How is a main draught fan different from an ID fan or a dust-extraction fan?
They are close cousins that sit at different points. An ID fan can sit either side of the collector and is defined by the boiler or kiln draft it holds. A dust-extraction fan often sits dirty-side, ahead of the collector, and takes the full abrasive load. The ESP / baghouse main fan is specifically the clean-side draught fan at the tail of the gas train: it pulls the whole system through the precipitator or baghouse to the stack, handling gas that is already collected and therefore light on dust. Because it is clean-side, the engineering focus is efficiency, curve stability across the moving collector dP, and the upset case, rather than the continuous erosion that dominates a dirty-side fan.
The baghouse pressure drop keeps changing as the bags load. How do you size for that?
That moving resistance is the core of the duty. Baghouse dP climbs as media loads between pulse-clean cycles and steps back down after each pulse; an ESP fouls and is rapped clean field by field. We size the operating point onto the falling, stable portion of the selected wheel, typically 5 to 15 percent to the right of the peak, and set the curve to span the clean-collector and fully-loaded points so the fan never runs at a control limit as the resistance moves. VFD speed control is our default so the fan holds target draft across the dP swing instead of hunting. We then verify the curve on the 200 HP VFD test rig before dispatch.
It is clean-side, so do I still need wear protection?
Usually not for the nominal duty, but the upset case matters. Downstream of a working collector the inlet loading is light, so a plain backward-curved wheel is fine. But clean-side is only clean while the collector works: a burst bag row, a tripped ESP field or a start-up puff can dump abrasive dust onto a wheel selected for light loading, which is the documented way an otherwise-clean main fan loses balance early. We choose the impeller geometry and material with that upset case in mind, and where your collector's failure mode warrants it we offer hard-faced leading edges and bolted-in AR400 wear plates that are replaceable in place. We size the protection to your collector, not a default.
This is the biggest motor on the line. How efficient are your main fans?
We design for high static efficiency on standard clean-gas duty and higher again on high-efficiency airfoil builds. It matters more here than almost anywhere because the main draught fan is usually the largest single motor in the plant, running continuously at high power. A few points of static efficiency held for 8,000 hours a year across a 20-year life decides whether the fan is quietly cheap or quietly expensive to run, and the efficiency choice can outweigh the original purchase price. We tell you the offered efficiency on the quote, not a generic catalogue figure.
Should I specify VFD or an inlet vane damper for control?
VFD is our default, and this duty makes the case for it plainly. The collector dP swings across every pulse-clean cycle and the process turns down, so the operating point is inherently variable. VFD speed control holds target draft across that moving resistance and is more efficient than an inlet vane damper across the range because it avoids the throttling loss at part-load. Inlet vane dampers remain available for legacy retrofit where the existing motor and starter cannot accommodate a drive. We quote whichever your installation calls for.
Can the fan handle hot-ESP service or acid dew-point risk?
Yes. Most clean-side main fans run 120 to 200 °C, but a hot-side ESP can put 350 °C or more into the fan, and some gas carries acid dew-point risk near the stack. For elevated temperature we upgrade the casing to IS 2062 or 16Mo3, fit expansion joints for the thermal growth and size the shaft accordingly. Where the wall risks falling below the acid dew point (typically around 120 to 150 °C for sulphur-bearing gas) we add casing insulation and heat tracing and select corrosion-resistant metallurgy such as 316L or Corten on the wetted surfaces. We size the material and the dew-point margin to your gas analysis, not a default.
We're a pollution-control OEM building the ESP or baghouse. Can you supply just the fan?
Yes. We supply main draught fans separately to precipitator and baghouse builders as a sub-package. You specify the duty and the integration interface — flange dimensions, mounting orientation, damper and expansion-joint scope, electrical interface and control protocol — and we document it up front and deliver the fan ready to mate to your collector and stack. The engineering is identical to a direct-buyer fan; only the integration interface and who buys it differ. The main fan is one of our strongest applications by track record, with 34 customer duties across cement, power, iron and steel and pollution-control OEMs.
Do you performance-test before dispatch, and what standards actually apply?
Yes. Every fan is performance-tested in-house to the AMCA 210 / ISO 5801 method on our 200 HP VFD test rig, and dynamically balanced to ISO 21940 G6.3 as standard, with G2.5 or G1.0 on application. To be precise about the claims: that is testing to the AMCA 210 method in-house, not an AMCA certification, and we are not an AMCA member. CE is self-declared per 2006/42/EC and 2014/35/EU, and ATEX Zone 2/22 is self-declared per 2014/34/EU (Category 3) where the area classification calls for it — self-declarations of conformity, not third-party certifications. Our only third-party certification is ISO 9001:2015. Bearing life is a design target of L10h at least 40,000 hours. The test and FAT take about a week and are customer-witnessed on request.
