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Liquid CO2
- Thread starter ciise
- Start date
We had a liquid CO2 service until recently. I do not have any specifications specifically related to this service. But, I do have a few suggestions. Fundamentally, CO2 is no different that other fluids. You have to assure that the pump is flooded, vented and that it has adequate NPSH margin. The difference to most fluids is the extreme low temperature. In order to avoid flashing, gassing up and loosing flow, it is important that the pump is very well insulated and that a good procedure is used to get the pump down to temperature before it is started. We had a struggle with our operators. When they see a pump with a ball of ice and frost around it, they are tempted to grab a steam hose to thaw it out. We had to break that habit right away.
The biggest problem we had with out pumps was mechanical seals. CO2 will absorb into some o-rings resulting in explosive decompression when the pressure is removed. Seal faces can become frozen together if moist atmosphere is allowed to contact the ID of the seal faces. We used a CO2 vapor quench to keep the seal face area dry and this helped some. We used special face materials and light loading to reduce heat generation. We considered converting to a gas seal, but did not have CO2 vapor at high enough pressure available.
If I was starting with a blank piece of paper to design a CO2 pumping station, I would use horizontal, overhung pumps. I would have a continuous vent through an orifice back to the vapor space in the tank to automatically vent the high point of the case and the seal chamber (API Plan 13). I would use a single seal with a gland bushing and a CO2 vapor quench on the atmosphere side. I would insulate the pump very will with cold-service insulation. And I would have very specific procedures for my operators regarding flooding and venting prior to start-up.
Johnny Pellin
The biggest problem we had with out pumps was mechanical seals. CO2 will absorb into some o-rings resulting in explosive decompression when the pressure is removed. Seal faces can become frozen together if moist atmosphere is allowed to contact the ID of the seal faces. We used a CO2 vapor quench to keep the seal face area dry and this helped some. We used special face materials and light loading to reduce heat generation. We considered converting to a gas seal, but did not have CO2 vapor at high enough pressure available.
If I was starting with a blank piece of paper to design a CO2 pumping station, I would use horizontal, overhung pumps. I would have a continuous vent through an orifice back to the vapor space in the tank to automatically vent the high point of the case and the seal chamber (API Plan 13). I would use a single seal with a gland bushing and a CO2 vapor quench on the atmosphere side. I would insulate the pump very will with cold-service insulation. And I would have very specific procedures for my operators regarding flooding and venting prior to start-up.
Johnny Pellin
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