Centrifugal Blowers for Dust Collection and Filtration

Dust collection is one of the many jobs a centrifugal blower does, and it has a particular set of design points. The blower must pull air through hoods, ducts, and a filter, against a resistance that changes as the filter loads, and where the blower sits relative to the filter decides which wheel it needs. This page covers how a dust collection system asks for pressure, where to place the blower, and what the range covers.

A Dust Collection System in Four Parts

1. Hoods capture the dust at the source.
2. Ducts convey the dusty air at a velocity high enough to keep particles moving.
3. The collector, a bag filter, cartridge filter, cyclone, or scrubber, separates the dust from the air.
4. The blower provides the pressure that pulls air through all of it, and discharges clean air.

The blower is sized for the sum of all the resistances, at the worst case, which is the loaded filter.

Where the Blower Sits

In many dust collection systems the blower is placed on the clean side, after the filter. There are good reasons.

• The air is clean, so a higher-efficiency backward-curved wheel can be used, and wear is minimal.
• The ducting between the hoods and the filter runs under negative pressure, so leaks draw air in instead of blowing dust out into the plant.

A blower placed on the dirty side, before the filter, handles dusty air. That calls for more abrasion protection, heavier construction, and careful attention to build-up on the blades, and radial-blade wheels are often used for heavy dust and material handling. Radial wheels are not part of our range, so our dust collection blowers are the clean-side and light-dust type. See dust collection system design.

Adding Up the System Pressure

Pressure comes from every element between the hood and the discharge.

Illustrative example. A dust collection system moves 12 m³/s. The pressure budget is:

Element	Resistance
Hood entry losses	500 Pa
Duct and fittings	700 Pa
Filter (loaded)	1,500 Pa
Stack and outlet	300 Pa
Total	3,000 Pa (about 306 mm WC)

Air power is 12 × 3,000 = 36 kW. At 75% total efficiency the blower needs 48 kW at the shaft. This total sits in the high-pressure class, and it is inside our 500 mm WC standard maximum. The figures in the table are illustrative, not a design, because real filter and hood resistances depend on the specific equipment.

Filter Loading Moves the Operating Point

A filter’s resistance rises as dust builds up, and drops again after each cleaning cycle. So the operating point drifts between a clean-filter condition and a loaded-filter condition. A blower on a steep curve keeps airflow steadier as resistance rises, while a blower with a flat curve loses flow. Size for the loaded filter, and where the process needs steady airflow, use speed control to hold the flow as resistance changes. See blower curves, system curves and operating point drift.

Margins: A Debate Worth Knowing

Designers often add margins to dust collection blowers for leakage, filter loading, and future expansion. Common practice adds around 10 to 15% on airflow, and more on pressure, and practitioners disagree about how much is sensible. Too little margin leaves the system short as filters age, and too much moves the operating point away from the best-efficiency region, wastes energy, and can overload the motor if resistance drops. Calculate the worst case directly, add a modest margin, and control the flow. See how to size a centrifugal blower.

Hot Gas from Kilns and Ovens

Some dust collectors handle hot gas, for example from a kiln or a dryer. Hot gas is less dense, the blower develops less pressure, and the materials, bearings, and motor position need to suit the temperature. See high-temperature blowers for furnaces, kilns and ovens. Corrosive or wet gas needs attention to materials and drains, and condensation can turn dust into a paste that clogs the wheel.

Combustible Dust

Many dusts can burn or explode: coal, grain, sulfur, wood, aluminium, and many chemicals. A dust collection system handling combustible dust needs a dust hazard analysis, explosion protection such as venting and isolation, and equipment suited to the hazardous zone. NFPA 660 is the consolidated combustible dust standard, and NFPA 68 and 69 cover explosion venting and prevention. Zoning is the plant’s responsibility. We do not currently manufacture ATEX-certified or AMCA 99 spark-resistant blowers, so a blower in a classified zone, or handling combustible dust that requires such equipment, needs a specialist supplier. See combustible dust and hazardous atmospheres.

Build-Up, Wear, and Vibration

Dust on the blades changes balance and shows up as rising vibration, so schedule cleaning and monitor vibration. Abrasive dust wears blades and housing, and heavy abrasion is a reason to keep the blower on the clean side. See maintaining industrial blowers.

Where Our Range Fits

NextAir Systems manufactures centrifugal blowers up to 800 HP (about 597 kW) and up to 500 mm WC (about 4.9 kPa) static pressure, with backward-curved and forward-curved wheels and single-inlet and double-inlet designs. That covers clean-side blowers on dust collection and filtration systems, up to 500 mm WC. Radial-blade wheels for heavy dirty-side duty, the very largest process dedusting fans above 800 HP, and blowers for classified hazardous areas are outside our range, and we will say so early.

What to Specify

1. Airflow at the collector inlet, and how it was derived.
2. System resistance: hoods, ducts, filter clean and loaded.
3. Gas conditions: temperature, humidity, and dust type.
4. Whether the blower sits on the clean or dirty side.
5. Hazardous-area classification and dust explosion data.
6. Control approach to hold flow as the filter loads.
7. Site altitude, drive arrangement, and noise limits.

Get a Blower Selection for Your Dust Collection System

Send your airflow, system resistance, and dust conditions, and we’ll size the blower and confirm whether it is within range. Contact us for a free quote.

Frequently Asked Questions