Prediction of viscosity based on sludge type and characteristics and its significance for thermal hydrolysis economy: PRESENTATION ONLY
Svensson, K. and Dadgar, F., Cambi Group AS, Norway
(free)
Thermal Hydrolysis is applied worldwide as sludge pre-treatment to reduce required digestion volume, increase methane yield, increase cake dryness, and assure hygienic safety of the final cake product. Cambi THP is an energy efficient process owing to energy recovery system that uses the heat from hydrolysed sludge to preheat the feed. Specific energy demand for thermal hydrolysis, i.e. required steam per ton treated dry matter, is inversely proportional to dry solid (DS) content of the feed. Raw sludge pre-dewatering assures that the THP-feed has a dry solids (DS) ~17 %, avoiding unnecessary heating of water. Nevertheless, data from full-scale operations show that some THP plants operates with feed DS% as high as 20 % and above. Increase of feed DS from 17% to 20% decreases plant’s specific steam consumption by 15% and increases specific throughput by 18%. This indicates a major energy saving potential for plants operating with sub-optimal DS in the feed.
While THP specific capacity and energy efficiency is highly dependent on feed DS, one maximum DS cannot be defined for all sludges. Instead, the maximum DS depends on rheological properties of sludge. Hence, to design and operate THP more energy efficiently, more knowledge of sludge viscosity is needed. Rheological data on high DS sludge is scarce in literature and reported data is inconsistent mainly due to dissimilar measurement protocols and instruments.
In this study, sludge from different origins including Primary Sludge (PS), Surplus Activated Sludge (SAS) and mixtures of the two were analysed and rheological properties of the samples were determined at a range of temperatures and dry solid contents. Finally, these rheological properties were correlated to other sludge characteristics.
