşmuş buhar damlacıklarından elde edilen üretim verimliliğimiz, kavitasyondan elde edilen üretim verimliliğinden daha yüksektir.”

Sorununuz tam olarak nedir? Tam ayrıntıları verebilir misiniz?

Arkadaşım merhaba;

Ben metalurji ve malzeme mühendisiyim. Aldığım termodinamik dersi biraz daha metalurji üzerine olsa da bu dersleri aldım. Lisede çok sayıda kimya dersi aldım. Entalpinin ve entropinin ne olduğunu çok iyi biliyorum. Sadece valf üzerinde nasıl yorumlanacağını sordum. Resimdeki tablo karmaşık bir şekilde geldi. Sorum şu, sadece gaz fazında olan bir akışkan kavitasyona neden olur mu? Çünkü metalürji mühendisliğinde akışkanlar mekaniği dersi yok. yavaş yavaş için çalışma başlıyorum.

Yine de teşekkürler

 

[neroverdi41]

Doğal gazın davranışı hakkında aşağıdakilere bakınız.

https://petrowiki.spe.org/Natural_gas_properties

Vanadaki riskleri tam olarak değerlendirmek için vana tedarikçinize danışmalısınız ve proses mühendisi vana kararlarını belirler. Diğerlerinin de devam ettiği gibi genel olarak tamamen gazlı bir bölgede başlıyorsunuz. Gazın beklenen akış akışını veya sıcaklık kontrol vanasının geri dönüşüm faktörünü ne kadar büyük bir basınç düşüşüyle karşı karşıya kaldığınızı belirtmediniz. Boyut yalnızca genel tavsiyelerde bulunabiliriz.

Giriş koşullarındaki kesintilerin olması gereken iki şey JT soğuması ve olası damlacık yoğuşmasıdır.

P1= 55 bar
P2= 17 bar
Q= 50000 m3/saat

Valfteki kurtarma olayları hakkında çok az bilgim var.