New from the global multi-disciplinary technology company, SEGERSbetter technology, is a hard pelletiser which it hopes will extend the acceptance of sludge drying by industry leaders as an alternative to incineration.

The company offers a wide range of sludge treatment processes and in more than 60 countries is involved in the construction and engineering of waste-to-power plants (co-generation of energy), municipal and industrial waste treatment, hazardous waste treatment, sludge drying and pelletising, evaporation and combustion, glue gas cleaning, dynamic uninterruptable power supply systems (UPS), and energy recovery from biomass.

SEGHERS’ Bart van Sichem de Combe said, ‘Today’s environmental hot issue is undoubtedly sludge. Mechanically dewatered sludge remains a huge problem for the wastewater treatment industry. Many of the formerly employed solutions are no longer viable. For example, transport of dewatered sludge is difficult, inefficient and environmentally unsustainable.

‘Landfilling is detrimental for human, animal and vegetal ecosystems because of the risk of pathogen contaminations. Stricter legislation is hitting companies and municipalities alike, so that only inert sludge (low in heavy metals and micro-pollutants) is likely to be allowed to be landfilled,’ he said.

Hard pellet technology

The SEGHERS hard pelletiser is a vertical multiple-tray dryer unit producing hard pellets of triple-A quality – i.e. the granules are pasteurised and completely dust and pathogen-free.

The unit consists of a hermetically closed cylinder with horizontally installed trays, heated by thermal oil in a closed loop. The thermal oil can be heated by a boiler or heat exchanger, recovering heat from hot flue gases or steam.

Safe, clean, sustainable

Recirculated pellets are coated with mechanically dewatered sludge before entering the pelletiser again to eventually be disposed. The hard pellets have an average diameter of 2-4mm and a dry solid content of >90%. The main advantages of this system include: one-step pelletising, and safe to minimal dust explosion risk, thanks to very low oxygen content in the pelletiser. Other advantages are high thermal efficiency due to absence of sweep air, odour treatment not required, lower power consumption, absence of abrasion as the scrapers do not touch the tray and no pressure is exerted on the pellets.

Large metropolitan areas – Toronto, Antwerp, Sao Paulo and Baltimore have taken up the technology and Barcelona now has the world’s largest indirect heat sludge drying facility. Global companies such as OTV, Bechtel, USF, Hitachi have also signed up.

A recent contract is with the Aquafin wastewater plant in Bruges, Belgium. A hard pelletiser with a capacity of 5500 kg per hour was constructed to form part of an integrated system with a fluidised combustor.

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