Dust collectors are essential for ensuring workers' health and safety in various industrial settings, and airlocks serve an important function within these systems. Before we look into the purpose behind airlocks, let's look first at how dust collection systems work.
How Do Dust Collection Systems Work?
Industrial dust collectors provide essential air pollution control in manufacturing, agricultural, and other commercial settings where particulates in the air can lead to safety hazards. They help keep the environment in and around industrial buildings safe by removing and controlling potentially harmful particulates emitted during production.
Dust collection systems filter contaminants out of the air to improve air quality. Though the specifics are different for each industry, as are the methods for extracting these pollutants, all have the same purpose. They work by drawing air through filters to remove dust and other particles, capturing and separating the contaminants before returning purified air back into the environment.
Dust collection systems play integral roles in:
* Chemical production
* Coal power plants
* Food processing
* Grain elevators
* Lumbermills and other woodworking facilities
* Metal processing plants
* Pharmaceutical manufacturing
* Recycling facilities
Dust collection systems consist of blowers, dust filters, filter-cleaning systems, dust-containment receptacles, and dust-removal systems. For dust collectors to operate most efficiently, dust containment receptacles--which store the contaminants removed from the air--must be isolated from the outside so that these contaminants cannot leak back out. To ensure this is the case, these receptacles must be connected directly to the rest of the machinery, or airlocks must be used.
The Importance of Airlocks
When looking at how industrial dust collection systems work, it's clear why airlocks are an essential part. Without an airlock, dust would simply escape via the discharge valve, essentially negating the whole system. For systems under vacuum--which are more commonly used--this lowers removal efficiency, as much of the dust returns to contaminate clean air. For pressurized systems, this allows air to blow dust everywhere, creating additional and unnecessary maintenance costs.
Besides the risk of contamination and the need for additional maintenance, there is a real danger of dust-related industrial accidents occurring. Airlocks help prevent explosions and fires caused due to dust, with specially designed rotary valves used to avoid this from happening. An example of this occurred in the not-so-distant past in an industrial building just northwest of Savannah, GA.
In February 2008, the Imperial Sugar Co. experienced an explosion and fire at its Port Wentworth packaging facility. The accident resulted in 14 deaths and 38 injuries, 14 of which were severe and life-threatening burns. The cause of this was later determined to be the result of an over-accumulation of combustible sugar dust throughout the building.
Under specific conditions, many types of material can combust. These include:
- Agricultural products (grains, egg whites, cornstarch, flour, sugar, potatoes, etc.)
- Chemical dust (from coal, sulfur, etc.)
- Metals and alloys (aluminum, bronze, zinc, etc.)
- Pesticides and herbicides
Furthermore, airlocks allow you to change the dust collection bin without shutting off the system. Without airlocks, the entire system needs to be shut down or the unit must operate without any isolation, contaminating the air.
Different Airlocks for Dust Collection Systems
Airlocks come in various designs. Generally, these use vacuums to separate the dust and prevent it from escaping, which helps protect exhaust fans, though certain systems pressurized dust collectors. Common types of airlocks for dust collectors include:
- Double dump valves
- Knife gate valves
- Rotary valves
- Trickle valves
These airlocks can additionally be categorized by whether they are low leakage (double dump and trickle valves) or continuous leakage, such as rotary valves. Rotary airlocks are most commonly used, while trickle valves offer the simplest solution. However they work, these valves all essentially work to prevent high-pressure air from leaking into and contaminating lower pressure environments.
Double dump valves--also known as double flap gates or double flap valves--are used in industrial applications to handle and discharge fibrous or chunky material in bulk. Used for both vacuum and pressurized environments, they serve as a transition point to keep the pressure constant over and under the valve. It's an ideal valve to use for abrasive or bulky material that tends to jam rotary feeders.
Knife gate valves work in some of the harshest environments, typically using a sharpened stainless-steel blade to cut through heavy liquids. It's used in wastewater treatment and in other applications where corrosion is an issue. These valves are generally not used to regulate flow unless specifically designed to do so.
Also used for other applications, rotary valves in dust collection systems are used to unload dust, transitioning waste material from a pressurized point--the dust collector--to an unpressurized point, such as the dust collection bin. It seals systems to keep air pressure from being lost and controls the flow of material from silos, hoppers, or bins into conveying systems or during processing.
Also known as vacuum valves, trickle valves are used to maintain airlock seals for dust collector hoppers in industrial dust collection applications, which they were initially developed. Trickle valves tend to be less expensive than rotary airlocks, as they don't require an external power source.
Jeff Spisak is regional airlock sales manager, Prater Industries Inc. (Bolingbrook, IL). For more information, call 877-247-5625 or visit www.praterindustries.com.