ACS designed and supplied a Hurricane Cyclone System to reduce PM emissions of existing dryer cyclones at Glowood Pellet Plant. The plant occupies a total area of 3.8 hectares and a total investment amounting to 10 M€. Production (100.000 ton/y) is 100% for export, as Portugal consumes under 10% of what it manufactures on a global basis (approximately 1M ton/y in 2012). A warm climate may until now have been the main reason for the inexistence of pellet consuming district heating facilities in Portugal. Unlike most pellet plants which are located above the Tejo River, Glowood is located in the South, near the Port of Sines. It uses as raw material mainly sawdust from sawmills and unprocessed eucaliptus and pine wood .
Identifying the problem and solution
Like many pellet producers Glowood uses a biomass boiler with the exhaust stream heating a rotary dryer to dry the incoming feedstock. The material is dried and carried over via dryer cyclones to the next stage in the pelleting process. In addition to separating wet wood particles from the dryer, a much smaller amount of fly ash from the biomass combustion is captured in these dryer cyclones. PM emissions could be reduced to approximately 700 mg/Nm3 in the worst drying conditions. Part of the flow rate was being recirculated back to the dryer for heat recovery, but the remaining part (71,839 m3/h at 87ºC) was thrown into the atmosphere. This represented losses of material and essentially an environmental problem which is common to many European pellet manufacturing facilities. In order to design the most efficient system for this case, an isokinetic dust sample was collected at the stack and measured by ACS in a laser sizer to obtain the Particle Size Distribution (PSD). After confirming what PSD to consider for the case (Fig.3), ACS designed a Hurricane system comprising 6 Hurricane HR numerically optimized cyclones, with ø1550 mm, disposed in line. The system is capable of guaranteeing emissions under 150 mg/Nm3 (expected under 50 mg/Nm3) at a pressure drop of 1.2 kPa, maintaining the dryer cyclone emissions under 700 mg/Nm3. An additional fan was included next to the stack to overcome the additional pressure drop of the system controlled by a frequency driver.