Immersion frying for the thermal drying of sewage sludge: An economic assessment

Abstract : Three different continuous process flowsheets for fry-drying sewage sludge using recycled cooking oil (RCO) as frying oil scale were simulated on a commercial scale. The main difference consisted in the systems used to manage the exhaust vapors. Simulated PROCESS 1 was supposed to condensate the water vapors with cooling water. Closed and open loops heat pumps technologies were implemented in the simulated PROCESS 2 and 3 respectively. Detailed operating conditions and equipments design for each process were obtained. Then, a technological and an economic assessment were carried out. Analysis showed that PROCESS 1 required the simplest process flowsheet, although the main equipments were the largest. This produces a small economic advantage for the heat pump processes, yet the range of accuracy of the study did not allow to conclude definitively which of the processes was the most economical. Results were then compared with available data concerning the current thermal dryers for sewage sludge. On the basis of this study, it was observed that fry-drying offers a smaller fixed capital cost per unit of processed dry solids than current sewage sludge thermal dryers. Equivalent direct manufacturing costs were found for conventional and fry-drying processes. There, it was observed that unlikely the conventional dryers, energy requirements were not the main contributor of the fry-drying running costs but the RCO cost, which should be the focus of efforts to improve the economic performance of the fry-drying process.
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Carlos Peregrina, Victor Rudolph, Didier Lecomte, Patricia Arlabosse. Immersion frying for the thermal drying of sewage sludge: An economic assessment. Journal of Environmental Management, Elsevier, 2008, 86, pp.246-261. ⟨10.1016/j.jenvman.2006.12.035⟩. ⟨hal-01165238⟩

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