Fluid Velocity and Static Charge

[jeebusmn]

Hi,

We have an ethanol plant that we are working on starting back up. When we are loading a barge, we will be pumping out at 3000 GPM. A large pump is pumping the denatured ethanol through an 18 inch pipe that is reduced to 6 inches and then is run through a coriolis mass meter and a 6 inch on/off butterfly valve and then through a hose out to the barge. The reduction was put in to save money on the coriolis meter. I can't say that this makes a lot of sense in the long term because you'll have to spend more money on a bigger pump and extra electricity for the pump. My basic question revolve around if it will work.

I don't think static charge will be an issue since ethanol is more conductive than 50 pS/M (API Protection Against Ignitions Arising Out of Static, Lighting, and Stray Currents).

I don't think cavitation will be an issue since the downstream pressure is 9 PSI and this is about the 2.5-3 PSI denatured ethanol vapor pressure.

The flow velocities through the pipe are 3.73 fps in the 18 inch section and 33.16 fps in the 6 inch portion. What will this do to the pipe? What will it do to the 6 inch butterfly valve?

 

[hacksaw]

doesn't look like a good design to me, 33 fps is pretty excessive for the piping and the inlet velocity for your valve

 

[25362]

An example of charge build-up while transferring ethanol can be found in Crown and Louvar's Chemical Process Safety: Fundamentals with applications, Prentice Hall.

 

[jeebusmn]

Thanks. 26362. I will be going to the University of Houston tomorrow to give that book a look. This will be covered in the book some I suppose but what is done if you have a fluid that builds up a charge? Do you just avoid transporting above certain velocities or can you solve your problems with better grounding? Are there any general guidelines or industry standards that I can use to support my case? I have found stuff on this forum covering static electricity and hydrocarbons but ethanol isn't really a "true" hydrocarbon.

Hacksaw, it is kind of a messed up project. The owners want to get the plant running with as little money as possible. If all goes as plan, they'll be in the black after one full year of operation. The owners are junk dealers who bought the plant for scrap. They decided to try to restart the plant instead when they saw how much money there's in ethanol.

 

[hacksaw]

been there done that, cheap to install ten times the price to make work, some how it is the instrumentation that isn't working...right

the 10 fps rule is to reduce volitization and static build up in the tank. the brewer doesn't refer to ethanol as a hydrocarbon, but the fire marshall does, and it is just as hazardous as can be when something goes wrong. at 33 fps something already has...

how long do you want the valve to function?

 

[jeebusmn]

Not long I suppose since they are looking to try into get into the black as soon as possible. I suppose they are looking for a year or two.

 

[BigInch]

33 fps! Watch the water hammer pressures when you close one of those valves! Then fix your meter.

http://virtualpipeline.spaces.msn.com

 

[hacksaw]

my guess is that the valve is toast in the design stage.

at a minimum the actuator is not sized for that service, and will not allow stroking,if the valve shaft (depends on the design) or the shaft bearing survives start up. Should failure occur the disk will pass merrily downstream and the shaft generally is projected into the area depending on the service pressure.

A call to the valve manufacturer to check actuator requirements might be a good place to start.

 

[GL431]

At that velocity you should expect erosion of the pipework and fittings as well as cavitation damage. (Cavitation due to localised pressure drops in eddies behind obstacles - such as that butterfly valve disk - and subsequent pressure recovery; all on the micro-scale; damage might be seen on the piece of pipe immediately downstream of the valve disk) Will the coriolis work at such a velocity? (I do not know their limits.)