Isothermal Optimization for Anaerobic Digestion Mixture in Jacketed Vessel

Wong, Kai Wen (2020) Isothermal Optimization for Anaerobic Digestion Mixture in Jacketed Vessel. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

With increasing worldwide demand for palm oil, increasing extraction of palm oil generates a highly polluting liquid waste which called as Palm Oil Mill Effluent (POME) at the same time. POME is the solid and liquid by-products that contain a high content of chemical oxygen demand (COD) and biochemical oxygen demand (BOD). Anaerobic digestion is presently the most effective method that is widely applied in wastewater treatment of POME. The temperature in an anaerobic digester is the key factor that affects the performance of the digester and also the digestion rate. According to previous studies by Kim et al. (2002), the thermophilic temperature is the most suitable operating temperature for a digester. Thus, this research aims to encourage wider application of thermophilic anaerobic digester with a jacketed vessel. Jacketed vessel is functioned to heat the wastes in the digester via heat transfer between two fluids with different temperature and circulating fluids is playing an important role in this parameter. On top of that, there are three circulating fluids heights and patterns have been manipulated to simulate the heat transfer efficiency between POME and circulating fluids. Not only the fluids heights and circulating patterns, but the materials of jacketed vessels are also varied as well. The size of the digester and the presence of radiation have been manipulated as another two parameters as well. Numerical modelling and simulation techniques are applied in this research to simulate heat transfer between POME and circulating fluids in the jacketed vessel. With COMSOL Multiphysics®, simulation of heat transfer between POME and circulating fluids in the jacketed vessel with different fluids heights and different tank materials are performed. Simultaneously, the effects of tank sizes and radiation have been performed on the numerical model developed as well. The results showed that fully covered is the optimal circulating pattern for a digester and carbon steel is selected as the inner tank’s material as well. The bigger tank is preferable while radiation is assumed to be negligible. As a conclusion, a digester made of carbon steel, with a fully covered circulating pattern, a diameter of 4200mm and height of 6290mm, and negligible radiation is optimal to maintain a constant operating temperature for anaerobic digestion.