Browsing by Author "Vermaak, Rynhardt Petrus"
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- ItemThermal and hydraulic modeling of an anaerobic digestion plant(Stellenbosch : Stellenbosch University, 2016-03) Vermaak, Rynhardt Petrus; Dobson, Robert Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: The use of an anaerobic digestion (AD) process to treat municipal sewage sludge is one of the few options that provides the ability to treat sludge, offers a sustainable option for a carbon-neutral energy source and ability to reclaim wastewater back to potable water. The importance of the anaerobic digestion plant layout is investigated in terms of its process capacity, energy production and electrical energy generation based on thermal numerical modelling. A design is proposed in the study that is able to treat 986.742 m3/day at 4%TS (81 %) of the available sludge at the wastewater treatment plant, generating 1.293 MW net electrical power and still meet the heat requirements of the anaerobic digestion plant as well as the quality of effluent discharged by the plant. The proposed design is able to treat 53 % more sludge and generate 45.4 % more electrical net power compared to the first conceptual plant layout using a 3/2 two-stage digester configuration. With the use of hydraulic numerical modelling and experimental work, a mixing system was developed and proposed, that satisfies the biological requirement of micro bacteria inside the digester. The benefits of selecting the proposed mixing system over the mechanical draft tube method include: all the mechanical equipment of the mixing system is located outside the digester, it has no moving parts inside the digester, tedious downtime of clogged rotating equipment is eliminated and a reduction in biogas production rate when the digester is opened and exposed to air for maintenance can be eliminated. The proposed mixing system consists of five 518 mm draft tubes using a two-phase plug-flow regime formed by five plug-flow generators placed at the bottom of the draft tubes. The mixing system proposed was able to achieve a digester volume turn over time (DVTT) from 0.82 to 1.3 h, at a mixing intensity (G) from 70.58 to 35.88 s-1 requiring a unit power per volume (UP) from 3.41 to 0.88 W/m3. Stellenbosch University https://scholar.sun.ac.za