Powder dosing into a pressurized vessel

[SR2211]

Hello,

We feed powder into a vessel (vessel pressure slightly atm) through a funnel with a long pipe (7m length) and at times
due to the slight over pressure of the vessel, the powder is not strong enough to flow and is thrown out.
What are the possible solutions to depressurize this pressure before feeding into the vessel or to avoid such scenarios.
A pneumatic conveying system would be ideal but we dont want to go for a high end solution.

thanks

 

[jari001]

Can't you open the vent line valve to relieve the pressure before charging or is there no vent line?

What are the dimensions of the vessel, amount of powder charged, exact pressures?

 

[SR2211]

There is no vent line directly above the vessel and the vessel volume is around 10000L. Amount of powder charged is around 100 kg per day and the reactor pressure is around 600 mbarg.
Since the powder is very fine, there is a huge volume of air purging upwards and spraying the powder all over the floor. We tried to create enough vacuum to feed in, still its not helping.

 

[moltenmetal]

You either need to open a very large vent to provide a path for the excess pressure above atmospheric PLUS the air volume displaced by the falling solid, or you need to dump through a divided chute so that the vapour has a separate path from the solid. If neither of these are possible, then you need to invest in a vented rotary valve and/or lock-hopper system.

 

[jari001]

I worked in a place that had a rotary valve setup where the powder was charged into the holding bin and then slight N[sub]2[/sub] pressure was added to ensure the powder would flow and then air blanket would sweep the dregs when the bin ran empty. The lock-hopper system is also a proven solution.

 

[Jobst]

Can you make a slurry out of the powder beforehand (or pre-dissolve it in some substance) before adding to the tank? Or encapsulate the powder in some material soluble in, but not harmful to the tank's contents? Any feed lines or exterior circulation loops where you could add a venturi feeder to? Or convert your funnel and hose into a simple venturi feeder, using plant air or nitrogen, if available?

Presumably there's some air feed or sweep on the tank, or it would eventually depressurize itself through your funnel/hose.

More questions than answers here, some more details would help clarify the situation.

 

[don1980]

The simple solution that I've seen used for adding powders is to use a pressurized charge pot. This pot is mounted on the top side of the vessel, with an on/off valve between the pot and the vessel. After charging the pot with powder, it's pressurized with gas (usually N2) to a pressure that a little higher than the main vessel. When it's time to add the powder, the valve is opened and in it goes.

 

[Compositepro]

You can also pump some light, aerated powders using an air-operated double diaphragm (AODD) pump. Here is a YouTube video of this being done:

https://www.youtube.com/watch?v=7l89Ho1m9-w

 

[SR2211]

Hello all,

thanks for your replies, i believe so with a slight N2 pressure, it could be resolved. Also, the vented rotary valve with a lock/hopper system, needs to be checked. But since its a Zone 0 classified we need to make sure the effective solution complies within the scope.

bye

 

[moltenmetal]

If it's zone 0, you absolutely cannot continue with your current practice of dumping stuff in through an open funnel.

 

[Latexman]

moltenmetal,

You may be right, but it's not clear to me why or what (gas) is causing this ---> "at times
due to the slight over pressure of the vessel, the powder is not strong enough to flow and is thrown out."

What if the RX is inerted and the inert gas is causing this? What if the powder has no contained oxygen? How do they guarantee during the powder transfer that air (oxygen) is not transported into the RX too?

I think the OP needs to clarify some of these details, but you do have a very, very good point!

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[moltenmetal]

If the vessel contains flammable contents, I don't care that it's mostly inert pad gas coming out through that open hole- that pad gas will still be full of flammable vapour or else they wouldn't be padding it.

We are short details, but what has been described is potentially an accident waiting to happen.

 

[SR2211]

Hi Moltenmetal and all,

Let me add some more details. The vessel is normally at around 900 mbar abs pressure, the valve is located just above the vessel, connected to the dosing pipe (100mm) which is about 7m long, where we feed the fine powder through a hopper (during this process there is no reaction its only for stabilization), the volume of air, which is trying to leave the pipe while opening the valve, during the dosing is creating this dust/smoke during dosing, leaving the area sprayed with some powder on the floor. There is no inert gas or vapor causing this, its just the volume of air in the pipe trying to escape, and pushing the fine dust upwards.

 

[Latexman]

Can you describe the temperature(s) during this processing? Can you characterize the flammability/explosivity potential of the powder? Has any testing been done? How much history does the process have? Is this an aqueous process? Any incidents?


Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[SR2211]

Hi, the temperature at the vessel is around 85°C, its a non-hazardous powder, the process is running like this since 30 years or so and no incidents. It is an aqueous process.

 

[Latexman]

Good, that helps a lot.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[moltenmetal]

OK, good. Then explain why the heck this is a zone 0 area?

 

[SR2211]

Until now its not clear to me, but i suppose there are other hazardous vap/chemicals in other equipment in the same area, which is way this is subjected to Zone 0.

 

[Latexman]

Wait, I thought we were talking about inside the vessel, but you are talking about outside the vessel. A Zone 0 in a general, large area outside a vessel, that is not below grade or at the end of a vent, is quite rare in my experience. Why would "hazardous vap/chemicals" be normally present in a large area? Don't your employees complain, get sick, or worse?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[moltenmetal]

Zone 0 means normally or very frequently full of hazardous vapour, and I totally agree with Latexman. Either somebody doesn't know how to actually do area classification and hence has painted a whole area unnecessarily as zone 0 "just to be safe", or there's something else fishy going on here.