Hurricane EX System to Reduce Particulate Matter from Sawdust & Wood Shavings

FOREWORD
OneFortyOne (OFO) is a world-class sustainable forest grower and forest products company with a multi-regional approach to investing and growing its business in Australia and New Zealand. OFO produces and distributes a range of wood-based building products from Jubilee Highway Sawmill in Mount Gambier. Facing an environmental problem identified by ACS representative Windsor Engineering, OFO selected an ACS high efficiency cyclone solution to reduce its particulate matter emissions.

IDENTIFYING THE PROBLEM AND SOLUTION
The current emission legislation in Australia by the Environmental Protection Agency (EPA), made it mandatory for the two 20MWth biomass boilers, which supply steam for the whole plant operation, to comply with less than  33mg/Nm3 corrected for 12% CO2. Furthermore, PM2.5 emissions need to be under 96mg/Nm3. The boilers, two Babcock & Wilcox Bi-Drum type boilers with single pass primary and secondary super heater, with regular cyclones as end stage dedusters, had emissions of near 400mg/Nm3 (≈650mg/Nm3 before the cyclones). Combustion was not complete as indicated by the high CO levels reaching 4000mg/Nm3. The particles were expected to be very fine due to the presence of soot in the combustion. This restricts the use of usual off-line sizing methods, such as laser sizers after re-dispersion in ethanol with ultrasounds. Therefore, a Cascade Impactor was used to determine the aerodynamical particle size, under the same method used for determination of the PM10 and PM2.5 (US EPA Method 201A). The very small particle size (median size of just 4μm) allowed ACS to design a system based on its second most efficient cyclone family – the EX. Each boiler comprises one Hurricane system composed of two SD (ø1900mm) pre-separator cyclones and forty “EX” (Ø950mm) high efficiency cyclones. Despite the very fine particles, this system allows for emissions on site to be under 100mg/Nm3 at 12% CO2.