Drum Hood Vent Flow Design 2

[Anthony_J]

Hello,

I am working on designing a ventilation system for a 55-gallon drum. The goal is to remove as much contaminated airborne material from this drum as possible. My question is how to determine the point of diminishing returns on the throat opening to the vent device. I currently opened it from 1.25" opening to a 3.75" opening figuring I'd sacrifice some air velocity for more surface area. I don't have fluid flow software to model this so anyone with practical knowledge would be greatly appreciated. The air scrubber provides up to 750CFM.

Does anyone have any input/experience with this?

Thanks,


~Anthony

 

[HVAC-Novice]

How open does the drum have to be? Obviously closing it or a more enclosed exhaust hood would be better.

What is in there and what access is needed or why is it open?

a lot will depend on volatility and toxicity of what is in the drum.

 

[Anthony_J]

The drum contains highly radioactive material, beyond that I can't share. Workers are in their own breathing apparatus while working around the drums as an intake of this material could be detrimental to their health.


The operators are reaching into the Drum, so I need to keep it as open as possible so they can work unobstructed. They are OK with the design I have thus far, utilizing this hood design tangent to the drum.


My worry is if I close the opening too much, increasing the velocity, there may be material that won't be received by the hood due to minimal opening of the hood. Or will opposite happen, will the increased velocity flowing into the hood actually pull more from the drum?

 

[Sal Sham]

Hi Anthony
The most important factor is the density of the gases that you want to suck. I had a similar case 15 years ago and it was about a solfor drum that the workers opened in the workshop and after opening they felt a bad smell.
If you have 750 CFM in the extracting hole, It will help you if you put an opening opposite this area with only 3-5 fpm airflow. This small airflow in the opposite will help your goal a lot. you can make that hole only with 1/2" height around the half of the top of the drum.
Let me know whether this is helpful or not.

 

[Anthony_J]

Hey Sal,

To my current knowledge, it'll be more of a dust rather than a gas that will be escaping from the drum. I don't currently have material density parameters at the moment.

Unfortunately, I cannot put holes in the drums in any way since they will be reused to seal other materials in the future. Thank you though for the idea.

 

[HVAC-Novice]

Could they add a lid with hole they can reach through? Is closing the lid between filling an option?

Sounds like this is a material you want zero contamination. Doesn't sound like something you want to have open. what about when the exhaust system fails or needs to be maintained? For that type of material and hazard it would be worthwhile to have proper design done with CFD etc. I assume this is regulated by some authority. Maybe they have design guidelines?

Probably want to have that collection system all around. The room itself may have air currents that impact your system.

 

[Sal Sham]

Hi Anthony
Is it possible for you to make that sucking frame with a full circle shape? even with one or 1 1/2" height? if you suck the air from all the sides of the drum it will work. In this case the only risky part will be the center of the drum which is solvable.

 

[Compositepro]

Very little information here. Are you loading or unloading the drum. I've seen this design used. It is about the cheapest option possible but works better than nothing. Air being drawn from behind the operator will form eddies that blow dust into his face, but the respirator takes care of that.

There are many better options but all are a lot more costly. Google "powder unloading from drums" for ideas.

 

[Anthony_J]

Sorry for the lack of information, I know it makes helping more difficult. It's government work so there's only so much I can share. I appreciate the feedback from everyone.

A full circular shape profile is definitely plausible, thank you for those suggestions.

Also Compositepro, I checked out the "powder unloading from drums", definitely has some better methods that I will look into as well.

 

[Snickster]

This is the go-to book for industrial ventilation system design:

https://portal.acgih.org/s/store#/store/browse/detail/a158a00000CgqcfAAB

 

[Anthony_J]

Thanks Snickster, I have downloaded an older edition and will do some reading.

 

[apollowolfe]

I attached an image from the ACGIH Industrial ventilation manual.

Variables:
Q = flowrate CFM
h_e = overall hood entry loss
VP_s = slot velocity pressure
VP_d = duct velocity pressure