The Importance of Hood Design

Poor hooding or no hooding can be a major problem for your ventilation system. They are an important component to your system and its performance. Many dust collection systems ventilate processes that are not fully enclosed. You may need access to a kettle, one belt transfers to another, or many other manufacturing realities that make dust collection difficult. Several specific elements need to be addressed during the hood design process including air volume, velocity, shape, and placement.

“Pick-Up Points” are areas in industrial manufacturing where direct dust collection is needed. These areas are “open,” making proper ventilation of the process difficult. As a result, one of three solutions are used to improve ventilation in these examples:

1) A properly designed hood is placed at the appropriate point near the process requiring ventilation

2) The area surrounding the process is enclosed, or

3) A combination of 1 & 2

Most hoods are located above a dust transfer point (like on a conveyor) or above a dust generating process (like a hood over a wood cutter). Anytime dry material is moved, there needs be a way to ventilate the corresponding airborne dust into the duct and then baghouse. Common hood shapes include plain (tapered), slot (slot with plenum), canopy, and elephant trunk (raw edge), or even a round duct properly placed from the ventilation point.

To illustrate the importance of hood design, consider a belt conveyor transfer. A very typical problem in a lot of plants is when you’ve got a transfer from one belt to another. Your vent system should keep this instance under negative pressure so that dust is contained. This means your velocity should be low enough to pull airborne particles into the hood, but not so strong it pulls heavier particles from the conveyor itself. Hoods are designed to effectively induce an inward airflow pattern for airborne particles in the work environment.

Some systems with no or poor hooding require the operator to “choke” the vent system to avoid pulling too much material. If the hood is dampened back too much, the volume and velocity of “pick-up” will be lessened, which will cause the area to be “dusty” again. When airborne dust is not removed from the environment, it can be a danger to employees and the facility.

Some dust, such as emissions from electric arc furnaces, require an enclosure where the only opening is for material input and output. Enclosing an entire area of dust generation in the process is the most effective way to eliminate dust contamination or exposure.

Enclosing the area where dust is generated contains it within a controlled area, but also lessens the required volume of air to properly ventilate the physical space in question. Hooding may still be considered for additional capture velocity, but keep in mind: baghouse ventilation systems, unless they are process-related equipment, should be considered dust containment systems, not dust collection systems.

At IAC, we have experts that can recommend proper enclosure design and hood placement to ensure you contain the airborne dust while not creating improper capture velocity issues, which can overload baghouses with dust intended for other places (on a belt, in a bag, stored in a silo, etc). To discuss in more detail how you can get the most out of your system, call 800-334-7431.