ACS installation at Glowood 100,000ton/y pellet plant achieves 12mg/Nm3 - Case Study
Located in Cercal do Alentejo near the Port of Sines in southern Portugal, Glowood Indústria S.A. is a 100 000 tonne-per-annum pellet plant. Commissioned in 2012, the 10 million Euro facility uses pine sawdust LOCATED IN CERCAL Do Alentejo near the Port of Sines in southern Portugal, Glowood Indústria S.A. is a 100 000 tonne-per-annum pellet plant. Commissioned in 2012, the 10 million Euro facility uses pine sawdust.Conventional limitations
The total concentration of wood dust ash entering dryer cyclones from a rotary dryer is typically in the 200- 300g/Nm3 range. Whilst dryer cyclones are capable of capturing the larger particles to a high degree (>99%), particulate matter (PM) emissions exiting dryer cyclones are still around 200-350mg/ Nm3 exceeding existing regulatory limits in many countries. As a result additional end-stage dust removal systems need to be installed if PM emissions are to be brought under 50mg/Nm3, a threshold under discussion for the upcoming EU Medium Combustion Plant (MCP) directive.
However conventional end-stage dust removal systems have limitations. Flue-gas tars essentially rule out the use of bag filters, and Dry Electrostatic Precipitators (ESPs) cannot be used because of dust explosion hazards. Energy consumption, corrosion and secondary pollutant issues limit the use of Venturi scrubbers. While able to handle tars and very efficient at PM 10 and 2.5 removal, Wet Electrostatic Precipitators (WESPs) come with high investment costs along with water consumption and wastewater treatment issues. Finally conventional multi-cyclones have a removal efficiency of less than 50 percent.
In July 2014, Advanced Cyclone Systems (ACS), a Portuguese compatriot company specialised in the development and manufacturing of particle separators for PM emission control in various applications including biomass boilers, dryers and gasifiers, installed a line of newly developed mechanical cyclones for Glowood. These were installed downstream of the existing dryer cyclones. The objective for Glowood was to radically reduce PM emissions from its pellet manufacturing process to under 150 mg/Nm3 at all times to ensure regulatory compliance.
To design the most efficient system, 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 Glowood, ACS designed a cyclone system comprising of six Hurricane HR numerically-optimised cyclones, with ø1550 mm, disposed in line. A frequency-driven fan was also installed next to the stack to overcome the additional pressure drop. The system is capable of guaranteeing PM emissions under 150 mg/Nm3 at a pressure drop of 1.2 kPa, on condition that the incoming dryer cyclone emissions are below 700 mg/Nm3.
It's a bold claim, achieving WESPclass PM reduction values with a mechanical cyclone. Yet the most recent PM emission results from the Glowood installation were a mere 12mg/ Nm3, less than a tenth of the guaranteed 150mg/Nm3 limit and well below the expected 58mg/Nm3. Though the investment cost for Glowood remains undisclosed it is 'a small fraction of the alternative investment, in a WESP' according to Araújo.
Apart from the reduced environmental impact of the plant, another benefit is that feedstock material losses have been reduced by over 99 percent, resulting in process optimisation and additional operational savings for the company. Furthermore the installation process itself required minimum production downtime.
- Of course installation conditions are always site specific. The Glowood project took approximately three weeks and was done in parallel with the plant working. The actual tie in/ tie out installation took just a couple of days, said Araújo.
- I was confident that the project would be efficient. However the results are excellent and were achieved thanks to a brillant engineering project, said Álvaro Magalhaes, Founder and Managing Director of Glowood Indústrias.
Certainly it would seem that Glowood has a 'future proof' pellet plant in PM emission compliance terms. And this ought to create a stir amongst other pellet producers.
- We are looking at projects in France and Latvia and finding a lot of traction in North America. Here it seems that PM emission issues are taken more seriously than in many European countries. We feel that most companies simply don't know that they can solve their PM emission problem with high efficiency cyclones instead of a WESP, concluded Pedro Ribas Araújo.