static free solvent extraction line 2

[mechanicaldup]

Hi

what type of pipes would you recoment for a solvent extraction line? the solvent been pumped contain NO3, Cl, Na2CO3, H2SO4 and Entrained Organic Solvent.

the solvent is highly flammable and any sparks should be avoided at all cost. The pipes must be completely static free.

where can i find guidelines/ rules of thumb on static free pipelines regarding
-material
-flov velocity
-earthing
-others?

thks

 

[hollerg]

Conductive piping would be normally recommended and depending on the conductivity of the fluid, bonding the flanges around the gaskets, in addition to normal earthing of the piping. Vessels need to be padded, with gases that ensure being above the UEL or below the LEL under all conditions of start-up, shutdown, vacuum, etc.

Of greater concern would be the locations where phase separation occurs, where the dangerous charge separation can develop. It depends on geometry, transfer rate, etc. as to the magnitude of the hazard. Avoid free floating conductive objects or long probes in the vessel. Multiphase materials should be introduced into vessels through dip tubes or via bottom entry. Velocity should be controlled and splashing/spraying avoided. Vel of <1 m/s is usually safe for homogeneous fluids without dip pipes but yours is heterogeneous. Decelerate fluids upstream of discharge points. To know how far upstream requires knowing the relaxation time of the accumlated charge.

Insulative piping and vessels can be used by experienced industrial practitioners, but really pay attention to controlling intensity of motion, avoiding liquid surfaces that can accumulate charges, and providing pathways to ground, to remove eletrostatic charges. Electrostaticly conductive non-metals are preferred.

NFPA is a good source and API has a guide as well but I do not recall much specific advice on multiphase solutions.

There are books like "Avoiding Static Ignition Hazards in Chemical Operations" (a CCPS Concept Book)by L. Britton
that may be useful.

 

[mechanicaldup]

thks hollerg for a valuable post

what is your opinion of using GRP (glass fibre) piping for such an application?

 

[Compositepro]

You shouldn't have any static problems with the fluids you describe. The fluid itself will be conductive. Conductive piping is still a good practice. Ignition can only occur in vapor spaces that have the correct oxygen and fuel mixture, so inerting large vapor volumes is good practice if equipment cannot tolerate the overpresure caused by ignition. Most piping can tolerate such pressure with no problem and that is the safest approach.

 

[Engineer6512]

Conductive piping, properly grounded would be the best solution.

Steamguy2

http://www.SteamPlantEngineering.com

- Discussion & resources for professionals in the Power Generation Industry

 

[hollerg]

The use of FG piping depends on the conductivity and proportion of the two phases.

Solvents with some water solubility or contaminants will tend to be conductive. If the bulk is the aqueous phase you are in relatively good shape as long as the solvents are compatible with the resin. Excluding oxygen is also required if there is any scenario that would place the vapor space in the flammable range (above the LEL and below the UEL). I myself would be willing to use it but follow-up after maintenance is important. Leaving bonding and grounding disconnected would create a hazard that would not be obvious. Unless a heptane, toluene or hexane type of material is the solvent, the rest may not apply but it is useful context for you.

What I would also be careful of is the transitions between systems, metallic to nonmetallic piping, and operations e.g. pipeline to vessel, flow thorough a filter media).
Again it is the issue of charge separation occurring at transitions, S to L, L to L, conductive wall to nonconductive wall and the condition of the receiving vessel.

Having a conductive fluid may not be enough protection. For instance, if this were a batch system and the receiving vessel were also an insulator, the charge may not have a path to ground, due to an air gap from the inlet pipe to the liquid surface and a nonconductive closed block valve on the vessel outlet.

Construction that can create a capacitor also can be a problem. Glass reactors are often damaged by static discharges that punch holes through non-conductive glass to the steel, from mixing or filling with low conductivity fluids

Even with a path to ground, a low conductivity solvent phase that settles out (or to the top) may have a significant relaxation time. This would mean that activities like dipping a sample immediately after filling could be hazardous, regardless of whether the vessel or pipe was conductive or not.

Metal has the advantage of providing most of the path to ground. With nonmetals, dissipative or conductive construction is preferred, if feasible. Otherwise careful earthing and bonding is necessary to assure that induced charges and capacitors are not formed.

Gary

 

[hollerg]

Rather than "formed", I meant left behind (undissipated).

 

[moltenmetal]

What the original poster fails to mention is that depending on the SX process in question, some of this stuff will in practice eat just about any known metallic piping material for breakfast. In many of these applications, conductive metallic piping is pretty much out of the question. That's why FRP is being considered.

The answer is that this material is handled safely, day in, day out at numerous metal purification facilities worldwide, using non-metallic piping in properly designed equipment. There have also been some recent, catastrophic fires at such facilities. Others will know the details of the fires far better than I do. But the principal problem seems to be inadequate inerting and other design flaws rather than a lack of consideration for the possibility of static discharge, or the mere use of non-metallic piping.

The organic diluant used also matters greatly. If the diluant is being used sufficiently below its flash point, there's no issue because a static discharge will not generate a fire.

 

[Compositepro]

There is a new product available called Ion Cord (

http://www.fibraplex.com/IonCord2.htm)that

can be very useful in helping to solve static problems in petro-chemical plants. It is basically a string made from carbon fiber which is conductive and chemically very inert, even at very high temperatures. It is intended primarily to neutralize charge on non conductive surfaces by ionizing the ambient gas which will then neutralize any static charge. It is powered by the electric field of the static charge itself and requires no external power. In a liquid environment it would work simply as a corrosion resistant ground wire. It is carbon so you do have to be aware of galvanic corrosion issues where it may contact metal in an electrolyte.

 

[moltenmetal]

Compositepro: sounds great. However, FRP equipment generally has a "corrosion barrier" layer of pure resin on the interior. Is the intent to wind this cord into the inner layer of the piping and forego this inner corrosion barrier resin layer?

 

[Compositepro]

The cord would be used for addressing static charge problems only. FRP or plastic is usually used in place of metals where corrosion is an issue, but the lack of electrical coductivity creates a static problem that can lead to fire and explosions. Ion Cord is conductive but will not corrode so it can be used in almost any chemical environment. In a tank it can be draped across the bottom and attached to a ground near the top. The charge on liquids entering a non-conductive tank is attached to the liquid molecules which are mobile. These molecules are attracted to ground and will be attracted toward any grounded object. The object could be the earth outside the tank. The non-conductive walls block charge transfer and create a capacitor that stores charge on one side.

A common example is a plastic bucket or gasoline container that gets filled. The gasoline gets charged by flowing though a pipe and then falls into the bucket. The charge will accumulate in the bucket and be attacted to the bottom which is close to the ground. The charged liquid cannot flow back up the falling column of liquid. However, if the fill pipe is conductive and lowered to the bottom of the bucket, the charged liquid will be attracted to the pipe (or any ground wire) and be neutralized. In the case where the charge has accumulated on the bottom of the bucket it will slowly bleed-off by various mechanisms. If the bucket is immediately lifted off the ground after filling the electrical capacitance of the bucket falls drastically and the voltage of the accumulated charge will rise proportionally. The charge will now be attacted to the nearest ground which is likely to be the wire bail on the bucket and a spark is likely to occur at the surface of the gasoline which will result in an ignition.

 

[mechanicaldup]

thks gents

I take note.
What is your oppinion regarding the use of HDPE?

 

[ElderX]

I'm not expert at this, but shouldn't he consider using dip tubes and inerting for vessle transfers or fills in addition to the other good stuff mentioned?

 

[mechanicaldup]

What formula (guide) could be used to determine the temperature rise due to friction over the length of the pipeline.
Our application is a relative long line (1.2 km) and I want to ensure the liquid remain below its flash point