wax and hydrate issues 1

[process8design]

Dear all,

Just got a question about blowdown system. My system is to blowdown well stream (345 barg, 10 oC, 0.6 m3) to atmosphere pressure during choke maintainence. The outlet temperature is around -82 oC. The wax cloud point is 42 oC. Could the wax and hydrate be an issue in this case? Thanks in advance.

Regards,

 

[krossview]

Hi,
I struggled with the same question on your interesting problem and my thinking is this.

Yes, hydrate and wax formation are very much a concern because of the high pressure and resulting large temperature drop in normal blowdown cases. With normal I mean large volume systems requiring blowdown. From a thermodynamic point of view the outlet temperature will be very cold as you predicted. However, your system volume of 0.6 m3 is quite small and should depressure quickly, while the outlet gas temperature would increase quickly from the intial -80°C temp. The relative small gas volume may not have enough mass to create a hydrate or wax plug. Also, the relative hot piping system can have a lot of mass that needs to cool down and will work to your advantage and slow the hydrate/wax formation down. It is hard to tell what exactly is going to happen, but I believe if you blow down the system down slowly you may not have a problem at all.

Only experience would tell you the real story. If in doubt, utilize a two-stage blowdown and preheat the gas in the intermediate pressure stage to keep it out of the hydrate/wax formation region.

I am very much interested in hearing more about this from other engineers with more field experience. Hydrates and wax plugs can set-up fast, but they do require a bit of time to develop.

Krossview/OK

 

[25362]

I've heard of a russian engineer trying to use ultrasound to dislodge and melt any wax/hydrate crystals that may appear.